EFFECTS OF INTRAMOLECULAR SPIN POLARIZATION ON THE PHYSICAL AND PHOTOPHYSICAL PROPERTIES OF EXCHANGE - COUPLED SYSTEMS By Shuxuan Li A DISSERTATION Submitted to Michigan State University i n partial f ulfillment of the r equirements for the d egree of Chemistry - Doctor of Philosophy 201 9 ABSTRACT EFFECTS OF INTROMOLECULAR SPIN POLARIZATION ON THE PHYSICAL AND PHOTOPHYSCIAL PROPERTIES OF EXCHANGE - COUPLED SYSTEMS By Shuxuan Li Heisenberg spin exchange takes place when two or more unpaired spins in close proximity interact, so that their relative orientations are no longer independent of one another. Previous studies on dimeric complexes of [MM (tren) 2 (CA n - )] m+ (M, M = Cr III or Ga III , CA ) is the bisdentate chloranilate ligand, tren is tris( 2 - aminoethyl)amine ) provide d experimental evidence that the presence of spin exchange can affect optical and magnetic properties. The bridging ligand is redox active, which can be changed to yield various redox states via redox reactions, e.g. semiquinone, catecholate, or qui n one. These simple systems provide a convenient platform for the studies of both spectroscopic and magnetic behaviors. In semiquinone form, the unpaired electron s on Cr III can interact with the unpaired electron on the brid ging ligand. The the exchange coupling interactions within the dimeric complex. The Heisenberg model of these systems predicts that the introduction of spin exchange results in a net thermodynamic stabilizat ion of the system. The results seen in cyclic voltammetry (CV) experiments suggest that the larger potential echem ) of [Cr 2 (tren) 2 (CA)] m+ may be a thermodynamic consequence of spin exchange compar ed to [Ga 2 (tren) 2 (CA)] m+ . This may be the first time that the thermodynamic stabilization energy of spin exchange is possibly quantified by other physical measurements. In order to examine the effects of the thermodynamic stabilization by the spin exchange interaction and establish the thermodyn amic correlation seen in both electrochemical and magnetic behaviors, Cr III and Ga III analogues with various substituents on the tetraoxolene bridge are synthesized and characterized. R = H, F, Cl, Br, I, cyano, phenyl, and piperidino make excellent choice s of substituents. Additionally, horizontally - elongated bridging ligands, anthracene and naphthalene tetraoxo - derivatives, were synthesized and coordinated to Cr III for the studies, because the electron mobility within the se conjugated ligands can delocali ze the spin density further away from the metal ions. In addition, t he effects of intraligand electron delocalization can be examined by incorporating N,N - dimethylaminophenyl and cyanophenyl substituents on an anilate - bridging ligand to change the directionality of spin polarization. D ensity Functional T heory (DFT) calculations were employed to validate synthetic viability and provide some in - depth insight of the experimental data. The cyclic voltammetry and variable - temperature magne tic susceptibility data of these [Cr 2 (tren) 2 (L)] n+ and [Ga 2 (tren) 2 (L)] n+ systems were collected and compared. Among all, the thermodynamic stabilization observed in the [Cr 2 (tren) 2 ( Me 2 - AnT )] n+ complex is the weakest . This result matches the prediction of b oth our hypothesis and our DFT calculations. Both electrochemical and magnetic measurements are employed to provide experimental evidence, which will become advantageous tools for the further study of spin polarization, photophysics and photoelectronic pro perties of spin - coupled systems. Copyright by SHUXUAN LI 201 9 v This is dedicated to my mother, Lanhuan Tang ( ) , my husband, and Felix Zhai ( *jˆe ) and my parents - in - law, Yuxia Qiu ( 4j"â7Ø ) and Guang Zhai ( ), who are being extremely understanding and supportive for my P h.D. career. vi ACKNOWL E DGEMENTS I would like to thank my Ph. D. advisor, Jim K. McCusker, for all the support and guidance he has provided me throughout the years , for opening the gateway to the spintronic world, and for all the opportunities for me to see my potential and capabilities . T he McCusker group is a huge support group scientifically and socially. Their help and synthetic advice are priceless during group meetings, literature seminar preparation, second - year oral exam practice, especially my final defense practice, and for all the fun moments in the lab. I would like to specially thank Monica Carey to be my best friend by not only discussing science but also talk ing about cats, music, movies, and makeup , listening to my complaints, and hanging out with me outside of school, and Sara Adelman to be my glovebox buddy by spending all the late - nights in lab, educating me with Jewish culture and customs, motivating me to exercise, and especially fixing the gloveboxes with me. Although I never enjoy those moments when they happen, I do appreciate these two ladies tr ying to persuade me to rest, yelling at me when I was sick, sleep - deprived, or over - work , and calling me stubborn when I refuse d to listen . In addition, Shannon Kraemer and Olivia Chesniak have been am azing friends for physical exercises and coffee break . I have enjoyed my x - ray crystallography time with Dr. Richard Staples tremendously , because he has been an extremely helpful and patient mentor. He has taught me all the amazing techniques about cryst allography, listened to me and advised me my break - through of the bottle neck in science, and been providing me as much scientific assistance as he can. Without the constant assistan ce of Dr. Reza Loloee with the SQUID magnetometers , I would not be able to collect all of my variable - temperature magnetic susceptibility data , so I would l ike to thank him too. To Glenn Wesley, Bob Rasico, Dan Holmes, and other staffs in the MSU chemistry vii department, for their generosity of sharing their knowledge and support. Research would be million times harder without their help. I would also love to express my gratitude to my undergraduate advisor, Dr. Kathleen Murphy, and chemistry professors, Dr. Sally Smesko and Dr. Joe Ward at Daemen College. Even though m y gratitude toward my family cannot be solely expressed in words, I would like to let them know my deep appreciation for their endless support and understanding so I can pursue my dream free from inhibitions. To my beloved husband, Felix Zhai, I am tremendously thank ful to have you in my life. Your high tolerance of my grumpy temperament spoils me, your workout advice strengthens my health, your unconditional love enables me, and your approval of getting a corgi after my graduation fulfill my life. To my super - heroin mom, your mental and physical support allows me excel and help me fly higher , and you r open mind gives me huge space to roam and explore my interest. I am fully aware of how much a pain I was as a child, and you did a wonderful job of raising me alone. I am your proud daughter, and hopefully I will become a daughter you are proud of. viii TABLE OF CONTENT S LIST OF TABLES ................................ ................................ ................................ ......................... xi LIST OF FIGURES ................................ ................................ ................................ ...................... xii LIST OF SCHEMES ................................ ................................ ................................ ................. xx iv KEY TO SYMBOLS AND ABBREVIATIONS ................................ ................................ ....... xxv Chapter 1. Introduction of Heisenberg Exchange Coupling and the Impact on Spin Density Polarization and Delocalization ................................ ................................ ................................ ....... 1 1.1 Introduction on Heisenberg Exchange Interaction s ................................ ............................... 1 1.1.1 Introduction of Spin Exchange Coupling ................................ ................................ ....... 2 1.1.2 Determination of Exchange Coupling Constant, J , with Heisenberg - Dirac - van - Vleck Hamiltonian ................................ ................................ ................................ .............................. 3 1.1.3 Direct Exchange and Superexchange Interactions ................................ .......................... 4 1.2 Effects of Spin Density Polarization ................................ ................................ ...................... 8 1.3 Thermodynamic Effects of Spin Coupling ................................ ................................ .......... 1 1 1.4 Previous Work on [M 2 (tren) 2 (CA)] n+ ................................ ................................ ................... 1 3 1.5 Comproportionation Free Energy ................................ ................................ ........................ 1 5 1.6 Contents of Dissertation ................................ ................................ ................................ ....... 1 7 REFERENCES ................................ ................................ ................................ .............................. 20 Chapter 2. Substituent Effects on Spin Density and Charge Density of Tetraoxo - Semiquinoidal Radical Ligands ................................ ................................ ................................ ............................. 2 7 2.1 Introduction ................................ ................................ ................................ .......................... 2 7 2.2 DFT Calculation on Spin and Charge Polarization in Substituted Phenoxy, o - Semiquinone, and o - Phenanthrenesemiquinone Radicals ................................ ................................ ................ 2 7 2.3 Substituent Effects on Spi n Density and Charge Density of Tetraoxo - Semiquinoidal Radicals ................................ ................................ ................................ ................................ ...... 2 9 2.4 Computational Details of DFT Calculations ................................ ................................ ........ 3 1 2.4.1 Geometry Optimizations and Single - Point Energy Calculations ................................ .. 3 1 2.5 Results and Discussion ................................ ................................ ................................ ........ 3 2 2.5.1 Spin and Charge Density of Substituted Tetraoxo - Semiquinoidal Trianionic Radicals ... ................................ ................................ ................................ ................................ ................ 3 3 2.5.1.1 Charge Density Polarization in 3,6 - R - tetraoxosemiquinones ................................ 3 6 2.5.1.2 Spin Density Polarization in 3,6 - R - tetraoxosemiquinones ................................ .... 3 9 2.6 Concluding Comments ................................ ................................ ................................ ......... 4 1 APPENDIX ................................ ................................ ................................ ................................ .... 4 3 REFERENCES ................................ ................................ ................................ .............................. 60 Chapter 3. Magnetic Properties and Substituent Effect on the Modulation of Heisenberg Exchange Coupling Interactions in Chromium (III) Tetraoxo - Dimeric Complexes ..................... 6 5 3.1 Introduction ................................ ................................ ................................ .......................... 6 5 ix 3.2 Experimental Section ................................ ................................ ................................ ........... 6 7 3.2.1 Synthetic Procedures of Substituted Tetraoxoanilate, Naphthalene, and Anthracene Ligands ................................ ................................ ................................ ................................ ... 6 8 3.2.2 Synthetic Procedures and Schemes of Chromium (III) Dimeric Analogues ................ 7 6 3.2.3 Physical Measurements ................................ ................................ ................................ . 8 4 3.3 SQUID Variable - Tempearture Magnetic Susceptibility Measurements ............................. 8 7 3.3.1 Sample Prepara tion for Powders ................................ ................................ ................... 8 8 3.3.2 Temperature Sequence for Variable - Temperature Magnetic Data Collection ............. 90 3.4 Results and Discussion ................................ ................................ ................................ ........ 9 1 3.4.1 Synthesis and Characterization ................................ ................................ ..................... 9 1 3.4.2 Single Crystal X - Ray Structures ................................ ................................ ................... 9 8 3.5 Magnetic Susceptibility Measurements ................................ ................................ ............. 10 6 3.5.1 Previous Studies on Similar Systems: Experimental and Theoretical Examination of Cr (III) Phenanthrenesemiquinone ................................ ................................ ....................... 10 6 3.5.2 Magnetic Susceptibility Measurement and Extrapolation of J - coupling on [Cr 2 (tren) 2 (L cat,cat )] 2+ ................................ ................................ ................................ ............ 10 7 3.5.3 Magnetic Susceptibility Measurement and Extrapolation of J - coupling on [Cr 2 (tren) 2 (L sq,cat )] 3+ ................................ ................................ ................................ ............. 11 3 3.6 Concluding Comments ................................ ................................ ................................ ....... 12 7 APPENDIX ................................ ................................ ................................ ................................ .. 12 9 REFERENCES ................................ ................................ ................................ ............................ 17 8 Chapter 4. Magnetic Properties and Substituent Effects of Gallium (III) Tetraoxo - Dimeric Complexes ................................ ................................ ................................ ................................ .... 18 4 4.1 Introduction ................................ ................................ ................................ ........................ 18 4 4.1.1 Previous Studies on Similar Systems: An EPR, ENDOR, and Density Functional Study on Ga (III) Phenanthrenesemiquinone Complexes, [Ga 2 (tren) 2 (CA sq,cat )] 3+ and [Ga 2 (tren) 2 (DHBQ sq,cat )] 3+ ................................ ................................ ................................ .... 18 5 4.2 Computational Details of DFT Calculations ................................ ................................ ...... 18 6 4.2.1 Geometry Optimization and Single Point Energy Calculations ................................ . 18 7 4.3 Experimental Section ................................ ................................ ................................ ......... 18 8 4.3.1 Synthetic Procedures of Substituted Tetrao hydroxy - Ligands ................................ .... 18 9 4.3.2 Synthetic Procedures of Gallium(III) Dimeric Complexes ................................ ........ 1 90 4.3.3 Physical Measurement s ................................ ................................ ............................... 19 4 4.4 SQUID Variable - Temperature Magnetic Susceptibility Measurement on [Ga 2 (tren) 2 (L sq,cat )] 3+ ................................ ................................ ................................ ................. 19 6 4.5 Results and Discussion ................................ ................................ ................................ ...... 19 6 4.5.1 Synthesis and Characterization ................................ ................................ ................... 19 6 4.5.2 Single Crystal X - Ray Structures ................................ ................................ ................. 200 4.5.3 DFT Calculations ................................ ................................ ................................ ........ 20 6 4.5.4 Magnetic Properties of [Ga 2 (tren) 2 (L sq,cat )](BPh 4 ) 2 (BF 4 ) ................................ ............ 2 11 4.6 Concluding Comments ................................ ................................ ................................ ....... 21 3 APPENDIX ................................ ................................ ................................ ................................ .. 21 5 REFERENCES ................................ ................................ ................................ ............................ 2 32 x Chapter 5. Thermodynamics of Heisenberg Spin Exchange Coupling Reflected on Electrochemical Properties: Comparison of Chromium(III) and Gallium(III) Dimeric Complexes ................................ ................................ ................................ ................................ ...................... 23 6 5.1 Introduction ................................ ................................ ................................ ........................ 23 6 5.2 Electronic Absorption Spectroscopy of Chromium(III) and Gallium(III) Dimeric Complexes ................................ ................................ ................................ ................................ 23 7 5.3 Electrochemistry Studies of Chromium(III) and Gallium(III) Dimeric Complexes ......... 23 7 5.3.1 Experimental Sections ................................ ................................ ................................ 23 7 5.3.2 Electrochemical Properties of [M 2 (tren) 2 (L)] n+ (M = Ga 3+ or Cr 3+ ) ........................... 23 9 5.3.3 Thermodynamic Stabilization of Spin Exchange Interactions ................................ .... 2 50 5.3.3.1 Comproportionation Free Energy ................................ ................................ ........ 2 51 5.4 Extrapolation of Thermodynamic Stabilization Energies of Cr(III) Dimers from Magnetic Susceptibility Data by Referencing Ga(III) Analogues ................................ ........................... 25 4 5. 5 Concluding Comments ................................ ................................ ................................ ...... 25 8 APPENDIX ................................ ................................ ................................ ................................ .. 2 60 REFERENCES ................................ ................................ ................................ ............................ 26 7 Chapter 6. Conclusion and Future Directions ................................ ................................ ............. 2 70 6.1 Future Works ................................ ................................ ................................ .................... 2 70 6.1.1 DFT Calculations ................................ ................................ ................................ ........ 2 70 6.1.1.1 Geometry Optimization and Single Point Energy Calculations ......................... 2 71 6.1.2 Finish the Other Derivatives of the Substituted Anilate and Anthracene Bridging Systems ................................ ................................ ................................ ............................... 2 71 6.1.2.1 Synthes is ................................ ................................ ................................ .............. 27 2 6.1.2.2 Discussion ................................ ................................ ................................ ............ 27 3 6.1.3 Expand the Conjugation of Tetraoxo - Bridging Ligands with 9,10 - Diphenylanthracene, Terrylene , and Pyrene ................................ ................................ ................................ .......... 27 5 6.1.3.1 Synth esis ................................ ................................ ................................ .............. 27 8 6.1.3.2 Discussion ................................ ................................ ................................ ............ 27 9 6.1.4 Fast - Scan Cyclic Voltammetry Measurements ................................ .......................... 27 9 6.1.5 Electron Paramagnetic Resonance and DF T Studies of the Electronic Structures of the Semiquinoidal Gallium(III) Dimeric Systems ................................ ................................ ..... 2 80 6.1.6 A Broken Symmetry DFT Study for the Spin Exchange Coupling Constants of the Semiquinoidal Cr(III) Dimeric Systems ................................ ................................ .............. 2 81 6.1.7 Solution - Phase SQUID M agnetic S usceptibility M easurement s ................................ 28 2 6.2 Concluding Comments ................................ ................................ ................................ ....... 28 3 APPENDIX ................................ ................................ ................................ ................................ .. 28 5 REFERENCES ................................ ................................ ................................ ............................ 2 92 xi LIST OF TABLES Table 2.1. Net spin density, charge density, and - HOMO - - LUMO gap (eV) of 3,6 - R - semiquinone ................................ ................................ ................................ ................. 4 1 Table 3.1. Crystallographic data for Complex 1 , 2 , 4 and 5 ................................ ......................... 8 5 Table 3.2. Crystallographic data for Complex 6 , 7 and 10 ................................ ........................... 8 6 Table 3.3. 1 , 2 , 4 , and 5 .......................... 9 9 Table 3.4. 6 , 7 , and 10 .......................... 10 2 Table 3.5. Magnetic Properties and J - Couping Constants of [Cr 2 (tren) 2 (L cat,cat )](BPh 4 ) 2 .......... 11 2 Table 3.6. Magnetic Properties and J - Couping Constants of [Cr 2 (tren) 2 (L sq,cat )](BPh 4 ) 2 (BF 4 ) ....... ................................ ................................ ................................ ................................ .... 12 2 Table 3.7. Crystal data and structural refinement for 2,7 - dimethoxy - 3,6 - di(N,N - dimethylaminophenyl)benzoquinone) ................................ ................................ ...... 14 3 Table 3.8. Bond lengths for 2,7 - dimethoxy - 3,6 - di(N,N - dimethylaminophenyl)benzoquinone) ................................ ................................ ................................ ................................ .... 14 3 Table 3.9. Bond angles for 2,7 - dimethoxy - 3,6 - di(N,N - dimethylaminophenyl)benzoquinon e) ...... ................................ ................................ ................................ ................................ .... 14 3 Table 3.10. Crystal data and structural refinement for [Cr(II)(tren)Cl](BPh 4 ) ........................... 16 8 Table 4.1. Crystallographic data for Complex 20 , 21 , 23 , and 24 ................................ .............. 19 5 Table 4.2. 20 , 21 , 23 , and 24 ................ 202 Table 5.1. Electrochemical Properties of [M 2 (tren) 2 (L)] n+ (M = Ga 3+ or Cr 3+ ) ......................... 2 48 Table 5.2. Electrochemical and Magnetic Data for [M 2 (tren) 2 (L)] n+ (M = Ga 3+ or Cr 3+ ) .......... 2 54 xii LIST OF FIGURES Figure 1.1. Spin ladders of a system with antiferromagnetic interaction ( J < 0) between two S = ½ spins resulting in a singlet ground spin state ................................ ............................ 5 Figure 1.2. Spin ladders of a system with ferromagnetic interaction ( J > 0) between two S = ½ spins resulting in a triplet ground spin state ................................ ................................ . 5 Figure 1.3. Molecular orbital diagram with d - p orbital mixing of superexchange interaction between two metals and one intervening O 2 - via - bonding ................................ ........ 6 Figure 1.4. and one intervening O 2 - via - - bonding (b) ................................ ...... 6 Figure 1.5. d orbitals and diamagnetic ligand p orbitals overlap. Antiferromagnetic interaction is shown in (a), whereas ferromagnetic interaction is shown in (b) ................................ ................................ ................................ .................. 7 Figure 1.6. A quinoidal ligand undergoing one - electron redox reactions ................................ ...... 9 Figure 1.7. Multiple possible chelating forms tetraoxolene quinone undergoing one - electron redox reactions ................................ ................................ ................................ ............ 10 Figure 1.8. The structural representation of protein cluster rubredoxin (a) and ferredoxin (b) active sites ................................ ................................ ................................ ................. 1 2 Figure 1.9. Cyclic voltammograms of [Ga 2 (tren) 2 (CA cat,cat )](BPh 4 ) 2 (blue), and [Cr 2 (tren) 2 (CA cat,cat )](BPh 4 ) 2 (red). All data were recollected in degassed acetonitrile containing 0.1 M NBu 4 PF 6 at a scan rate of 100 mV/s ................................ .............. 12 Figure 1.10. Cr(III) and Ga(III) - tetraoxolene quinodal complexes ................................ ............. 13 Figure 1.11. Indication of spin exchange couplings for [Cr 2 (tren) 2 (CA sq,cat )] 3+ , see text for details on notation ................................ ................................ ................................ ........................ 1 4 Figure 2. 1. Resonance structure of a ketyl radical ................................ ................................ ........ 29 Figure 2. 2. A quinoidal ligand undergoing one - electron redox reactions ................................ .... 29 Figure 2.3. Substituted 2,3,5,6 - tetraoxoanilate (left), 2,3,6,7 - tetraoxonaphthalene (middle), and 2,3,6,7 - tetraoxoanthracene (right) ................................ ................................ ............. 31 Figure 2.4. Resonance structure of substituted anilate ................................ ................................ .. 33 xiii Figure 2.5. Shift in spin (red) and charge (blue) density at the oxygen atom for a series of substituted - anilate, naphthalene, and anthracene bridging radicals ........................... 35 Figure 2.6. Resonance effects of amino - - donors ................................ ................................ ........ 36 Figure 2.7. Percent change charge density vs. additive Hammett parameters for 3,6 - R - tetraoxosemiquinones ................................ ................................ ................................ . 37 Figure 2.8. Percent change charge density vs. meta Hammett parameters for 3,6 - R - tetraoxosemiquinones ................................ ................................ ................................ . 38 Figure 2.9. Percent Change charge density vs. ortho Hammett parameters for 3,6 - R - tetraoxosemiquinones ................................ ................................ ................................ . 38 Figure 2.10. Total spin density plots of DHBQ sq,cat (left), CA sq,cat (middle), and NMe 2 A sq,cat (right) ................................ ................................ ................................ ......................... 40 Figure 2.11. Total spin density plots of CN sq,cat ................................ ................................ ............ 40 Figure 2.12. Percent Change spin density vs - HOMO - - LUMO gap (eV) parameters for 3,6 - R - tetraoxosemiquinones ................................ ................................ ............................. 41 Figure 2.13. Cr 3+ or Ga 3+ - tetraoxolene quinodal complexes with combination of diamagnetic or paramagnetic substituted - bridging ligands, where R 1 are the s ubstituents on tetraoxoanilate, and R 2 are the substituents on 2,3,6,7 - tetraoxoanthracene ............... 42 Figure 2.14. Total spin density plots of FA sq,cat (left), BA sq,cat (middle), and IA sq,cat (right) ........ 57 Figure 2.15. Total spin density plots of CF 3 An sq,cat (left), OMeAn sq,cat (middle), and PipAn sq,cat (right) ................................ ................................ ................................ ......................... 58 Figure 2.16. Total spin density plots of PhAn sq,cat (left), NMe 2 PhAn sq,cat (middle), and CNPhAn sq,cat (right) ................................ ................................ ................................ ... 58 Figure 2.17. Total spin density plots of CF 3 PhAn sq,cat (left), NAT sq,cat (middle), and AnT sq,cat (right) ................................ ................................ ................................ .......................... 58 Figure 2.18. Total spin density plots of MeAnT sq,cat (left), PhAnT sq,cat (middle), and CNPhAnT sq,cat (right) ................................ ................................ ................................ .. 58 Figure 2.19. Total spin density plots of pyrene sq,cat (left) and terrylene sq,cat (right) ..................... 59 Figure 3.1. Cr III - tetraoxolene quinodal complexes with combination of diamagnetic or paramagnetic substituted - bridging ligands, where R 1 are the substituents on tetraoxoanilate, and R 2 are the substituents on 2,3,6,7 - tetraoxoanthracene ............... 65 xiv Figure 3.2. Quantum Design D elrin ® liquid sample holder ................................ .......................... 89 Figure 3.3. (a) Quantum Design Delrin ® powder sample holder; (b) Brass half - tube; (c) a Delrin ® powder sample holder snapped into a brass half - tube ................................ ... 90 Figure 3.4. Resonance structure of substituted 3,6 - R - tetraoxoquinone ................................ ....... 94 Figure 3.5. Oxidation of naphthalene and anthracene to their quinone derivatives ...................... 95 Figure 3.6. ORTEP drawing of Complex 1 (a), 2 (b), 4 (c), and 5 (d) obtain from single crystal x - ray structure determination ................................ ................................ ................... 100 Figure 3.7. ORTEP drawing of Complex 6 (a), 7 (b), and 10 (c) obtain from single crystal x - ray structure determination ................................ ................................ ............................. 101 Figure 3.8. Plots of the effective magnetic moment versus temperature for Complex 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 and 10 acquired in solid states ................................ ................................ ... 108 Figure 3.9. Spin latters of [Cr 2 (tren) 2 (L cat,cat ) 2+ due to the Heisenberg Hamiltonian ................. 109 Figure 3.10. The effective magnetic moment of Complex 1 ( blue square ), and the solid line represents a fit to the data using parameters described in the text .......................... 11 1 Figure 3.11. Indication of spin exchange coupling interactions for [Cr 2 (tren) 2 (L sq,cat )] 3+ , see text for details on notation ................................ ................................ ............................. 113 Figure 3.12. The DSC plots of Complex 13 , 14 and 16 ................................ .............................. 11 5 Figure 3.13. Plots of the effective magnetic moment versus temperature for all samples in solid states, Complex 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 and 19 ................................ ............ 116 Figure 3.14. Plot of the eigenvalues of various spin states for [Cr 2 (tren) 2 (L sq,cat )] 2+ . J <0 and J* <0 with both superexchange and direct exchange interactions considered as antiferromagnetic were used to generate this plot. Each state is labeled as |S T , S A > ..... ................................ ................................ ................................ ................................ .. 117 Figure 3.15. Plot of the eigenvalues of various spin states for [Cr 2 (tren) 2 (L sq,cat )] 2+ . J <0 and J* >0 with direct exchange and superexchange interactions considered as antiferromagnetic and ferromagnetic respectively were used to generate this plot. Each state is labeled as |S T , S A > ................................ ................................ ............... 11 8 Figure 3.16. A spin ladder diagram for of [Cr 2 (tren) 2 (L sq,cat )](BPh 4 ) 2 (BF 4 ) ............................... 11 9 Figure 3.17. Molecular orbital diagram with d - p orbital mixing of superexchange interaction between two metals and one intervening O 2 - via - bonding ................................ .. 1 20 xv Figure 3.18. The effective magnetic moment of Complex 12 ( blue square ), and the solid lin e represents a fit to the data using parameters described in the text .......................... 121 Figure 3.19. Excess spin density associated with the highest energy, singly - occupied molecular orbital of (BA sq,cat ) 3 - (a) and (IA sq,cat ) 3 - (b) ................................ .............................. 12 3 Figure 3.20. The inter - ring torsion angle ( ) of phenyl - substituted complexes ......................... 12 4 Figure 3.21. Multiple possible chelating forms of deprotonated 2,3,6,7 - tetraoxoanthracene undergoing one - electron redox reactions ................................ ................................ 12 6 Figure 3.22. 1 H NMR of 2,5 - dimethoxy - 1,4 - benzoquinone in CDCl 3 ................................ ....... 1 30 Figure 3.23. 13 C NMR of 2,5 - dimethoxy - 1,4 - benzoquinone in CDCl 3 ................................ ...... 1 30 Figure 3.24. 1 H NMR of 2,5 - dibromo - 3,6 - dimethoxy - 1,4 - benzoquinone in CDCl 3 .................. 13 1 Figure 3.25. 13 C NMR of 2,5 - dibromo - 3,6 - dimethoxy - 1,4 - benzoquinone in CDCl 3 ................. 13 1 Figure 3.26. ESI - MS of H 2 BA. Top: calculated isotope pattern for [M - H] - (C 6 H 1 O 4 Br 2 ). Bottom: experimental result. ................................ ................................ ................................ 13 2 Figure 3.27. ESI - MS of H 2 FA. Top: calculated isotope pattern for [M - H] - (C 6 H 1 O 4 F 2 ). Bottom: experimental result. ................................ ................................ ................................ . 13 2 Figure 3.28. 13 C NMR of bromanil (left) and iodanil (right) in benzene - d 6 ............................... 13 3 Figure 3.29. ESI - MS of H 2 IA. Top: calculated isotope pattern for [M - H] - (C 6 H 1 O 4 I 2 ). Bottom: experimental result. ................................ ................................ ................................ . 13 3 Figure 3.30. 1 H NMR of 2,5 - dimethoxy - 3,6 - diphenyl - 1,4 - benzoquinone in CDCl 3 .................. 13 4 Figure 3.31. 13 C N MR of 2,5 - dimethoxy - 3,6 - diphenyl - 1,4 - benzoquinone in CDCl 3 ................ 13 4 Figure 3.32. ESI - MS of 2,5 - dimethoxy - 3,6 - diphenyl - 1,4 - benzoquinone. Top: calculated isotope pattern for [M+H] + (C 10 H 15 O 4 ). Bottom: experimental result. ............................... 13 5 Figure 3.33. 1 H NMR of H 2 PhA in acetone - d 6 ................................ ................................ ........... 13 5 Figure 3.34. 13 C NMR of H 2 PhA in acetone - d 6 ................................ ................................ .......... 13 6 Figure 3.35. ESI - MS of H 2 PhA. Top: calculated isotope pattern for [M - H] - (C 18 H 11 O 4 ). Bottom: experimental result. ................................ ................................ ................................ . 13 6 Figure 3.36. 1 H NMR of 2,3,6,7 - tetramethoxy - 9,10 - dimethylanthracene in CDCl 3 .................. 13 7 xvi Figure 3.37. 13 C NMR of 2,3,6,7 - tetramethoxy - 9,10 - dimethylanthracene in CDCl 3 ................. 13 7 Figure 3.38. ESI - MS of 2,3,6,7 - tetramethoxy - 9,10 - dimethylanthracene. Experimental result for [M+H] + (C 20 H 23 O 4 ). ................................ ................................ ............................... 13 8 Figure 3.39. 1 H NMR of H 4 (Me - AnT) in dmso - d 6 ................................ ................................ ..... 13 8 Figure 3.40. ESI - MS of H 4 (Me - AnT). Experimental result for [M - H] - (C 12 H 15 O 4 ) ................... 13 9 Figure 3.41. 1 H NMR of 4 - (N,N - Dimethylamino)phenylboronic acid in dmso - d 6 .................... 13 9 Figure 3.42. 11 B NMR of 4 - (N,N - Dimethylamino)phenylboronic acid in dmso - d 6 ................... 1 40 Figure 3. 43. 1 H NMR of 2,7 - dimethoxy - 3,6 - di(N,N - dimethylaminophenyl)benzoquinone in CDCl 3 ................................ ................................ ................................ .................... 1 40 Figure 3.44. 13 C NMR of 2,7 - dimethoxy - 3,6 - di(N,N - dimethylaminophenyl)benzoquinone in CDCl 3 ................................ ................................ ................................ .................... 14 1 Figure 3.45. ESI - MS of 2,7 - dimethoxy - 3,6 - di(N,N - dimethylaminophenyl)benzoq uinone. Top: calculated isotope pattern for [M+H] + (C 24 H 27 O 4 N 2 ). Bottom: experimental result ................................ ................................ ................................ ................................ . 14 1 Figure 3.46. ORTEP drawing of 2,7 - dimethoxy - 3 - bromo - 6 - (N,N - dimethylaminophenyl)benzoquinone from single - crystal x - ray structure determination ................................ ................................ ................................ .......... 14 2 Figure 3.47. ORTEP drawing of 2,7 - dimethoxy - 3,6 - di(N,N - dimethylaminophenyl)benzoquinone from single - crystal x - ray structure determination ................................ ................... 14 2 Figure 3.48. 1 H NMR of H 2 NMe 2 - PhA in dmso - d 6 ................................ ................................ .... 14 4 Figure 3.49. ESI - MS of H 2 NMe 2 - PhA. Left: top, calculated isotop e pattern for [M - H] - (C 22 H 21 O 4 N 2 ); bottom: experimental result. Right: top, calculated isotope pattern for [M+H] + (C 22 H 23 O 4 N 2 ); bottom: experimental result ................................ .............. 14 4 Figure 3.50. 1 H NMR of 3,6 - dibromo - 2,7 - dihydroxynaphthalene in DMSO - d 6 ........................ 14 5 Figure 3.51. 1 H NMR of 3,6 - dibromo - 2,7 - dimethoxynaphthalene in CDCl 3 ............................. 14 5 Figure 3.52. 13 C NMR of 3,6 - dibromo - 2,7 - dimethoxynaphthalene in CDCl 3 ............................ 14 6 Figure 3.53. 1 H NMR of 2,3,6,7 - tetramethoxynaphthalene in CDCl 3 ................................ ........ 14 6 Figure 3.54. 13 C NMR of 2,3,6,7 - tetramethoxynaphthalene i n CDCl 3 ................................ ....... 14 7 xvii Figure 3.55. 1 H NMR of H 4 NAT in dmso - d 6 ................................ ................................ .............. 14 7 Figure 3.56. 13 C NMR of H 4 NAT in dmso - d 6 ................................ ................................ ............ 14 8 Figure 3.57. 1 H NMR of 2,3,6,7 - Tetramethoxyanthraquinone in CDCl 3 ................................ ... 14 8 Figure 3.58. 13 C NMR of 2,3,6,7 - Tetramethoxyanthraquinone in CDCl 3 ................................ .. 14 9 Figure 3. 59. 1 H NMR of 2,3,6,7 - tetramethoxyanthracene in CDCl 3 ................................ .......... 14 9 Figure 3.60. 13 C NMR of 2,3,6,7 - tetramethoxyanthracene in CDCl 3 ................................ ......... 1 50 Figure 3.61. 1 H NMR of H 4 AnT in acetone - d 6 ................................ ................................ ........... 1 50 Figure 3.62. 13 C NMR of H 4 AnT in acetone - d 6 ................................ ................................ .......... 15 1 Figure 3.63. ESI - MS of H 4 AnT. Top: calculated isotope pattern for [M - H] - (C 14 H 9 O 4 ). Bottom: experimental result ................................ ................................ ................................ .. 15 1 Figure 3.64. ESI - MS of [FeCp* 2 ](BF 4 ). Top: calculated isotope pattern for [M] + (C 20 H 30 Fe 2 ). Bottom: experimental result ................................ ................................ ................... 15 2 Figure 3.65. ESI - MS of Complex 11 . Top: cal culated isotope pattern for [M] 3+ (Cr 2 C 18 H 38 O 4 N 8 ). Bottom: experimental result ................................ ................................ .................... 15 2 Figure 3.66. ESI - MS of Complex 13 . Left: top, calculated isotope pattern for [M] 3+ (Cr 2 C 18 Cl 2 H 36 O 4 N 8 ); bottom, experimental result. Right: top, calculated isotope pattern for [Cr(tren)(C 6 Cl 2 O 4 )] + (CrC 12 H 18 O 4 N 4 Cl 2 ); bottom, experimental result ................................ ................................ ................................ ................................ . 15 3 Figure 3.67. ESI - MS of Complex 4 . Upper left: top, calculated isotope pattern for [M] 2+ (Cr 2 C 18 O 4 Br 2 H 35 N 8 ); bottom: experimental result. Upper right: top, calculated isotope patte rn for [M] 3+ (Cr 2 C 18 O 4 Br 2 H 36 N 8 ); bottom: experimental result. Lower: top, calculated isotope pattern for [Cr(tren)(C 6 O 4 Br 2 )] + (CrC 12 H 18 O 4 N 4 Br 2 ); bottom, experimental result. ................................ ................................ ................................ . 15 4 Figure 3.68. ESI - MS of Complex 14 . Left: top, calculated isotope pattern for [M] 3+ (Cr 2 C 18 H 36 O 4 N 8 Br 2 ); bottom, experimental result. Right: top, calculated isotope pattern for [Cr(tren)(C 6 O 4 Br 2 )] + (CrC 12 H 18 O 4 N 4 Br 2 ); bottom, experimental result ................................ ................................ ................................ ................................ . 15 5 Figure 3.69. ESI - MS of Complex 2 . Upper left: top, calculated isotope pattern for [M] 2+ (Cr 2 C 18 H 36 O 4 N 8 F 2 ); bottom, experimental result. Upper right: top, calculated isotope pattern for [M] 3+ (Cr 2 C 18 H 36 O 4 N 8 F 2 ); bottom, experimental result. Lower: top, calculated isotope pattern for [Cr(tren)(C 6 F 2 O 4 )] + (CrC 12 H 18 O 4 N 4 F 2 ); bottom, experiment al result ................................ ................................ ................................ .. 15 6 xviii Figure 3.70. ESI - MS of Complex 12 . Top: calculated isotope pattern for [M] 3+ (Cr 2 C 18 H 36 O 4 N 8 F 2 ). Bottom: experimental result. [Cr(tren)(C 6 O 4 F 2 )] + (CrC 12 H 18 O 4 N 4 F 2 ) ................................ ................................ ................................ ... 15 7 Figure 3.71. ESI - MS of Complex 5 . Upper left: top, calculated isotope pattern for [M] 2+ (Cr 2 C 18 H 36 O 4 N 8 I 2 ); bottom, experimental result. Upper right: top, calculated isotope pattern for [M] 3+ (Cr 2 C 18 H 36 O 4 N 8 I 2 ); bottom, experimental result. Lower: top, calculated isotope pattern for [Cr(tren)(C 6 O 4 I 2 )] + (CrC 12 H 18 O 4 N 4 I 2 ); bottom , experimental result ................................ ................................ ................................ .. 15 8 Figure 3.72. ESI - MS of Complex 15 . Left: top, calculated isotope pattern for [M] 3+ (Cr 2 C 18 H 36 O 4 N 8 I 2 ); bottom, experimental result. Right: top, calculated isotope pattern for [Cr(tren)(C 6 O 4 I 2 )] + (CrC 12 H 18 O 4 N 4 I 2 ); bottom, experimental result .... 15 9 Figure 3.73. ESI - MS of Complex 6 . Top: calculated isotope pattern for [M] 2+ (Cr 2 C 30 H 46 O 4 N 8 ). Bottom: experimental result ................................ ................................ ................... 1 60 Figure 3.74. ESI - MS of Complex 16 . Left: top, calculated isotope pattern for [M] 3+ (Cr 2 C 30 H 46 O 4 N 8 ); bott om, experimental result. Right: top, calculated isotope pattern for [Cr(tren)(C 18 O 4 H 10 )] + (CrC 24 H 28 O 4 N 4 ); bottom, experimental result ............... 1 60 Figure 3.75. ESI - MS of Complex 7 . Left: top, calculated isotope pattern for [M] 2+ (Cr 2 C 18 O 4 Br 2 H 36 N 8 ); bottom, experimental result. Right: top, calculated isotope pattern for [M] + (Cr 2 C 18 O 4 Br 2 H 36 N 8 ); bottom, experimental result ....................... 16 1 Figure 3.76. ESI - MS of Complex 17 . Left: top, calculated isotope pattern for [M] 3+ (Cr 2 C 34 H 54 O 4 N 10 ); bottom, experimental result. Righ t: top, calculated isotope pattern for [Cr(tren)(C 22 H 20 O 4 N 2 )] + (CrC 28 H 38 O 4 N 6 ); bottom, experimental result ................................ ................................ ................................ ................................ . 16 2 Figure 3.77. ESI - MS of Complex 10 . Left: top, calculated isotope pattern for [M] 2+ (Cr 2 C 18 H 14 O 4 N 8 ); bottom, experimental result. Right: top, calculated isotope pattern for [Cr(tren)(C 14 H 8 O 4 )] + (CrC 22 H 30 O 4 N 4 ); bottom, experimental result ................ 16 3 Figure 3.78. ESI - MS of Complex 19. Left: top, calculated isotope pattern for [M] 3+ (Cr 2 C 18 H 14 O 4 N 8 ); bottom, experimental result. Right: top, calculated iso tope pattern for [Cr(tren)(C 14 H 8 O 4 )] + (CrC 22 H 30 O 4 N 4 ); bottom, experimental result ................ 16 3 Figure 3.79. ESI - MS of Complex 8 . Upper left: top, calculated isotope pattern for [M] 2+ (Cr 2 C 22 H 40 O 4 N 8 ); bottom, experimental result. Upper right: top, calculated isotope pattern for [M] 3+ (Cr 2 C 22 H 40 O 4 N 8 ); bottom, experimental result. Bottom: top, calculated isotope pattern for [Cr(tren)(C 10 H 6 O 4 )] + (CrC 16 H 24 O 4 N 4 ); bottom, experimental result ................................ ................................ ................................ .. 16 4 xix Figure 3.80. ESI - MS of Complex 18 . Left: top, calculated isotope patte rn for [M] 3+ (Cr 2 C 22 H 40 O 4 N 8 ); bottom: experimental result. Right: top, calculated isotope pattern for [Cr(tren)(C 10 H 6 O 4 )] + (CrC 16 H 24 O 4 N 4 ); bottom: experimental result ................ 16 5 Figure 3.81. ESI - MS of Complex 9 . Left: top, calculated isotope pattern for [M] 2+ (Cr 2 C 18 H 14 O 4 N 8 ); bottom, experimental result. Right: top, calculated isotope pattern for [M] 3+ (Cr 2 C 18 H 14 O 4 N 8 ); bottom, experimental result ................................ ....... 16 6 Figure 3.82. ESI - MS of Complex 9 . Top, calculated isotope pattern for [Cr(tren)(C 14 H 8 O 4 )] + (CrC 20 H 26 O 4 N 4 ); bot tom, experimental result ................................ ........................ 16 7 Figure 3.83. ORTEP drawing of [Cr(tren)Cl](BPh 4 ) from single - crystal x - ray structure determination. Atoms are represented as 50% thermal ellipsoids .......................... 16 8 Figure 3.84. The effective magnetic moment of Complex 2 ( blue square ), and the solid line represents a fit to the data using MagFit ................................ ................................ . 16 9 Figure 3.85. The effective magnetic moment of Complex 3 ( blue square ), and the solid line represents a fit to the data using MagFit ................................ ................................ . 16 9 Figure 3.86. The effective magnetic moment of Complex 4 ( blue square ), and the solid line represents a fit to the data using MagFit ................................ ................................ . 1 70 Figure 3.87. The effective magnetic moment of Complex 5 ( blue square ), and the solid line represents a fit to the data using MagFit ................................ ................................ . 1 70 Figure 3.88. The effective magnetic moment of Complex 6 ( blue square ), and the solid line represents a fit to the data using MagFit ................................ ................................ 1 71 Figure 3.89. The effective magnetic moment of Complex 7 ( blue square ), and the solid line represents a fit to the data using MagFit ................................ ................................ 17 1 Figure 3.90. The effective magnetic moment of Complex 8 ( blue square ), and the solid line represents a fit to the data using MagFit ................................ ................................ . 17 2 Figure 3.91. The effective magnetic moment of Complex 9 ( blue square ), and the solid line represents a fit to the data using MagFit ................................ ................................ 17 2 Figure 3.92. The effective magnetic moment of Complex 10 ( blue square ), and the solid line represents a fit to the data using MagFit ................................ ................................ . 17 3 Figure 3.93. The effective magnetic moment of Complex 11 ( blue square ), and the solid line represents a fit to the data using MagFit ................................ ................................ . 17 3 Figure 3.94. The effective magnetic moment of Complex 13 ( blue square ), and the solid line represents a fit to the data using MagFit ................................ ................................ . 17 4 xx Figure 3.95. The effective magnetic moment of Complex 14 ( blue square ), and the solid line represents a fit to the data using MagFit ................................ ................................ . 17 4 Figure 3.96. The effective magnetic moment of Complex 15 ( blue square ), and the solid line represents a fit to the data using MagFit ................................ ................................ 17 5 Figure 3.97. The effective magnetic moment of Complex 16 ( blue square ), and the solid line represents a fit to the data using MagFit ................................ ................................ 17 5 Figure 3.98. The effective magnetic moment of Complex 17 ( blue square ), and the solid line represents a fit to the data using MagF it ................................ ................................ 17 6 Figure 3.99. The effective magnetic moment of Complex 18 ( blue square ), and the solid line represents a fit to the data using MagFit ................................ ................................ 17 6 Figure 3.100. The effective magnetic moment of Complex 19 ( blue square ), and the solid line represents a fit to the data using MagFit ................................ ................................ 17 7 Figure 4.1. Chemical structures of [Ga 2 (tren) 2 (DHBQ sq,cat )] 3+ (left) and [Ga 2 (tren) 2 (CA sq,cat )] 3+ (right) ................................ ................................ ................................ ....................... 18 5 Figure 4.2. 3,6 - diphenyl - tetraoxoanilate undergoing one - electron redox reactions ................... 19 9 Figure 4.3. ORTEP drawing of Complex 20 (a), 21 (b), 23 (c), and 24 (d) obtain from single crystal x - ray structure determination ................................ ................................ ........ 201 Figure 4.4. Shift in spin ( red ) and charge ( blue ) density at the oxygen atom for a series of substituted - anilate, naphthalene, and ant hracene bridging radicals. The % change is referenced to the parameters obtained for [Ga 2 (tren) 2 (DHBQ sq,cat )] 3+ (i.e. R = H, - electron and charge = - 0.558 electron) ................................ . 20 5 Figure 4.5. Excess spin density associated with the highest energy, singly - occupied molecular orbital of Complex 25 (a), 26 (b), 28 (c) and 29 (d) ................................ ................. 20 7 Figure 4.6. Weak bonding interaction between the Ga(III) 3d , 4s , 4p orbitals and two energetically different SQ - SOMO - HOMO - - LUMO gap is labeled in red ................................ ................................ ................................ ............ 20 8 Figure 4.7. % Change spin density vs. - HOMO - - LUMO gap (eV) parameters for digallium (III) - tetraoxosemiquinones complexes ................................ ................................ ..... 20 8 Figure 4.8. The SOMO (a) orbital picture and total spin density ( b) distribution plot of [Ga 2 (tren) 2 (NMe 2 - PhA sq,cat )] 3+ based on NPA of single point energy calculations . 2 10 Figure 4.9. Plots of the effective magnetic moment versus temperature for all samples in solid states, Complex 25 , 26 , 27 and 28 ................................ ................................ ............ 21 2 xxi Figure 4.10. 1 H NMR of THB in CD 3 CN ................................ ................................ ................... 21 6 Figure 4.11. 13 C NMR of THB in CD 3 CN ................................ ................................ .................. 21 6 Figure 4.12. ESI - MS of H 4 CA. Top: calculated isotope pattern for [M - H] - (C 6 O 4 H 3 Cl 2 ). Bottom: experimental result. ................................ ................................ ................................ . 21 7 Figure 4.13. ESI - MS of H 4 BA. Top: calculated isotope pattern for [M - H] - (C 6 O 4 H 3 Br 2 ). Bottom: experimental result ................................ ................................ ................................ ... 21 7 Figure 4.14. ESI - MS of H 4 FA. Top: calculated isotope pattern for [M - H] - (C 6 O 4 H 3 F 2 ). Bottom: experimental result ................................ ................................ ................................ .. 21 8 Figure 4.15. ESI - MS of H 4 IA. Top: calculated isotope pattern for [M - H] - (C 6 O 4 H 3 I 2 ). Bottom: experimental result ................................ ................................ ................................ .. 21 8 Figure 4.16. ESI - MS of Complex 20 . Upper left: top, calculated isotope pattern for [M] 2+ (Ga 2 C 18 O 4 H 38 N 8 ); bottom, experimental result. Upper right: top, calculated isotope pattern for [M] 3+ (Ga 2 C 18 O 4 H 38 N 8 ); bottom, experim ental result. Lower: top, calculated isotope pattern for [Ga(tren)(C 6 H 2 O 4 )] + (GaC 12 H 20 O 4 N 4 ); bottom, experimental result ................................ ................................ ................................ ... 21 9 Figure 4.17. ESI - MS of Complex 25 . Left: top, calculated isotope pattern for [M] 3+ (Ga 2 C 18 O 4 H 38 N 8 ); bottom, experimental result. Right: top, calculated isotope pattern for [Ga(tren)(C 6 H 2 O 4 )] + (GaC 12 H 20 O 4 N 4 ); bottom, experimental result .................. 2 20 Figure 4.18. ESI - MS of Complex 22 . Left: top, calculated isotope pattern for [M] 2+ (Ga 2 C 18 H 36 O 4 N 8 Cl 2 ); bottom, experimental result. Right: top, calculated isotope pattern for [Ga(tren)(C 6 Cl 2 O 4 )] + (GaC 12 H 18 O 4 N 4 Cl 2 ); bottom, experimental result ...... ................................ ................................ ................................ ................................ .. 2 21 Figure 4.19. ESI - MS of Complex 21 . Left: top, calculated isotope pattern for [M] 2+ (Ga 2 C 18 H 36 O 4 N 8 F 2 ); bottom, experimental result. Right: top, calculated isotope pattern for [Ga(tren)(C 6 F 2 O 4 )] + (GaC 12 H 18 O 4 N 4 F 2 ); bottom, experimental result ......... ................................ ................................ ................................ ................................ .. 2 22 Figure 4.20. ESI - MS of Complex 26 . Left: top, calculated isotope pattern for [M] 3+ (Ga 2 C 18 H 36 O 4 N 8 F 2 ); bottom, experimental result. Right: top, calculated isotope pattern for [Ga(tren)(C 6 F 2 O 4 )] + (GaC 12 H 18 O 4 N 4 F 2 ); bottom, experimental result ......... ................................ ................................ ................................ ................................ .. 22 3 Figure 4.21. ESI - MS of Complex 23 . Upper left: top, calculated isotope pattern for [M] 2+ (Ga 2 C 18 H 36 O 4 N 8 Br 2 ); bottom, experimental result. Upper right: top, calculated isotope pattern for [M] 3+ (Ga 2 C 18 H 36 O 4 N 8 Br 2 ); bottom, experimental result. Lower: top, calculated isotope pattern for [Ga(tren)(C 6 Br 2 O 4 )] + (GaC 12 H 18 O 4 N 4 Br 2 ); bottom, experimental result ................................ ................................ ................................ ... 22 4 xxii Figure 4.22. ESI - MS of Complex 28 . Left: top, calculated isotope pattern for [M] 3+ (Ga 2 C 18 H 36 O 4 N 8 Br 2 ); bottom, experimental result. Right: top, calculated isotope pattern for [Ga(tren)(C 6 Br 2 O 4 )] + (GaC 12 H 18 O 4 N 4 Br 2 ); bottom, experimental result ..... ................................ ................................ ................................ ................................ .. 22 5 Figure 4.23. ESI - MS of Complex 24 . Left: top, calcula ted isotope pattern for [M] 3+ (Ga 2 C 18 H 36 O 4 N 8 I 2 ); bottom, experimental result. Right: top, calculated isotope pattern for [Ga(tren)(C 6 Br 2 O 4 )] + (GaC 12 H 18 O 4 N 4 I 2 ); bottom, experimental result ........ ................................ ................................ ................................ ................................ .. 22 6 Figure 4.24. ESI - MS of [Ga 2 (tren) 2 (PhA cat,cat )](BPh 4 ) 2 . Left: top, calculated isotope pattern for [M] 2+ (Ga 2 C 30 H 46 O 4 N 8 ); bottom, experimental result. Right: top, calculated isotope pattern for [Ga(tren)(C 18 H 10 O 4 )] + (GaC 24 H 28 O 4 N 4 ); bottom, experimental result ......... ................................ ................................ ................................ ................................ .. 22 7 Figure 4.25. Total spin density associated with the h ighest energy, singly - occupied molecular orbital of [Cr 2 (tren) 2 (CA sq,cat )] 3+ (left), and [Cr 2 (tren) 2 (CNA sq,cat )] 3+ (right) ............ 22 7 Figure 4.26. Total spin density associated with the highest energy, singly - occupied molecular orbital of [Cr 2 (tren) 2 (CF 3 A sq,cat )] 3+ (left), and [Cr 2 (tren) 2 (OMeA sq,cat )] 3+ (right) ...... 22 8 Figure 4.27. Total spin density associated with the highest energy, singly - occupied molecular orbital of [Cr 2 (tren) 2 (NMe 2 A sq,cat )] 3+ (left), and [Cr 2 (tren) 2 (PipA sq,cat )] 3+ (right) ..... 22 8 Figure 4.28. Total spin density associated with the highest energy, singly - occupied molecular orbital of [Cr 2 (tren) 2 (PhA sq,cat )] 3+ (left), and [Cr 2 (tren) 2 (NMe 2 - PhA sq,cat )] 3+ ............ 22 9 Figure 4.29. Total spin density associated with the highest energy, singly - occupied molecular orbital of [Ga 2 (tren) 2 (NH 2 - PhA sq,cat )] 3+ (left), and [Ga 2 (tren) 2 (CN - PhA sq,cat )] 3+ (right) ................................ ................................ ................................ ................................ .. 22 9 Figure 4.30. Total spin density associated with the highest energy, singly - occupied molecular orbital of [Ga 2 (tren) 2 (CF 3 - PhA sq,cat )] 3+ (left), and [Ga 2 (tren) 2 (NAT sq,cat )] 3+ (right) . 2 30 Figure 4.31. Total spin density associated with the highest energy, singly - occupied molecular orbital [Ga 2 (tren) 2 (AnT sq,cat )] 3+ (left), and of [Ga 2 (tren) 2 (Me - AnT sq,cat )] 3+ (right) .... 2 30 Figure 4.32. Total spin density associated with the highest energy, singly - occupied molecular orbital of [Ga 2 (tren) 2 (Ph - AnT sq,cat )] 3+ (left), and [Ga 2 (tren) 2 (CNPh - AnT sq,cat )] 3+ (right) ................................ ................................ ................................ ........................ 2 31 Figure 4.33. Total spin density associated with the highest energy, singly - occu pied molecular orbital of [Ga 2 (tren) 2 (Pyrene sq,cat )] 3+ (left) and [Ga 2 (tren) 2 (Terrylene sq,cat )] 3+ (right) ................................ ................................ ................................ ................................ .. 2 31 Figure 5.1. The structural representation of protein cluster rubredoxin (left) and ferredoxin (right) active sites ................................ ................................ ................................ ..... 23 6 xxiii Figure 5.2. The cyclic vo ltammogram of [Cr 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. All potentials are referenced to the DmFc +/0 couple (E 1/2 =0 V in MeCN), and the inserts show the DPV traces ......................... 23 8 Figure 5.3. The cyclic voltammogram of [Ga 2 (tren) 2 (PhA)] n+ in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. The redox potential of ferrocene is at 0.324V ..................... 2 40 Figure 5.4. The cyclic voltammogram of [Cr 2 (tren) 2 (NMe 2 - PhA)] n+ in MeCN with 1.0 M TBAPF 6 as supporting electrolyte and Pt working elec trode ................................ ... 2 41 Figure 5.5. The cyclic voltammogram of [Cr 2 (tren) 2 (NMe 2 - PhA)] n+ in MeCN with 1.0 M TBAPF 6 as supporting electrolyte and glassy carbon working electrode ................. 2 41 Figure 5.6. Possible reaction of [Cr 2 (tren) 2 (NMe 2 - PhA)] n+ with MeCN to produce HCN and a n acetonitrilo - coordinated complex ................................ ................................ ............. 2 42 Figure 5.7. Resonance structures of dianionic anilate bridging ligand ................................ ....... 24 3 Figure 5.8. The cyclic voltammogram of [Cr 2 (tren) 2 (NAT)] n+ in MeCN with 1.0 M TBAPF 6 as supporting electrolyte with Fc +/0 as internal reference ................................ ............. 24 4 Figure 5.9. Multiple possible chelating forms of deprotonated 2,3,6,7 - tetraoxonaphthalene undergoing one - electron redox reactions ................................ ................................ . 24 4 Figure 5.10. The cyclic voltammogram of [Cr 2 (tren) 2 (NAT)] n+ in MeCN with 1.0 M TBAPF 6 as supporting electrolyte with Fc +/0 as internal reference. The reported potential is referenced to DmFc couple at 0V vs DmFc +/0 . DPV shows in the inserts collected at the 1 st sweep (a), and 2 nd sweep (b) ................................ ................................ ......... 24 5 Figure 5.11. Cyclic voltammograms of the [Cr 2 (tren) 2 (CA)] n+ in MeCN with 1.0 M TBAPF 6 collected at 20 mV/s ( red dash ), 50 mV/s ( green dash ), and 100 mV/s ( blue solid ) ..... ................................ ................................ ................................ ................................ .. 24 7 Figure 5.12. Cyclic voltammograms of [Cr 2 (tren) 2 (IA)] n+ ( red ) and [Ga 2 (tren) 2 (IA)] n+ ( blue ) in MeCN with 1.0 M TBAPF 6 as supporting electrolyte ................................ .............. 24 8 Figure 5.13. Energy level diagram for [Cr 2 (tren) 2 (L sq,cat )] 3+ with (left) stronger spin exchange interaction, larger J ; (right) weaker spin exchange interaction, smaller J ................ 2 50 Figure 5.14. The spin ladder of a molecule with S 1 = S 2 = ½ based on the Heisenberg exchange Hamitonian. The red arrow indicates a net thermodynamic stabilization resulted from spin exchange coupling ................................ ................................ ................... 2 51 Figure 5.15. CV of [Cr 2 (tren) 2 (FA)](BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. All potentials are referenced to the DmFc +/0 couple ............................. 2 61 xxiv Figure 5.16. CV of [Cr 2 (tren) 2 (CA)](BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. All potentials are referenced to the DmFc +/0 couple ............................ 2 61 Figure 5.17. CV of [Cr 2 (tren) 2 (BA)](BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. All potentials are referenced to the DmFc +/0 couple ............................ 2 62 Figure 5.18. CV of [Cr 2 (tren) 2 (PhA)](BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. All potentials are referenced to the DmFc +/0 co uple ............................ 2 62 Figure 5.19. CV of [Cr 2 (tren) 2 (Me 2 - AnT)](BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. All potentials are referenced to the DmFc +/0 couple ............................. 26 3 Figure 5.20. CV of [Ga 2 (tren) 2 (DHBQ)](BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. All potentials are referenced to the DmFc +/0 couple ............................. 26 3 Figure 5.21. CV of [Ga 2 (tren) 2 (CA)](BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. All potentials are referenced to the DmFc +/0 couple ............................. 26 4 Figure 5.22. CV of [Ga 2 (tren) 2 (BA)](BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. All potentials are referenced to the DmFc +/0 couple ............................ 26 4 Figure 5.23. CV of [Ga 2 (tren) 2 (PhA)](BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. All potentials are re ferenced to the DmFc +/0 couple ............................ 26 5 Figure 5.24. CV of ferrocene (at 0.569V) and decamethylferrocene (at 0.06V) in MeCN with 1.0 M TBAPF 6 as supporting electrolyte ................................ ................................ ........ 26 5 Figure 5.25. Cyclic voltammograms of the [Cr 2 (tren) 2 (CA cat,cat )](BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 collected from 50 mV/s to 400 mV/s ................................ ......................... 26 6 Figure 6.1. The calculated structures of 4,5,9,10 - tetraoxopyrene (left), and 4,5,12,13 - tetraoxoterrylene (right) ................................ ................................ .......................... 27 7 Figure 6.2. Shift in spin ( red ) and charge ( blue ) density at the oxyge n atom for a series of deprotonated trianionic tetraoxo - substituted phenylanilate, naphthalene, anthracene, pyrene (PAH), and terrylene bridging radicals ................................ ........................ 27 7 Figure 6.3. Shift in spin ( red ) and charge ( blue ) density at the oxygen atom for a series of tetr aoxo - substituted phenylanilate, naphthalene, anthracene, pyrene (PAH), and terrylene Ga (III) complexes ................................ ................................ .................... 2 81 xxv LIST OF SCHEMES Scheme 3.1. General synthetic routes of [Cr 2 (tren) 2 (Anilate cat,cat )](BPh 4 ) 2 and [Cr 2 (tren) 2 (Anilate sq,cat )](BPh 4 ) 2 (BF 4 ), where anilate represents substituted anilate bridging ligands, DHBQ, FA, CA, BA, IA, PhA, or NMe 2 - PhA ............................. 95 Scheme 3.2. General synthetic routes of [Cr 2 (tren) 2 (L cat,cat )](BPh 4 ) 2 and [Cr 2 (tren) 2 (L sq,cat )](BPh 4 ) 2 (BF 4 ), where L represents naphthalene or anthrac ene bridging ligands, NAT, AnT, or Me - AnT ................................ ................................ . 96 xxvi K EYS T O S YMBOLS AND A BBREVIATIONS BA: Bromanilate BF 4 - : tetrafluoroborate BPh 4 - : tetraphenylborate CA: Chloranilate CV: Cyclic Voltammetry DCM: Dichloromethane DFT: Density Functional Theory DHBQ: 2,5 - Dihydroxy - 3,6 - benzoquinone DMF: Dimethylformamide DMSO: Dimethyl Sulfoxide DPV: Differential - Pulse Voltammetry DSC: Differential Scanning Calorimetry EDG: Electron Donating Group ENDOR: Electron Nuclear Double Resonance EPR: Electron Paramagnetic Resonance ES: Excited State ESI - MS: Electrospray Ionization Mass Spectrometry EtOH: Ethanol EWG: Electron Withdrawing Group FA: Fluoranilate GS: Ground State H 2 BA: Bromanilic acid xxvii H 2 CA: Chloranilic acid HDVV: Heisenberg - Dirac - van - Vlec k H 2 FA: Fluoranilic acid H 2 IA: Iodanilic acid HOMO: Highest Occupied Molecular Orbital IA: Iodanilate LMCT: Ligand - to - Metal Charge Transfer LUMO: Lowest Unoccupied Molecular Orbital MeCN: Acetonitrile MeOH: Methanol MLCT: Metal - to - Ligand Charge Transfer SOMO: Singly Occupied Molecular Orbital SQUID: Superconducting Quantum Interference Device TBAPF 6 : Tetrabutylammonium hexafluorophosphate TGA: Thermogravimetry Analysis THB: 2,3,5,6 - tetrahydroxybenzene tren: Tris(2 - aminoethyl)amine 1 Chapter 1. Introduction of Heisenberg Exchange Coupling and the Impact on Spin Density Polarization and Delocalization 1.1 Introduction on Heisenberg Exchange Interaction s In quantum mechanics, s pin is an intrinsic form of angular momentum carried by particle s, 1 and it refers to unpaired electrons possessing magnetic ally induced dipole moment in magnetism. 2,3 The spin has direct impact on the physical or photophysical properties of molecular system . For example, a spin - allowed transition process, fluorescence, and a spin - forbidden process, phosphorescence, present various emission lifetime when a molecule stays in its excited state before emitting a photon. 4,5 Understanding the physical nature of how spin affecting a molecular system allows us to learn and interpret its optical property. In addition, it plays an important role in biological systems , molecular structures and practical applications to assist in interpreting the nature of metalloproteins, advancing the computing technology, and improving data r eading, storage, and transfer. The stud y of spin and magnetism in various chemical systems has been ongoing for decades in many different areas, 2 including single - molecule magnets, 6 - 9 bioinorganic chemistry, 10 - 1 2 material science, 1 3 ,1 4 and more recently, q uantum computing, 1 5 ,1 6 giant magnetoresistance 17 and spintronics. 1 8 - 2 3 Spin polarization is an important parameter in understand ing the perturbation of spins in nature, and it is generally defined as specific spin location s and alignment s inside a molecule. Recently, there has been increased interest in studying the influence of exchange coupling in structure to more complicated systems with application in biology and mate rials science. 2 , 2 4 - 2 7 A r ising number of research paper s prove that spin exchange interactions have direct impact on the photophysical properties and photo - induced reactivity of magnetic systems. 2 8 - 30 Furthermore, i ntramolecular 2 spin polarization appears t o have some effects on the strength of exchange coupling interaction. 3 1 - 3 4 Metalloprotein is a type of protein that contains a metal cofactor , and most of the se metal cofactors are paramagnetic because of the presence of unpaired electrons. 35,36 T hese transition metal ions within the cofactors play an important role in both the magnetic property and the redox chemistry. 11 ,35,36 The study of Bertrand and Gayda 97 suggested spin exchange coupling interactions relate to the shift in the reduction poten tials, which is potentially a thermodynamic consequence of the spin exchange effect. The goal of this project is to design and synthesize molecular systems to tune the spin exchange interaction in order to perceive the cause - and - effect of the thermodynamic s of spin - exchanged systems . However, the syntheses and characterization of metalloproteins can be quite complicated. Instead, simple inorganic molecular systems are designed and synthesized in this project to facilitate my study. Previous work by our grou p members has been conducted to discern this relationship. 3 7 - 3 9 1.1.1 Introduction of Spin Exchange Coupling When two or more paramagnetic spin centers are located far away from one another, they do not interact with each other. In this case, their relative spi n orientations have no effect on the energy in the system. As this distance diminishes, 40 the parallel (ferromagnetic) or antiparallel (antiferromagnetic) orientation between the magnetic orbitals on the paramagnetic centers will change the energy of the system, which is known as an exchange coupling interaction. 41 Spin exchange interaction is described as an quantum electrostatic interaction aris ing exclusion principle between two spin operators mathematically , 2, 4 2 and spin coupling is a zero - field effect in the absence of external magnetic field. Exchange interactions can take place between two directly bound spin centers (direct exchange) or through a diamagnetic bridge (superexchange). Direct exchange requires direct orbital overlap through a bonding interaction 3 and has been widely observed in metal nitroxide, 4 3 - 4 6 pyrazine, 4 7 verdazyl, 4 8 thiazyl, 4 9 , 50 carbene 51 and semiquinone compounds . 41 , 5 2 , 5 3 Superexchange is a relatively weak coupling interaction, because the exchange coupling pathway needs to be mediated by a diamagnetic bridging ligand. This indirect coupling interaction has been observed generally in transition metal dimers. 3 7 , 5 4 ,5 5 Interm olecular or through - space exchange interactions between paramagnetic molecules are another commonly seen exchange coupling, but they are very weak, even weaker than superexchange intramolecular exchange coupling in magnitude . 5 6 Both intermolecular and intr amolecular exchange interactions play important roles in determining the ground state magnetic properties, 2 but the focus of my project is intramolecular exchange. 1.1.2 Determination of Exchange Coupling Constant, J , with Heisenberg - Dirac - van - Vleck Hamiltonian The Heisenberg - Dirac - van Vleck (HDVV) Hamiltonian ( ), shown in E q. 1 .1 , can be used to describe spin exchange interactions between t wo spin operators, and . The strength of the exchange coupling interaction is reflected in the mag nitude of the exchange coupling constant, J . In general, the HDVV Hamiltonian is the simplest formalism for molecular magnetism, 5 6 and works well with systems in which each paramagnetic site contains only one unpaired electron with well - defined and localized magnetic orbitals. 5 7 There are examples of well - predicted spin ladders of Cr (III) ( S = 3/2) spin - exchanged complexes by the HDV V Hamiltonian reported in literature. 5 8 In addition, t he HDVV Hamiltonian can also be applied to systems with multiple paramagnetic centers , and this will be discussed later in this chapter . ( 1 .1 ) The HDVV Hamiltonian only applies for spin - only ions, and S is not a good quantum number and its associated operator cannot commute with the Hamiltonian when spin - orbit 4 coupling arises from orbital moments. 4 2 Therefore, the value of Landé g - factor derived from the Hamiltonian is very close to 2.0, in which L , the orbital angular momentum, is considered zero ( E q. 1. 2 ). This project focuses on systems of dichromium(III) and digallium(III) compounds with C 2v or C i symmetry, where spin - orbit coupling will not be a concern since orbit angular momentum is quenched either partially (with a negligible L value) or completely ( L = 0). 60 When the symmetry of a system is lower than octahedral, orbit al angular momentum is quenched due to the fact that an electron in an orbital of a degenerate set cannot rotate into the other orbital. 60 ( 1. 2 ) 61 to find the eigenvalues of a spin Hamiltonian, the total spin operator is defined as , where , . W hen this is substituted into E q. 1 .1 , the expression in E q. 1. 3 is obtained. From that expression, the eigenvalue for the system can be calculated ( E q. 1. 4 ). ( 1. 3 ) E (S T ) = J [S T (S T +1) S 1 (S 1 +1) S 2 (S 2 +1)] ( 1. 4 ) 1.1.3 Direct Exchange and Superexchange Interactions Direct exchange interaction requires direct orbital overlap between two paramagnet ic centers since it is a through - bond intramolecular exchange, and the Pauli exclusion principle keeps spins away to reduce the coulombic repulsion. 4 2 An energy diagram for a simple case of two spin centers with S 1 = S 2 = ½ undergoing an exchange coupling interaction is shown in Fig. 1.1. Two spin orientations are possible, and the energy difference between them depends on J . When antiparallel is the preferred orientation between two spins, antiferromagnetic interaction is 5 be lower in energy. When two spins orient parallel, ferromagnetic interaction arises with a total spin of 1, and a triplet ground state was stabilized to have lower energy (see Fig. 1.2). The magnetic orbitals of these two spin centers are orthogonal to each other. The form used in eq. 1.1 indicates that antiferromagnetic coupled system if J < 0, and ferromagnetic coupled system if J > 0. The case of two S = ½ with the Cu(II) dimers was studied by Bleaney and Bower. 62 Figure 1.1. Spin ladder s of a system with a ntiferromagnetic interaction ( J < 0) between two S = ½ spins resulting in a singlet ground spin state . Figure 1. 2 . Spin ladders of a system with ferromagnetic interaction ( J > 0) between two S = ½ spins resulting in a triplet ground spin state. Superexchange coupling describes the exchange coupling interaction between two paramagnetic centers through intermediate a diamagnetic ionic ligand with d - p orbital mixing , which results in two orbitals: one bonding orbital and one antibonding orbital . 6 1 A spin transfer red from one magnetic metal d orbital to the other magnetic d orbital by extending its orbital overlap via the antibonding orbital on this intervening bridging ligand (Fig. 1.3) . 6 3 Kramers first noticed 6 this coupling interaction in crystalline MnO. 64 Due to the overlap of wavefunction between O 2 - pz and two Mn 2+ dz 2 - axis, one electron from O 2 - ext ends to couple with the unpaired spin in Mn 2+ . The remaining p electron will then exchange - couple with the spin in the other Mn 2+ (left in Fig. 1.4). 77 The strength of the exchange coupling, J , can also be described by Eq. 1.1, where S 1 = S 2 = 5/2 are the spins of the two Mn 2+ sites. The example of MnO superexchange is via - - bonding (right Fig. 1.4), 59 where the overlap of wavefunction is between O 2 - p x and two metal dxz z - axis. This systems according to the Goodenough - Kanamori - Anderson rules. 67 - 69 Figure 1.3. Molecular orbital diagram with d - p orbital mixing of superexchange interaction between two metals and one intervening O 2 - via - bonding. (a) (b) Figure 1. 4 . metals and one intervening O 2 - via - bonding ( a - bonding ( b ) . 7 S uperexchange coupling can : the interaction is antiferromagnetic if one metal occup ying the dz 2 overlaps with the other metal occup ying the dxz through p and p orbitals of the diamagnetic ligand; the interaction is weakly ferromagnetic if two dz 2 magnetic orbitals overlap through the px and pz orbitals of the diamagnetic ligand (Fig. 1. 5 ) . 6 7 - 6 9 (a) (b) Figure 1. 5 . d orbitals and diamagnetic ligand p orbitals overlap. Antiferromagnetic interaction is shown in (a) , whereas ferromagnetic interaction is shown in (b) . Variable - temperature magnetic susceptibility measurement is generally used to experimentally determine t he strength of coupling between paramagnetic spin centers, in which the macroscopic magnetization (M) is evaluated as a function of temperature (usually ranging from 2 - 350K) reflecting the Boltzmann distribution ( Eq. 1. 5 ). 4 2 The macroscopic magnetization i s a sum of microscopic magnetization of all spin states. At low temperature, more spins locate at the lower energy level (N + ), and energy embodied as temperature (T) is applied to populate spins into the higher energy level (N - ). ( 1.5 ) The magnetization has a relation ship with magnetic susceptibility shown in Eq. 1.6, where is the molar magnetic susceptibility and H is the applied magnetic field. (1.6) 8 The magnetic susceptibility c an also be expressed by the van Vleck equation in Eq. 1.7, (1. 7 ) where N A k is , E n (0) is energy of level n in zero field (H = 0), E n (1) and E n (2) is the first and second order Zeeman coefficients, which are energies dependent upon applied magnetic field (Eq. 1. 7 ). Magnetic data obtained from variable - temperature magnetic susceptibility measurement can be fitted in Eq. 1.7, and the exchange coupling constant, J , can be determined by a least - square fitting. This method will be used to extrapolate J for exchange - cou pling systems in this thesis . 70 1.2 Effects of Spin Density Polarization This dissertation focus es on transition metal complexes directly coordinate to organic radicals , so spin density can be manipulated via spin delocalization or localization by synthetic substitution on these organic radicals. Transition metal - quinone complexes have been widely studied over the last two decades with regard to their synthetic, physical, and optical properties. 41 , 71 - 7 3 o - S emiquinone is known to be able to bind to metal ions to create a wide range of different couplings , including both ferromagnetic and antiferromagnetic couplings . 7 4 Quinone is a redox - active ligand with various oxidation states, each of which has a different spin. A quinone (q, with S = 0) can be reduced into a seqmiquinone radical (sq, with S = ½) and also to a catechol (cat, with S = 0) as illustrated in Fig. 1. 6 . 41 These electrochemical processes are reversible, which is another reason why quinones have been widely studied and used as chelating ligands. 41 , 6 5 - 6 7 T he radical nature of semiquinone produces compounds with unusual magnetic and optical properties arising when b ound to a metal. 7 3 , 7 5 , 7 6 9 Figure 1. 6 . A quinoidal ligand undergoing one - electron redox reactions. A simple o - semiquinone does not possess an appropriate binding geometry to act as a bridging ligand between two metal ions to form a symmetric system , so tetraoxolene was proposed for the construction of extended magnetic systems. The advantages of associating tetra oxolene - quinoidal ligand are : (1) the four redox reactions are accessible to this compound as a free ligand and also when coordinated to metals; 3 7 (2) it has four oxygen donor atoms to coordinate with two metal ions; 7 4 (3) it possesses multiple chelating modes (Fig. 1. 7 ). 7 7 1,4,5,8 - Tetra oxo naphthalene was first employed by Dei and co - workers for a study of [Ru 2 (bpy) 4 (tetraoxo)] n+ , but no radical species was observed after redox reactions had occurred . 7 8 2,5 - Dihydroxy - 1,4 - benzoquinone (DHBQ) was then used i nto their study of radical species because of the (sq, cat) 3 - and (q, sq) - . 7 4 Incorporating quinone with a paramagnetic metal ion, with semiquinone being reduced to catechol or oxidized to quinone . 10 Figure 1. 7 . Multiple possible chelating forms tetraoxolene quinone undergoing one - electron redox reactions. orbitals of tetra oxolene - based ligand are closer in energy to the metal - based d orbitals to introduce more orbital mixing , and metal tetraoxolene complexes thus exhibit vast variety of intramolecular electrochemical and spectroscopic properties. 7 9 More detail about orbital information supported by computational results will be discussed in Ch ap. 2 and 4. First - row transition metal (Cu 2+ , Ni 2+ , Fe 3+ , and Cr 3+ ) 7 4 , 80 - 8 3 tetraoxolene complexes present localized charge distribution with various substituted ( X = H, Cl, or NO 2 ) 8 4 tetraoxolene dianionic (sq, sq) form. Spin distribution within the tetraoxolene ligand can be po ssibly manipulated by switching to electron donating (EDG) or electron withdrawing groups (EWG). Associating paramagnetic metal centers with the substituted tetraoxolene ligands provides a platform for spin polarization effects on spin exchange coupling. 11 1.3 Thermodynamic Effects of Spin Coupling One of the biggest forces driving the interest in exchange coupling is to understand the polynuclear metal clusters at the active site of metalloprotein. 10 , 8 5 - 90 The research of metalloprotein has concentrated on the spectroscopic and magnetic properties related to how exchange coupling affects the electronic structures, chemical reactivity, and biological functions. 91 - 9 6 The studies by Bertrand and Gayda 9 7 on rubredoxin and ferredoxin extracted from plant and algae extracts show the redox potential of Fe 2+/3+ in ferredoxin [2Fe - 2S] is generally more negative than th at of rubredoxin (Fig. 1. 8 ) . The active site of ferredoxin consists of two [ Fe III S 4 ] centers with an antiferromagnetic coupling interaction induced by the two Fe(III) paramagnetic centers, while rubredoxin only contain one [Fe III S 4 ] center without any exchange coupling interaction. In DMF solution, rubredoxin [Fe III S 4 ] is reduced to [Fe II S 4 ] at - 1 .02V, 9 8 whereas [2Fe - 2S] is reduced at - 1.49V. 9 9 Bertrand and Gayda 9 7 collected electrochemical data of desulforedoxin - one Fe(III) coordinating to four cysteine group s - and [2Fe - 2Se], and compared the ir redox potentials with those of rubredoxin and ferredoxin. Previous studies reported significant structural difference between all four of the moieties based on Mössbauer, UV - vis, and infrared (IR) spectroscopy. 9 9 Ho wever, desulforedoxin and rubredoxin exhibited redox potentials relati vely close in values, 100 while [2Fe - 2Se] and [2Fe - 2S] presented similar redox behaviors to each other . 101 These results indicated exchange coupling interaction stabilized the oxidation states of [2Fe - 2Se] and [2Fe - 2S] by lowering c.a. 100 mV in their redox potentials. 97 97,101 are the first experimental evidence proposing the hypothesis of Heisenberg spin exchange affecting the electrochemical properties of a system. 12 (a) (b) Figure 1. 8 . The structural representat ion of protein cluster rubredoxin ( a ) and ferredoxin ( b ) active sites . Density Function al Theory (DFT) calculations were later conducted on similar systems, Fe clusters with one , two, and four Fe metal centers , by Mouesca et al . 10 2 The information obtained on effects of electron exchange, electron delocalization, charge distribution, and solvation energies agrees with the finding of one and two [Fe III S 4 ] centers, as reported by Bertrand and Gayda. 9 7 Figure 1. 9 . Cyclic voltammograms of [Ga 2 (tren) 2 (CA cat,cat )](BPh 4 ) 2 (blue), and [Cr 2 (tren) 2 (CA cat,cat )](BPh 4 ) 2 (red). All data were recollected in degassed acetonitrile containing 0.1 M NBu 4 PF 6 at a scan rate of 100 mV/s. Similar thermodynamic stabilization was observed from the electrochemical data collected for [Cr 2 (tren) 2 (CA)] n+ , where CA is the chloranilate and tren is tris(2 - aminoethyl)amine, reported by Dr. Guo in our group (Fig. 1.9). 37 The goal of this project is to 13 further examine the effect of the thermodynamic stabiliza tion through spin exchange interaction s and establish the thermodynamic correlation seen in both electrochemical and magnetic behaviors . 1.4 Previous Work on [M 2 (tren) 2 (CA)] n+ Tetraoxolene complexes provide a good avenue to study the correlation between t he photophysical properties of molecules and the spin exchange interactions that define their electronic structures. Previously, our group has studied several different chloranilate - bridge (CA) bimetallic complexes, shown in Fig. 1.10, with R = Cl. Cr (III) ion (S = 3/2) was chosen because it is redox - inert and not easily reduced to Cr (II) . Incorporating Ga III into the binuclear motif provides a spectroscopically silent d 10 ion (S = 0) with a similar charge - to - radius ratio as Cr (III) . 41 The chloranilate brid ge was chosen as a free radical ligand for the molecular assemblies because of its accessibility to its multiple oxidation states. 37 Only the semiquinone - catechol (sq, cat; S = ½), catechol - catechol (cat, cat; S = 0) and semiquinone - semiquinone (sq, sq; S = 0) forms will be discussed in detail, because the quinone - semiquinone (q, sq) and quinone - quinone (q, q) forms only coordinate to one metal, which then rapid ly degrades upon further oxidation. Figure 1.10. Cr(III) and Ga(III) - tetraoxolene quinodal co mplexes . A variety of magnetic behaviors are exhibit ed among these systems. [Ga 2 (tren) 2 (CA cat,cat )] 2+ is a diamagnetic compound, while [Ga 2 (tren) 2 (CA sq,cat )] 3+ is paramagnetic with the [CA sq,cat ] 3 - radical ligand. [Cr 2 (tren) 2 (CA cat,cat )] 2+ is a superexchange coupling system 14 with two paramagnetic Cr(III) centers linked by a diamagnetic [CA cat,cat ] 4 - intermediate. [Cr 2 (tren) 2 (CA sq,cat )] 3+ possesses both superexchange and direct exchange coupling interactions, and exhibit rich magnetic charac , ter : i t is composed of three paramagnetic centers, two Cr(III) ( S = 3/2) , Center 1 and 3, and a [CA sq,cat ] 3 - radical bridge , Center 2 . There is superexchange coupling between the two Cr(III) ions, while direct exchange interactions, J 12 and J 23 , take place between the Cr(III) centers and CA sq,cat (Fig. 1.10). Figure 1.1 1 . Indication of spin exchange couplings for [Cr 2 (tren) 2 (CA sq,cat )] 3+ , see text for details on notation. In order to better explain the complicated magnetic behavior of this system, the HDVV Hamiltonian is employed again. With three paramagnetic centers, the total spin operator of the system is defined as (where ) here, S 1 = S 3 = 3/2 correspond the two Cr(III) ions and S 2 to the CA sq,cat bridge. In this way, the Hamiltonian operator can be derived from Eq. 1.12 using two coupling constants, where J quantifies the Cr III - CA sq,cat direct exchange, and J* is the superexchange coupling for Cr III - Cr III (this coupling scheme is shown in Fig. 1.10). Eq.1.13 is the eigenvalue equation for this system. (1.12 ) E= - J [S T (S T +1) S A (S A +1) S 2 (S 2 +1)] J* [S A (S A +1) S 1 (S 1 +1) S 3 (S 3 +1)] (1.13) 15 It is known that the HDVV Hamiltonian is used to best describe systems with two spin centers contributing only one unpaired electron; 106 thus, it will be nece ssary to actually compare the magnetic experimental results of systems with more than one unpaired electrons modelled by the HDVV Hamiltonian for multiple - spin systems with S > ½ to determine the effectiveness of this spin - only Hamiltonian. 1. 5 Comproport ionation Free Energy Comproportionation is a chemical reaction between one oxidized reactant and one reduced reactant with the same composition of elements with different oxidation states to form a product of an intermediate oxidation state ( E q. 1.8 ). The c omproportionation constant, K C , is the equilibrium constant as illustrated in E q. 1 .9 . ( 1.8 ) (1 .9 ) The comproportionation constant can provide insight into the thermodynamics o f the system. Cyclic voltammetry has been developed and widely employed to evaluate t he thermodynamic stability and metal - metal coupling of mixed - valence complexes. 10 3 - 10 5 The reaction to occur. According to the to the free energy of comproportionation ( E q. 1 .10 ) C , which also evaluates the strength of the exchange coupling between redox centers through the ligand bridge. 10 3 C can be considered equivalent to the thermodynamic stabilization energy i nduced by spin exchange . In this regard, an ing the thermodynamic stabilization of a system. 16 C = - - 2.303RT log (K C ) (1 . 1 0 ) A proof - of - concept experiment has already been performed to verify the hypothesis. Between the two electrochemical waves in Fig . 1.8 , the potential difference of [Cr 2 (tren) 2 (CA cat,cat )](BPh 4 ) 2 is larger than [Ga 2 (tren) 2 (CA cat,cat )](BPh 4 ) 2 . The observation r eveals that there should be an intrinsic factor caus ing the CA sq,cat form of the Cr III - Cr III dimer to be more stable than the Ga III - Ga III dimer. This intrinsic factor is thought to be the spin exchange interaction suggested by the finding of Betrand and Gayda . 9 7 Based on the electrochemical data for [Cr 2 (tren) 2 (CA cat,cat )] 2+ , a net thermodynamic stabilization larger in magnitude is suggested to be induced by the direct exchange interaction between Cr(III) and the C A sq,cat C can be calculated from the redox potential difference ( E q. 1 . 1 0 ), 10 6 and it corresponds to the comproportionation constant, K C , in accordance to the Gibbs free energy ( E q. 1 . 1 0 ) and the Nernst equation (Eq. 1 .11 ). 10 4 (1 .11 ) K C >1 reflects the stability of the semiquinone form of the system relative to the other two states illustrated in E q. 1 . 9 . Exchange coupling inherent in [Cr 2 (tren) 2 (CA sq, cat )] 3+ is thought to be the contribution of the thermodynamic stabilization, 10 7 since the CA sq,cat species is subject to significant direct exchange interaction rather than the CA sq,sq and CA cat,cat forms of the diamagnetic bridge . T he redox potential shift shown on [Cr 2 (tren) 2 (CA)] n+ compared with [ Ga 2 (tren) 2 (CA sq, cat )] n+ indicate a thermodynamic stabilization possibly induced by the spin exchange interaction ; however, it is unknown if this phenomenon exclusively exhibits in these systems. In this project, similar Cr(III) and Ga(III) assemblies with various substituents on the bridging ligands will be synthesized and characterized magnetically and electrochemically, so we 17 can further examine the relationship between the redox chemistry and spin exchange interaction. By varying the electron withdrawing and donating substituents on the targeted systems in this project, the connection between the spin density on a molecular system and the strengt h of spin exchange will be perceived , and the strength of the spin coupling can be systematically and synthetically manipulated. 1. 6 Contents of Dissertation This research can be divided into four main components: (1) computational studies of spin polarization in tetraoxo - semiquinone ligand radicals and Ga(III) tetraoxo - semiquinoidal compounds ; (2) the synthesis and magnetic characterization of Cr(III) and Ga(I II) dimeric semiquinoidal complexes; (3) the electrochemical behavior of Cr(III) and Ga(III) dimeric moieties; (4) the thermodynamics of spin exchange interaction, and the correlation between electrochemical and magnetic properties. The literature reports stabilization of an oxidation state as induced by the exchange interaction; 9 4 however, it is lacking a quantitative method to directly measu re the Heisenberg stabilization energy. The J coupling constant measured from variable - temperature magnetic susceptibility experiment only show s the relative energy levels of each spin state induced by the spin exchange interaction. The thermodynamic consequence extrapolated from electrochemical data can provide some insights by measuring absolute stabilization energy of a spin - coupled system. Chap ter 2 begins with the Density Functional Theory (DFT) calculation of a series of substituted tetraoxo - semiquinoidal radicals to understand the factors infl uencing spin and charge density distribution in systems. These calculations facilitate the assessment of synthetic viability of a series of proposed substituted ligands. In addition, they reveal inductive and resonance 18 effects are the major factors i n char ge polarization within a molecule. The mixing between the HOMO of the substituent and the SOMO of the semiquinone moiety explains the spin localization on the oxygen binding sites. Chap ter 3 show s the synthesis and physical characterization of both substi tuted ligands and Cr(III) quinoidal dimeric complexes. Meanwhile, magnetic data collection and sample preparation are discussed in an attempt to contribute to the systematic procedures reported , which are sadly lacking in the literature. The variable - tempe rature magnetic susceptibility data of various substituted Cr(III) dimers show a trend of fluctuation in the exchange coupling constants. The implication of how spin polarization affect s the exchange coupling interactions will be discussed. In Chap ter 4, the DFT calculations examin ing spin and charge density distribution in open - shell digallium(III) systems are compared with those of the free ligands. The synthesis and physical characterizations of substituted tetrahydroxy ligands and Ga(III) quinoidal com pounds are presented. Variable - temperature magnetic data collected for [Ga 2 (tren) 2 (L sq,cat )] 3+ are discussed in term of their magnetic behaviors. In Chapter 5 , the electrochemical data are presented for both Cr(III) and Ga(III) dimeric analogues, a s well as the thermodynamic stabilization observed for their various oxidation states. It correlates the relationship between the electrochemical and magnetic properties, and proposes a hypothesis of how electrochemical data will be able to quantify the thermodyn amic stabilization induced by the Heisenberg exchange interaction. Chapter 6 details some ongoing synthetic routes for more substituted ligands, including EWG and EDG substituents, intraligand electron delocalizing ligands, and horizontal aromatic extensi on ligands , and possible modification s and improvement s to existing procedures . 19 Polycyclic aromatic hydrocarbons (PAHs) are proposed to be the next series of bridging ligands to further examine the spin polarization on spin exchange. Liquid variable - temperature magnetic susceptibility measurement will be proposed to characterize magnetic behaviors of the systems involving solvation properties. 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The deep understanding of the interplay between spin and charge density in radicals is still lacking, and the need to develop more in - depth knowledge about them a rises in spintronics. 1 - 3 Sp in refers to spin angular momentum, and it generally manifests as unpaired electrons in a system. 4 Spin density measures the probability of an electron to be present at a certain location. Charge density quantifies the amount of electric charge per unit ar ea, length, surface area, or volume, and is considered to relate to electronegativity in molecular systems. Density Functional Theory (DFT) calculations have been employed to provide energ y mapping analysis of spin states along with spin Hamiltonian parame ters, spin and electron delocalization. 5 - 7 The spin - unrestricted formalism is a powerful computational tool to give important insight that explain experimental spectra, reactivity trend, and electronic structures of molecular systems directly 8,9 or indirec tly. 10 - 12 2.2 DFT Calculation s on Spin and Charge Polarization in Substituted Phenoxy , o - Semiquinone, and o - Phenanthrenesemiquinone Radicals. The general assumption about spin and charge density is that they should track each other accord i n g ly, since the intrinsic nature of both spin and charge is from the electron. However, they illustrate significantly different properties in magnetism. The strength of exchange 28 interaction reflects the spatial distribution of unpaired spin, whereas charge d ensity indicates the stability of metal complex formation. 13 Previous studies conducted in our group examine d the intimate movement between spin and charge density distribution, and para - substituent effects of phenoxy radicals , 13 o - semiquinone , o - phenanthrenesemiquinone with DFT calculations. 1 4 Fehir in our group discover ed that spin and charge distribution are not correlated in para - substituted phenoxy radicals . 13 Within the phenoxy radicals with various electron withdrawing group s ( EWG ) and ele ctron donating group s ( EDG ) , c harge density distribution is induced by the resonance effect and shows a Hammett - type relationship. 1 3 The Hammett equation describes the change in free energy of activation correspond ing to the change in Gibb s free energy whe n meta - or para - substituted aromatic reactants differ in substituents. 15 Nevertheless, s pin density plots generated from the DFT calculations match the SOMO orbital pictures , and show a trend consistent with the - HOMO - - LUMO gap . 13 Fehir concluded that spin polarization is governed by the nature of the unpaired electron in a system, whereas charge polarization reflects the overall electron distribution over the entire molecule. 13 Similar density functional studies were carried out by Fehir on o - semiquinone and o - phenanthrenesemiquinone. These systems also exhibit the spatial characteristics of spin density consistent with the - HOMO - - LUMO gap. 13,14 However, d ue to the different a rene substitution pattern , ortho - substituted, from th e phenoxy radicals, the calculations indicate very different spin and charge polarization of these systems, and the spin density induced by charge - dipole is mostly concentrated on the oxygen atoms in both types of radicals , 14 unlike the typical resonance structure of ketyl radicals (Fig. 2.1) , where spin and charge density oscillates between the carbonyl carbon and oxygens. 1 6 Substituent effects are more profound in these systems: EWG stabilize the negative charge on the rings to decrease spin density on t he oxygens, while EDG 29 destabilize the charge to increase spin density. 14 More details will be discussed for the DFT results obtained for the tetraoxo - semiquinoidal radicals in my project, and similar phenomena were observed. Figure 2.1. Resonance struct ure of a ketyl radical. 2. 3 Substituent Effects on Spin Density and Charge Density of Tetraoxo - Semiquinoidal Radicals The significant amount of charge density localized on the oxygen atoms in o - catechol makes them strong Lewis acids (Fig. 2.2). 1 7 After binding to a metal ion, the Heisenberg exchang e interaction can be turned on when the complex is oxidized to metal - semiquinone. Magneto researchers have extensively studied th ese kind s of the metal quinoidal complexes over decades. 18 - 24 Figure 2.2. A quinoidal ligand undergoing one - electron redox reactions. Instead of using o - semiquinone as ligands, tetra dentate tetraoxo - semiquinone ligands were chosen to be the bridging ligands in our binuclear metal systems. The benefit of employing the tetraoxo - qui noidal ligands is their ability to coordinate with two metal ions to yield metal complexes with higher symmet ry orientation s . By com bin ing these quinoidal ligands with relatively redox - inert metal ions, Cr(III) and Ga(III), it allow ed us to systematically study the effect of spin exchange on the physical and magnetic properties without changing their overall composition , connectivity of element s, or geometry . Previously in our group, DFT calculations 30 were performed on deprotonated trianionic forms of chlora nilate and 2,5 - dihydroxy - 3,6 - benzoquinone radicals to characterize their electronic structures and provide insightful information to help interpret and simulate electron paramagnetic resonance (EPR) spectra . 25 In th e project outlined in this chapter , similar DFT calculation s with natural population an a lysis (NPA) were carried out on substituted - tetraoxoanilate, tetraoxonaphthalene, and tetraoxoanthracene. V arious EWG and EDG were incorporated into the substituents to facilitate the study of the spin de nsity delocalization effects on the spin exchange properties , including - donor/ - acceptors : F (FA) , Cl (CA) , Br (BA) , I (IA) , and phenyl (Ph) ; - donors : OMe, NMe 2 , and piperidino ; - acceptor, CN ; and a - acceptor, CF 3 . Other derivatives are also includ ed to investigate the effect of the intraligand electron delocalization, CN - phenyl (CNPh) , NMe 2 - phenyl (NMe2Ph) , and CF 3 - phenyl (CF3Ph) . Bridging ligands with extended h orizontal conjugation extension, naphthalene (NAT) and anthracene (AnT) , are good candi date s for our systems to decrease J for determination of the strength of the spin exchange due to their extended conjugated systems . Literature studies show a very strong direct exchange interaction on Cr(III) semiquinoidal complexes, 55 - 57 and their magnetic data show temperature independence and J cannot be extrapolated accurately due to the lack of thermal population of more spin states. However, if the substituents destabilize the negative charge on the aromatic rings to an extreme level , it will largely decrease the formation constants , resulting in instability of the desired metal - semiquinone compounds or even prevent the ir formation. DFT has been proved to be a useful tool for spin and charge density calculations , so it can examine th e charge distribution of certain substituted tetraoxo - quinoidal ligands (Fig. 2.3) to glean their synthetic viability . S econd ly , it w as used to map out the spin distribution in these 31 radicals for their magnetic behaviors , since the strength of spin exchang e coupling is suggested to be proportional to the spin density of paramagnetic centers in magnetism . 2 6 - 29 Figure 2.3. Substituted 2,3, 5 , 6 - tetraoxo anilate (left) , 2,3,6,7 - tetraoxonaphthalene (middle) , and 2,3,6,7 - tetraoxoanthracene (right). 2. 4 Computational Details of DFT Calculations General Methods . All electronic structure calculations of semiquinodal anion s were carried out using density functional theory implemented in Gaussian 09 30 on HPCC at Institute for Cyber - Enabled Research at Michigan State University . The B3LYP functional with open shell was used in the calculation s . 31 - 34 The calculation s w ere performed using the default tight convergence criteria with a fine grid. 35 Analysis of atom ic charge and spin densities were performed using natural population analysis (NPA) framework developed by Weinhold et al. 36 2. 4 .1 Geometry Optimizations and Single - Point Energy Calculations The initial geometries of all semiquinoidal ligands were genera ted using GaussView 3 7 and subsequently optimized using the UB3LYP functional and a 6 - 31G basis set with imposed symmetries of D 2h , and default f ine grid in Gaussian09. Final geometries were checked with frequency calculations at the UB3LYP/6 - 31G level, and the absence of negative imaginary frequencies indicate d that the final structures ha d reached the ir global minima. Single - point energy calculations were performed usi ng the unrestricted open shell density function UB3LYP with the 6 - 311G basis set assuming a doublet ground state and a molecular charge of 3 - . 32 2. 5 Results and Discussion Geometry . T he electron spin resonance spectrum of chloranilic trianionic radical has been reported in aqueous NaOH along with Na 2 S 2 O 4 ; 38 nevertheless, there are no literature reports of the successful isolation of t he protonated or deprotonated DHBQ sq,cat and CA sq,cat as free ligands as far as we know. Thus, it is difficult to predict if t he optimized structures of the free ligands can accurately represent their true geometries. It has been widely observed that the C - C and C - O bond lengths within the ring of o - semiquinone can indicate the oxidation state of the quinoidal ligand when binding to first - row transition metals, 39 - 41 so the C - C and C - O bond lengths from the calculated trianionic structures can be used as reasonable parameters to gauge the validity of these geomet ry by comparing them with the corresponding x - ray crystal structures. Alternating short and long C - C bonds should be observed in semiquinone radicals due to the localization of electrons in the C=C bonds. In all calculated structures, the C - C bond distance s rang e from 1.35 to 1.55 Å (See Appendix for detail), and this suggests that the structures obtained are in their semiquinone form. The C - O bonds within a semiquinone radical should be shorter and show a larger difference compared with the catechol for m, 1 7 ,39 and the optimized structures indicate d a similar trend. In addition, the crystal structures of various protonated anilic acid, the dianionic form, have been intensively studied and characterized, 42 - 51 and the bond lengths and bond angles in these str uctures can be treated as reference s for the legitimacy of the calculated geometries calculated . The x - ray crystal structural analysis show ed that these substituted dianionic anilates generally contain four C - C bonds with similar bond lengths (1.404 1.43 5 Å), and two longer C - C bonds whose bond lengths vary as a function of substituents. 52 33 2.5. 1 Spin and Charge Density of Substituted Tetraoxo - Semiquinoidal Trianionic Radicals The results of DFT calculations on ortho - 1,2 - semiquinone radicals previously reported by our group reveal ed that the interaction between EDG or EWD substituents with the delocalized negative charge density in the semiquinoidal aromatic ring impacted the spin delocalizing ability of these substituents . 14 In this project, 3,6 - R - tetraoxo - semiquinone bridging ligands served to examine the spin polarization effect instead of the o - 1,2 - semiquinones, and it will be unreasonable to predict the substituents exert similar effects with four electron - donating oxy gens. Due to the strong resonance effects within a quinoidal ring along O - C - C( - R) - O bonds (Fig. 2.4), parallel offset ing - stacking interactions are dominate between bromanilic alkali salt to minimize electron - electron repulsion . 54 - stacking in teraction s present in anilic molecules allow electrons to move more freely. Polycyclic aromatic hydrocarbons (PAHs), e.g. naphthalene (NAT), and anthracene (AnT ) , are also consider ed good candidates for bridging ligands in our systems due to the presence o f lighter elements (i.e. C, H, O) for low spin - orbit - stacking for good electron mobility by spin delocalization. 5 3 Figure 2.4. Resonance structure of substituted anilate. As mentioned above, a wide range of substituents were chosen in the se calculations to examine their interactions with the anilate and anthracene rings, and the unsubstituted anilate (R=H) radical was used as a reference point for comparisons. Fig. 2.5 show s the computational results of spin and charge density at the oxygens for substituted ligand radicals. The percent change is referenced to the parameters obtained for the tetrahydroxyanilate radical (i.e. R = H, where spin = 0.146 - electron and charge = - 0.648 electron). A positive change shows an 34 increase in the m agnitude of either parameter, and a negative change indicate s a decrease in that parameter. Most of the substituents exhibit spin and charge density percent change tracking to each other, except the halogenated, OMe, CN, CF 3 , phenyl - anthracene (Ph - AnT), an d cyanophenylanthracene. C oncern s were raised about the low Lewis basicity of these anilate s and PAHs , due to their strong electron delocalization , potentially negatively affecting the information constant of the transition metal complexes. C omputational r esults indicat e d a general decreas e in charge density (Fig. 2 . 5 ), so all complexes studies proved to be weaker Lewis base s . The most considerable decrease was shown in trianionic IA, CnPh, CF 3 Ph, and CNPh - AnT. Synthetic evidence is needed to provide s uppor ting information about how low the level of Lewis bas icity would be needed to prevent the formation of their corresponding metal complexes . The succe ss ful syntheses of both [Cr 2 (tren) 2 (IA cat,cat )](BPh 4 ) 2 and [Cr 2 (tren) 2 (IA sq,cat )](BPh 4 ) 2 (BF 4 ) are reported in Chapter 3, so iodanilic acid can stably coordinate s with Cr(III) ions. However , the reaction between Ga(III) and the iodanilate ligand is thermodynamically unfavorable with Ga(III). B oth [Ga 2 (tren) 2 (IA cat,cat )](BPh 4 ) 2 and [Ga 2 (tren) 2 (IA sq ,cat )](BPh 4 ) 2 (BF 4 ) are synthesizable (reported in Chapter 4), but they are both unstable even being stored in the dark under inert atmosphere. Therefore, we can predict that either the coordination between Ga (III) and CNPh or CF 3 Ph will be synthetically i nfeasible, or their products will be unstable in a c c ordance to the degree of charge density. The attenuation of charge density is quite pronounced in trianionic Me - AnT, Ph - AnT, and CNPh - AnT. Successful synthe is of [Cr 2 (tren) 2 (Me - AnT cat,cat )](BPh 4 ) 2 and [Cr 2 (tren) 2 (Me - AnT cat,cat )](BPh 4 ) 2 (BF 4 ) are reported in Chapter 3 . However, the synthesis of Ga (III) - Me - AnT adduct has failed after multiple attempts, which will be further discussed in Chapter 4. Thus, we can anticipate the similar difficulties will be encountered for the coordination between Ga(III) 35 Figure 2.5. Shift in spin ( red ) and charge ( blue ) density at the oxygen atom for a series of substituted - anilate, naphthalene, and anthracene bridging radicals. 36 and Ph - AnT or CNPh - AnT. - donors, piperidino exhibits a decrease in both spin and charge density, while OMe and NMe 2 show slight increases of spin density. Piperidino possesses a strong inductive effect due to the long electron - donating alkyl chain attached to the nitrogen, so the nitrogen is even more electron donating/basic than the one in NMe 2 (Fig. 2.6). However, hi gher electrostatic repulsion will occur within the semiquinone ring to destabilize the radical system, and possibly resulting in a decrease in both spin and charge densities in order to reduce the unfavorable electron - electron repulsion. Figure 2.6. Res onance effects of amino - - donors. 2.5. 1 .1 Charge Density Polarization in 3,6 - R - tetraoxosemiquinones The Hammett equation has been widely used for the study and interpretation of organic reactions and their mechanisms, 58 and has show n success in describing a linear free - energy relationship between reaction rates and equilibrium constan ts for reactions involving meta - and para - substituted benzoic acid. 59 According to arene substitution pattern s , the installation of the substituents in the tetraoxo - ligands is locat ed o n meta - and ortho - positions to the oxygen atoms . Therefore, a n additive Hammett parameter, i.e. = m + o , was used to consider both the meta and ortho effects. 6 0 The plot generated does not show a strong enough correlation (R 2 = 0.68) to 37 indicate either inductive effects ( I - effects ( R ) as the dominating effect o n charge polarization (Fig. 2. 7 ) . Both the meta - Hammett plot (R 2 = 0.73, Fig. 2. 8 ) and the ortho - Hammett plot (R= 0.62, Fig. 2. 9 ) show s some correlation with the change of charge density, but not well enough to suggest either are the dominant effect of charge polarization. m is indicative of stronger inductive effects ( I - effects ( R ), where m = I + 0.33 R ; 60,61 while o - effect dominates, where o = I + R . 61 Figure 2. 7 . Percent c hange charge density vs. additive Hammett parameters for 3,6 - R - tetraoxosemiquinones. 38 Figure 2. 8 . Percent c hange charge density vs. meta Hammett parameters for 3,6 - R - tetraoxosemiquinones. Figure 2. 9 . Percent Change charge density vs. ortho Hammett parameters for 3,6 - R - tetraoxosemiquinones. 39 There may not be a clear picture about how charge is polarized by the substituents studied , but th e Lewis basicity , as related to the change of charge density calculated by DFT , seem ed to reflect well on the experimental reactivity of the corresponding ligands. This matches the synthetic observation s of the series of dichromium(III) and digallium(III) - tetraoxo bridging complexes described in later chapters . 2.5. 1 .2 Spin Density Polarization in 3,6 - R - tetraoxosemiquinones As shown in Fig. 2.5, the change in spin density and charge density inflicted by various substituents mostly track each other , except in the case of - donor/ - - acceptor, and a - acceptor. This trend does not agree with the spin density calculated for 3,6 - R - o - semiquinone s . 14 The extra two ortho - oxygens may exert extra donating effect s on the aromatic ring, alter ing th e substituent effects. Total spin density plot s of these deprotonated trianionic free ligands can provide some useful information. Previous study with EPR spectroscopy on [Ga 2 (tren) 2 (DHBQ sq,cat )](BPh 4 ) 2 (BF 4 ) and [Ga 2 (tren) 2 (CA sq,cat )](BPh 4 ) 2 (BF 4 ) by our gr oup 25 reported Cl induced spin delocalization, and its total spin density picture reinforced the experimental results with - spin density on the chlorine. Fig. 2. 9 shows - spin density on the CA sq,cat trianionic ligand, and the heavier - spin density is seen on the [Ga 2 (tren) 2 (CA sq,cat )] 3+ and the [Ga 2 (tren) 2 (NMe 2 - PhA sq,cat )] 3+ (see figures in Chapter 4 Appendix) - donors are - spin donors with - spin delocalized onto the substituents, 6 2 which is reflect ed on the total spin orbital picture shown in Fi g. 2. 10 for NMe 2 A sq,cat with increasing spin density on the oxygen atoms . This may be caused by the dominating resonance effect from NMe 2 to induce charge separation with stronger charge - dipole repulsion. 63 40 Figure 2. 10 . Total spin density plots of DHBQ sq,cat (left), CA sq,cat (middle), and NMe 2 A sq,cat (right). - - acceptors are - acceptors and can stabilize charge density on oxygen by reducing electrostatic repulsion within the aromatic ring. 62 This effect only impacts on the charge density in 3,6 - R - tetraoxosemiquinones , and an increase of spin density was observed. The spin density picture (Fig. 2. 1 1 ) also has both spin and spin density spread onto the CN group. It is likely that the four oxygen atoms exert more electron density on the ring; therefore, the effect of - acceptors is not sufficient enough to reduce the unfavorable charge - dipole repulsion. Figure 2. 1 1 . Total spin density plots of CN sq,cat . The change in spin density does not correlate to - HOMO - - LUMO gap (Fig. 2.1 2 ), which also disagrees with the DFT calculations done previously on phenoxy and 3,6 - R - semiquinone s . 14 In addition to that, spin density calculated for deprotonated trianioanic 3 ,6 - R - semiquinone exhibits discrepancies with the ones calculated for digallium - semiquinone complexes, which will be discussed in Chapter 4. The spin density information about free ligand s may not be relevant to spin polarization when coordinating to a meta l ion. 41 Table 2.1. Net spin density, charge density, and - HOMO - - LUMO gap (eV) of 3 ,6 - R - semiquinone R Spin Density a Charge Density b - HOMO - - LUMO gap (eV) c H 0.145636 - 0.648431 3.81 F 0.150166 - 0.625116 4.64 Cl 0.153349 - 0.558264 2.70 Br 0.153577 - 0.545560 2.09 I 0.167597 - 0.456596 1.58 Ph 0.156225 - 0.519430 1.01 OMe 0.147429 - 0.597403 1.42 NMe 2 0.145744 - 0.576497 1.23 Pip 0.119366 - 0.560983 0.48 CN 0.162844 - 0.532202 2.19 CF 3 0.158722 - 0.546376 2.64 a Spin density = b Charge density = c - HOMO - - LUMO gap = [energy level ( - LUMO ) energy level ( - HO MO )] in a.u. Figure 2. 1 2 . Percent Change s pin de nsity vs - HOMO - - LUMO gap (eV) parameters for 3,6 - R - tetraoxosemiquinones. 2.6 Concluding Comments The goal of this chapter was to utilize density functional calculation s to examine spin and charge distribution and understand their underlying mechanism s . In addition, the information provided for charge density can validate the synthetic viability of the substituents proposed. The Lewis basicity predicted by the trend in charge density matches the synthetic characteristics of 42 the corresponding bimetallic complexes, whic h will be further discussed in Chapter s 3 and 4. Although no absolute Hammett - typed relationship was established to explain if the substituents effects are dominate d by - effect s , the information provided about Lewis basicity is very handy for synthetic proposal before proceeding to the reactions. Based on this information, a series of bimetallic tetraoxolene - quinodal complexes were proposed as our synthetic targets (Fig. 2. 1 3 ), and the synthetic design for spin exchange - coupled syste ms focuses on these substituents. Figure 2. 1 3 . Cr 3+ or Ga 3+ tetraoxolene - quinodal complexes with a combination of diamagnetic or paramagnetic substituted - bridging ligands , where R 1 are the substituents on tetraoxoanilate, and R 2 are the substituents on 2,3,6,7 - tetraoxoanthracene . Spin polarization resulted from NPA analysis show ed inconsistent t r end s with the DFT result s of 3,6 - R - o - 1,2 - semiquinone s . 14 Again, no correlation can be established with the trend of spin density, and the electronic structure of the tetraoxo - quinoidal ligands may be altered from 3,6 - R - o - 1,2 - semiquinone because of the four che la ting oxygens. In the future, EPR studies can be perfo r med on trianionic free ligands in aqueous NaOH solution in the presence of Na 2 S 2 O 4 to experimentally validate if the DFT calculation s are legit imate benchmarks for spin polarization. 43 APPENDIX 44 APPENDIX Cartesian Coordinates and Bonding Information Used in the Single - Point Energy Calculations 1. [THB sq,cat ] 3 - Element Bond Length Bond Angle X Y Z O 1 - 0.2544210 - 2.2096230 1.7004450 O 2 2. 8782385 - 0.0659190 - 2.5512650 - 1.1512220 C 3 2.4024056 88.4994841 - 0.0901600 0.1633600 1.3635140 C 4 1.3018761 30.1935377 - 0.1357600 - 1.1928360 0.8961160 C 5 1.3018711 58.3061691 - 0.0368140 - 1.3721070 - 0.6002160 O 6 3.7005098 131.9656342 0.2544210 2.2096230 - 1.7004450 O 7 2.4023986 176.9995151 0.0659190 2.5512650 1.1512220 C 8 1.4352057 122.6637102 0.0901600 - 0.1633600 - 1.3635140 C 9 1.3018761 17.8408281 0.1357600 1.1928360 - 0.8961160 C 10 1.3018711 30.1938622 0.0368140 1.3721070 0.6002160 H 11 1.1033722 88.5011709 - 0.1624100 0.2943600 2.4566970 H 12 1.1033722 115.6407720 0.1624100 - 0.2943600 - 2.4566970 2. [FA sq,cat ] 3 - Element Bond Length Bond Angle X Y Z O 1 - 0.2492820 - 2.2073370 1.6958030 O2 2.8687275 - 0.0700450 - 2.5473140 - 1.1470630 C 3 2.3996327 88.2059208 - 0.0865180 0.1612240 1.3470000 C 4 1.2952874 29.7776638 - 0.1342250 - 1.1937980 0.8975110 C 5 1.2952584 58.4280626 - 0.0395580 - 1.3730720 - 0.6012420 O 6 3.6821176 132.4385159 0.2492820 2.2073370 - 1.6958030 O 7 2.3995650 176.4172903 0.0700450 2.5473140 1.1470630 C 8 1.4285047 123.4464186 0.0865180 - 0.1612240 - 1.3470000 C 9 1.2952874 17.7838734 0.1342250 1.1937980 - 0.8975110 C 10 1.2952584 29.7841880 0.0395580 1.3730720 0.6012420 F 11 1.4267483 88.2132747 - 0.1756230 0.3304900 2.7608670 F 12 1.4267483 114.9741541 0.1756230 - 0.3304900 - 2.7608670 3. [CA sq,cat ] 3 - Element Bond Length Bond Angle X Y Z Cl 1 - 0.1925700 0.3839140 3.2139340 O 2 3.0382799 - 0.2438260 - 2.2261730 1.6595970 O 3 2.7916885 127.4310024 - 0.0779870 - 2.5567720 - 1.1074820 C 4 2.4130483 38.3704779 - 0.0805510 0. 1606100 1.3443030 C 5 1.2789978 67.0749334 - 0.1321060 - 1.1992830 0.9053750 C 6 1.2789989 60.3557610 - 0.0414370 - 1.3800540 - 0.6076450 45 Element Bond Length Bond Angle X Y Z Cl 7 2.7999637 88.0478582 0.1925700 - 0.3839140 - 3.2139340 O 8 3.6599435 132.1802437 0.2438260 2.2261730 - 1.6595970 O 9 2.4130501 178.1200129 0.0779870 2.5567720 1.1074820 C 10 1.4298915 125.8542314 0.0805510 - 0.1606100 - 1.3443030 C 11 1.2789978 19.1153007 0.1321060 1.1992830 - 0.9053750 C 12 1.2789989 28.7037 276 0.0414370 1.3800540 0.6076450 4. [BA sq,cat ] 3 - Element Bond Length Bond Angle X Y Z O 1 - 0.2420170 - 2.2266010 1.6585800 O 2 2.7893483 - 0.0798100 - 2.5567100 - 1.1064120 C 3 2.4133491 88.9076789 - 0.0783690 0.1596060 1.3368820 C 4 1.2761865 28.4399103 - 0.1313780 - 1.2004460 0.9079690 C 5 1.2761877 60.4674447 - 0.0423570 - 1.3816640 - 0.6099050 O 6 3.6534789 132.4258537 0.2420170 2.2266010 - 1.6585800 O 7 2.4133472 177.8147481 0.0798100 2.5567100 1.1064120 C 8 1.4270585 126.3537159 0.0783690 - 0.1596060 - 1.3368820 C 9 1.2761865 19.1342360 0.1313780 1.2004460 - 0.9079690 C 10 1.2761877 28.4396263 0.0423570 1.3816640 0.6099050 Br 11 2.0529546 114.1144733 0.1976860 - 0.4025350 - 3.3719180 Br 12 2.0529546 88.9069346 - 0.1976860 0.4025350 3.3719180 5. [IA sq,cat ] 3 - Element Bond Length Bond Angle X Y Z O 1 - 0.2441640 - 2.2586950 1.6809260 O 2 2.8262540 - 0.0821910 - 2.5929630 - 1.1208130 C 3 2.4479835 88.7548796 - 0.0765930 0.1607880 1.3482920 C 4 1.3092510 28.2395506 - 0.1304110 - 1.2053090 0.9117860 C 5 1.3092774 60.5129668 - 0.0439200 - 1.3870470 - 0.6123750 O 6 3.6986836 132.6737299 0.2441640 2.2586950 - 1.6809260 O 7 2.4479449 177.5122225 0.0821910 2.5929630 1.1208130 C8 1.4352032 126.1778812 0.0765930 - 0.1607880 - 1.3482920 C9 1.3092510 19.0867737 0.1304110 1.2053090 - 0.9117860 C10 1.3092774 28.2451836 0.0439200 1.3870470 0.6123750 I11 2.2715344 88.7556259 - 0.2060890 0.4294360 3.6001640 I12 2.2715344 114.3343536 0.2060890 - 0.4294360 - 3.6001640 6. [CF 3 A sq,cat ] 3 - Element Bond Length Bond Angle X Y Z O 1 - 1.4996370 2.3225230 0.0000010 O2 2.7441211 1.2390000 2.4959240 - 0.0000250 C3 2.3974024 91.8264303 - 1.4244790 - 0.0737010 0.0000030 46 Element Bond Length Bond Angle X Y Z C4 1.2799636 30.9593169 - 0.8071000 1.2460940 - 0.0000040 C 5 1.2785370 61 .2732390 0.6965680 1.3381570 - 0.0000140 O 6 3.6888557 129.3590205 1.4996350 - 2.3225260 - 0.0000070 O 7 2.4293173 177.4176001 - 1.2389960 - 2.4959270 - 0.0000170 C 8 1.4590116 124.9684190 1.4244800 0.0736970 - 0.0000070 C 9 1.2799621 19.6819369 0.8071040 - 1.2460950 - 0.0000060 C 10 1.2785368 29.4823894 - 0.6965710 - 1.3381570 - 0.0000090 C 11 1.4705222 87.2369764 - 2.8947920 - 0.048 8960 0.0000040 C 12 1.4705221 120.8940401 2.8947930 0.0488980 0.0000020 F 13 1.3727628 116.9324586 - 3.5371270 - 1.2621080 0.0000170 F 14 1.4062044 115.8691195 - 3.4973980 0.6050 720 - 1.0893090 F 15 1.4062107 115.8687605 - 3.4973910 0.6050920 1.0893170 F 16 1.4062138 115.8686728 3.4973890 - 0.6050360 1.0893530 F 17 1.3727612 116.9323018 3.5371190 1.2621130 - 0.0000400 F 18 1.4062043 115.8690039 3.4974040 - 0.6051250 - 1.0892750 7. [OMeA sq,cat ] 3 - Element Bond Length Bond Angle X Y Z O 1 - 1.7858720 2.1246410 - 0.2827190 O2 2.8314301 0.9704730 2.6096660 0.1465940 C 3 2.4011586 89.1811938 - 1.3437400 - 0.2348580 - 0.2293690 C 4 1.3018743 30.0483459 - 0.9454970 1.1381180 - 0.1585460 C 5 1.2890101 59.3843300 0.5185310 1.4042930 0.0804770 O 6 3.6916031 131.4689861 1.7858610 - 2.1246380 0.2827470 O 7 2.4053789 178.1802706 - 0.9704780 - 2.6096570 - 0.1465880 C 8 1.4389917 123.61 23390 1.3437430 0.2348660 0.2293490 C 9 1.3018753 18.4892136 0.9454910 - 1.1381100 0.1585690 C 10 1.2890104 29.8818875 - 0.5185350 - 1.4042840 - 0.0804730 O 11 1.4485209 89.8550771 - 2.7414230 - 0.4992170 - 0.5028820 O 12 1.4485216 115.1222759 2.7414280 0.4992370 0.5028440 C 13 1.3958182 111.7148571 3.5672620 0.0123260 - 0.5116630 H 14 1.1161057 108.2147314 4.6282880 0.1763060 - 0.2066610 H 15 1.1020178 109.9856829 3.3892360 - 1.0653870 - 0.6575560 H 16 1.1147781 112.8748570 3.4245850 0.54 57980 - 1.4800540 C 17 1.3958174 111.7142607 - 3.5672480 - 0.0123660 0.5116600 H 18 1.1020189 109.9858844 - 3.3892420 1.0653450 0.6576000 H 19 1.1161065 108.2148868 - 4.6282780 - 0.1763460 0.2066690 H 20 1.1147751 112.8747157 - 3.4245440 - 0.5458790 1.4800210 8. [PipA sq,cat ] 3 - Element Bond Length Bond Angle X Y Z O 1 - 1.5706160 2. 2651810 - 0.3344560 47 Element Bond Length Bond Angle X Y Z N 2 4.9249259 2.8640030 0.1346390 - 0.1112070 C 3 1.2992675 29.9292638 - 0.8385180 1.2002060 - 0.2004530 C 4 1.4992567 119.9621465 0.6542790 1.3008340 - 0.2963790 C 5 1.4373292 116.8351415 1.4016960 0.0937240 - 0.0723960 C 6 1.4333101 97.1560662 3.6089750 1.3089010 0.2 359290 H 7 1.0896846 108.9920317 2.9773800 1.9658340 0.8333730 H 8 1.1179864 113.1825880 3.9045500 1.9209840 - 0.6516990 C 9 1.5479535 109.8260299 4.9119140 0.9065680 0.9684850 H 10 1.1098191 111.0156676 5.5267380 1.7993860 1.2063210 H 11 1.0996445 108.8619872 4.6495560 0.4196120 1.9188850 C 12 1.5383701 110.1204264 5.7288040 - 0.06546 90 0.0999130 H 13 1.1062212 108.0231355 6.0936870 0.4898060 - 0.7845390 H 14 1.1073608 111.3968835 6.6311730 - 0.4228850 0.6330470 C 15 1.5368804 111.0779781 4.8605500 - 1.2377560 - 0.3836980 H 16 1.1077229 109.7945609 5.4365640 - 1.8633320 - 1.0935660 H 17 1.0976321 110.5790596 4.5579230 - 1.8683840 0.4621870 C 18 1.436 1307 131.6366403 3.5504260 - 0.7377310 - 1.0223960 H 19 1.1272872 113.3441850 3.8001200 - 0.2484320 - 2.0067820 H 20 1.0934237 106.5624266 2.8967780 - 1.5998630 - 1.1806620 O 21 2.3995159 152.6948248 1.5705880 - 2.2650910 0.3339830 N 22 2.4455602 89.6437714 - 2.8639980 - 0.1344670 0.1107440 C 23 1.2992689 30.3522375 0.8385770 - 1.2000430 0.2000710 C 24 1.4993714 119.9569452 - 0.6543220 - 1.3006670 0.2962070 C 25 1.4370988 122.4592312 - 1.4016440 - 0.0936010 0.0719540 C 26 1.4333272 147.8640719 - 3.6088630 - 1.3088940 - 0.2361340 H 27 1.0896633 108.9927521 - 2.9774350 - 1.9656010 - 0.8339640 H 28 1.1179598 113.1846683 - 3.9038600 - 1.9211420 0.6515390 C 29 1.5479442 109.8256266 - 4.9122060 - 0.9068100 - 0.9680880 H 30 1.1099782 111.0155030 - 5.5270410 - 1.7998770 - 1.2057030 H 31 1.0995630 108.8718650 - 4.6505780 - 0.4197350 - 1.9185340 C 32 1.5383609 110.1216915 - 5.7289760 0.0649450 - 0.0991040 H 33 1.1061906 108.0315160 - 6.0933750 - 0.4903320 0.7855080 H 34 1.1073806 111.3967084 - 6.6316 150 0.4222640 - 0.6318870 C 35 1.5369965 111.0750874 - 4.8607070 1.2375050 0.3841870 H 36 1.1077247 109.7958940 - 5.4365440 1.8629770 1.0942930 H 37 1.0976454 110.5775823 - 4.5585660 1.8681840 - 0.4618510 C 38 1.4361561 98.3424727 - 3.5502310 0.7376910 1.0223190 H 39 1.1272744 113.3442628 - 3.7993850 0.2482630 2.0067630 H 40 1.0934226 106.5599530 - 2.8966180 1.5998740 1.1804440 O 41 1.2949128 120.0930878 1.2131150 2.4406780 - 0.5518340 O 42 1.2945424 120.0872694 - 1.2128370 - 2.4401710 0.5520030 48 9. [PhA sq,cat ] 3 - Element Bond Length Bond Angle X Y Z O 1 - 1.4943450 0.0000000 - 0.0000050 C2 1.4684744 - 0.7519820 - 1.2670100 - 0.0000160 C3 1.5039640 120.3668108 0.7519820 - 1.2670110 0.0000170 C4 1.4684753 120.3667149 1.4943450 0.0000000 0.0000030 C5 1.4684758 119.2664603 0.7519810 1.2670110 - 0.00 00100 C 6 1.4684758 119.2664405 - 0.7519810 1.2670110 0.0000050 C 7 1.4664640 120.3667530 2.9608090 0.0000000 0.0000020 C 8 1.4397667 123.2226260 3.7496480 1.2044340 - 0.0000280 C 9 1.4397681 123.2226375 3.7496490 - 1.2044350 0.0000310 C 10 1.3919874 122.7915825 5.1415960 1.1939620 - 0.0000310 H 11 1.0847265 115.4486969 3.1856480 2.13 10060 - 0.0000490 C 12 1.3919864 122.7915525 5.1415960 - 1.1939620 0.0000280 H 13 1.0847257 115.4486579 3.1856490 - 2.1310060 0.0000540 C 14 1.4040872 122.1815603 5.8804570 0.0000000 - 0.0000030 H 15 1.0966372 118.4639777 5.6714980 2.1540750 - 0.0000560 H 16 1.0966377 118.4639819 5.6714990 - 2.1540750 0.0000510 H 17 1.0942180 121.7505169 6.9746750 0.0000000 - 0.0000040 C 18 1.4664640 120.3667728 - 2.9608090 0.0000000 - 0.0000040 C 19 1.4397667 123.2226260 - 3.7496480 1.2044340 0.000 0350 C 20 1.4397676 123.2226042 - 3.7496480 - 1.2044350 - 0.0000370 C 21 1.3919874 122.7915825 - 5.1415960 1.1939620 0.0000400 H 22 1.0847265 115.4486969 - 3.1856480 2.1310060 0.0000590 C 23 1.3919874 122.7915195 - 5.1415960 - 1.1939620 - 0.0000320 H 24 1.0847257 115.4486912 - 3.1856480 - 2.1310060 - 0.0000660 C 25 1.4040867 122.1 815256 - 5.8804560 0.0000000 0.0000070 H 26 1.0966377 118.4640234 - 5.6714990 2.1540750 0.0000710 H 27 1.0966377 118.4639822 - 5.6714990 - 2.1540750 - 0.0000590 H 28 1.0942190 121.7504822 6.9746750 0.0000000 0.0000090 O 29 1.2811311 115.7410342 1.3083820 - 2.4210110 0.0000490 O 30 1.2811311 123.8922311 - 1.3083820 - 2.4210100 - 0.0000440 O 31 1.2811316 123.8921769 1.3083820 2.4210110 - 0.0000260 O 32 1.2811307 123.8921575 - 1.3083820 2.4210100 0.0000190 10. [NMe 2 PhA sq,cat ] 3 - Element Bond Length Bond Angle X Y Z O 1 - 1.2211130 2.4652000 - 0.0002120 O2 2.6169188 1.3941550 2.3722640 - 0.0001320 N 3 6.4795882 158.4429104 - 7.3282150 0.2999360 - 0.0000280 C 4 2.4268932 94.3894525 - 1.4926740 0.0535480 - 0.0000930 C 5 1.4623803 94.3341056 - 2.9540810 0.1068940 - 0.0000740 49 Element Bond Length Bond Angle X Y Z C 6 1.2794654 30.1954772 - 0.7053870 1.2942780 - 0.0001650 C 7 1.4408114 123.1303192 - 3.7850400 - 1.0701550 0.0003500 H 8 1.0846785 115.4525123 - 3.2537780 - 2.0158230 0.0005980 C 9 1.2798365 64.1934748 0.7964320 1.2405800 - 0.0001210 C 10 1.4613198 23.0577732 - 5.8696770 0.2098110 - 0.0000310 C 11 1.3900124 122.8825734 - 5.1738950 - 1.0134430 0.0003920 H 12 1.0952854 118.5676035 - 5.7364660 - 1.9532110 0.0007490 C 13 1.4034556 120.1501030 - 5.0912630 1.3776120 - 0.0004730 H 14 1.0937246 118.1117743 - 5.6081410 2.3414950 - 0.0008200 C 15 1.3904600 122.0714760 - 3.7013550 1 .3384360 - 0.0004760 H 16 1.0844356 121.5836513 - 3.1075870 2.2458720 - 0.0007730 C 17 1.4523879 121.6665625 - 7.9457680 - 0.2400610 - 1.1985530 H 18 1.0944355 108.9280624 - 7.4698400 0.2085020 - 2.0760910 H 19 1.1059259 110.4093683 - 9.0241610 0.0042080 - 1.2203080 H 20 1.1110945 114.2829550 - 7.8591180 - 1.3431230 - 1.2999280 C 21 1.4523874 121.6476865 - 7.9456980 - 0.2388350 1.1990840 H 22 1.1110936 114.2835270 - 7.8590900 - 1.3417970 1.3015670 H 23 1.1059260 110.4092563 - 9.0240780 0.0055060 1.2206780 H 24 1.0944367 108.9276532 - 7.4696850 0.2105980 2.0761320 O 25 3.7025135 126.4406418 1.2211020 - 2.4651870 - 0.0001930 O 26 2.4278003 171.2493628 - 1.3941420 - 2.3722520 - 0.0000600 N 27 6.4795961 117.6129906 7.3282180 - 0.2999390 0.0003190 C 28 1.4695236 123.8777465 1.4926760 - 0.0535390 - 0.0000760 C 29 1.4623808 120.3715451 2.9540830 - 0.1068970 - 0.0000060 C 30 1.2794597 23.3647957 0.7053970 - 1.2942620 - 0.0001110 C 31 1.4408114 123.129 9936 3.7850450 1.0701500 - 0.0001270 H 32 1.0846805 115.4515210 3.2537680 2.0158120 - 0.0002830 C 33 1.2798307 30.1668343 - 0.7964390 - 1.2405640 - 0.0000620 C 34 1.4613202 23.0572048 5.8696790 - 0.2098240 0.0002580 C 35 1.3900106 122.8825078 5.1738980 1.0134330 - 0.0000180 H 36 1.0952852 118.5675827 5.7364720 1.9531990 - 0.0001520 C 37 1.4034539 120.1506906 5.0912620 - 1.3776210 0.0003570 H 38 1.0937240 118.1117419 5.6081370 - 2.3415050 0.0005800 C 39 1.3904611 122.0715059 3.7013530 - 1.3384410 0.0002240 H 40 1.0844342 121.5832828 3.10 75890 - 2.2458780 0.0002700 C 41 1.4523785 121.6740670 7.9457640 0.2401650 1.1987880 H 42 1.0944383 108.9285031 7.4698570 - 0.2083350 2.0763730 H 43 1.1059253 110.4092470 9.0241600 - 0.0040870 1.2205570 H 44 1.1110930 114.2834520 7.8591070 1.3432330 1.3000760 C 45 1.4523954 121.6393335 7.9456930 0.2387160 - 1.1988590 H 46 1.1110967 114.2821189 7.8589940 1.3416620 - 1.3014710 H 47 1.1059255 110.4105932 9.0240920 - 0.0055420 - 1.2204200 H 48 1.0944337 108.9273368 7.4697120 - 0.2108530 - 2.0758510 50 11. [CNPhA sq,cat ] 3 - Element Bond Length Bond Angle X Y Z O 1 1.2064550 - 2.3207790 0.5413500 O2 2.6442863 - 1.2063100 - 2.3208940 - 0.5406920 C3 2.4059253 91.9131798 1.5370390 0.0000830 0.0002490 C4 1.4545130 97.89829 57 2.9915520 0.0000520 0.0000450 C5 1.2498681 29.4166312 0.7551460 - 1.2106860 0.1861260 C 6 1.4422212 123.0582005 3.7782520 1.1690560 - 0.3074200 H 7 1.0823137 116.9030065 3.236465 0 2.0735060 - 0.5520420 C 8 1.2498755 63.5296203 - 0.7550870 - 1.2107510 - 0.1854890 C 9 2.4632489 93.6707771 5.9245520 0.0000160 - 0.0002770 C 10 1.3777257 123.1556727 5.1559750 1.1716900 - 0.3067030 H 11 1.0912852 119.2073798 5.6868580 2.0932860 - 0.5510950 C 12 1.4343916 86.9884173 5.1560060 - 1.1716610 0.3063000 H 13 1.0912837 118.4896049 5.6869360 - 2.0932700 0.5505340 C 14 1.3777190 122.3016804 3.7782900 - 1.1689930 0.3073370 H 15 1.0823003 119.9413630 3.2365310 - 2.0734110 0.5520800 O 16 3.6337656 151.0722129 - 1.2064580 2.3208700 0.541 2640 O 17 2.4059284 164.2019230 1.2063400 2.3209990 - 0.5405640 C 18 1.4532241 125.5960749 - 1.5370400 0.0000020 0.0002180 C 19 1.4545160 122.5510890 - 2.9915560 - 0.0000290 0.0000780 C 20 1.2498628 15.2239333 - 0.7551750 1.2107520 0.1861040 C 21 1.4422366 123.0580541 - 3.7782250 - 1.1690760 - 0.3073750 H 22 1.0823098 116.9024297 - 3.2364000 - 2.0735040 - 0.5519770 C 23 1.2498675 29.4151573 0.7551140 1.2108250 - 0.1854900 C 24 2.4632481 93.6701761 - 5.9245510 - 0.0000760 - 0.0002680 C 25 1.3777218 123.1551020 - 5.1559440 - 1.1717430 - 0.3066550 H 26 1.0912 847 119.2077897 - 5.6868120 - 2.0933550 - 0.5510170 C 27 1.4343835 86.9889319 - 5.1560470 1.1716170 0.3063150 H 28 1.0912840 118.4896470 - 5.6870060 2.0932020 0.5505780 C 29 1.3777219 122.3015328 - 3.7783280 1.1689880 0.3073580 H 30 1.0823016 119.9425847 - 3.2365750 2.0734150 0.5520870 C 31 1.4039230 150.6134235 7.3284750 - 0.0000170 - 0.0004040 N 32 1.1844500 179.9927690 8.5129250 - 0.0001930 - 0.0005310 C 33 1.4039260 150.6131303 - 7.3284770 - 0.0000670 - 0.0004540 N 34 1.1844520 179.9958813 - 8.5129290 0.0000030 - 0.0005530 12. [CF 3 PhA sq,cat ] 3 - Element Bond Length Bond Angle X Y Z O 1 1.2110170 2.3263940 0.5288050 O2 2.6429266 - 1.2110280 2.3263800 - 0.5289090 C3 2.4065358 92.0267027 1.5 393070 0.0040980 - 0.0102510 C4 1.2513435 29.4564356 0.7564520 1.2141630 0.1792720 51 Element Bond Length Bond Angle X Y Z C5 1.2513425 63.5961145 - 0.7564560 1.2141580 - 0.1793600 O6 3.6341139 150.9883293 - 1.2063370 - 2.3199940 0.5376900 O 7 2.4063468 164.2036758 1.2063480 - 2.3199800 - 0.5377970 C 8 1.4536317 125.4985590 - 1.5393070 0.0040910 0.010 1850 C 9 1.2514248 15.2059206 - 0.7545370 - 1.2068540 0.1871760 C 10 1.2514252 29.4792407 0.7545410 - 1.2068480 - 0.1872650 C 11 1.4541348 97.9028178 2.9933790 0.0055830 - 0.0236800 C 12 1.4447335 123.1445685 3.7817350 - 1.1668450 - 0.3256110 C 13 1.4447485 123.1368974 3.7845870 1.1807940 0.2594580 C 14 1.3783228 123.1245538 5.1599570 - 1.1640160 - 0.3420380 H 15 1.0822704 116.8491312 3.2392970 - 2.0746660 - 0.5556790 C 16 1.3782961 123.1267434 5.1627480 1.1835370 0.2403540 H 17 1.0822897 116.8583772 3.2446380 2.0881460 0.4971940 C 18 1.4288318 122.1865991 5.9218730 0.015071 0 - 0.0758370 H 19 1.0910153 118.9895562 5.6877500 - 2.0873160 - 0.5854840 H 20 1.0910092 118.9884341 5.6927780 2.1108190 0.4628790 C 21 1.4541351 122.6075176 - 2.9933790 0.0055770 0.0236450 C 22 1.4447332 123.1445599 - 3.7817290 - 1.1668500 0.3255940 C 23 1.4447483 123.1368920 - 3.7845920 1.1807890 - 0.2594740 C 24 1.3783222 123.1245796 - 5.1599500 - 1.1640190 0.3420580 H 25 1.0822701 116.8490868 - 3.2392860 - 2.0746720 0.5556450 C 26 1.3782957 123.1267442 - 5.1627520 1.1835350 - 0.2403330 H 27 1.0822901 116.8584227 - 3.2446480 2.0881400 - 0.4972270 C 28 1.4288327 122.1866196 - 5.921872 0 0.0150700 0.0758780 H 29 1.0910149 118.9895778 - 5.6877380 - 2.0873180 0.5855170 H 30 1.0910092 118.9884953 - 5.6927870 2.1108170 - 0.4628460 C 31 1.4420742 122.0524497 - 7.3621270 - 0.0039750 0.0060160 C 32 1.4420751 122.0523807 7.3621270 - 0.0039760 - 0.0059360 F 33 1.4287295 117.5149208 - 7.9577260 - 0.3193860 - 1.2537640 F 34 1.3819196 114.4308080 - 7.9644450 1.2055880 0.2956230 F 35 1.3821708 114.4313941 - 7.9621740 - 0.9370250 0.8304900 F 36 1.3821707 114.4313766 7.9621940 - 0.9370360 - 0.8303840 F 37 1.3819203 114.4308362 7.9644560 1.2055830 - 0.2955400 F 38 1.4287275 117.5148913 7.95 76900 - 0.3193740 1.2538620 13. [NAT sq,cat ] 3 - Element Bond Length Bond Angle X Y Z C 1 - 2.5356630 - 0.7650380 0.0000020 C2 1.4241907 - 1.2579070 - 1.3940520 0.0000010 C3 1.4213172 126.0449867 0.0000000 - 0.7323780 0.0000000 C4 1.4647560 117.7449024 0.0000000 0.7323780 0.0000020 C5 1.4213172 117.7449024 - 1.2579070 1.3940520 0.0000000 52 Element Bond Length Bond Angle X Y Z C6 1.4241907 126.0449867 - 2.5356630 0.7650380 - 0.0000030 H7 2.1685599 98.0161215 1.2673190 - 2.4920810 - 0.0000010 H8 1.0980693 115.7189472 - 1.2673200 - 2. 4920810 0.0000000 C9 1.4213172 124.5101952 1.2579070 - 1.3940520 0.0000000 C10 1.4213172 117.7449024 1.2579070 1.3940520 0.0000010 H11 1.0980693 118.2360661 - 1.2673200 2.4920810 0.0000000 C12 1.4241898 126.0449690 2.5356620 0.7650380 0.0000020 C13 1.4241907 126.0449867 2.5356630 - 0.7650380 0.0000020 H14 1.0980693 118.2360139 1.2673190 2.4920810 0.0000000 O15 1.2828617 123.2019129 - 3.6400130 1.4178360 0.0000000 O16 1.2828617 123.2019129 - 3.6400130 - 1.4178360 - 0.0000010 O17 1.2828626 123.2019179 3.6400130 1.4178360 - 0.0000010 O18 1.2828612 1 23.2019513 3.6400130 - 1.4178350 - 0.0000020 14. [AnT sq,cat ] 3 - Element Bond Length Bond Angle X Y Z C1 - 0.7691250 3.7724360 - 0.0000250 C2 1.4226812 - 1.4034070 2.4989730 - 0.0000330 C 3 1.4163938 125.3948525 - 0.7356510 1.2498640 - 0.0003770 C 4 1.4713030 118.1276279 0.7356520 1.2498820 - 0.0003930 C 5 1.4164233 118.1283461 1.4034070 2.4990250 - 0.0002010 C 6 1.4226418 125.3947463 0.7691250 3.7724440 - 0.0003210 C 7 1.4124184 124.1145416 - 1.3934490 - 0.0000270 - 0.0003530 C 8 1.4123861 117.7570706 1.3934490 0.0000270 - 0.0003530 C 9 1.4124184 12 4.4851009 0.7356510 - 1.2498640 - 0.0003770 C 10 1.4123861 124.4851009 - 0.7356520 - 1.2498820 - 0.0003930 C 11 1.4164233 124.1145822 - 1.4034070 - 2.4990250 - 0.0002010 H 12 1.0955513 118.5396057 - 2. 4989300 - 2.5069020 - 0.0000250 C 13 1.4226418 125.3947463 - 0.7691250 - 3.7724440 - 0.0003210 C 14 1.5382500 116.4773072 0.7691250 - 3.7724360 - 0.0000250 C 15 1.4163938 124.1145416 1.4034070 - 2.4989730 - 0.0000330 H 16 1.0955418 116.0618199 - 2.4989200 2.5069080 0.0001540 H 17 1.0955513 118.5396057 2.4989300 2.5069020 - 0.0000250 H 18 1.0955418 118.5433274 2.4989200 - 2.5069080 0.0001540 O 19 1.2723320 123.4142545 1.4073690 4.8731130 0.0006520 O 20 1.2723340 123.4124587 - 1.4074200 4.8730780 0.0006300 O 21 1.2723340 120.1104232 1.4074200 - 4.8730780 0.0006300 O 22 1.2723320 123.4142545 - 1.4073690 - 4.8731130 0.0006520 H 23 1.0949120 117.7585564 2.4883610 0.0000120 - 0.0001680 H 24 1.0949120 117.7563422 - 2.4883610 - 0.0000120 - 0.0001680 53 15. [MeAnT sq,cat ] 3 - Element Bond Length Bond Angle X Y Z C1 - 3.7790180 - 0.7633690 0.0668410 C2 1.4236161 - 2.5030950 - 1.3934520 0.0256250 C3 1.4197233 126.1738947 - 1.2456940 - 0. 7367650 - 0.0319860 C4 1.4735590 117.5520286 - 1.2456860 0.7367940 - 0.0321060 C5 1.4196705 117.5507719 - 2.5030620 1.3934520 0.0250800 C6 1.4236528 126.1739380 - 3.7790180 0.7633450 0.0 661750 C7 1.4237644 123.6269593 - 0.0000280 - 1.4231080 - 0.0979760 C8 1.4237860 118.8189206 0.0000270 1.4231080 - 0.0979760 C9 1.4237699 122.0712972 1.2457010 0.7367670 - 0.0319980 C 10 1.4237915 122.0712972 1.2456930 - 0.7367960 - 0.0321180 C 11 1.4196724 123.6292852 2.5030720 - 1.3934510 0.0250840 H 12 1.0902412 119.6367945 2.5411070 - 2.4819260 0.0740880 C 13 1.4236529 126.1741100 3.7790280 - 0.7633440 0.0661830 C 14 1.5267131 116.2706099 3.7790280 0.7633690 0.0668480 C 15 1.4197251 123.6273568 2.5031050 1.3934510 0.0256280 H 16 1.0902354 114.1668283 - 2.5410020 - 2.4819060 0.0750640 H 17 1.0902431 119.6365443 - 2.5410900 2.4819300 0.0740640 H 18 1.0902336 119.6320482 2.5410190 2.4819020 0.0750870 O 19 1.2716324 123.1618307 - 4.8728190 1.4099570 0.1165870 O 20 1.2716386 123.1661115 - 4.8728490 - 1.4099040 0.1177420 O 21 1.2716382 120.5602054 4.8728580 1.4099030 0.1177730 O 22 1.2716325 123.1618217 4.8728280 - 1.4099560 0.1166190 C 23 1.5141367 118.9605802 0.0000090 2.9318680 - 0.2254640 H 24 1.0977509 110.9798658 - 0.8859470 3.2801020 - 0.7721560 H 25 1.1079179 114.2534549 - 0.0001970 3.4704070 0.7427600 H 26 1.0977690 110.9799861 0.8862050 3.2801650 - 0.7717630 C 27 1.5141377 118.9624385 - 0.0000570 - 2.9318690 - 0.2254640 H 28 1.0977492 110.9802775 0.8857770 - 3.2801220 - 0.7723380 H 29 1.1079166 114.2534364 0.0003250 - 3.4704070 0.7427590 H 30 1.0977699 110.9794211 - 0.8863750 - 3.2801440 - 0.7715810 16. [PhAnT sq,cat ] 3 - Element Bond Length Bond Angle X Y Z C1 0.7600170 - 3.7881570 - 0.1338160 C2 1.4259003 1.3894720 - 2.5092170 - 0.0978900 C3 1.4132598 126.2800162 0.7372930 - 1.2582110 - 0.0145250 C4 1.4747220 117.4854175 - 0.7374290 - 1.2581120 - 0.0147250 C5 1.4132580 117.4857632 - 1.3897600 - 2.5090030 - 0.0985940 C6 1.4259083 126.2799801 - 0.7604830 - 3.7880440 - 0.1343560 C7 1.4362072 123.6086371 1.4298110 - 0.0000770 - 0.0000710 C8 1.4362194 118.8272500 - 1.4298490 0.0000880 - 0.0001140 54 Element Bond Length Bond Angle X Y Z C 9 1.4362228 122.3468013 - 0.7372910 1.2582170 0.0144030 C 10 1.4361915 122.3493982 0.7374290 1.2581150 0.0142800 C 11 1.4132743 123.6064062 1.3897890 2.5090470 0.0975860 H 12 1.0871224 119.5498381 2.4742320 2.5447490 0.1649940 C 13 1.4258870 126.28 02341 0.7605280 3.7880730 0.1333180 C 14 1.5204981 116.1912514 - 0.7599700 3.7881530 0.1339070 C 15 1.4132450 123.6076638 - 1.3894360 2.5091990 0.0981430 H 16 1.0871204 114.1533760 2. 4739110 - 2.5451100 - 0.1652290 H 17 1.0871229 119.5514086 - 2.4741740 - 2.5447070 - 0.1664740 H 18 1.0871205 119.5527859 - 2.4738450 2.5450940 0.1659640 O 19 1.2667202 123.0134315 - 1.4087880 - 4.8748310 - 0.1907010 O 20 1.2667277 123.0129362 1.4081980 - 4.8750600 - 0.1895140 O 21 1.2667207 120.7806057 - 1.4081380 4.8750230 0.1902380 O 22 1.2667302 123.0142152 1.4088410 4.87489 70 0.1890790 C 23 1.4840380 118.8258406 - 2.9138870 0.0001470 0.0000390 C 24 1.4145690 122.0887771 - 3.6654260 0.6884300 - 0.9810120 C 25 1.4145692 122.0825844 - 3.6651490 - 0.6881110 0.98 13200 C 26 1.3939545 122.2143262 - 5.0593770 0.6893560 - 0.9839890 H 27 1.0858771 117.9879586 - 3.1238350 1.2356620 - 1.7467440 C 28 1.3939556 122.2150151 - 5.0591000 - 0.6889290 0.9847870 H 29 1.0858744 117.9871700 - 3.1233310 - 1.2354080 1.7468410 C 30 1.3996353 120.7187102 - 5.7769060 0.0002470 0.0005210 H 31 1.0912797 119.3842019 - 5.5927980 1.2315060 - 1.7665660 H 32 1.0912789 119.3839898 - 5.5922840 - 1.2310450 1.7675480 H 33 1.0905830 120.8468505 - 6.8674890 0.0003230 0.0007150 C 34 1.4840650 118.8242950 2.9138760 - 0.0001800 0.0000360 C 35 1.4145462 122.08635 73 3.6653970 0.6877650 - 0.9812330 C 36 1.4145579 122.0823786 3.6650830 - 0.6881440 0.9815490 C 37 1.3939635 122.2135435 5.0593570 0.6886080 - 0.9842530 H 38 1.0858764 117.9879540 3.1238020 1.2347760 - 1.7471190 C 39 1.3939575 122.2134615 5.0590360 - 0.6890560 0.9849730 H 40 1.0858761 117.9873942 3.1232290 - 1.2351570 1.7472500 C 41 1.3996310 120.7174050 5.7768460 - 0.0002380 0.0004640 H 42 1.0912779 119.3854600 5.5928060 1.2304930 - 1.7669920 H 43 1.0912774 119.3850989 5.5922250 - 1.2309430 1.7678870 H 44 1.0905840 120.8460364 6.8674300 - 0.0002590 0.0006130 17. [CNPh - AnT sq,cat ] 3 - Element Bond Length Bond Angle X Y Z C1 - 0.7570440 3.7883960 - 0.1397280 C2 1.4303917 - 1.3853500 2.5037820 - 0.1078100 C3 1.4059423 126.3784644 - 0.7372500 1.2610220 0.0025880 C4 1.4745660 117.4515974 0.7373160 1.2609920 0.0027600 55 Element Bond Length Bond Angle X Y Z C5 1.4059726 117.4511267 1.3854960 2.5037780 - 0.1072610 C6 1.4303506 126.3795658 0.7572610 3.7883750 - 0.1394210 C7 1.4456395 123.0619408 - 1.4440680 - 0.0000390 - 0.0000770 C 8 1.4455900 119.2659635 1.4439880 - 0.0 000940 0.0000940 C 9 1.4455460 121.4678093 0.7372810 - 1.2611100 - 0.0025740 C 10 1.4455921 121.4640280 - 0.7373770 - 1.2611170 - 0.0026600 C 11 1.4059368 123.0683060 - 1.3854550 - 2.5038930 0.10761 70 H 12 1.0853041 119.9233421 - 2.4651140 - 2.5442150 0.2105520 C 13 1.4303831 126.3806846 - 0.7571600 - 3.7884970 0.1397680 C 14 1.5143390 116.0558430 0.7571790 - 3.7884950 0.1396780 C 15 1.4059573 123.0641786 1.3854120 - 2.5038800 0.1077210 H 16 1.0852965 113.6717808 - 2.4649830 2.5440780 - 0.2109470 H 17 1.0853069 119.9215567 2.4651820 2.5440220 - 0.2099720 H 18 1.0853041 119.9207908 2.4650730 - 2.5441140 0.2106690 O 19 1.2606352 122.7741356 1.4091910 4.8654450 - 0.2035190 O 20 1.2606199 122.7720457 - 1.4089460 4.8654490 - 0.2040950 O 21 1.2606183 121.1394670 1.4090790 - 4.8655620 0.2038000 O 22 1.2606116 122.7732196 - 1.4090480 - 4.8655490 0.2041320 C 23 1.4653260 119.2654405 2.9093140 - 0.0001100 0.0000600 C 24 1.4254250 122.3979399 3.6730220 - 0.7935250 - 0. 9049700 C 25 1.4254063 122.3959270 3.6730290 0.7933490 0.9050160 C 26 1.3816567 122.7386361 5.0545890 - 0.7889280 - 0.9200260 H 27 1.0847106 118.0886318 3.1386870 - 1.4080440 - 1.6215240 C 28 1.3816781 122.7387871 5.0546200 0.7889380 0.9198870 H 29 1.0847127 118.0907364 3.1387430 1.4077720 1.6216920 C 30 1.4187930 120.9799158 5.7923560 0.0000600 - 0.0001080 H 31 1.0881617 119.8862350 5.5908640 - 1.3903110 - 1.6513560 H 32 1.0881627 119.8846580 5.5908860 1.3903660 1.6511880 C 33 1.4652590 119.2676452 - 2.9093270 0.0000300 - 0.0000620 C 34 1.4254517 122.3983399 - 3.6 731340 - 0.7936330 - 0.9048330 C 35 1.4254457 122.3997437 - 3.6730670 0.7937980 0.9046640 C 36 1.3816495 122.7407671 - 5.0546950 - 0.7890810 - 0.9197930 H 37 1.0847119 118.0885976 - 3.1388660 - 1.4082440 - 1.6213600 C 38 1.3816525 122.7401659 - 5.0546310 0.7893160 0.9196420 H 39 1.0847099 118.0904743 - 3.1387810 1.4084540 1.6211360 C 40 1.4188219 120.9816726 - 5.7924590 0.0001200 - 0.0000530 H 41 1.0881660 119.8840983 - 5.5909700 - 1.3906590 - 1.6509690 H 42 1.0881665 119.8839361 - 5.5908640 1.3909590 1.6507960 C 43 1.4175910 121.3304251 7.2099470 0.0001480 - 0.0001800 N 44 1.17 34380 179.9985842 8.3833850 0.0002150 - 0.0002680 C 45 1.4175720 121.3336969 - 7.2100310 0.0001540 0.0000010 N 46 1.1734440 179.9958599 - 8.3834750 0.0001460 - 0.0000310 56 18. [pyrene] 3 - Element Bond Length Bond Angle X Y Z C1 - 0.0000010 3.5211880 - 0.0003670 C2 1.4032882 - 1.2182940 2.8247830 - 0.0003070 C3 1.4060200 121.5287941 - 1.2618570 1.4194380 - 0.0001610 C4 1.4542966 118.0348379 0.0000010 0.6964630 - 0.0000720 C5 1.4542953 120.3792694 1.2618570 1.4194390 - 0.0001350 C6 1.4032894 120.4934693 1.2182940 2.8247840 - 0.0002820 C7 1.4728133 119.1838874 - 2.5693440 0.7414580 - 0.0001050 C8 1.3929260 119.8103287 0.0000010 - 0.6964630 0.0000730 C9 1.4542966 119.8103286 - 1.2618570 - 1.4194380 0.0001350 C10 1.4728133 122.7812746 - 2.5693440 - 0.7414580 0.0000500 C11 1.4060200 118.0348378 - 1.2182940 - 2.8247830 0.0002820 H 12 1.0899604 116.6433026 - 2.1769060 - 3.3435090 0.0003260 C 13 1.4032882 121.5287942 - 0.0000010 - 3.5211880 0.0003680 C 14 1.4032894 120.4934693 1.2182940 - 2.8247840 0.0003080 C 15 1.4060200 121.5287181 1.2618570 - 1.4194390 0.0001620 C 16 1.4728138 119.1839220 2.5693440 - 0.7414580 0.0001050 C 17 1.4728138 122.7811667 2.5693440 0.7414580 - 0.0000500 H 18 1.0974370 119.7533033 - 0.0000010 4.6186250 - 0.0004820 H 19 1.0899604 121.8279033 - 2.1769060 3.3435090 - 0.0003720 H 20 1.0899613 121.8278868 2.1769060 3.3435120 - 0.0003260 H 21 1.0974370 119.7533034 - 0.0000010 - 4.6186250 0.0004820 H 22 1.0899613 121.8278868 2.1769060 - 3.3435120 0.0003720 O 23 1.2801697 121.3229526 - 3.6635600 1.4059320 - 0.0001860 O 24 1.2801697 121.3229526 - 3.6635600 - 1.4059320 0.0001070 O 25 1.2801691 121.3229564 3.6635600 - 1.4059310 0.0001850 O 26 1.2801691 121.3229563 3.6635600 1.4059310 - 0.0001090 19. [terrylene] 3 - Element Bond Length Bond Angle X Y Z C1 - 1.4523900 1.2362110 0.1590140 C2 1.4392563 - 0.7326700 - 0.0000070 0.0001840 C3 1.4392603 119.9941306 - 1.4523360 - 1.2362590 - 0.1586620 C4 1.4570781 119.9101781 - 2.9061450 - 1.2233910 - 0.2553600 C5 1.4520151 119.8224196 - 0.7272880 2.4934570 0.2026890 C6 1.4653420 120.0034071 0.7326720 0.0000140 0.0001840 C7 1.4392618 120.0024274 1.4523380 1.2362670 - 0.1586680 C8 1.4520097 119.8231067 0.7272300 2.4935170 - 0.2019470 C9 1.457079 7 119.9098592 2.9061490 1.2233920 - 0.2553580 C10 1.4417606 119.5581000 3.6251170 0.0000270 - 0.0001390 C11 1.4417630 120.1789189 2.9062240 - 1.2233340 0.2553240 C12 1.4392566 120.0032170 1.4523880 - 1.2362060 0.1590190 57 Element Bond Length Bond Angle X Y Z C13 1.4520160 119.8225060 0.7272810 - 2.4934490 0.2027270 C14 1.4520093 119.8231332 - 0.7272300 - 2.4935 100 - 0.2019300 O15 1.2610144 125.5986512 - 1.2221150 3.6165310 0.4925310 O16 1.2610203 125.5994048 1.2220340 3.6166960 - 0.4914470 O17 1.2610150 125.5991239 1.2220960 - 3.6165230 0.4 925920 O18 1.2610190 125.5992622 - 1.2220320 - 3.6166840 - 0.4914470 C 19 1.4417599 119.5578852 - 3.6251160 - 0.0000300 - 0.0001340 C 20 1.4481290 119.9104952 - 5.0732450 - 0.0000320 - 0.0003650 C 21 1 .4192233 119.6145630 - 5.7746210 1.1982410 0.2935880 H 22 1.0923789 118.8496928 - 6.8668900 1.1828170 0.2951050 C 23 1.3845019 119.5841533 - 5.0657170 2.3533940 0.5762930 H 24 1.0942465 119.6181268 - 5.6058530 3.2746460 0.8148790 C 25 1.4417618 120.1788288 - 2.9062250 1.2233290 0.2553370 C 26 1.3964044 121.7159173 - 3.6696370 2.3799540 0.5621320 C 27 1.4192235 119.6145650 - 5.7745240 - 1.1983070 - 0.2945420 C 28 1.3845014 119.5842520 - 5.0655290 - 2.3534650 - 0.5769960 C 29 1.3964053 121.7158778 - 3.6694530 - 2.3800280 - 0.5623670 C 30 1.4194016 122.9370674 3.6694640 2.3800300 - 0.5623430 C 31 1.4481280 119.9105380 5.0732450 0.0000250 - 0.0003650 C 32 1.4192235 119.6145959 5.7745290 1.1983020 - 0.2945220 H 33 1.0923795 118.8496238 6.8667980 1.1828760 - 0.2963840 C 34 1.3845001 119.5842762 5.0655400 2.3534650 - 0.5769640 H 35 1.0942465 119.6181943 5.6056020 3.2747210 - 0.8157020 C 36 1.4192242 119.6146985 5.7746200 - 1.1982530 0.2935740 C 37 1.3845004 119.5841339 5.0657150 - 2.3534090 0.5762570 C 38 1.3964054 121.7159473 3.6696340 - 2.3799670 0.5620970 H 39 1.0795639 121.2079926 - 3.1253500 3.2893190 0.7677170 H 4 0 1.0923795 118.8496113 - 6.8667930 - 1.1828840 - 0.2964090 H 41 1.0942462 119.6181053 - 5.6055880 - 3.2747180 - 0.8157510 H 42 1.0795614 121.2082371 - 3.1250970 - 3.2894000 - 0.7677250 H 43 1.0795621 121.2081726 3.1253440 - 3.2893310 0.7676690 H 44 1.0942467 119.6181085 5.6058500 - 3.2746660 0.8148270 H 45 1.0923790 118.8496612 6.8668890 - 1.1828290 0.2950940 H 46 1.0795626 117.1547971 3.1251140 3.2894100 - 0.7676880 Figure 2.1 4 . Total spin density plots of FA sq,cat (left), BA sq,cat (middle), and IA sq,cat (right). 58 Figure 2.1 5 . Total spin density plots of CF 3 A n sq,cat (left), OMeA n sq,cat (middle), and PipA n sq,cat (right). Figure 2.1 6 . Total spin density plots of PhA n sq,cat (left), NMe 2 PhA n sq,cat (middle), and CNPhA n sq,cat (right). Figure 2.1 7 . Total spin density plots of CF 3 PhA n sq,cat (left), NAT sq,cat (middle), and AnT sq,cat (right). Figure 2.1 8 . Total spin density plots of MeAnT sq,cat (left), PhAnT sq,cat (middle), and CNPh - AnT sq,cat (right). 59 Figure 2.1 9 . Total spin density plots of pyrene sq,cat (left) and terrylene sq,cat (right). 60 REFERENCES 61 REFERENCES (1) Wolf, S. A.; Awschalom, D. D.; Buhrman, R. A.; Daughton, J. M.; von Molnár, S.; Roukes, M. L.; Chtchelkanova, A. Y.; Treger, D. M. Science 2001 , 294 , 1488. (2) Fert, A. Re v . Mod. Phys. 2008 , 80 , 1517. (3) Bogani, L.; Wernsdorfer, W. Nat. Mater. 2008 , 7 , 179. (4) Kahn, O. 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Correlation analysis in organic chemistry: an introduction to linear free - energy relationships. Oxford University Press: Oxford, 1973. (62) Wayner, D. D. M.; Arnold, D. R. Can. J. Chem. 1985 , 63 , 2378. (63) Clark, K. B.; Wayner, D. D. M. J. Am. Chem. Soc . 1991 , 113 , 9363. 65 Chapter 3. Magnetic Properties and Substituent Effect on the Modulation of Heisenberg Exchange Coupling Interactions in Chromium (III) Tetraoxo - Dimeric Complexes 3.1 Introduction The application of spin exchange interaction in biology usually involve complicated metalloprotein molecules or their active site synthetic analogues. 1 - 7 These systems are synthetically more challenging for the manipulation of spin exchange. It will be more be neficial without composition change , the fundamentals for spin polarization can be determined more easily with experimental tools , e.g. x - ray crystallography . The desig n of more advanced metalloprotein analogues then can be accomplished for similar purposes. Figure 3.1. Cr III - tetraoxolene quinodal complexes with a combination of diamagnetic or paramagnetic substituted - bridging ligands , where R 1 are the substituents on tetraoxoanilate, and R 2 are the substituents on 2,3,6,7 - tetraoxoanthracene . Cr (III) - tetraoxoquinoidal systems are chosen to be the system , since Cr III ion ( S = 3/2) is redox - inert and not easily reduced to Cr II , 8 and it is well - studied spectroscopically in the absence 66 of spin exchange. 9,10 When coordinating to metal center, catecholate bridging ligands can be oxidized to semiquinone ( S The computational results obtained in Chapter 2 can facilitate the synthetic design of the substituted analogues. The charge density of the trianionic and tetr a anionic radicals can provide the information about their Lewis basicity, since increasing the negative charge density at the chelating oxygen atoms will increase the formation constant for better stability, and vice versa. 11 A series of dichromium (III) tetraoxo - quinoidal complexes are proposed as experimental targets in our studies (Fig. 3.1). The strength of spin exchange in transitional me tal complexes is proportional to the spin density of the atom in one paramagnetic center, which is directly binding to the metal center. 12 - 15 Thus, the control of spin density distribution can cause stronger or weaker exchange interaction. Several studies present the modulation of spin coupling constants by substituents effects in Mn(II) and Cu(II) 5 - aryl - substituted semiquinones, 16 and Co (III) iminosemiquinone. 17 Cr (III) is a d 3 ion with three unpaired electrons sitting in dxz, dyz, dxy - symmetry, and they - symmetric unpaired electron of semiquinone ligand to have antiferromagnetic interactions. The antiferromagnetic interaction of Cr (III) - semiquinone has been observed experimentally in [Cr 2 (CTH) 2 (DHBQ)Y 3 (Y = ClO 4 - , PF 6 - ) , 18 [Cr(tren)(3,6 - DTBSQ)](PF 6 ) , 19 and [Cr 2 (tren) 2 (CA sq,cat )](BPh 4 ) 2 . 8 No temperature dependence was observed in the variable - temperature magnetic susceptibility data for all three Cr (III) complexes because the direct exchange J coupling i s too strong. The thermal energy applied during the SQUID measurement is not enough to overcome the spin energy gap (>> kT ) to populate spins into the second excited spin states. In order to accurately fit J coupling constant with MagFit, 46 thermal populati on to access more higher energy spin states is required. Thus, the J constants of these Cr (III) - semiquinone systems are only estimations, > 400 cm - 1 . Although the exchange coupling 67 interactions are predicted to be strong, the trend of J constants can provide some insight about the substituent effects on the strength. 3.2 Experimental Section General. All chemicals were of reagent grade, purchased from Alfa Aesar, Sigma - Aldrich, Acros Organics, TCI Chemicals, Oakwood Chemicals, Strem C hemicals, or Matrix Chemicals, and used as received unless otherwise noted. Solvents were purchased from Sigma - Aldrich, Jade Scientific, Alfa Aesar, Fisher Scientific, EMD Chemicals, Mallinckrodt, or CCI and were purified usi ng standard purification techni ques. All air - sensitive and water - sensitive reactions were carried out under inert atmosphere either by standard Schlenk techniques or in dryboxes. The solvents u sed for these air - sensitive reactions were thoroughly dried by being stored over 4 Å molecular sieve and deoxygenated by the freeze - pump - thaw method. The ligand tris(2 - aminoethyl)amine (tren) was purchased from either Sigma - Aldrich or Alfa Aesar, vacuum - distilled from NaOH with activated carbon , then degassed by the freeze - pump - thaw method , and sto red in the glovebox prior to use. 1 H NMR and 13 C NMR were collected on Agilent DDR2 500 MHz NMR spectrometers equipped with 7600AS 96 - sample autosamplers. Electrospray mass spectra (ESI - MS) were obtained on Waters Xevo G2 - XS QTof Quadruple UPLC/MS/MS at Mi chigan State University Mass Spectromet ry and Metabolomics Core . CHN elemental analyses were obtained on a Perkin - Elmer 2400 Series II CHNS/O Analyzer through the analytical facilities in the Chemistry department of Michigan State University. 68 3.2.1 Syn thetic Procedures of Substituted Tetraoxo anilate , Naphthalene, and Anthracene Ligands 2,5 - Dimethoxy - 1,4 - benzoquinone (DHBQ) . 8 BF 3 ·OEt 2 ( 46.5% BF 3 basis, 9 mL , 33.8 mmol ) was added to a solution of 2,5 - dihydroxy - 1,4 - benzoquinone ( 1.67 g , 12 mmol ) in MeOH ( 50 mL). The reaction mixture was orange brown precipitate formed. The orange br own product was filtered, washed by c old MeOH (3 x 30 mL ), and dried under vacuum overnight. Yield: 1.72 g ( 95%). 1 H N MR (CDCl 3 , 500 MHz) (ppm): 3.83 (s, 6H, CH 3 ), 5.85 (s, 2H, Aromatic CH). 13 C NMR (CDCl 3 , 500 MHz) (ppm): 56.84, 105.68, 159.75, 181.88. 2,5 - Dibromo - 3,6 - dimethoxy - 1,4 - benzoquinone. 21 N - Bromosuccinimide (NBS) was recrystallized from boiling water before use (10 g of NBS for 100 mL of water). NBS is incompatible in contact with iron or iron salts, and plastic spatula should be used to handle it. NBS (7.2g, 40.4 mmol) was added slowly to a solution of 2,5 - dimethoxy - 1,4 - benzoquinone (3.4g, 20.0 mmol) in DMF (100 mL), and it was stirred at room temperature (RT) for 15 hours. 50 mL of H 2 O was added to quench the reaction, and the aqueous layer was extracted with EtOAc (3 x 10 mL) and followed by Et 2 O (3 x 200 mL). Both EtOAc and Et 2 O extracted organic layers w ere combined, and washed by H 2 O (2 x 20 mL), brine (2 x 20 mL) , and dried over Na 2 SO 4 . The crude product was purified by silica gel plug with hexane/CHCl 3 (1:1) - ( 0:1 ) , and orange red product was collected. Yield: 4.58 g (70%). 1 H NMR (CDCl 3 , 500 MHz) ( ppm): 4.24 (s, CH 3 ). 13 C NMR (CDCl 3 , 500 MHz) (ppm): 20.09, 62.49, 110.21, 174.93. Bromanilic acid ( H 2 BA ) . Route 1. A solution of 2,5 - dibromo - 3,6 - dimethoxy - 1,4 - benzoquinone (1.4 g, 4.3 mmol) in anhydrous CH 2 Cl 2 (100 mL) was degassed by freeze - pump - thaw method. To this solution, BBr 3 (1.6 mL, 17.3 mmol) was added slowly by a syringe at - 2 . The reaction 69 mixture was stirred overnight until room temperature was attained gradually. The reaction was quench ed by 10 mL of MeOH, and the solvent was evaporated under vacuum. The orange solids were washed by H 2 O, and recrystallized from AcOH. Yield: 1.1 g (86%). Route 2. 23 DHBQ (7.8 g, 5. 6 mmol) was suspended in EtOH (1 00 mL). Br 2 (5.7 mL, 111.2 mmol) was added dropwise to the EtOH suspension above, and it was stirred at RT for 12h. The solvent was evaporated down in volume. The orange product was filtered, washed with CHCl 3 (3 x 20 mL), and dried under vacuum. Yield: 16.2 g (97%). Anal. Calc d C 6 H 2 O 4 Br 2 : C, 24.2; H, 0.7; N, 0. Found: C, 24.6; H, 0.6; N, 0. HRMS [ESI - TOF, m/z (rel. int.)]: [M - H] - Calcd for [ C 6 H 1 O 4 Br 2 ] - , 296.8221; Found , 296.8231. Fluoranilic acid (H 2 FA). 24 , 25 Tetrafluoro - 1,4 - benzoquinone (1.0 g, 5.6 mmol) was dissolved in 1,4 - dioxane (8 mL) hand for 30 min with intermittent cooling at formed, and they were filter ed and recrystallized from 30 mL of hot H 2 O resulting in the brown purple sodium salt. The brown purple product was filtered and re - dissolved in hot H 2 O (20 mL). While the solution is hot, 37% concentrated HCl was added dropwise into the sodium salt soluti on until the solution turned red with the formation of red precipitates. The red solids were filtered, washed with H 2 O (3 x 10 mL), and dried under vacuum. Yield: 0.36 g (37%). HRMS [ESI - TOF, m/z (rel. int.)]: [M - H] - Calcd for [C 6 HO 4 F 2 ] - , 174.9843; Found , 174.9918. Tetraiodo - 1,4 - benzoquinone. 24,25 KI (4.0 g, 24 mmol) and tetrabromo - 1,4 - benzoquinone (2.0 g, 4.5 mmol) were mixed in EtOH (40 mL), and this suspension was refluxed for 2h. After being cooled to RT, brown red product was filtered, and washed wit h H 2 O (3 x 10 mL), EtOH (2 x 10 mL). The brown red solids and KI (1.6 g, 9.6 mmol) were refluxed for 70 additional 2h. The resulted brown solids were filtered and recrystallized from EtOAc to obtain dark grey crystals. Yield: 1.55 g (56%). M. P. 270 and decompose upon melting. 13 C NMR (benzene - d 6 , 500 MHz) (ppm): 130.22, 170.02. Anal. Calcd C 6 O 2 I 4 : C, 72.1; H, 0 ; N, 0. Found: C, 24.6; H, 0.6; N, 0. Iodanilic acid (H 2 IA). 24,25 Tetraiodo - 1,4 - benzoquinone (1.0 g, 1.6 mmol) was suspended in EtOH/H 2 O (1:2, 4.5 mL). 1.5 mL of 50% (w/v) NaOH aqueous solution was added dropwise into the suspension, and they were stirred overnight. The resulted brown purple solids were filtered, and washed with EtOH (1 x 10 mL). The solids were dissolved in H 2 O (20 mL) , an d acidified by dropwise addition of diluted H 2 SO 4 aqueous solution. Orange precipitates formed slowly durin g the addition, and the product was filtered and re - dissolved in H 2 O (40 mL) while heating. The solution was acidified with diluted H 2 SO 4 solu tion ag ain, and the red product was obtained by filtration and washed with H 2 O (3 x 10 mL). Yield: 0.43 g (68%) . HRMS [ESI - TOF, m/z (rel. int.)]: [M - H] - Calcd for [C 6 HO 4 I 2 ] - , 390.7964; Found, 390.8028. 2,5 - Dimethoxy - 3,6 - diphenyl - 1,4 - benzoquinone. 25 A mixture of K 2 CO 3 (0.69 g, 5.0 mmol), phenylboronic acid (0.533 g, 4.0 mmol), and Pd(PPh 3 ) 2 Cl 2 (0.07 g, 10 mol%) in 1,4 - dioxane/H 2 2 . H 2 O was added to facilitate the dissolution of K 2 CO 3 , due to the low solubility of K 2 CO 3 in dioxane. 2,5 - Dibromo - 3,6 - dimethoxy - 1,4 - benzoquinone (0.326 g, 1.0 mmol) was added into the mixture, and the 24 h. After the reaction was cooled to RT, the reaction was diluted with 50 mL of DCM, and dried over M g 2 SO 4 . The mixture was filtered through a pad of Celite and concent rated under vacuum. Red product was obtained after purification by silica flash column chromatography (n - pentane/DCM, 3:7). Yield: 0.24 g (75%). 1 H NMR (CDCl 3 , 500 MHz) (ppm): 3.81 (s, 6 H, OCH 3 ), 7.30 - 7.50 (m, 10 H, ArH). 13 C NMR (CDCl 3 , 500 71 MHz) (ppm): 61.3, 126.1, 127.5 , 128.6, 129.8, 130.5, 154.0, 184.9 . HRMS [ESI - TOF, m/z (rel. int.)]: [M+ H] + Calcd for [C 20 H 1 5 O 4 ] - , 321.1136; Found, 321.1127 . 2,5 - Dihydroxy - 3,6 - diphenyl - 1,4 - benzoquinone (H 2 PhA) . The synthetic procedure is similar with the demethylation to obtain H 2 BA in Route 1. 2,5 - Dimethoxy - 3,6 - diphenyl - 1,4 - benzoquinone (0.24 g, 0.75 mmol) reacted with BBr 3 (0.34 mL, 3.6 mmol) under N 2 . Brown product was obtained after recrystallization from dioxane. Yield: 0.16 g (73%). 1 H NMR (acetone - d 6 , 500 MHz) (ppm): 7.33 (t , 2 H, ArH ) , 7.41 (t, 4 H, ArH) , 7.54 (d, 4H, ArH), 10.3 (br. s, 2H, OH) . 13 C NMR ( acetone - d 6 , 500 MHz) (ppm): 128.4, 128.5, 131. 4, 131.5 , 131.8 . HRMS [ESI - TOF, m/z (rel. int.)]: [M - H] - Calcd for [C 18 H 11 O 4 ] - , 291.0657; Found, 291.0658. 2,3,6,7 - T etramethoxy - 9,10 - dimethylanthracene . 25 , 26 Acetaldehyde (7 mL, 125 mmol) in MeOH (10 mL) was added dropwise in a stirring solution of veratrole (9 mL, 72.4mmol) in 9 0% aq. H 2 SO 4 (35 mL) solution was added over 1 - hour period the mixture was vigorously stirred. As more H 2 SO 4 solution was added, the reaction mixture became viscous. The dark purple mixture was poured into 500 mL of ice H 2 O, and precipitation happen over time. The solvent was decanted , and the viscous tacky produc t was triturated and washed with EtOH. Beige product was obtained after recrystallization in CHCl 3 . Yield: 4.4 g (37%). 1 H NMR (CDCl 3 , 500 MHz) (ppm): 2.93 (s, 6 H, CH 3 ), 4.06 (s, 12 H, OCH 3 ), 7.38 (s, 4H, ArH). HRMS [ESI - TOF, m/z (rel. int.)]: [M+H] + Ca lcd for [C 20 H 23 O 4 ] + , 327 .1597; Found, 327.1595. 2,3,6,7 - Tetrahydroxy - 9,10 - dimethylanthracene (H 4 ( Me - AnT ) ) . 25 , 26 1 M BBr 3 in DCM (8.6 mL, 8.6 mmol) was injected into a suspension of 2,3,6,7 - tetramethoxy - 9,10 - dimethylanthracene (1.0 g, 3.06 mmol) in DCM (50 mL) at - 2 , and the mixture was stirred for 1 h until the temperature slowly retained to RT. The reaction mixture was reflux for 24 72 h until the it turned from purple red to o range. The yellow brown product was filtered, washed by 0.2 M aq. HCl (3 x 100 mL), and H 2 O (3 x 100 mL). Black product was obtained after recrystallization in AcOH. Yield: 0.68 g (82%). 1 H NMR (DMSO - d 6 , 500 MHz) (ppm): 2.69 (s, 6 H, CH 3 ) , 7.33 (s, 4 H, ArH ) , 9.44 ( br. s, 4H, O H). HRMS [ESI - TOF, m/z (rel. int.)]: [M - H] - Ca lcd for [C 12 H 15 O 4 ] - , 269.0814; Found, 269.0815 . 4 - ( N,N - Dimethylamino ) phenylboronic acid. 2 7,2 8 Mg turnings (1.22 g, 50 mmol) were added into the solution of 0.5 M LiCl in THF (50 mL) under N 2 .1.0 M diisobutylaluminum hydride (DIBAL - H) in THF (0.2 mL, 0.2 mmol) was added by a syringe into the reaction mixture, and they were stirred for 5 min. 4 - Bromo - N,N - dimethylaniline (4.0 g, 20 mmol) was added in, and the mixture was stirred for 15 h at RT. B(OMe) 3 was injected into the mixture , and stirred for an additi on of 3 h at - 2 . The reaction was quenched with 0.1 M HCl (100 mL), and extracted with EtOAc (3 x 200 mL), and dried over Na 2 SO 4 . The solution was concentrated under vacuum, washed by MeCN, and Et 2 O. Yield: 2.0 g (61%). 1 H NMR (DMSO - d 6 , 500 MHz ) (ppm): 2.89 (s, 6 H, N CH 3 ) , 6.64 (d, 2 H, ArH) , 7.60 ( d, 2H, Ar H) , 7.64 (s, 2H, OH) . 11 B NMR (DMSO - d 6 , 500 MHz) (ppm): 26.67. 2,7 - Dimethoxy - 3,6 - di - (N,N - dimetylaminophenyl)benzoquinone . 30 A mixture of K 2 CO 3 (0.5 g, 3.6 mmol), 4 - (N,N - dimethylamino)phenylboronic a cid (0.62 g, 4.0 mmol), and Pd(PPh 3 ) 4 ( 0.06 g, 5 mol%) in 1,4 - dioxane/H 2 under N 2 . H 2 O was added to facilitate the dissolution of K 2 CO 3 , due to the low solubility of K 2 CO 3 in dioxane. 2,5 - Dibromo - 3,6 - dimethoxy - 1,4 - benzoquinone ( 0.326 g, 1.0 mmol) and Ag 2 O ( 0.25 g, 1.0 mmol ) were 24 h. After the reaction was cooled to RT, the reaction was diluted with 5 0 mL of DCM, and dried over Mg 2 SO 4 . The mixture was filtered through a pad of Celite an d concentrated under 73 vacuum. Purple product was obtained after purification by silica flash column chromatography (first eluent: n - pentane/DCM, 3:7, 2 nd eluent: hexane/D CM/EtOAc, 8:1:1). Purple crystals were formed in hexane/DCM (8:1), which is suitable for x - ray diffraction. Yield: 0.147 g ( 36 %). 1 H NMR (CDCl 3 , 500 MHz) (ppm): 2.99 (s, 12 H, NCH 3 ), 3.78 (s, 6 H, OCH 3 ), 6.72 (d, 4H, ArH), 7.28 (d, 4 H, ArH). 13 C NMR (CD Cl 3 , 500 MHz) (ppm): 40.49, 61.39, 111.61, 117.54, 127.78, 131.99, 150.65, 154.06, 184.59. HRMS [ESI - TOF, m/z (rel. int.)]: [M+H] + Calcd for [C 24 H 27 O 4 N 2 ] + , 407.1987; Found, 407.1971 . 2,7 - Dihydroxy - 3,6 - di - (N,N - dimetylaminophenyl)benzoquinone (H 2 NMe 2 - PhA) . The synthetic procedure is similar with the demethylation to obtain H 2 BA in Route 1. 2,7 - Dimethoxy - 3,6 - di - (N,N - dimetylaminophenyl)benzoquinone (0.26 g, 0.64 mmol) reacted with BBr 3 (0.3 mL, 3.1 mmol) under N 2 . Purple grey product was obtained after recry stallization from AcOH. Yield: 0.20 g (83%). 1 H NMR (dmso - d 6 , 500 MHz) (ppm): 2.96 (s, 12 H, NCH 3 ), 6.80 (br. s , 2 H, O H) , 7.29 (d , 4 H, ArH), 7.54 (d, 4H, ArH ) . 13 C NMR ( dmso - d 6 , 500 MHz) (ppm): 128.4, 128.5, 131.4, 131.5, 131.8. HRMS [ESI - TOF, m/z (rel. int.)]: [M - H] - Calcd for [C 22 H 2 1 O 4 N 2 ] - , 377.1505; Found, 3 77.1501 . [M+H] + Calcd for [C 22 H 23 O 4 N 2 ] + , 379.1658; Found, 179.1598. 3,6 - Dibromo - 2,7 - dihydroxynaphthalene. 29 A solution of Br 2 (1.7 mL, 32.4 mmol) in AcOH (10 mL) was added dropwise over a 20 - min period to a stirring solution of 2,7 - dihydroxynaphthalene (1.3 g, 9.2 mmol) in AcOH (30 mL). The reaction mixture was refluxed for 12 h. After 4 mL of H 2 O was added into the mixture, yellow fluffy precipitates formed. Sn (1.0 g, 8.4 mmol) was added int o the reaction portionwise, and the reaction mixture was continuously refluxed until all the yellow precipitate re - dissolved and the solution turned yellow. If that does not happen, 0.1 g of Sn should be added with sufficient reaction time unt il the 74 solut ion turned yellow. After additional 3 h reflux, white precipitates form ed. The white product was collec ted through filtration, and was recrystallized from AcOH. Yield: 2.3 g (78%). 1 H NMR (DMSO - d 6 , 500 MHz) (ppm): 7.05 (s, 2 H, ArH - OH), 8.02 (s, 2 H, ArH - Br), 10.52 (s, 2H, OH). 3,6 - Dibromo - 2,7 - dimethoxynaphthalene. 30 KOH (0.42 g, 7.5 mmol) was mixed with DMSO (10 mL) and stirred for 5 min at RT under N 2 . To the suspension above, 3,6 - Dibromo - 2,7 - dihydroxynaph thalene (0.3 g, 0.94 mmol) and methyl iodide (0.23 mL, 3.76 mmol) were added , and the mixture was stirred at RT overnight. The mixture was diluted with H 2 O (10 mL) with white preci pitate crashed out. The product was filtered, washed by H 2 O (3 x 20 mL), MeO H (1 x 10 mL), and dr ied under vacuum. Beige product was obtained from recrystallization in EtOH. Yield: 0.27 g (83%). 1 H NMR (CDCl 3 , 500 MHz) (ppm): 3.97 (s, 6 H, OCH 3 ), 7.04 (s, 2 H, ArH - OCH 3 ), 7.86 (s, 2H, ArH - Br). 13 C NMR (CDCl 3 , 500 MHz) (ppm): 56 .44, 105.92, 111.60, 125.48, 131.22, 134.10, 154.50. 2,3,6,7 - T etramethoxynaphthalene. 2 9 , 31 Na metal ( 0.16 g, 3.2 mmol) was added po rtionwise to anhydrous MeOH (22 mL) under N 2 . Upon complete dissolution, CuI (1.23 g , 6.4 mmol) and DMF (3.7 mL) were added. 3,6 - Dibromo - 2,7 - dimethoxynaphthalene (1.12 g, 3.2 mmol) was added to result in an orange suspension . After t he react ion was refluxed for 24 h, a dditional CuI (0.62 g, 3.26 mmol) and saturated NaOCH 3 (1.58 g Na in 15 mL MeOH, 15 mL) MeOH solution were added in order to regenerate the catalyst. The reaction was refluxed for an additional 12 h. After cooling down to RT, the reaction mixture was quenched by 11 mL of 2 M aq. HCl. It was diluted with H 2 O (44 mL), and extracted with DCM (3 x 50 mL). The orga nic layer was washed by H 2 O (3 x 30 mL), dried over MgSO 4 , and concen trated in vacuum. Beige product was recry stallized from EtOH. Yield: 0.57g (71 %). 1 H NMR (CDCl 3 , 500 MHz) 75 (ppm): 3.95 (s, 12 H, OCH 3 ), 7.02 (s, 4 H, ArH). 13 C NMR (CDCl 3 , 500 MHz) (pp m): 56.04, 106.07, 124.47, 148.31. 2,3, 6,7 - T etrahydroxynaphthalene (H 4 NAT) . The synthetic procedure is similar with the demethylation to obtain H 2 BA in Route 1. 2,3,6,7 - Tetramethoxynaphthalene (0.57 g, 2.3 mmol) reacted with BBr 3 (1.8 mL, 18.4 mmol). The p roduct was washed by H 2 O, and dried under vacuum over P 2 O 5 . Yield: 0.2 g (45%). 1 H NMR (DMSO - d 6 , 500 MHz) (ppm): 6.80 (s, 4 H, ArH), 8.94 (br. s, 4 H, OH). 13 C NMR (DMSO - d 6 , 500 MHz) (ppm): 108.44, 123.82, 144.41. 2,3,6,7 - T etramethoxyanthraquinone . 27 , 32 , 33 2,3,6,7 - Tetramethoxy - 9,10 - dimethylanthracene (4.0 g, 12.3 mmol) and Na 2 Cr 2 O 7 (20.0 g, 76.6 mmol) were mixed in AcOH (200 mL), and refluxed for 1 h. After the mixture was cooled to RT, it was filtered to obtain bright yellow product. The product was w ashed by H 2 O and Et 2 O. Yield: 3.2 g (79%). 1H NMR (CDCl 3 , 500 MHz) (ppm): 4.05 (s, 12 H, OCH 3 ), 7.67 (s, 4 H, ArH). 13 C NMR ( CDCl 3 , 500 MHz) (ppm): 56.77, 108.60, 128. 65, 153.64, 182.20 . 2,3,6,7 - Tetramethoxyanthracene . 33 In order to activate Zn powders, they were washed by 3% (w/v) HCl aqueous solution twice, and H 2 O, EtOH, and Et 2 O once respectively. 2,3,6,7 - Tetramethoxyanthraquinone (2.0 g, 8.26 mmol) and Zn (33.5 g, 510 mmol) were added to a stirring aqueous solution o f 2 M NaOH (130 mL) under N 2 48 h. After the reaction was cooled to RT, solids were obtained through filtration. The solids were washed by 37% HCl until no more Zn powder left. White crystals were obtained after purific ation by silica flash column chromatography (DCM). Yield: 1.06 g (43%). 1 H NMR (CDCl 3 , 500 MHz) (ppm): 4.01(s, 12 H, OCH 3 ), 7.12 (s, 4 H, ArH), 8.01 (s, 2 H, ArH). 13 C 76 NMR (CDCl 3 , 500 MHz) (ppm): 56.04, 104.96, 122.23, 127.60, 149.60. HRMS [ESI - TOF, m/ z (rel. int.)]: [M+H] - Calcd for [C 20 H 23 O 4 ] + , 327.1597; Found, 327.1595. 2,3,6,7 - Tetrahydroxyanthracene ( H 4 AnT) . 3 4 , 3 5 BBr 3 (1.4 mL, 14.4 mmol) was added by syringes into the suspension of 2,3,6,7 - Tetramethoxyanthracene (0.534 g, 1.8 mmol) in DCM (50 mL) at - 2 . The reaction mixture was stirred overnight until its temperature slowly rose back to RT. The suspension w as poured to 0.1 M aq. HCl (300 mL) with white precipitate crashed out. The product was extracted with Et 2 O (3 x 200 mL), and washed by H 2 O (1 x 50 mL), brine (1 x 50 mL), and dried over MgSO 4 . Beige powders were obtained after the reduction of solvent. Yi eld: 0.38 g (87%). 1 H NMR (acetone - d 6 , 500 MHz) (ppm): 7.18(s, 4 H, ArH), 7.86 (s, 2 H, ArH), 8.49 (s, 4 H, OH). 13 C NMR (acetone - d 6 , 500 MHz) (ppm): 108.47, 121.62, 128.66, 146.99. HRMS [ESI - TOF, m/z (rel. int.)]: [M - H] - Calcd for [C 14 H 9 O 4 ] - , 241.0501 ; Found, 241.0489. 3.2.2 Synthetic Procedures of Chromium (III) Dimeric Analogues (Et 3 NH) 2 (DHBQ) (where DHBQ is the deprotonated dianionic form of 2,5 - dihydroxy - 1,4 - benzoquinone). To an orange solution of DHBQ (2.8 g, 20 mmol) in EtOH, Et 3 N (6.4 mL, 46 mm ol) was added slowly. Upon addition, the solution turned pink and precipitate formed. The dark red solids were filtered, washed with Et 2 O, and dried under vacuum overnight. Yield: 5.5 g (80%). (1) [Cr 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 . 8 Under N 2 , tren (0.07 mL, 0.44 mmol) was added dropwise to a rapidly stirring solution of CrCl 2 (0.05 g, 0.4 mmol) in MeOH (40mL). A solution of (Et 3 NH) 2 (DHBQ) in 20 mL MeOH was added dropwise to the above solution, resulting in an emerald green solution. Following by additiona l 30 min stirring of the solution, NaBPh 4 (0.68g, 77 2 mmol) in 80 mL of MeOH was layered carefully on top. The solution was allowed to stand overnight without disturbing, and brown red crystals, suitable for X - ray diffraction, were formed slowly over time. ( Do not use excess CrCl 2 for recrystallization, because it would form crystals of Cr(tren)Cl 2 , which requires extra purification steps.) The product was filtered, and washed with MeOH (3 x 40 mL). Yield: 0.15 g (65%). Anal. Calcd Cr 2 C 66 H 78 O 4 N 8 B 2 ·CH 3 OH: C, 6 6.8; H, 6.9; N, 9.3. Found: C, 66.3; H, 6.8; N, 9.3. [FeCp* 2 ](BF 4 ). 35,36 1,4 - benzoquinone (0.07 g, 0.65 mmol) was dissolved in 20 mL of Et 2 O, and it was filtered to yield yellow filtrate. 48% concentrated HBF 4 (0.5 mL, 3.8 mmol) was added into the yellow filtrate while stirring. After 10 min of reaction time, a solution of decamethylferrocene, FeCp* 2 , (0.423 g, 1.3 mmol) in Et 2 O (20 mL) was added dropwise into the reaction. Green precipitates formed after the addition, and the product was washed by Et 2 O an d dried und er vacuum. Yield: 0.45 g (84%). HRMS [ESI - TOF, m/z (rel. int.)]: [M] + Calcd for [ C 20 H 30 Fe] + , 362. 169 7 ; Found, 362.17 04 . (11) [Cr 2 (tren) 2 (DHBQ sq,cat )](BPh 4 ) 2 (BF 4 ). 8 , 37 Under N 2 , a solution of ( FeCp* 2 )(BF 4 ) ( 0.14 g, 0.34 mmol) in MeCN ( 20 mL) was added dropwise into a stirring solution of [Cr 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 ( 0.2 g, 0.17 mmol) in MeCN ( 10 mL). The solution was stirred for 6 h, which turned yellow - green. After filtration, the solvent volume of the filtrate was reduced under vacuum to 10 mL. 30 mL of DCM was added, and the mixture was filtered to eliminate excess [FeCp* 2 ] (BF 4 ) salt. The filtrate was reduced in volume under vac uum again to 10 mL, and 30 mL of Et 2 O was added to yield yellow brown solids. The product was filtered, washed by DCM (3 x 10 mL), and Et 2 O (3 x 10 mL). Yield: 0. 12 g ( 56 %). HRMS [ESI - TOF, m/z (rel. int.)]: [M] 3+ Calcd for [ Cr 2 C 18 H 38 O 4 N 8 ] 3+ , 178.0609; Foun d, 178.0 618 . Anal. Calcd Cr 2 C 66 H 78 O 4 N 8 B 3 F 4 ·CH 3 OH ·CH 3 CN : C, 6 2.2 ; H, 6. 4 ; N, 9.5 . Found: C, 6 2.0 ; H, 6.8; N, 9 . 1 . 78 (Et 3 NH) 2 (CA). The synthesis of this compound was similar to that for (Et 3 NH) 2 (DHBQ). H 2 CA (2.1 g, 10 mmol) was used to react with Et 3 N (3.0 mL, 22 mmol), and pink product was obtained. Yield: 3.1 g (76%). (2) [Cr 2 (tren) 2 (CA cat,cat )](BPh 4 ) 2 . 8 The synthesis of this complex was similar to that for [Cr 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 . (Et 3 NH) 2 (CA) (0.07 g, 0.2 mmol) was used. Yellow green crystals , suitable for x - ray diffraction, were obtained by layering a solution of NaBPh 4 in MeOH. Yield: 0.20 g (86%). Anal. Calcd Cr 2 C 66 H 76 Cl 2 O 4 N 8 B 2 ·CH 3 OH: C, 63.2; H, 6.3; N, 8.8. Found: C, 63.0 ; H, 6.4 ; N, 8.8 . (12) [Cr 2 (tren) 2 (CA sq,cat )](BPh 4 ) 2 (BF 4 ). Under N 2 , a solution of (CPh 3 )(BF 4 ) (0.09 g, 0.2 7 mmol) in MeCN ( 10 mL) was added dropwise into a stirring solution of [Cr 2 (tren) 2 ( CA cat,cat )](BPh 4 ) 2 (0.1 7 g, 0. 13 7 mmol) in MeCN ( 2 0 mL). The solution was stirred for 6 h, which turned yellow - green. After filtration, the solvent volume of the filtrate was reduced under vacuum to 10 mL. 30 mL of DCM was added, and the mixture was filtered to eliminate excess (CPh 3 )(BF 4 ) salt. The filtrate was reduced in volume under vacuu m again to 10 mL, and 30 mL of Et 2 O was added to yield yellow brown solids. The product was filtered, washed by DCM (3 x 10 mL), and Et 2 O (3 x 10 mL). Yield: 0. 117 g ( 64 %). HRMS [ESI - TOF, m/z (rel. int.)]: [M] 3+ Calcd for [ Cr 2 C 18 H 36 O 4 N 8 Cl 2 ] 3+ , 200.70 16 ; Fo und, 200.70 25 . [Cr(tren)(C 6 O 4 Cl 2 )] + Calcd for [ CrC 12 H 18 O 4 N 4 Cl 2 ] + , 404.0111 ; Found, 404.01 17 . Anal. Calcd Cr 2 C 66 H 76 Cl 2 O 4 N 8 B 3 F 4 ·CH 3 OH·CH 3 CN: C, 59.1; H, 6.0; N, 9.0 . Found: C, 59.0; H, 6.4; N, 8 .6. (Et 3 NH) 2 (BA). The synthesis of this compound was similar to that for (Et 3 NH) 2 (DHBQ). H 2 BA (0.12 g, 0.4 mmol) was used to react with Et 3 N (0.14 mL, 1 mmol), and pink product was obtained. Yield: 0.16 g (80%). 79 (3) [Cr 2 (tren) 2 (BA cat,cat )](BPh 4 ) 2 . The synthesis of this complex was similar to that for [Cr 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 . (Et 3 NH) 2 (BA) (0.07 g, 0.2 mmol) was used. Brown crystals, suitable for x - ray diffraction, were obtained by layering a solution of NaBPh 4 in MeOH. Yield: 0.20 g (86%). Anal. Calcd Cr 2 C 66 H 76 Br 2 O 4 N 8 B 2 · CH 3 OH: C, 59.1; H, 5.9; N, 8.2. Found: C , 59.5; H, 6.2; N, 8.2. HRMS [ESI - TOF, m/z (rel. int.)]: [M] 2+ Calcd for [Cr 2 C 18 H 36 O 4 N 8 Br 2 ] 2+ , 34 5.4971 ; Found, 34 5.4992 . [M] 3 + Calcd for [Cr 2 C 18 H 3 5 O 4 N 8 Br 2 ] 3 + , 230.6674; Found, 230.6693. [Cr(tren)(C 6 O 4 Br 2 )] + Calcd for [ CrC 12 H 18 O 4 N 4 Br 2 ] + , 493.9081; Found, 493.9102. (13) [Cr 2 (tren) 2 (BA sq,cat )](BPh 4 ) 2 (BF 4 ). The synthetic procedure of this compound was similar to that of [Cr 2 (tren) 2 ( CA sq,cat )](BPh 4 ) 2 (BF 4 ). Instead, (CPh 3 )(BF 4 ) (0.04 g, 0.12 mmol) was used to react with [Cr 2 (tren) 2 (BA cat,cat )](BPh 4 ) 2 (0.11 g, 0.08 mmol). Yield: 0.08 g (68%). HRMS [ESI - TOF, m/z (rel. int.)]: [M] 3+ Calcd for [Cr 2 C 18 H 36 O 4 N 8 Br 2 ] 3+ , 230.6674; Found, 230.6 680 . [Cr(tren)(C 6 O 4 Br 2 )] + Calcd for [ CrC 12 H 18 O 4 N 4 Br 2 ] + , 493.9 081 ; Found, 493. 9088 . Anal. Calcd Cr 2 C 66 H 76 Br 2 O 4 N 8 B 3 F 4 ·CH 3 OH·CH 3 CN: C, 55.6; H, 5 . 6 ; N, 8 . 5 . Found: C, 55.5; H, 6.0; N, 8 .2. (Et 3 NH) 2 (FA). The synthesis of this compound was similar to that for (Et 3 NH) 2 (DHBQ). H 2 FA (0.11 g, 0.6 mmol) was used to react with Et 3 N (0.2 mL, 1.3 mmol), and violet product was o btained. Yield: 0.2 g (87%). (4) [Cr 2 (tren) 2 (FA cat,cat )](BPh 4 ) 2 . The synthesis of this complex was similar to that for [Cr 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 . (Et 3 NH) 2 (FA) (0.076 g, 0.2 mmol) was used. Red purple crystals , suitable for x - ray diffraction, were obtained by layering a solution of NaBPh 4 in MeOH. Yield: 0.22 g (80%). Anal. Calcd Cr 2 C 66 H 76 F 2 O 4 N 8 B 2 ·CH 3 OH: C, 64.8; H, 6.5; N, 9.0 . Found: C, 64.6 ; H, 6.4 ; N, 9.3 . HRMS [ESI - TOF, m/z (rel. int.)]: [M] 2+ Calcd for [ Cr 2 C 18 H 3 6 O 4 N 8 F 2 ] 2+ , 80 285.0819; Found, 285.0822. [M] 3+ Calcd for [ Cr 2 C 18 H 3 6 O 4 N 8 F 2 ] 3+ , 190.0546; Found, 190.0597. [Cr(tren)(C 6 O 4 F 2 )] + Calcd for [ CrC 12 H 18 O 4 N 4 F 2 ] + , 372.0701; Found, 372.0719. (14) [Cr 2 (tren) 2 (FA sq,cat )](BPh 4 ) 2 (BF 4 ). The synthetic procedure of this compound was similar to th at of [Cr 2 (tren) 2 ( CA sq,cat )](BPh 4 ) 2 (BF 4 ). Instead, (CPh 3 )(BF 4 ) ( 0.1 g, 0.33 mmol) was used to react with [Cr 2 (tren) 2 (FA cat,cat )](BPh 4 ) 2 ( 0.2 g, 0.17 mmol). Light yellow brown product was obtained after filtration and washing with DCM and Et 2 O. Yield: 0.09 g ( 42 %). HRMS [ESI - TOF, m/z (rel. int.)]: [M] 3+ Calcd for [ Cr 2 C 18 H 34 O 4 N 8 F 2 ] 3+ , 190.0546; Found, 190.05 56 . [Cr(tren)(C 6 O 4 F 2 )] + Calcd for [ CrC 12 H 18 O 4 N 4 F 2 ] + , 372.0701; Found, 372.070 6 . Anal. Calcd Cr 2 C 66 H 76 F 6 O 4 N 8 B 3 ·CH 3 OH·CH 3 CN: C, 60.5; H, 6.1; N, 9 . 2 . Found: C, 60.6; H, 6.4; N, 8 .9. (Et 3 NH) 2 (IA). The synthesis of this compound was similar to that for (Et 3 NH) 2 (DHBQ). H 2 IA (0.2 g, 0.6 mmol) was used to react with Et 3 N (0.2 mL, 1.32 mmol), and magenta product was obtained. Yield: 0.29 g (81 %). (5) [Cr 2 ( tren) 2 (IA cat,cat )](BPh 4 ) 2 . The synthesis of this complex was similar to that for [Cr 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 . A solution of (Et 3 NH) 2 (IA) ( 0.12 g, 0.2 mmol) in MeOH (4 0 mL) was added to a mixture of CrCl 2 (0.05 g, 0.4 mmol) and tren ( 0.07 mL, 0.44 mmol) in MeOH (4 0 mL) . Brown c rystals , suitable for x - ray diffraction, were obtained by layering a solution of NaBPh 4 (0.68 g, 2.0 mmol) in MeOH (40 mL) . Yield: 0. 16 g ( 57 %). Anal. Calcd Cr 2 C 66 H 76 I 2 O 4 N 8 B 2 ·CH 3 OH: C, 55.2; H, 5.5; N, 7.7. Found: C, 55.3 ; H, 5.8 ; N, 7.9 . HRMS [ESI - TOF, m/z (rel. int.)]: [M] 2+ Calcd for [Cr 2 C 18 H 3 5 O 4 N 8 I 2 ] 2+ , 392.4841 ; Found, 392.48 61 . [M] 3+ Calcd for [Cr 2 C 18 H 36 O 4 N 8 I 2 ] 3+ , 261.9920 ; Found, 261.99 50 . [Cr(tren)(C 6 O 4 I 2 )] + Calcd for [CrC 12 H 18 O 4 I 2 ] + , 587.8823 ; Found, 587.88 48 . (15) [Cr 2 (tren) 2 (IA sq,cat )](BPh 4 ) 2 (BF 4 ). The synthetic procedure of this compound was similar to that of [Cr 2 (tren) 2 ( CA sq,cat )](BPh 4 ) 2 (BF 4 ). Instead, (CPh 3 )(BF 4 ) ( 0.06 g, 0.17 mmol) 81 was used to react with [Cr 2 (tren) 2 (IA cat,cat )](BPh 4 ) 2 ( 0.152 g, 0.11 mmol). Brown product was obtained. Yield: 0.12 g ( 72 %). HRMS [ESI - TOF, m/z (rel. int.)]: [M] 3+ Calcd for [ Cr 2 C 18 H 34 O 4 N 8 I 2 ] 3+ , 261.99 20 ; Found, 261. 99 37 . [Cr(tren)(C 6 O 4 I 2 )] + Calcd for [ CrC 12 H 18 O 4 N 4 I 2 ] + , 587.88 2 3 ; Found, 587.88 4 3 . Anal. Calcd Cr 2 C 66 H 76 I 2 O 4 N 8 B 3 F 4 ·CH 3 OH·CH 3 CN: C, 52.3; H, 5.3; N, 8 . 0 . Found: C, 52.3; H, 5.7; N, 7 .9. (Et 3 NH) 2 (PhA). The synthesis of this compound was similar to that for (Et 3 NH) 2 (DHBQ). H 2 PhA (0.14 g, 0.5 mmol) was used to react with Et 3 N (0.17 mL, 1.3 mmol) , and pink purple product was obtained. Yield: 0. 16 g ( 67 %). (6) [Cr 2 (tren) 2 (PhA cat,cat )](BPh 4 ) 2 . The synthesis of this complex was similar to that for [Cr 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 . (Et 3 NH) 2 (PhA) (0.07 g, 0.2 mmol) was used. Yellow brown c rystals , suitable for x - ray di ffraction, were obtained by layering a solution of NaBPh 4 in MeOH. Yield: 0.26 g ( 93 %). Anal. Calcd Cr 2 C 78 H 86 O 4 N 8 B 2 ·CH 3 OH : C, 69.9; H, 6.7; N, 8.3 . Found: C, 69 .8 ; H, 7.1 ; N, 8.5 . HRMS [ESI - TOF, m/z (rel. int.)]: [M] 2 + Calcd for [Cr 2 C 30 H 46 O 4 N 8 ] 2+ , 343.1227; Found, 343.1237 . (16) [Cr 2 (tren) 2 (PhA sq,cat )](BPh 4 ) 2 (BF 4 ). The synthetic procedure of this compound was similar to that of [Cr 2 (tren) 2 ( DHBQ sq,cat )](BPh 4 ) 2 (BF 4 ). Instead, (FeCp* 2 )(BF 4 ) ( 0.15 g, 0. 36 mmol) was used to react with [Cr 2 (tren) 2 (PhA cat,cat )](BPh 4 ) 2 (0. 2 g, 0.1 5 mmol). The product was filtered, washed by DCM (3 x 10 mL), and Et 2 O (3 x 10 mL). Yield: 0.06 g ( 26 %). HRMS [ESI - TOF, m/z (rel. int.)]: [M] 3 + Calcd for [Cr 2 C 30 H 46 O 4 N 8 ] 3 + , 228.74 8 4 ; Found, 228.7 494 . [Cr(tren)(C 18 O 4 H 10 )] + Calcd for [ CrC 24 H 28 O 4 N 4 ] + , 488.151 6 ; Found, 488.151 9 . Anal. Calcd Cr 2 C 78 H 86 O 4 N 8 B 3 F 4 ·CH 3 OH·CH 3 CN: C, 65.5; H, 6.3; N, 8.5. Found: C, 65.8; H, 6.1; N, 8.5. (Et 3 NH) 2 (NMe 2 - PhA). The synthesis of this compound was similar to that for (Et 3 NH) 2 (DHBQ). H 2 NMe 2 PhA (0.53 g, 1.41 mmol) was used to react with Et 3 N (0.8 mL, 5.6 82 mmol), and purple product was obtained. Yield: 0.5 g (74 %). HRMS [ESI - TOF, m/z (rel. int.)]: [M +H ] + Calcd for [ C 22 H 23 O 4 N 2 ] + , 379.1658 ; Found, 379.1598 . [M+2H ] 2 + Calcd for [ C 2 2 H 24 O 4 N 2 ] 2 + , 190.0868 ; Found, 190.0761 . [Et 3 NH ] + Calcd for [ C 6 H 16 N] + , 102.1283 ; Found, 102.1238 . [M - H ] - Calcd for [ C 2 2 H 2 1 O 4 N 2 ] - , 377.1501; Found, 377.1551 . (7) [Cr 2 (tren) 2 (NMe 2 - PhA cat,cat )](BPh 4 ) 2 . The synthesis of this complex was similar to that for [Cr 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 . (Et 3 NH) 2 (NMe 2 PhA ) (0.12 g, 0.2 mmol) was used. Red c rystals , suitable for x - ray diffraction, were obtained by layering a solution of NaBPh 4 in MeOH. Yield: 0.25 g (87%). Anal. Calcd Cr 2 C 82 H 9 6 O 4 N 10 B 2 · 3 CH 3 OH: C, 67.7; H, 7.2; N, 9.3 . Found: C, 67.3 ; H, 7.8 ; N, 9.3 . HRMS [ESI - TOF, m/z (rel. int.)]: [M] 2 + Calcd for [ Cr 2 C 34 H 54 O 4 N 10 ] 2 + , 385.6610; Found, 385.6565. [M] 3+ Calcd for [ Cr 2 C 34 H 54 O 4 N 10 ] 3+ , 257.4433; Found, 257.4416. (17) [Cr 2 (tren) 2 (NMe 2 - PhA sq ,cat )](BPh 4 ) 2 (BF 4 ) . The synthetic procedure of this compound was similar to that of [Cr 2 (tren) 2 ( DHBQ sq,cat )](BPh 4 ) 2 (BF 4 ). Instead, (FeCp * 2 )(BF 4 ) ( 0.2 g, 0.13 mmol) was used to react with [Cr 2 (tren) 2 (NMe 2 - PhA cat,cat )](BPh 4 ) 2 ( 0.11 g, 0.26 mmol). Yield: 0.09 g ( 45 %). HRMS [ESI - TOF, m/z (rel. int.)]: [M ] 3+ Calcd for [ Cr 2 C 34 H 54 O 4 N 10 ] 3+ , 257.4433; Found, 257.44 50 . [Cr(tren)(C 22 H 20 O 4 N 2 )] + Calcd for [CrC 28 H 38 O 4 N 6 ] + , 274.2360; Found, 274.23 55 . Anal. Calcd Cr 2 C 82 H 96 O 4 N 10 B 3 F 4 ·3CH 3 OH·CH 3 CN: C, 63.9; H, 6.8; N, 9.4. Found: C, 63.7; H, 6.8; N, 9.3. ( 10 ) [Cr 2 (tren) 2 (Me - AnT cat,cat )](BPh 4 ) 2 . [Cr(tren)Cl 2 ]Cl (0.12 g, 0.4 mmol) in MeOH/H 2 O (1:1, 40 mL) was degassed by the freeze - pump - thaw method. In a drybox, Et 3 N (0.2 mL, 1.0 mmol) was added dropwise to a rapidly stirring suspension of Me - AnT ( 0.05 g, 0.2 mmol) in MeOH (20 mL). Under N 2 , the above solution was cannula - transferred to the [Cr(tren)Cl 2 ]Cl solution. The reaction mixture was stirred under reflux ( c.a. After the reaction was cooled to RT, the solvents were evaporated under vacuum, and the 83 reaction was pumped into the drybox for workup. In the drybox, the product was dissolved in MeCN, and filtered. NaBPh 4 (0.68g, 2 mmol) in 80 mL of MeCN was layered carefully on top the filtrate for metathesis and recrystallization. Dark green crystals , suitable for x - ray diffraction, were obtained. Yield: 0.09 g (59 %). Anal. Calcd Cr 2 C 76 H 8 6 O 4 N 8 B 2 ·CH 3 OH : C, 69.4; H, 6.8; N, 8.4 . Found: C, 69.8 ; H, 6.6 ; N, 8.6 . HRMS [ESI - TOF, m/z (rel. int.)]: [M] 2+ Calcd for [ Cr 2 C 18 H 14 O 4 N 8 ] 2+ , 317.1070; Found, 317.1066. [Cr(tren)(C 14 H 8 O 4 )] + Calcd for [ Cr 2 C 34 H 54 O 4 N 8 ] + , 438.1359; Found, 438.1385. (18) [Cr 2 (tren) 2 (Me - AnT sq,cat )](BPh 4 ) 2 (BF 4 ). The synthetic procedure of this compound was similar to that of [Cr 2 (tren) 2 ( CA sq,cat )](BPh 4 ) 2 (BF 4 ). Instead, (CPh 3 )(BF 4 ) ( 0. 04 g, 0. 12 mmol) was used to react with [Cr 2 (tren) 2 (Me - AnT cat,cat )](BPh 4 ) 2 ( 0. 1 g, 0. 08 mmol). Yield: 0. 06 g ( 58 %). HRMS [ESI - TOF, m/z (rel. int.)]: [M] 3+ Calcd for [ Cr 2 C 18 H 14 O 4 N 8 ] 3+ , 220.7484 ; Found, 220.7482 . [Cr(tren)C 16 H 12 O 4 ] + Calcd for [CrC 22 H 30 O 4 N 4 ] + , 446.1672 ; Found, 446.1670. Anal. Calcd Cr 2 C 76 H 86 O 4 N 8 B 3 F 4 ·CH 3 OH·CH 3 CN: C, 64.9; H, 6.4; N, 8.6. Found: C, 64.8; H, 6.6; N, 8.6. ( 8 ) [Cr 2 (tren) 2 (NAT cat,cat )](BPh 4 ) 2 . The synthesis of this complex was similar to that for [Cr 2 (tren) 2 (Me - AnT cat,cat )](BPh 4 ) 2 .Green c rystals were obtained by layering a solution of NaBPh 4 in MeOH; however, the crystals were too small for x - ray diffraction. Yield: 0.12 g ( 51 %). Anal. Calcd Cr 2 C 70 H 80 O 4 N 8 B 2 ·2CH 3 OH·CH 3 CN: C, 66.9; H, 6.9; N, 9.5. Found: C, 66.5; H, 6.6; N, 9.1. HRMS [ESI - TOF, m/z (rel. int.)]: [M] 2+ Calcd for [ Cr 2 C 22 H 40 O 4 N 8 ] 2+ , 292.0992; Found, 292.1009. [M ] 3 + Calcd for [ Cr 2 C 22 H 40 O 4 N 8 ] 3+ , 194.7328; Found, 194.7341 . [Cr(tren)(C 10 H 6 O 4 )] + Calcd for [ CrC 16 H 24 O 4 N 4 ] 3+ , 388.1203; Found, 388.1195. (18) [Cr 2 (tren) 2 (NAT sq,cat )](BPh 4 ) 2 (BF 4 ). The synthetic procedure of this compound was similar to that of [Cr 2 (tren) 2 (DHBQ sq,cat )](BPh 4 ) 2 (BF 4 ). Instead, (CPh 3 )(BF 4 ) ( 0.05 g, 1.4 mmol) 84 was used to react with [Cr 2 (tren) 2 (NAT cat,cat )](BPh 4 ) 2 ( 0.12 g, 0.096 mmol). Yield: 0.048 g ( 38 %). HRMS [ESI - TOF, m/z (rel. int.)]: [M] 3+ Calcd for [ Cr 2 C 22 H 40 O 4 N 8 ] 3+ , 194.7328; Found, 194.7334. [Cr(tren)(C 10 H 6 O 4 )] + Calcd for [CrC 16 H 24 O 4 N 4 ] + , 388.1203; Found, 388.1248. ( 9 ) [Cr 2 (tren) 2 (AnT cat,cat )](BPh 4 ) 2 . The synthesis of this complex was similar to that for [Cr 2 (tren) 2 (Me - AnT cat,cat )](BPh 4 ) 2 . Recrystallization was unsuccessful, so no crystal structure for x - ray diffraction was obtained. Yield: 0.14 g ( 55 %). Anal. Calcd Cr 2 C 74 H 82 O 4 N 8 B 2 · 2 CH 3 OH ·2CH 3 CN : C, 6 7 . 7 ; H, 6. 8 ; N, 9.9 . Found: C, 68.1 ; H, 7.2 ; N, 9.6 . HRMS [ESI - TOF, m/z (rel. int.)]: [M] 2+ Calcd for [ Cr 2 C 18 H 14 O 4 N 8 ] 2+ , 317.1070; Found, 317.1066. [Cr(tren)(C 14 H 8 O 4 )] + Calcd for [ Cr 2 C 34 H 54 O 4 N 10 ] 3+ , 438.1359; Found, 438.1385. 3.2.3 Physical Measurements X - Ray Single - Crystal Structure Determinations . Single - crystal structure measurement for all Cr (III) dimeric complexes was acquired at the center for crystallographic research of Michigan State University. The crystals were mounted on nylon loops using sma ll amount of paratone oil. X - ray diffraction data were collected at 173 K on Bruker SMART APEX II CCDs (charge coupled device) either with Mo K radiation ( = 0.71073 Å) using a 3 - axis goniometer with Oxford 600 low - temperature device or with Cu K radia tion ( = 1.54178 Å) using a 3 - axis goniometer APEX II diffraction system with Oxford Cyrosystream 700 low - temperature device . Each system is equipped with a camera for viewing the crystals and a Pentium PC to control the diffractometer. The total number of runs and images was based on results from the program COSMO , 38 of which redundancy was expected to be 4.0 and completeness of 100% out to 0.83 Å for the Mo K Å for the Cu K parameter s wer e retrieved and refined using the SAINT software . 39 Scaling and absorption 85 corrections were applied by the SAINT 39 for Lorentz and polarization factors . A multi - scan absorption correction was performed by SADABS - 2014/5. 40 The structures were solved by intrinsic phasing using ShelXT 41 structure solution program. The structures were refined by least squares using XL - 2014/6 42 with Olex2 43 incorporated. All non - hydrogen atoms were refined anisotropically. The positions of h ydrogen atom were calculated geometrically and refined using the riding model, except for the hydrogen atom s on the non - carbon atom s, which was found by difference Fourier methods and refined isotropically. Table 3. 1 . Crystallographic data for Complex 1 , 2 , 4 and 5 . 1 2 4 5 Empirical Formula C 68 H 86 B 2 Cr 2 N 8 O 6 C 72 H 100 B 2 Cr 2 F 2 N 8 O 10 C 68 H 84 B 2 Cr 2 Br 2 N 8 O 6 C 68 H 76 B 2 Cr 2 I 2 N 8 O 6 Formula Weight (g/mol) 1237.07 1 401.22 1394.87 1488.85 Temperature (K) 173(2) 173(2) 173(2) 173(2) Crystal System Monoclinic monoclinic Monoclinic monoclinic Space Group P2 1 /c P2 1 /n P2 1 /n P2 1 /n a (Å) 9.6548(12) 9.9610(9) 13.5437(16) 13.4573(3) b (Å) 14.919(2) 29.248(3) 9.7886(12) 9.9351(2) c (Å) 22.171(3) 12.8274(12) 25.008(3) 25.0568(5) 98.059(2) 104.313(6) 96.2718(15) 96.674(2) Volume (Å 3 ) 3162.0(8) 3621.1(6) 3295.5(7) 3327.38(12) Z 2 2 2 2 D calc (g/cm 3 ) 1.299 1.278 1.406 1.486 Radiation MoK Cu K MoK Cu K Goodness of Fit (F 2 ) 1.050 1.0 53 1.029 1.0 3 6 R 1 (I 2 (I)) a 0.0403 0.0 691 0.0414 0.04 55 wR 2 (I 2 (I)) b 0.105 2 0. 191 3 0.099 5 0. 1230 a R 1 = b wR 2 =[ ] 1/2 , w=1/[ , where P=[ . 86 Table 3. 2 . Crystallographic data for Complex 6 , 7 and 10 . 6 7 10 Empirical Formula C 80 H 94 B 2 Cr 2 N 8 O 6 C 44.5 H 62 BCrN 5 O 5.5 C 76 H 86 B 2 Cr 2 N 8 O 6 Formula Weight (g/mol) 1389.25 817.8 1301.14 Temperature (K) 173(2) 173(2) 173(2) Crystal System Monoclinic monoclinic Triclinic Space Group P2 1 /c P2 1 /c P a (Å) 19.4630(6) 14.0445(7) 9.6955(2) b (Å) 16.0465(5) 10.1824(5) 10.3278(2) c (Å) 23.1461(7) 31.2970(13) 18.9856(4) 90.00 90.00 102.6000(10) 101.534(2) 95.492(3) 91.614(2) 90.00 90.00 96.949 (2) Volume (Å 3 ) 7082.9(4) 4455.1(4) 1838.75(7) Z 4 4 1 D calc (g/cm 3 ) 1.303 1.219 1.175 Radiation Cu K Cu K Cu K Goodness of Fit (F 2 ) 1.022 1.044 1.043 R 1 (I 2 (I)) a 0.063 1 0.0782 0.0690 wR 2 (I 2 (I)) b 0.153 9 0.209 2 0.190 5 a R 1 = b wR 2 =[ ] 1/2 , w=1/[ , where P=[ . Electronic Absorption Measurement. Electronic absorption spectra were measured using a Varian Cary 50 UV - vis spectrophotometer for all [Cr 2 (tren) 2 (L cat,cat )](BPh 4 ) 2 at a spectral resolution of nm , due to the extreme air - sensitivity of the samples and the spectra were corrected and normalized based on the spectra of [Cr 2 (tren) 2 (L sq,cat )](BPh 4 )(BF 4 ). The high - resolution spectra of [Cr 2 (tren) 2 (L sq,cat )](BPh 4 )(BF 4 ) were recorded on a Perkin - Elmer Lambda 1050 UV - vis /NIR spectrophotometer at a spectral resolution of 0.2 nm. Data were obtained on samples dissolved in MeCN, which had been degassed , dried over neutral alumina, and stored under an inert atmosphere. All solutions were prepared in a N 2 - flushed drybox in 1 cm pat hlength air - tight optical cells. Differential Scanning Calorimetry. Differential scanning calorimetry (DSC) measurement were conducted for thermal characterization of solid samples, including melting behavior, degree of crystallinity, sample morphology, and possible purity. The DSC reactor is 87 Science at Michigan State University. The data were collected by Dr. Jared Williams on a Netzsch DSC 200 - F3 Maia with alumin um crucibles. This instrument has a temperature range of 50 100 mg of a Al 2 O 3 single crystal standard for the calculation of heat capacity before measurement . All measurements were performed under constant flow of argon to en sure sample stability from oxidation, and sample masses are c.a. 50 to 200 mg. 3.3 SQUID Variable - Temperature Magnetic Susceptibility Measurements General. Magnetic susceptibility measurement was collected in direct - current (DC) scan mode using a Quantum Desgien MPMS ® 3 SQUID magnetometer Cryogen Free with EverCool® He gas regulator interfaced to a Dell PC. Data were collected in an applied field of 1 T. [TMENH 2 ](CuCl 4 ) (TMEN = (CH 3 ) 2 N(CH 2 ) 2 N(CH 3 ) 2 ) was used as a calibration standard and temperature error check. 44 Temperature was ramped up with small temperature increments to ensure the samples were thermally equilibrated. Data were corrected for diamagnetism of the 45 and the measured susceptibility of the sample holder, in cluding a plastic straw and a plastic sealed bag . Magnetic data for all measured complexes were fitted to an operator - equivalent form of the Heisenberg - Dirac - van - Vleck Hamiltonian given in Eq. 3.1 using MAGFIT , 46 and were reported as effective magnetic mom ent (µ eff ). Paramagnetic impurity (5 mol % of an S = ½ compound) and temperature - independent paramagnetism (200 x 10 - 6 cgsu for each Cr (III) center) were included in fitting. 88 3.3.1 Sample Preparation for P owder s SQUID measurement is widely used for me asurement the magnetic properties of materials or tightly packed and pressed solid both in academia and industry. T he sample packing and mounting techniques have been maturely developed by Quantum Design, and various sample holders for materials are commer cially available by the company. However, magnetic measurement done for powder samples is not as common. As far as I know, it is not very commonly done in industry, and materialists and physicists usually conduct their magnetic experiments on materials in academia. Magnetochemists, who conduct powder measurement, each develop their own SOPs, which are not widely accessible for other users. The way we prepared powder samples is to pack them in a 1.5 x 1.5 cm plastic bag, and roll the packed sample into a 5 x 5 mm square so that it can be fit into a plastic straw holder. Before packing the sample, it needs to be ground into fine powder. The packing of powder samples w as performed in a N 2 - flushed drybox due to the air sensitivity of the Cr(III) complexes. Another way to pack air - food vacuum sealer, and it can vacuum seal the powder sample in a drybox to prevent it from exposing to air. After that, similar technique was used to roll and fi t the sealed sample into a straw holder. One problem arise from both preparations is that the shapes of these rolled 5 x 5 mm samples are not identical. Since SQUID measurement is a very sensitive measurement, the slight shape change can cause c.a. 1 - 5% de viation in sample data. Gelatin capsules are recommended by Quantum Design as sample holders with cotton filler to prevent powder from moving while performing DC scan measurement. 47 Two issues can be caused by these capsules: one is that the background con tribution of the capsule and cotton is too large to convolute the 89 sample signal if the sample is a magnetically diluted sample; anther one is that the size of this capsule exceeds 5 x 5 mm. The sample is moved linearly over several centimeters up and down through second - order gradiometer superconducting detection coils during the DC scan. The single turn - wound clockwise upper coil ( - 1) , the two turn - wound counter - clockwise center coils (+1) , and another single turn - wound clockwise bottom coil (+1) in the d etection coils within the MPMS ® 3 SQUID magnetometer are each about 2 c m apart. 30 If the sample size exceeds 5 x 5 mm, the sample moved through the coils can be detected by both the upper and center coils at a time , and the signal will be partly cancelled . Therefore, the data collected will all be resulted in smaller magnetic moment. The sample need to be centered in the plastic straw at 66 3 mm. If the height of the sample exceeds greater than 10 mm, reduced magnetization will be obtained due to the samp le position outside of the second - order gradiometer superconducting detection coils. Figure 3. 2 . Quantum Design Delrin ® liquid sample holder. Quantum Design provides a Delrin ® liquid sample holder (Fig. 3. 2 .). This sample holder can be used as a powder holder in the future. The re are two major advantages of employing this sample holder: one is that the size of the sample socket is consistent, so we will not have the concern about size change between sample m easurements ; another one is its heat resistance for higher temperature measurement, > 350 K. However, the cost of this holder is $220, which is much more expensive than using plastic bags to pack samples. Quantum Design provides another Overall length: 8.5cm Sample pocket: 8mm 90 alternative sample holder, including a Delrin ® liquid sample holder and a brass half - tube. This Delrin ® liquid sample holder will be snapped into the center of a brass tube for the measurement. However, this setup is not recommended, because the sample socket of this Delrin ® liquid sample holder is very small, which cannot hold a lot less sample (Fig. 3. 3 .), and the background contribution of brass material is too intense magnetic signal to convolute magnetic diluted sample signal. Figure 3. 3 . (a) Quantum Design Delrin ® powder sample holder; (b) Brass half - tube; (c) a Delrin ® powder sample holder snapped into a brass half - tube. 3.3.2 Temperature Sequence for Variable - Temperature Magnetic Data Collection For variable - temperature mag netic measurement, the system is generally kept at each temperature point for additional 5 to 10 min before data collection to ensure thermal equilibrium of the sample and the sample chamber (see Sequence 3.1 in Appendix). Instead, the sequence (Sequence 3 .2 in Appendix) employed for my samples is to ramp up temperature with small increments to ensure thermally equilibrium. Data were collected using both sequences for the same sample, and they are the same within error, <1%. T emperature in dependence of the [Cr 2 (tren) 2 (CA sq,cat )] 3+ data 1 at 2 350 K fails to populate higher - energy spin states to accurately determine J. The energy applied at 350K is not ® 3 SQUID has a temperature rang e of 1.8 400 K, and it provides an option to use an external oven heater stick Sample pocket: 5mm (a) (b) (c) 91 for higher temperature measurement, 300 1000 K. Magnetic data of all [Cr 2 (tren) 2 (L sq,cat )] 3+ were obtained from 2 to 400 K, because specially tailored sample holder is requi red for the use of an external oven. However, the plastic bag holding the sample starts to melt at above 350 K. When holding sample at above 350 K for 5 or more minutes, the plastic bag will be broken eventually and cause sample spilling inside the sample to cause contamination of the instrument and inaccurate data. The same problem will not be encountered when change the temperature point with small increments, and this is another reason that Sequence 3.2 was used for data collection. 3.4 Results and D iscussions 3.4.1 Synthesis and Characterization. The benefit of employing the quinoidal ligands is their reversible redox properties. By combining these quinoidal ligands with relatively redox - inert metal ions, Cr(III), it allows us to systematically stu dy the effect of spin exchange on the physical and photophysical properties without changing their overall composition of elements and drastically altering their structures. Complexes prepared for this study are based off the previous work of Dr. Dong Guo 8 , a former group member in the McCusker group. The dianionic solid forms of THB, H 2 FA, H 2 CA, H 2 BA, H 2 IA, H 2 PhA, and H 2 NMe 2 - PhA are stable in air , and their dianionic forms are used as starting materials for synthesis of dichromium (III) complexes. The synthetic procedures of these quinoidal organic compounds are vastly different even though they are the derivatives of one another. Both THB and H 2 CA are commercially available, which are used without further purification. The synthesis of H 2 IA starts with bromanil, and it is a two - step synthetic procedure. After obtaining iodanil, which cannot be 92 needs to be hand shaken. Both H 2 PhA, and H 2 NMe 2 - PhA are synthesi zed through Suzuki coupling. These reactions proceed to increase the solubility of all starting materials in 1,4 - dioxane and allow fully coupling to the 1,4 - positions of 2,5 - Dibromo - 3,6 - dimethoxy - 1,4 - benzoquinone . Mono - coupling benzoquinone w ill be formed as the primary product at . However, t he products can be reduced fully into their benzene forms under high heat . Ag 2 O therefore was added to prevent the reduction of benzoquinone. Both compounds have to be purified by running through a silica gel flash column. For H 2 PhA, the product will be eluted out from the first orange band due to its low polarity . However, one eluent cannot fully purify H 2 NMe 2 - PhA. With the first eluent, DCM/n - pentane (6:4), the first yellow - orange impurity band can be eliminated , and the product was stuck on top of the stationary phase due to its high polarity . With the second eluent, hexane/EtOAc/DCM (8:1:1), the product was collected as the first magenta band. When mono - coupling benzoquinone product was formed, th e band was violet. DCM was added into the eluent to increase the solubility of the mixture, since H 2 NMe 2 - PhA is insoluble in hexane. Alumina can be used as the stationary phase for H 2 NMe 2 - PhA for its weakly acidity . But the impurity eluted out in DCM/n - pentane is weakly basic, silica gel is chosen as the stationary phase instead. Sands are not recommended to be used during the packing of these silica gel column, because the compound mixtures will bleach on sands. The synthesis of other derivatives , including 2,7 - d ihydroxy - 3,6 - di (4 - cyano phenyl)benzoquinone ( H 2 (CN - PhA) ), 2,7 - d ihydroxy - 3,6 - di cyano benzoquinone ( H 2 CNA ), 2,7 - d ihydroxy - 3,6 - dipiperidino benzoquinone (H 2 PipA) , and 2,3,6,7 - tetrahydroxy - 9,10 - diphenylanthracene (H 4 (Ph - AnT)) , was attempted. The synthetic procedures involve multiple 93 steps, and some of them have been established. Future s tudents, who follow up this project, can attempt the synthesis based on my suggestions, which will be further discussed in Chap. 6. The synthetic procedures for the halogen series and phenyl derivatives metal complexes are very similar. However, due to the ligand nature of the naphthalene and anthracene quinoidal ligands, the synthesis was modified. The choice of metals was determined by the desire of limiting re dox activity only to the quinoidal ligands. As discussed previous in our introduction, tren is widely used as a capping ligand in many transition metal complexes due to its formation of a single isomer when bound to metal, and it will not directly affect t he absorption spectra of the compounds. The dianionic forms of THB, H 2 FA, H 2 CA, H 2 BA, H 2 IA, H 2 PhA, and H 2 NMe 2 - PhA are used as starting materials to react with Cr (II) , and these dianionic forms are very air stability. Deprotonated anilates appear to have four resonance structure (Fig. 3. 4 ) . These ligands are chosen for their redox properties and multiple chelating/binding modes. Upon one electron reduction, the dianionic version (L 2 - ) is converted into their radical form [L sq,cat ] 3 - . We believe that neith er any of the protonated or deprotonated isolated form of [L sq,cat ] 3 - has been reported in literature. The only report about the detection of CA sq,cat formation was in aqueous NaOH with a reductant Na 2 S 2 O 4 added. 31 The fully reduced form, [L cat,cat ] 4 - , is extremely air sensitive, and its deprotonated form is only stable in solution in the presence of a strong reductant, i.e. Na metal or Na 2 S 2 O 4 . Some of the protonated form, H 4 L, can be prepared and isolated, when stored dry under inert atmosphere. However, not all derivatives were able to prepared and isolated, and more information will be discussed in Chap ter 4. 94 Figure 3. 4 . Resonance structure of substituted 3,6 - R - tetraoxoquinone . The choice of chromium was not only motivated by its relatively redox - inert property, but also its well - studied and well - documented physical and photophysical properties. 9,10,49 These properties simplify the characterization features contributed by Cr (III), and allow us to focus on the effect of spin exchange across t he series of complexes. Our initial synthetic approach of the anilate bridging Cr (III) dimers is inspired by the route of a similar system, [Cr 2 (CTH) 2 (DHBQ)](PF 6 ) 2 , reported by Dei and co - workers. 18 Cr (II) is a much more labile form , and two Cr (II) reac t with the dianionic ligands , the (sq, sq) form, via redox reactions . [Cr II (tren)Cl]Cl was generated in situ because of its extreme air - sensitivity. When binding to [ Cr (tren) Cl ]Cl , the ligand got fully reduced to its (cat, cat) form ; meanwhile, Cr (II) was oxidized to Cr (III) formed. The summary of syn thetic routes is shown in Scheme 3 . 1. Only 2 equivalents (eq.) or slight over amount of [Cr(tren)Cl]Cl should be used to react with anilate bridging ligands. When 3 or more eq. of [Cr(tren)Cl]Cl were added to the reaction, the crystal form of [Cr(tren)Cl](BPh 4 ) w as grown (Appendix Figure 3 .8 2 ) and mixed with the desired Cr (III) dimers, which increases the difficulty of product isolation. If starting from two Cr (III) with the (cat, cat), fully reduced, form o f the ligands , the coordination reaction require heat to be appl ied, and the (cat, cat) form is extremely air - sensitive as mentioned above. This will increase the difficulty of preserving the reaction from oxidation under inert atmosphere, since [Cr 2 (tren) 2 ( Anilate cat,cat )] 2+ complexes are also extremely air - sensitive in both solid and solution states. The paramagnetism of these complexes make NMR spectroscopy inaccessible for 95 characterization, and these products were characterized by ESI mass spectrometry and x - ray crystallography. [Cr(tren)( Anilate cat,q )] + was detected by ESI+; however, it is not known that whether this product was formed during the reaction or via the ionization and fragmentation while passing through instrument under high voltage. Scheme 3.1. General synthetic routes of [Cr 2 (tren) 2 (Anilate cat,cat )](BPh 4 ) 2 and [Cr 2 (tren) 2 (Anilate sq,cat )](BPh 4 ) 2 (BF 4 ), where anilate represents substituted anilate bridging ligands, DHBQ, FA, CA, BA, IA, PhA, or NMe 2 - PhA. Due to the binding nature of anth racene (AnT) and naphthalene (NAT) , the reaction of Cr (III) dimers have to start with H 4 NAT, H 4 AnT, and H 4 (Me - AnT) . Direct oxidation of these kind of polycyclic aromatic hydrocarbons (PAHs), such as naphthalene, anthracene, phenanthrene, terrylene, and pyrene, happen readily and are reported in literature (Figure 3 .5 ) . 51 - 53 However, these quinone derivatives alter the b inding motives between these PAHs ligand with metal ion. Figure 3 . 5 . Oxidation of naphthalene and anthracene to their quinone derivatives . Instead of using our original approach with [ Cr II (tren) Cl ]Cl and quinones , [Cr III (tren)Cl 2 ]Cl was added to react with H 4 NAT, H 4 AnT, or H 4 (Me - AnT) for our systems . The synthetic routes of these AnT/NAT bridging Cr (III) dimeric systems are summarized and shown in Scheme 3 . 2. However, the reaction needed to be transferred out from the drybox and refluxed using Schlenk line technique in order to maximize the formation of product due to the unlability 96 of Cr (III). The maximum reaction time is 48 h for the highest yield of product s , and it needs to . When refluxing for longer time or at higher temperature , the product start ed to decompose into the monomeric form, [Cr(tren)(L q,cat )] + for the halogen series and phenyl derivatives, and [Cr(tren)(L cat,cat )] + for t he naphthalene and anthracene analogues (Figure 3. 1), which was detected by ESI+ mass spectrometry . Two types of Cr (III) monomers can be produced during the reaction of these Cr (III) dimeric systems: for anilate bridging dimers, [Cr(tren)(L cat,q )] + was p roduced with the bridging ligand in (cat, q) form; for the horizontally extended aromatic bridging dimers, e.g. NAT, Me - AnT, and AnT, [Cr(tren)(L cat,cat )] + was produced with the bridging ligand in (cat, cat) form. Scheme 3.2. General synthetic routes of [C r 2 (tren) 2 (L cat,cat )](BPh 4 ) 2 and [Cr 2 (tren) 2 (L sq,cat )](BPh 4 ) 2 (BF 4 ), where L represents naphthalene or anthracene bridging ligands, NAT, AnT, or Me - AnT. The crystallines of [Cr 2 (tren) 2 (L cat,cat )](BPh 4 ) 2 (L: NAT, AnT, or Me - AnT) were obtained by metathesis from solution prior oxidation. Both anthracene and naphthalene have an extended conjugated system, which can reduce electron - electron repulsion within a system. Our initial thought of employing them into our bridging system is t heir ability to delocalize the spin density - system of PAHs cause them to be less soluble. Both H 4 AnT and H 4 (Me - AnT) are insoluble in MeOH. The resulting product of 97 Cr 2 (tren) 2 (Me - AnT cat,cat )Cl 2 is also ins oluble in MeOH; therefore, it needed to be recrystallized and metathesized in MeCN. The solubility of Cr 2 (tren) 2 (AnT cat,cat )Cl 2 is even poorer, and it is only very slightly soluble in MeCN, which makes its recrystallization extremely difficult. Growing x - r ay diffraction suitable crystals require the modulation of solvents and solution concentration, and the method will be further discussed below. ( 3. 1) ( 3.2 ) [Cr 2 (tren) 2 (L cat,cat )] 2+ can be oxidized to [Cr 2 (tren) 2 (L sq,cat )] 3+ by mild chemical oxidants (eq. 1a) . The choice of oxidants is determined from comparing the redox p otentials, which will be further discussed in Chap ter 5, measured by cyclic voltammetry with the redox potentials of some common chemical oxidants. 54 [FeCp* 2 ](BF 4 ) with a redox potential of - 0.535 V (vs Fc/Fc + ) was chosen as the oxidizing agent for [Cr 2 (tr en) 2 (DHBQ cat,cat )] 2+ , [Cr 2 (tren) 2 (PhA cat,cat )] 2+ , and [Cr 2 (tren) 2 (NMe 2 - PhA cat,cat )] 2+ to prevent over - oxidizing the starting materials into their monomer derivatives , because its redox potential is more negative than the ones of [Cr 2 (tren) 2 (L)] 3+/4+ (eq. 1b) . [CPh 3 ](BF 4 ), - 0.11 V vs Fc/Fc + , a slightly stronger oxidant than [FeCp* 2 ](BF 4 ) , was the choice of oxidant for the other [Cr 2 (tren) 2 (L cat,cat )] 2+ for the similar reason . The reaction time of these oxidations should be limited to 4 to 8 h. Long re action time can re sult in over - oxidation, and the only product detected by ESI+ was Cr (III) monomeric systems after 12 h oxidation. It is likely that the oxidation equilibrium gets shifted as more [Cr 2 (tren) 2 (L sq,cat )] 3+ formed, so it potentially stimulat es the production of [Cr 2 (tren) 2 (L sq,sq )] 4+ even with the two mild oxidants (Scheme 3 . 2 ) . [Cr 2 (tren) 2 (L sq,sq )] 4+ is unstable, because the preferred binding motif of the bridging ligand is (L cat, q ). When the meta - unstable form of 98 [Cr 2 (tren) 2 (L sq,sq )] 4+ pro duced, it potentially rearranges into [Cr(tren)(L cat,q )] + for better stability. This can potentially explain the detection of Cr (III) monomer by ESI+ with long reaction, and the quasi - reversibility of [Cr 2 (tren) 2 (L)] 3+/4+ observed during electrochemistry. The CV of Cr 2 (tren) 2 (AnT) 2+/3+ is irreversible, which will be further discussed in Chap. 5. The irreversibility of Cr 2 (tren) 2 (AnT) 2+/3+ indicate that the formation of Cr 2 (tren) 2 (AnT cat,cat ) 3+ is likely to be thermodynam ically unfavorable . The oxidation of Cr 2 (tren) 2 (AnT cat,cat ) 2+ to Cr 2 (tren) 2 (AnT sq,cat ) 3+ with [FeCp* 2 ](BF 4 ) was unsuccessful. No [M] 3+ species was detected by ESI+ after the similar synthetic procedure as [Cr 2 (tren) 2 (DHBQ sq,cat )](BPh 4 ) 2 (BF 4 ). These experimental evidence supports my hypothesis. 3.4.2 Single Crystal X - Ray Structures X - ray diffraction quality crystal structures were collected for [Cr 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 ( 1 ), [Cr 2 (tren) 2 (FA cat,cat )](BPh 4 ) 2 ( 2 ), [Cr 2 (tren) 2 (BA cat,cat )](BP h 4 ) 2 ( 4 ), [Cr 2 (tren) 2 (I A cat,cat )](BPh 4 ) 2 ( 5 ), [Cr 2 (tren) 2 (PhA cat,cat )](BPh 4 ) 2 ( 6 ), [Cr 2 (tren) 2 (NMe 2 - PhA cat,cat )](BPh 4 ) 2 ( 7 ), and [Cr 2 (tren) 2 (Me - AnT cat,cat )](BPh 4 ) 2 ( 10 ). The crystal structure of [Cr 2 (tren) 2 (CA cat,cat )](BPh 4 ) 2 ( 3 ) has been reported by Dr. Guo in our group. 1 The crystals of Complex 1 , 2 , 4 , 5 , 6 , and 7 were grown via metathesis by carefully layering NaBPh 4 MeOH solution on top of its product MeOH solution in a N 2 - filled drybox . The crystals were grown in dark after 2 weeks. The most challen ging part of growing crystals is the modulation of solution concentration. If the mother solution is too concentrated, the product would either be too small or powder out. Chromium complexes naturally do not diffract well under x - ray, so the size of the cr ystal for x - ray analysis is crucial . The recrystallization of [Cr 2 (tren) 2 (NAT cat,cat )](BPh 4 ) 2 was attempted a few times . Small crystal was grown; however, the 99 diffraction rate of these crystals was too weak. Future students should consider adding aromatic - stacking or viscous alcohol for hydrogen bonding to facilitate bigger crystal grown. All of the compounds mentioned above are extremely air - sens itive; thus, mounting the crystal is also challenging. These crystal s we re confined in their lattices with solvent molecules. The crystal needs to be picked out, mounted on a goniometer, and placed under a stream of liquid He quickly. Exposing the product too long in air will result in product decomposition and solvent lost. C olor change of the crystal indicates t he decomposition, and structur al disorder implies the loss of solvent. Table 3. 3 . Complex 1 , 2 , 4 , and 5 . 1 2 4 5 Bond Length (Å) Cr(1) O(1) 1.9422(15) 1.947(3) 1.949(2) 1.952(3) Cr(1) O(2) 1.9136(15) 1.936(3) 1.920(2) 1.914(3) Cr(1) N(1) 2.1031(18) 2.102(3) 2.084(2) 2.091(3) Cr(1) N( 2 ) 2.0974(19) 2.095(4) 2.076(3) 2.117(4) Cr(1) N( 3 ) 2.092(2) 2.077(4) 2.113(3) 2.082(3) Cr(1) N( 4 ) 2.0692(19) 2.075(3) 2.075(3) 2.080(3) O(1) C(8) 1.388(2) 1.368(4) 1.364(3) 1.360(5) O(2) C(9) 1.357(3) 1.356(4) 1.348(3) 1.342(5) C(7) C(8) 1.384(3) 1.386(5) 1.392(4) 1.394(5) C(8) C(9) 1.395(3) 1.396(5) 1.407(4) 1.417(5) C(7) C(9) 1.395(3) 1.384(5) 1.39 4 (4) 1.391(5) Cr Cr a 7.628 7.644 7.667 7.657 O(1) Cr(1) N(1) 97.31(7) 95.98(12) 93.95 (9) 94.78(12) O(1) Cr(1) N(2) 99.34(7) 98.96(14) 100.02(10) 94.56(14) O(1) Cr(1) N(3) 93.03(7) 95.14(13) 94.82(11) 100.20(12) O(1) Cr(1) N(4) 177.05(7) 178.29(14) 175.64(10) 175.99(13) O(2) Cr(1) O(1) 86.42(6) 86.06(11) 86.21(8) 86.23(11) O(2) Cr(1) N(1) 175.72(7) 177.08(13) 178.97(10) 178.91(13) O(2) Cr(1) N(2) 86.58(7) 87.46(14) 86.54(12) 86.51(14) O(2) Cr(1) N(3) 86.55(8) 86.37(14) 86.32(12) 86.18(13) O(2) Cr(1) N(4) 92.59(7) 94.36(13) 96.02(9) 95.51(12) N(1) Cr(1) N(2) 94.82(8) 94.28(15) 94.43(12) 92.99(15) N(1) Cr(1) N(3) 91.17(8) 91.35(15) 92.66(13) 94.06(14) N(1) Cr(1) N(4) 83.57(7) 83.54(14) 83.76(10) 83.46(13) N(2) Cr(1) N(3) 165.43(8) 164.17(16) 163.06(13) 163.04(14) N(2) Cr(1) N(4) 83.36(8) 82.72(15) 83.89(11) 81.96(15) N(3) Cr(1) N(4) 84.14(8) 83.23(15) 81.61(11) 83.55(13) a Non bonding metal - to - metal distance. 100 Complex 1 , 4 and 5 contains two MeOH solvent molecules in their crystal lattice. The molecular formula of Complex 2 shows that the crystal lattice contained six MeOH solvent molecules. All of these crystal structures do not show structural disorder. Figure 3. 6 . ORTEP drawing of Complex 1 ( a ), 2 ( b ), 4 ( c ), and 5 ( d ) obtain from single crystal x - ray structure determination. Atoms are represented as 50% probability thermal ellipsoids. Hydrogen atoms are omitted for clarity. The molecular formula of Complex 7 shows that the crystal lattice contained six MeOH solv ate molecules with solvent disorder. Due to the solubility issue of Complex 10 , its crystal was grown by layering NaBPh 4 MeCN solution on top of its MeCN/MeOH solution. The crystal collected show solvent disorder, which does not affect the body structure of th e product. However, modelling the various solvent disorder was unsuccessful. The crystal has a R 1 of 6.90% with solvent mask, which indicate a high - quality crystal structure with omitted structural disorder. The bond lengths and bond angles are still use f ul for our discussion here. A few approaches were attempted, including adding a few drops of octanol into the crystallization chamber. The reasoning behind is that the hydrogen bonding between alcohol and the complex (a) (b) (c) (d) 101 will potentially help confine solvate m olecules in the crystal lattice. An aliphatic alcohol is more viscous with higher boiling point, so it will not easily evaporate and leave crystal lattice resulting in structural disorder. However, no crystal was grown. Better quality crystal with no s tru ctural disorder or analyzable disorder should be grown in the future with other alternative approach . Figure 3. 7 . ORTEP drawing of Complex 6 ( a ), 7 ( b ), and 10 ( c ) obtain from single crystal x - ray structure determination. Atoms are represented as 50% probability thermal ellipsoids. Hydrogen atoms are omitted for clarity. Due to the solubility issue , the crystals of Complex 10 were grown by layering NaBPh 4 MeCN solution on top of its MeCN/MeOH solution. The crystal collected show solvent disorder, which does not affect the body structure of the product. However, modelling the disorder was unsuccessful. The crystal has a R 1 of with solvent mask, which indica te s a high qualitystructure without the solvent disorder. The bond lengths and bond angles are used for our discussion here. (a) (b) (c) 102 Better quality crystal with no solvent disorder or analyzable disorder should be grown in the future. Table 3. 4 . Selected Bond Le Complex 6 , 7 , and 10 . 6 7 10 Bond Length (Å) Bond Length (Å) Cr(1) O(1) 1.9 35 (2) 1.913(3) Cr(1) O(1) 1.9 16 ( 3 ) Cr(1) O(2) 1.9 06 (2) 1.939(3) Cr(1) O(2) 1.9 46 ( 3 ) Cr( 2 ) O( 3 ) 1.943(2) Cr( 2 ) O( 4 ) 1.910(2) Cr(1) N(1) 2.107(3) 2.099(3) Cr(1) N(1) 2.0 7 7 ( 4 ) Cr(1) N( 2 ) 2.121(3) 2.087(4) Cr(1) N( 2 ) 2.0 85 ( 4 ) Cr(1) N( 3 ) 2.083(3) 2.093(4) Cr(1) N( 3 ) 2.113( 4 ) Cr(1) N( 4 ) 2.074(3) 2.091(4) Cr(1) N( 4 ) 2.07 8 ( 4 ) Cr( 2 ) N( 5 ) 2.093(3) Cr( 2 ) N( 6 ) 2.097(3) Cr( 2 ) N( 7 ) 2.087(3) Cr( 2 ) N( 8 ) 2.085(3) O(1) C(8) 1.376(4) 1.377(5) O(1) C(8) 1.3 55 (3) O(2) C(9) 1.361(4) 1.364(5) O(2) C(9) 1.3 57 (3) O(3) C(23) 1.379(4) C( 11 ) C(13) 1.4 50 ( 6 ) O(3) C(24) 1.361(4) C(12) C(13) 1.401(6) C(7) C(8) 1.401(4) 1.395(6) C(7) C(8) 1.3 56 ( 6 ) C(8) C(9) 1.404(5) 1.408(6) C(8) C(9) 1.4 32 ( 6 ) C( 9 ) C( 22 ) 1.40 4 ( 4 ) 1.418(6) C( 9 ) C( 10 ) 1.365(6) C( 22 ) C( 23 ) 1.4 05 (4) C( 7 ) C(1 3 ) 1. 439 ( 5 ) C(23) C(24) 1.404(5) C(10) C(11) 1.429(6) C(7) C(24) 1.401(4) C(11) C(12) 1.420(5) Cr Cr a 7.646 7.652 Cr Cr a 12.545 O(1) Cr(1) N(1) 98. 5 9(11) 97.67(14) O(1) Cr(1) N(1) 9 4.71 ( 14 ) O(1) Cr(1) N(2) 92.50(12) 95.14(15) O(1) Cr(1) N(2) 97.00 (1 4 ) O(1) Cr(1) N(3) 101.94(11) 98.40(15) O(1) Cr(1) N(3) 9 8.31 (1 6 ) O(1) Cr(1) N(4) 173.95(12) 178.57(14) O(1) Cr(1) N(4) 17 8.25 (1 3 ) O(2) Cr(1) O(1) 85.87(10) 85.74(11) O(2) Cr(1) O(1) 8 5.20 ( 12 ) O(2) Cr(1) N(1) 174.90(11) 176.55(16) O(2) Cr(1) N(1) 17 9.41 (1 5 ) O(2) Cr(1) N(2) 88.19(13) 88.58(15) O(2) Cr(1) N(2) 8 7.14 (1 4 ) O(2) Cr(1) N(3) 84.23(12) 87.44(16) O(2) Cr(1) N(3) 8 8.60 (1 6 ) O(2) Cr(1) N(4) 92.99(11) 94.04(13) O(2) Cr(1) N(4) 96. 50 ( 13 ) N(1) Cr(1) N(2) 94.06(12) 91.65(17) N(1) Cr(1) N(2) 9 2.30 (1 5 ) N(1) Cr(1) N(3) 92.39(12) 91.51(18) N(1) Cr(1) N(3) 9 1.99 (1 7 ) N(1) Cr(1) N(4) 82.83(11) 82.56(15) N(1) Cr(1) N(4) 83. 59 (1 5 ) N(2) Cr(1) N(3) 163.12(13) 165.56(18) N(2) Cr(1) N(3) 163. 70 (1 7 ) N(2) Cr(1) N(4) 81.52(12) 83.44(16) N(2) Cr(1) N(4) 8 2.69 (1 3 ) N(3) Cr(1) N(4) 83.84(12) 83.01(16) N(3) Cr(1) N(4) 8 2.18 (1 5 ) a Non bonding metal - to - metal distance. 103 The halogenated Cr (III) complexes are isostructural in monoclinic space group P2 1 /n (a more orthogonal cell) , and crystallographic details are shown in Table 3. 4 . with selected bond lengths and angle given in Table 3. 4 . Complexes 1 , 6 , and 7 are isostructural in monoclin ic space group P2 1 /c , a more oblique cell compared with P2 1 /n . These complexes are all structurally similar w ith centrosymmetric monoclinic space group s , and complexes 1 , 2 , 3 , 1 4 , 5 , and 7 are situated on inversion centers making only half of a dimer unique in a cell. The entire dimeric system of complex Ph is unique due to the inter - ring torsions within the phenylanilate bridging ligand. The ORTEP drawings of the cations are shown in Fig . 3. 6 and Fig . 3. 7 , respectively. The chromium center is coordinated with four aliphatic nitrogens from the tren capping ligand and two oxygens from the catecholate bridging ligand to form a distorted octahedral environment. This kind of distorted octahedral coordination is typically observed in other chromium - catecholate complexes, e.g. [Cr(tren)(3,6 - DTBCat)](ClO 4 ). 55 The bite angles around be seen for tetradentate tripodal tren ligand. The Cr - N bond lengths are ranging from 2.087 to 2.096 Å, which are similar to those observed in [Cr(tren)(3,6 - DTBCat)](ClO 4 ) (average 2.098 Å) 40 and slightly longer than those in [Cr(tren)(3,6 - DTBSQ)](PF 6 ) (average 2.07 Å) . 19 The Cr - O bond distances are ranging between 1.906 and 1.952 Å (Table 3. 3 and 3.4 ); for example, the bond distances are 1.942 Å and 1.913 Å respectively in complex H . It was believed that the discrepancy in Cr - O bond distances was due to one positioning shoulder - by - shoulder to the NH 2 in tren, and the other one locating in between two NH 2 . This phenomenon was observed in complexes 1 , 2 , 3 , 1 4 , 5 , and 6 . However, the opposite situation was observed for complexes NMe 2 Ph and MeAnT. Similar situa tions were seen in [Cr(tren)(3,6 - DTBCat)](ClO 4 ) 55 with larger difference and [Cr(tren)(3,6 - DTBSQ)](PF 6 ) 19 with smaller difference. 104 It has been widely observed that the C - C bond length within the ring can indicate the oxidation state of the quinoidal ligand when binding to first - row transition metals. 56 - 58 For the fully reduced catecholate form, the C - C bond distances are nearly identical indicating the aromatic nature of th e ligand. For the semiquinoidal radical form, the ring shows alternating single and double C - C bond feature, because the electrons are more localized in the C=C bond. This reflects on the short and long C - C bond lengths seen in x - ray crystal structure. The C - C bond lengths within the bridging ring show a narrow range for some complexes: 1.384 1.395 Å in complex H; 1.386 1.396 Å in complex F; 1.393 1.402 Å in complex Cl 1 ; 1.392 1.407 Å in complex Br; 1.401 1.405 Å in complex Ph. However, C - C bond d istances in complexes Br (1.391 1.417 Å) and NMe 2 Ph (1.395 1.418 Å) show a m uch wider range. Based on this evidence, Complex 5 and 7 are potentially less stable and easier to be oxidized into their semiquinone forms. More physical evidence will be disc ussed in Chap ter 5 to support this hypothesis. The C - O bonds in quinoidal ligands can also provide information about the oxidation state of the ligands. 56 - 58 The C - O bond lengths are generally different in semiquinodal complexes, e.g. 1. 293 Å and 1.3 12 Å in [Cr(tren)(3,6 - DTBSQ)](PF 6 ) , 19 which is consistent with the pseudo single and double C - C character. The C - O bond distances are nearly identical in catecholate complexes, e.g. 1.372 and 1.378 Å in [Cr(tren)(3,6 - DTBCat)](ClO 4 ). 55 However, C - O bond dista nces cannot be a valid indication for the oxidation state in the chromium complexes reported here, since their differences are not negligible (Table 3. 3 and 3. 4 ) except for Complex 8 . Even though the C - O bond lengths are not identical, they are all much lo nger than the reported C - O bond length in chromium - semiquinoidal complexes. 19 Tetraoxoanthracene ligand was incorporated in our systems to greatly increase the spin delocalization and steel electron density away from the oxygens coordinating to the chromiu m 105 centers. The structure in this system is more planar compared with other Cr analogues. Although Complex 10 contains a horizontally extended conjugated ligand, it does not make a huge impact on its Cr - N and Cr - O bond distances and the coordination environ ment around its Cr centers. The C - C bond lengths within the rings show slightly large r discrepancies, but it does not have the alternating long and short bond character. Two C - C bonds are significantly shorter, 1.356 and 1.365 Å, compared with the rest of the bond s with an average of 1. 429 Å. These C - C bond distances are consistent with the reported anthracene bond lengths with an average value of 1.395 Å. 5 9 Kalescky et al. report ed that the middle ring contain ed the shortest C - C distance of 1.246 Å, 6 0 whic h indicates the middle ring of anthracene exhibit double or even triple bond character with more electron localized in the center . However, the C - C bond distance in the middle ring of Complex 10 presents an opposite phenomenon, because it contains the longest bond length of 1.450 Å. As suggested in the computational results, spin density localizes more on the chelating oxygens, and this is likely to cause spin move away from the middle ring . The difference of C - O bonds is statistically negligible, 1.355 and 1.357 Å. It is still unknown what is the directly cause of these kinds of discrepancy in bond lengths observed for Complex 10 . It will be highly desirable to structurally compare [Cr 2 (tren) 2 (L cat,cat )] 2+ and [Cr 2 (tren) 2 (L sq,cat )] 3+ so that more evide nce of how the oxidation state impact the various bond distance can be discussed. Unfortunately, the recrystallization of x - ray quality crystal for [Cr 2 (tren) 2 (L sq,cat )] 3+ has thus far unsuccessful. Future students who follow this project can attempt to gr ow them to extend the discussion. The phenylanilate bridging ligands are incorporate to change the directionality of the spin delocalization vertically and examine the steric effect on electron delocalization . 61 , 62 The dihedral angles between two rings ha ve found to provide information of the relative oxidation 106 state, and reduced ligand generally prefer a more planar geometry. 44 One important information is the inter - ring torsion between the anilate ring and the phenyl ring . The inter - ring torsional angle s , , in Complex 6 in Complex 7 These dihedral angles are all twisted, and do not exhibit coplanar geometry as predicted in other findings in our group . Given the fact that they we re confined in solid lattice, these torsional angles may be affected by the coordination and packing environment around. 3. 5 Magnetic Susceptibility Measurement s 3.5.1 Previous Studies on Similar Systems: Experimental and Theoretical Examination of Cr ( III) Phenanthrenesemiquinone Previous work done by Dr. Fehir in our group of substituted Cr(III) phenanthrenesemiquinone provide some insight about the magnetic behavior of Cr(III) semiquinone, and these systems were studied experimentally and computatio nally. 63 Broken symmetry formalism was perfomed to calculate J on substituted [Cr(tren)(PSQ)] 2+ systems. This calculation formalism is not conducted in this project, so the underlying principle will not be discussed here. It shows that EWG increase J by in creasing the spin localization on the interacting oxygens, whereas EDG decrease J by increasing the spin delocalization. 63 It suggests that the unpaired spin in EDG sitting in an orbital has a closer energy level with the spins in Cr(III), so - HOMO - - LUMO gap is smaller to allow mixing between two orbitals to induce spin delicalization. 63 Inversely, the orbital of the unpaired electron in EWG is lower in energy than the one in Cr(III) to cause a larger - HOMO - - LUMO gap and prevent orbital mixing. 63 The m agnetic susceptibility data collected on [Cr(tren)(PSQ)](BPh 4 ) and [Cr(tren)(3,6 - NO 2 - PSQ )](BF 4 ) 2 show temperature independence and indicate a very strong exchange coupling interaction between Cr(III) and PSQ - radical, 63 107 which agree with both the computational results and literature finding of Cr(III) semiquinoidal compounds. 8,18,19 Variable - temperature magnetic susceptibility measurement is generally used to experimentally determine the strength of coupling between paramagnetic spin centers, in wh ich the magnetization of a sample is evaluated as a function of temperature (usually ranging from 2 - 350K) reflecting the Boltzmann distribution ( Eq. 3. 3 ). At low temperature, more spins locate at the lower energy level (N + ), and energy embodied as temperat ure will be applied to populate spins into the higher energy level (N - ). ( 3. 3 ) 3.5. 2 Magnetic Susceptibility Measurement and Extrapolation of J - coupling on [Cr 2 (tren) 2 (L cat,cat )] 2+ Variable - temperature magnetic susceptibility data were collected for [Cr 2 (tren) 2 (L cat,cat )](BPh 4 ) 2 in solid state in a temperature range of 2 350 K at applied field of 0.50 T, 1.00 T, and 2.50 T. The results at all three field were the same within error. The magnetic data collected were plotted as effective magnetic moment, µ eff , versus temperature, T, and paramagnetic susceptibility, para , versus T. Sample m agnetic moment, m exp , is corrected with the magnetic moment of the sample holder, m bag (Eq. 3. 4 ). The experimental magnetic susceptibility, exp , is then calculated following Eq. 3. 5 , where M is molar mass in g/mol, m is the mass of the sample in g, and H is the applied field in Gauss. para is obtained 45 for diamagnetic correction in the sample ( Eq. 3. 6 ) . Effective magnetic moment, µ eff , is calculated for data analysis (Eq. 3. 7 ) , where k , (3. 4 ) 108 (3. 5 ) (3. 6 ) (3. 7 ) N A B is Bohr Magneton , and (3.8) Figure 3. 8 . Plots of the effective magnetic moment versus temperature for Complex 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 and 10 acquired in solid states. For [Cr 2 (tren) 2 (L cat,cat )] 2+ , the presence of the two paramagnetic Cr (III) ( S =3/2) centers gives rise to superexchange interaction since they are bridged by a diamagnetic catecholate ligand. The obtained experimental values of µ eff at room temperature are 5.3 3 µ B for Complex 1 , 5. 68 µ B for Complex 2 , 5.40 µ B for Complex 3 , 5.51 µ B for Complex 4 , 5.49 µ B for Complex 5 , 5.5 7 µ B for Complex 6 , 5.5 6 µ B for Complex 7 , 5.5 7 µ B for Complex 8 , 5. 51 µ B for Complex 9 , 5. 54 µ B for Complex 10 . Except Complex 2 , all the other experimental µ eff values are close to the 109 spin - only value of 5.48 µ B for two Cr (III) ions (Eq. 3. 8 ). T he magnetic moment drops below 100 K until µ eff =1.8 µ B at 2 K indicating S T =0. A general spin la dd er is generated for [Cr 2 (tren) 2 (L cat,cat )] 2+ based on the HDVV Hamiltonian (Fig. 3. 9 ), and the experimental results are consistent with our predicted magnetic properties. Figure 3. 9 . Spin latters of [Cr 2 (tren) 2 (L cat,cat ) 2+ due to the Heisenberg Hamiltonian. The outliner among this series shown in Fig. 3. 8 is Complex 2 with F as the substituent on the anilate bridging ligand , and it shows an elevation of magnetic moment. F has a large gyromagnetic ratio, and it generally shows a higher magnetic moment. This agrees with our experimental result of Complex 2 showing a slightly higher of µ eff . The temperatures were fitted with MagFit 46 by using a form of van Vleck equation 64 shown in Eq. 3. 7 , where N A k , g is the Landé g factor of an electron, (3. 9 ) µ B is Bohr Magneton, T is the temperature, S is the total spin quantum number of given spin state s, and E(S) (Eq. 3. 9 ) is the eigenvalue from the Heisenberg exchange Hamiltonian (Eq. 3. 10 ). (3 . 10 ) 110 65 to find the eigenvalues of a spin Hamiltonian, the total spin operator is defined as , where , , i.e. = 0, 1, 2, 3. When this is substituted into Eq. 3 . 10 , the expression in Eq. 3 . 11 is obtained. From that expression, the eigenvalues for the system can be calculated ( Eq. 3 . 1 2 ). ( 3 . 11 ) E (S T ) = - J [S T (S T +1) S 1 (S 1 +1) S 2 (S 2 +1)] ( 3 . 1 2 ) The experimental data of para was compared with data calculated from the fit in Eq. 3. 7 and J can be determined by the least - squares fitting. The J and g - factor values are variables allowed to vary (see Appendix for input file detail) . g - factor obtained from the fit should be equal or close to 2.0 , since Cr(III) is a metal ion with minimum spin - orbit coupling. The temperature independent paramagnetism ( TIP ) is fixed at 400 x 10 - 6 cm 3 mol - 1 analogous to Cr (II) dimers 66 and Cr III (H 2 O) 6 (NO 3 ) 3 ·3H 2 O. 67 The plot of the fit for Complex 1 is shown in Fig. 3. 10 (see Appendix for the fit plots of other complexes). The fit to the experimental data gave J shown in Table 3.5 . The M ag F it program utilizes the HDVV Hamiltonian formalism as in Eq. 3. 11 . for the data analysis, where the energy difference between the first and second spin states is 2 J , the second and third spin states is 4 J , and third and fourth spin states is 6 J ( Eq . 3. 12 ) . 111 Figure 3. 10 . The effective magnetic moment of Complex 1 ( blue square ), and the solid line represents a fit to the data using parameters described in the text. The variable - temperature magnetic susceptibility data were collected at 2 350 K, and the thermal energy applied during the experiment is large enough to overcome the energy barrier (>> kT) to populate the spin fully to its S T = 3 spin state, and even to their uncoupled situation to indicate a very weak antiferromagnetic interaction between two Cr(III) centers. J coupling constants (Table 3. 5 ) are very small , and the extrapolation of J constants with the HDVV Hamiltonian by MagFit 46 may not be accurate when the strength of the spin exchange interaction is close to the first - order Zeeman splitting. First - order Zeeman effect is a magnetic field induced phenomenon, and it gives rise to the splitting of energy levels as the electron spins can only be orient ed parallel or antiparallel in the presence of static magnetic field. 63 The magnitude of the Zeeman splitting (Eq. 3. 13 ) is small with respect to the coulomb energy even in the presence of very strong magnetic field. (3.1 3 ) 112 where is the magnetic quantum number, is the electron spin quantum number, B is an external applied magnetic field, a B When J is small and relatively close to the energy of the Zeeman splitting, the HDVV Hamiltonian is not able to distinguish if the splitting is soley caused by the spin exchange interaction or a mixing of the spin exchange and the Zeeman splitting. In this case, a full matrix diagnolization will be the analytical method for the fitting and extrapolation of small J values. Unfortunately, we do not have an access of a software/program equipped with the full matrix diagnolization at the moment. Therefore, the results shown in Table 3.5 are not able to conclude if the substituents have any effect on the strength of the spin exchange interaction . Table 3.5 . Magnetic Properties and J - Couping Constants of [Cr 2 (tren) 2 (L cat,cat )](BPh 4 ) 2 . Complex J - Coupling (cm - 1 ) 1 - 1.3 2 - 1.1 3 - 1.4 4 - 1.3 5 - 1.3 6 - 1. 6 7 - 1.0 8 - 0.6 9 - 0.6 10 - 0.5 If we treat these results as reference to provide some information about the substituent effect regardless the accuracy of the data, these values are considered the same within analytical error. Complex 8 , 9 and 10 with naphthalene and anthracene briding l igands exhibit a slight deviation compared with the other systems. 2,3,6,7 - tetraoxonaphthalene and 2,3,6,7 - tetraoxoanthracene are introduced as bridging ligands to weaken the strength of spin exchange due to the extended aromatic conjugation along 113 the orb ital x - - symmetry mobilizes electrons and strengthens the spin delocalization horizontally within the systems. Both Complex 8 - 10 show sight decrease of J among all Cr(III) catecholate analogues (Table 3.5) . Overall, the magnetic results collected and analyzed on Complex 1 - 10 are inconclusive, and the magnetic data of [Cr 2 (tren) 2 (L sq,cat )] 3+ are more detrimental for the analysis in this project. 3. 5. 3 Magnetic Susceptibility Measurement and Extrapolation of J - coupling on [Cr 2 (tren) 2 (L sq ,cat )] 3 + As discussed in Chapter 1 , [Cr 2 (tren) 2 (L sq,cat )] 3+ contains three paramagnetic centers, so there is a direct exchange interaction between the Cr(III) ion and the semiquinone ligand, and a superexchange interaction between the two Cr(III) centers (Fig. 3.11). The magnetic data collected previously on Complex 13 8 show a very strong direct exchange interaction within the system, and the magnetic susceptibility measured at 2 350 K exhibits no significant temperature d ependence. Several research papers show that the direct exchange interaction between Cr(III) and semiquinone is very strong with J over 400 cm - 1 . 8,18,19,63 Figure 3.1 1 . Indication of spin exchange coupling interactions for [Cr 2 (tren) 2 (L sq,cat )] 3+ , see te xt for details on notation. In order to fit data with HDVV Hamiltonian (Eq. 3.7) to extrapolate two variables, J and J* , thermal population of more spin states are required. The lack of temperature dependence 114 prevents the accurate determination of J * . In the case of [Cr 2 (tren) 2 (L sq,cat )] 3+ measurement, temperature yielding higher thermal energy is required to overcome the energy difference between spin states , but the temperature cannot be too high to decompose the samples. Differential scanning calorimetr y (DSC) analysis were performed to test the thermal stability of the molecules. DSC is a thermoanalytical technique measure the heat flow of a sample at constant temperature, and this sample may undergo one or more phase change during the measurement. In a DSC experiment, the heat flow measured for a sample is relative to the heat flow to a reference material. The DSC plots for Complex 13 , 14 and 1 6 are presented in Fig. 3.1 2 . The negative heat flow indicates an endothermic consequence and implies a melting of a sample. The sharp negative peak of Complex 13 represent a melting point of 290 (563 K) , and the little shoulder next to the sharp peak is possibly indicative of amorphous sample. According to the DSC, the melting point of Complex 14 is around 300 (573 K) . The data trace of Complex 16 is more complicated without an obvious indication of melting. A second run of this sample should be performed after slow cool. However, the information provided by DSC measurement is inconclusive about thermal degradation of samples. It will be more ideal if we can have access to thermalgravimetric analysis (TGA), because it is a simpler thermoanalytical technique, which measure sample weight loss as a function of temperature in a defined atmosphere. Thi s is a more intuitive analysis for thermal stability. 115 Figure 3.1 2 . The DSC plots of Complex 13 , 14 and 16 . Since the temperature range of MPMS ® 3 SQUID magnetometer is 1.8 400 K without an external oven heater stick, the data were collected in solid state from 2 to 400 K at applied field of 1.00 T. The use of an external oven requires a new design of sample holder, so higher temperature measurement was not performed here . [Cr 2 (tren) 2 (L sq,cat )] 3+ is a more complicated mag netic system , with three paramagnetic centers (both Cr (III) ions and the bridge). In order to better explain the magnetic data, the Heisenberg model is employed again. With three paramagnetic centers, the total spin operator of the system is defined as (where ) here, S 1 = S 3 = 3/2 correspond the two Cr (III) ions and S 2 = ½ corresponds to the L sq,cat bridge. In this way, the Hamiltonian operator can be derived from Eq. 3.1 4 using two coupling constants, where J quantifies the Cr III - L sq,cat direct exchange, and J* is the superexchange coupling for Cr III - Cr III . Eq.3.1 5 is the eigenvalue equation for this system. 116 (3.1 4 ) E= - J [S T (S T +1) S A (S A +1) S 2 (S 2 +1)] J* [S A (S A +1) S 1 (S 1 +1) S 3 (S 3 +1)] (3.1 5 ) The effective magnetic moment data (Fig. 3.1 3 ) of [Cr 2 (tren) 2 ( L sq ,cat )] (BPh 4 ) 2 (BF 4 ) collected experimentally show temperature dependence above 100 K . Th e highest µ eff observed from the sets of data is c.a. 5.6 4 µ B for Complex 11 , 5.52 µ B for Complex 12 , 5.5 3 µ B for Complex 13 , 5.5 0 µ B for Complex 14 , 5.5 5 µ B Complex 15 , 5. 62 µ B for Complex 16 , 6.02 µ B for Complex 17 , 5. 67 µ B for Complex 18 , and 5.5 4 µ B for Complex 19 . T he µ S.O. value for a S =5/2 ground state is 5.916 µ B (Eq. 3.6) , so | S T = 5/2, S A =3> is predicted to be the ground spin state according to the HDVV Hamiltonian (Eq. 3.1 1 ) . Figure 3.1 3 . Plots of the effective magnetic moment versus temperatu re for all samples in solid states, Complex 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 and 19 . Based on the information obtained for ground states on [Cr 2 (tren) 2 (CA cat,cat )](BPh 4 ) 2 and [CrGa(tren) 2 (CA sq,cat )](BPh 4 ) 2 (BF 4 ), 8 the coupling interaction for both Cr III - L sq ,cat and Cr III - Cr III is expected to both be antiferromagnetic. This indicates that both J and J* are negative. A plot of 117 eigenvalues can be generated (Fig. 3.1 4 ) to show the correlation between J and J* . From this plot, the energy splitting of each spin state is governed by J, the direct exchange coupling. The energy levels of |5/2, 3> and |3/2, 2> (the second spin state predicted by the Hamiltonian) intersect at J/J* =6 (Fig. 3.15), and |5/2, 3> will be raised as the second spin state if J/J* >6. Thus, the magnitude of J should be more than 6 times larger than J* for the predicted ground state, |5/2, 3>, in accordance to the Heisenberg exchange Hamiltonian (Eq. 3.1 2 ). If both direct exchange and superexc hange interactions in this system are antiferromagnetic, these magnetic interactions are frustrated, because it is impossible to orient the configuration of the third set of spin to be both antiferromagnetic to the first two sets of spin. Figure 3.1 4 . P lot of the eigenvalues of various spin states for [Cr 2 (tren) 2 ( L sq,cat )] 2+ . J <0 and J* <0 with both superexchange and direct exchange interactions considered as antiferromagnetic were used to generate this plot. Each state is labeled as |S T , S A >. 71 118 Figur e 3.1 5 . Plot of the eigenvalues of various spin states for [Cr 2 (tren) 2 ( L sq,cat )] 2+ . J <0 and J* > 0 with direct exchange and superexchange interaction s considered as antiferromagnetic and ferromagnetic respectively were used to generate this plot. Each state is labeled as |S T , S A >. Since the direct exchange interaction is the dominant effect within the system, and it was experimentally proved to be antiferromagnetic on [CrGa(tren) 2 (CA sq,cat )](BPh 4 ) 2 (BF 4 ). 8 The superexchange interaction between two Cr(III) ions is ferromagnetic, i.e. J* > 0, to prevent spin frustration. Another plot of eigenvalues is generated (Fig. 3.1 5 ). With |5/2, 3> as the first spin state, |3/2, 2> is predicted as the second spin state a gain. Unlike in Fig. 3.13, this plot does not provide information about the relative magnitude s of J * and J. A generic spin ladder (Fig. 3.1 6 ) of [Cr 2 (tren) 2 ( L sq ,cat )] (BPh 4 ) 2 (BF 4 ) with |5/2, 3> as the ground state is generated based on the models (Fig. 3.1 4 and 3.1 5 ) and the Heisenberg exchange Hamiltonian (Eq. 3. 11 ). The energy difference between the first and second spin states is ( *) with this Hamiltonian (Eq. 3.1 2 ), and this could be the reason why temperature dependence is shown in the magnet ic data 119 for Cr(III) semiquinone dimers compared with Cr(III) semiquinone monomers reported in literature. 8,18,19 Figure 3.1 6 . A spin ladder diagram for of [Cr 2 (tren) 2 ( L sq ,cat )] (BPh 4 ) 2 (BF 4 ) . The variable - temperature magnetic susceptibility measurement reflects the Boltzmann distribution across the spin ladder and provides information on the energy separation between spin - coupled states. In order to extrapolate two coupling constants accurately with the HDVV Hamiltonian, thermal population of three or more spin state is required. Therefore, thermal population to the third spin state, |1/2, 1> (S = ½, µ s.o. = 1.87 µ B ), need to be observed experimentally. T he temperature dependence of the data (Fi g. 3.1 3 ) shows thermal population beyond the first spin state, |5/2, 3>, but t he thermal energy applied up to 400K is still not high enough to overcome energy gap and thermally populate up to the spin state of |1/2, 1> for accurate determination of J * . Bas ed on the magnetic data collected, J is believed to be very large in magnitude. The magnetic data collected on [Cr 2 (tren) 2 (L cat,cat )](BPh 4 ) 2 indicate very weak superexchange interactions with small J*. Therefore, the superexchange interaction is considered too small to perturb the overall spin exchange interaction, and the determination of J* may not be as meaningful. 120 The existence of superexchange along with strong direct exchange interaction is quest ionable. If superexchange interaction actually exists in these complicated exchange coupling systems, temperature dependence of the data has to be obtained and fitted in order to extrapolate two variables, both J and J*. If not, a higher temperature range for magnetic susceptibility measurement is not necessary. In order to explore the existence of this interaction, a better understanding of superexchange interaction and its coupling pathway is required. Figure 3.1 7 . Molecular orbital diagram with d - p o rbital mixing of superexchange interaction between two metals and one intervening O 2 - via - bonding. Superexchange coupling describes the exchange coupling interaction between two paramagnetic centers through intermediate a diamagnetic ionic ligand with d - p orbital mixing, which results in two orbitals: one bonding orbital and one antibonding orbital. 72 The superexchange pathway requires the antibonding orbital to be energetically accessible. However, the strong direct exchange in [Cr 2 (tren) 2 ( L sq ,cat )] (BP h 4 ) 2 (BF 4 ) stabilizes the bonding orbital between the paramagnetic centers; meanwhile, it destabilizes the antibonding orbital and cause it to be much higher in energy (Fig. 3.1 7 ) . This either prevents or greatly weakens the d - p orbital mixing for superexch ange from happening. In this case , J* is considered to be either zero or negligibly small. Based on both hypothes e s described above , the determination of J* does not 121 seem to be detrimental for our understanding and analysis of the magnetic properties of [Cr 2 (tren) 2 ( L sq ,cat )] (BPh 4 ) 2 (BF 4 ) . The experimental data of para was compared with data calculated from the fit in Eq. 3. 9 , and J and J* constants were determined by the least - squares fitting. The J and J* were allowed to vary. The g - f actor was fixed at 2.0 , and TIP was fixed at 400 x 10 - 6 cm 3 mol - 1 analogous to Cr(II I ) dimers 66 and Cr III (H 2 O) 6 (NO 3 ) 3 ·3H 2 O. 67 The plot of the fit for Complex 12 is shown in Fig. 3.1 8 . Only the J constants extrapolated by MagFit 46 is reported in Table 3.6 , and the J* constants were not reported here because of the inaccurate determination described above. Figure 3.1 8 . The effective magnetic moment of Complex 12 ( blue square ), and the solid line represents a fit to the data using parameters described in the text. 122 Table 3.6. Magnetic Properties and J - Couping Constants of [Cr 2 (tren) 2 (L sq,cat )](BPh 4 ) 2 (BF 4 ). Complex J - Coupling (cm - 1 ) 11 - 380 12 - 380 13 - 390 14 - 380 15 - 380 16 - 380 17 - 3 5 0 18 - 3 4 0 19 - 3 4 0 - donor and - acceptor due to their relatively high electronegativity. Since halogen is binding to the tetraoxolene ligand via a sigma bond, they are considered more - electron withdrawing. The spin polarization effect should be different among the halogen series due t o their various electronegativity and the size of the electron cloud. However, the J values of Complex 12 , 14 and 15 are the same with Complex 1 1 , while Complex 13 shows a slightly larger J (Table 3.6). In general, electron withdrawing groups ( EWG ) increase the double bond character in an aromatic ring by rearranging electrons in the p orbitals . F is the most electronegative element in the periodic table with strong coulombic attraction due to the distance factor, and it has very strong electronegat ivity dipole. In addition, F possesses strong resonance effect because of its sufficient 2 p - 2 p overlap with the aromatic carbon because of their same relative sizes, and it is more donating than other halides. The electronegativity dipole and the resonance dipole cancel out each other resulting in a zero - net dipole in F so that F presents no inductive effect when substituting aromatic rings. 68 The Hammett parameter for fluorine in para position is +0.15, which also prove that F is only very weakly electron withdrawing. 69 Unlike F, chlorine has insufficient 3 p - 2 p overlap with the aromatic C, its resonance dipole is much weak er that the electronegativity dipole dominates, which makes it more electron 123 withdrawing. The empty * orbital of Cl is high in energy t o prevent spin delocalization, so Complex 1 3 presents a higher J value compared with Complex 1 1 . Similar with Cl, electron withdrawing properties should dominate in Br and I. However, their huge electron clouds shield their nuclei to weaken the withdrawin g effects. The long C - Br and C - I bond distances agree with this hypothesis. The spin density plots of (BA sq,cat ) 3 - and (IA sq,cat ) 3 - generated from DFT calculations show sparse spin density on the oxygen atoms (Fig. 3.1 9 ), and this also support our hypot hesis about the experimental trend (see detail explanation of the computational results on spin polarization in Chapter 2). Figure 3.1 9 . E xcess spin density associated with the highest energy, singly - occupied molecular orbital of (BA sq,cat ) 3 - ( a ) and (IA sq,cat ) 3 - ( b ). The six sp 2 hybridized carbons in phenyl group show the conjugation of the C - C bonds within the ring, and the patial - double bond characters are equally distributed. Phenyl is considered both an inductively withdrawing group ( - I ) and a resonance donating group ( +M ) because of its higher electronegative sp 2 carbons and electron - system, respectiv ely. 78 79 on Cu - bipyridine (bpy) systems shows that the phenyl group is very weakly withdrawing when substituting on a bpy ligand. Therefore, the substituent effect of phenyl is possibly similar to F with - I and + M cancelling out each other, which presents no intraligand delicalization. The J constant extrapolated by experimental data agrees with this theory. Computational and photophysical experimental results previously conducted on Ru (II) - bpy complexes in our gr oup 61,80 show that both steric effect and the inter - (a) ( b ) 124 ring torsional angle are detrimental for intraligand delocalization. Coplanar orientation between the aromatic ring substituent and the ligand in a system facilitates spin delocalization, while orthogonal configuration will prevent delocalization by reducing both steric hindrance and electron - electron repulsion. 61,80 Orthogonal twist angle between two rings therefore is indicative of thermodynamic stabilization. The inter - ring torsion can be used to evalua te the spin polarization in the system (Fig. 3. 20 ). Unfortunately, the growth of [Cr 2 (tren) 2 (L sq,cat )](BPh 4 ) 2 (BF 4 ) crystals was unsuccessful to provide structural information. Figure 3. 20 . The inter - ring torsion angle ( ) of phenyl - substituted complexes. NMe 2 - Ph is chosen to change the directionality, i.e. vertical extension, of spin - donor, NMe 2 will delocalize spins by introducing more orbital mixing and decrease HOMO - LUMO gap; thus, J determined from the fit of Complex 1 7 should be smaller compared with Complex 1 6 . However, the difference in J coupling constants between the two complexes are in significant. Computational studies of substituent effects on Fe(II) chromophore reported by J akubikova and coworkers 70 suggest that an aromatic linker group between the ligand and EDG or EWG will attenuate the substituent effect of spin delocalization. Since the magnitude of J is small, and it will be hard to gauge the significance of the effect. Both anthracene and naphthalene were introduced to delocalize spin from the interacting oxygens because of their extended conjugated system. The J values of both Complex 18 and 19 125 are greatly reduced (Table 3.6) to prove that polyaromatic hydrocarbon liga nds are the most sufficient to decrease the strength of the spin exchange interaction . No magnetic data was collected for [Cr 2 (tren) 2 (AnT sq,cat )](BPh 4 ) 2 (BF 4 ) since the synthesis of this complex is unsuccessful. Upon oxidation of [Cr 2 (tren) 2 (AnT cat,cat )](BPh 4 ) 2 , ESI - MS spectrum shows no detection of [Cr 2 (tren) 2 (AnT sq,cat )] 3+ species. The electrochemical data of [Cr 2 (tren) 2 (AnT cat,cat )](BPh 4 ) 2 exhibits an irreversible redox wave beyond one - electron oxidation, and the electrochemical properties will be fu rther discussed in Chapter 5. These experimental evidences suggest that [Cr 2 (tren) 2 (AnT sq,cat )] 3+ is unstable , and the chelating mode of (Me - AnT sq,cat ) 3 - with Cr (III) ions is likely to be form (3) (Fig. 3. 2 1 ) , where the spin is more delocalized within the inner aromatic ring. This causes the decomposition of the dimer. 126 Figure 3. 2 1 . Multiple possible chelating forms of deprotonated 2,3,6,7 - tetraoxo anthracene undergoing one - electron redox reactions. 127 Electrons are highly delocalized within the anthracene rings, and the resonance effect (Fig. 3.17) reduces the basicity of (AnT sq,cat ) 3 - and makes it very weakly chelating to one Cr(III) ion. It may be surprising that [Cr 2 (tren) 2 (AnT sq,cat )] 3+ is highly unstable, and [Cr 2 (tren ) 2 (Me - AnT sq,cat )](BPh 4 ) 2 (BF 4 ) ( 19 ) is stable. The stability of complex 19 may be a cause of substituent effect. The inductive effect of - donor methyl group on Me - AnT stabilizes the ring and attenuates spin delocalization to increase the stability of [Cr 2 (tren) 2 (AnT sq,cat )](BPh 4 ) 2 (BF 4 ). 3. 6 Concluding Comments Our goal in this chapter was to establish the relationship of how substituent affects spin delocalization/polarization, and how it manifests on magnetic properties. The variable - temperature magnetic data collected for the Cr(III) dimeric series provide some experimental evidence to support the correlation , because the strength of the spin exchange interaction decreases when Cr(III) ions are coordinated to naphthalene and anthracene bridging ligands (Complex 18 and 19 ) . However, there is no trend can be established among the halogenated Cr(III) dimers. No significant substituent effect is observed with a phenyl linker. The result obtained from the vertical spin polariz ation is preliminary, and more substituents, CN - phenyl and CF 3 - phenyl, should be developed for magnetic studies in order to further rationalize our hypothesis. To modulate the J value, the proper substituents need to be chosen, and our series developed is - - acceptor to show all possible variations. The syntheses of these substituents are still under development, and some of them will be discussed in Chapter 6 . The syntheses of all substituted ligands are quite challenging becau se they do not follow similar synthetic schemes. It will be problematic to randomly choose a few substituents and start 128 the syntheses. Computational calculations prove to be a useful tool to provide insight about the synthetic viability. DFT calculations c ollected on the free ligands (Chapter 2) are informative , which should be u sed continuously in the future. MagFit 46 employs the HDVV Hamiltonian to extrapolate J by comparing the experimental data and then fitted them with the least - square fit. When the m agnitude of J is very small and relatively close to the Zeeman splitting, the HDVV Hamiltonian fails. In this case, a suitable software with full matrix diagonalization will need to be used for accurate determination of the superexchange coupling constants among the [Cr 2 (tren) 2 (L cat,cat )](BPh 4 ) 2 complexes. However, the appropriate software with full matrix diagonalizations is not available during my graduate career. Unfortunately, the experimental data collected for this series fail to provide insightful information about the substituent effect without the proper software. One of the biggest obstacles is to accurately determine J* superexchange constants for the [Cr 2 (tren) 2 (L sq ,cat )](BPh 4 ) 2 (BF 4 ) series . The magnetic data collected up to 400 K do not show enough thermal population to higher spin - coupled state . We propose that the superexchange interaction is too weak to perturb the overall exchange interaction within t hese systems, so the determination of J* might not be detrimental for our analysis in this project. It is not impossible to collect magnetic data to accurately extrapolate J* by MagFit. 46 The magnetic data will need to be collected over higher range of tem perature, > 400 K, to thermally populate more spins into the third spin state. Therefore, a heat resistant sample holder with minimal magnetic background should be developed to be compatible with the MPMS ® 3 SQUID external oven. TGA analysis should be acqu ired before conducting high temperature magnetic susceptibility measurement for the thermal stability of samples. 129 APPENDIX 130 APPENDIX Figure 3 . 2 2 . 1 H NMR of 2,5 - d imethoxy - 1,4 - benzoquinone in CDCl 3 . Figure 3 . 2 3 . 13 C NMR of 2,5 - d imethoxy - 1,4 - benzoquinone in CDCl 3 . 131 Figure 3 . 2 4 . 1 H NMR of 2,5 - dibromo - 3,6 - dimethoxy - 1,4 - benzoquinone in CDCl 3 . Figure 3 . 2 5 . 13 C NMR of 2,5 - dibromo - 3,6 - dimethoxy - 1,4 - benzoquinone in CDCl 3 . 132 Figure 3 . 2 6 . ESI - MS of H 2 BA. Top: calculated isotope pattern for [M - H] - (C 6 H 1 O 4 Br 2 ). Bottom: experimental result. Figure 3 . 2 7 . ESI - MS of H 2 FA. Top: calculated isotope pattern for [M - H] - (C 6 H 1 O 4 F 2 ). Bottom: experimental result. 133 Figure 3 . 2 8 . 13 C NMR of bromanil (left) and iodanil (right) in benzene - d 6 . Figure 3 . 2 9 . ESI - MS of H 2 IA. Top: calculated isotope pattern for [M - H] - (C 6 H 1 O 4 I 2 ). Bottom: experimental result. 134 Figure 3 . 30 . 1 H NMR of 2,5 - dimethoxy - 3,6 - diphenyl - 1,4 - benzoquinone in CDCl 3 . Figure 3 . 3 1 . 13 C NMR of 2,5 - dimethoxy - 3,6 - diphenyl - 1,4 - benzoquinone in CDCl 3 . 135 Figure 3 . 3 2 . ESI - MS of 2,5 - dimethoxy - 3,6 - diphenyl - 1,4 - benzoquinone. Top: calculated isotope pattern for [M+H] + (C 10 H 15 O 4 ). Bottom: experimental result. Figure 3 . 3 3 . 1 H NMR of H 2 PhA in acetone - d 6 . 136 Figure 3 . 3 4 . 13 C NMR of H 2 PhA in acetone - d 6 . Figure 3 . 3 5 . ESI - MS of H 2 PhA . Top: calculated isotope pattern for [M - H] - (C 1 8 H 1 1 O 4 ). Bottom: experimental result. 137 Figure 3 . 3 6 . 1 H NMR of 2,3,6,7 - t etramethoxy - 9,10 - dimethylanthracene in CDCl 3 . Figure 3 . 3 7 . 13 C NMR of 2,3,6,7 - t etramethoxy - 9,10 - dimethylanthracene in CDCl 3 . 138 Figure 3 . 3 8 . ESI - MS of 2,3,6,7 - t etramethoxy - 9,10 - dimethylanthracene . Experimental result for [M+H] + (C 20 H 23 O 4 ). Figure 3 . 3 9 . 1 H NMR of H 4 (Me - AnT) in dmso - d 6 . 139 Figure 3 . 40 . ESI - MS of H 4 (Me - AnT). Experimental result for [M - H] - (C 12 H 15 O 4 ). Figure 3 . 4 1 . 1 H NMR of 4 - (N,N - Dimethylamino)phenylboronic acid in dmso - d 6 . 140 Figure 3 . 4 2 . 11 B NMR of 4 - (N,N - Dimethylamino)phenylboronic acid in dmso - d 6 . Figure 3 . 4 3 1 H NMR of 2,7 - dimethoxy - 3,6 - di(N,N - dimethylaminophenyl)benzoquinone in CDCl 3 . 141 Figure 3 . 4 4 . 13 C NMR of 2,7 - dimethoxy - 3,6 - di(N,N - dimethylaminophenyl)benzoquinone in CDCl 3 . Figure 3 . 4 5 . ESI - MS of 2,7 - dimethoxy - 3,6 - di(N,N - dimethylaminophenyl)benzoquinone. Top: calculated isotope pattern for [M+H] + (C 24 H 27 O 4 N 2 ). Bottom: experimental result. 142 Figure 3. 4 6 . ORTEP drawing of 2,7 - dimethoxy - 3 - bromo - 6 - (N,N - dimethylaminophenyl)benzoquinone from single - crystal x - ray structure determination. Atoms are represented as 50% thermal ellipsoids. Hydrogen atoms are omitted for clarity. Figure 3 . 4 7 . ORTEP drawing of 2,7 - dimethoxy - 3,6 - di(N,N - dimethylaminophenyl)benzoquinone from single - crystal x - ray structure determination. Atoms are represented as 50% thermal ellipsoids. Hydrogen atoms are omitted for clarity. 143 Table 3 . 7 . Crystal data and structural refinement for 2,7 - dimethoxy - 3,6 - di(N,N - dimethylaminophenyl)benzoquinone). Empirical formula C 12 H 14 NO 2 Formula weight (g/mol) 204.24 Temperature (K) 173(2) Crystal system Triclinic Space group P Cell dimension: a (Å) 8.1020(7) b (Å) 8.3200(7) c (Å) 8.7689(7) 98.2520 (10) 113.4700 (10) 101.4940 (10) Volume (Å 3 ) 514.73(7) Reflections measured 8864 unique reflections 2034 Z 2 µ(MoK ) (mm - 1 ) 0.090 D calc (g cm - 3 ) 1.318 R int 0.0272 R 1 (I>2 (I)) a 0.0547 wR 2 b 0.1712 a R 1 = b wR 2 =[ ] 1/2 , w=1/[ , where P=[ . Table 3 . 8 . Bond lengths for 2,7 - dimethoxy - 3,6 - di(N,N - dimethylaminophenyl)benzoquinone). Atoms Length/Å Atoms Length/Å Atoms Length/Å O1 - C1 1.223(2) C1 - C2 1.484(2) C4 - C9 1.394(3) O2 - C2 1.364(2) C1 - C3 1.490(2) C5 - C6 1.378(3) O2 - C12 1.417(3) C2 - C3 1.350(2) C6 - C7 1.409(3) N1 - C7 1.371(2) C3 - C1 1.490(2) C7 - C8 1.405(3) N1 - C10 1.447(2) C3 - C4 1.479(2) C8 - C9 1.382(2) N1 - C11 1.445(3) C4 - C5 1.391(3) Table 3 . 9 . Bond angles for 2,7 - dimethoxy - 3,6 - di(N,N - dimethylaminophenyl)benzoquinone). Atoms Atoms Atoms O 2 - O2 - C12 113.76(15) C4 - C3 - C1 118.79(15) O1 - C1 - C2 118.93(15) C7 - N1 - C10 119.84(16) C5 - C4 - C3 121.33(16) O1 - C1 - C3 121.79(16) C7 - N1 - C11 119.82(17) C5 - C4 - C9 117.01(16) C2 - C1 - C3 119.27(16) C11 - N1 - C10 117.97(16) C9 - C4 - C3 121.65(16) O2 - C2 - C1 114.29(15) C3 - C2 - O2 122.33(15) C2 - C3 - C1 117.32(16) C6 - C5 - C4 122.01(17) C3 - C2 - C1 123.38(15) C2 - C3 - C4 123.88(15) C5 - C6 - C7 121.09(17) N1 - C7 - C6 121.48(17) N1 - C7 - C8 121.56(17) C8 - C7 - C6 116.95(16) C9 - C8 - C7 120.97(17) C8 - C9 - C4 121.95(17) 144 Figure 3 . 4 8 . 1 H NMR of H 2 NMe 2 - PhA in dmso - d 6 . Figure 3 . 4 9 . ESI - MS of H 2 NMe 2 - PhA. Left: t op , calculated isotope pattern for [M - H] - (C 22 H 21 O 4 N 2 ) ; b ottom: experimental result. Right: top, calculated isotope pattern for [M+H] + (C 22 H 23 O 4 N 2 ); bottom: experimental result. 145 Figure 3 . 50 . 1 H NMR of 3,6 - dibromo - 2,7 - dihydroxynaphthalene in DMSO - d 6 . Figure 3 . 5 1 . 1 H NMR of 3,6 - dibromo - 2,7 - dimethoxynaphthalene in CDCl 3 . 146 Figure 3 . 5 2 . 13 C NMR of 3,6 - dibromo - 2,7 - dimethoxynaphthalene in CDCl 3 . Figure 3 . 5 3 . 1 H NMR of 2,3,6,7 - tetramethoxynaphthalene in CDCl 3 . 147 Figure 3 . 5 4 . 13 C NMR of 2,3,6,7 - tetramethoxynaphthalene in CDCl 3 . Figure 3 . 5 5 . 1 H NMR of H 4 NAT in dmso - d 6 . 148 Figure 3 . 5 6 . 13 C NMR of H 4 NAT in dmso - d 6 . Figure 3 . 5 7 . 1 H NMR of 2,3,6,7 - Tetramethoxyanthraquinone in CDCl 3 . 149 Figure 3 . 5 8 . 13 C NMR of 2,3,6,7 - Tetramethoxyanthraquinone in CDCl 3 . Figure 3 . 5 9 . 1 H NMR of 2,3,6,7 - t etra methoxy anthra cene in CDCl 3 . 150 Figure 3 . 60 . 13 C NMR of 2,3,6,7 - t etra methoxy anthra cene in CDCl 3 . Figure 3 . 6 1 . 1 H NMR of H 4 AnT in acetone - d 6 . 151 Figure 3 . 6 2 . 13 C NMR of H 4 AnT in acetone - d 6 . Figure 3 . 6 3 . ESI - MS of H 4 AnT. Top: calculated isotope pattern for [M - H] - (C 14 H 9 O 4 ). Bottom: experimental result. 152 Figure 3 . 6 4 . ESI - MS of [FeCp* 2 ](BF 4 ). Top: calculated isotope pattern for [M] + (C 20 H 30 Fe 2 ). Bottom: experimental result. Figure 3 . 6 5 . ESI - MS of Complex 11 . Top: calculated isotope pattern for [M] 3+ ( Cr 2 C 18 H 38 O 4 N 8 ). Bottom: experimental result . 153 Figure 3 . 6 6 . ESI - MS of Complex 13 . Left: top, calculated isotope pattern for [M] 3+ ( Cr 2 C 18 Cl 2 H 36 O 4 N 8 ); bottom, experimental result. Right: top, calculated isotope pattern for [Cr(tren)(C 6 Cl 2 O 4 )] + (Cr C 12 H 1 8 O 4 N 4 Cl 2 ); bottom, experimental result. 154 Figure 3 . 6 7 . ESI - MS of Complex 4 . Upper left: t op , calculated isotope pattern for [M] 2+ (Cr 2 C 18 O 4 Br 2 H 3 5 N 8 ) ; b ottom: experimental result. Upper right: t op , calculated isotope pattern for [M] 3 + (Cr 2 C 18 O 4 Br 2 H 3 6 N 8 ) ; b ottom: experimental result. Lower: top, calculated isotope pattern for [Cr(tren)(C 6 O 4 Br 2 )] + ( CrC 12 H 18 O 4 N 4 Br 2 ); bottom, experimental result. 155 Figure 3 . 6 8 . ESI - MS of Complex 14 . Left: t op , calculated isotope pattern for [M] 3+ ( Cr 2 C 18 H 36 O 4 N 8 Br 2 ) ; b ottom , experimental result. Right: top, calculated isotope pattern for [Cr(tren)(C 6 O 4 Br 2 )] + ( CrC 12 H 18 O 4 N 4 Br 2 ) ; bottom, experimental result. 156 Figure 3 . 6 9 . ESI - MS of Complex 2 . Upper left: top, calculated isotope pattern for [M] 2+ (Cr 2 C 18 H 36 O 4 N 8 F 2 ); bottom, experimental result. Upper right: top, calculated isotope pattern for [M] 3+ (Cr 2 C 18 H 36 O 4 N 8 F 2 ); bottom, experimental result. Lower: top, calculated isotope pattern for [ Cr (tren)(C 6 F 2 O 4 )] + (Cr C 12 H 18 O 4 N 4 F 2 ); bottom, experimental result. 157 Figure 3 . 70 . ESI - MS of Complex 12 . Top: calculated isotope pattern for [M] 3+ ( Cr 2 C 18 H 36 O 4 N 8 F 2 ). Bottom: experimental result. [Cr(tren)(C 6 O 4 F 2 )] + ( CrC 12 H 18 O 4 N 4 F 2 ) . 158 Figure 3 . 7 1 . ESI - MS of Complex 5 . Upper left: t op , calculated isotope pattern for [M] 2+ (Cr 2 C 18 H 36 O 4 N 8 I 2 ) ; b ottom , experimental result. Upper right: top, calculated isotope pattern for [M] 3+ (Cr 2 C 18 H 36 O 4 N 8 I 2 ) ; bottom, experimental result. Lower: t op , calculated isotope pattern for [Cr(tren)(C 6 O 4 I 2 )] + (CrC 12 H 18 O 4 N 4 I 2 ) ; bottom, experimental result. 159 Figure 3 . 7 2 . ESI - MS of Complex 15 . Left: t op , calculated isotope pattern for [M] 3+ ( Cr 2 C 18 H 36 O 4 N 8 I 2 ) ; b ottom , experimental result. Right: top, calculated isotope pattern for [Cr(tren)(C 6 O 4 I 2 )] + ( CrC 12 H 18 O 4 N 4 I 2 ) ; bottom, experimental result. 160 Figure 3 . 7 3 . ESI - MS of Complex 6 . Top: calculated isotope pattern for [M] 2+ (Cr 2 C 30 H 46 O 4 N 8 ). Bottom: experimental result. Figure 3 . 7 4 . ESI - MS of Complex 16 . Left: top, calculated isotope pattern for [M] 3+ (Cr 2 C 30 H 46 O 4 N 8 ) ; b ottom , experimental result. Right: top, calculated isotope pattern for [Cr(tren)(C 18 O 4 H 10 )] + ( CrC 24 H 28 O 4 N 4 ) ; bottom, experimental result. 161 Figure 3 . 7 5 . ESI - MS of Complex 7 . Left: top, calculated isotope pattern for [M] 2+ (Cr 2 C 18 O 4 Br 2 H 36 N 8 ); bottom, experimental result. Right: top, calculated isotope pattern for [M] + (Cr 2 C 18 O 4 Br 2 H 36 N 8 ); bottom, experimental result. 162 Figure 3 . 7 6 . ESI - MS of Complex 17 . Left: top, calculated isotope pattern for [M] 3+ ( Cr 2 C 34 H 54 O 4 N 10 ) ; b ottom , experimental result. Right: top, calculated isotope pattern for [Cr(tren)(C 22 H 20 O 4 N 2 )] + (CrC 28 H 38 O 4 N 6 ) ; bottom, experimental result. 163 Figure 3 . 7 7 . ESI - MS of Complex 10 . Left: top, calculated isotope pattern for [M] 2+ ( Cr 2 C 18 H 14 O 4 N 8 ); bottom, experimental result. Right: top, calculated isotope pattern for [Cr(tren)(C 14 H 8 O 4 )] + ( CrC 22 H 30 O 4 N 4 ); bottom, experimental result. Figure 3 . 7 8. ESI - MS of Complex 19. Left: top, calculated isotope pattern for [M] 3+ ( Cr 2 C 18 H 14 O 4 N 8 ) ; b ottom , experimental result. Right: top, calculated isotope pattern for [Cr(tren)(C 14 H 8 O 4 )] + ( CrC 22 H 30 O 4 N 4 ) ; bottom, experimental result. 164 Figure 3 . 7 9 . ESI - MS of Complex 8 . Upper l eft: top, calculated isotope pattern for [M] 2+ ( Cr 2 C 22 H 40 O 4 N 8 ); bottom, experimental result. Upper right: top, calculated isotope pattern for [M] 3+ ( Cr 2 C 22 H 40 O 4 N 8 ); bottom, experimental result. Bottom : top, calculated isotope pattern for [Cr(tren)(C 10 H 6 O 4 )] + ( C rC 16 H 24 O 4 N 4 ); bottom, experimental result. 165 Figure 3 . 80 . ESI - MS of Complex 18 . Left: top, calculated isotope pattern for [M] 3+ ( Cr 2 C 22 H 40 O 4 N 8 ) ; b ottom: experimental result. Right: top, calculated isotope pattern for [Cr(tren)(C 10 H 6 O 4 )] + ( CrC 16 H 24 O 4 N 4 ) ; bottom: experimental result. 166 Figure 3.8 1 . ESI - MS of Complex 9 . Left: top, calculated isotope pattern for [M] 2+ ( Cr 2 C 18 H 14 O 4 N 8 ); bottom, experimental result. Right: top, calculated isotope pattern for [M] 3+ ( Cr 2 C 18 H 14 O 4 N 8 ); bottom, experimental result. 167 Figure 3 . 8 2 . ESI - MS of Complex 9 . T op, calculated isotope pattern for [Cr(tren)(C 14 H 8 O 4 )] + ( CrC 20 H 26 O 4 N 4 ); bottom, experimental result. 168 Figure 3. 8 3 . ORTEP drawing of [Cr(tren)Cl](BPh 4 ) from single - crystal x - ray structure determination. Atoms are represented as 50% thermal ellipsoids. Hydrogen atoms are omitted for clarity. Table 3 . 10 . Crystal data and structural refinement for [Cr(II)(tren)Cl](BPh 4 ). Empirical formula C 102 H 152 B 4 Cl 4 Cr 4 N 16 Formula weight 2211.62 Temperature (K) 173(2) Crystal system Triclinic Space group P a (Å) 13.7322(9) b (Å) 10.3019(7) c (Å) 20.2201(13) 94.3310(10) Volume (Å 3 ) 2852.3(3) Z 1 Radiation MoK D calc (g cm - 3 ) 1.288 Goodness of fit (F 2 ) 1.017 R 1 (I>2 (I)) a 0.0405 wR 2 (I>2 (I)) b 0.1042 a R 1 = b wR 2 =[ ] 1/2 , w=1/[ , where P=[ . 169 Figure 3. 8 4 . The effective magnetic moment of Complex 2 ( blue square ), and the solid line represents a fit to the data using MagFit. 46 Figure 3. 8 5 . The effective magnetic moment of Complex 3 ( blue square ), and the solid line represents a fit to the data using MagFit. 46 170 Figure 3. 8 6 . The effective magnetic moment of Complex 4 ( blue square ), and the solid line represents a fit to the data using MagFit. 46 Figure 3. 8 7 . The effective magnetic moment of Complex 5 ( blue square ), and the solid line represents a fit to the data using MagFit. 46 171 Figure 3. 8 8 . The effective magnetic moment of Complex 6 ( blue square ), and the solid line represents a fit to the data using MagFit. 46 Figure 3. 8 9 . The effective magnetic moment of Complex 7 ( blue square ), and the solid line represents a fit to the data using MagFit. 46 172 Figure 3. 90 . The effective magnetic moment of Complex 8 ( blue square ), and the solid line represents a fit to the data using MagFit. 46 Figure 3. 9 1 . The effective magnetic moment of Complex 9 ( blue square ), and the solid line represents a fit to the data using MagFit . 46 173 Figure 3. 9 2 . The effective magnetic moment of Complex 10 ( blue square ), and the solid line represents a fit to the data using MagFit. 46 Figure 3. 9 3. The effective magnetic moment of Complex 11 ( blue square ), and the solid line represents a fit to the data using MagFit. 46 174 Figure 3. 9 4 . The effective magnetic moment of Complex 13 ( blue square ), and the solid line represents a fit to the data using MagFit. 46 Figure 3. 9 5 . The effective magnetic moment of Complex 14 ( blue square ), and the solid line represents a fit to the data using MagFit. 46 175 Figure 3. 9 6 . The effective magnetic moment of Complex 1 5 ( blue square ), and the solid line represents a fit to the data using MagFit. 46 Figure 3. 9 7 . The effective magnetic moment of Complex 1 6 ( blue square ), and the solid line represents a fit to the data using MagFit. 46 176 Figure 3. 9 8 . The effective magnetic moment of Complex 17 ( blue square ), and the solid line represents a fit to the data using MagFit. 46 Figure 3. 9 9 . The effective magnetic momen t of Complex 18 ( blue square ), and the solid line represents a fit to the data using MagFit. 46 177 Figure 3. 100 . The effective magnetic moment of Complex 19 ( blue square ), and the solid line represents a fit to the data using MagFit. 46 178 REFERENCES 179 REFERENCES (1) Bertrand, P.; Guigliarellia, B.; Gayda, J. - P.; Beardwood, P.; Gibson, J. F. Biochim. Biophys. Acta . 1985 , 831 , 261. (2) Luneau, D. Curr. Opin. Solid State Mater. Sci. 2001 , 5 , 123. (3) Öhrstrom, L. C. R. Chimie 2005 , 8 , 1374. (4) Shultz, D. A. Polyhedron 2001 , 20 , 1627. (5) Caneschi, A.; Gatteschi, D.; Sessoli, R.; Rey, P. Acc. Chem. Res. 1989 , 22 , 392. (6) Vostrikova, K. E. Coord. Chem. Rev. 2008 , 252 , 1409. (7) Kahn, O.; Martinez, C. J. Science 1998 , 279 , 44. (8) Guo, D.; McCusker , J. K. Inorg. Chem. 2007 , 46 , 3257 - 3274. (9) Kirk, A. D. Chem. Rev. 1999 , 99 , 1607 - 1640. (10) Forster, L. S. Chem. Rev. 1990 , 90 , 331. (11) Mishustin, A. I. Russ. J. Inorg. Chem. 2008 , 53 , 1376. (12) Osanai, K.; Okazawa, A.; Nogami, T.; Ishida, T. J. Am. Chem. Soc. 2006 , 128 , 14008. (13) McConnell, H., M, J. Chem. 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H.; Boussie, T. R.; Devenney, M.; McCusker, J. K. J. Chem. Soc. 1997 , 119 , 8253. (81) Scalettar, R. T. An Introduction to the Hubbard Hamiltonian . Edicted by Pavarini, E. ; Koch, E.; van den Brink, J.; Sawatzky , G. Quantum Materials: Experimentals and Theory. Vol. 6; Forschungszentrum J lich : J lich , Germany, 2016 . 184 Chapter 4. Magnetic Properties and Substituent Effects of Gallium (III) Tetraoxo - Dimeric Complexes 4.1 Introduction T he substituent effects o f spin delocalization on free radicals were discussed in Chapter 2 , and transition metal radical complexes should be the next models for the examin at ion of whether the same principle s apply. When a radical is incorporat ed to a Lewis acidic metal ion, the empty metal orbitals can accommodate lone electrons from the ligand to form a coordination compound. The formation of coordination compound alters the overall electronic structure through linear combination of metal and ligand atomic orbitals . 1 Upon formation, reduction in interelectronic repulsion and spin - orbit coupling can be observed experimentally due to the expansion of valence electron cloud arou nd the metal centers. 2 - 4 Th is similar situation manifests on the magnetic moment of transition metal complexes because the orbital contribution is decreased by covalency. 5 This predicts that t he magnetic behaviors may be very different from that of a free radical ligand , and t he Lewis acidity of metal ion and orbital overlaps between metal and ligands may change the spin distribution. Therefore, it will be unreasonable to employ the computational information of free ligands for transition metal complexes ev en though the ligands remain the same. The c oordinati on of such quinoidal ligands with relatively redox - inert metal ions allows the systematical study of the substituent effect s on the physical properties without changing the overall elemental composition or drastically altering the structures upon oxidation . Ga(III) complex es are good s model for the study of paramagnetic metal complexes due to their diamagnetic d 10 electronic configuration with no Heisenberg exchange interaction . Ga(III) has been widely e mployed in literature for the study of bound - semiquinone ligands. 6 - 1 2 185 In addition, Ga (III) - quinoidal complexes are treated as a reference to the Cr (III) analogues , because of Ga (III) nearly identical charge - to - radius ratio to Cr (III) and its spectros copic silent property. In order to understand changes in spin polarization of substituted semiquinone radical when coordinating to a metal center , and establish the thermodynamic correlation between electrochemical and magnetic behavior induced by spin exc hange interaction , Ga (III) - semiquinone complexes are synthesized and reported here . 4.1.1 Previous Studies on Similar Systems : An EPR, ENDOR, and Density Functional Study on Ga (III) Phenanthrenesemiquinone Complexes, [Ga 2 (tren) 2 (CA sq,cat )] 3+ and [Ga 2 (tren) 2 (DHBQ sq,cat )] 3+ Electron Paramagneti c Resonance (EPR) spectroscopy is a powerful tool to study the electronic structure of radical s by detecting unpaired electrons . It can help identify paramagnetic species and short - lived reactive free radicals un der applied field , so it has been widely used in the field of biomedical engineering, pathologies, and other life science related studies. Electron nuclear double resonance ( ENDOR ) and electron spin echo envelope modulation ( ESEEM ) are two methods to measu re the interactions between unpaired electrons and the surrounding nuclei. 42 - 44 Previous studies in our group conducted DFT computational and EPR studies on Ga (III) Phenanthrenesemiquinone Complexes, 3 6 [Ga 2 (tren) 2 (CA sq,cat )] 3+ and [Ga 2 (tren) 2 (DHBQ sq,cat )] 3+ . 36 DFT calculations were conducted to interpret the overall mechanism of spin delocalization of these Ga (III) complexes, and EPR spectroscopy was employed to experimentally examine the validity of the computational results. 3 6 ,3 7 Figure 4.1. Chemical structures of [Ga 2 (tren) 2 (DHBQ sq,cat )] 3+ (left) and [Ga 2 (tren) 2 (CA sq,cat )] 3+ (right). 186 In the studies of [Ga 2 (tren) 2 (CA sq,cat )] 3+ and [Ga 2 (tren) 2 (DHBQ sq,cat )] 3+ (Fig. 4.1) , EPR spectroscopy was used experimentally for the spatial disposition of the unpaired electrons on the bridging ligands, and DFT calculations were incorporated to provide guidance for the simulated and experimental EPR spectra. 3 7 The DFT calculation predicted that excess spin on the four interacting oxygens, the ones directly co ordinate to Ga (III), which is consistent with experimental observation from EPR spectra. 3 7 The spin character within the ligand gives rise to negative hyperfine coupling constants, and the number of signal obtained experimentally agrees with the predic tion of the number of signals from DFT. 3 7 This study also suggests that the presence of triplet state in EP R spectra could be the consequence of comproportionation of [Ga 2 (tren) 2 (CA sq,cat )] 3+ (Eq. 4.1) in solution . 3 7 The spin density spreading over to t wo chlorines is possible residual effect caused by the - SOMO, because Cl effectively induces spin delocalization in the system. 36 (4.1) (4.2) Although EPR spectroscopy is not utilized as a characterization technique in this project, similar DFT natural population analysis (NPA) was performed on various substituted [Ga 2 (tren) 2 (L sq,cat )] 3+ to better understanding the substituent effect on spin polarization and used as a tool to help interpret experimental results. 4.2 Computational Details of DFT Calculations General Methods . All electronic structure calculations of [Ga 2 (tren) 2 (L sq,cat )] 3+ cations were carried out using density functional theory implemented in Gaussian 09 1 3 on HPCC at 187 Insti tute for Cyber - Enabled Research at Michigan State University . The B3LYP functional with open shelled was used in the calculation. 1 4 - 1 8 The calculation was performed using the default tight convergence criteria with ultrafine integration grid. Analysis of a tomic charge and spin densities were performed using natural population analysis (NPA) framework developed by Weinhold et al. 1 9 4.2.1 Geometry Optimization and Single Point Energy Calculations The initial geometries of [Ga 2 (tren) 2 (DHBQ sq,cat )] 3+ ( 20 ) , [Ga 2 (tren) 2 (FA sq,cat )] 3+ ( 21 ) , [Ga 2 (tren) 2 (CA sq,cat )] 3+ ( 22 ) , [Ga 2 (tren) 2 (BA sq,cat )] 3+ ( 23 ) , and [Ga 2 (tren) 2 ( I A sq,cat )] 3+ ( 24 ) were modified from the crystal structure of their catecholate derivatives, and subsequently optimized using the UB3LYP functional and a 6 - 31G basis set with imposed symmetries of C i . The initial geometries of other Gallium (III) dimeric derivatives were generated using GaussView 20 with subsequently optimized using the U B3LYP functional and a 6 - 31G basis set with imposed symmetries of C i . Final geometries were checked with frequency calculations at the UB3LYP/6 - 31G level . Imaginary frequencies were obtained for some sterically bulky structures or structures with extended aromatic conjugation. Those structures were reoptimized with in creased convergence cycles (default maxcycle = 64) and the exact computed Hessian matrix f or frequency calculations with CalcFC or CalcAll command. Heissian matrix is the matrix of second derivatives of the energy in regard to displacement of atoms. 2 1 Freq uency calculations generally are based on an estimated Hessian from geometry optimization. 2 2 Geometry optimizations were then re - run for all structures with UltraFine grid to help obtain smoother convergence to the stationary point. Structures were reoptim ized with subsequent frequency calculations until no imaginary frequencies , which indicates that the final structures have reached 188 the global minima. The final optimized structures were then used for single - point energy calculations. Single - point energy c alculations were performed using the unrestricted open shelled density function UB3LYP with the 6 - 311G basis set with natural population analysis assuming the doublet ground state and a molecular charge of 3+. 4.3 Experimental Section General. All chemic als were of reagent grade, purchased from Alfa Aesar, Sigma - Aldrich, Acros Organics, TCI Chemicals, Oakwood Chemicals, Strem Chemicals, or Matrix Chemicals, and used as received unless otherwise noted. Solvents were purchased from Sigma - Aldrich, Jade Scien tific, Alfa Aesar, Fisher Scientific, EMD Chemicals, Mallinckrodt, or CCI and were purified using standard purification techniques. All air - sensitive and water - sensitive reactions were carried out under inert atmosphere either by standard Schlenk technique s or in dryboxes. The solvents utilizing for these reactions were thoroughly dried by being stored over 4 Å molecular sieve and deoxygenated by the freeze - pump - thaw method. The ligand tris(2 - aminoethyl)amine (tren) was purchased from either Sigma - Aldrich o r Alfa Aesar, vacuum - distilled, and degassed by the freeze - pump - thaw method prior to use. 1 H NMR and 13 C NMR were collected on Agilent DDR2 500 MHz NMR spectrometers equipped with 7600AS 96 - sample autosamplers. Electrospray mass spectra (ESI - MS) were obtai ned on Waters Xevo G2 - XS QTof Quadruple UPLC/MS/MS at Michigan State University Mass Spectrometry and Metabolomics Core. CHN elemental analyses were obtained on a Perkin - Elmer 2400 Series II CHNS/O Analyzer through the analytical facilities at Chemistry of Michigan State University. 189 4.3.1 Synthetic Procedures of Substituted Tetrahydroxy - Ligands . 2,3,5,6 - Tetrahydroxybenzene (THB) . 2 3 , 2 4 DHBQ (2.0 g, 14.3 mmol) and 37% (w/v) HCl (50 mL) were mixed together and stirred for 10 min. After addition of Sn metal (4.0 g, 33.7 mmol), the reaction was refluxed under N 2 until the solution turned colorless. The hot solution was filtered under N 2 and cooled to RT, resulting in white microcrystalline. The product was washed with cooled degassed H 2 O under N 2 , and dried un der vacuum overnight. The product is air - sensitive, and needs to be stored under inert - gas environment. Yield: 1.03 g ( 51 %). 1 H NMR (CD 3 CN, 500 MHz) (ppm): 6.04 (s, 4 H, OH), 6.35 (s, 2 H, ArH). 13 C NMR (CD 3 CN, 500 MHz) (ppm): 105.08, 138.58. Tetrahyd roxy - 1,4 - dichlorobenzene (H 4 CA). 2 4 The synthetic procedure was similar to that of THB. Instead, H 2 CA ( 2.0 g, 9.6 m mol), 37% (w/v) HCl (50 mL), and Sn ( 4.0 g, 34 mmol) were used for the reaction. Yield: 0.8 g ( 40 %). HRMS [ESI - TOF, m/z (rel. int.)]: [M - H] - Calcd for [C 6 O 4 H 3 Cl 2 ] - , 208.940 8 ; Found, 2 08 . 9406. Tetrahydroxy - 1,4 - dibromobenzene (H 4 BA) . 2 5 - 2 7 H 2 BA (1.04 g, 3.5 mmol) was dissolved in degassed EtOAc under N 2 . 0.5 M aq. Na 2 S 2 O 4 solution (25 mL) was added dropwise into the solution above while stirring. The reaction was allowed to react overnight. The work - up procedure was performed in N 2 - inflated glove bag due to the sensitivity of the fully reduced product. The product was extracted with EtOAc (3 x 30 mL), washed by 1 M HCl (2 x 30 mL), H 2 O (2 x 20 mL) , and dried over Na 2 SO 4 . Beige product was obtained after the solvent was completely evaporated under vacuum. Yield: 0.85 g ( 82 %). HRMS [ESI - TOF, m/z (rel. int.)]: [M - H] - Calcd for [C 6 O 4 H 3 Br 2 ] - , 298.8378; Found, 298.8354 . Tetrahydroxy - 1,4 - difluorobenzene (H 4 FA) . The synthetic procedure is similar to that of H 4 BA. 0.5 M aq. Na 2 S 2 O 4 solution (20 mL) was added dropwise to a solution of H 2 FA (0.36 190 g, 2.0 mmol) in EtOAc (20 mL). Yield: 0.28 g ( 78 %). HRMS [ESI - TOF, m/z (rel. int.)]: [M - H] - Calcd for [C 6 O 4 H 3 F 2 ] - , 176.9999; Found, 177.0058 . Tetrahydroxy - 1,4 - diiodobenzene (H 4 IA) . The synthetic procedure is similar to that of H 4 BA. Due to the light sensitivity of iodo compounds, this reaction needs to be carried out in the dark. An aq. solution of Na 2 S 2 O 4 (0.12 g, 1.2 mmol ) in H 2 O (5 mL) was added dropwise to a solution of H 2 IA (0.12 g, 0.3 mmol) in EtOAc (5 mL). Light yellow/brown oil was obtained; however, the product is unstable even under inert gas environment. It has to be freshly prepared prior use, and the next reaction with H 4 IA as starting material needs to be carried out immediately after due to its instability. Yield: 0.11 g ( 92 %). HRMS [ESI - TOF, m/z (rel. int.)]: [M - H] - Calcd for [C 6 O 4 H 3 I 2 ] - , 392.8121; Found, 392.8141. 4.3.2 Synthetic Procedure s of Gallium(III) Dimeric Complexes Ga(tren)(NO 3 ) 3 . 2 3 A solution of Ga(NO 3 ) 3 (0.76 g, 3.0 mmol) in EtOH (10 mL) was added dropwise into a stirring sol ution of tren (0.52 mL, 3.3 mmol) in 5 mL of EtOH under N 2 . White precip itates formed upon addition. The solids were filtered, washed by EtOH (3 x 1 0 mL), and Et 2 O (1 x 1 0 mL). The product is extremely hygroscopic, and needs to be stored under i nert - gas environment. Yield: 1.0 g (85 %). (20) [Ga 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 . THB (0.042 g, 0.2 mmol) was deprot onated by Et 3 N (0.11 mL, 0.8 mmol) in 5 mL of MeOH. After 5 min, the deprotonated THB solution was added dropwise into a solution of Ga(tren)(NO 3 ) 3 (0.16 g, 0.4 mmol) in MeOH (40 mL) resulting in a cloudy yellow mixture. The mixture was filtered through a pad of Celite. A solution of NaBPh 4 (0.34 g, 1.0 mmol) in MeOH (40 mL) was layered carefully on top of the filtrate, and allowed to stand overnight without being disturbed. Yellow crystals, suitable for x - ray 191 diffraction, were obtained, if the solution was allowed to stand for over one week without disturbance. Yield: 0. 2 g ( 83 %). HRMS [ESI - TOF, m/z (rel. int.)]: [M] 2+ Calcd for [Ga 2 C 18 H 38 O 4 N 8 ] 2+ , 282.0760; Found, 282.0767. [M] 3+ Calcd for [Ga 2 C 18 H 38 O 4 N 8 ] 3+ , 190.0507; Found, 190.0516. [Ga(tren)(C 6 H 2 O 4 )] + Calcd for [Ga C 1 2 H 20 O 4 N 4 ] + , 353.0740; Found, 353.0744 . (25) [Ga 2 (tren) 2 (DHBQ sq,cat )](BPh 4 ) 2 (BF 4 ). Under N 2 , a solution of (FeCp* 2 )(BF 4 ) ( g, mmol) in MeCN ( 10 mL) was added dropwise into a stirring solution of [ Ga 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 ( 0.20 g, 0.16 6 mmol) in MeCN ( 10 mL). The solution was stirred for 6 h, which turned yellow - green. After filtration, the solvent volume of the filtrate was reduced under vacuum to 10 mL. 30 mL of DCM was added, and the mixture was filtered to eliminate excess [FeCp* 2 ](BF 4 ) salt. The filtrate was reduced in volume under vacuum again to 10 mL, and 30 mL of Et 2 O was added to yield yellow brown solids. The product was filtered, washed by DCM (3 x 10 mL), and Et 2 O (3 x 10 mL). Yield: 0.1 g ( 47 %). HRMS [ESI - TOF, m/z (rel. i nt.)]: [M] 3+ Calcd for [Ga 2 C 18 H 38 O 4 N 8 ] 3+ , 190.0507 ; Found, 190.0510 . [Ga(tren)(C 6 H 2 O 4 )] + Calcd for [Ga C 12 H 20 O 4 N 4 ] + , 353.0740; Found, 353.0736. (21) [Ga 2 (tren) 2 (CA cat,cat )](BPh 4 ) 2 . 2 4 The synthesis of this compound is similar to that of [Ga 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 . H 4 CA (0.042 g, 0.2 mmol) was deprotonated by Et 3 N (0.11 mL, 0.8 mmol) in 3 mL of MeOH. A solution of Ga(tren)(NO 3 ) 3 (0.162 g, 0.4 mmol) in MeOH (80 mL) was added into the reaction mixture. Crystals suitable for x - ray diffraction were obta ined by carefully layering a solution of NaBPh 4 (0.34 g, 1.0 mmol) in MeOH (10 mL). Yield: 0.19 g (75 %). HRMS [ESI - TOF, m/z (rel. int.)]: [M] 2+ Calcd for [Ga 2 C 18 H 36 O 4 N 8 Cl 2 ] 2+ , 319.0367; Found, 319.0361. [Ga(tren)(C 6 H 2 O 4 )] + Calcd for [Ga C 12 H 18 O 4 N 4 Cl 2 ] + , 44 2.9943; Found, 442.9969. 192 (26) [Ga 2 (tren) 2 (CA sq,cat )](BPh 4 ) 2 (BF 4 ). 2 4 The synthesis of this compound is similar to that of [Ga 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 . A solution of [FeCp* 2 ](BF 4 ) in MeCN (20 mL) was added dropwise to [Ga 2 (tren) 2 (CA cat,cat )](BPh 4 ) 2 (BF 4 ) (0.16 g, 0.12 mmol) in 25 mL of MeCN while stirring. After 30 min, the solution was filtered. Et 2 O (100 mL) was added to the filtrate, and yellow precipitates were formed. The product was filtered and washed by Et 2 O (3 x 20 mL). Yield: 0.11 g (66%). HRMS [ESI - TOF, m/z (rel. int.)]: [M] 3+ Calcd for [Ga 2 C 16 H 38 O 4 N 8 Cl 2 ] 3+ , 212.6902 ; Found, 212.6905 . [Ga(tren)(C 6 H 2 O 4 )] + Calcd for [Ga C 12 H 18 O 4 N 4 Cl 2 ] + , 442.9943; Found, 442.9966. (22) [Ga 2 (tren) 2 (FA cat,cat )](BPh 4 ) 2 . The synthesis of this compound is similar to that of [Ga 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 . H 4 FA (0.018 g, 0.1 mmol) was deprotonated by Et 3 N (0.13 mL, 0.8 mmol) i n 3 mL of MeOH. A solution of Ga(tren)(NO 3 ) 3 (0.081 g, 0.2 mmol) in MeOH (60 mL) was added into the reaction mixture. Crystals suitable for x - ray diffraction were obtained by carefully layering a solution of NaBPh 4 (0.34 g, 1.0 mmol) in MeOH (20 mL). Yield: 0.88 g ( 71 %). HRMS [ESI - TOF, m/z (rel. int.)]: [M] 2+ Cal cd for [ Ga 2 C 1 8 H 3 6 O 4 N 8 F 2 ] 2+ , 303.0666; Found, 303.0664. [Ga (tren)(C 6 F 2 O 4 )] + Calcd for [ Ga 2 C 1 2 H 18 O 4 N 4 F 2 ] + , 389.0552; Found, 389.0537 . (27) [Ga 2 (tren) 2 (FA sq,cat )](BPh 4 ) 2 (BF 4 ). The synthesis of this compound is similar to that of [Ga 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 . Instead, [FeCp* 2 ](BF 4 ) ( 0.08 g, 0.19 mmol) was used to react with [Ga 2 (tren) 2 (FA cat,cat )](BPh 4 ) 2 (0.15 g, 0.12 mmol) , and the reaction mixture was stirred for 2 h . Yield: 0.085 g ( 53 %). [ESI - TOF, m/z (rel. int.)]: [M] 3+ Calcd for [Ga 2 C 16 H 38 O 4 N 8 F 2 ] 3+ , 202.0444 ; Found, 202.0448 . [Ga(tren)(C 6 F 2 O 4 )] + Calcd for [Ga 2 C 12 H 18 O 4 N 4 F 2 ] + , 389.0552; Found, 389.0538. 193 (23) [Ga 2 (tren) 2 (BA cat,cat )](BPh 4 ) 2 . The synthesis of this compound is similar to that of [Ga 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 . H 4 BA (0.85 g, 2.8 mmol) was deprotonated by Et 3 N (1.6 mL, 11.5 mmol) in 10 mL of MeOH. A solution of Ga(tren)(NO 3 ) 3 (2.24 g, 5.6 mmol) in MeOH (60 mL) was added into the reaction mixture. Crystals suitable for x - ray diffraction were obtained by carefully layering a solutio n of NaBPh 4 in MeOH. Yield: 2.0 g ( 54 %). HRMS [ESI - TOF, m/z (rel. int.)]: [M] 2+ Calcd for [Ga 2 C 18 H 36 O 4 N 8 Br 2 ] 2+ , 363.9854; Found, 363.9865. [M] 3+ Calcd for [Ga 2 C 18 H 36 O 4 N 8 Br 2 ] 3+ , 242.6570; Found, 242.6592. [Ga(tren)(C 6 Br 2 O 4 )] + Calcd for [ Cr 2 C 18 H 18 O 4 N 4 ] + , 510. 8934; Found, 510.8938. (28) [Ga 2 (tren) 2 (BA sq,cat )](BPh 4 ) 2 (BF 4 ). The synthesis of this compound is similar to that of [Ga 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 . Instead, [FeCp* 2 ](BF 4 ) ( 0. 14 g, 0.34 mmol) was used to react with [Ga 2 (tren) 2 (BA cat,cat )](BPh 4 ) 2 (0.23 g, 0.17 mmol) . Yield: 0.138 g ( 57 %). [ESI - TOF, m/z (rel. int.)]: [M] 3+ Calcd for [Ga 2 C 16 H 38 O 4 N 8 Br 2 ] 3+ , 242.6570 ; Found, 242.6578 . [Ga(tren)(C 6 Br 2 O 4 )] + Calcd for [ Cr 2 C 18 H 18 O 4 N 4 ] + , 510.8934; Found, 510.8962. (24) [Ga 2 (tren) 2 (IA cat,cat )](BPh 4 ) 2 . The synthesis of this compound is similar to that of [Ga 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 , except that H 4 IA has to be prepared freshly due to its instability. H 4 IA (0.11 g, 0.28 mmol) was deprotonated by Et 3 N (0.16 mL, 1.1 mmol) in 6 mL of MeOH. A solution of Ga(tren)(NO 3 ) 3 (0.227 g, 0.56 mmol) in MeOH (60 mL) was added into the reaction mixture. The product is stable under inert - gas environment after H 4 IA bind to Ga 3+ . Light yellow crystals suitable for x - ray diffraction were obtained by carefully layering a solution of NaBPh 4 in MeOH. The product slowly degrades even being stored under inert atmosphere, color change to brown indicates the decomposition. No [M] 2+ specie s was observed in HRMS. Yield: 0.12 g ( 60 %). HRMS [ESI - TOF, m/z (rel. int.)]: [M] 3 + Calcd for [Ga 2 C 18 H 34 O 4 N 8 I 2 ] 3 + , 194 273.9818; Found, 273.9857. [Ga(tren)(C 6 I 2 O 4 )] + Calcd for [ Cr 2 C 18 H 18 O 4 N 4 ] + , 604.8673; Found, 604.8649. (29) [Ga 2 (tren) 2 (IA sq,cat )](BPh 4 ) 2 (BF 4 ). The synthesis of this compound is similar to that of [Ga 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 . Instead, [FeCp* 2 ](BF 4 ) ( 0.04 g, 0.11 mmol) was used to react with [Ga 2 (tren) 2 (IA cat,cat )](BPh 4 ) 2 (0.08 g, 0.055 mmol) . Yield: 0.036 g ( 42 %). [ESI - TOF, m/z (rel. int.) ]: [M] 3+ Calcd for [Ga 2 C 18 H 34 O 4 N 8 I 2 ] 3+ , 273.9818; Found, 273.9857. [Ga(tren)(C 6 I 2 O 4 )] + Calcd for [ Cr 2 C 18 H 18 O 4 N 4 ] + , 604.8673; Found, 604.8649. [Ga 2 (tren) 2 (PhA cat,cat )](BPh 4 ) 2 . The synthesis of this compound is similar to that of [Ga 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 . H 4 PhA (0.03 g, 0.1 mmol) was deprotonated by Et 3 N (0. 06 mL, 0.4 mmol) in 3 mL of MeOH. A solution of Ga(tren)(NO 3 ) 3 (0.08 g, 0.2 mmo l) in MeOH (5 0 mL) was added into the reaction mixture. Pink product was obtained; however, no [M] 2+ was observed from ESI+ spectrum. Several attempts of recrystallization for x - ray diffraction were unsuccessful. HRMS [ESI - TOF, m/z (rel. int.)]: [M] 3 + Calcd for [Ga 2 C 30 H 46 O 4 N 8 ] 3+ , 240.7383; Found, 240.7348. [Ga(tren)(C 18 H 10 O 4 )] + Calcd for [ Ga C 24 H 2 8 O 4 N 4 ] + , 505.1366; Found, 505.1329 . 4.3.3 Physical Measurements X - Ray Single - Crystal Structure Determinations. Single - crystal structure measurement for all Cr (III) dimeric complexes was acquired at the center for crystallographic research of Michigan State University. The crystals were mounted on nylon loops using small amount of paratone oil. X - ray diffraction da ta were collected at 173 K on Bruker SMART APEX II CCDs (charge coupled device) either with molybdenum radiation using a 3 - axis goniometer with Oxford 600 low - temperature device or with copper radiation using a 3 - axis goniometer APEX II 195 diffraction system with Oxford Cyrosystream 700 low - temperature device. Each system is equipped with a camera for viewing the crystals and a Pentium PC to control the diffractometer. The total number of runs and images was based on results from the program COSMO , 2 7 of which redundancy was expected to be 4.0 and completeness of 100% out to 0.83 Å for the Mo K Å for the Cu K s were retrieved and refined using the SAINT software . 2 8 Scaling and absorption corrections were applied by the SAINT 2 9 for Lorentz and polarization factors. A multi - scan absorption correction was performed by SADABS - 2014/5. 30 The structures were solved by intrinsic phasing using ShelXT 3 1 structure solution program. The structures were refined by least squares using XL - 2014/6 3 1 with Olex2 3 2 incorporated. All non - hydrogen atoms were refined anisotropically. The positions of h ydrogen atom were calculated geometrically and refined using the r iding model, except for the hydrogen atom s on the non - carbon atom s, which was found by difference Fourier methods and refined isotropically. Table 4. 1 . Crystallographic data for Complex 20 , 21 , 23 , and 24 . 20 21 23 24 Empirical Formula C 68 H 86 B 2 Ga 2 N 8 O 6 C 47 H 67 BGa 2 F 2 N 9 O 9 C 68 H 84 B 2 Ga 2 Br 2 N 8 O 6 C 68 H 84 B 2 Ga 2 I 2 N 8 O 6 Formula Weight (g/mol) 1272.51 1090.3 5 1430.31 1524.29 Temperature (K) 173(2) 173(2) 173(2) 173(2) Crystal System Monoclinic monoclinic Monoclinic monoclinic Space Group P2 1 /c P2 1 /n P2 1 /n P2 1 /n a (Å) 9.5971(6) 9.34520(10) 13.5579(2) 13.4607(8) b (Å) 14.9395(10) 17.4847(2) 9.72430(10) 9.8773(6) c (Å) 22.1237(14) 30.8815(3) 25.0744(4) 25.1172(15) 97.9990(10) 93.8800(10) 96.4290(10) 96.6560(10) Volume (Å 3 ) 3141.1(3) 5034.41(9) 3285.05(8) 3317.0(3) Z 2 4 2 2 D calc (g/cm 3 ) 1.345 1.439 1.446 1.526 Radiation MoK Cu K Cu K Mo K Goodness of Fit (F 2 ) 1.048 1.01 5 1.052 1.052 R 1 (I 2 (I)) a 0.046 2 0.0465 0.0420 0.057 3 wR 2 (I 2 (I)) b 0.10 70 0.1 12 4 0.124 4 0.172 8 a R 1 = b wR 2 =[ ] 1/2 , w=1/[ , where P=[ . 196 4.4 SQUID Variable - Temperature Magnetic Susceptibility Measurement on [Ga 2 (tren) 2 (L sq,cat )] 3+ General. Magnetic susceptibility measurement was collected using a Quantum De sgien MPMS ® 3 SQUID magnetometer Cryogen Free with EverCool® He gas regulator interfaced to a Dell PC. Data were collected in an applied field of 1 T. Temperature was ramped up with small temperature increments to ensure the samples were thermally equilibrated. Data were corrected 3 4 and the measured susceptibility of the sample holder, including a plastic straw and a plastic sealed bag. and were reported as effective magnetic moment (µ eff ). Paramagnetic impurity (5 mol % of an S = ½ compound) and temperature - independent paramagnetism (200 x 10 - 6 cgsu for each Ga (III) center) were included in fitting. Sample preparation has been discussed in Chap ter 3. 4.5 Results and Discussion 4.5.1 Synthesis and Characteriza tion Gallium (III) ion was incorporated in our binuclear motif as a reference to chromium (III) dimeric system because of its spectroscopically silent and diamagnetic d 10 electronic configuration and its nearly identical charge - to - radius ratio to that of C r (III). Complex 22 and 27 were previously prepared and reported by Dr. Dong Guo, 2 4 a former group member in the McCusker group. Synthesis of Ga (III) analogues starts with Ga(tren)(NO 3 ) 3 , and H 4 L. Ga(tren)(NO 3 ) 3 is extremely hygroscopic, and H 4 L is air - sensitive, so all synthetic procedures were performed under inert atmosphere. Then, [Ga 2 (tren) 2 (L cat,cat )] 2+ was oxidized with [FeCp* 2 ](BF 4 ) to result in [Ga 2 (tren) 2 (L sq,cat )] 3+ , where [FeCp* 2 ](BF 4 ) was prepared following a literature method, 2 5 and detailed procedure was reported in Chap ter 3. 197 THB and H 4 CA were synthesized according to a procedure modified from literature methods 2 3 - 2 4 with Sn and 37% HCl under reflux. However, this condition is too harsh for the other halogenated tetrahydroxyani late, and no desired product was detected for H 4 BA when following this reaction condition. The hypothesis of why this reaction condition has failed for reducing H 2 BA to H 4 BA is that bromine is a much better leaving group than H and Cl. Under reflux with su ch an acidic condition, C - Br bond may break resulting from the decomposition of H 2 BA before the reduction. Therefore, a much milder condition was employed, 2 6 ,2 7 where H 2 BA reacted with a reductant, Na 2 S 2 O 4 , at room temperature. Since Na 2 S 2 O 4 is insoluble i n most of the common organic solvent, this reaction cannot be conducted inside a n air - free and water - free drybox , where most of the air - sensitive reactions in this project were performed in. The reaction was conducted with Schlenk line technique. Due to th e extreme air - sensitivity of the product, reaction workup has to be done under an inert atmosphere, so it was performed in a N 2 - filled glovebag. The colors of these halogenated - anilates are very vibrant (e.g. H 2 CA is orange ), and the solution changed to wh ite upon reduction, which were observed for most of these compounds. After the formation of the reduced H 4 L, it was dried under vacuum and pumped into a drybox to react with Ga(III) source. Most of these H 4 L compounds can be stored under N 2 without decomposition, but H 4 IA. Upon reduction, the H 4 IA product was yellow beige color , and [ H 3 IA ] - was detected by ESI - mass spectrometry. Color change was observed over a one - hour period even under N 2 . Eventually, the product turned completely dark pu rple brown, and no product was detected with ESI - . Thus, H 4 IA is suspected to be extremely sensitive, and iodine is too nucleophilic to result in a very weak C - I bond. The dark purple brown color is suspected to be I 2 , which is coincide with its purple col or in solid state. Therefore, H 4 IA has to be freshly prepared each time before 198 the reaction of [Ga 2 (tren) 2 (IA cat,cat )] 2+ . After binding to Ga (III), the compound can be stored stably under N 2 for c.a. one month , then it slowly decomposes over time even und er inert atmosphere. The color of Complex 24 is yellow beige, and its color change to brown indicate the degradation of the product. T he synthesis of t etrahydroxy - 1,4 - diphenylbenzene (H 4 PhA) was attempted with 0.5 M aq. Na 2 S 2 O 4 solution (5 mL) added drop wise in EtOAc (15 mL). However, ESI - spectra indicate that only the starting material, H 2 PhA, was observed after the reaction . I t is unknown whether the negative charge species was re - oxidized under high voltage inside the Taylor cone in the ESI mass spectrometer or simply no reduction happens. DFT calculations results obtained on a series of phenyl - substituted pyridine previously in our group 45 indicates that no intraligand electron delocalization at these systems are stabilized by electron delocalization at Therefore, it requires significant driving force in order to achieve a coplanar delocalized structure. 46 The reaction of H 4 PhA is a two - electron reduction involving (1) a reduction to a coplanar delocalized form (Fig. 4 . 2 form (2) and (3) ), (2) a further reduction to a twist angle fully reduced form (Fig. 4 . 2 form (4), (5) and (6) ). This means the reduction will first need to overcome a huge thermodynamic energy barri er, and this reaction is possibly too thermodynamically unfavorable to happen. Ga(III) coordination reaction was then proceeded in the presence of Na 2 S 2 O 4 . Nude pink product was collected after the reaction, and ESI+ spectra were collected for the characte rization of this product. [Ga(tren)(PhA q,cat )] + and [Ga 2 (tren) 2 (PhA sq,cat )] 3+ were detected with matching isotope patterns. However, no [Ga 2 (tren) 2 (PhA cat,cat )] 2+ species was observed. It is hard to conclude whether all [M] 2+ species was oxidized to [M] 3+ inside the mass spectrometer, or [M] 2+ product was never formed during the reaction. We incline to propose the former hypothesis, 199 because there will not be [M] 3+ without the initial formation of [M] 2+ . However, it is still too early to conclude anything u ntil more experimental evidence are presented. Discussion will be continued in Chapter 5 along with the electrochemical data. Figure. 4. 2 . 3,6 - diphenyl - tetraoxoanilate undergoing one - electron redox reactions. The synthesis of [Ga 2 (tren) 2 (Me - AnT cat,cat )] 2+ was attempted many times in the past. Even though NO 3 - has very low coordination ability, 3 5 it may not be the best leaving group. The reaction has been conducted with Ga(tren)I 3 . They have all failed without the observation of the product with various characterization techniques, including ESI mass spectrometry and NMR spectra. One problem is the solubility of the starting materials. Both H 4 (Me - AnT) and Ga(tren)(NO 3 ) 2 was insoluble in MeOH. For the reaction of [Cr 2 (tren) 2 (Me - AnT cat,cat )] 2+ , [Cr(tren)Cl](Cl) 2 is soluble in MeOH/H 2 O mixed solvent system even though the other one is not . As the reaction proceeds, the equilibrium is shifted to the product side as more product 200 formed. In addition, h eat can be applied to increase the solubility of all starting materials. The next modification of the reaction is to apply heat, and monitor the reaction with ESI for product formation. Another option is to change the solvent system to make the starting materials more soluble. The biggest concern is that the formation of [Cr 2 (tren) 2 (Me - AnT cat,cat )] 2+ is unfavorable, since Ga (III) is a much weaker Lewis acid compared with Cr (III), and H 2 Me - AnT is a weak Lewis base due to its highly conjugated structure. If this is the main reason why the synthesis of thi s complex is challenging, it will not be stable even if it can form after all attempts eventually. 4.5.2 Single Crystal X - Ray Structures X - ray diffraction quality crystal structures were collected for Complex 20 , 21 , 23 and 24 . The crystal structure of C omplex 22 has been reported by Dr. Guo in our group. 2 4 The crystals of H, F, Br, and I were grown via metathesis by carefully layering NaBPh 4 MeOH solution on top of its product MeOH solution in a N 2 - filled drybox. The crystals were grown in dark after 2 w eeks. The challenging par ts of growing crystals are similar as those for [ Cr 2 (tren) 2 (L cat,cat )](BPh 4 ) 2 , i. e. concentration of mother solution and air - sensitivity . The benefit of incorporating Ga(III) in complexes for x - ray structure determination is that Ga(III) has high diffraction rate. However, some crystals were not packed as large to diffract well even under Cu K radiation when following our conventional approach. In order to grow larger crystals for [Ga 2 (tren) 2 (FA cat,cat )] 2+ , a few drop s of benzene w ere added into the Me OH mother solution before layering NaBPh 4 Me OH solution. The addition of benzene was thought to facilitate the - stacking. 201 Figure 4. 3 . ORTEP drawing of Complex 20 ( a ), 21 ( b ), 23 ( c ), and 24 ( d ) obtain from single crystal x - ray structure determination. Atoms are represented as 50% probability thermal ellipsoids. Hydrogen atoms are omitted for clarity. Complex 20 , 23 , and 24 contained two MeOH solvent molecules in their crystal lattice. The crystal of [Ga 2 (tren) 2 (FA cat,cat )] 2+ is a mixed counteranionic salt with BPh 4 - and NO 3 - . The lattice was confined with two MeOH solvent molecule s and one disordered benzene . Benzene was a dded to facilitate the packing of a bigger crystal. More e fforts were made to grow purely BPh 4 - salt, but those attempts were unsuccessful. When increasing the equivalent of NaBPh 4 for metathesis, the product crashed out from the solution too quickly resul ting in small crystals. Modulation of solution concentration was attempted, but the optimized concentration has not been configurated thus far. Since BPh 4 - and NO 3 - are both considered very we a k ly coordinating counteranions f or different reason, they are u nlikely to alter the overall structure of this compound. We believe that its bond lengths and bond angles will still be comparable with other Ga (III) complexes with BPh 4 - as their only counteranion. BPh 4 - has low coordinating ability because of the bulky structure and increased charge delocalization, and the low coordinating (a) (b) (c) (d) 202 ability of NO 3 - is caused by its high electronegative external atoms . 3 5 Thus, the structure of mixed counteranionic complex F is reported and compared here. Table 4. 2 . Selected Complex 20 , 21 , 23 , and 24 . 20 ( H ) 21 ( F ) 23 ( Br ) 24 ( I ) Bond Length (Å) Ga (1) O(1) 1.9 1 85 (1 7 ) 1.9 120 ( 19 ) 1.9 28 (2) 1.9 28 (3) Ga (1) O(2) 1.91 31 (1 7 ) 1.9 86 ( 2 ) 1.92 1 (2) 1.9 20 (3) Ga (1) N(1) 2. 08 2 ( 2 ) 2. 072 ( 2 ) 2.0 70 ( 3 ) 2.0 65 ( 4 ) Ga (1) N( 2 ) 2. 152 ( 2 ) 2.095( 3 ) 2.0 8 6(3) 2. 083 (4) Ga (1) N( 3 ) 2.0 96 (2) 2.07 6 ( 3 ) 2.1 82 (3) 2. 190 ( 4 ) Ga (1) N( 4 ) 2.0 83 ( 2 ) 2. 102 ( 2 ) 2.0 97 ( 2 ) 2.0 99 ( 4 ) O(1) C(8) 1.3 87 ( 3 ) 1.36 2 (4) 1.3 70 ( 4 ) 1.36 6 (5) O(2) C(9) 1.3 56 (3) 1.3 6 1 ( 3 ) 1.34 2 (3) 1.34 3 (5) C(7) C(8) 1.38 7 (3) 1.3 8 6 ( 4 ) 1.3 8 2(4) 1.39 0 ( 6 ) C(8) C(9) 1. 400 (3) 1. 4 07 (5) 1.407(4) 1.4 09 ( 6 ) C(7) C(9) 1.386(3) 1.3 77 ( 4 ) 1.397(4) 1.398 (6) Ga Ga a 7.551 7.643 7.595 7.594 O(1) Ga (1) N(1) 94.69 ( 7 ) 9 2.41 ( 9 ) 9 1.38 ( 9 ) 9 3.38 (1 5 ) O(1) Ga (1) N(2) 93.23 ( 8 ) 9 6.00 ( 10 ) 10 1.71 (10) 101.87 (1 5 ) O(1) Ga (1) N(3) 100.95 ( 8 ) 9 9.66 (1 0 ) 94. 76 (11) 94.64 (1 7 ) O(1) Ga (1) N(4) 17 5.70 ( 8 ) 17 6.13 ( 9 ) 17 3.27 (10) 175. 53 (1 5 ) O(2) Ga (1) O(1) 8 8.48 ( 7 ) 86. 96 ( 8 ) 8 8 . 18 ( 9 ) 8 8.13 (1 4 ) O(2) Ga (1) N(1) 175. 68 ( 8 ) 17 8.91 ( 10 ) 17 7.30 (10) 17 7.05 (1 7 ) O(2) Ga (1) N(2) 86. 40 ( 9 ) 8 8.33 (1 0 ) 8 7.41 (1 0 ) 8 7.87 (1 6 ) O(2) Ga (1) N(3) 8 7.81 (8) 8 8.21 (1 0 ) 86. 18 (1 1 ) 91.63 (1 7 ) O(2) Ga (1) N(4) 92. 69 (7) 9 6.10 ( 9 ) 9 5.93 ( 10 ) 9 4.78 ( 15 ) N(1) Ga (1) N(2) 9 0.48 ( 9 ) 9 0.85 (1 0 ) 9 5.29 (1 1 ) 9 4.90 (1 7 ) N(1) Ga (1) N(3) 9 4.45 ( 9 ) 9 2.78 (1 0 ) 9 1.20 (1 1 ) 9 1.63 (1 7 ) N(1) Ga (1) N(4) 83. 94 ( 8 ) 8 4.49 (1 0 ) 8 4.26 (1 0 ) 8 4.53 (1 6 ) N(2) Ga (1) N(3) 165. 53 ( 9 ) 16 3.75 (1 0 ) 16 2.12 (1 1 ) 16 1.96 (1 7 ) N(2) Ga (1) N(4) 8 2.72 ( 9 ) 8 1.76 (1 0 ) 83. 84 (1 0 ) 8 4.03 (1 5 ) N(3) Ga (1) N(4) 8 3.23 ( 9 ) 8 2.83 (1 0 ) 8 0.25 (11) 79.86 (1 7 ) a Non bonding metal - to - metal distance. The halogenated Ga (III) complexes are isostructural in monoclinic space group P2 1 /n (a more orthogonal cell), and crystallographic details are shown in Table 4 . 1 . with selected bond lengths and angle given in Table 4 . 2 . [Ga 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 ( 20 ) and [Cr 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 ( 1 ) are isostructural in monoclinic space gro up P2 1 /c , a more oblique cell compared with P2 1 /n . These complexes are all structurally similar with centrosymmetric monoclinic space groups, and complexes 20 , 21 , 22 , 1 23 , and 24 are situated on 203 inversion centers making only half of a dimer unique in a ce ll. The ORTEP drawings of the cations are shown in Figure 4 . 3 . The gallium center is also coordinated tripodally with four aliphatic nitrogens from the tren capping ligand and two oxygens to form a distorted octahedral environment. The bite angles around t he chromium coordination site for a given complex are c.a. are larger than those observed in the Cr (III) analogues reported in Chap ter 3 . The Ga - N bond lengths are ranging from 2.087 to 2. 101 Å, which are slightly longer than those collected for the Cr (III) analogues . The Ga - O bond distances are nearly identical (Table 4 . 2 ) , except for the Cl derivative ; for example, the bond distances are 1.9 13 Å and 1.91 9 Å respectively in complex H, and 1.944 and 1.918 Å in the Cl analogue . These bond distances are much shorted than those seen in [Ga(Cat) 3 ] 3 - , 1.983 Å. 3 2 No discrepancy in Ga - O bond distances were observed except in [Ga 2 (tren) 2 (CA cat,cat )](BPh 4 ) 2 . This is not consistent with those observed in the Cr (III) dimers. The C - C bond length within the ring can indicate the oxidation state of the quinoidal ligand. 3 1 - 33 In fully reduced catecholate ligand , the difference of C - C bond distances is statistically negligible indicating the aromatic nature of the ligand : [Ga(Cat) 3 ] 3 - shows C - C bond lengths of 1.366, 1.382, 1.391, 1.397, 1.398, and 1.411 Å . 3 7 T he ring shows alternating single and double C - C bond feature in semiquinone , because the electrons are more localized in the C=C bond. This generally exhibit on the short and lon g C - C bond lengths seen in x - ray crystal structure : the C - C bonds are 1.494, 1.430, 1.327, 1.437, 1.355, and 1.402 Å in [Ga(3,6 - DTBSQ) 3 ]. 40 The C - C bond lengths within the bridging ring show a various range (Table 4. 2 .) : 1.38 2 1. 400 Å in complex H; 1.38 2 1. 414 Å in complex F; 1.3 93 1.40 1 Å in C omplex 22 1 ; 1.3 82 1.407 Å in C omplex 23 ; 1. 390 1.40 9 Å in C omplex 24 . More physical evidence and characterization are needed to interpret the bond information, and will be further discussed in Chap ter 5. 204 Th e C - O bonds in quinoidal ligands can also provide information about the oxidation state of the ligands. 3 6 - 3 8 The C - O bond lengths are close in values in semiquino i dal complexes, e.g. 1.2 71 Å and 1. 262 Å in [Ga(3,6 - DTBSQ) 3 ]. 3 7 The C - O bond distances exhibit similar difference in catecholate complexes compared with the semiquinoidal analogue , e.g. 1.3 37 and 1.3 51 Å in [Ga(Cat) 3 ] 3 - . 30 However, C - O bond distances cannot be a valid indication for the oxidation state in the se gallium complexes reported her e, since their differences are not negligible (Table 4 . 1 and 4.2 ). Even though the C - O bond lengths are not identical, they are all much longer than the reported C - O bond length in chromium - semiquinoidal complexes. 3 8 The information obtained from the cryst al structure determination of these gallium systems are preliminary. There are not enough similar structures reported in literature for a fair comparison, although the ones cited here are Ga(L) 3 complexes instead of Ga(tren)(L). The development of [Ga(tren )(3,6 - DTBCat)] + and [Ga(tren)(3,6 - DTBSQ)] 2+ can be useful and informative to better understand how C - C and C - O bond distances manifest on the oxidation states on both chromium and gallium complexes , since our group already develop a mechanism for the synth esis and recrystallization of their chromium analogues. It will still be highly desirable to structurally compare [ Ga 2 (tren) 2 (L cat,cat )] 2+ and [ Ga 2 (tren) 2 (L sq,cat )] 3+ so that more evidence of how the oxidation state impact the various bond distance can be discussed. The similar challenge is faced for the recrystallization of x - ray quality crystal for [Cr 2 (tren) 2 (L sq,cat )] 3+ , and they ha ve thus far been unsuccessful. 205 Figure 4.4. Shift in spin ( red ) and charge ( blue ) density at the oxygen atom for a series of substituted - anilate, naphthalene, and anthracene bridging radicals. The % change is referenced to the parameters obtained for [Ga 2 (tren) 2 (DHBQ sq,cat )] 3+ (i.e. R = H, where spin = 0.102 - electron and charge = - 0.558 electron). 206 4.5.3 DFT Calculations The same substituents and derivatives calculated for the deprotonated trianionic ligand radicals in Chap ter 2 were performed on the Ga(III) dimeric systems to further examine the spin and charge delocalization effects when these radi cal ligands are coordinated to two Lewis acid Ga(III) ions. The spin and charge density of Ga(III) paramagnetic complexes show slight discrepancy compared with the computational results of deprotonated trianionic free ligands in Chapter 2. Among the halogen series, the DFT results predict spin delocalization corresponding a decrease of spin density on the interacting oxygens . T he spin delocalization effect is the most significant in I - substituted Ga(III) complex. Excess - spin on the four ox ygen and the adjacent carbon atoms of L sq,cat bridge is shown in Fig. 4. 4 , and this essentially reflect on the molecular orbital picture of the SOMO of the complexes (see f ig ures in Appendix). The - spin induces - spin at adjacent positions, i.e. the midd le two carbons and the substituents, is a result of the spin - polarization mechanism. 41 - spin density is sparse on the oxygens in the Br and I - substituted Ga (III) complexes, and this shows that as the electronegativity of the halogenated substituents decr eases. The spin moving away from the oxygen atoms is indicative of spin delocalization. - spin density on F and Cl indicates they effectively induce spin delocalization, whereas no such an effect is observed on the protio, Br, and I - substituted systems (F ig. 4. 5 ). Charge density is the smallest in [Ga 2 (tren) 2 (IA sq,cat )] 3+ , which suggests the formation of this complex is unfavorable. Both Complex 24 and 29 are proved to be unstable even being stored in the dark under inert atmosphere. The instability of these complexes matche s the DFT results . 207 (a) (b) (c) (d) Figure 4. 5 . E xcess spin density associated with the highest energy, singly - occupied molecular orbital of Complex 25 ( a ) , 26 ( b ), 28 ( c ) and 29 ( d ). According to J coupling constants obtained for dichromium(III) analogues, no significant change of J was caused by substituting F, Br, and I, except the Cl - substituted moiety. A drastic increase of J is observed for both Complex 3 and 13 . The experimental results of the halogenated Cr(III) dimers disagree with the trend predicted by NPA analysis . However, it will be insufficient to equate Cr(III) with Ga(III). Ga(III) is a much weaker Lewis acid and it does not have a partially filled metal d orbital for orbital overlap between the metal and ligand . F is a special halogen with extremely large electronegati vity, and it has almost no effect when substituting on aromatic rings. Iodine is less electronegative with extreme large electron cloud and weaker electron withdrawing effect. In general, DFT calculation fails to correctly calculate spin density trend for halide. In order to evaluate how well DFT predicts spin delocalization in both vertical and horizontal extended conjugated system, the Cr(III) series is used as reference due in fact that the Ga(III) analogues have not been successfully synthesized. In ge neral, reduction of J caused by spin delocalization is observed both experimentally and computationally in naphthalene and 208 anthracene dichromium(III) assemblies (Fig. 4.2). With NMe 2 electron donating group substituting on the phenyl group, more metal and ligand orbital mixing is promoted to delocalize spins. The diminishing of J is observed, which is consistent with the computational result. Figure 4.6. Weak bonding interaction between th e Ga(III) 3d , 4s , 4p orbitals and two energetically different SQ - SOMO orbitals, where the - HOMO - - LUMO gap is labeled in red . Figure 4 . 7 . % Change spin density vs . - HOMO - - LUMO gap (eV) parameters for digallium (III) - tetraoxosemiquinones complexes. 209 Orbital mixing is considered as the major reason of spin delocaliz ation caused by substituents or ligands with extended conjugated structures. When a substituent is strongly electron withdrawing (left in Fig. 4.6), the ligand SO MO is lower in energy with less mixing between Ga(III) 4s orbital and ligand LUMO to stabilize - HOMO. This results in a larger - HOMO - - LUMO gap. If a substituent is strongly electron donating (right in Fig. 4.6), the ligand SO MO is higher in energy with more mixing between Ga(III) 4s orbital and ligand SO MO to destabilize - HOMO, and a smaller - HOMO - - LUMO gap is resulted. Therefore, spin density should increase as a function of - HOMO - - LUMO gap. A correlation (r = 0.88) between the change of spin density and the frontier molecular orbital gap is plotted based on the result obtained computati onally (Fig. 4.7) . This correlation is not very strong with NMe 2 - Ph A as an outliner, so it is inconclusive to based off computational results for the prediction of spin polarization by the cause of - HOMO - - LUMO gap. A better understanding of the electron ic structures is required for a more complete orbital picture, and EPR spectroscopy of this substituted Ga (III) series will be useful. The J values extrapolated from the magnetic data of both [Cr 2 (tren) 2 (NMe 2 - PhA cat,cat )](BPh 4 ) 2 ( 7 ) and [Cr 2 (tren) 2 (NMe 2 - PhA sq,cat )](BPh 4 ) 2 (BF 4 ) ( 17 ) show a slight weakening effect of spin exchange. The spin density plot (Fig. 4. 8 ) shows that - spin density spreading from the two Cs in the middle to the N Me 2 substituted phenyl ring as an indication of spin delocalization i nduced by the substituted phenyl ring. 210 Figure 4. 8 . The SOMO ( a ) orbital picture and total spin density ( b ) distribution plot of [Ga 2 (tren) 2 ( N Me 2 - Ph A sq,cat )] 3+ based on NPA of single point energy calculations. As reported previously in our group, 45 electron polarization in complexes with inter - ring structure reflects mostly as a function of 2 p - 2p orbital overlap between the inter - ring C - C. Better overbital overlap with coplanar geometry facilitates electron delocal ization. Orbital overlap can be quantified with overlap intergral S as a function of distance r (Eq. 4.1) and dihedral angles (Eq. 4.2) between orbitals. 45 ,47 (4.1) (4.2) where , Z* is the effective atomic number, n is the principle quantum number, and a o is the Bohr radius. 47 Unfortunaly, no x - ray quality crystal was collected for [Ga 2 (tren) 2 (Ph A cat,cat )] (BPh 4 ) 2 , and [ Ga 2 (tren) 2 (Me - AnT cat ,cat )](BPh 4 ) 2 has not been synthesized. These two systems are essential for a better understanding on how substituent affect the electronic structure of paramagnetic (a) (b) 211 species . Therefore, the syntheses of these tw o Ga(III) complexes need to be continuously pursued to illustrate this effect. Both [Cr 2 (tren) 2 (Me - AnT cat,cat )](BPh 4 ) 2 ( 10 ) and [Cr 2 (tren) 2 (Me - AnT sq ,cat )](BPh 4 ) 2 (BF 4 ) ( 19 ) were synthesized, quasi - reversible and reversible redox potential were observed electrochemically (detail discussion see Chapter 5) . However, only [Cr 2 (tren) 2 (AnT cat,cat )](BPh 4 ) 2 was detected by ESI - MS, and the electrochemical data indicate th is system is not chemically reversible. This implies [AnT sq,cat ] 3 - is a weaker Lewis base compared with [Me - AnT sq,cat ] 3 - . The larger charge density in [Ga 2 (tren) 2 (Me - AnT sq,cat )] 3+ (Fig. 4.2) is indicative of better stability compared with [Ga 2 (tren) 2 (AnT sq,cat )] 3+ . 4.5.4 Magnetic Properties of [Ga 2 (tren) 2 (L sq,cat )](BPh 4 ) 2 (BF 4 ) Variable - temperature magnetic susceptibility data were collected for [Ga 2 (tren) 2 (L sq,cat )](BPh 4 ) 2 (BF 4 ) in solid state in a temperature range of 2 350 K at applied field of 1.00 T. [Ga 2 (tren) 2 (L sq,cat )](BPh 4 ) 2 (BF 4 ) is a paramagnetic complex without exchange coupling taken, because it only contains one paramagnetic center, the bridge radical ( S = ½ ) . The spin of ground state for these systems can be calculated from the effective magnetic momen t (Eq. 4.1). While the plot shows the magnetic moment of Complex 27 was constant while temperature increased. The constant experimental magnetic moment, µ eff =1.64 µ B , reflected in the data indicates S = ½ (i.e. µ s.o. =1.73 µ B ) , as expected for the semiquinone form of the bridge. (4.1) However, the magnetic data of Complex 25 and 28 show temperature dependence, which should not be observed for a paramagnetic sample (Fig. 4 . 9 ) . Magnetic defect was also observed 212 in Complex 26 with a huge increase of magnetic moment when temperature increases. It is suspected that these samples are not pure , because temperature independent paramagnetism (TIP) contribution will not be as signif icant. This set of data need to be recollected with pure complexes. Figure 4. 9 . Plots of the effective magnetic moment versus temperature for all samples in solid states, Complex 25 , 26 , 27 and 28 . Magnetic susceptibility measurement cannot be performed on [ Ga 2 (tren) 2 ( IA sq ,cat )] (BPh 4 ) 2 (BF 4 ), because this compound slowly decomposes even under inert atmosphere. Therefore, [ Ga 2 (tren) 2 ( IA cat ,cat )] (BPh 4 ) 2 needs to be freshly prepared and immediately oxidi zed to [ Ga 2 (tren) 2 ( IA sq ,cat )] (BPh 4 ) 2 (BF 4 ) for measurement. 213 4.6 Concluding Comments This chapter illustrated the development of digallium(III) - semiquinone complexes. This series is developed initially for the study of ground state electronic structure due to d 10 spectroscopic silent characteristic of gallium(III). Ga(III) is chosen also due to it similar charge - over - radius ratio to Cr(III). DFT calculation has continuously be proven as effective tool to provide insight about spin delocalizatio n effects. The spin polarization calculated computationally on the digallium(III) semiquinone complexes manifest on the experimental of the corresponding Cr(III) analogues, and the trend of spin polarization predicted computationally matches the experiment al observation. One of the biggest obstacles is the synthesis of t he fully reduced anilate , because they are extremely air - sensitive . T heir syntheses and purification procedures need to be performed under inert atmosphere with Schlenk line technique , and the purification steps have to proceed in an inert gas - filled glovebag for product extraction . In addition, the fully reduced iodoanilate is extremely unstable even stored in dark under inert atmosphere. It has to be coordinated to Ga(III) immediately; oth erwise, the ligand will decompose within one hour. Even with the difficulties, a complete series of the halogenated digallium(III) complexes was synthetized usefully , and x - ray quality structure of the catecholate derivatives were determined. [Ga 2 (tren) 2 (I A cat,cat )](BPh 4 ) 2 is light sensitive and unstable even stored under inert atmosphere. This complex is stable for about a week upon coordination with Ga(III); however, it slowly starts to decompose over 1 month. In order to study the photophysical and magne tic properties of this iodo analogue, it needs to be freshly prepared. Similar instability was observed for [Ga 2 (tren) 2 (IA cat,cat )](BPh 4 ) 2 (BF 4 ). 214 In general, the synthesis of the digallium(III) assemblies is harder than their dichromium(III) analogues , sin ce Ga(III) is a weaker Lewis acid . For the reaction of the Ga(III) phenylanilate compound, [M] 3+ species was observed by ESI - MS with no detection of [M] 2+ species. i t is hard to conclude the identity of the product solely based on the result from mass spectrometry . DFT calculation s conducted on this free ligand suggests it is a very weak Lewis base with significant decrease of charge density in Chapter 2, so this complex is likely to be synthetically unfavorable wit h small formation constant. The identification of this compound will be continuously discussed along with its electrochemical data in Chapter 5. As a paramagnetic compound with S = ½, the magnetic data should show temperature independence at high temperat ure with µ eff close to 1.73 µ B . All of the data collected for these halogenated series (Fig. 4.6) have effective magnetic moment around 1.6 µ B . However, significant temperature dependence trend was observed in Complex 26 , 27 , and 28 . The products may cont ain impurity contribute to this feature. Due to the instability of Complex 29 , there was not enough sample for magnetic measurement. Therefore, variable - temperature magnetic susceptibility measurement should be conducted on the halogenated di gallium(III) c omplexes again, even though the absence of these data does not affect the discussion in this project. 215 APPENDIX 216 APPENDIX Figure 4 . 10 . 1 H NMR of THB in CD 3 CN. Figure 4 . 11 . 13 C NMR of THB in CD 3 CN. 217 Figure 4 . 12 . ESI - MS of H 4 CA. Top: calculated isotope pattern for [M - H] - (C 6 O 4 H 3 Cl 2 ). Bottom: experimental result. Figure 4 . 1 3 . ESI - MS of H 4 BA. Top: calculated isotope pattern for [M - H] - (C 6 O 4 H 3 Br 2 ). Bottom: experimental result. 2 18 Figure 4 . 1 4 . ESI - MS of H 4 FA. Top: calculated isotope pattern for [M - H] - (C 6 O 4 H 3 F 2 ). Bottom: experimental result. Figure 4 . 1 5 . ESI - MS of H 4 IA. Top: calculated isotope pattern for [M - H] - (C 6 O 4 H 3 I 2 ). Bottom: experimental result. 219 Figure 4 . 1 6 . ESI - MS of Complex 20 . Upper left: top, calculated isotope pattern for [M] 2+ (Ga 2 C 18 O 4 H 38 N 8 ); bottom, experimental result. Upper right: top, calculated isotope pattern for [M] 3+ (Ga 2 C 18 O 4 H 38 N 8 ); bottom, experimental result. Lower: top, calculated isotope pattern for [Ga(tren)(C 6 H 2 O 4 )] + (Ga C 12 H 20 O 4 N 4 ); bottom, experimental result. 220 Figure 4. 1 7 . ESI - MS of Complex 25 . Left: top, calculated isotope pattern for [M] 3+ (Ga 2 C 18 O 4 H 38 N 8 ); bottom, experimental result. Right: top, calculated isotope pattern for [Ga(tren)(C 6 H 2 O 4 )] + (Ga C 12 H 20 O 4 N 4 ); bottom, experimental result. 221 Figure 4 . 1 8 . ESI - MS of Complex 22 . Left : top, calculated isotope pattern for [M] 2+ (Ga 2 C 18 H 36 O 4 N 8 Cl 2 ); bottom, experimental result. Right : top, calculated isotope pattern for [Ga(tren)(C 6 Cl 2 O 4 )] + (GaC 12 H 18 O 4 N 4 Cl 2 ); bottom, experimental result. 222 Figure 4 . 1 9 . ESI - MS of Complex 21 . L eft: top, calculated isotope pattern for [M] 2+ (Ga 2 C 18 H 36 O 4 N 8 F 2 ); bottom, experimental result. R ight: top, calculated isotope pattern for [Ga(tren)(C 6 F 2 O 4 )] + ( Ga C 12 H 18 O 4 N 4 F 2 ); bottom, experimental result. 223 Figure 4. 20 . ESI - MS of Complex 26 . Left: top, calculated isotope pattern for [M] 3+ (Ga 2 C 18 H 36 O 4 N 8 F 2 ); bottom, experimental result. Right: top, calculated isotope pattern for [Ga(tren)(C 6 F 2 O 4 )] + (Ga C 12 H 18 O 4 N 4 F 2 ); bottom, experimental result. 224 Figure 4 . 21 . ESI - MS of Complex 23 . Upper left: top, calculated isotope pattern for [M] 2+ (Ga 2 C 18 H 36 O 4 N 8 Br 2 ); bottom, experimental result. Upper right: top, calculated isotope pattern for [M] 3+ (Ga 2 C 18 H 36 O 4 N 8 Br 2 ); bottom, experimental result. Lower: top, calculated isotope pattern for [Ga(tren)(C 6 Br 2 O 4 )] + (Ga C 12 H 18 O 4 N 4 Br 2 ); bottom, experimental result. 225 Figure 4. 22 . ESI - MS of Complex 28 . Left: top, calculated isotope pattern for [M] 3+ (Ga 2 C 18 H 36 O 4 N 8 B r 2 ); bottom, experimental result. Right: top, calculated isotope pattern for [Ga(tren)(C 6 Br 2 O 4 )] + (Ga C 12 H 18 O 4 N 4 Br 2 ); bottom, experimental result. 226 Figure 4 . 2 3 . ESI - MS of Complex 24 . L eft: top, calculated isotope pattern for [M] 3 + (Ga 2 C 18 H 36 O 4 N 8 I 2 ); bottom, experimental result. R ight: top, calculated isotope pattern for [Ga(tren)(C 6 Br 2 O 4 )] + (Ga C 12 H 18 O 4 N 4 I 2 ); bottom, experimental result. 227 Figure 4 . 2 4 . ESI - MS of [Ga 2 (tren) 2 (PhA cat,cat )](BPh 4 ) 2 . Left: top, calculated isotope pattern for [M] 2+ (Ga 2 C 30 H 46 O 4 N 8 ); bottom, experimental result. Right: top, calculated isotope pattern for [Ga(tren)(C 18 H 10 O 4 )] + (Ga C 24 H 28 O 4 N 4 ) ; bottom, experimental result . Figure 4.25. Total spin density associated with the highest energy, singly - occupied molecular orbital of [ Ga 2 (tren) 2 ( CA sq,cat )] 3+ (left), and [ Ga 2 (tren) 2 ( CN A sq,cat )] 3+ (right). 228 Figure 4.26. Total spin density associated with the highest energy, singl y - occupied molecular orbital of [ Ga 2 (tren) 2 (CF 3 A sq,cat )] 3+ (left), and [ Ga 2 (tren) 2 (OMeA sq,cat )] 3+ (right). Figure 4.27. Total spin density associated with the highest energy, singly - occupied molecular orbital of [ Ga 2 (tren) 2 (NMe 2 A sq,cat )] 3+ (left), and [ Ga 2 (tren) 2 (PipA sq,cat )] 3+ (right). 229 Figure 4.28. Total spin density associated with the highest energy, singly - occupied molecular orbital of [ Ga 2 (tren) 2 (PhA sq,cat )] 3+ (left), and [ Ga 2 (tren) 2 (NMe 2 - PhA sq,cat )] 3+ (right). Figure 4.29. Total spin density associated with the highest energy, singly - occupied molecular orbital of [Ga 2 (tren) 2 (NH 2 - PhA sq,cat )] 3+ (left), and [Ga 2 (tren) 2 (CN - PhA sq,cat )] 3+ (right). 230 Figure 4.30. Total spin density associated with the highest energy, singly - occupied molecular orbital of [Ga 2 (tren) 2 (CF 3 - PhA sq,cat )] 3+ (left), and [Ga 2 (tren) 2 (NAT sq,cat )] 3+ (right). Figure 4.31. Total spin density associated with the highest energy, singly - occupied molecular orbital [Ga 2 (tren) 2 (AnT sq,cat )] 3+ (left), and of [Ga 2 (tren) 2 (Me - AnT sq,cat )] 3+ (right). 231 Figure 4.32. Total spin density associated with the highest energy, singly - occupied molecular orbital of [Ga 2 (tren) 2 (Ph - AnT sq,cat )] 3+ (left), and [Ga 2 (tren) 2 (CNPh - AnT sq,cat )] 3+ (right). Figure 4.33. 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Thermodynamics of Heisenberg Spin Exchange Coupling Reflected on Electrochemical Properties: Comparison of Chromium (III) and Gallium (III) Dimeric Complexes 5.1 Introduction Metalloproteins have been intensively researched for decades on the spectroscopic and magnetic properties on how exchange coupling affects the electronic structures, chemical reactivity, and biological func tions. 1 - 6 Many metalloproteins contain one or more paramagnetic metal ions in their active sites. For those systems with two or more paramagnetic center, the spin exchange interaction can be an important phenomenon to affect their electronic structure, opt ical, electrochemical properties, and even biological function. The studies by Bertrand and Gayda 7 on rubredoxin and ferredoxin show a shift of the redox potential of Fe 2+/3+ in superexchange - coupled ferredoxin [2Fe - 2S] is generally c.a. 100 mV more negati ve than the non - coupled rubredoxin (Fig. 5.1 ) . first experimental evidence proposing the hypothesis of Heisenberg spin exchange affecting the electrochemical properties of a biological system. Similar phenomenon was obs erve d on the electrochemical properties of [Cr 2 (tren) 2 (CA)] n+ reported by Dr. Guo in our group. 8 Spin exchange - coupled [Cr 2 (tren) 2 (CA)] n+ echem , compared with the non - coupled [Ga 2 (tren) 2 (CA)] n+ echem reflects the greater stability of [Cr 2 (tren) 2 (CA)] n+ , which suggests the spin exchange interaction introduces an added thermodynamic stabilization. Figure 5.1 . The structural representation of protein cluster rubredoxin (left) and ferre doxin (right) active sites. 237 T o further examine the effect of the thermodynamic stabilization by spin exchange interaction and establish the correlation between electrochemical and magnetic behaviors, cyclic voltammetry measurement s w ere performed on Cr (III ) - Cr (III) and Ga (III) - Ga (III) semiquinoidal complexes. 5.2 Electronic Absorption Spectroscopy of Chromium(III) and Gallium(III) Dimeric Complexes General. Electronic absorption spectra were measured using a Varian Cary 50 UV - vis spectrophotometer for all [Ga 2 (tren) 2 (L cat,cat )](BPh 4 ) 2 at a spectral resolution of nm. The high - resolution spectra of [Ga 2 (tren) 2 (L sq,cat )](BPh 4 )(BF 4 ) were recorded on a Perkin - Elmer Lambda 1050 UV - vis/NIR spectrophotometer at a spectral resolution of 0.2 nm. Data were obtained on samples dissolved in MeCN, which had been degassed, dried over neutral alumina, and stored under inert atmosphere. All solutions were prepared in a N 2 - flushed drybox in 1 cm pathlength air - tight optical cells. 5.3 Electrochemistry Studies of Chromium(III) and Gallium(III) Dimeric Complexes 5.3.1 Experimental Sections Electrochemical measurement s w ere collected using CH Instruments CH620D electrochemical analyzer to determine the E 1/2 for the redox properties of [ M 2 (tren) 2 (L cat,cat )](BPh 4 ) 2 , M = Cr (III) or Ga (III ) , in an argon - filled drybox . Solutions of the compounds were prepared in degassed and distilled CH 3 CN or DMF containing NBu 4 PF 6 (ca. 0.1 M) as the supporting electrolyte. The NBu 4 PF 6 salts were crystallized twice in hot EtOH before use. 238 A standard three - electrode setup 9 was used with a platinum or glassy carbon working electrode, a platinum wire counter electrode, and an Ag wire pseudo - reference electrode. 10 All measurements were conducted inside an Ar - purge d glovebox. Data were acquired by cyclic voltammetry (CV) at a scan rate of 100 mV/s , and the differential pulse voltammetry (DPV) data were collected at a scan rate of 20 mV/s with a pulse width of 50 mV . After data collection, ferrocene (Fc +/0 ) 11 , 1 2 or d ecamethylferrocene (DmFc +/0 ) , 13 , 14 depending on where the redox potentials lie for the specific compounds, was added to subsequent solution as internal reference for reported potentials and the reversibility of the compounds. E 1/2 values obtained both from CV and DPV (Fig. 5. 2 ) are comparable : the reversibility of the redox couples was based on the data from CV, and the reported redox potentials were obtained from the DPV peak values. 1 5 Figure 5. 2 . The cyclic voltammogram of [Cr 2 (tren) 2 (DHBQ cat,cat )](BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte . All potentials are referenced to the DmFc +/0 couple (E 1/2 =0 V in MeCN) , and the inserts show the DPV traces . 239 5.3. 2 Electrochemical Properties of [M 2 (tren) 2 (L)] n+ (M = Ga 3+ or Cr 3+ ) . In order to examine the thermodynamic stabilization induced by spin exchange interaction, the cyclic voltammetry electrochemical data of [Cr 2 (tren) 2 (L)] n+ and [Ga 2 (tren) 2 (L)] n+ w ere collected and compared for the effects of thermodynamic stabili zation induced by spin exchange interaction . Decamethylferrocene was used as internal reference for most of our bimetallic complexes, because the potential window of ferrocene, the most common ly used internal reference, overlap s with one of the redox trace s in all dichromium (III) - quinoidal complexes, and the halogenated digallium (III) analogues , except for [Ga 2 (tren) 2 (PhA)] n+ and [Cr 2 (tren) 2 (NAT)] n+ . Thus, data are reported as potential vs the DmFc +/0 coupl ed . The potential window of DmFc slight ly interfere s with the redox trace in [Ga 2 (tren) 2 (PhA)] n+ , and two separate CVs were collected with DmFc +/0 (see Fig. 5. 24 in Appendix) and Fc +/0 (Fig. 5. 3 ) , respectively , for accurate determination of redox reversibility . The electrochemical data is still re ported as V vs DmFc +/0 in order to compare data among the entire series of complexes. To ensure the validity and consistency of reported potential with internal references, another CV was collected with the presence of both DmFc and Fc (see Fig. 5. 25 in Ap pendix). 240 Figure 5. 3 . The cyclic voltammogram of [Ga 2 (tren) 2 (PhA cat,cat )] (BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. The redox potential of ferrocene is at 0.324V. Pt working electrodes were generally employed for most of the CV measurements, but a glassy carbon was used for the data collection of [Cr 2 (tren) 2 (NMe 2 - PhA)] n+ . Some weird features were observed for the CV of [Cr 2 (tren) 2 (NMe 2 - PhA)] n+ (Fig. 5.4) with a Pt working electrode at more oxidative potential, > 0.5 V vs DmFc +/0 , and these features may correspond to the formation of solvento species. Pt is a catalytic and electrocatalytic material, so it might have a more reactive surface. 17 It has been reported that N,N - dimethylaniline can react with tetracyanoethylene to produce N,N - dimethyl - 4 - tricyanovinylaniline and HCN. 16 Since the measurement was conducted in MeCN to ensure consistency for data comparison, similar reaction is predicted to happen, and one of the possible reactions is shown in Fig. 5.6. The CV data was recollec ted for this system with a glassy carbon working electrode, because glassy carbon has slower electron transfer kinetics for most inner sphere processes, 18 so it can prevent overpotential and electrochemical side product deposit on the surface. As shown in Fig. 5.5, 241 weird electrochemistry happened at more positive potential and potentially appeared as solution impurities, so the use of glassy carbon may prevent the side products electrochemical features from reflecting on the CV traces. Figure 5. 4 . The cyc lic voltammogram of [ Cr 2 (tren) 2 (NMe 2 PhA cat,cat )](BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte and Pt working electrode. Figure 5. 5 . The cyclic voltammogram of [ Cr 2 (tren) 2 (NMe 2 - PhA cat,cat )](BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte and glassy carbon working electrode. 242 Figure 5. 6 . Possible reaction of [Cr 2 (tren) 2 (NMe 2 - PhA)] n+ with MeCN to produce HCN and an acetonitrilo - coordinated complex. The cyclic voltammogram (Fig. 5. 5 ) collected in a set - up with a glassy carbon working electrode exhibits less electrochemical features of side products beyond 0.5 V vs DmFc +/0 . It might be not possible to completely eliminate the electrochemical feature if it is caused by the solvento - species. Inert solvents, e.g. dich loromethane, can be used to see if it can eliminate the production of side product; however, the solubility of the complex raises a concern of switching solvent to DCM. The quasi - reversible process is indicative of the instability of [M 2 (tren) 2 (L sq,sq )] 4+ . Upon oxidation, the preferred resonance of the bridging ligand is (L cat,q ) 2 - instead of (L sq,q ) 2 - (Fig. 5. 7 ). This leads to the decomposition of the bimetallic dimer resulting in a monomer, which is detected by ESI - MS as a major byproduct shown in Chapte r 3 and 4 . CVs were collected with various scan rate ranging from 5 0 mV/s to 400 mV/s (Fig. 5.2 5 in Appendix) . At fast scan rate, it showed better reversibility of [M 2 (tren) 2 (L)] 3+/4+ ; at slow scan rate, the intensity of the peak on the reverse scan dimini shed . The reason could be that the slow scan rate allowed sufficient time for the formation of the monomer. Once the production of the monomer happens, this is a direct 243 result of the dimeric complex decomposition. The deformation of the peak on the reverse scan at slow scan rate indicates this redox process is chemically irreversible . Figure 5.7. Resonance structures of dianionic anilate bridging ligand. In [Cr 2 (tren) 2 (NAT)] n+ , only one redox potential with E 1/2 = 0.057 V vs DmFc +/0 was observed (Fig. 5. 8 ), which suggests only one electron redox reaction occured under applied potential. Two possible rationales are rised about the identity of this complex: (1) this is the redox reaction of the monomeric version, ; (2) [Cr 2 (tren) 2 (NAT sq,cat )] 3+ does not e xhibit electrochemical properties at more positive potential. Compared with the other Cr(III) and Ga(III) complexes in the series, E 1/2 +2/+3 generally occur at more negative potential s , but the redox potential observed here is more positive. The change of molecular composition may reflect on its electrochemical properties. Thus, the directionality of potential energy required is not enough to predict the identity of this complex. All three charged species, i.e. [M] 2+ , [M] 3+ , and [monomer] + , were detected by ESI - MS and reported in Chapter 3. Unfortunately, the experimental evidence we have is inconclusive. To rational ize the CV data observed here , a better understanding of the redox and resonance properties of the deprotonated 2,3,6,7 - tetraoxonaphthalene is n ecessary. 244 Figure 5.8. The cyclic voltammogram of [ Cr 2 (tren) 2 (NAT cat,cat )](BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte with Fc +/0 as internal reference. The reported potential is referenced to DmFc couple at 0V vs DmFc +/0 . Figure 5. 9 . Multiple possible chelating forms of deprotonated 2,3,6,7 - tetraoxonaphthalene undergoing one - electron redox reactions. As a highly conjugated system, electrons are more delocalized within the naphthalene rings (Fig. 5. 9 ) with decreased charge density o n the interacting oxygens, so it makes 2,3,6,7 - 245 tetraoxo naphthalene a weaker Lewis base. This implies that the formation of dichromium complex is not as favorable resulting in a less stable system. Upon oxidation, [Cr 2 (tren) 2 (NAT sq,cat )] 3+ may quickly decom pose into the monomer without the formation of [Cr 2 (tren) 2 (NAT sq,sq )] 4+ intermediate. The detection of both [M] 2+ and [M] 3+ also proves the possible occurrence of the redox potential between them. At this point, we cannot assert the mechanism of this redo x reaction, but we incline to proposed the redox trace is indicative of [Cr 2 (tren) 2 (NAT)] 2+/3+ process. No reversible redox process was observed for [Cr 2 (tren) 2 (AnT)] n+ , and the redox potential in DPV traces move as the number of sweep increases (Fig. 5.10) . The unsuccessful synthesis of [Cr 2 (tren) 2 (AnT sq,cat )](BPh 4 ) 2 (BF 4 ) agrees with the electrochemical data collected experimentally, that the formation of [M] 3+ is unfavorable due to the preferred resonance structure of [AnT] 3 - . Fi gure 5. 10 . The cyclic voltammogram of [ Cr 2 (tren) 2 (A n T cat,cat )] (BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte with Fc +/0 as internal reference. The reported potential is referenced to DmFc couple at 0V vs DmFc +/0 . DPV shows in the inserts collected at the 1 st sweep (a), and 2 nd sweep (b). (a) (b) 246 Electrochemical reversibility describes the rate of electron transfer, and a reversible electrochemical reaction needs to meet four requirements. 19 According to the Nernst equation (Eq. 5. 1 ) and the Gibbs Free Energy equilibrium constant , ( 1) the voltage separation between the current peak is p a E p c = in aqueous solution p a is the anodic peak potential, E p c is the cathodic peak potential, and n is the number of electrons , and (2) the position of peak potential, E p a and E p c , will not change as a function of scan rate; (3) the ratio of peak current is , where i p a is the andodic peak current, and i p c is the cathodic peak current; (4) the peak current is proportional to the square root of scan rate. 19 1 ) where E is the applied potential, and Q is the reaction quotation between the concentration of oxidized and reduced species at the electrode surface . Since the electrochemical measurement s w ere performed in nonaqueous solution, 59 mV in organic solvent with lower dielectric constants. Therefore, Fc +/0 and DmFc +/0 couple s are also used as a reference for electrochemical reversibility because of their well - studied electrochemical reversible properties . In reversible reactions, the electron transfer rate is greater than the mass transfer rate, so the peak potential is independent of the applied scan rate during CV measurement. 20 In quasireversible reactions, the electron transfer rate and mass transfer rate are similar; therefore, the peak potential increases as the scan rate increases. 20 The total c urrent of quasireversible redox processes is relatively lower than the one of reversible processes because of the thickness of the diffusion layer in solution. The diffusion layer is thick at fast scan rate, and thinner at slow scan rate. As illustrated ab ove, the reversibility of a n electrochemical process reflects the competition between the electrode 247 kinetics and mass transport, so faster scan rate will encou ra ge electro chemical irreversibility. However, the [Cr 2 (tren) 2 (CA)] 3+/4+ redox trace (Fig. 5. 11 ) shows more electrochemical reversibility with 0/+ ) at higher scan rate , which implies the formation of [Cr(tren)(CA cat,q )] + at more positive potentials and the decomposition of the dichromium(III) dimer . Figure 5. 11 . C yclic voltammograms of the [Cr 2 (tren) 2 (CA cat,cat )] (BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 collected at 20 mV/s ( red dash ), 50 mV/s ( green dash ), and 100 mV/s ( blue solid ). The redox trace of [M 2 (tren) 2 (L)] 2+/3+ observed at negative potential s matches the characteristics of reversibility, whereas the trace of [M 2 (tren) 2 (L)] 3+/4+ shows quasireversible characteristics as shown in the following Eq. 5.2 and 5.3: E 1/2 +2/+3 (5.2) E 1/2 +3/+4 (5.3) vs AgCl/Ag 248 As shown in Fig 5. 12 echem (Eq. 5.4) of [ Cr 2 (tren) 2 (IA)] n+ is smaller than the one of [Ga 2 (tren) 2 (IA)] n+ echem of the Me 2 AnT - Cr (III) complex is the smallest among all the other Cr (III) analogues. echem = E 1/2 +3/+4 - E 1/2 +2/+3 (5.4) Figure 5. 12 . Cyclic voltammograms of [ Cr 2 (tren) 2 ( I A cat,cat )] (BPh 4 ) 2 ( red ) and [Ga 2 (tren) 2 (IA)] n+ ( blue ) in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. All potentials are referenced to the DmFc +/0 couple (E 1/2 =0 V in MeCN) , and Ag wire is the pseudo reference electrode. The Heisenberg exchange interaction occu rs within [ Cr 2 (tren) 2 (IA)] n+ , whereas no intramolecular exchange coupling exists in [Ga 2 (tren) 2 (IA)] n+ echem in the Cr analogue may be the prediction of thermodynamic stabilization induced by the exchange interaction , which will be further elaborated below along with comproportionation constant. T his trend is generally observed throughout the entire series (Table 5.1), so it will be reasonable to believe this as a thermodynamic consequence of exchange interaction. 249 Table 5.1. Electrochemical Properties of [M 2 (tren) 2 (L)] n+ (M = Ga 3+ or Cr 3+ ) . a a All potentials are referenced to the decamethylferrocenium/decamethylferrocene couple ( E 1/2 = 0V). b p anodic E p cathodic . c echem = E 1/2 +3/+4 - E 1/2 +2/+3 . d n.a. indicates the complexes has either not been synthesized, or the redox potential was not detected. e electrochemical reversibility is referenced to Fc 0/+ because of the overlap potential window between the product and DmFc 0/+ . Due to the quasireversi bility and the highly variable oxidative electrochemistry of [M 2 (tren) 2 (L)] 3+/4+ 1/2 3+/4+ echem calculated is also an estimation. echem is only an estimation of the thermodynamic stabilization, it can still be useful for analytical comparison among the substituted complexes to gauge the substituent effect on the electron delocalization. echem of the [ Cr 2 (tren) 2 (Me 2 - AnT)] n+ complex is the smallest among all the other Cr (III) analogues. This provides f urther experimental evidence to rationalize our hypothesis about the attenuation of exchange coupling by spin delocalization reflected both magnetically and computationally, since [ Cr 2 (tren) 2 (Me 2 - AnT)] n+ complex should possess the weakest J (Fig. 5. 13 ) . Some may agree the slight shift of redox potentials may be the cause by the different metal centers. Ga(III) is a weaker Lewis acid than Cr(III), so its ability to attract electrons will be stronger , which may cause the redox potential of Ga(III) complexes more positive and easier to be reduced. If this is true for the prediction of metal redox potentials, Bridging Ligand M +2/+3 +3/+4 echem (V) c DmFc ) (mV) b E 1/2 (V) b E 1/2 (V) b H Cr III - 0.515 72 0.439 119 0.954 85 Ga III - 0.491 78 0.241 128 0.732 72 F Cr III - 0.253 68 0.705 112 0.958 65 Ga III - 0.206 80 0.402 184 0.608 74 Cl Cr III - 0.316 69 0.644 136 0.960 66 Ga III - 0.272 84 0.332 130 0.604 66 Br Cr III - 0.333 72 0.617 137 0.950 79 Ga III - 0.276 80 0.450 124 0.726 68 I Cr III - 0.348 80 0.594 115 0.942 74 Ga III - 0.308 86 0.396 140 0.704 78 Ph Cr III - 0.568 77 0.394 117 0.962 80 Ga III - 0.508 77 0.176 84 0.684 74 N(Me) 2 Ph Cr III - 0.586 66 0.358 100 0.944 66 Ga III n.a. n.a. n.a. n.a. n.a. n.a. NAT Cr III 0.057 71 n. a. n.a. n.a. 70 (vs Fc 0/+ ) e Ga III n.a. n.a. n.a. n.a. n.a. n.a. Me 2 AnT Cr III - 0.19 60 0.503 103 0.693 63 Ga III n.a. n.a. n.a. n.a. n.a. n.a. 250 this trend should be applied for both redox traces in a complex. More positive potential is observed in the redox trace of [Ga 2 (tren) 2 (L)] 2+/3+ , but the potential of [Ga 2 (tren) 2 (L)] 3+/4+ is more negative, which implies it is harder to be reduced. Thus, we predict that the larger potential separation of both redox potentials in the Cr(III) analogues are not a reflection of different metal centers. Figure 5. 13 . Energy level diagram for [Cr 2 (tren) 2 (L sq,cat )] 3+ with (left) stronger spin exchange interaction, larger J ; (right) weaker spin exchange interaction, smaller J. The energy of the lowest energy spin state relative to the spin barycenter , E = 0 (i.e., the energy in the limit of no spin coupling) reflects the thermodynamic influence of spin exchange. 5.3.3 Thermodynamic Stabilization of Spin Exchange Interactions As it has been previously discussed, the Heisenberg model predic ts that the introduction of spin exchange results in the spin state with preferred orientation being stabilized, as illustrated in Fig . 5. 14 . 21 , 22 ex , is a thermodynamic consequence of spin exchange interaction. larger E ex smaller E ex 251 Figure 5. 14 . The s pin ladder of a molecule with S 1 = S 2 = ½ based on the Heisenberg exchange Hamitonian. The red arrow indicates a net thermodynamic stabilization resulted from spin exchange coupling. J values can be extrapolated with the Heisenberg exchange Hamilt onian from variable - temperature magnetic susceptibility measurements. This experimental method reflects the Boltzmann distribution across the spin states of the spin ladder of a magnetic system. Thus , it only provide s information concerning the energ y sepa rations between the spin states relative to each other (Fig. 5. 14 ) . 23 The relative magnitude of ex can be calculated by the eigenvalues generated from the Heisenberg Hamiltonian with J extrapolated from magnetic data . A measurement of the absolute energy of each spin - coupled state is necessary to quantify the thermodynamic consequence induced by the spin exchange interaction. In order to validate the net thermodynamic stabilization energy calculated from magnetic data, an independent experimental analysis is necessary. Electrochemical measurement may be a good choice in accordant to the phenomena observed in our series of dichromium(III) and digallium(III) complexes. 5.3.3.1 Comproportionation Free Energy Comproportionation is a chemical reaction between two reactants with the same composition of elements with different oxidation states to form a product of another oxidation 252 state , which is commonly used to meausre the stability and charge transfer of mixed valence complexes . 21 , 22 , 2 4 Cyclic voltammetry has been developed and widely employed to evaluate the thermodynamic stability of mixed - valence (MV) complexes (Eq. 5.5) . 25 - 27 The c omproportionation constant, K C , (Eq. 5.6) and the free energy of comproportio nation constant, G C , provide alternative means to determin e the degree of electronic delocalization. (5.5) where (5.6) In the studies of MV complexes, K C reflects the stability of the mixed - valence form of the system relative to the other two isovalent species. The bimetallic systems studied in this project are analogous to the MV complexes (Eq. 5.7). According to the EPR studies conducted previously in our group on [Ga 2 (tren) 2 (CA sq,cat )](BPh 4 ) 2 (BF 4 ), the observation of the triplet state suggests the presence of [Ga 2 (tren) 2 (CA cat,cat )] 2+ and [Ga 2 (tren) 2 (CA sq,sq )] 4+ formed by comproportionation. 28 The magnitude of K C repre sents how strongly coupled the metal ion and the bridging lig and are (Eq. 5.8). Therefore, we attempt to use comproportionation constant, K C , to analyze the electrochemical data and the free energy of our systems , since its magnitude reflects a thermodynamic stabilization inherent to the system . (5. 7 ) where (5. 8 ) (5.9) 253 1 - 2 | , (Eq. 5. 9 ) between the electrodes of a cell is a measure of the tendency for a reaction to occur. and Gibb Free energy energy of comproportionation ( E q. 5. 10 ) C , which also evaluates the strength of the exchange coupling between redox centers through the ligand bridge. 25 In this case C ex . In this regard, an electrochemical n experimental mean to determine the thermodynamic stabilization of a system. C = - - 2.303RT log (K C ) ( 5. 10 ) Between the two electrochemical waves in Fig . 5. 12 , the potenti al difference of [Cr 2 (tren) 2 ( I A)] n+ is larger than [Ga 2 (tren) 2 ( I A)] n+ . Compared with [Ga 2 (tren) 2 ( I A)] n+ , the redox potential of [Cr 2 (tren) 2 ( I A)] 2+/3+ is more negative, and the one of [Cr 2 (tren) 2 ( I A)] 3+/4+ is more positive. In other words, [Cr 2 (tren) 2 ( I A sq,cat )] 3+ is harder to be oxidized and reduced at the same time. Th is observation reveals that there should be an intrinsic factor cause [Cr 2 (tren) 2 ( I A sq ,cat )] 3+ to be more stable than the Ga(III) analogue . This intrinsic factor is thought to be spin excha nge interaction, because no exchange interaction presents within the noncoupled [Ga 2 (tren) 2 (CA sq ,cat )] 3+ system . Based on the electrochemical data for [Cr 2 (tren) 2 (CA cat,cat )] 2+ , a net thermodynamic stabilization larger in magnitude is suggested to be induced by the direct exchange interaction between the Cr(III) ions and the CA sq,cat C can be calculated from redox potential difference ( E q. 5.7 ), 29 a nd it corresponds to the comproportionation constant, K C in aqueous solution at 2 98 K ( E q. 5. 10 and 5. 11 ). 26 ( 5. 11 ) 254 K C >1 reflects higher stability of the semiquinone form of the system relative to the other two states as illustrated in E q. 5.8 . Exchange coupling inherent in [Cr 2 (tren) 2 (CA sq, cat )] 3+ is considered to be the contribution of the thermodynamic stabilization, 30 since the CA sq,cat species is subject to significant direct exchange interaction rather than the CA sq,sq and CA cat,cat forms of the diamagnetic bridge. 5.4 Extrapolation of Thermodynamic Stabil ization Energies of Cr(III) Dimers from Magnetic Susceptibility Data by Referencing Ga(III) Analogues T he other intrinsic effects associated with the redox chemistry of the bridge must also be considered . This concept was also introduced for the study of mixed - valence (MV) complexes stating that G C c ould be divided into five intrinsic energetic components of the system. 25 , 31 In E q. 5.9 s is an entropic factor dealing with statistic distribution of comproportionation equilibrium , implying K c = 4 for a symmetric system ; 22 , 2 4 e is the electrostatic force arising from the repulsion of two metal ions bridged by a ligand ; 32 i is an inductive factor dealing with bonding coordination due to metal - ligand interaction ; 32 r is the stabilziation energy of resonance exchange due to electron delocalization . 29 ex term was added later for measur ing a stabilizing influence introduced by exchange coupling, e.g. superexch ange coupling in a MV complex. 25 , 26 c = ( s e i r ) ex ( 5.9 ) c in MV complexes is modified and adopted into our systems. C will be used to evaluate the thermodynamic stabilization arise from exchange interaction for all Cr ( III) dimeric systems, the Ga(III) analogues will be used as a reference point for the electrochemical data acquired on the Cr(III) complex to eliminate oth er energetic factors. With the same oxidation state of the s e may be negligible. Since the 255 overall composition of these tetraoxolene bimetallic compounds are similar with ionic metal - ligand interaction r can also be cancel ed . Cr 3+ and Ga 3+ have similar charge - to - radius ratio and are both relatively redox - inert i is considered to be eliminated by referencing the gallium complex. In c,echem (defined in E q. 5.1 2 ) larger than 1 will reflect s the added stabilization associated with the introduction of spin exchange upon substitution of Ga(III) by Cr(III) (the data is shown in Table 5.1 and 5.2 ). C echem = K C /K C Ga(III)Ga(III) ( 5.1 2 ) i relates to the bonding interaction and coordination between metal centers and the bridging ligand. Ga(III) is a d 10 metal ion with fully occupied d - orbitals, but Cr(III) has only half - filled t 2g orbitals. Table 5.2. Electrochemical an d Magnetic Data for [M 2 (tren) 2 (L)] n+ (M = Ga 3+ or Cr 3+ ) . a Bridging Ligand M echem (V) a K c b ( x 10 12 ) c,echem c ( x 10 3 ) J (cm - 1 ) c,mag d H Cr 3+ 0.954 ± 0.01 14800 5 .8 - 38 0 1 486 Ga 3+ 0.732 ± 0.01 2.55 1 n.a. n.a. F Cr 3+ 0.958 ± 0.01 1 7300 856 - 38 0 1 486 Ga 3+ 0.608 ± 0.01 0. 202 1 n.a. n.a. Cl Cr 3+ 0.960 ± 0.01 1 8800 1081 - 4 30 38 84 Ga 3+ 0.604 ± 0.01 0.173 1 n.a. n.a. Br Cr 3+ 0.950 ± 0.01 12600 6 .3 - 380 1 486 Ga 3+ 0.726 ± 0.01 2.02 1 n.a. n.a. I Cr 3+ 0.942 ± 0.01 9250 10.8 - 38 0 1 486 Ga 3+ 0.704 ± 0.01 0.855 1 n.a. n.a. Ph Cr 3+ 0.962 ± 0.01 2 0200 51.5 - 38 0 1 486 Ga 3+ 0.684 ± 0.01 0.392 1 n.a. n.a. a echem = E 1/2 +3/+4 - E 1/2 +2/+3 . b see Eq. 5.8. c see Eq. 5.10. d see Eq. 5.11. Electrochemical and K C data obtained for Ga (III) - Ga (III) and Cr (III) - Cr (III) complexes are summarized in Table 5.2 . There is an increase of 600 - fold or more in the magnitude of K C upon replacing Ga (III) for Cr (III) depending on the substituents . Therefore, a significant thermodynamic stabilization is se en for the exchange - coupled complex compared with the non - 256 coupled one. The various elevation of c,echem also implies the substituent effect on the strength of spin exchange. Variable - temperature magnetic susceptibility measurements have been performed on ex , a net thermodynamic stabilization energy , is treated as free energy change caused by intramolecular exchange interaction at room temperature. Then, the equilibrium constant can be calculated with th e estimated J value for the c ,mag (Eq. 5.11). c ,mag = exp ( - ex /RT) (5.11) ex corresponds to the ground spin state |5/2, 3>, 4 J , generated by the Heisenberg spin Hamiltonian (F ig. 5. 14 ). c ,mag c ,echem obtained for a particular system agree with each other, a thermodynamic stabilization of spin states is likely to be induced by exchange coupling, which will be proved to be effectively measured by cyclic voltammetr y. T c,echem c,mag even after error propagations . As discussed above, the thermodynamic stabilization observed in electrochemical data reflects thermodynamic free energy, which is a sum of various intrinsic energetic contributions within a spin - coupled system mentioned above . Nevertheless , the thermodynamic stabilization observed in magnetic data is solely contributed from the magnetic spin exchange. Therefore, simply using the Ga(III) - Ga(III) compound as reference may not be able to eliminate i s term s as illustrated in Eq. 5.9 . i C , the free energy of comproportionation cannot be directly used to evaluate the thermodynamic consequence of exchange interaction. There are two possible way to determine and evaluate the strength of ligands and metal ions coordination in Cr(III) - Cr(III) dimer. One way is to conduct infrared or Raman spectroscopy and compare the stretching mode of the metal - oxygen interaction; the other way is to d etermine 257 the metal - oxygen bond length by x - ray crystallography subject to metal ion radius to eliminate the uncertainty. The latter option is more challenging because all attempts of growing single x - ray crystal structure of [M 2 (tren) 2 (L sq,cat )](BPh 4 ) 2 (BF 4 ) have failed. Since x - ray structures were determined for various assemblies of [M 2 (tren) 2 (L cat,cat )](BPh 4 ) 2 , the M - O bond distances can be treated as a reference to provide some insight about the differences between Cr - O and Ga - O bonding nature (see Chapt er 3 Table 3.3 and 3.4, and Chapter 4 Table 4.2). The range of Ga - O bond length is 1.91 1.92 Å , while Cr - O can range from 1.90 1.95 Å. This implies their metal - ligand interactions are different with Cr (III) being a stronger Lewis acid. Even though s , was initially considered as negligible, the entropic contribution of Cr (III) and Ga (III), d 3 vs d 10 , may not be comparable. For a d 5 spin - crossover system, there are less entropic contributions in the high spin state, 33 so it is m ore stabilized than the low spin state and it undergoes a spin - transition at lower temperature . 34 If the similar principle is applied to compare the entropy of d 3 and d 10 , d 3 is more entropically favorable with less electron - electron repulsion. Unfortunate ly, various contradictory theories about the entropy of d 10 electron configuration are reported in literature , it is not certain either d 3 or d 10 has more entropic contribution. In addition to that, the magnetic data were all collected in solid state, an d the electrochemical measurements were performed in solution. Interaction between solvent molecules and the spin - exchanged compounds were not considered based on our comparison. Liquid SQUID variable - temperature magnetic susceptibility should be measured to obtain magnetic data that is comparable with the electrochemical data. 258 5.5 Concluding Comments In this chapter, our main motive is to seek for analytical methodology to establish the thermodynamic correlation seen in both electrochemical and magnetic behaviors . UV - vis spectr oscopy is useful tool to facilitate our understanding of electronic transitions arising by spin exchange interaction. The absorption features observed in our systems match the one reported by Dr. Dong Guo, who previously re ported a thorough study and interpretation on 2 (CA)] n+ . 8 The comparison of electrochemical data collected for both Cr (III) and Ga (III) dimers reve a ls thermodynamic stabilization induced by spin exchange interaction, since Cr (III) complexes gen echem . Spin delocalization effects also reflect on the electrochemical data with [Cr 2 (tren) 2 (Me 2 - AnT)] n+ echem . The spin polarization effect is not pronounced within the halogen series, no drastic differenc e is observed. Unfortunately, the CV trace of [Cr 2 (tren) 2 (NAT cat,cat )] (BPh 4 ) 2 only show one - electron redox echem can be calculated for comparison. Similar situation is observed in [Cr 2 (tren) 2 (AnT cat,cat )](BPh 4 ) 2 . If we want to continue use the horizontal extension of conjugated series as an avenue for the study of substituent effects, EDG need to be installed on the 2,3,6,7 - tetrahydroxynaphthalene to stabilized the system. echem calculated is only an estimation due to the quasireversibilit y of [M 2 (tren) 2 (L)] 3+/4+ , fast - scan cyclic voltammetry measurements with microelectrodes will be useful to learn about the nature of this quasireversible redox process in the future. The concept of comproportionation free energy and constant can be modified and applied in ou r systems as an analytical method to compare electrochemical and magnetic data for evaluating thermodynamic stabilization. H owever, the K c extracted from electrochemical data 259 contains energetic components arising from various term s not just from spin exchange contribution. A more effective way needs to be developed to eliminate the other intrinsic components for a valid comparison. The data comparison also ignores the solvent - molecule interaction in solution by simply comparing sol ution - phase electrochemical data and solid - state magnetic data. Therefore, liquid SQUID measurement should be performed to account for the solvent effect. Overall, we have established a rough thermodynamic correlation between electrochemical and magnetic behaviors . In order to use electrochemical measurement as a quantitative analysis to assess thermodynamic consequence induced by spin exchange interaction, more unknown properties need to be understood with more experimental procedures. 260 APPENDIX 261 APPENDIX Figure 5. 15 . CV of [ Cr 2 (tren) 2 (FA)] (BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. All potentials are referenced to the DmFc +/0 couple . Figure 5. 16 . CV of [ Cr 2 (tren) 2 (CA) ](BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. All potentials are referenced to the DmFc +/0 couple . 262 Figure 5. 17 . CV of [ Cr 2 (tren) 2 (BA)] (BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. All potentials are referenced to the DmFc +/0 couple . Figure 5. 18 . CV of [ Cr 2 (tren) 2 (PhA)] (BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. All potentials are referenced to the DmFc +/0 couple . 263 Figure 5. 19 . CV of [ Cr 2 (tren) 2 (Me 2 - AnT)] (BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. All potentials are referenced to the DmFc +/0 couple . Figure 5. 20 . CV of [Ga 2 (tren) 2 (DHBQ)] (BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. All potentials are referenced to the DmFc +/0 couple . 264 Figure 5. 2 1 . CV of [Ga 2 (tren) 2 (CA)] (BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. All potentials are referenced to the DmFc +/0 couple . Figure 5. 2 2 . CV of [Ga 2 (tren) 2 (BA)] (BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. All potentials are referenced to the DmFc +/0 couple . 265 Figure 5. 2 3 . CV of [Ga 2 (tren) 2 (PhA)] (BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. All potentials are referenced to the DmFc +/0 couple . Figure 5. 2 4 . CV of ferrocene ( at 0.569V) and decamethylferrocene (at 0.06V) in MeCN with 1.0 M TBAPF 6 as supporting electrolyte. 266 Figure 5.2 5 . Cyclic voltammograms of the [Cr 2 (tren) 2 (CA cat,cat )](BPh 4 ) 2 in MeCN with 1.0 M TBAPF 6 collected from 50 mV/s to 400 mV/s . 267 REFERENCES 268 REFERENCES (1) Picraux, L. B.; Smeigh, A. L.; Guo, D.; McCusker, J. K. Inorg. Chem. 2005 , 44 , 7846. (2) Picraux, L. B.; Weldon, B. T.; McCusker, J. K. Inorg. Chem. 2003 , 42 , 273. (3) Blondin, G.; Girerd, J. - J. Chem. Rev. 1990 , 90 , 1359. (4) Wei, P. P.; Skulan, A. J.; Wade, H.; DeGrado, W. F.; Solomon, E. I. J. Am. Chem. Soc. 2005 , 127 , 16098. (5) Chen, P.; Solomon, E. I. J. Am. Chem. Soc . 2004 , 1 26 , 4991. (6) Holm, R. H.; Kennepohl, P.; Solomon, E. I. Chem. Rev. 1996 , 96 , 2239 2314. (7) Bertrand, P.; Gayda, J. Biochim. Biophys. Acta . 1982 , 680 , 331 - 335 . (8) Guo, D.; McCusker, J. K. Inorg. Chem. 2007 , 46 , 3257 - 3274. (9) Elgrishi, N.; Rountree, K. J.; McCarthy, B. D.; Rountree, E. S.; Eisenhart, T. T.; Dempsey, J. L. J. Chem. Educ. 2018 , 95 , 197 - 206. (10) McCarthy, B. D.; Martin, D. J.; Rountree, E. 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Conclusion and Future Directions 6. 1 Future Works Proper substituents need to be chosen with dramatic electron withdrawing , donating , or delicalization effect to systematically modify the strength of the spin exchange interaction . As we observed in Chapter 3, the magnitude of the J constants of the halogenated Complex 2 , 3 , 4 , 5 , 12 , 13 , 14 and 15 falls in the same scale within analytical error, and Complex 8 , 9 , 10 , 18 and 19 with polyaromatic hydrocarbon bridging ligands present more pronounced difference in the magnitude of the J values. T hus, it is important to explore the spin polarization effects on more substituents in order to provide more insightful guide on the choice of substituents. The series of dichromium (III) and digallium (III) complexes in this project are still lacking - d - acceptor to show all possible variations to modulate spin polarization. The syntheses of all substituted ligands are quite challenging because they do not follow similar synthetic schemes. The ir synthe tic routes are still under development, and they will be discussed below along with some suggestions. 6. 1 .1 DFT Calculations General Methods. All electronic structure calculations of deprotonated (L sq,cat ) 3 - anions and [Ga 2 (tren) 2 (L sq,cat )] 3+ cations were carried out using density functional theory implemented in Gaussian 09 20 on HPCC at Institute for Cyber - Enabled Research at Michigan State University . The B3LYP functional with open shelled was used in the calculation. 21 - 25 The calculation wa s performed using the default tight convergence criteria with ultrafine integration grid. Analysis of atomic charge and spin densities were performed using natural population analysis (NPA) framework developed by Weinhold et al. 26 271 6. 1 .1.1 Geometry Optimiz ation and Single Point Energy Calculations The initial geometries of the deprotonated free ligands and Gallium (III) dimeric derivatives were generated using GaussView 27 with subsequently optimized using the UB3LYP functional and a 6 - 31G basis set with imp osed symmetries of C i . Final geometries were checked with frequency calculations at the UB3LYP/6 - 31G level. Imaginary frequencies were obtained for some sterically bulky Ga (III) structures or structures with extended aromatic conjugation. Those structures were reoptimized with increased convergence cycles (default maxcycle = 64) and the exact computed Hessian matrix for frequency calculations with CalcFC or CalcAll command. Heissian matrix is the matrix of second derivatives of the energy in regard to disp lacement of atoms. 28 Frequency calculations generally are based on an estimated Hessian from geometry optimization. 29 Geometry optimizations were then re - run for the Ga (III)structures with UltraFine grid to help obtain smoother convergence to the stationa ry point. Structures were reoptimized with subsequent frequency calculations until no imaginary frequencies, which indicates that the final structures have reached the global minima. The final optimized structures were then used for single - point energy cal culations. Single - point energy calculations were performed using the unrestricted open shelled density function UB3LYP with the 6 - 311G basis set with natural population analysis (NPA) assuming the doublet ground state and a molecular charge of 3+. 6. 1 . 2 Finish the Other Derivatives of the Substituted Anilate and Anthracene Bridging Systems A few other substituents are chosen due to their electron withdrawing and donating ability to complete the series in this project, so we can target and study more thoroughly on substituent effect on the thermodynamics of the spin exchange interactions . The s ynthe ses of these 272 substituted derivatives have been attempted ; however, some of the multi - step synthe tic routes are slightly more challenging. The se synthetic pr ocedures and purification are still under development , which include - CN, - piperidino, and - cyanophenyl . The developed steps are listed below with some suggestion s for improvement in the future . 6. 1 . 2 .1 Synthesis Potassium 2 - hydroxy - 3 - chloro - 6 - cyanoanil ate . 1,2 2,3 - Dichloro - 5,6 - dicyano - 1,4 - benzoquinone (DDQ) (1.44 g, 6.34 mmol) was suspended in 40 mL of H 2 O, and the yellow added dropwise into the DDQ suspension, and the suspension slowly turned dark red. It was was cooled down to RT, the volume of the solution was reduced to one half of its original volume under vacuum, and then it was kept in the fridge overnight for recrystallization. Red crystals formed, which is suitable for x - ray diffraction. The product was filtered, washed with 3M KOH (3 x 30 mL), acetone (3 x 20 mL), and dried in air. Yield: 0.4 g (26%). HRMS [ESI - TOF , m/z (rel. int.)]: [M - K] - Calcd for [C 7 O 4 HNCl] - , 197.9594; Found, 197.9602. [M - K - H - Cl] - Calcd for [C 7 O 4 N] - , 161.9827; Found, 161.9832. 2,5 - Dichloro - 3,6 - dipiperidino - 1,4 - benzoquinone. 5 Unscented laundry detergent (0.5% mol LD) was added in H 2 O (50 mL) to serve as a surfactant to facilitate the dissolution of all reactants. Following by the addition of piperidine (4 mL, 40 mmol), chloranil (2.46g, 10 mmol) and K 2 CO 3 (5.53g, 40 mmol) were added into the suspension while stirring. The suspension turned from y ellow to brown. After overnight stirring, brown products were filtered and washed by H 2 O and Et 2 O. Purple crystals, suitable for x - ray diffraction, were obtained from 273 recrystallization from EtOAc/hexane (4:1). Yield: 1.2 g (35%). 1 H NMR (CDCl 3 , 500 MHz) (ppm): 1.6 - 1.7 (d, 12 H, CH 2 ), 3.48 (d, 8 H, NCH 2 ). 13 C NMR (CDCl 3 , 500 MHz) (ppm): 24.48, 27.12, 53.49, 115.52, 149.55, 176.24. HRMS [ESI - TOF, m/z (rel. int.)]: [M+H] + Calcd for [C 16 O 2 H 21 N 2 Cl 2 ] + , 343.0965; Found, 343.1077. 2,7 - Dimethoxy - 3,6 - di - ( 4 - cyano phenyl )benzoquinone . A mixture of Cs 2 CO 3 (1.6 g, 5.0 mmol), 4 - cyanophenylboronic acid (0.147 g, 4.0 mmol), and Pd(PPh 3 ) 4 (0.06 g, 5 mol%) in 1,4 - 2 . 2,5 - Dibromo - 3,6 - dimethoxy - 1,4 - benzoquinone (0.326 g, 1 .0 mmol) and Ag 2 O (0.58 g, 2.5 mmol) were added into the mixture, and it was filtered through a pad of Celite. Purification of flash silica column with DCM/n - pen tane (6:4) and hexane/DCM/EtOAc (8:1:1) was attempted; however, impurity was still present. The yield of this reaction is too low to be reported. The product was detected by HRMS. HRMS [ESI - TOF, m/z (rel. int.)]: [M+H] + Calcd for [C 20 O 4 H 15 N 2 ] + , 371.1032; Found, 371.1012. 6. 1 . 2 .2 Discussion 3,6 - cyananilic acid , H 2 (CN) 2 An, and 3,6 - piperidinoanilic acid, H 2 ( Pip ) 2 A n, are chosen to examine the electron - withdrawing (EW) and electron - donating (ED) effects respectively on the spin exchange coupling effect , when these substituents directly bind to the benzoquinoidal bridging ligand. Phenyl and 4 - (N,N - dimethylamino) - phenyl substituted Cr(III) dimers have been successfully synthesized to investigate the effects of intraligand electron delocalization, while EW G and EDG are indirectly connect ed through a phenyl group on the bridging ligand. Therefore, the synthesis and study of 4 - cyanophenyl substituted moiety will provide another piece of useful information for our studies on intraligand electron delocalization . In addition, 274 9,10 - diphenylanthracene substituted Cr(III) analogues will serve as an important role for our studies on the effects of horizontal electron delocalization, and whether they will possess added effect on decreasing the strength of spin exchang e coupling. Some of these products have been successfully synthesized, but the reaction yield is too low to be proceeded further. The intermediates of other products have been synthesized; however, some difficulties are encountered for the remaining steps due to the reactivity of th e intermediate products . H 2 ( Pip ) 2 A n . 2,5 - Dichloro - 3,6 - dipiperidino - 1,4 - benzoquinone has been synthesized, 5 and the crystal suitable for x - ray diffraction was collected. However, the hydroxylation of this compound with NaO H following by protonation with HCl was unsuccessful, which can be due to the fact that ch lorine is not acting as a better leaving group with such a strong EWG, piperidino, binding on the 3,6 - positions. The suggestion is to make 2,5 - dibromo - 3,6 - dipieridino - 1,4 - benzoquinone with bromanil as reactant , since brom ine is a better leaving group than chlor ine , and bromanil is commercially available. The resulting product can then be hydroxylated with NaOH, and acidified with H 2 SO 4 , which has the similar procedure with H 2 IA. 6,7 If 2,5 - Di amino - 3,6 - di hydroxy - 1,4 - benzoquinone (H 2 ( NH 2 ) 2 A n ) can be synthesized, it serves the same purpose as H 2 ( Pip ) 2 A n , which is also a n EDG derivative. However, the literature reported methods 8 , 9 are not clear, and the success of synthesis for 2,5 - Dichloro - 3,6 - dipiperidino - 1,4 - benzoquinone lead us to continue pursue piperidino as the chosen EDG. H 2 ( CN ) 2 A n . 1 , 2 Potassium 2 - hydroxy - 3 - chloro - 6 - cyanoanilate (HKCNA n ) was synthesized and obtained as red crystals. 10 ,1 1 In order to substitute the chloro on the 3 - position, this potassium salt was reacted with 2 eq. of KCN in MeOH/ H 2 O (1:1) . 1 2 The reaction was refluxed for 2 h. No product was detected by ESI+ mass spectrometry, and HKCNA was fully recovered. The failure 275 of this reaction can be due to the fact that chloro becomes a worse leaving when being para - substituted with the cyano group . My suggestion is to react either chloranil or bromanil with 4 eq. of KCN under refluxing temperature. H 2 (CN - Ph ) 2 A n . 2,7 - Dimethoxy - 3,6 - di - (4 - cyanophenyl)benzoquinone was synthesized by Suzuki coupling with commercially available 4 - cyanophenylboronic acid r eported in Chap ter 3 with a very low yield. Several different column chromatography , including flash or gravitational columns with silica gel or neutral alumina with various eluents, were attempted, and the purification was unsuccessful. In order to improv e the yield of this step, the first thing is to investigate the most effective and optimal route of the reaction with various Pd catalysts , solvents, reaction time, and temperature based on the work reported by Hu et al 1 3 and Langer et al . 1 4 After finding the most effective Pd catalyst, eluent combination needs to be optimized for column chromatography purification process. Pet. Et 2 O/EtOAc (4:1) is recommended as the first combination to be tested out. 1 5 Another route is to synthesize 2,7 - Dimethoxy - 3,6 - di - ( 4 - bromo phenyl)benzoquinone as an intermediate ; this intermediate can then react with ZnCN with Pd 2 (dba) 3 as a catalyst 1 6 to possibly form 2,7 - Dimethoxy - 3,6 - di - (4 - cyanophenyl)benzoquinone . The latter route is not my primary option, because it involves more steps, which can potentially lead to even lower yield. 6. 1 . 3 Expand the Conjugation of Tetraoxo - Bridging Ligands with 9,10 - Diphenylanthracene, Terrylene, and Pyrene Polyaromatic aroma tic hydrocarbon - system in order to reduce electron repulsion within the rings for its planarity. 18 - stacking in the extended conjugated network allows these ligands to effectively delocalized electrons . The use of naphthalene and anthracene as bridging ligands discussed in Chapter 3 proves that they can 276 effectively delocalize electrons within the systems to exhibit the most significant decrease on the strength of the spin exchange interaction. Pyrene and terr ylene (Fig. 6. 1 ) will be the next targets for our study of spin polarization in spin exchange coupled systems. Density functional calculations were performed on the PAHs free ligands , the change in spin and charge density generated computationally match computational results reported in literature, which suggest that PAHs show bond length alternation with more localized bond and aromatic dilution. 19 - delocalized conjugation, the Lewis basicity of PAHs can be very weak . If they are too weak, the coordination chemistry between the transition metal ions and the deprotonated PAHs may not be thermodynamically favorable. The computational results indicate the decrease of charge density on tetraoxo - phenylanthracene, pyrene and terrylene (F ig. 6.2), so they are proved to be weaker Lewis base computationally. It will be hard to determine if the formation of bimetallic terrylene is feasible due to the drastic decrease shown in its charge density. The charge density of pyrene is comparable with 9,10 - dimethyltetraoxoanthracene, and both [Cr 2 (tren) 2 (Me - AnT cat,cat )](BPh 4 ) 2 and [Cr 2 (tren) 2 (Me - AnT cat,cat )](BPh 4 ) 2 (BF 4 ) were successfully synthesized. Thus, the synthesis of bimetallic pyrene seems to be thermodynamically viable. However, it will be har d to determine if the formation of bimetallic terrylene is feasible due to the drastic decrease of the charge density shown computationally. Figure 6. 1 . The calculated structures of 4,5,9,10 - tetraoxopyrene (left) , and 4,5,12,13 - tetraoxoterrylene (right) . 277 Figure 6.2. Shift in spin ( red ) and charge ( blue ) density at the oxygen atom for a series of deprotonated trianionic tetraoxo - substituted phenylanilate, naphthalene, anthracene, pyrene (PAH), and terrylene bridging radicals. A considerable decrease of charge density was also observed computationally in 9,10 - di phenyl - tetraoxo anthracene (Ph - ANT) , and 9,10 - di( cyano ) phenyl - tetraoxo anthracene (CNPh - ANT) (Fig. 6.2) to show their diminishing Lewis basicity . Thus, the DFT calculations suggest the coordinati on between these bridging ligands and the transitional metal ions may not be thermodynamically favorable. Since the synthesis of H 4 (Ph - AnT) has been developed, characterization and transition metal coordination should be reasonably easy to examine the comp utational prediction . My suggestion is to coordinate the deprotonated H 4 (Ph - AnT) with [Cr(tren)Cl 2 ]Cl . If the synthesis is successful, CNPh - ANT should be synthesized after that, because the DFT result shows a drastic increase on spin density. However, if t he synthesis 278 between H 4 (Ph - AnT) and [Cr(tren)Cl 2 ]Cl is unsuccessful, then the synthesis of CNPh - ANT might be as meaningful. Bimetallic 9,10 - di(cyano)phenyl - tetraoxoanthracene complex may not worth the attempt because its formation does not seem thermodynam ically viable based on the change of charge density shown in DFT calculations . 6. 1 . 3 .1 Synthes is 2,3,6,7 - Tetramethoxy - 9,10 - diphenylanthracene. 3,4 Benzaldehyde (12.5 mL, 122.5 mmol) in MeOH (10 mL) was added dropwise in a stirring solution of veratrole (16 mL, 128.7 mmol) in 2 SO 4 (62 mL) solution was added over 1 - hour period 2 SO 4 solution was added, the reaction mixture became v iscous. The dark purple mixture was poured into 500 mL of ice H 2 O, and precipitation happen over time. The solvent was decanted, and the viscous tacky products were triturated and washed with EtOH. Beige products were dissolved in CHCl 3 , and filtered to el iminate impurity. The solvent was evaporated under reduced pressure. The solids were washed by MeOH. Light pink products were recrystallized from acetone. However, impurity was shown in the 1 H NMR spectrum. Purification with silica flash column (DCM) was a ttempted; however, it was unsuccessful. The impurity is 2,3,6,7 - tetramethoxy - 9,10 - diphenyl - 9,10 - dihydroanthracene, which is the reduced version of the product. 1 H NMR (CDCl 3 , 500 MHz) (ppm): [Product] 3.71 (s, 12 H, OCH 3 ), 6.80 (s, 4 H, ArH), 7.47 (d, 4 H, phenyl - H), 7.52 (t, 2 H, phenyl - H), 7.59 (t, 4 H, phenyl - H). [Reduced form] 3.68 (s, 12 H, OCH 3 ), 5.15 (s, 2 H, 9,10 - dihydro), 6.52 (s, 4 H, ArH), 7.14 (d, 4 H, phenyl - H), 7.20 (t, 2 H, phenyl - H), 7.28 (t, 4 H, phenyl - H). 279 6. 1 . 3 .2 Discussion H 4 (Ph - AnT). 3,17 2,3,6,7 - Tetramethoxy - 9,10 - diphenylanthracene was successfully synthesized; however, a byproduct , 2,3,6,7 - tetramethoxy - 9,10 - diphenyl - 9,10 - dihydroanthracene, which is the reduced form of the product, was also produced. Due to the similarity of size and polarity of this by product with the desired product, purification becomes extra difficult. To prevent the reduction of the product, O 2 can be bubbled through the reaction, or small amount of Ag 2 O can be added at the next attempt. 6.1.4 Fast - Scan Cyclic Vo ltammetry Measurement s As discussed in Chapter 5, [M 2 (tren) 2 (L)] 3 + /4+ is a quasi - reversible redox process , which indicates highly variable oxidative chemistry of [M 2 (tren) 2 (L sq, cat )] 3 + 1/2 extrapolated c,echem may not accurately reflect the degree of thermodynamic stabilization , and this certainly introduces analytical error to c,echem c,m ag . The cyclic voltammetry measurement of both Cr(III) and Ga(III) show s better reversibility of [M 2 (tren) 2 (L)] 3+/4+ at a faster scan rate compared with the data collected at a slow scan rate. In order to establish a qualitative or even a quantitative rela tionship between the electrochemical and magnetic properties for the explanation of the thermodynamic consequence induced by the spin exchange interaction, an accurate c,echem is necessary. The fast - scan cyclic voltammetry measurement e mploying microelectrode methods with a scan rate up to V/s will allow us to investigate if this is a kinetic phenomenon , since increased reversibility of [M 2 (tren) 2 (L)] 3+/4+ was observed at higher scan rate. Unfortunately, this kind of measurement was not done due to the instrumental limitation in our lab. The fast - scan 280 cyclic voltammetry measurement should be researched and conducted for my samples in the 1/2 on the [M 2 (tren) 2 (L )] 3+/4+ redox trace. 6. 1 . 5 Electron Paramagnetic Resonance and DFT Studies of the Electronic Structures of the Semiquinoidal Gallium(III) Dimeric Systems Electron paramagnetic resonance (EPR) spectroscopy can be used to develop a more comprehensive electronic structures of all digallium(III) semiquinone complexes studied in this project, and it has been proved to be an effective tool to characterize the ground states of [Ga 2 (tren) 2 (CA sq,cat )](BPh 4 ) 2 (BF 4 ) and [Ga 2 (tren) 2 (DHBQ sq,cat )](BPh 4 ) 2 (BF 4 ) in a previous stud y reported by our group. 30 Meanwhile, DFT calculations effectively predict spin densities of these paramagnetic systems. 30 DFT calculations were performed on the digallium(III) phenylanthracene, pyrene, and terrylene complexes to provide som e insights about their spin density to verify if their syntheses are necessary (Fig. 6.3). Spin delocalization effects of phenylanthracene, cyanophenylanthracene, and pyrene are predicted to be similar, and decrease of spin density is generally seen in all these three Ga(III) complexes in accordance to the DFT results. The resonance effect makes the most impact on terrylene, but the decrease is similar to the one of Me - AnT. The substituent effects were not making a huge impact on the strength of spin exchan ge for the halogenated Cr(III) complexes, even though the computational results indicate a change in spin density. There might not be significant change of the exchange coupling constants observed experimentally in bimetallic terrylene complexes. Thus, onl y the synthesis of bimetallic pyrene complex is necessary. DFT calculations should be employed to evaluate spin polarization in the future work of this project, since it was able to predict the synthetic difficulty of [Ga 2 (tren) 2 (IA sq,cat )] 3+ elaborated in Chapter 4. 281 Figure 6.3. Shift in spin ( red ) and charge ( blue ) density at the oxygen atom for a series of tetraoxo - substituted phenylanilate, naphthalene, anthracene, pyrene (PAH), and terrylene Ga (III) complexes. 6.1.6 A Broken Symmetry DFT Study for the Spin Exchange Coupling Constants of the Semiquinoidal Cr(III) Dimeric Systems For multiple paramagnetic centered systems, broken symmetry DFT calculations can be conducted on [Cr 2 (tren) 2 (L cat,cat )] 2+ and [Cr 2 (tren) 2 (L sq,cat )] 3+ , so they can provid e information about orbitals involving in the spin exchange interaction and computationally calculate their J values. J values were not accurately determined for neither [Cr 2 (tren) 2 (L cat,cat )] 2+ nor [Cr 2 (tren) 2 (L sq,cat )] 3+ , due in fact that the superexchan ge coupling strength resulted from [Cr 2 (tren) 2 (L cat,cat )] 2+ is too small and the MagFit program fails accurately extrapolate J s. T he 282 magnitude of J constants obtained from the halogenated [Cr 2 (tren) 2 (L sq,cat )] 3+ are too close to show any variation due to the substituent effect . In this case, c omputational results may provide useful information about whether the estimation of J extrapolated from the least square fit falls in a right direction. 6. 1 . 7 Solution - Phase SQUID Magnet ic Susceptibility Measurement s c,echem c,mag reported in Chapter 5 track each other, no trend can be observed to conclude substituent effects caused by electron localization/delocalization within the Cr(III) bimetallic series. One of the hypotheses is that t he magnetic data collected in solid state of these samples do not account for the solvent effect , since the electrochemical measurements were performed in solution. The comparison of thermodynamic energy extrapolated from electroche mical and magnetic data will not be valid by disregarding the solvent interaction. Liquid SQUID variable - temperature magnetic susceptibility should be measured to obtain magnetic data that is comparable with the electrochemical data . MeCN and DMF can be us ed to dissolve the samples for the magnetic measurement due to the solubility of the Cr(III) dimeric complexes in these two solvents. The temperature range suggested for the measurement in MeCN is 230 350 K, and the measurement in DMF is 220 400 K. Liquid SQUID measurement is challenging because of its complicated sample preparation. Former group member, Rich Fehir, attempted to conduct the experiment in a flame seal ed Quartz t ube . 31 Concentration of the samples is one of the biggest challenges in hi s measurement. Since Quartz contributes significantly large diamagnetic background signal , the magnetization of a less concentrated sample can be convoluted by the background signal. Therefore, the concentration of the sample is crucial for liquid SQUID me asurements. Regarding 283 the background signal of a Quartz cell, Dr. Rodolphe Clérac from University of Bordeaux was consulted. His research group focusing on molecular material and magnetism is experienced with various types SQUID measurements and have been employing a sealed plastic straw as a sample holder , which is a similar holder material used for the solid - state SQUID measurement . The background signal of plastic straw is relatively low . Sara Adelman in our group has success with variable - temperature magnetic susceptibility measurement of liquid samples with this kind of sample holder. The challenging part is how to seal the straw to prevent leaking, and it will be beneficial for student s who fallow up this project to talk to Sara about this type of measurement before proceeding. 6. 2 Concluding Comments This chapter described the developed synthetic routes for substituted briding ligands in pursuit of a more complete series of Cr (III) and Ga (III) complexes to fulfil our understanding of substituent effects on spin polarization of spin exchange interactions. A few more choices of substituents , i.e. H 2 ( CN ) 2 A n , H 2 ( Pip ) 2 A n , and H 2 (CN - Ph ) 2 A n , H 4 (Ph - AnT), and H 4 pyrene, are proposed along wit h synthetic modification/sugguestion and computation results. The viability of the synthesis was discussed to avoid unnecessary synthetic difficulties . The syntheses of these ligands are not without obstacles; however, H 4 (Ph - AnT) has been successfully synt hesized and its purification requires more work. The synthetic routes of H 2 ( CN ) 2 A n , H 2 ( Pip ) A n , and H 2 (CN - Ph ) 2 A n are half - developed, and the most challenging parts are the reactivity on the ortho - substituting positions and the development of column chromatography for purification purposes. DFT calculation continuously prove s as an effective tool for the prediction of charge and spin polarization on both paramagnetic deprotonated free ligand and digallium (III) complexe s. It 284 provides useful synthetic direction of PAHs, e.g. the spin polarization effect of b imetallic pyrene does not show drastic impact. Although the spin polarization effect is non - zero, the necessity of the synthesis is low. There are still many unknown properties of these bimetallic - semiquinone complexes. Without better understanding of their electronic structures, the interpretation of certain experimental features will be difficult. EP R spectroscopy is a powerful tool for the study of paramagnetic comp ounds, and it can hopefully provide more insight to facilitate our understanding of the substituent effect on the spin polarization and the spin exchange interaction. The a nalysis to correlate comproportionation constant from electrochemical data and equ ilibrium constant magnetic data were demonstrated. Unfortunately, a few missing pieces of information prevented this analysis from quantifying the thermodynamic consequence of Heisenberg spin exchange. One of them is the disregard of solvent interaction in solid - state variable - temperature magnetic measurement. Herein, liquid SQUID measurement was proposed to consider the solvent effects. Overall, a rough relationship is established between electrochemical and magnetic properties of the molecular systems de veloped in this project. In the future, there are many advantageous and plausible avenues in theoretical chemistry, SQUID magnetic susceptibility, EPR spectroscopy, and synthetic chemistry to continuously pursue the goal of this project. 285 APPENDIX 286 APPENDIX Figure 6 . 4 . ESI - MS of p otassium 2 - hydroxy - 3 - chloro - 6 - cyanoanilate . Right: t op , calculated isotope pattern for [M - K] - ( C 7 O 4 HNCl ) ; b ottom , experimental result. Left: top, calculated isotope pattern for [M - K - H - Cl] - (C 7 O 4 N); bottom, experimental result. 287 Figure 6 . 5 . ORTEP drawing of p otassium 2 - hydroxy - 3 - chloro - 6 - cyanoanilate from single - crystal x - ray structure determination. Atoms are represented as 50% thermal ellipsoids. Hydrogen atoms are omitted for clarit y. Table 6. 1 . Crystallographic data of p otassium 2 - hydroxy - 3 - chloro - 6 - cyanoanilat e. Empirical formula C 7 HCl K N O 4 Formula weight 237.64 Temperature (K) 173(2) Crystal system mono clinic Space group P 2 1 /c a (Å) 7.08810 ( 10 ) b (Å) 1 6.9447 ( 3 ) c (Å) 6.95160 (1 0 ) 102.3740 (10) Volume (Å 3 ) 815.53 ( 2 ) Z 4 Radiation Cu K D calc (g cm - 3 ) 1. 935 Goodness of fit (F 2 ) 1. 201 R 1 (I>2 (I)) a 0.04 72 wR 2 (I>2 (I)) b 0.1 792 a R 1 = b wR 2 =[ ] 1/2 , w=1/[ , where P=[ . 288 Figure 6 . 6 . 1 H NMR of 2,3,6,7 - t etramethoxy - 9,10 - diphenylanthracene in CDCl 3 . The insert showed the formation of 2,3,6,7 - tetramethoxy - 9,10 - diphenyl - 9,10 - dihydroanthracene, the reduced form of the product. 289 Figure 6 . 7 . 1 H NMR of 2,5 - dichloro - 3,6 - dipiperidino - 1,4 - benzoquinone in CDCl 3 . Figure 6 . 8 . 13 C NMR of 2,5 - dichloro - 3,6 - dipiperidino - 1,4 - benzoquinone in CDCl 3 . 290 Figure 6 . 9 . ESI - MS of 2,5 - dichloro - 3,6 - dipiperidino - 1,4 - benzoquinone. Top: calculated isotope pattern for [M+H] + (C 16 H 21 O 2 N 2 Cl 2 ). Bottom: experimental result. Figure 6 . 10 . ORTEP drawing of 2,5 - dichloro - 3,6 - dipiperidino - 1,4 - benzoquinone from single - crystal x - ray structure determination. Atoms are represented as 50% thermal ellipsoids. Hydrogen atoms are omitted for clarity. 291 Table 6. 2 . Crystallographic data of 2,5 - dichloro - 3,6 - dipiperi dino - 1,4 - benzoquinone. Empirical formula C 1 6 H 2 0 Cl 2 N 2 O 4 Formula weight 323.24 Temperature (K) 173(2) Crystal system mono clinic Space group P 2 1 /c a (Å) 6.3855 ( 6 ) b (Å) 8.9434 ( 9 ) c (Å) 13.7532 (13) 9 9 . 9 310(10) Volume (Å 3 ) 773.65 ( 1 3) Z 2 Radiation MoK D calc (g cm - 3 ) 1. 473 Goodness of fit (F 2 ) 1.0 49 R 1 (I>2 (I)) a 0.0 381 wR 2 (I>2 (I)) b 0. 0953 a R 1 = b wR 2 =[ ] 1/2 , w=1/[ , where P=[ . Figure 6 . 11 . ESI - MS of 2,7 - d imethoxy - 3,6 - di - (4 - cyanophenyl)benzoquinone . Top: calculated isotope pattern for [M+H] + (C 20 O 4 H 15 N 2 ). Bottom: experimental result. 292 REFERENCES 293 REFERENCES (1) Atzori, M. 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