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ENE. ouc'\‘.-F\fl.cfl ‘I. l, 0 ‘0: o I ‘I if: .llflt‘l n! ~|c l‘}u’ll.\.$»\(1|n\|‘xl1ur§1| Q" ‘3 I4! «.41. O‘III‘I‘III‘a ‘21“id. 1:01.! .Sio; . ...Ad},». ‘1 I ‘ n ¢ . Y- 2 v ‘leJJIC~|o. tl. .4110 fit-”Haul I 3 . t . u‘!l :tbla . ‘ll‘oI no} I: .. .\.' I \It 4 l\ .\I\‘.I.\1IKIIJ 1L 1 ’ §. - II. .OA ntlt I VII... . . u I 0 J v 4 t‘ k :1)? ) ‘lt 00‘0“ . ‘- Ly! . ‘ A. . 13,! 0 ;s \t. if. :\.yvl.l.o\t\ {32‘ i. 0115‘ Otlvto‘lt ‘t 10 3:00 . . \. 1‘51). 1‘ it: . .3110 n c .‘..v A‘ .. p‘ w u; ‘ . ‘ o . ‘ )1‘.‘(.1 3! 0. k, 1"“; Ii‘lt. I ‘1} le'Qfl-bttlltt. 91.“ ‘ .7 . I , ‘ - tau-I‘ll! Ll- ; Ill. 4 3.» A ‘ ‘ has.“ n v.1!!..1zn1.4-.1A I.. . .. I11 [,1. . ‘ .‘. .i‘nni .‘IVI. .00.!!VJ‘ } | I w. , .: yfr. .. . in! f . 1 -I ill if... Tyt’éffi‘ ’- LIBRARY Michigan State University This is to certify that the m— .. dissertation entitled PHYSICOCHEMICAL STUDIES OF LITHIUM ION SOLVATION AND MACROCYCLIC COMPLEXATION IN AlCl3-BPC1 MOLTEN SALTS . presented by -1 - , Rick R. Rhinebarger has been accepted towards fulfillment of the requirements for Ph.D. degreein Chemistry I Major professor C/ v Date November 7, 1985 MS U i: an Affirmative Action/Equal Opportunity Institution 0-12771 MSU LIBRARIES \— RETURNING MATERIALS: Place in book drop to remove this checkout from your record. FINES will be charged if book is returned after the date stamped below. PHYSICOCHEMICAL STUDIES OF LITHIUM ION SOLVATION AND MACROCYCLIC COMPLEXATION IN AlClg-BPCI MOLTEN SALTS By Rick R. Rhinebarg'er A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Chemistry 1985 ABSTRACT PHYSICOCHEMICAL STUDIES OF LITHIUM ION SOLVATION AND MACROCYCLIC COMPLBXATION IN AlCl3-BPCI MOLTEN SALTS By Rick R. Rhinebarger Multinuclear NMR measurements have been used to study the solvation of various metal ions in the AlCl3-N-butylpyridinium chloride molten salt system. Potentiometry, far-IR spectrophotometry, and x-ray crystallography have provided important supplemental information regarding the nature of the various species and their interactions which occur in this ionic liquid. In addition, the complexation of the lithium ion by crown ethers and cryptand complexants in basic AlClg-BPCI melts has been investigated. Lithium-7 NMR studies indicate that in basic melt at 40°C, the lithium ion exists as both the monomer (Lile) and the dimer (Li20142') chlorocomplexes, with the latter species predominating by a factor of 9:1 at an analytical lithium ion concentration of 1.0 mol96. Potentiometric data confirm that two chloride ions are associated with each lithium ion in basic melt solutions. Lithium-7 chemical shift and spin-lattice relaxation measurements. and the potentiometry results indicate that anions (other than the chloride ion) which are added to basic melt as the lithium salts do not interact with the lithium ion. Rick R. Rhinebarger Concentration formation constants for the 12C4, 15C5, 81505, and 18C6 crown complexes of the lithium ion in basic melt have been determined from the variations of the 7Li chemical shifts with the crown/Li+ mole ratios. The strong ion pairing occuring in these solutions tends to reduce the selectivity of complexation. The crown complex stabilities decrease in the order 15C5 181505 > 1204 > 1806. Slow chemical exchange has been observed in 7Li NMR studies of the complexation of the lithium ion with cryptands C211, C221, 0222, and C2322 at 40°C and a field strength of 42.28 kG. Concentration formation constants for the 0221, C222, and C2322 complexes have been determined, with the complex stabilities decreasing in the order C221 > C222 > C2322. The CZ322°LiAlCl4 complex has been isolated from basic melt, and its crystal structure determined. Potentiometric titrations of LiCl in basic melt with 1505 and C2322 indicate that complexation proceeds with retention of the chloride ions in the crown complex, while the chloride ions are released into the solution in the process of cryptate formation. Far-IR and multinuclear NMR methods have been used to confirm the existence of chlorocomplexes of various heavy metal ions in dilute basic melt solutions of the parent heavy metal chlorides. These complexes appear to be discrete, rather than polymeric species in these solutions. DEDICATION It has been said that tolerance, sensitivity, kindness, love, patience, and a willingness to work hard are all important in the pursuit of an advanced degree. Seemingly endless quantities of these things have been supplied by my wife Carolyn throughout this experience. So to her, and to my daughter Rachel, I dedicate this dissertation. ii I have always had warm regard for the teachers; those who have helped me to learn. However, I have never had much use for professors of know ledge. iii ACKNOWLEDGEMENTS I would like to thank all of the professional staff for their fine work on my behalf over the past four years. I refuse to refer to these people as just "technical staff" since this devalues their true worth; without them, the job just does not get done. I would like to thank Professor Popov for his guidance and friendship throughout this study. I would also like to thank Dr. Klaus Hallenga for his patience as I struggled to learn the NMR technique, and for our many helpful discussions. My very special thanks goes to Sharon Corner who put up with all of my mistakes and the many corrections during the typing of this dissertation. Her fine skills have helped to make this work something of which I can truly be proud. iv TABLE OF CONTENTS CHAPTER PAGE LIST OF TABLES .................................................................................... x LIST OF FIGURES ................................................................................... xiv CHAPTER I - INTRODUCTION AND HISTORICAL PART .......................... 1 A. Introduction .............................................................. 1 B. Historical Part ..................................................................... 2 1. Molten Salts ................... . ................................................... 2 a. Semi-empirical models ................................................ 2 b- Computer simulations .................................................. 4 c. Experimental studies .................................................... 7 (1) general ................................................................. 7 (2) ambient temperature systems ................................. 11 (3) chlorocomplex formation. ....................................... 19 2. Multinuclear NMR .............................................................. 34 a. Introduction ................................................................ 34 b. Lithium-7 .................................................................... 35 c. Other metal nuclei ....... . ............................................... 41 3. Crown and Cryptand Complexation of Lithium Ion ............... 42 a. Introduction ........................................................ . ...... 42 b. Solution studies ................................................... . ....... 43 c. Complex structures ..................................................... 47 v CHAPTER PAGE CHAPTER II - EXPERIMENTAL PART AND DATA TREATMENT .............. 51 A. Experimental Part. ..................................................................... 51 1. Molten Salts ................................................................... 51 a. Melt Preparation .......................................................... 51 (1) AlCl3 distillation ................................................... 51 (2) BPCl synthesis ...................................................... 53 (3) melt batch mixtures .............................................. 54 b. Purification of Solutes .................................................. 55 (l) lithium salts ......................................................... 55 (2) heavy metal compounds ......................................... 55 (3) crown and cryptand ligands ..................................... 56 c. Melt Solution Preparation ............................................. 56 (1) mole ratio samples ................................................ 56 (2) isolation of solid compounds .................................. 58 2. Lithium-7 N MR ................................................................... 59 a. NMR of Solutions ......................................................... 59 (1) chemical shift measurements .................................. 59 (2) spin-lattice relaxation measurements ...................... 61 b. NMR of Solids ............................................................. 63 3. NMR of Other Nuclei .. ........................................................ 65 4. Potentiometry .................................................................... 67 . a. Cell Design .................................................. . .............. 67 b. Titration Methods .. .......... . ........... . ............ ....... . ...... 74 (1) titration of pure basic melt and basic melt solutions of lithium salts .......... ................... 74 vi CHAPTER (2) titration of LiCl-basic melt solutions with crown and cryptand ligands........ ............................. 5. Infrared Spectrophotometry .................................................. a. Instrumentation ........................................................... b. Cell Configuration ....................................................... B. Data Treatment ........................................................................ 1. Lithium-7 NMR .......................................... . ....................... a. KINFIT Nonlinear Least Squares Curve Fitting Program ............................................... . ....................... b. Nicolet 1180 NTCCAP Subroutine......... ......................... c. Relaxation Data Reduction ............................................ 2. Potentiometry ................................... . ....... ...................... CHAPTER III - SOLVATION AND CROWN ETHER COMPLEXATION OF THE LITHIUM ION IN THE AlCl3-BPCI SYSTEM .......... A. Introduction ............................................................................... B. Salvation of Lithium Salts in Basic and Acidic AlClg-BPCI Melts ...................................................................... 1. Lithium-7 NMR .................................................................. a. Chemical Shift Studies ........................ , ........................... (1) Lithium Salts in Basic Melt ........... I ......................... (2) Lithium Salts in Acidic Melt ................................... b. Spin-Lattice Relaxation Measurements ............................ 2- Aluminum-27 NMR ............................................................... 3- Potentiometry ...................................................................... 4. Far-IR Measurements ........................................................... C. Complexation of the Lithium Ion in Basic Melt by Crown Ethers ........................................................................................ 1. Lithium-7 NMR .................................................................... 2. Potentiometry .......................................................... . ........... vii PAGE 75 75 75 76 76 76 76 77 78 80 84 84 84 84 84 84 95 98 109 113 121 126 126 136 CHAPTER PAGE D. Conclusions ........ . ........ .............. . ........................................... 1 40 CHAPTER IV - LITHIUM CRYPTATE FORMATION IN THE AlCl3—BPCl SYSTEM ........................................................ 142 A. Introduction .............................................................................. 142 B. Basic Melt Solution Studies ......................................................... 142 1. Lithium-7 NMR ................................................................... 142 2. Potentiometry ....................................................... . ............. 165 C. Characterization of the Solid Lithium Cryptate Complexes ........... 168 1. Elemental Analyses .. ........... . ........ . ................. . .................... 168 2- Lithium-7 Magic Angle Spinning NMR .................................. 170 3. The X—ray Crystal Structure of C2322-LiA1C14, ...................... 177 D. Conclusions ............................................................................... 184 CHAPTER V - HEAVY METAL CHLOROCOMPLEX FORMATION IN THE AlCl3-BPCl SYSTEM .......................... . .................. 188 A. Introduction .............................................................................. 188 B. Salvation of Heavy Metal Salts in Basic and Acidic AlCl3-BPC1 Melts ...................................................... 188 1. Basic Melt Solutions ........................................................... 188 2. Acidic Melt Solutions .......................................................... 192 C. Solution NMR Studies ................................................................ 194 1. Cadmium-113 NMR ............................................................ 194 2. Tin-119 and Tin-117 NMR .................................................... 196 3. Zinc-67 NMR .............................................................. 201 4. Mercury—199 NMR ................ . ............................................. 201 5. Copper-63 and Lead-207 NMR ................... . ......................... 205 D. Far-IR Measurements of Heavy Metal Salt—Basic AlCl3-BPCI Melt Mixtures ......................................................... 205 E. Conclusions .............................................................................. 213 viii CHAPTER PAGE CHAPTER VI - SUGGESTIONS FOR FUTURE STUDIES ............................. 217 A. Lithium Chloracomplexes in Basic Melt ....................................... 217 B. Macracyclic Complexation of the Lithium Ian and Other Alkali Metal Ions .............................................................. 217 C. Heavy Metal Ion Chlorocomplex Formation .................................. 218 APPENDICES ......................................................................................... 220 Appendix 1 ........................................................................................ 220 A. The Two-Site Fast Exchange Model for the Determination of Equilibrium Constants ...................................................... 220 l. SUBROUTINE EQNS. .................................................... 223 B. The Three-Site Fast Exchange Model for the Determination of Equilibrium Constants ..................................................... 227 1- SUBROUTINE EQN- ...................................................... 229 Appendix 2 ...................................................................................... 231 A. Crystallographic Data for the 02322°LiAlCl4 Complex .......... 231 1. Bond Distances and Bond Angles ..................................... 231 2- Least Squares Planes .................................................... 231 REFERENCES ........................................................................................ 241 Table 10 11 LIST OF TABL. Melting Points of Some Low-Melting (Tm < 300°C) Organic Salts. ......................................................................................... Law and Ambient Temperature Halacuprate Molten Salt Mixtures. ............ . ........................................... . ......... . ........... Physical and Transport Properties of the AlCl3-BPCl and AlC13—ImCl Molten Salt Systems. ............ ‘ ............................... Species Characterization in the AlCl3-BPCI and AlClg—ImCl Molten Salt Systems. .................................................................. Absorption Spectroscopic Parameters for Chloracomplexes in AlCl3-BPCI and AlClg-ImCl Melts. ........................................... Lithium-7 T1 Relaxation Times in Various Media. ......................... Crystalline Crown Complexes of the Lithium Ion. ......................... NMR Characteristics of Selected Nuclei Studied in AlCl3-BPC1 Melts ........................................................................ Chemical Shift Reference Solutions Used in NMR Measurements of Other Nuclei in AlClg-BPCI Melts. ..................... Lithium-7 Chemical Shift Data for LiCl—Basic Melt Solutions at 40°C. .................................................. . .................................. Lithium-7 Chemical Shift Data for LiCl-Acidic Melt Solutions at 40°C. ....................................................................... Page 12 17 23 32 38 49 66 69 88 99 Table Page 12 Lithium-7 T1 Relaxation times for Aqueous LiCl and LiClO4 Solutions at 25°C and 40°C. ........... . .................................... 101 13 Lithium-7 T1 Relaxation Times for Some Lithium Salts in the AlCl3-BPCI System at 25°C and 40°C.. .............. . ................... 103 14 Lithium-7 Nuclear Quadrupole Coupling Constants in Various Substances. ...................................................................... 106 15 Lithium-7 T1 Relaxation Times for 1.0 M0196 MC] in Basic Melt as a Function of Temperature (40°C to 85°C). ........................ 107 16 Linewidths (Avl/g) and Apparent Spin-Spin Relaxation Times (rig) for the 7Li NMR Signal of 1.0 M0196 LiCl in Basic Melt as a Function of Temperature (27°C to 150°C). ........... 110 17 Potentiometric Titration Data: Corrected Values of X01- Calculated by Using Equation 53; pCl = -Log X01" ......................... 117 18 Values for nP9e, n*Cl", “°LiX9 and "*total Used in the Calculation of x for the Assumed LiClxu‘X) Chloracomplexes Formed in MG] and LiClO4—Basic Melt Solutions...“ ................................................................................. 122 19 Lithium-7 Chemical Shifts as a Function of Crown/Lithium Ion Mole Ratio in Basic Melt at 40°C- ............................................ 128 20 Lithium Ion-Crown Complex Formation Constants and Limiting Chemical Shifts for the Crown Complexes in Basic Melt at 40°C. ................................ . .................................... 134 21 Log K3 and 5c Values for Lithium Ion-Crown Complexes in Basic AlCl3-BPCI Melts and in Various Nonaqueaus Solvents. ...................................................................................... 1 3 5 xi Table Page 22 Potentiometric Titration Data: Observed Cell Potentials as a Function of 1505 Titrant(mg) and the 1505/Lithium Ion Mole Ratio at 35°C. ................................................................. 137 23 Lithium-7 Chemical Shifts Observed for the Cryptand 0211, 0221, 0222, and 02322 - Lithium Ion Mole Ratio Studies in Basic Melt at 40°C. ........................................................ 152 24. Calculated Linewidths of the 7Li NMR Signals of the Li+-0222 Complex in Basic Melts at 40°C. ..................................... 158 25 The Fractions of "Free" and Complexed Lithium Ion Obtained by Deconvolution of 7Li NMR Spectra in the Cryptand/Lithium Ion Mole Ratio Studies in Basic Melt. Cryptate Complex Formation Constants Calculated by Using Equation 13. ...................................................................... 162 26 Lithium Cryptate Stability Constants in Basic Melt, Water, and Various Nonaqueaus Solvents. ............................. . .................... 164 27 Potentiometric Titration Data: Observed Cell Potentials as a Function of 02322 Titrant(mg) and the 02322/Lithium Ion Mole Ratio. .......................................... . .......... ............... 167 28 Summary of the Elemental Analyses of the 02322-LiA1012 and 0211-LiA1014 Cryptate Complexes. .......................................... 169 29 Lithium-7 Solid State NMR Results for Various Lithium Compounds. .............................................. ...... . ......... . ............. 175 30 Crystallographic Parameters and Data Collection Conditions for the Determination of the Structure of the 02322-LiAlCl4 Cryptate Complex. ................................................ 179 xii Table Page 31 Some Important Bond Distances (X) and Band Angles (Degrees) for the 02322-LiAlCl4 Cryptate Complex. ....................... 130 32 Least Squares Calculations: The Deviations (X) of the Lithium Ion from Coincidence with Planes Defined by Sets of Oxygen and Nitrogen Atoms in the 02322~LiAlCl4 Cryptate Complex. ...................................................................... 186 33 Heavy Metal Chlorides in Basic AlCl3-BP01 Melt: Minimum Solubilities at 25°C. ..................................................................... 189 34 Elemental Analyses of the Solid Adduct of SnCl4 Isolated from Basic AlClg-BPCI Melt Solution. ........................... . ................ 193 35 Mercury-199 NMR Chemical Shift Data for HgClZ-Basic AlCl3-BP01 Melt Solutions. .......................................................... 203 36 Far-IR Bands and Assignments for the Normal Mode Vibrations of the A1014‘ Ion in Basic AlCl3-BPCI Melt. ,,,,,,,,,,,,,,,, 203 37 Far-IR Studies of Heavy Metal Chloride-Basic A1013-BP01 Melt Solutions: Band Frequencies and Assignments. ,,,,,,,,,,,,,,,,,,,,,,, 210 38 Raman and Far-IR Studies of the Sn0162‘ Chloracomplex in the Solid State. ........................................................................ 215 xiii LIST OF FIGURES Log N versus M0196 A1013: Populations of AlCl4", A12017‘, and 01' ions as a function of mole fraction A1013 in the AlCl3-BPCl molten salt system. ................................................... E(V) is, Al reference electrode versus mole fraction A1013: Potentiometric titration curve for the Co/Co2+ couple as a function of mole fraction A1013 in the AlCl3-BPCl molten salt system. Taken from reference 74. . ....... .................. Schematic curve depicting the potentiametric titration of dilute metal chloride - basic AlCl3-BPCI melt solutions. ............ Pyrex ampule used for A1013 distillations ...................................... Intensities of the 7Li NMR signal of 4 _lV_I LiClO4 in D20 versus pulse width for the 10 mm high frequency probe. ................. Concentration electrochemical cell used in potentiametric titrations of basic AlCl3-BPCl melt solutions. .............................. Lithium-7 NMR spectrum: 1.0 M0196 LiCl in basic AlCl3-BPCl melt at 40°C. .......................................................... Concentration dependence of the 7Li chemical shift of LiCl in basic melt at 40°C. ......................................................... Computer analysis of the observed dependence of 7Li chemical shifts on LiCl concentration in basic melt. ..................... xiv Page 15 29 30 52 64 73 85 87 90 ii Figure 10 ll 12 13 14 15 16 17 18 19 Structures of the LiSCN dimers and tetramers in nonaqueaus solvents: A. Dimer; B. Tetramer. Taken from references 164 and 165. .............. . .................................................................. Proposed structure of the lithium enalate triple ion - Li+C211 complex. ......................................................................... Proposed structure of the lithium dimer Chloracomplex in LiCl—basic melt solutions. .................................. . ...................... Lithium-7 chemical shifts versus temperature for 1.0 mol96 LiCl in basic melt. ............................................................... Lithium-7 NMR spectrum: 1.0 mol% LiCl in acidic AlCl3-BP01 melt at 40°C. ............................................................ Lithium—7 NMR spectra: Signal intensities versus delay time for 4 M LiClO4 in D20 at 40°C. ............................................. Ln (1/1‘1) versus 1/T(K) for 7m in 1.0 mol% LiCl-basic melt solution. .......................................................... . ................... Ln(1/T*2) versus 1/T(K) for 7Li in 1.0 mal% LiCl—basic melt solution. ............................................................................... Aluminum-27 NMR spectrum: 45 mol% AlCl3-BPCl melt Aluminum-27 NMR: linewidth as a function of composition in AlCl3-BPCl melts at 36°C. Taken from reference 182. ............................................................................................. XV Page 91 93 94 96 97 100 108 111 112 114 Figure 20 21 22 23 24 25 26 27 Patentiametry:Ecen versus acidic melt titrant (g) for the titration of 45 mol% AlCl3-BP01 melt. The results for duplicate titrations are shown: Titration #1 (O), Titration #2 (0). The uncertainties in the cell potentials and in the mass of the titrant are smaller than the size of the data points. ........................................... Patentiametry:Ecen versus pCl (corrected) for the titration (#1) of basic melt with acidic melt titrant. Potentiometry:Ecen versus acidic melt titrant (g) for the titrations of 0.977 mal96 LiCl-basic melt (0) and 0.960 mol% LiClO4-basic melt (D) solutions. The uncertainties in the cell potential and in the mass of the titrant are smaller than the size of the data points. ........... ............. Far-IR spectra (150 to 600 cm‘l): A. Basic melt; B. 1 mol96 LiCl-basic melt solution; 0. 1 mal% LiCl-1.5 mol96 0211-basic melt solution. .......................... ...... . .......... Far-IR spectrum (150 to 650 cm‘l): 1.0 mol96 6LiCl in basic melt. .............................................................................. The structures of 1204, 1505, 31505, and 1806. Lithium-7 chemical shifts as a function of ligand/lithium ion mole ratio for the determination of the concentration formation constants of Li+-crawn complexes in basic melt at 40°C. Solid lines are the computer-generated curves. 00 OOOOOOOOOOOOOOOOOOOOOOOOOOOOOO 00 ....... 0 000000000000 0000000000000 000000 0 0000000000 Potentiametry:Eceu versus 1505 titrant (mg) and 1505/lithium ion mole ratio. ..................................................... Page 115 119 120 123 125 127 132 139 Figure Page 28 The structures of 0211, 0221, 0222 and 023222. ........... ............ 143 29 Lithium-7 NMR spectrum: 0.985 mol% LiCl—0.888 mal96 0211 in basic melt at 40°C. The upfield signal is assigned to the complexed lithium ion site .................................................... 144 30 Lithium-7 NMR spectrum: 0.992 mol% Li01-0.988 mol96 0221 in basic melt at 40°C. The upfield signal is assigned to the complexed lithium ion site. .................................................. 145 31 Lithium-7 N MR spectrum: 0.980 mol96 LiCl—0.987 mol96 0222 in basic melt at 40°C. The position of the maximum of the unresolved bandshape is taken to correspond to the chemical shift of the complexed lithium ion site. ...................... 146 32 Lithium-7 N MR spectrum: 1.00 mol% LiCl—0.949 mol96 02322 in basic melt at 40°C. The upfield signal is assigned to the complexed lithium ion site. ................................................. 147 33 Lithium-7 chemical shifts for "free" and complexed lithium ion at 40°C as functions of the 0211/lithium ion mole ratio in basic melt. Uncertainties in the chemical shifts are indicated by the size of the data points. .......... . ........ .............. 149 34 Lithium-7 chemical shifts for "free" and complexed lithium ion at 40°C as functions of the 0221/lithium ion mole ratio in basic melt. ....................................................................... 150 35 Lithium-7 chemical shifts for "free" and complexed lithium ion at 40°C as functions of the 02322/lithium ion mole ratio in basic melt ......................................................................... 151 36 Lithium-7 NMR spectra: Observed bandshapes at 40°C for 0222/lithium ion mole ratios of 0.757 to 2.80:1. ........................ 155 Figure ‘ Page 37 Lithium-7 chemical shifts for the Li+-0222 complex in basic melt at 40°C as a function of the 0222/lithium ion mole ratio. ............................................................................. 157 38 Patentiametry:Eceu versus 02322 titrant (mg) and the 02322/lithium ion mole ratio. ....................................................... 166 39 Lithium-7 solid state NMR spectra: Static (tap) and magic . angle spinning (@2.7 kHz) (bottom) spectra for polycrystalline LiCl at 22°C (100 scans). ........................................ 171 40 Lithium-7 Solid State NMR spectra: Static (top) and magic angle spinning («11.8 kHz) (bottom) spectra for polycrystalline LiAlCl4 at 22°C (100 scans). .................................... 172 41 Lithium-7 solid state NMR spectra: Static (top) and magic angle spinning (@2.1 kHz) (bottom) spectra for polycrystalline 02322-LiAlCl4 at 22°C (20,000 scans). ..................... 173 42 Lithium-7 solid state NMR spectra: Static (top) and magic angle spinning («10.8 kHz) (bottom) spectra for polycrystalline 0211-LiAlCl4 at 22°C (20,000 scans). ....... . .............. 174 43 Atomic numbering scheme for heavy atoms in the 02322 molecule. .................................................................................... 178 44 The crystal structure of 02322-LiA1014: The 02322- LiAlCl4molecule viewed along the _b_ axis. ....................................... 181 45 The crystal structure of 02322-LiA1014: A view of the unit cell-along the 9 axis. . ........................ . ......... ..................... 182 46 The crystal structure of 02322-LiAlCl4: A view of the unit cell along the _a_ axis. .............................................................. 183 xviii Figure 47 48 49 50 51 52 53. 54 55 56 The crystal structure of 02322-LiA1014: A closeup view of the cryptated lithium ion. The oxygen and nitrogen atoms are labeled according to the scheme in Figure 43. ............... Cadmium-113 NMR spectrum: 2.88 mol% 0d012 in basic AlCl3-BP01 melt at 40°C. Chemical shifts are scaled to 0.5 M 0d012/D20 taken as 0.0 ppm. ........................................ Cadmium-113 NMR spectrum: 3.95 mol% 0d012 in acidic AlCl3-BP01 melt at 40°C. Chemical shifts are scaled as in Figure 48. ......................................................................... Tin-119 NMR spectra: 3.29 mal96 SnClg (A) and 0.955 mal% SnClg (B) in basic AlCl3-BPCI melt. ................................... Tin-117 NMR spectrum: 3.29 mol% Sn012 in basic AlCl3-BPCI melt. ...................................................................... Zinc-67 NMR Spectrum: 1.56 mal96 Zn012 in Basic AlCl3-BPCI melt. ...................................................................... Mercury-199 NMR: Chemical shifts versus mol96 HgClz in basic AlCl3-BPCl melts. ........................................................ Far-IR spectrum (150 to 600 cm'l): Basic AlCl3-BPCl melt; A. 0.05 mm spacer; B. 0.1 mm spacer. .............................. Far-IR spectra (150 to 600 cm‘l): Basic AlCl3-BPCl melt solutions of heavy metal chlorides. A. 2.98 mol% CdClz; B. 1.56 mol% ZnClg; C. 6.66 mol% CuCl; D. 2.37 mol% H8C12; E- 3-29 mol96Sn012. ........................................................ Far-IR spectrum (200 to 515 cm‘l): The Sn014 adduct isolated from Basic AlCl3-BPCl melt solution. ............................. xix Page 185 195 197 198 200 202 204 207 209 214 CHAPTER I INTRODUCTION AND HISTORICAL PART A. Introduction A comprehensive theory of liquids must account for the physical chemical behavior exhibited by all classes of liquids. The historical development and refinement of this theory has largely proceeded from the viewpoint of molecular liquids and dilute electrolyte solutions. The wealth of experimental data and theoretical contributions of such notables as Raoult, Henry, Gibbs, Fuoss, and many others testify to the tremendous interest in these systems. For molten salts, no less effort has been expended in the development of theoretical models for melt structure, mass transport in molten salts, and melt thermodynamic properties. However, generation of a similarly large experimental data base which could be used to refine these models, has proceeded more slowly than for aqueous and nonaqueaus solutions. This information gap has been most pronounced in the area of spectroscopy. Information from this source could provide valuable insight into melt structure, and aid in the identification of discrete complex ions, whose existence can be inferred from thermodynamic and transport property measurements. Spectroscopic studies have been hampered, at least in part, by the extensive instrumental modifications and special containment methods required for measurements on corrosive, high temperature molten salts. These limitations have had significant impact in the area of nuclear magnetic resonance, where few investigations of molten salts exist. With the recent expansion of the NMR technique to include dozens of nuclei in the periodic table besides proton and carbon-l3, the potential for applications of this method to studies of molten salts is clear. The feasibility for such investigations by N MR techniques has been dramatically improved through the recent development of a new class of molten Salts. These compounds and mixtures have been found to exist as stable, anhydrous ionic liquids near, or even below room temprature. These materials, which usually contain large organic cations and polyatomic inorganic anions, contain several N MR-active nuclei which can be used to probe the chemical and magnetic environment of the melt. Their structural diversity gives rise to numerous vibrational modes that can be studied by using infrared and Raman spectroscopy. Studies of the thermodynamics and kinetics of metal ion solvation and complexation in nonaqueous solvents by using NMR and vibrational spectroscopy have been conducted in this laboratory for many years. Therefore, it seemed logical to include a molten salt as a unique alternative medium, with which similar investigations could be performed. The system chosen for these studies consists of mixtures of aluminum chloride and N-butylpyridinium chloride (AlCl3-BPCI), which are found to be stable liquids near room temperature. Recent work has shown that several alkali metal ions, heavy metal ions, and neutral synthetic ionophores (crowns and cryptands) are soluble in these media. NMR, vibrational spectroscopy, and potentiometry have been used to study ionic association (aggregate formation, metal ion chlorocomplexation) and macrocyclic complex formation in the melt. In this dissertation, the chemical and structural factors that influence these interactions are discussed. 8. Historical Part 3.]. Molten Salts B.1.a. Semi-empirical models Theoretical treatments of the structural features of ionic liquids are usually derived from one of two viewpoints. Lattice-oriented models are formulated by considering the liquid state to originate from the fusion of a solid ionic lattice. For gas-oriented models, the liquid is obtained by condensing a vapor of ions. The principal observation that a given model must account for is that the volume of an ionic substance usually increases on fusion, while the mean interionic distance usually decreases (electrostriction). Empty space is therefore introduced in the melting process. The description of this empty space, how it is distributed within the melt, and how it arises (from ionic lattice or ionic vapor), are the main features which differentiate these various models. An early (1964) review by Bloom and Bockris (1) traces the chronological development of these theories from their first formulations in the late 1800's. Based on its ability to better predict thermodynamic and transport properties, Bockris (2) has argued that the hole model (lattice-oriented) originally proposed by Furth (3) must be considered superior to both gas.oriented models, and rigid lattice models. The success of this model may be attributed to its greater structural flexibility, which rigid lattice models do not possess. Holes are imagined to be of variable size, randomly distributed throughout the liquid. More stringent limitations are placed on the size and distribution of the vacancies proposed in the quasi-lattice model of Frenkel (4). The main difficulties encountered with the gas-oriented models are their inability to account for the observed entropies of fusion, and the aforementioned positive volume change and electrostriction on melting (5). It should be noted that the models just described are semi-empirical in nature. Macroscopic properties are calculated as adjustable parameters in the phenomenological expressions for these properties. None of these models provide a complete description of the microphysical situation concerning the type and magnitude of interactions of species in the molten salt. B.l.b. Computer simulations Methods which provide a theoretically more satisfying modeling of molten salt physical properties than empirical models are Monte Carlo (MC) or molecular dynamics (MD) calculations. In these techniques, a mathematical expression assuming pair-wise potential of interaction of the ions is used to compute thermodynamic, transport and structural properties of the ionic liquid. The potential function can include terms for charge-charge, charge-dipole, dipole-dipole, and higher order charge-multipole and multipole-multipole interactions. The starting point for the simulation is usually taken as the rigid ionic lattice at a given temperature (MC), or total energy (MD). Experimental values for lattice distances, ionization energies, and electron affinities are provided for the system to be simulated. With the ever-increasing speed and capacity of modern digital computers, simulations of 1000 or more interacting ions are becoming feasible. The simulation proceeds by first allowing the ionic lattice to "melt", so that a thermally-equilibrated liquid state can be achieved after a number of incremental steps. Pre-equilibrated or "aged" liquid configurations may also be chosen as the starting point of the simulation. In the Monte Carlo method, the multidimensional integrals derived from statistical mechanics are evaluated numerically, allowing calculation of the average energy of the system. A series of configurations (and associated energies) are generated by a random walk procedure, in which the position of a random particle is varied in small, random steps. A comparison of the energy of the new configuration with the previous one is made. If the new configuration is of higher energy, it is discarded. If lower in energy, the new configuration is retained. The resulting configuration chain is used to calculate ensemble average properties. This process can provide exact values in the limit of infinite chain length. To alleviate problems with edge or boundary limits, the small system can be made to behave as an infinite (macroscopic) one by surrounding it with periodically repeated images of itself. Due to the practical (computer time) limits on ensemble size and chain length, the accuracy of calculations of, for example, specific heats or hydrostatic pressures can be poor (6). The molecular dynamics method performs a numerical solution of Newton's equations of motion for a group of particles (ions) constituting a system. The increment used here is a time step, and the computer calculates the forces acting on each particle once during each time step of the simulation. This method enables calculation of time-dependent (transport) phenomena as well as the system thermodynamic properties. The longest calculations of this type cover a time span of about 10’9 seconds, with time steps ranging from 10"15 to 10'11 seconds. The first extensive Monte Carlo computation for an ionic liquid was by Woodcock and Singer (6). These workers calculated the radial distribution function (RDF), normal melting point, and a number of thermodynamic properties (molar heat capacity, compressibility, entropy, etc.) for potassium chloride by using a Born-Mayer-Huggins pair potential of the form «5,410 = cicjr'l + be(B(oij—r)) + Cijl"6 + dijr-s (1 ) where oij, cij, and (iii are obtained from X-ray and spectroscopic data for this salt. By using the MC method, Larsen and co-workers (7) calculated the molar volume, internal energy, entropy, and free energy at zero pressure for liquid sodium chloride and potassium chloride at 1083 K, as well as AV, AE, AS, and AG of mixing for the 1:1 (Na,K)Cl system under the same conditions. The agreement between the calculated and experimental RDF's for the mixture was excellent. Recently, analyses of structure and deviations from ideal behavior for binary molten salt mixtures have been carried out in MD studies of the LiCl-KCI system. In the work by Caccamo and Dixon (8), partial RDF's were calculated for all possible (+,+), (+,-), and (-,-) interactions as functions of melt composition and temperature. Their results indicated that the coordination number (n) of lithium ion was four, and that the partial RDF for Li+-Cl' (gCl-Li (r)) had a well-defined peak at 2.2 2. Both of these results were unaffected by composition or temperature. For comparison, the sum of the Pauling ionic radii for lithium and chlorine is 2.4 X (9). These authors also noted an increase in the calculated Coulombic energy as the concentration of lithium ions was increased. In a latter MD study of the LiCl—KCI eutectic (58.3 mol% LiCl) by Okada e_t a_l. (10), a coordination number of four was also obtained for lithium ion. In addition, the angular distribution function (P-+- (6)) was determined at 668 and 913 K. The P_+.. (6) curves for Cl‘-Li+-Cl" interaction showed maxima at 6 = 100° and 105°, respectively. This indicated that lithium ion has a nearly regular tetrahedral environment of chloride ions in this melt. Moreover, the tendency was toward the perfect tetrahedral angle (109.47°) with increasing temperature, or decreasing lithium ion concentration. Both of these factors would be assumed to produce less interference from the second-neighbor lithium ions. An additional MD study of MX, AX3, and MAX4 mixtures by Saboungi e_t 21' (11) relates most closely to the AlCl3-BPC1 system studied in this dissertation. Their results showed that characteristics of binary MAX4 melts (eg. NaAlCl4) ascribed to covalency and other nonionic pair interactions could be simulated by using the MD technique. Coordination numbers and angular distribution functions indicated the presence of A2X7' (A12C17‘) and A3X10’ (A13Cllo') complexes. For the NaAlCl4 system, the equilibrium constants involving these species were far too large in comparison with experimental data for this system. These authors stated that this lack of quantitative agreement with experiment was due to the fact that no dispersion force terms (which could have produced polarization or covalency effects) were not included in the pair interaction potential. Woodcock has recently reviewed progress in the application of MD calculations to ionic liquids (12). To date, no similar studies of ambient temperature binary molten salt mixtures such as the AlCl3-BPCI system have been published. In addition, the potentially powerful local ordering effect of lithium ion (thus providing a ternary salt system) has not been studied in an ambient temperature mixture. In view of the extensive organometallic chemistry exhibited by lithium, it is possible that the polarizing influence and/or covalent bonding tendency of lithium could result in the formation of lithium complexes with polarizable anions (such as chloride) in a room-temperature melt. B.1.c. Experimental Studies B.1.c.(l) general Experimental investigations of molten salts date back to Michael Faraday, who studied about fifty of these materials. A comparative electromotive force series of the elements, and the fundamental law of electrolysis which bears his name were obtained in these studies (13). Molten salts may be conveniently catagorized in terms of the temperature at which these exist as stable liquids. Alkali and alkaline earth halides, metal chalcogenides, and most transition metal halides and oxides have melting points above 300°C, and are thus referred to as high temperature molten salts. In the liquid state these materials are usually highly corrosive, requiring special containment such as noble metal, quartz, or refractory oxide vessels. A wide range of inorganic and organic salts and their mixtures have melting points between room temperature and 300°C, and may be termed as low-melting molten salts. Silver nitrate (m.p. = 212°C), potassium thiocyanate (m.p. = 173°C), and thallium(III) carbonate (m.p. = 273°C) are typical of the few anhydrous inorganic salts that melt within this temperature range (14). The organic salts in this group possess tremendous structural diversity, combining large organic cations with inorganic (halide, nitrate, perchlorate, etc.) or organic (picrate, benzoate, etc.) anions. A representative list of some of these compounds and their melting points is provided in Table 1. These organic salts are generally non-corrosive to borosilicate glass, and may be handled with high vacuum and controlled atmosphere techniques. A liquid range of 30°C to 100°C is normally accessible for the measurement of temperature-dependent properties, which is small compared to the ranges for high temperature melts. For example, the liquid range for NaCl is in excess of 600°C (14). However, some organic salts, such as 4—methyl-N-methylpyridinium chloride, decompose at their melting points (18‘). The third class of salts are liquid at, or below, room temperature, and sometimes are referred to as room, or ambient temperature melts. Examples of pure compounds of this type are ethylammonium nitrate (m.p. = 8°C) and tetra-N-hexylammonium benzoate (m.p. = -50°C) (15). In addition, 4-ethyl-N-methylpyridinium bromide is a viscous red oil at 25°C (26). However, the majority of ambient temperature melts developed since the early 1950's 3 a: 822.35%ng =5:oneseifiosélzfio-s «a mm 3983 EzzgaEEZEBomTfi mu v2 823:0 E:__onmEE_;5oumn352::fl «a 3 62595 5252:3235-" a N2 863 8352:2235-“ 2 a: 8:26 5352.333234 2 a: 62595 52539335654 3 SN 62595 525223 2 S; 62.520 5253.3 S a: 8225 5352:2232 2 2 82233 eafizcaafimeezi "mu—mm EzzosaEE 28 . 5253.3 . 83:: Eu 3 a: 62.820 Eacofimofiaucofi3.55 3 Sn outage Ezmcowaacozaahou ”33m Since—among 98 82:83 E2333 3 a: 3983 SicoEanaoEnzuobou 2 3 «Eve 535553285-3522285650 2 3 32.3825 Eases—633592-953 3 was 39829.3 EicoEEwgusnuzuabou 3 can oEEoS 535552355953 2 2: 868 EE:oEE£3:omo£Lb "33m EonEEa Enigma one 5355523: 43— 8; «5o.— mfizo: c.5858 83o. 3..an 8.8» v 5.: ”532-33 2:8 «a 3:6.— mfiofiz A Sea... 10 are mixtures of aluminum halides with organic halides. The first system of this type was reported in 1951 by Hurley and Wier (27), who studied the electrodeposition of several metals from a 2:1 mixture of aluminum chloride and N-ethylpyridinium bromide (AlCl3-EPBr; m.p. = -40°C). The same solvent was used by Chum e_t £1, (28) in electrochemical studies of organometallic iron complexes and hexamethylbenzene at 25°C. Osteryoung and co-workers also investigated the electrochemical properties of transition metal carbonyls (28), and electroinitiated Friedel—Crafts transalkylations (29) in AlCl3-EPBr mixtures with benzene. The principal disadvantage of this molten salt system is that only a very narrow composition range, close to the 2:1 mole ratio, is liquid at room temperature. In 1979, Robinson and Osteryoung (20) reported the synthesis of a 'closely related system composed of aluminum chloride and N-butylpyridinium chloride (AlCl3~BPCl). It was found that these mixtures are stable liquids at 40°C over the composition range 0.75:1 to 2:1 AlCl3-BPC1. Since this initial investigation, more than 100 papers have been published describing various studies of this, and other room temperature melts. Chum and Osteryoung (30) have reviewed some of this work (through 1981). In 1981, Wilkes and Levisky (31) described the synthesis of a series of dialkylimidazolium halide salts which, when combined with AlCl3(AlCl3-ImX mixtures), give ionic liquids at or below room temperature across an even wider composition range (0.30:1 to 2:1 AlClg-ImX) than that of the AlCl3-BPC1 system. Two of these salts, l-methyl-3-butylimidazolium iodide and 1-methyl-3-benzyl—imidazolium chloride, were found to be liquid at room temperature. Because of accessibility as liquids at room temperature across a wider composition range, the imidazolium salts have been used more frequently than BPCl in recent room temperature molten salt studies. 11 A novel group of low-melting and ambient temperature molten salt mixtures has been reported by Yoke (32-34) and Bowmaker (25). These materials are combinations of tertiary or quaternary arsonium, phosphonium, piperidinium, or ammonium halides, with cuprous halides. A list of these is given in Table 2. These systems are of interest mainly due to the presence of copper chlorocomplexes such as Cule in these melts. In this historical review, no attempt is made to thoroughly discuss the considerable body of data which has been generated concerning the chemical, spectroscopic, and transport properties of the high temperature and low-melting molten salts. However, specific information on these sytems which relates to this work, particularly in regard to NMR and chlorocomplex formatiOn in molten salts, is referred to as necessary. Readers interested in these data for the high and low-melting systems are referred to the extensive compilations of Janz and various co-workers (35—42). Reviews by Boston (43) and Lind (44) cover progress in the investigations of molten haloaluminate salts, and the physical properties of molten organic salts, respectively. Additional periodic reviews of all aspects of molten salt chemistry by Blomgren and Van Artsdalen (13), Kleppa (45), Yosim and Reiss (46), and Angeli (47) are recommended. B.1.c. (2) ambient temperature systems Mixtures of AlCl3 and BPCl consitute an acid-base system where A1C13 serves as a Lewis acid (chloride ion acceptor), and BPCl as a Lewis base (chloride ion donor). By analogy with the low-melting A1013-MCI (M = alkali metal cation) systems, a number of equilibria involving various melt species have been proposed as follows (48). 12 mm mm mm «m «on «m «m mm mm mm vm 3.7%: azim: mm 2: wcgnmcfi a: o -3096 as H: o -305 8532.820 EESEESESéLh _: o 3896 93 H: o $8.6 "998226 Easctaaafioi mm @ $305 23 H: 9 $85 8:0?2320 Eacofimofiafisb 355:3 ..m=0\oEEo.5 EB:oEE33=n:Zua.53 55032595 8338833523“ gnu—532.820 Eacofigzcocaaboa ~O:U\o£..ozo EsEoEEaEuBuznahoa ~O=O\oc€o_:o #:2558333 _O=O\oo€ozo EsEoEEw—anaboa as o -305 «+£2.55 8:38:26 52855232935 ”Basia. ”5:2..- 33 £3— 8: «5o.— 953: 2:3: $55: :8 :83: ouaasooia 238850... “535‘ o5. 33 .u via... 13 A13+ + 40' =AICI4- (1) 2.41014- : A12C17' + Cl“ (2) A12016 + Cl' ;_-__-‘ A12017' (3) 2.41013 :2 A12C16 (4) AlCl4‘ + A12C16 : A13C110‘ (10) On the basis of Raman vibrational spectra, Gale e_t a_l. (49) reported that unlike the AlCl3-MCI systems, no evidence for free A1013 or A12015 could be found for the AlCl3-BPCI system, even at high (2:1) AlClg-BPCI mole ratios. Assuming that the activities of Al3+ and A13C110‘ ions were negligible, Gale and Osteryoung (48) found that potentiometric data could be adequately fitted to the equilibrium shown in equation (2). Thus, a mole fraction scale equilibrium constant of 3.8 x 10"13 at 30°C was obtained. As the temperature was increased to 175°C, this constant increased to values approaching those found in the AlCl3-MC1 systems at 400°C or 450°C. Schoebrechts and Gilbert (50) obtained a value of 1.2 (:t 0.2) x 10'13 at 40°C. Robinson and Osteryoung (51) later found that addition of 50% (v/v) of benzene in a similar titration had little effect on the equilibrium constant (Keq = 2.2 x 10'13 at 30°C). In solution, AlgCl7‘ and Cl’ ions are the predominant acidic and basic species, respectively. The melt acidity can be changed by variation of the starting component mole ratio within which a homogeneous liquid state is attainable at a given temperature. A convenient means by which the melt acidity can be monitored is by measurement of the chloride ion concentration, 14 or pCl, which is defined by pCl E - log XCI- (6) where xCl" is the mole fraction of free chloride ion in the melt. From the standpoint of A12Cl7' ion, an expression analogous to equation (6) can be defined for p(A12Cl7), but the pCl definition is traditionally used in the literature. This definition presumes the Temkin ideal solution model (52), where the activity of an ion is equal to its mole fraction in solution. Thus, the p01 range for the AlClg—BPCI system spans about 1015 in XCI" at room temperature, which is comparable to the pH acidity scale for aqueous solutions. Mixtures containing excess A1013 (X A1C13 > 0.5) are referred to as acidic melts, while melts with XAICI3 < 0.5 are termed as basic. The neutral melt naturally corresponds to the 50:50 AlCl3-BPC1 composition. In acidic melts, A12Cl7" and AlCl4' ions are the predominant anionic species, and Cl‘ and AlCl4‘ ions predominate in basic melts. A graphical representation of the populations of these anions as a function of A1013 mole fraction is shown in Figure 1. In the Raman experiments cited above (49), bands consistent with chloroaluminate ions were observed at 40°C. The four observed bands were assigned to the AICI4' ion (1:1 melt), verifying the supposed Td symmetry for this species. The relatively poor quality of spectra for the 2:1 melt did not allow an unequivocal interpretation to confirm the expected D3d symmetry for the A12017’ ion. This symmetry group would have been appropriate for an assumed linear Al-Cl-Al bridge. 15 -—..-.-":":"" ., .......-—- \ \ ,."\\ 'ZT \ I. ‘r 15!. -4. _ A|C|4 —-—--— cu- --- '6‘ AI2CI; —.—. 'BP -10)' .‘K x'/ \\ -12L 0......" ‘~~-._ \\ .40 .50 ' .60 L mole fraction AICI3 Figure 1. Log N versus mol% A1C13: Populations of Alle, A12017', and Cl" ions as a function of mole fraction AlC13 in the AlCl3-BPCI molten salt system. 16 Infrared measurements by Gale and Osteryoung (53), and Tait and Osteryoung (54) showed that the v3(F2) band for AlCl4' ion (490 cm‘l, strong) was split into three bands. Thus, the normally infrared-inactive v1(A1) and v2(E) modes appeared as shoulder bands at 476 cm‘1 and 525 cm'l, respectively. This strong perturbation was cited as evidence for substantial association between BP" and AlCl4' ions in these melts. The latter work (54), which included study of the AlCl3-ImCl (ImCl = l-methy1—-3-ethy1imidazolium chloride) system, provided a detailed interpretation of the vibrational modes observed. for the BP+ and Im+ cations. The broadening and low frequency shifts (by 2 to 6 cm‘l) of the cation bands, as compared with those reported for solid N—methylpyridinium iodide, were cited as support for the idea of strong cation—anion associations in the melts. These effects were minimized in highly acidic melts. Only a few investigations of the transport properties of the AlClg-BPCI melts have been reported. Carpio e_t a}: (55) determined the density, specific conductance, and dynamic viscosity of several N-alkyl-pyridinium halides and their mixtures with AlC13 (including 2:1 AlCl3-BPCI) as functions of temperature. Nanjundiah and co-workers (56) measured the density and dynamic viscosity of the AlCl3-BPCI system at 40°C as functions of melt composition. Fannin 93 a1. (57) conducted similar studies on several AlCl3-l,3-dialkylimidazolium chloride mixtures at various temperatures and compositions. Some representative data from these and other studies are shown in Table 3. Ultraviolet and visible spectrophotometric studies of the AlCl3-BPCI melts have been directed mainly to the investigation of chlorocomplexes of various metal cation solutes. A discussion of these studies is given in the following section on chlorocomplexation. 17 62.5.5 5588.52.50-.-.ESE. u .05. A: m. .2... «L: x .... 3... 8 -m.0.< .30... .05. m. 2.... «L: x N... 2.... S. -30.... .u. .05. m... .8... NL: x ..N S... 2. -m.0.< .u. .000 3 En... - 2.... 3. -m.0.< 3.... a. ..~.° m-a. x a.” «a... as .0mm 5. 3.... - 3... 2. -....0.< .n. .m as... - mm... :4 mm .w... «.9. x e.. «a... a. an c...c m-c. x m.m 0.... mm .0mm 3 3.... «L: x m... 2.. a. L”.0... .“N .3. 33%. :LE 7.. . 3:83 3.22. .0... .95... 53% :o: 5.89.; 85:26.80 058% 95E... :8 5...... 3.05.5.0... 0.... 8.3-90... 2.. .c 8.289... 282...... Ba 3322.. .n «3.... 18 The majority of N MR studies of the AlCl3-BPCl melts have been devoted to characterization of ionic associations in these media. Robinson gt a_l. (58) obtained the 1H and 13C NMR spectra for the 1:1 and 2:1 AICl3-BPCI melts, as well as solutions of these melts with benzene. Upon addition of benzene, the aromatic carbon signals of the BP+ cation were observed to shift upfield compared to their positions in the pure melts. This was interpreted as indicating that addition of benzene was responsible for the distruption of cation-anion ion pairing in the 1:1 or 2:1 melt solutions. Taullele and Popov (59) obtained similar results in a high resolution 1H and 13C NMR study of 1:1 AlCl3-BPC1 melt, and mixtures of this melt with nitromethane-D3. For the pure melt, sharp breaks in the 1H chemical shift versus AlCl3-BPC1 mole ratio curves occured at the 1:1 composition at 40°C. These authors concluded that BP+—AICI4' association was essentially quantitative at this temperature. It was also reported in this study that LiCl is soluble in several basic (0.45 5 XA1013 5 0.47) and acidic (0.50 5 XAICI3 5 0.67) AlCl3-BPCI mixtures, as evidenced by the observation of 7Li NMR signals in these samples at 40°C. Lithium chloride appeared to be insoluble (no 7Li NMR signal observed) in melts with the composition of 0.48 _<_ X A1013 5 0.50. Matsumoto and Ichikawa (60) have recently measured the 27A1 NMR spin-lattice (T1) relaxation times for the A1C13-BPCl system at various compositions and temperatures. Single-exponential magnetization recovery curves (inversion-recovery method) were observed for melts with 0.45 _<_ X “(313 5 0.50 and xAlCl3 = 0.67 compositions. The resulting relaxation rates (Ri) were RAICI4- = 55 d: 5 sec"1 (T1 = 18.2 :i: 1.7 'ms) and RA12C17' = ca. 1000 sec‘1 (T1 *1 ms). Between 50 mol% A1013 and 67 mol% A1C13, and above 67 mol% A1C13 compositions, nonlinear logarithmic recovery curves were 19 obtained, indicating the presence of chemical exchange between AlCl4' and AIZCl-y‘, and AIZCI7' and A13C11 0‘ ions, respectively. Wilkes it. a_l. (61) and Fannin _e_t_ £1: (62) have used 1H NMR to study the AlClg-ImCl molten salt system and its mixtures with LiCl or nonaqueous solvents. In the former study, correlations between 1H NMR chemical shifts of the Im+ cation with melt composition were cited as a suitable basis for an analytical method for determining melt composition. In the latter study, the dependence of proton chemical shifts of the 1-methyl-3-ethy1imidazolium cation on the mole fraction of A1013 was observed to be qualitatively similar to that observed for the AlCl3-BPC1 system (58,59), with a clear break in the chemical shift - mole fraction A1C13 curve at X A1013 = 0.5. It was observed that the proton at ring position 2 (H—Z) of the Im+ cation exhibited even greater chemical shift sensitivity to melt composition than that of the ring protons adjacent to nitrogen in the BP+ cation (AS =-l.6 ppm versus -0.45 ppm, respectively). The H-2 proton also showed a small effect (AG =-0.40 ppm) on addition of LiCl as a third component. This was interpreted as indicating that the Li+ cation was competing with the Im+ cation for the Cl“ anion in the melt. The authors devised a quantitative model to fit these chemical shift data by assuming association of the Im+ ion with two or more of the Cl“, AlCl4', or AIZCI7“ ions in the melt (triple ions or higher aggregates; 5-site fast chemical exchange). Efforts to obtain a good fit of chemical shift data for the ternary system containing LiCl were not successful. B.1.c.(3) chlorocomplex formation One of the most controversial concepts in studies of the structure of molten salts is the existence of discrete complex ions. These species have been invoked to explain the non-ideal behavior sometimes exhibited by these systems. For 20 example, for molten mixtures of KCl and CdClz at 780°C, a minimum of equivalent conductance is observed near 2KCl-CdC12 stoichiometry, implying the existenceof the CdCl42’ chlorocomplex (63). The microscopic structural situation in a molten salt is clearly different from that found in an aqueous or nonaqueous electrolyte solution. In the latter, ions are solvated by neutral solvent molecules, whereas in the former, ions are "solvated" by other ions. Therefore, one is faced with the difficult task of trying to distinguish a particular set (m) of X‘ anions clustered about an- M"|+ cation (forming a MXm("’m) chlorocomplex) from all other X‘ anions in the molten salt. Most workers in this area have taken the observation of a vibrational spectrum, consistent with the number of fundamental modes predicted for the assumed symmetry group for the complex, as "proof" of the existence of that species. However, Wilmshurst (64) has argued that for most binary molten salt systems, one can not distinguish between a discrete complex species (a kinetic entity exhibiting normal mode vibrations), and a polymeric complex (exhibiting quasi-lattice vibrations). Although UV-visible absorption spectrophotometry has been used in numerous molten salt studies, the time scale for this technique ("'10'15 sec) is too short compared to the diffusion time (10'5 to 10"8 sec) for the term "complex ion" to be meaningful. Terms such as "configuration" or "center" are used to describe the local structure about the metal ion. Typical examples of these studies are the investigations of nickel(ll) coordination (NiCl42' chlorocomplex) in molten ZnClz-KCI mixtures at 250-900°C by Angell and Gruen (65), and cobalt(ll) coordination (CoCl42‘ chlorocomplex) in molten AlClg-KCI mixtures at 300°C by Oye and Gruen (66). With a time scale of 10’5 to 10"8 seconds, the NMR technique has the 21 potential for providing more convincing evidence for the existence of a complex species in a molten salt than any other experimental method (67). The earliest reported use of NMR to investigate halocomplex formation in these media was by Rowland and Bromberg (68) who observed 205Tl NMR resonance lines for both TP‘ and TlX4" (x = 01- or Br" ions) in molten TlX-TIX3 mixtures. They estimated the average lifetimes of these species to be 10‘5 seconds at 500°C. Hafner and Nachtrieb (69) concluded that overlap of the cation-anion wavefunctions (incipient covalency), rather than induced polarization of the thallium ion by halide ions, was the cause of the observed high sensitivity of 205T1 chemical shifts (AG 'h 2500 ppm) to changes in counterion. Chlorocomplex formation is, of course, a central feature in the AlCl3-BPC1 molten salts. Evidence for the AICI4‘ and A12Cl7' chloroaluminate ions in this system has already been discussed. One of the principal practical reasons for studies of ambient temperature molten salts is their potential use as anhydrous electrolytes in new high specific energy battery systems (70). In the development of such a system, the performance characteristics of anodic and cathodic materials, as well as identification of the majority charge carriers and their transport properties, are of fundamental interest. Therefore, much attention has been devoted to characterizing the properties of metal-metal ion couples, and chlorocomplexes of these metal ions in these melts. Electrochemical methods, UV-visible spectrophotometry, and transport property measurements have been used to acquire this informaiton. Chlorocomplexes of representative, transition, lanthanide, and actinide elements have been studied in the AlClg-BPCI system. In addition, chlorocomplexes of halogens, coordination complexes of several transition metal ions, and the behavior of electrically-conducting polymer films have 22 been studied in these melts (56,71-92). A list of these systems and the techniques used in these investigations is given in Table 4. Chlorocomplex formation constants, where available, are also shown. For dilute solutiOns of solute metal ions in basic melts, free chloride ion is available for coordination of these metal ions, thus forming the metal chlorocomplexes. Chlorocomplexes 'can also form in acidic melt mixtures that contain these metal ions, but the resulting chlorocomplexes have chloride ion/metal ion stoichiometries that are different from those observed in basic melts (see, 93., ref. 89 and 91). With the exception of w20193- and w20192- (83), only mononuclear chlorocomplexes have been observed in the A1C13-BPC1 or A1C13-ImCl melts. Potentiometry has been used to determine the coordination numbers and chlorocomplex formation constants for these species at various temperatures. Using standard cell notation, the cell used in these studies is fritted 67 mol% A1C13- AlCl3-BPC1 glass n+ (7) Al BPCI melt separator melt , M M (see, gg., ref. 76). In this cell, the aluminum electrode dipping into an acidic melt serves as the reference electrode. 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(10) For the cases where other M/Mn+ couples are used in the working compartment, a specific example illustrating the determination of chlorocomplex coordination number (n) and the mole fraction scale formation constant (Kx) is useful. Hussey and Laher (74) studied potentiometrically the Co/Co2+ couple in the AlCl3-BPCI system at 36°C. For the reaction 002+ + 4c1- :2 CoCl42', f (11) the cobalt electrode potential is given by 13w = Eo'x + 51 In xCoz+ (12) 2F 1 where E°x is the mole fraction-based apparent standard potential of the Co/Coz"' couple in a 67 mol% AlCl3-BPC1 melt at 36°C. The titration is carried out by measuring the cell potential as weighed amounts of A1013 are added to the working compartment to increase the melt acidity. The titration curve 28 which is obtained in this experiment is shown in Figure 2. Substituting the equilibrium expression for reaction (11) into the Nernst equation (1 2) yields RT RT __ _ __ _ El 4 _ 2F 1n xCoC142‘ 21, In Kx In x Cl (13) = 0' Ew E x + 2F where the liquid junction potential is assumed to be negligible (82). A plot of Ecell versus in XCI‘ gives a straight line with a least squares slope of 121 :t 2 mV, in good agreement with the theoretical value of 122 mV predicted for fourth-power dependence of the cell potential on xCl‘ for the CoCl42‘ chlorocomplex. In a separate experiment, a value for E“); for the Co/Co2+ couple is determined by adding weighed amounts of CoC12 to 67 mol% AlCl3-BPCI melt in the working compartment, and measuring the cell potential. Using equation (12), the intercept of a plot of Ecell versus ln XC02+ is +0.894 i» 0.002 Volts at 36°C. An average Kx value is then calcualted from several XCI‘ values. Thus, a Kx value of 1.6 x 1046 for CoCl42' is obtained at this temperature. The curves obtained in titrations of this type can be broken down into three regions. This is shown in Figure 3. In the first region, free chloride ion from the melt reacts with the solid AlCl3 titrant to form A1C14‘ ion in solution Cl—(melt) 4' AlCl3 --) AlCl4' . (14) Once the free chloride ion is consumed, chloride ion from the metal chlorocomplex (with general formula MCIX(“‘X)) reacts with AlCl3 according to 29 10 06*- OH- 02’- 6“" vs Al mm, Figure 2. E (V) 1.3- A1 reference electrode versus mole fraction A1013: Potentiometric titration curve for the 00/00” couple as a function of mole fraction A1013 in the AlClg-BPCI molten salt system. Taken from reference 74. 30 l I IIIICI,1 t I dissolved _. REGION 2 I (n-x) J! I MCI complex I I " l titrated I l I I I ' l .J l I < _ l- l I z I m | | " l 2 REGION 1 l I _I K— free chloride ion _‘1 I l -' titrated m | l o .. I l ITI 1‘ REGION 3 MCI" MC' 0 PM forms titrated L l l TITRANT ADDED —-) Figure 3. Schematic curve depicting the potentiametric titration of dilute metal chloride - basic AlCl3-BPC1 melt solutions. 30 l | i um" i I dissolved .— REGION 2 i (n-X) 1' I MCI complex I II " l titrated I I I I I ' I .1 I i ‘ b l- l I z I In | I " I 2 REGION I I I .1 ‘— rree chloride ion —5i I l -1 titrated u: I | o I- I | ITI 1‘ REGION 3 "c'" MCIn PM forms titrated L L L TITRANT ADDED —’ Figure 3. Schematic curve depicting the potentiametric titration of dilute metal chloride - basic AlCl3-BPCl melt solutions. 31 MClx(“'X) + (x—n)AlC13 -—>.MCln + (x-n)AlCl4" (15) Precipitation of the metal chlorides has been reported in potentiametric studies in the AlCl3-BPCI and A1C13-ImCl molten salt systems (FeClg, refs. 56,76; CoClz, ref. 74; NiClz, ref. 71; AgCl, ref. 76; and CuCl, refs. 77,81). From the equivalence point of the titration, the dispersed MCIn precipitate reacts with the titrant to produce the Mn+ cation in solution. M01n + nAlCl3 _, M!” + nAIC14" (16) Further addition of titrant at this point alters the coordination of the metal ion from AlCl4‘ to A12Cl7‘ ions (eq. 17). M(AlCl4)n + nAlZCl7‘ :3 M(A12017)n + nAlCl4" (17) Supporting evidence for the existence of chlorocomplex species and their inferred structures in the AlClg-BPCI or AlCl3-ImCl systems has been given by UV-visible and near-IR spectroscopic studies. A summary of these results is given in Table 5. The number and positions of band maxima observed in these studies are consistent with results previously obtained in aqueous, nonaqueous, or other molten salt media. The UV cutoff of the AlClg-BPCI melts in ca. 275 nm, and ca. 300 nm for the A1013-ImCl mixtures. This has proven to be a serious limitation in the case of FeCl42’ (75), where the nature of the coordination of the metal ion could not be determined due to background absorption of the melt. In summary, electrochemical techniques have been the methods of choice 32 mm 3:. 562383 2. 3m 5:: S 363:8 83. 2:. -202 *BE «.3. $3035 3.... 23 8a 5:: 3 so 82 SN 5:0? $22: «:3 $303 25.: man 5:: 8 no I. 23 m: -302 $3.: «.3. -303 E. 33 2:. m 8:: . v S .36 $3 «2 I 52 835 n 2. IN 55 a; 23 en New 8. so 2 a? :05: 3:. .303: «we cam mam . ace 3. a... ma. ”2 Comm: 3... INEOoO :. we 3: 8o 29:: 3... INEOE .uom PaGEEhm AEO 3.53 A55 San—mud! :0! NOE—=00 v.5. 5...: 65.902 .23 8.5.302 E axe—QEOOEOEO new 230593.— Omaoogaoonw 8398.: m 039—. 33 £829.82 359.8 9: E .52» «o: 983 2536888 :2: Ogooam $5.853 wow: 98 9:9: 553030 "302 a; 3m ccc_ semH sees «a 033:8 ~95 S 5O II 6:3 98% m I202 33 .30: _0mm 3 ... II 2x .302 32%.. $829 8.5 2 ... II «.3 I302 .3689. $8.5 8mm 2. so I. m2 I303. :33“... $30.; _Omm E. ... II 8” .30? £2: 8 +39; 3 .32: II c3 can :05: 3 I20 8 .32: II 2:. 20%: H: 8 32.: I. one 20%: 3. H2 Gem EOE—aha AEO 3.53 A55 SEEN-.2 :0: 5.3500 E 8:528 m «a: 34 in investigations of chlorocomplexation in the ambient temperature melts. While a few studies have included UV-visible spectrophotometric measurements, no detailed studies that use vibrational spectroscopy or multinuclear N MR techniques to investigate chlorocomplexes in the melts have been published. Although the solute metal ions studied thus far in the melts possess NMR-active nuclei, the lack of NMR data is somewhat understandable. With a few possible exceptions (95Mo/97Mo and 63Cu/65Cu), the nuclei of these metal ions have low receptivities, large quadrupole moments, or oxidation states which are not observable by NMR. These factors, or combinations of them, can render NMR measurements difficult (94). However, some other metal chlorides, such as HgClz, SnClz, and CdClz, which have not been studied in these melts, have nuclei with favorable NMR chracteristics. Moreover, these solutes have a marked tendency to form chlorocomplexes in solvents with high chloride ion activities. Such a condition, without the influence of molecular solvents, is provided in the ambient temperature molten salt environment. In addition, the solvation of alkali metal salts in these molten salts has not been studied. Since several of these M+ ions have NMR-active nuclei which are easily observed (gg., 6Li, 7Li, 23Na, 13303), it would be possible to probe their chemical environment in the melt by using NMR. 8.2 Multinuclear NMR 3.2.11. Introduction The rapidly expanding interest in multinuclear NMR for the study of solution chemistry has resulted from dramatic technological advances in this field. The development of powerful microcomputers which use fast Fourier transfrom algorithms and sophisticated software, pulse programming units for tailor-made 35 pulse sequences, and high effeciency wide-bore superconducting magnets, has made N MR experiments feasible for most elements in the periodic table. High resolution NMR spectra have now been obtained for nuclei with very low natural abundances (_eg., 2H, 170, 43Ca) or low sensitivities (gg., 109Ag, 183W). An extensive amount of thermodynamic, kinetic, and structural information has been obtained from these NMR studies in various solvents. For thorough treatments of the basic theory and practice of NMR, the texts of Abragam (95), Martin, Delpeuch, and Martin (96), and Farrar and Becker (97)Iare recommended. Periodic reviews of progress in selected NMR topics are available (98,99). Excellent reviews of recent multinuclear NMR results are given by Harris and Mann (100), Lambert and Ridden (101), and Laszlo (102). In the following two sections, the NMR characteristics and selected literature results for 7Li and other metal nuclei NMR solution studies are discussed. B.2.b. Lithium-7 By virtue of its high receptivity (1540 E. 13C), 7Li is one of the easiest nuclei in the periodic table to detect in an NMR experiment. With a spin of 3/2, it is a quadrupolar nucleus, and the quadrupolar relaxation mechanism is expected to contribute to the observed spin-lattice (T1) relaxation rate in solution. The expression for this relaxation pathway is given in equation (18). 2 RIQ = 1/T1Q = .31. El. 1 . g? eZun-ym) 2 .c (18) 10 12(21-1) 3 h 36 In this expression, I is the nuclear spin, dis the asymmetry parameter, Q is the nuclear quadrupole moment (in mZ/CMI» is the Sternheimer antishielding factor, eq is the electric field gradient (EFG; eq = aZV/BZZ, ref, 101) about the nucleus, and Tc is the molecular rotational correlation time (isotopic tumbling). Several of the quantitites in this expression are sometimes grouped together to define the nuclear quadrupole coupling constant (X) as x = eZqQ/h (19) The asymmetry parameter measures the deviation of the electronic environment of the nucleus from axial symmetry, and is given by 0' = (Qxx " ny)/qu; 05 as 1. (20) For axial or spherical symmetry, 0 = 0, and quadrupolar relaxation becomes inoperative. The Sternheimer factor is a correction for the screening influence of the closed shell electrons intervening between the bare nucleus and the RFC produced by the ions or molecules which make up the coordination shell of the ion. For the lithium ion, this factor is 0.249, which is the smallest of all of the alkali metal cations (101). Lithium-7 has the eight-smallest quadrupole moment (Q = -4.5 x 10'30 m2) of all quadrupolar nuclei. Therefore, other relaxation mechanisms can make large contributions to the observed R1 relaxation rate. From measurements of 7Li T1 relaxation times in D20 and H20, Hertz and co-workers (103) determined that the quadrupolar and dipole-dipole (intermolecular) mechanisms contribute about equally to the observed relaxation rate at 25°C. The intermolecular dipole-dipole mechanism is given by 37 ' . ° . 2 2 2 ltfitgr "115%; u. NSYI YSZrI s l4-crown-4 > 13-crown-4 > 16-crown-4 (25) for lithium ion in water. Using the 7Li NMR method described in reference 135, Chen e_t 31: (139) have determined the formation constants for complexation of lithium ion with a series of alkyl-substituted dibenzo-l4-crown-4 derivatives in seven nonaqueous solvents. In comparing their results to those cited in reference 135, these authors stated that the larger ring size (14-membered E- 12-membered) accounted for the larger stability constants obtained for the l4-crown-4 derivatives. In addition, the observed increasing KF values as a function of increased alkyl substitution on the benzo rings was attributed to greater electron-release of these substituents to the coordinating oxygen atoms, thus increasing the basicity of these donor atoms. In another 7Li NMR study of the effect of heteroatom replacement on Li+-crown complexation, Shamsipur and Popov (140) investigated the complexation of lithium ion with 18-crown-6 and 1,10—diaza-18—crown-6 in several nonaqueaus solvents. With the single exception of pyridine, the K}? 46 values for the diaza-analogue exceeded those for l8-crown-6 in these solvents. Assuming direct interaction between Li+ and the two nitrogen donor atoms of the diaza—crown molecule, these results were difficult to reconcile with the hard-soft interaction argument outlined at the beginning of this section. One possible explanation for these data would be that in solution, the diaza-crown molecule does not assume, on average, a conformation which makes all donor atoms coplanar. Instead, it may assume a slightly folded conformation, such that the four oxygen donor atoms are presented in a 12-crown-4 - type of arrangement. Thus, it is possible that the nitrogen atoms do not participate in the coordination of the lithium ion. However, the influence of solvent-ligand interactions must also be considered, since it has been shown recently (141) that these interactions can have significant impact on the macrocyclic complexation of metal cations. Cryptand ligands provide three-dimensional cavities for complexation of metal ions. The hydrophobic outer "skin" of these molecules tends to screen out interactions between the cation being complexed, and the counterion and solvent molecules outside the cavity. The completeness of this screening effect is dependent on the match between cation size and ligand cavity size, as well as the other factors just discussed for crown complexation. The importance of cation/cavity size matching was demonstrated by Cahen _et 21. (142) in a 7Li NMR study of lithium ion complexation with cryptands C211, 0221, and C222 in NM, DMSO, THF, PC, chloroform, dimethylformamide (DMF), formamide, and water at 30°C. When corrected for differences in solvent magnetic susceptibilities, the chemical shifts of the 7Li NMR signals observed for the Li-C211 complexes were found to be independent of solvent and counterion (6c = -0.41 ppm )5. infinite dilution). Similar constancy of complex chemical shifts versus solvent was not observed for cryptands 0221 47 and C222, whose cavity sizes are somewhat too large for the lithium ion. The authors interpreted these results as indicating that the 0211 molecule was able to completely shield the lithium ion from the solvent molecules, whereas cryptands C221 and 0222 could not, due to their larger cavity sizes. In addition, slow chemical exchange between free and complexed lithium sites (at ligand/lithium ion mole ratios < 1.0) was observed at 30°C and a magnetic field strength of 14.09 kG only for the Li-C211 and Li-CZZI systems. Fast chemical exchange was observed for the other two cryptand ligands under these conditions. Hourdakis and Popov (143) have also used 7Li N MB, to study complexation of lithium ion by C222-dilactam in water, and four nonaqueous solvents. They reported that the complexing ability of this cryptand was somewhat weaker than C222, and that fast chemical exchange was observed at 33°C and 14.09 kG at all C222—dilactam/lithium ion mole ratios studied. Since these two previous studies, only one additional 7Li N MR study of lithium ion-cryptand complexation has been reported (ref. 117). Khazaeli observed slow chemical exchange for the Li-Cle system in methylamine and liquid ammonia at -51°C and 14.09 kG, with 5c = -0.42 ppm. Thus, in these two additional solvents, it was shown that the C211 molecule effectively isolates the lithium cation from the surrounding environment of anions and solvent molecules. Lithium cryptate complex formation constants (determined by several techniques) in various solvents have been recently compiled by Chantooni and Kolthoff (144). » B.3.c. Complex structures Since 1980, several crystalline lithium-crown complexes have been isolated, and their crystal structures determined. A summary of these results is provided 48 in Table 7. In only two of the nine structures listed Li(ISC6)ClO4~2H20 and (LiSCN)2(18C6)'2H20) does the lithium ion reside in the basal plane formed by the crown ether oxygen atoms. These deviations from the plane appear to be larger for the smaller rings (1204 and 1304) than the larger 1404 and 1806 rings. The large deviation observed in the case of the Li-sym-dibenzo-l4C4-oxyacetate complex most likely is due to the steric requirements of the two bulky benzene rings, and participation by the side arm carboxylate group in lithium ion coordination. For the 18C6 complexes, conformational flexibility allows the ring skeleton to elongate so that only two of the six ether oxygen atoms are in close proximity to the lithium ion. The remaining coordination sites are supplied by encapsulated water molecules (perchlorate complex), or thiocyanate ions. In the benzo-1505 complex, bidentate coordination by the picrate ion, and monodentate coordination by two water molecules effectively remove the lithium ion from any influence which could be exerted by the crown ether. While these data (and attendant interpretations) seem to support the idea of complex stability being promoted by a good fit between the cation and crown cavity sizes, one must be careful not to make direct comparisons between the solid state (static) structures, and the dynamic structural situations in solutions. Structure determinations for lithium ion-crown complexes which contain large, non-coordinating counterions, and no waters of crystallization could enable a more straightforward assessment of the effect of cavity size on cation coordination geometries. Since the original crystal structure determination for the Li(Cle)I cryptate by Moras and Weiss (153) in 1973, no further lithium cryptate structures have been reported. The structure of 0221 or C222 cryptates of lithium ion would be very interesting to aid in the evaluation of the effect of the lithium 49 .m:_._ 35o 550.8 9: an 8:36.88 «o: fl :2 8253 A3 N2 2... m omzmgfiocmeueeag 3383 3v 5 H m Emmoavzsgss a... H g . a m. ONE. . e. ABSeeeréow.7855353 E a: E . c .. e "0233 722.35 2: w... m. 282878533 :1 a e o~m~.$o~3£zo£d 2; a e cumueoasomss 3; 35 m 2832:: m: 3 e 0314.53.83 302-85%; mucououom A v 9.0930 hogan +5 now 53:52 flea—=00 :3 «5 no «53 2:. 5:86.80 3 +3 3 8:83: .3— 5353 93 no memoir—30 53.—O 0.5—SEC b 03.09 50 ion-cryptand cavity size relationship on the observed coordination symmetry about the lithium ion. CHAPTER II EXPERIMENTAL PART AND DATA TREATMENT A. Experimental Part A.l. Molten Salts A.1.a. Melt Preparation A.1.a.(l). A1013 distillation Aluminum chloride (Fluka AG; > 9996 as AlC13) contained trace amounts of boron and iron from the commerical manufacture of this compound. To remove these impurities, and to reduce any aluminum oxide contaminant, the AlClg‘ was distilled in a sealed Pyrex ampule over aluminum wire (Alfa; n5N purity) through an extra coarse (150-250 micron) Pyrex glass frit. A schematic diagram of the ampule is shown in Figure 4. The aluminum wire (1.0 mm dia. ) was cut to 3 or 4 cm lengths, and each segment allowed to soak in a 30:30:40 HZSO4-HNO3-H3PO4 (v/v/v) concentrated acid solution for thirty seconds to remove any oxide coating. The segments were then rinsed with deionized water and technical grade acetone, and briefly air-dried. The cleaned wire was stored in a Vacuum/Atmospheres Corp. DRI-LAB HE-43-2 dry atmosphere box (combined H20 and 02 estimated to be < 10 ppm). In the dry box, the A1013 was first inspected visually for contaminants. The boron and iron impurities may be identified as yellow, reddish-orange, or grey granules dispersed throughout the white solid. Any granular pieces exhibiting this discoloration were removed from the bulk material with tweezers. The ampule was loaded with three aluminum wire segments and ca. 30 g of AlCl3. After filling, the ampule was capped, removed from the dry box, and placed on a high vacuum line (_<_ 10‘5 torr) for evacuation. After 24 h of pumping at this pressure, the ampule was flame-sealed in preparation for the distillation step. The ampule was inverted (empty chamber up) and suspended vertically 51 52 L 93353.. «62 .8 we»... 2.5:: ~23 .4 959m Eu EN "0 «a 6 Eu ¢ 8 Eva 3 :83 "a r —I Ema.” 2a.: rm oi: 9 g N k, K T 0 ll»— HE mesa omewoo «Sam 0 ; We a ‘ m Ad. U J1. 0 LF 53 in an aluminum-body tube furnace fitted with a small mica observation window. Temperature was adjusted with a Love Controls Corp. model 149 proportional controller equipped with a chromel—alumel thermocouple. Over a period of three hours, the ampule temperature was raised slowly (2‘, 5°C per 5 min.) to ca. 190°C. Between 190 and 205°C, the solid melted to give a clear colorless liquid. Because of the volatility of AlC13 near its melting point, extreme care was taken to avoid sudden jumps in ampule temperature which would produce surges in pressure (est. 3 to 5 atmospheres). Despite all precautions, ampule explosions did occur occasionally, with sufficient force to crack laminated safety glass hood sashes. After melting of the AICI3, the ampule was raised (3 1 cm per hour) out of the furnace exposing the upper part of the empty chamber to the cooler atmosphere. Thus, the thermal gradient required to begin distillation was established. After passing through the glass frit, the AlCl3 vapor crystallized in the upper chamber forming very large transparent crystals. The ampules were opened in the dry box, and the crystals of AlCl3 ground for use in preparing the A1013-BPCI melts. A.1.a.(2) BPCI synthesis Pyridine (MCB; A.C.S. reagent grade) was refluxed over barium oxide for two to three days, and fractionally distilled under nitrogen atmosphere. The 1-chlorobutane (Eastman; 9896) was washed with concentrated sulfuric acid, deionized water, dilute aqueous sodium carbonate solution, and again with deionized water. The material was then fractionally distilled over P205 under nitrogen atmosphere. Acetonitrile (Mallinckrodt; analytical reagent grade) was refluxed over calcium hydride for two days, and fractionally distilled under nitrogen atmosphere. Ethyl acetate (Mallinckrodt; analytical reagent grade) was fractionally distilled under nitrogen atmosphere. 54 The l-chlorobutane (975 ml) was added dropwise (2 ml/min.) to a three-liter reaction vessel containing 750 ml of pyridine under nitrogen atomosphere. The reaction mixture was maintained at 70°-80°C for three days, or until no additional white needle-like crystalline product was formed. The mother liquor was decanted off, and the product rinsed with acetonitrile to remove traces of the mother liquor. The crude product was recrystallized from 1 liter of acetonitrile at 60°C. On cooling to room temperature, 5 m1 portions of ethyl acetate were added to promote precipitation of the product from ‘ solution. Addition of the ethyl acetate was halted when no further precipitate was observed to form. The acetonitrile and ethyl acetate were pumped off at 10‘3 torr until the purified crystals of BPCI were just slightly damp with solvent. The product was ground to a powder and dried at 60°C under high vacuum (_<_ 10‘5 torr) for four days. The melting point of the dried product was 131 :t 2°C determined using a Thomas Hoover capillary melting point apparatus. A.1.a.(3) melt batch mixtures Melt batches were prepared by mixing weighed amounts of A1013 and BPCI in Pyrex weighing bottles, using Teflon-coated magnetic stirring bars. All operations were carried out at room temperature in the molten salt dry box described in section A.1.a.(1). Since the reaction was exothermic, initially small weights (0.1 g) of each component were added together to avoid thermal decomposition. Once a 1-2 ml volume of melt was prepared, larger amounts (0.5 g) of each component could be added until the desired mole ratio and final batch size were obtained. Batches of 2 to 45 g of melt were prepared in this manner. After stirring for one day, each batch was vacuum-filtered through a medium porosity Pyrex glass frit (5-15 micron), and stored in a capped weighing bottle in the dry box. 55 In the absence of thermal decomposition or contamination from oxygen or moisture, the melts were clear and colorless. While exclusion of these contaminants was largely accomplished through the use of high purity starting materials in the dry, oxygen-free atmosphere of the dry box, thermal decomposition on mixing was difficult to avoid completely. As a result, the melt solutions usually exhibited a very pale yellow color. A darkening of the color was observed whenever oxygen or moisture contamination occurred. Acidic melt mixtures (X AlCl3 > 0.5) were more sensitive to this contamination, showing more rapid and deeper coloration. Any melts with color darker than the minimum pale yellow were discarded. A.1.b. Purification of Solute: A.1.b.(l). Lithium salts Lithium chloride and lithium bromide (Fisher; analytical reagent grade), lithium perchlorate and lithium hexafluoroarsenate (Alfa; reagent grade), and lithium fluoride (Allied; reagent grade) were dried for three days at 100°C. Lithium chloride enriched with 6Li was prepared by treating 6L12C03 (originally 6Li metal from Oak Ridge National Laboratory; 9596 6Li isotopic enrichment) with concentrated hydrochloric acid, and evaporated to dryness. The product was then ground and durther dried at 100°C for three days. Lithium tetrachloroaluminate was prepared by fusing equimolar amounts of LiCl (1.2062 g) and AlCl3 (3.7983 g) in an evacuated (< 10"5 torr) Pyrex ampule at 150°C. The resulting grey crystalline solid was ground and stored in the dry box. The melting point of this product was 144 t.2°C. A.1.b.(2) heavy metal compounds Lead chloride (99.999996), cuprous chloride (99.9996), and stannic chloride (99.99996) were used as received from Aldrich. Mercuric chloride (Mallinckrodt; analytical reagent grade), zinc chloride (Alfa; ultrapure grade), lead nitrate 56 (Fisher; A.C.S. reagent grade), stannous chloride (Alfa; A.C.S. reagent grade), and cadmium chloride (J.T. Baker; A.C.S. reagent grade) were dried for three days at 100°C, and stored in the dry box. Silver acetate (Matheson, Coleman and Bell; 99.5%) was used as received. A.1.b.(3) crown and cryptand ligands The 12-crown-4 (Aldrich; 9896) was dried at room temprature under vacuum (5 10‘5 torr) for eight hours. The 15-crown—5 (Aldrich; 9896) was distilled, then dried under vacuum (3“: 10"2 torr) for three days. Benzo-l 5-crown-5 (Parish; reagent grade) was recrystallized from n-heptane, and dried under vacuum (310'2 torr) for three days. The 18-crown-6 (Aldrich; 9996) was recrystallized from acetonitrile and pumped under high vacuum (_<_ 10‘5 torr) for one day to remove the weakly bound acetonitrile. Cryptands 0211, C221, C222, and C2322 (MCB) were used as received. A.1.c. Melt Solution Preparation A.1.c.(1) mole ratio sampr All samples for NMR measurements were contained in 5 mm o.d. Pyrex NMR tubes (Wilmad) which had been washed with hot concentrated nitric acid, rinsed with deionized water and acetone, and oven-dried. Once filled with a sample, the tubes were degassed and flame-sealed under high vacuum (_<_ 10‘5 torr). Initial samples were prepared by combining weighed amounts of melt and solutes (both to 1 0.0001 g) in the NMR tubes in the dry box prior to flame-sealing. Thereafter, a batch processing technique was developed to provide more precise control of the ligand-metal chloride salt mole ratio in the melt. In this method, a stock solution was prepared by adding the metal chloride (eg. LiCl) to the melt, and the mixture stirred until it was homogeneous (ca. 24 hr.). Ligand was then added to the stock solution by weight in small 57 (0.01 g, typically) amounts. After each addition of ligand, the solution was stirred for 0.5 to 1 hr. to ensure complete mixing. After this waiting time, a 0.5 g sample was removed from the solution, and loaded into a 5 mm N MR tube. This procedure was repeated, enabling the preparation of 12 to 17 N MR tube samples from a 10 g stock solution. Thus, mole ratios of up to 5 to 1 were attainable with very little (0.05 mol%) dilution of the salt of the metal ion. After flame-sealing under vacuum, all NMR tube samples were conditioned for at least three weeks at 70°C to ensure sample equilibration. In the cases of some of the heavy metal salts, this period was extended to several months. A variation of this method was used to prepare basic melt samples containing LiCl at various concentrations. In this case, a 2.0 mol% LiCl - basic melt stock solution was prepared as just described. Pure basic melt was then added so as to dilute the LiCl (by 0.1 mol% increments). Stock solution mixing and sampling procedures were the same as those used for the mole ratio studies described above. The lowest LiCl concentration obtained in basic melt using this procedure was 0.10 mol% LiCl, which was close to the detection limit for the NMR sample configuration used in these studies (see section A.2.a(1)). In the remainder of this work all molten salt compositions and solute concentrations are expressed in mole per cent (mol96). Thus, a melt with a 2:1 AlCl3-BPCI mole ratio is referred to as 67 mol% A1013 melt. For solutes in the melts, a benchmark for comparison with molar concentrations is useful; a 1.0 mol96 LiCl-45 mol96 AlCl3 melt is equivalent to 0.077 _M LiCl. For convenience, 45.0 mol% AlCl3 melt is referred to simply as the "basic melt". Likewise 67 mol% AlCl3 is the "acidic melt". For any other A1013-BPCI mixtures used in this study, the full composition (in mol96 A1013) is given 58 explicitly. A.1.c.(2) isolation of solid compounds Stock solutions of 1.0 mol% LiCl in basic melt (10.0 g total weight) were prepared as described in section A.1.c(1). Weights of cryptands C211, 0221, and C222 were added to the stock solutions to obtain the 1:1 ligand-to-lithium ion mole ratio. These solutions were stirred at room temperature in the dry box for 2-3 days. One liter of benzene (Fisher; A.C.S. spectrophotometric grade) was washed with successive 250 ml portions of concentrated sulfuric acid until no visible yellow color (thiophene impurity) was observed in the acid layer. In practice, three portions of acid were usually required to obtain this colorless condition. The material was washed with deionized water, and distilled over calcium hydride. The benzene was further dried over freshly activated (at 300°C) 3 A molecular sieves (Davision) for three days, then stored over additional sieves. The water content of the purified benzene was less than 10 ppm as determined by gas chromatography (154). Benzene (ca. 10 ml) was added to each LiCl-cryptand-basic melt solution, and the mixtures shaken. Only partial miscibility of the two liquids was observed. After initial emulsion formation, layer separation ensued, with benzene floating on top of the benzene-saturated basic melt solution. This behavior is in contrast to that observed by Robinson e_t _a_l_. (51), who reported complete miscibility of benzene with acidic AlCl3-BPCl melts. After allowing to stand overnight, transparent crystalline products assumed to be the lithium cryptate complexes were precipitated from solution (bottom of the melt layers). The liquid layers from each solution were decanted off and the crystals washed with three successive 2 ml portions of benzene to remove the adhering melt. The crystals were then dried at 10"5 torr and room temperature for 59 one week to remove the benzene. In the case of cryptand C2322, treatment of the melt solution with benzene to force crystal growth was unnecessary. Precipitation of the lithium cryptate complex occurred as soon as the 1:1 ligand-lithium ion mole ratio was reached. The product was isolated by vacuum filtration of the solution in the dry box. The material was then washed with benzene, and dried on the vacuum line as described for the other cryptate complexes. It should be noted that for this ligand, the solid which was obtained was granular in appearance, with no transparent single crystals obtained, as with the other three cryptands. Samples of these solids were submitted to Galbraith Laboratories for carbon, hydrogen, nitrogen, oxygen, lithium, aluminum, and chlorine elemental analyses. A.2 Lithium-7 NMR A.2.a. N MR of Solutions A.2.a.(l) chemical shift measurements All 7Li NMR measurements were performed on a Bruker WH-180 superconducting NMR spectrometer (field strength = 42.28 kG) equipped with a Nicolet 1180 minicomputer, quadrature phase detection circuitry, deuterium lock system, and a temperature control unit. Spectra were obtained at a resonance frequency of 69.951 MHz using a home-built 10 mm bore probe which is tunable from 25 to 75 MHz. The 5 mm NMR sample tubes were mounted coaxially within 10 mm o.d. Pyrex NMR tubes (Wilmad) using Teflon spacers. The outer NMR tubes contained the external chemical shift reference solutions for the 7Li nucleus. Two different external reference solutions were used for chemical shift measurements. The primary reference solution was 0.015 _M_ LiCl in D20. Within experimental error (i 0.02 ppm), the chemical shift of the signal observed for this solution is equal to the infinite dilution value for 7Li in water (taken 60 as 0.00 ppm). For samples with resonance lines which overlapped the signal of the primary reference, a secondary reference solution was used. This secondary reference is 0.015 M LiCl in pyridine, whose 7Li N MR signal is +3.39 ppm downfield from the signal of the primary reference. When the secondary reference solution was used, the NMR spectra were obtained without deuterium lock. The pyridine reference was checked against the aqueous reference every third sample to ensure accuracy in sample signal chemical shifts corrected to aqueous lithium at infinite dilution. All 7Li NMR data were collected with a sweep width of t 1000 Hz and 4K memory size, with zero-filling to 16K prior to Fourier transformation. Free induction decay (FID) signals were stored on a magnetic hard disk (Diablo disk drive). For a superconducting magnet, the observed chemical shift can be corrected for the differences in the magnetic susceptibilities of various solvents by the relationship (94) 5CD". = dobs + 4—;'{xref-.xsample] x106. (26) where )(l'ef and xsample are the magnetic susceptibilities of the reference and sample solutions, respectively. The magnetic susceptibility of basic melt at 40°C was determined by J. Rovang using an S.H.E. Corp. 800 Series SQUID (Superconducting Quantum Interference Device) Susceptometer at a magnetic field strength of 5000 G. A value of x = -0.761 x 10‘6 was obtained for this sample. Thus, the correction factor (the second term in equation 26) for basic melt was determined to be +0.176 ppm versus water (reference solvent). This correction factor was not applied to the 7Li NMR chemical shift data for the calculations of crown complex formation constants reported herein 61 since this factor is a constant. However, the factor was applied to 7Li chemical shift data obtained in the cryptate complexation studies. This was necessary to permit direct comparison regarding structural details of cryptate complexes of lithium ion in basic melts with previous data in nonaqueous solvents. A.2.a.(2). spin-lattic relaxation measurements For spin-lattice relaxation measurements, data were collected on smaller block sizes (1K or 2K) than for the chemical shift studies. This enabled accumulation of more scans in a shorter time span, thereby maintaining adequate Signal-to-noise (S/N) ratios while keeping the total experiment times to a manageable length (2-3 hr). In addition, no zero-filling prior to transformation was utilized. In these measurements, the outer 10 mm NMR tube contained no lithium ion, but was filled with D20 for field locking. Data were obtained using the fast inversion-recovery technique (FIRFT) of Canet and co-workers (155). The pulse sequence for this method is identical to that used in the standard inversion-recovery (IRFT) method, and is given by PD - [180° - r- 90° - AT - PM}; (27) where PD is the sequence recycle time, T is the post-180° pulse delay time, AT is the post-90° acquisition time, and N is the number of times that the pulse sequence is repeated for a given I value. In the IRFT Method, PD is set to a value which is greater than, or equal to five times the longest T1 value to be measured, so that the magnetization of the spin ensemble may recover completely along the axis of the applied field (in the rotating frame). In the FIRFT ‘method, time savings are realized by setting PD $2T1, and later correcting for incomplete magnetization recovery in the calculation of T1 62 values. This is discussed in the Data Treatment section of this chapter. The value of N was set to 500 to 1000 scans so as to obtain S/N ratios of at least 5:1. This ratio was deemed necessary to clearly distinguish the signals from noise in the baseline. For signal intensities which were very low (rle), this was particularly important. The total experiment time for the FIRFT method is given by E T.T. = N E-(AT+PD) + 21 i; (28) i=1 where E is the total number of T values used (156). The L1 (Link) command in the Nicolet 1180 software enables construction of automation sequences for data acquisition and manipulation. For relaxation measurements, the sequence is L1 = ZG BC QS SA (29) In this list, ZG zeros the computer memory block and starts the FIRFT pulse sequence. BC corrects the dc offset of the real and imaginary parts of the FID when N is not an integer multiple of four (quadrature phase detection). QS corrects any mismatch between the quadrature phase detection channels using a Gram-Schmidt procedure which orthonormalizes the signals. Finally, SA stores each FID on the hard disk for processing. In each experiment, 14 spectra (one per I value) were obtained to calculate T1 values. In addition, duplicate runs were performed at each temperature for most samples. The inhomogeneity factor (W) for the Helmholtz coil of the 10 mm high frequency probe was measured by using the method of Hanssum, Maurer, and Ruterjans (157). In this method, the intensities of the single 7Li resonance 63 line for 4 _h_’l_ LiClO4 in D20 were measured as a function of the pulse width for single-scan spectra. A plot of intensities versus pulse width is shown in Figure 5. The pulse width corresponding to the 90° flip angle (P2) determined from this plot was 15 usec. This P2 value was used for all chemical shift, as well as T1 relaxation measurements. The 180° flip angle corresponded to a pulse width (P1) of 27 usec. The value for W was calculated from the expression w = 0.5 (1 + (A_27°°') (30) A900 where A2700 and A900 are the intensities of the signals obtained at the 270° and 90° flip angles, respectively. All 7Li NMR spectra for solutions were obtained at 40 i 1°C unless otherwise indicated. Temperature was measured by using a copper-constantan thermocouple, with temperature readout on a Doric Trendicator Type T digital display meter. Before each experiment, each sample was allowed to come to thermal equilibrium for 30 minutes prior to data acquisition. No chemical shift change in the signal for the primary chemical shift reference solution was observed between 25° and 90°C, within the experimental error (i 0.02 ppm) of these measurements. This was determined by referencing the position of the signal to the end of the spectrum across this temperature range while running with lock. A.2.b. NMR of Solids Solid state NMR spectra were obtained in the static (non-spinning) and magic angle spinning modes using a Doty Scientific probe equipped with a 7 mm dia. stator assembly mounted at the magic angle (54° 44'), at 22°C. 64 dawn—n 5:259: :3: EE 3 05 new 533 8.8 aims cage—US : w e E». as: Sp «5 .e 853.8... .... 2.5m..— . O . =8- 0 O r . ST .685 8 a... 2 ma . 3 2 m gm: p b p p p p p . b s p p p p g 81... 1 . =3 0 o O O . e8 0 O O r (8mm mama) Sustain! Ms 65 Sample spinning was driven by compressed nitrogen from the variable temperature unit of the Bruker WH-180 NMR spectrometer. Spin rates (0.8 to 2.5 kHz) were measured using an Eldorado Instruments model 1656 digital frequency counter. Solid samples were contained in Delrin or Vespel plastic rotors (7 mm dia. by 18 mm) with end caps. Samples were loaded in the dry box, capped, and transported to the instrument in a desiccator. Data were collected with a sweep width of i 15,000 Hz on 4K memory block size, and zero-filled to 16K for transformation. The optimum pulse width for the 90° flip angle was determined to be 6 usec. for this probe. A left shift (LS) of two data points was executed to eliminate baseline wobble in all spectra. Measurements were made without deuterium lock. The static spectrum of 0.015 M LiCl in water was measured for referencing purposes. In view of the need to operate the instrument without lock, the removal of the probe from the magnet to switch samples, and the uncertainty in phasing of the spectra for the solid sample, the uncertainty in chemical shifts for these sample was estimated to be t 0.1 ppm. A.3. NMR of Other Nuclei A list of NMR characteristics for other nuclei studied in this work is given in Table 8. Zinc-67 NMR measurements were obtained using a 20 mm bore Bruker probe with a tuning range of 8 to 24 MHz. Data were collected using a sweep width of :t 10,000 Hz on 2K block size, with zero-filling to 8K for transformation. The 90° flip angle was approximated with a 100 usec. P2 value. For all other nuclei, the 10 mm probe described in section A.2.a(l) was used. Data were collected on an 8K block size and zero-filled to 32K for transformation. Sweep widths were i 10,000 to 1: 20,000 Hz, and P2 = 15 usec. 66 SW do.— 5 355 9: $5" -- N: as: 22.4 a: 5.3 -- N: 933 35$ - «.3 :5 -- a: ems: 22..“ - 3.2 3.3 -- «2 amp: 285. - 3. 8.3 -- N: com: 5:: m8... 3: 2... S 5% 38;. 3... 2.3. 5.... - g .62 3:; 3: $3 2:... NS 22. 18a .55 a: 5 .82 .2; we. 3.5 u on @ Lassa-..“ 5 saw 8382 033— Aumzv 5.8.69..— 2.2.32 e§5§2 332.88. 8558: 33.5.30 «so: 6.5.902 5 86.5. 5.25 .8828 no 85:28:55 :52 a 039—. 67 For nuclei with very large (> 102 ppm) chemical shift ranges, the frequency synthesizer was reset so that successive spectral windows could be accessed to search for N MR signals across these shift ranges. The concentric N MR tube configuration described in section A.2.a(l) was used for all nuclei except 117Sn and 1198m For these latter nuclei, stannic chloride was sealed under vacuum in a 5 mm NMR tube for use as a chemical shift standard. Signals observed in basic melt solutions were referenced to the standard sample by exchange of 5 mm N MR tubes. Standard and sample tubes were contained inside 10 mm NMR tubes containing D20 for instrument lock. The uncertainty of the chemical shifts of the samples was estimated to be ca. 0.1 ppm when using this tube exchange method. Since all other chemical shift reference solutions were aqueous, only the susceptibility correction from basic melt to water was applied. For 117Sn and 119Sn NMR spectra, the magnetic susceptibility correction factor from basic melt to SnCl4 is -0.93 ppm. A list of the chemical shift reference solutions, and their shifts relative to the primary standards reported in the literature is given in Table 9. A.4. Potentiometry A.4.a. Cell Design As discussed in Chapter I, section B.1.c.(3), the cells used in the potentiametric determination of chlorocomplex formation constants and metal ion coordination numbers are constructed with an aluminum electrode dipping in acidic melt as the reference half cell, and the metal working electrode (M/M'” couple) which responds reversibly to changes in the metal ion activity in the working compartment. This method is based on the ability of the metal working electrode to remain in contact with the melt components without undergoing oxidation. Gale and Osteryoung observed this type of secondary 68 Table 9 Chemical Shift Reference Solutions Used in N MR Measurements of Some Nuclei Studied in the A1013-BPCI Melts Nucleus Reference Solution 6 (ppm) 67Zn 1.0 M Zn(NO3)2/D20 (0.0 113Cd 0.5 _M. CdClg/DZO + 93.2“!) 117Sn SnC14 (neat) -150(b) 119Sn SnCl4 (neat) -150(b) 199Hg 0.2 M. HgClg/Dzo -1533(C) 207% 1.0 M. Pb(NO3)2/D20 -2961(d) (a) Versus 0.1 M Cd(ClO4)2/H20; Ref. 159. (b) Versus (CH3)4Sn; Ref. 123. (c) Versus (CH3)2Hg; Ref. 94. ((1) Versus 3.7 M (CH3)4Pb/toluene; Ref. 158. 69 reaction at an aluminum electrode in basic AlCl3-BPCl melt (160). In this medium, the BP+ ion was reduced to 4,4'-tetrahydrobipyridine, which subsequently dissociated to the stable electroactive 1,1'-dibutyl-4,4'-bipyridinium radical cation. This latter species imparted a blue color to the melt solution. In devising a potentiometric technique to study lithium chlorocomplexation in basic melt, it was recognized that a similar reaction could very likely occur with the BP" ion if the Li/Li+ couple was used as an electrode of the first kind in the cell design. Further support for this supposition is that the reduction potential for the Li/Li“ couple is ca. 1.8 V more negative than the Al/Al3+ couple in the electromotive series determined in several molten halide systems (161). Therefore, an alternative approach that used a metal electrode of the second kind (responsive to changes in chloride ion activity) was devised. The cell design incorporates silver reference and working electrodes, with the reference electrode dipping in a 45.000 mol96 AlCl3 melt solution. In this solution, the chloride ion mole fraction (or activity, assuming the Temkin model) is 0.1000; is. the solution pCl is 1.000. Thus, changes in the pCl of the working compartment brought about by dissolution of LiCl or other lithium salts could be measured. It was also expected that, in the cases of crown or cryptand complexation of lithium ion in this medium, a change in solution pCl would accompany these macrocyclic complexation reactions. Laher and Hussey (76) studied silver chlorocomplex formation in the AlCl3-BPC1 and AlCl3-ImCl molten salt systems at 40°C and 60°C. Their results indicated that at 40°C, more than 9096 of the total silver in the 45.5 mol% AlCl3-BPCI melt exists as the AgCl43‘ chlorocomplex (see Table 4, Chapter I for 84 for this species). It is reasonable to expect that in very dilute basic melt solutions of silver ion, the concentrations of the other complexes 70 (Agle and AgC132') are negligible. For example, a basic melt solution with XAgCl = 10'3 has a chloride-to-silver ion ratio of ca. 100 0‘01" melt = 0.1). Thus, the silver working electrode is made reversible to the p01 of the solution without introducing significant errors in the calculation of the number of chloride ions associated with each lithium ion in the basic melt. For the equilibrium Ag+ + 401- :AgCl43’ the mole fraction-based formation constant is given by 84 = XAgCl43‘/(XAg+)(XC1‘)4 (31) (32) Using the approximation stated above about neglecting the Agle and AgCng‘ complexes, we get, which rearranges to xAgTotal = xAg+ + XAgC143' total A total 4 XAg'i' = XAg / 1 + B4XCl' ° (33) (34) (35) (36) 71 The potential of the silver working electrode is given by . , RT Ew = E°Ag/Ag+ + "F" 1" XAg+ (37) where E°'Ag/Ag"' is the apparent standard potential of the Ag/Ag+ couple in a melt with negligible chloride ion activity (33,, acidic melt). Substituting equation (36) for X Ag+ yields xtXtal g E = °' + EFT-1n 4 (38) Ag/Ag 1 4» 84x01- total x Ew = Egg/Ag. . g... T (39) 84Xc1- where the approximation that 1 << 84XCl-4 is used. If XCI‘ = 10'1 and 84 = 1023, it is clear that this approximation is justified. After regrouping terms and recalling the definition for pCl. total RT XA . . EW = Eo'Ag/Ag+ 4. _PT. In E + 2.303 4 RT pClw (40) 4 F By similar reasoning, the potential of the silver reference electrode is E _ Ea. RT ln XAgtOtal 2.303~4°RT pClREF REF - Ag/Ag“ + — + — (41) F 84 F 72 Taking Bright = Ew and Eleft = EREF’ the cell potential is 2.303.4-RT (pClw - pClREF) F Ecell = Eright "Eleft = (42) As basic melt is titrated with acidic melt in the working compartment, the pClw increases as the chloride ion is consumed. Thus, the cell potential increases as the titration progresses. A schematic diagram and the standard notation description for this cell is shown in Figure 6. The silver electrodes were prepared by rinsing 2 cm lengths of 1 mm dia. silver wire (Aldrich; 99.99% GOLD LABEL) with concentrated nitric acid, deionized water, and acetone, and then air—dried. These wire segments were then attached to copper wire leads by brazing with a torch to ensure good electrical contact. The reference compartment was constructed from 0.5 in. Pyrex glass tubing with fine porosity (4-5.5 micron) Pyrex frits sealed into the tube constrictions. The frits were conditioned prior to use in the titrations by placing ca. 0.25 g of basic melt, spiked with silver acetate (XAgtOtal = 2.0 x 10‘5), inside the tube, and soaking the outer surface of the frit in the same solution for two days. In this way, the pores of the frits were completely wetted with the melt. Before immersion in the melt solution to be titrated, excess melt was wiped from the outer surface of the frit, and a silver reference electrode was inserted into the tube so that the wire was in contact with the melt above the frit. The working compartment (a 25 x 40 mm Pyrex weighing bottle) was filled with 3.0 g of the solution to be titrated, and the working silver electrode was dipped into this solution. Cell potentials were measured with a Markson Science ElectroMark Analyzer multipurpose meter in the millivolt mode. The error 73 d ——-> e C $- b —\ A. V‘— E ' a > a: 4-5.5 micron Pyrex glass frit. b: basic melt reference melt solution (pCl = 1.000). c: silver working electrode. d: silver reference electrode. e: titrant. 1': basic melt solution to be titrated. g: Teflon-coated stirring bar. h: magnetic stirrer. A: + BASIC MELT cuss + Ag,(pc|=1.ooo)l "m lsnsuc MELT,Ag Ag Figure 6. Concentration electrochemical cell used in potentiametric titrations of basic AlCl3-BPC] melt solutions. 74 in cell potentials was estimated to be i 1 mV. All titrations were carried out at 35 i 2°C in the dry box. Factors which could contribute to the development of liquid junction potentials at the glass frits are discussed in the following sections. A.4.b. Titration methods A.4.b(l) titration of pure basic melt and basic melt solutions of lithium salts . The concentration cell was set up as described in the previous section, and the meter was adjusted to read zero millivolts. In practice, this adjustment was small (< 15 mV). This is consistent with previous studies which suggest that the liquid junction potentials for cells of this type are small, and may be neglected (77,164). Acidic melt titrant was prepared according to the procedures given in section A.1.a(3). After filtering the titrant through a medium porosity Pyrex glass frit (5-15 micron), silver acetate was added (X Agtotal = 2.0 x 10's), and the solution was stirred until it was homogeneous (310 min.). Since the basic melt solutions to be titrated contained an equivalent mole fraction of silver acetate, the buildup of a junction potential due to a concentration gradient for silver acetate across the frit as the titration proceeded, was avoided. The’ titrant was added with a Brinkmann Eppendorf digital pipettor (10 ul to 100 pl x 0.1 ul). Disposable glass pipette tips were calibrated just prior to the start of a titration. This was done by measuring the weight of five successive aliquots of titrant on an analytical balance (to t 0.0001 g). The mean aliquot weight and the standard deviations in these quantitites (N-l weighting) were then calculated. Aliquots ranging from 12 to 48 mg were used; smaller amounts were used near the equivalence point of the titrations. In general, the uncertainties in the amounts used were less than t 596. 75 Continuous mechanical stirring of the working compartment solutions was accomplished with a Teflon-coated magnetic stirring bar. A waiting time between aliquot additions of 5 to 15 minutes was used to ensure no further change in cen potentials. Cell potentials were found to stabilize within about 30 sec. after each aliquot addition. For titrations of basic melt solutions containing lithium salts, the lithium salts were added (to 1.0 mol%) to the silver-spiked basic melt solutions, and stirred for 24 hr until homogeneous. The solutions were than titrated as described above. A.4.b.(2) titration of LiCl-basic melt solutions with crown and cryptand ligands The procedure used in these experiments was identical to that described in the previous section up to the point of titration. Instead of the acidic melt, 15-crown-5 and cryptand C2322 were used as titrants. Pyrex glass pipet tips were calibrated for both liquid titrants. Ligand aliquots were 12 mg i 596, with titrations carried out to ligand-to-lithium ion mole ratios of 5:1. A.5. Infrared Spectrophotometry A.5.a. Instrumentation Infrared spectra of basic melt solutions were obtained by J. Rovang using a Bomem DA3 FTIR Spectrophotometer equipped with a glowbar source (range: 100 to 10,000 cm'l) for mid-IR, and a mercury-xenon arc lamp (range: 10 to 1000 cm‘l) for far-IR measurements. MCT (mercury-cadmium-tellurium; range: 400 to 10,000 cm’l) and pyroelectric (range: 10 to 1000 cm‘l) detectors were used for the mid- and far-IR regions, respectively. A KBr beam splitter was used for the mid-IR, and a 3 micron, Mylar beam splitter used in far-IR studies. Instrument operation was controlled by a Digital PDP-ll minicomputer 76 equipped with a 15.9 Mbyte Winchester hard magnetic disk drive, a Bomem high speed vector processor, and RSXllM version 4.1c software package. Data were collected on 32K memory block size, and treated with a Hamming apodization function prior to Fourier transformation to minimize fringe patterns in the spectra. Each spectrum resulted from the averaging of 1000 interferograms, with an estimated resolution of 2 cm‘l. The cell compartment was purged with nitrogen during acquisition to minimize the possibility of contamination of the contents of the cell with oxygen or water vapor from ' the atmosphere. A.5.b. Cell configuration Mid-IR spectra (550 to 3500 cm‘l) of melt solutions were obtained using an Aries model 20500 vacuum-tight liquid cell with 5 mm thick sodium chloride windows and 0.025 mm Teflon spacers. The pre-assembled cell was wrapped with Teflon tape to prevent leaking of the melt, and also to afford extra protection against 02/H20 contamination of the contents. Far—IR spectra (150 to 600 cm‘l) were obtained using the above cell, with 2 mm thick polyethylene windows and 0.1 mm Teflon spacers. After each run, the cell was flushed with 0014 (Fisher: "Spectranalyzed" grade), acetone (J.T. Baker; PHOTREX reagent grade), and again with C014. The remaining traces of these solvents were removed at 10’2 torr (pumped for 30 min.). From the dry box to the FTIR instrument, the filled cell was transported in a dessicator. B. Data Treatment 8.1. Lithium-7 NMR B.1.a. KINFIT Nonlinear Least Squares Curve-fitting Program The analysis of 7Li NMR chemical shift data was performed on a CDC 77 6500 computer system using the KINFIT Program (162). Data were fitted to equations derived from proposed solution equilibria models to calculate association constants, crown complex formation constants, and limiting chemical shifts of various solution species. These models are discussed in Chapter III. B.1.b. Nicolet 1180 NTCCAP Subroutine ’ This subroutine in the Nicolet 1180 software package permits the deconvolution of an N MR spectrum of up to 26 overlapping lines, providing the positions, intensities, widths, and relative areas of the individual lines. The position, height, and width parameters are varied by the operator to obtain optimum visual fit of the calculated spectrum to the experimental spectrum. The subroutine then calculates the peak areas and the root-mean square (RMS) deviation between the calculated and experimental spectra based on 1024 units full scale. The documentation for this subroutine does not provide a detailed explanation of just how the individual uncertainties for the height, 'width, and intensity parameters are incorporated into the calculated RMS error. However, experience has shown that the height and intensity parameters are both easier to adjust visually than the width parameter. This is particularly important for some of the broader (> 20 Hz) 7Li NMR lines observed in these studies. The multi-line 7Li N MR spectra observed in the cryptand complexation studies (Chapter IV) were deconvoluted using the NTCCAP subroutine. The calculated relative areas of the signals for free and complexed lithium ion in the melt solutions were used to determine the cryptate complex formation constants, using the expression __ fc ' CLi KF - (43) 78 where ff and fc are the fractions of free and complexed lithium ion, respectively. Cc and CL; are the analytical concentrations of the cryptand and the lithium ion, respectively. B.1.c. Relaxation Data Reduction Two subroutines are available in the Nicolet 1180 software package for treatment of relaxation data; TllR and T13R permit fitting of the data to two, and three parameter equations, respectively. In both .cases an (x,y) data set is constructed from the resonance line intensities associated with each I value (T, I). The automation sequence for transformation of the sequential FID data files acquired in the experiment (section A.2.a.((2)) is L1. = GA EM FT PS AI SB. (44) In this list, GA retrieves each FID in turn, EM applies the pre-set linebroadening factor (LB, in Hz), FT Fourier-transforms the data file, PS applies the pre-set zero and first order phase corrections to each spectrum, AI scales the spectra to enable direct comparison of signal intensities, and SB saves the spectra on the hard disk. In the final automation sequence, L1 = GR DR (45) GR extracts the (T, I) data set from the transformed spectra, and DR calls and applies the pre-selected data reduction subroutine (TllR or T13IR). In TllR, the data set is fitted to the equation 79 Mm = M41 -(2-e-PD/T1)e-T/T1} (46) where M('r) is the signal intensity at time ‘1‘, and Mo, is the intensity atr Z 5 T1. When PD >> T1, this expression reduces to, M( 1') = M031 - 2 e' T/ T1} (47) which is the equation for the standard IRFT experiment. Values for the adjustable parameters Mai and T1 (with their respective standard deviations) are caluclated by this subroutine. In T13R, the equation M(t) = Mm’l - [(1+W) - e'PD/T]l e‘T/TIH (48) is used, with Mac, T1, and W (see eq. (30)) as adjustable parameters. For a hypothetically perfect rf pulse, W = 1. According to Levy and Peat (156), the full equation which describes the recovery of the magnetization for the FIRFT experiment is 1_ “NW“ - e-PD/Tl . e- T/Tl} M( 1’) = M g. (49) 1 _ W2 e"PD/Tl. e-T /T1 Therefore, in the T13IR subroutine, the second term in the denominator of GQ- (49) is ignored. Weiss and Ferretti (163) have argued that this simplification is justified only when both PD and r are small compared to T1. As a check 80 on the values of M... and T1 (from THE), and M00 , T1, and W (from T13IR), the data were also fitted to eq. (49) using KINFIT. The (r ,I) data sets were obtained by reading off the intensity of each line in a set, and matching it with the associated I value. Since experience showed that the results calculated with KINFIT were more reliable (in some cases the GR command would ignore a spectrum if the line intensity was too small; thus, T1 values determined by the subroutines were at times based on fewer data points), all results for T1 relaxation times reported in Chapter III were obtained by using KIN FIT. B.2. Potentiometry In basic AlClg-BPCI melts (X A1013 < 0.5), the mole fraction of free chloride ions in solution is given by ‘ n°c1 n°Cl‘ XCI- :: = (50) "ototal "°A1C13 + n°BpCI where the supercript (°) refers to the initial number of moles. In addition, n°cr = "oBPCI - "0A1C13 (51) where the reaction between AlCl3 and chloride ion from the BPCI is assumed to be quantitative. By the same reasoning, the number of moles of A12C17‘ ions in each aliquot (m) of acidic melt titrant is given by n°A1017‘ = n4.1013 - "BPCI (52) Thus, the mole fraction of free chloride ion remaining in the working 81 compartment as the titration progresses is x n°cr - m "A12C17' (53) c1” = “total + m[nA1013 + nBPCl] where m = 0,1,2,... As discussed in section A.1.a.(3)., acidic melts are observed to be more , susceptible to Oz/HZO contamination than basic melt mixtures. Although the reactions which produce the darkening of color of acidic melts have not yet been fully characterized (86), it is clear that the contamination reduces the melt acidity to a value somewhat less than that expected based on the original melt composition. Therefore, the actual composition of acidic melt titrant was determined as follows. Prior to the start of a titration of basic melt with acidic melt (section A.4.b.(l)), the values of "A12C17-, "001-, and n°total are used to calculate the number of aliquots required to reach the equivalence point. This value is compared to the actual number of aliquots used in the titration. In practice, mactual is greater than mcalc. due to the lower actual titrant acidity. Assuming that contamination reduces only the amount of AlC13 (as AlgCl7‘) in the titrant, a new value 0f “AIZCI7‘, and the actual titrant composition is calculated. New values of XCl‘ are also determined, and the corrected titration curve (with respect to pCl) is obtained. Assuming that a lithium chlorocomplex of the general formula LiClxu‘X) is formed on dissolution of a lithium salt in basic melt, its reaction with acidic melt titrant is given by LiClxu’X) + (x—1)A12Cl7'-§LiCl(s) + 2(x-1)AlCl4‘ (54) 82 Thus, one mole of LiCl precipitates for each mole of the lithium chlorocomplex titrated. The formula for the lithium chlorocomplex is based on the assumption that one mole of this complex forms for each mole of LiCl added to the melt. At the onset of precipitation of LiCl, a small amount of free chloride ion from the melt remains to be titrated. Once the reaction in eq. (54) is nearly complete, the LiCl is titrated, and the equivalence point is reached. Therefore, the number of moles of titrant required to go from the precipitation point to the equivalence point is given by "pfie = n"'Cl‘ + (x’1)“complex + n"LiCl (55) where (*) refers to the precipitation onset point. If "complex = n°LiCl: eq. (55) reduces to npfie = "*C1' + xn°LiCl (56) To determine the value for n*cr, the potential at the precipitation point is equated with Ecell for the titration of pure basic melt. The value of pClw, and hence, XCl‘ is then obtained. Referring once again to the LiCl-basic melt titration, the total number of moles in solution at the point of precipitation (“'total) is known. Therefore, "*Cl' is given by n"'Cl‘ = 1""'total XCI‘ (57) Rearranging eq. (56), x = nP-‘e - “*Cl‘/n°LiCl (58) 83 It must be stressed that x is the number of chloride ions associated with each lithium ion added as LiCl. Thus, it is not possible to distinguish between monomeric lithium chlorocomplexes, and dimeric or higher aggregate complexes (which would all have the same Cl“/Li+ ratio), using this potentiametric technique. For titrations of LiCl-basic melt solutions with crown and cryptand titrants, the number of chloride ions released into solution as the macrocyclic complexation reactions occur is determined by calculating ApClw from the observed change in cell potential. Since these ligands are not electroactive in basic melt, it is assumed that no liquid junction potential is produced by their addition to the melt solution. CHAPTER III SOLVATION AND CROWN ETHER COMPLEXATION OF THE LITHIUM ION IN THE AlCl3-BPCI SYSTEM A. Introduction Taulelle and Popov (59) have reported that LiCl is insoluble in A1013-BPCI melts with 0.48 5 X AlCl3 5 0.50, but soluble in the composition reagions 0.45 _<_ XAIC13 5 0.47 and 0.50 < xAlCl3 < 0.67. Striking differences in chemical shifts and linewidths of the 7Li NMR signals were observed for LiCl solutions in basic versus acidic melts. These results were interpreted by the authors as indicating that the environment of the lithium ion changes dramatically from basic to acidic melts. The manner in which LiCl is solvated in basic melts is particularly intriguing. In basic melts, the chloride ion concentration can be as high as 10 mol%. Based on the common ion effect, one would not expect to observe high LiCl solubility in this medium. Taulelle and Popov proposed the Lile chlorocomplex in LiCl-basic melt solutions to account for the observed solubility of LiCl. In this work, multinuclear NMR (7Li and 27A1), potentiometry, and infrared spectrophotometry have been used to characterize the proposed LiClZ‘ complex in basic melt, and also to study solvation of the lithium ion in acidic melt. In addition, complexation of the lithium ion with crown ethers in basic melt has been studied by using 7Li NMR and potentiometry. B. Salvation of Lithium Salts in Basic and Acidic AlCl3-BPCI Melts B.1. Lithium-7 NMR B.1.a. Chemical Shift Studies B.1.a.(1) Lithium salts in basic melt The effects of lithium salt concentration, of type of counterion, and of temperature on the 7Li NMR chemical shifts and linewidths for these salts in basic melt were studied. The 7Li NMR signal for 1.0 mol96 LiCl in basic melt at 40°C is shown in Figure 7. The chemical shift of this signal (after 84 85 o— 5 (PPM) - - 1C1 in Bas c A - Melt at 40°C. ‘ 1013 BPCI 86 using the correction factor of +0.176 ppm to account for the difference in magnetic susceptibilities of basic melt and water) is +1.56 i 0.01 ppm. At 25 Hz, the linewidth of this signal is ca'. 102 times broader than the signals routinely observed for 4 M LiClO4 in D20 (Avl /2 = 0.3 Hz). The approximate solubility limit of LiCl in basic melt at 40°C is 2 mol%. As the temperature is lowered to 25°C, a 2 mol% solution of LiCl in basic melt becomes heterogeneous; fine needle-like transparent crystals are dispersed in the solution. Attempts to characterize this material were unsuccessful. The 7Li resonance line observed at 40°C for basic melt solutions of LiCl shifts downfield with decreasing LiCl concentration (Figure 8, TablelO). The LiCl concentrations given in Table 10 are expressed in molar units so that the calculated values of the equilibrium constants may be compared directly with literature values. Several two-site or three-site fast chemical exchange models were proposed to fit these data (equations 1-3). Lile + A1014‘ :2 LiC12AlCl42“ (1) LiClg‘ .1: Li+Cl" + Cl" _ (2) Lile :Li+Cl‘ + Cl‘ (3a) LiCl" = Li+ + Cl‘ (3b) It was found that the experimental data could not be fitted to any of the above models. However, the model tttttttttt ................. LLLLLLLL 88 Table l 0 Lithium-7 Chemical Shift Data for LiCl—Basic Melt Solutiom at 40°C LiCl Conc. LiCl Conc. (_hj x 10‘3) 6(ppm) (LI x 10'3) 6(ppm) 8.23 +1.83 61.2 +1.40 17.4 +1.65 65.5 +1.44 20.5 +1.58 69.2 +1.43 23.0 +1.59 73.7 +1.40 28.2 +1.55 79.0 +1.40 30.9 +1.56 86.2 +1.38 31.0 +1.53 95.4 +1.36 34.2 +1.51 102. +1.36 37.3 +1.50 108. +1.35 38.0 +1.49 117. +1.35 40.2 +1.49 125. +1.36 43.8 +1.48 132. +1.34 48.1 +1.45 150. +1.33 51.7 +1.44 152. +1.31 55.8 +1.44 153. +1.33 56.2 +1.43 156. +1.33 158. +1.33 (a) Versus external 0.015 M LiCl in D20 uncorrected for magnetic susceptibility; the uncertainty in 6 is i 0.02 ppm. 89 2LiC12- ‘—_I—{_-p__—h L12C142' (4) (suggested by J. Rovang) was found to adequately fit the 7Li chemical shift behavior of LiCl in basic melt (Figure 9). The limiting chemical shifts, calculated by using the KINFIT program (see Appendix 1 for SUBROUTINE EQN), for the monomer and dimer are +3.78 (1 0.99) ppm and +1.15 (1 0.01) ppm, respectively. When corrected for magnetic susceptibility, these values are +3.96 and +1.33 ppm, respectively. From the log KD value of 2.82 (:t 0.39), it is estimated that ca. 9096 of the total lithium ion in a 1.0 mol% LiCl-basic melt solution occurs as the dimer species. In addition, the free energy of dimerization (AGD = -RT In K9) is -4.1 (:t 0.5) kcal/mole. The formation of Li+X‘ ion pairs and higher order aggregates in nonaqueous solutions has been observed by several investigators. In a series of investigations by Chabanel and co-workers, vibrational spectroscopy was used to show the existence of dimers and tetramers of LiSCN in ether (164) and in tertiary amine (165) solutions. Most recently (166), dimerization of LiSCN was observed in THF and 1,3—dioxolane (KD = 0.24 and 0.45 M‘l, respectively). The structure of the dimer is known to be planar (D211), while the tetramer has a tetrahedral geometry (Figure 10). Similar structures have been shown to occur for covalently-bonded alkyllithium aggregates in ether solutions (167). In a 7Li NMR study of lithioisobutyrophenone/LiCl mixtures in dioxolane, dioxane and dimethoxyethane solutions at 40°C (field strength = 21.14 kG), Jackman and Szeverenyi (168) observed fast chemical exchange between free lithium ion and the tetramer species formulated as Li4Cl(C10H110)3, where C10H110' is the enolate ion. Slow chemical exchange at room temperature (field strength = 21.14 kG) has been reported by Cambillau and Ourevitch (169) in a 7Li NMR study of cryptated lithium enolates in dichloromethane and DMSO 4...: 38m 5 83955860 83 .3 «£5 33520 Sp 8 3:330 828C «5 .8 $524.. .8355 .a 959m 90 . In “on n a u u . o . . o o - I m J58 83> 8559.85 3.55 3585.. :22 .5555 .2 2a.»... «cow «on now no n mow mmw mow LIT! L. as am LCKLFLWLT a 3 and .3 .KS ”3:: :3: . Lithium-7 T1 Relaxation Times for Aqueous LiCl 101 Table 1 2 and LiC104 Solutions at 25°C and 40°C Sample Temp. (“0) T1 (sec) 4 M LiCl/H20 Run #1: 25 14.38 :t 2.68 Run #2: 25 12.27 :i: 1.23 Run #1: 40 17.58 :i: 2.30 Run #2: 40 17.33 :i: 1.90 4 M LiCl/D20 Run #1: 25 22.00 t 1.65 Run #2: 25 --- Run #1: 40 34.39 :i: 4.18 Run #2: 40 --- 4 1’1 LiClO4/D20 Run #1: 25 13.67 :t 0.77 Run #2: 25 --- Run #1: 40 19.38 i 1.79 Run #2: 40 16.98 i: 1.96 102 respectively. The average value for the inhomogeneity factor (W) determined from the fits of the T1 relaxation data is 0.9519, and is in good agreement with the value determined experimentally (W = 0.9541). With the reliability of the FIRFT method confirmed, the 7Li spin-lattice relaxation rates for LiCl and several other LiX salts in basic melt, and LiCl in acidic melt were measured at 25°C and 40°C (Table 13). No significant anion dependence in the calculated T1 values is observed at either temperature. These results are taken as further evidence for the coordination of the lithium ion by chloride ions to the exclusion of the counterions from the parent LiX salts. A substantial (ca. 20%) decrease in the T1 relaxation rate occurs as the LiCl concentration is increased from 1 mol% to 2 mol%. If the spin-lattice relaxation process for the 7Li nucleus is dominated by the quadrupolar mechanism (Chapter I, equation 18), this result is interpreted as follows. In equation 18 (Chapter I), the motional narrowing limit (m‘rc << 1) is assumed. If this condition is not met, the full expression is given by ‘1' 4T R1Q=-—1-=Cx2 __°__ + C (6) TlQ l +(wTC)2 1 +4(wtc)2 where C = (3"2X21+3)/10 12(21-1), x = equ/h, w is the resonance frequency in radians per second, and a is assumed to be zero for axial symmetry. If the rotational correlation time is known, the quadrupole coupling constants can be estimated. In the Gierer-Wirtz model (98), the rotational correlation time may be determined by using equation 7, 4171‘317f T =—— 7 C 3kT U 103 Table 13 Lithium-7 T1 Relaxation Times for Some Lithium Salts in the A1013-BPCI System at 25°C and 40°C T1 (see) Sample at 25°C at 40°C 1.0 M0196 LiCl 0.046 t 0.002 0.043 .002 2.0 M0196 LiCl 0.063 1 0.004 0.061 .003(8) 1.0 M0196 LiBr 0.050 4 0.003 0.049 .005“) 1.0 M0196 LiCIO4 0.051 4 0.003 0.048 .002 1.0 (“01% 1.1.4st 0.050 1 0.003 0.052 .003 1.0 M0196 LiN03 0.041 4 0.002 0.039 .008(8) 10 M0196 LiCl 1.10 4 0.27 1.52 .08 (a) acidic melt) Single experiment; all other values are the averages of two experiments. 104 where 1) is the dynamic viscosity and f is the microviscosity factor (( 1, equation 24). To calculate f for the monomer and dimer species, for a and as (radii of the solute ion and the solvent ion, respective estimated from the proposed structural model for the lithium ion in has (Figure 5). Taking a = PLi + 1‘01“ = 2.56 .94 (136) for the monomer, and as = 1 = 2.13 2 (Chapter IV, section 0.3), fmonomer = 0.19. For the dimer, a i as the radius of the sphere swept out in solution by this species = 5.3 as = 2.13 .2, fdimer = 0.36. Assuming that the dynamic viscosity of a or 2 mol% LiCl—basic melt solution is equal to that of pure basic m« 0.037 Kg/m s; Chapter I, Table 3) at 40°C, the rotational correlatim for the monomer (Tomonomer = 3.5 x 10‘1.0s) and the dimer (1 cdim‘ x 10’9s) are obtained. For comparison, the Tc value for D20 at 30°( x 10‘125 with n = 0.011 Kg/m s (112). Considering the approximation are made, the agreement of the TC values for the monomer and C acceptable. Since better than 9096 of the lithium species in basic r 1 mol% or 2 mol% LiCl concentrations) is found as the dimer, TCC used in the following calculation. < RIQ )1/2 x = -—- Ctr where Tr is given as the bracketed protion of equation 6. Assuming 1 Rearranging equation 6, T1 value obtained for the 2 mol% LiCl-basic melt solution at 40°C 4) is characteristic of the dimer only (Xmonomerk 0.07), a value of i 30 kHz is obtained. A similar calculation for 1.0 mol% LiCl in &Ci( 0 at 40°C yields f = 0.03 (a = "Li" = 0.86 X; as = PA12C17‘ 4.2 A), 105 x 10'13 s (77 = 0.0143 Kg/m s from Table 3, Chapter I), and X: 0.2 kHz. Some representative quadrupolar coupling constants for the 7Li nucleus in the gas, solution, and solid states are listed in Table 14 for comparison (101,176,174). The x value which is obtained for the lithium ion in basic melt is in good agreement with the values for concentrated aqueous lithium ion solutions. However, the 7Li coupling constant for the lithium ion in acidic melt is smaller than those for the aqueous solutions by a full order of magnitude. The tetrahedral coordination of the lithium ion in the dimer model must be viewed within the context of the dynamics of the liquid state. Collisions between ions can give rise to a nonzero EFG at the 7Li nucleus without permanently disrupting the nominal tetrahedral symmetry about the lithium ion. This collisional model for quadrupolar nuclei was developed by Deverell (177) to account for the nonzero NMR linewidths for these nuclei in highly symmetric solution environments. However, it is likely that some distortion from tetrahedral symmetry is occuring in the dimer considering the size of the coupling constant. For the lithium ion in acidic melt, it appears that the A12Cl7‘ ions provide a more symmetric environment (closer to a regular tetrahedron); thus, a smaller coupling constant is obtained. The 7Li T1 relaxation times for 1.0 mol% LiCl in basic melt were determined at six temperatures from 40°C to 85°C. these results are given in Table 15. A plot of In (l/Tl) versus 1000/T(K) for these data is shown in Figure 16. A roughly linear decrease in In (1/T1) with increasing temperature is observed between 40° and 75°C. A very slight increase of the relaxation rate (considering the size of the error bars) seems to occur between 80°C and 85°C. In view of the evidence presented thus far in support of the dimer model in LiCl—basic melt solutions, it is possible that this peculiar reversal Of temperature dependence may arise from a change in aggregation (i.e., dimer 106 Table 14 Lithium-7 Nuclear Quadrupole Coupling Comtants in Various Substances System X (kHz) Ref. Gas Phase: Liz 60 LiF 408 LiCl 192 176 LiBr 184 MI 172 Solutions: 6 M Lil/H20 35 6 M LiCl/H20 44 101 6.2 M LiCl/glycerol 28 Solid State : "A" zeolite(a) '62 174 L12C03 60 Li2S04-(H20) 45 (a) L111_67Nao.13(A102)12(S102)12°27H20 107 'Tabhals Lithium-7 T1 Relaxation Times for 1.0 Mol% LiCl in Basic Melt as a Function of Temperature (40°C to 85°C) Temp. (°C) T1(sec) 40 0.046 t 0.002 50 0.051 t 0.003 60 0.053 t 0.005 71 0.060 t 0.005 80 . 0.062 3: 0.007 85 0.057 t 0.008 108 3.1- 3,0... 0 .I' 2.94 b 3 0 O 2.8- O n I F 7 I 2.8 2.9 3.0 3.1 3.2 103 100 Figure 16. Ln (1/1‘1) Versus 1mm for 7Li in 1.0 M0196 LiCl-Basic Melt Solution. 109 monomer). Although the onset of the spin rotation relaxation mechanism is another possible explanation for this behavior, it is considered to be unlikely (107,110). More relaxation data at higher temperatures could aid in clarifying this point. The linewidth of the 7Li NMR signal for 1.0 mol% LiCl in basic melt is found to be sensitive to temperature. Values for 1101/2 and T2*( = l/Mv “2) are listed in Table 16 as a function of temperature (27°C to 150°C). These data are shown in the form of a plot of In (1/T2*) versus 1000/T(K) in Figure 17. Qualitatively, the curve described by these points is similar to the one in Figure 16 for the T1 relaxation data. However, the minima in these curves occur at two different temperatures; ca. 80°C in Figure 16, and ca. 125°C in Figure 17. If a change in aggregation at 80°C is the correct interpretation of the anomolous spin-lattice relaxation behavior, at 125°C it would be logical to assume that most of the total amount of the lithium ion is in the monomer form (LiClz‘). Since no further dissociation is likely, the onset of the spin rotation mechanism above 125°C could account for the increasing spin-spin relaxation rate of the 7Li nucleus. Spin rotation relaxation arises from the interaction between nuclear magnetic moments and rotational magnetic moments of the molecules containing these nuclei. With the exception of 73Ge, 7Li has the largest nuclear moment of all of the quadrupolar nuclei (2.13 x 10"26 J/T). In addition, the rotational magnetic moment for the monomer might be expected to be rather large. 8.2. Aluminum-27 NMR The Al27 NMR spectrum for pure basic melt at 40°C is shown in Figure 18. The downfield signal (6 = +102.4 t 0.5 ppm v_s_. external 0.5 M AI(NO3)3 in 1 M aqueous HNO3, Av 1/2 = 31 i 2 Hz) is assigned to the A1C14’ ion. The chemical shift of this signal is in agreement with the value of +102.6 ppm ILhIHlfiMflll710vl 110 'Pahh316 12, ) and Apparent Spin-Spin Relaxation Times (T2) for the 7Li NMR Signal of 1. 0 Mol% LiCl' in Basic Melt as a Function of Temperature (27°C to 150°C) Temp. (°C) Av 1/2 (“8““) T‘z (80¢) 27 25.8 0.012 0.006 35 22.5 0.014 0.006 40 20.0 0.016 0.007 45 18.3 0.017 0.009 55 14.8 0.022 0.011 65 ' 12.5 0.026 0.013 75 10.3 0.031 0.016 85 8.4 0.038 0.019 90 8.3 0.039 0.019 100 6.5 0.049 0.024 110 6.3 0.051 0.025 120 6.3 0.051 0.025 130 5.8 0.055 0.028 140 6.5 0.049 0.024 150 8.4 0.038 0.019 (a) The uncertainty in 1191/2 is estimated to be :t 0.5 Hz. 111 -4.5- -4.0- " (D A 0 * N .— \ ~3.5- 0 C a —l 0 1 '300‘s 0 ‘ 0 0 o l g Figure 17. Ln (1/'r2*) Versus 111710 for 71.1 in 1.0 M0196 LiCl-Basic Melt Solution. 112 .063 5 :0: 8.5.50? .502 5. 55.588 5:2 55:55:? .2 0.55 Asia: 0 3+ .W on... _ . _ n.2, on”: flier)... 113 by Kidd and Truax (178). Gray and Maciel (179) obtained Av 1/2 = 40 Hz for basic AlCl3-BPCI melt at 36°C. In this latter work, these authors observed a sharp increase in Av 1/2 for melt compositions with X AlCl3 > 0.5. their plot of AV 1/2 y_s_. melt composition is reproduced in Figure 19. Chemical exchange between the AlCl4' and AlZCl7' ions, and lower symmetry for the AlgCl7‘ ion (quadrupole effect) were cited as the sources of this broadening of the 27A1 line with increasing melt acidity (182). The 27A1 NMR spectra for 1 m0196 LiCl, LiBr, LiNO3, LiAst, and LiClO4-basic melt solutions were obtained at 40°C. No effect on the chemical shift, and very little effect on the linewidth (i 5 Hz) of the signal for the A101; ion was observed. Thus, it is concluded that the 27Al nucleus is not particularly useful as a secondary probe (to 7Li) for the study of dilute LiX-basic melt solutions. However, the extreme sensitivity of linewidths to changes in melt composition (above XAlCl3 = 0.5) suggests that 27Al NMR may be used, as an alternative to electrochemical methods, to further investigate the acid-base equilibria in AlCl3-based molten salt systems. 8.3. Potentiometry The potentiametric titration curves for the titration of pure basic melt with acidic melt titrant are shown in Figure 20. The reproducibility of the observed cell potential on the basic side of the equivalence point (i.e., from zero to ca. 1 g of the acidic melt titrant) is clearly demonstrated. Fluctuations in the cell potential beyond the equivalence point were often observed in these experiments; however, this behavior was considered to be unimportant since the behavior of the cell potential on the basic side was offoremost interest in these studies. The corrected composition of the titrant (section 8.2, Chapter II) is 65.51 mol96 A1013. The corrected mole fraction of the free chloride ion (Xer), pCl, and observed cell potentials for titration #1 used in subsequent 114 .5: 85.0.0: 50... :95... .98 .0 6:0: 500m -502 5 55508500 .8 55.055 s 8 55305.. 3.22 3555502 .2 0...»... 2:. :2. a... ”as: (1") HIOIMJNII lit; ad a; o; v; «a 0.. — p . _ _ _ h o w. o 0 100m 0 o o 180— o o o 0 loo...— 0 o 0 188 o o CEll POIEIIIII (NUS) 115 <90 000 1.00-1 0 O O O O O 0.781 0.5m O Q 0 O O O O O 0.254 o O .0 0.0 Q 00 90““ Q S o s 0 o ‘ 8 Q I I I l 0.25 050 0.75 1.00 ICIIIC IEII IIIIIII (I) Figure 20. Potentiometry: Ecell Versus Acidic Melt Titrant (g) for the Titration of 45 Mol% AlCl3- Basic Melt. The Results for Duplicate Titrations are Shown; Titration #1 (0), Titration #2 (O). The Uncertainties in the Cell Potential and in the Mass of the Titrant are Smaller than the Size of the Data Points. 116 calculations are given in Table 17. A plot of Ecell versus pCl (corrected) is shown in Figure 21. A least squares fit of the first ten data points to equation 42 (Chapter II) yields a slope of 0.2445 Volts at 35°C (theoretical slope = 0.2434 Volts). The "tailing off" of the actual curve is a consequence of the displacement of the equilibria involving the various silver chlorocomplexes (i.e., equation 42 no longer holds) as the chloride ions released by these species are titrated (7 6). The titration curves for 0.977 mol% LiCl and 0.960 mol% LiClO4-basic melt solutions titrated with acidic melt are shown in Figure 22. The points marked (PPT.) in each curve are the points where the first signs of cloudiness in the melt solutions (presumably, dispersions of LiCl precipitate) were observed. These precipitates persisted in the solutions until the end points of the titrations. The label (CLEAR) designates the points at which the precipitates could no longer be discerned. Both curves start at positive (ca. 30 to 40 mV), rather than zero potentials (cf. Figure 20). If each LiCl molecule requires one chloride ion from the melt to be solublized (i.e., LiClz‘ is formed), equation 42 (Chapter II) predicts a positive cell potential of ca. 10 mV for a 1.0 mol% LiCl-basic melt solution. For the same concentration of LiClO4 in basic melt, the potential should be ca. 24 mV. However, it should be recalled (Chapter II, section A.4.b(l).) that the zero adjustment at the start of a given titration amounted to about 15 mV. Thus, a quantitative interpretation of the nonzero starting potentials in these titrations is not justified. The two curves are shifted slightly with respect to each other since the cell potential is plotted versus the acidic melt titrant, and not pCl. The cell potentials at which the precipitates form in these solutions are 175 mV (LiCl) and 140 mV (LiClO4). Working from Figure 21, these potentials correspond 117 Table 17 Potentiometric Titration Data: Corrected Values of X01- Are Calculated by Using Equation 53; p01 = -Log Xcr. EC Aliq. : Titrant (g)(8) XCI- 9C] (106)“) 0 0.0 0.1000 1.000 0 1 0.0457 0.0938 1.028 8 2 0.0915 0.0878 1.057 16 3 0.1372 0.0819 1.087 24 4 0.1830 0.0762 1.118 31 5 0.2287 0.0707 1.151 39 6 0.2744 0.0653 1.185 47 7 0.3202 0.0601 1.221 56 8 0.3659 0.0550 1.260 64 9 0.4117 0.0501 1.300 74 10 0.4574 0.0453 1.344 83 11 0.5031 0.0406 1.392 94 12 0.5489 0.0360 1.443 105 13 0.5946 0.0316 1.500 117 14 0.6404 0.0273 1.565 129 15 0.6861 0.0230 1.638 145 16 0.7318 0.0189 1.723 162 17 0.7776 0.0149 1.827 185 18 0.8233 0.0110 1.959 211 19 0.8691 0.0072 2.145 252 Table 17 continued 118 Ec Aliq. # ' Titrant (g) (a) XCI' pCl (mV‘sld’) 20 0.8939 0.0050 2.298 285 21 0.9188 0.0029 2.532 337 22 0.9437 0.0009 3.063 418 23 0.9686 -- -- 1040 24 0.9935 -- -- 1045 25 1.0183 -- -- 1046 26 1.0432 -- -- 1046 27 1.0681 -- -- 104“ (a) 4 0.0001 g (b) :i: 1 mV 119 / O / 400% / / / / / O / 300- / O / / O 35: / 4... /. --4 ZOOJ / ¢ 2 / n z E 7. a. /. :1 lo 2‘. b 100‘1 .. O C O O C O O O O I; . . . , 1.0 2.0 3.0 pCl Figure 21. Potentiometry: Ecell Versus pCl (Corrected) for the Titration (#1) of Basic Melt with Acidic Melt Titrant. 120 1.00- db 0 ClflI—bo 075.. Ch 0 Cl: 3 '3 emu—i oqj 3 " o _, 0 ‘ 3 (b0 f, 0.50-( D o E -‘ O 3 03 o o o 06‘? :9 o O 025- #19 8 m. 886’ #9, of 0 D 0 D O "I. 0 00 0 ° T000399°° I 0:20 0150 0175 1100 1.25 ICIDIC I111 IIIIIII (I) Figure 22. Potentiometry: Ecell Versus Acidic Melt Titrant (g) for the 'l‘itrations of 0.977 Mol% LiCl-Basic Melt (O) and 0.960 Mol% LiClO4-Basic Melt ([3) Solutions. The Uncertainties in the Cell Potential and in the Mass of the Titrant are Smaller than in the Size of the Data Points. 121 to pCl values of 1.780 (LiCl) and 1.615 (LiClO4). These results are consistent with the model which is proposed for the solvation of lithium salts in basic melt; LiCl requires only one chloride ion from the melt to form LiClg‘ (and Li20142"), while LiClO4 requires two chloride ions. This is also further evidence (see section 8.1, this chapter) for the spectator status of the perchlorate ion. The values for nP9e, “*Cl‘: n°LiX’ and “*total used to calculate the value of x for the assumed LiClx(1‘X) complexes (see equations 50-58, section 8.2 Chapter II) for the LiCl and LiClO4-basic melt titrations are given in Table 18. Equation 55 is modified for the calculation of x for the titration of the LiClO4-basic melt solution. In this case, no chloride ion is provided to the solution by LiClO4. Then equation 55 becomes "p96 = "*C1‘ + (x‘1)"complex- (9) If ncomplex = n°LiC1049 x : npée _. "*C1- + 1 n°LiClO4 (10) The values of x which are obtained are in agreement with the value of two expected for the Lile or LiZCl42" chlorocomplexes. 8.4. Far-IR Measurements As discussed in Chapter V (section D.), the far-IR spectrum of basic melt is dominated by the v3(F2) (490 and 527 cm’l) and 04(F2) vibrational modes of the AlCl4" ion. The formally IR-forbidden v1(A1) mode for this ion is barely discernable at 345 cm‘1 (Figure 23). It is assumed that this mode can be observed in the IR due to strong ionic associations occurring in basic melt (59). 122 Table 18 Values for nP'”, "Cl” '91.in and "total Used in the Calculation of x for the Assumed LiClx Chlorocomplexes Formed in LiCl and LiClO4- Basic Melt Solutions Lithium Salt (Mol%) Value (moles) 0.977 LiCl 0.960 1.10104 np—ye 6.33 x 10-4 6.59 x10‘4 n*c1- 2.21 x 10'4 4.84 x 10'4 n°Lix 1.91 x 10‘4 1.70 x 10 mm“ 2.43 x 10'2 1.91 x 10-2 x 2.2 2.0 123 0.301- 0.30" 0.151 \N‘ 0.30- ABSORBANCE 0.15 CM“ Figure 23. Far-IR Spectra (150 to son cm-l): A. Basic Melt, B. l M0196 LiCl-Basic Melt Solution. C. 1 Mol% LiCl-1.5 M0196 C211-Basic Melt Solution. 124 The far-IR spectra for basic melt, 1.0 mol% LiCl-basic melt solution, and 1.0 mol% LiCl —l.5 mol96 0211-basic melt solution are shown in Figure 23. In view of the low S/N ratio of the 345 cm'1 band in all three spectra, the effects of the addition of LiCl or LiCl and C211 to basic melt are considered to be negligible. In either case, no new spectral features are observed. In the far-IR spectrum for 1.0 mol% 6LiCl in basic melt (Figure 24), two or more bands are observed between 275 and 425 cm“1 that are not seen for LiCl with a natural abundance of lithium-6. The positions of these bands at 293 cm'l, ca. 360 cm"1 (very broad), and ca. 400 cm’1 do not correspond to the values reported by Klemperer and Norris (180) for the Li2C12 gas phase dimer (335 and 460 cm‘l), nor those reported by Snelson and Pitzer (175) in inert gas matrices. Bands at 186 and 313 curl (6Li2C12), and 174 and 293 cm“1 (7Li2C12) have been observed in the matrix isolation far-IR study of Freiberg e_t _a_l. (176). Isotopic enrichment with 6Li causes high frequency shifts of ca. 20 cm”1 in far-IR spectra of lithium salts and cryptated lithium ion in nonaqueous solutions (143,181). If it is assumed that one or more bands for the Lile or Li2C142‘ chlorocomplexes are masked by the v4(F2) band for the AlCl4 ion at 184 cm‘1 for natural abundance LiCl in basic melt, it is difficult to believe that 6Li enrichment can enable a frequency shift of more than 100 cm‘1 to give rise to the 293 cm“1 (or higher frequency) band. A low frequency shift brought about by 5Li enrichment (thereby moving the band(s) from beneath the 490 cm‘1 band of the AlCl4' ion) is considered to be very unlikely; such an effect would be contrary to the supposed increase in the 6Li-Cl force constant versus that of 7Li-Cl. Thus a logical interpretation of the 6LiCl-basic melt far-IR spectrum is not possible at this time. Improved resolution in this region of the spectrum could aid in this interpretation. 125 $02 33.8 5 83a 83: a; 3:150 Se 3 S: 5:50on ELS— .§ cam JONVMIOSHV .129 owe ewe 2.... ma ,u "nuanuvu .““."1.J.u.."T :mod lvaoo 7-36 :86 fl F1 -e 126 C. Complexation of the Lithium Ion in Basic Melt by Crown Ethers C.l. Lithium-7 NMR C.1.a. Crown/lithium ion mole ratio studies Lithium-7 chemical shifts were measured at 40°C as a function of crown ether/lithium ion mole ratio for ligands 12C4, 1505, B15C5, and 1806 in 1.0 mol% LiCl-basic melt solutions. The structures of these ligands are shown in Figure 25. A single 7Li resonance line was observed (fast chemical exchange at this temperature and magnetic field strength), with signals shifting upfield H as the crown ether/lithium ion mole ratios were increased. Lithium—7 chemical shift data obtained in these studies is given in Table 19. A plot of 7Li chemical shifts versus crown/Li+ ion mole ratios is shown in Figure 26. Initial computer fits of these data were based on a model which assumed a two-site fast exchange between "free" and crown-complexed lithium ion in basic melt. KF "Li+" + crown Li+crown (1 1) After the successful fitting of the dependence of 7Li chemical shifts on LiCl concentration in basic melt (section B.1.a), the crown complexation data were fitted to a three-site fast exchange model. 21.1012- :: Li20142' (12) K “ Lile + crown :L_" Li-crown C12‘ (13) ./_\, {)0 (U: LU {W .i'\_/03 C“ ’1 9w?) Figure 25. The Structures of 1204, 15C5, 81505, and 18C6. BENZO-ts-OMW N-S 128 Table 19 Lithium-7 Chemical Shifts as a Function of Crown/Lithium Ion Mole Ratio in Basic Melt at 40°C 12m: Li+ = 0.0771 g Ligand (fl) Mole Ratio 6(ppm)(a) 0.0 ~- + 1.39 0.013 0.17 + 1.23 0.038 0.49 + 0.87 0.040 0.52 + 0.88 0.042 0.54 + 0.79 0.047 0.61 + 0.93 0.053 0.69 + 0.77 0.073 0.95 + 0.37 0.078 1.0 + 0345 0.079 1.0 + 0.32 0.089 1.2 + 0.25 0.092 1.2 + 0.10 0.132 1.71 + 0.08 0.152 1.97 + 0.06 0.286 3.71 - 0.05 0.339 4.40 - 0.08 0.399 5.18 - 0.09 1.027 13.3 - 0.22 129 Table 19 continued 1505: Li’r = 0.0774 g Ligand (fl) Mole Ratio 5 (ppm)(a) 0.0 -- + 1.39 0.022 0.28 + 0.93 0.041 0.53 + 0.65 0.046 0.60 + 0.53 0.046 0.59 ' + 0.23 0.074 0.96 - 0.33 0.074 , 0.96 - 0.58 0.079 1.0 - 0.30 0.089 1.2 - 0.75 0.095 0.96 - 0.70 0.111 1.44 - 0.78 0.137 1.78 - 0.86 0.187 2.43 - 0.90 0.218 2.83 - 0.91 0.285 3.70 - 0.92 0.421 5.46 - 0.93 0.506 6.56 - 0.93 130 Table 19 continued 81505: Li+ = 0.0776 M Ligand (fl) Mole Ratio 6(ppm)(a) 0.0 -- + 1.40 0.008 0.1 + 1.23 0.012 0.16 + 1.03 0.026 0.33 + 0.80 0.032 0.43 + 0.58 0.036 0.46 + 0.56 0.036 0.48 + 0.41 0.041 0.52 + 0.44 0.058 0.76 + 0.16 0.059 0.77 + 0.09 0.074 0.96 - 0.19 0.095 1.2 - 0.31 0.115 1.49 - 0.47 0.133 1.71 - 0.51 0.177 2.28 - 0.56 0.235 3.03 - 0.59 0.392 5.11 _ 0.60 131 Table 19 continued 18C6: Li+ = 0.0776 M Ligand (fl) Mole Ratio 5(ppm)(a) 0.0 -- + 1.39 0.007 0.09 + 1.35 0.018 0.24 + 1.33 0.026 0.34 + 1.29 0.038 0.49 + 1.22 0.045 0.57 + 1.18 0.059 0.77 + 1.12 0.098 1.3 + 0.98 A 0.148 1.91 + 0.82 0.239 3.08 + 0.56 (8) Versus external 0.015 _l\_/I_ LiCl in D20 uncorrected for magnetic susceptibility; the uncertainty in 6 is t 0.02 ppm. 132 - 1.0 - 15C5 J 3 I i . BENZO-ISCS . I I -o.5 « 1 I 1204 . ° 1 . é ' ‘ 8085 'I ° l8C6 (PPM) / . l O" ’ ’. 0.5- § . 1.0 ~ / 1.1 ..’.. ,2! 1.5 ' ' 2 3 4 5 MOLE RATIO(LIGAND/Li) Figure 26. Lithium-7 Chemical Shifts as a Function of Ligand] Lithium Ion Mole Ratio for the Determination of the ' Concentration Formation Constants of Li+-Crown Complexes in Basic Melt at 40°C. Solid Lines are the Computer-Generated Curves. 133 where, for the moment, it was assumed that the chloride ions maintain contact with the Li+ ion in the crown complex. In this model, the'values for KDiss.’ 8 monomer: and 5dimer were entered as constants. The formation constants and limiting chemical shifts for the crown complexes of the lithium ion in basic melt calculated from both models are given in Table 20. In comparing these results, it is clear that the monomer-dimer equilibrium does not appreciably effect the formation constants for the stronger 15C5 and B15C5-lithium ion complexes. However, the formation constants for the weaker 1204 and 18C6 complexes are increased by 0.25 and 0.92 log K}: units, respectively. The log K}: value for the 1806 complex is still the smallest of the four (crown complexes), reflecting the disparity between the size of the lithium ion and the diameter of the 18C6 molecule (rLi+ = 0.86 fig. d18C6 = 2.6 to 3.2 a). The results obtained with the three-site exchange model are listed in Table 21 along with the previous results of Smetana and Popov (135) for the crown complexation of the lithium ion in various nonaqueous solvents. The selectivity of the 15C5 ring size for the lithium ion (lg. 1204 and 18C6) is apparently reduced in the molten salt as compared to nonaqueous solvents. This leveling effect is probably due to the strength of the dimer formation (log KD = 2.82 i 0.39) in the melt. The 7Li chemical shift data give no indication as to the number (if any) of chloride ions which are associated with the lithium ion in the lithium-crown complexes. Considering the nominally two-dimensional geometry of the crown molecules, it is possible that one or two chloride ions remain coordinated to the lithium-crown complexes in basic melt. Several examples of counterion participation in the coordination of the lithium ion in crown complexes are discussed in section B.3.a, Chapter 1. Similar coordination of the lithium ion 134 Table 20 Crown Complexation of the Lithium Ion in Basic Melt; Complex Formation Constants and Limiting Chemical Shifts for the Complexes Model #1: "Lit" + cnown e——* 1.1+- cxowu Crown Log Kp 50 (ppm) 1204 1.87 1 0.12 - 0.18 4 0.05 1505 2.39 i 0.17 - 0.96 2 0.06 81505 2.33 :l: 0.05 - 0.64 :1: 0.02 18C6 0.59 i 0.12 - 0.48 4: 0.28 Model #2: Li2C142" = 2L1012- (A) 1.71le + CROWN .1: Li~CROWN°Clz"(B) Crown Log KP“) 50 (ppm) 1204 2.12 i 0.05 - 0.36 :1: 0.09 1505 2.32 1: 0.08 - 1.91 :1: 0.14 B15C5 2.36 1: 0.03 - 1.23 :1: 0.05 1806 1.51 d: 0.06 + 0.14 :1: 0.20 (8) Calculated errors do not reflect propagation of errors from the monomer—dimer equilibrium 135 2: 8538a 30 3 3%... .2 Bee: 52m 3 mm.c N=.c 1 mc.e 3°.o 1 em.e 85.: 1 cm.¢ eo.e 1 :m.: :mé ::.~ «5.: 34.: ::.: 3.: SA :03 11 11 11 11 11 11 m:.: m:.: H 11 11 11 11 11 11 m:.~ on: mOmfim m:.: ::.: H m:.: 11 m:.: ::.: H 3.: w:.: H :m.: :m.: 2.4 w A 3.: :v.: 3.: :m.: :03 m:.: m:.: an m:.: 34.: H ::.: m:.: L" ::.: m:.: H :m.: ::.H v:.~ m:.¢ 3.: ::.: :m.: :7: «0:: 25.: on an 84 Es... on my. 8.. 38. on em m3 ER. on an m3 is»: Eve—.3034 Evombmsoaooa‘ 3:26th A3302 3an 5520.0. 98:05.02 35> 5 6.3 v.30! Bank—02 use: 5 8803500 esp—01.5. 5353 .8 8:3, on 0.... mm m3 a: 036,—. 136 by chloride ions at axial positions (with respect to the planes of the crown molecules) in the basic melt solutions seems reasonable. C.2. Potentiometry The effect of the addition of 1505 to a 1.0 mol% LiCl-basic melt solution was measured at 35°C potentiometrically. Titration data are listed in Table 22, and a plot of these data is shown in Figure 27. If the crown complexation reaction proceeds by the release of one or two chloride ions from the LiClg‘ ion, it would be expected that the amount of free chloride ion in the melt would increase (i.e., the pCl of the working compartment of the cell would decrease), resulting in a lower cell potential as the 1505/lithium ion mole ratio is increased. If the complexation reaction proceeds with retention of both of the chloride ions, no change in the p01 (and cell potential) would be expected to occur. The slight increase in the cell potential with increasing 15C5/Li+ mole ratio is puzzling, since it suggests that additional chloride ions are being removed in the process of crown complexation. Although transport of the crown complex across the boundary might product a positive change in the cell potential, the lack of a time-dependence for this change is unexplainable at this time. In the electrochemical study by Dymek it. _a_l_. (93) of mass transport in the AlClg-lmCl (Im+ = 1-methyl-3-ethylimidazolium ion) molten salt system, the majority charge carrier in these melts was determined to be the Im+ ion (t+ = 0.80 :1: 0.09). Based on conductance measurements on NaI and RbI-acetonitrile solutions in the presence of various crown ethers, Della Monica _e_t a_l. (182) have concluded that "In the systems with crowns characterized by a central hole big enough to place the positive ion in the center of the molecule, the charge carried 137 Table 22 Potentiometric Titration Data: Observed Cell Potentials as a Motion of 1505 Titrant (mg) and the 1505/Lithium Ion Mole Ratio at 35°C 1505/n+0” Cell Aliq. 3 1505 (mgW') Mole Ratio Potential (mv)(°) 0 0.0 --— 29 1 10.4 0.24 32 2 20.8 0.49 33 3 31.2 0.73 33 4 41.6 0.97 33 5 52.0 1.2 34 6 62.4 1.5 35 7 72.8 1.7 36 8 83.2 1 9 36 9 93.6 2 2 37 10 104.0 2.4 38 11 114.4 2.7 38 12 124.8 2.9 39 13 135.2 3.2 39 14 145.6 3.4 39 15 156.0 3.7 40 16 166.4 3.9 40 17 176.8 4.1 40 18 187.2 4.4 40 19 197.6 4.6 40 Table, 22 continued 138 1505/Lit“) Cell Aliq. # 15C5. (mg)(3) Mole Ratio Potential (mV)(°) 20 208.0 4.9 40 21 218.4 5.1 40 22 228.8 5.4 40 (a) 10.1 mg (b) [Li+] = 0.0790 M (c) tlmV 139 6:3. so: .3. 5353.302 .5 3.5 no...“ 95> zoom “5053238 2:. =3 .2 +:\.1__-.:1: w m m u - n =0. .32: 7.3.31: 02 . 0‘. O”. on .2. 2:03 (A') "HINDI 1113 140 by the cations is sufficiently shielded so that both interactions between the cation and the solvent, and those with the negative ions of the solution are greatly decreased." It may be possible to apply this argument to explain the anomolous behavior of the cell potential in the titration of the LiCl-basic melt solution with 1505, but conductance or transference number measurements would be required to shed more light on this phenomenon. D. Conclusiom The 7Li NMR data obtained in this study indicate that two different chlorocomplexes of the lithium ion are formed in basic melt solutions of LiCl and other lithium salts. Although the only evidence for the monomer-dimer equilibrium is based on a computer fit of these data, no other reasonable model was successful in accounting for the observed chemical shift behavior. The magnitudes of the 7Li quadrupole coupling constants calculated from spin-lattice relaxation rates of the lithium ion in basic and acidic melts suggest that the electric field gradient at this nucleus in basic melt is similar to that of lithium halide dimers in the gas phase. In acidic melt, the EFG for the 7Li nucleus is more comparable to that of the lithium ion in aqueous or nonaqueous solutions. The results obtained from the potentiometric titrations of LiCl and LiClO4-basic melt solutions confirm that two chloride ions are associated with each lithium ion in basic melt solutions. The cell which was designed for these experiments seems well suited to the studies of chlorocomplex formation with other metal ions in basic melt. The crown-lithium ion complex formation constants obtained in basic melt solutions decrease in the same order (15C5 > 1204 > 18C6) as that observed for lithium-crown complexation in nonaqueous solutions. However, it appears that the monomer-dimer equilibrium tends to minimize the selectivity of 141 complexation (correlation of the complex stability with matching of the ion/cavity size) as compared with macrocyclic complexation in nonaqueous solutions. Further electrochemical studies of LiCl-basic melts with 1505 are called for to ascertain the cause for the observed increase in cell potential with increasing 1505/m“ mole ratio. CHAPTER IV CRYPTAND COMPLEXATION OF THE LITHIUM ION IN THE A1013-BPCI SYSTEM A. Introduction Previous investigations have demonstrated the utility of 23Na (183), 39K (184), and 133Cs (185) NMR methods for the study of cryptand complexation of the respective alkali metal cations in aqueous and nonaqueous solutions. Similar 7Li NMR solution studies are discussed in Chapter I (142,143). It should be pointed out that in these previous studies, all 7Li N MR measurements were made at a field strength of 14.09 kG. Cahen e_t 31: (142) observed slow exchange at 30°C (two 7Li NMR signals at cryptand/lithium ion mole ratios less than. 1:1) for the Li+-CZII system in various solvents, and for the Li+-0221 system in pyridine. The purpose of this study was to investigate the complexation of the-lithium ion in basic melt by cryptands C211, €221, 0222, and 02322. The structures of these cryptands are shown in Figure 28. In addition to 7Li N MR, potentiometry and x—ray crystallography have been used in these investigations. 8. Basic Melt Solutions Studies B.1. Lithium-7 NMR Lithium-7 NMR spectra were obtained at 40°C for cryptand/lithium ion mole ratios from zero up to 4.2:] (0211), 3.3:1 (C221), and 1.2:1 (C2322) in basic melt solutions. For 0222, 0222/lithium ion mole ratios from 0.76 to 2.8:1 were studied. Some typical spectra from these studies are shown in Figures 29-32. No samples were prepared for the Li+-02322 system in basic melt above the 1.2:1 mole ratio due to precipitate formation. Attempts to resolublize the precipitate by adding excess cryptand (mole ratio 2:1) were unsuccessful. On warming to ca. 60°C, some of the solid dissolved, but reappeared when the melt was cooled to room temperature. Over the three week conditioning period for the Li+-C211 mole ratio 142 C222 143 02822 Figure 28. The Structures of 0211, 0221, 0222, and 02322. 144 ' T I Y I— -s 8 (PPM) Figure 29. Lithium-7 NMR Spectrum: 0.985 Mol% LiCl- 0.888 M0196 0211 in Basic Melt at 40°C. The Upfield Signal is Assigned to the Complexed Lithium Ion Site. 145 Q-n Nu ‘- «E. q _, ... .1 8 (PPM) Figure 30. Lithium-7 NMR Spectrum: 0.992 Mol% LiCl - 0.988 Mol% C221 in Basic Melt at 40°C. The Upfield Signal is Assigned to the Complexed Lithium [on Site. 146 Figure 31. 5 (PPM) Lithium-7 NMR Spectrum: 0.980 Mol% LiCl - 0.98? Mol% C222 in Basic Melt at 40°C. The Position of the Maximum of the Unresolved Bandshape is Taken to Correspond to the Chemical Shift of the Complexed Lithium Ion Site. 147 .33 :3 5353 853500 «5 8 3.552 a 35m 23...: 2:. .93 «a :0: 98m 5 «~50 8...: a3... . 83 8.0: 2: “52825 :22 p.535..— Ea... .m VI NI M _N .2 in 148 samples, small amounts of a crystalline material were observed to precipitate from the solutions with a mole ratio of less than 1:1. Above this mole ratio, all samples were homogeneous. This precipitate did not completely dissolve on warming the solutions to 40°C. All samples prepared for the 0221-LP“ and 0222-Li+ mole ratio studies remained homogeneous at 25°C or 40°C. Slow chemical exchange was observed under the stated experimental conditions of 40°C and 42.28 kG field strength for all four lithium-cryptand systems in basic melt. For 0211, (3221 and 02322, the chemical shift of the lithium ion complex signals were observed to be insensitive to the cryptand/lithium ion mole ratios. However, the chemical shift of the signal for "free" lithium ion (ie., the fast exchange signal due to the monomer and dimer lithium chlorocomplexes) was observed to shift downfield with increasing cryptand/lithium ion mole ratio (Figures 33-35; Table 23). This downfield shift is taken as strong evidence for the dissociation of the LiZCl42' dimer, and subsequent complexation of the lithium ion coming from the dissociation of the Lile species. The constancy of the chemical shifts of the complex signals suggests that the lithium ion is shielded from the chloride ions in the melt by the organic "skin" of the cryptands; i.e., the lithium ion resides within the cryptand cavities (inclusive complexes). If this is the case, then upon complexation two chloride ions must be released from the Lile ion. Therefore, the chloride ion activity of the melt solution should increase (decreasing p01) as the complexation reaction proceeds. A test of this hypothesis is provided in the potentiometry experiment discussed in the following section. The 7Li NMR spectra for the Li+-0222 system in basic melt were observed to be much different from those for the other three Li+-cryptand systems (Figure 36). In this case, the "free" and complexed lithium signals overlapped yielding broad (ca. lOZHz) lineshapes. In addition, the signal assigned to the 149 .358 3s: «5 do 3mm 2: E c8885 93 9.5 3359.0 2: 5 meringue: 4...: 39m 5 .53— 2e: :3 5353230 2: do Eczefim es . 0.3 as .6. £353 vane—e58 o5 :02? .8 £5 33525 T5353 .8 933m 2:; :2: + :\:3 o; . _ ‘ UIHS 1V3lW3H3 '1‘ (de) ’ti cntmcu sum (my 150 -t.5-4 d}— V ~0— —\ 7— + -O-- —O— + -1.4« 4.3— u-t 1.5-I 1.6“ + 1.74 1 I I f ' 1 ’ 0,2 04 05 08 10 12 1‘ C221/IN uou mm Figure 34. Lithium-7 Chemical Shifts for "Free" and Complexed Lithium Ion at 40°C as Functions of the C221/Lithium Ion Mole Ratio in Basic Melt. 151 #3: cum-5 5 65.3— 362 :O— EEfianum—NU 9:. no 9.03055 no 03‘ «a :0— 5353 85358 o5 :98? .8 93a 3359.0 #5355 .3 953m 22.. so: + :\-__3 N... 3 ad ad . . h _ _ _ Jo JO [6.— A .l .7 s . H 11 Im.— W M. v .I S H H l Iv; ) P a .\ .d W \\ l\ [0.7. e ._ e e e + e r..- 152 Table 23 Lithium-7 Chemical Shifts Observed for the Cryptand 0211, 0221, 0222, and 02322 - Lithium Ion Mole Ratio Studies in Basic Melt at 40°C C211 C221 Cryptand/Li+ a Mole Ratio F (ppm)(a) 60 (ppm)(8) 0.0 + 1,55 __ 0.089 + 1.54 -- 0.31 +1.57 - 0.79 0.645 + 1.66 - 0.79 0.759 + 1.75 - 0.79 0.901 + 1.73 - 0.79 1.03 + 1.86 - 0.79 1.18 + 1.91 - 0.79 1.35 (b) - 0.79 1.53 (b) - 0.79 1.93 (b) - 0.79 2-42 (b) - 0.79 2.96 (b) - 0.79 3.63 (b) - 0.79 4-37 (b) - 0.79 0.0 + 1.55 -- 0.23 + 1.55 - 1.44 0.41 + 1.55 - 1.46 0.594 + 1.58 - 1.46 'Table 23 commhuuxl C222 02322 153 (hauflmuuflflj+ _ Mole Ratio 5,. (ppm)(a) dc (ppmfia) 0.716 + 1.66 - 1.44 0.835 + 1.68 - 1.43 1.00 + 1.67 - 1.43 1.12 + 1.80 - 1.42 1.28 + 1.79 - 1.43 1.65 (b) - 1.42 2.06 (b) - 1.43 2.53 (b) - 1.43 3.44 (b) - 1.43 0.757 + 0.94 - 1.000) 0.791 (b) - 1.01M 0.842 (b) -1.01 0.876 (b) - 1.08 1.01 (b) — 1.19 1.14 (b) - 1.34 1.45 (b) - 1.41 1.76 (b) - 1.49 2.80 (b) - 1.50 0.0 + 1.56 -_ 0.046 + 1.55 -- 0.092 + 1.57 -- 154 Table 23 continued (10.61%? 5F (ppm)(a) 5c (pme’) 0.14 + 1.53 -- 0.23 + 1.53 -- 0.318 + 1.55 - 1.08 0.439 + 1.55 - 1.09 0.635 + 1.57 - 1.09 0.740 + 1.58 ' - 1.08 0.948 + 1.63 - 1.08 1.18 + 1.61 - 1.08 (a) Versus external 0.015 M LiCl/D20; chemical shifts are corrected for the magnetic susceptibility of basic melt vs. that of water. (b) Signal no longer detectable. (c) Calculated from the NTCCAP deconvolution of the spectrum. 155 C222/U" MOLE RATIO: . 2.80 #fj k 1.76 .3. A 0.847 0.791 0.757 U I I' I r V l T I U I -t I 5 O 5 8 (ppm) Figure 36. Lithium-7 NMR Spectra: Observed Bandshapes at 40°C for C222/Lithium Ion Mole Ratios of 0.7 57 to 2.80; 1. 156 Li+-0222 cryptate complex exhibited a significant (AG = -0.5 ppm) upfield chemical shift as the mole ratio was increased (Figure 37). It should be noted that the linewidths of the complex signals for the other three Li+-cryptand systems ranged from ca. 8 Hz (C221) to ca. 20 Hz (02322). The spectra for the Li+-0222 system were deconvoluted by using the NTCCAP subroutine (section B.1.b., Chapter II) to estimate the linewidths of the complex signals as a function of the C222/lithium ion mole ratio. These results are given in Table 24. The linewidths of the complex signals decrease with increasing mole ratio, tending to values similar to those of the other cryptate complexes (ca. 13 Hz). Thus, it seems that the temperature at which these spectra were measured (40°C) is near, but slightly below the coalescence temperature for the system. The exchange is slow on the N MR time scale, with two signals observed ("free" and complexed lithium ion) which are broadened by the exchange to the point where the signals overlap. At the coalescence temperature, the rate of a first-order decomplexation process (k-1) is given by (186), TTAv (l) where Av: v A - 9 B and A and B refer to the free and complex sites in the absence of exchange. Let us assume that equation (1) applies to the Li+—C222 system at 40°C, and that the chemical shift observed for the complex at a C222/Li+ mole ratio of 2.80:1 (6: 5B = -1.49 ppm) is a fair approximation of the limiting chemical shift of the complex site. The chemical shift of "free" lithium ion (site A; no 0222 present) is 6A = +1.55 ppm. Thus, AG = 3.04 ppm which, with a resonance frequency of 69.951 MHz, gives a value of Av = 213 157 .3qu 3°: :0— E=_53\NNNU 05 no 603055 a no 0...: «a «no: unnam— 5 Nay—9:00 NNNUILA 05 3m 53.—m naomEusO r1535: Sn 95.3% 9:: :3. + :\-.3 O. n O.“ . — — 0% TO? INA! lJIHS IVOIWIHI) ”t (me) If [m.pl 158 Table 24 Calculated Linewidths of the 7Li NMR Signals of the Li+czzz Complex in Basic Melt at 40°C 0222/Li+ Mole Ratio AUl/z complex (113)“) 0.7577 177 1 44 0.791 123 1 8 0.842 121 1 6 0.876 101 1 6 1.01 85 1 5 1.14 63 1 5 1.45 58 1 5 1 76 46 1 3 2 80 13 1 2 (a) Obtained by using the NTCCAP deconvolution subroutine. 159 Hz. Substituting this value into equation (1) yields k_1 = 5 x 102 s"1 (only one significant figure is given here in light of the assumptions upon which the calculation is based). Cox _e_t 31. (187) have estimated a k-1 value of > 3 x 102 s'1 for the Li+-0222 system in methanol at 25°C. The NTCCAP subroutine was also used to calculate integrated areas for the signals due to the "free" and complex sites in the Li+-C221, Li+-0222, and Li+C2322 systems at 40°C in basic melt. These areas were then used to calculate the respective cryptate complex formation constants. A similar procedure was not possible for the Li+—C21l system 'due to the observed precipitate formation. At mole ratios 1:1 where samples remained homogeneous, the "free" lithium ion signal was too low in intensity to be detected. According to Szczygiel (186), the absorption part of an NMR resonance line is given approximately by. 8(1/T*2)e(‘DE/T*2) (2) (1 /'I""2)2 + (A002 5(0)): where K is a constant, T*2 is the apparent spin-spin relaxation time, DE is the post-90° pulse delay time, and Aw is the frequency in rad/s. Since T*2 = 1/1T LW' (3) where LW' is the apparent linewidth (=AV true + LB) and 000 : ZAVTT (4) equation (2) becomes 160 K(wLw')e('DE"LW') S (00) = (5) (7 LW')2 + 4 (1169)2 Multiplying the numerator and denominator by 1/(1r LW')2, K(1rLW')‘1 e('DE"Lw') S ( t0) = (6) 1 + 4 (Av/LW')2 In the documentation for the Nicolet 1180 computer software, the expression for S( w) is given as I S : (w) 1 + 4(Av /Lw')2 (7) where I is the observed signal intensity. Comparing equations (6) and (7), I = K («an'r1 e('DE" LW') (8) Rearranging, K = InLW'e(DE "11W" (9) where K is now identified as the signal intensity corrected for artifical linebroadening (LB) and the delay time. Therefore, the corrected area of the resonance line is given by At = 11K (10) 161 and, At = I 112 LW' e(DE 7' LW') (11) This proceeding derivation has been suggested by R. Boss (188). In practice, it was found that corrections of the areas by using equation (11) did not significantly change the HF values, considering the uncertainties in these results. The fraction of complexed lithium ion is given by fc = Act / Aft Act (12) To explicitly take into account the monomer-dimer equilibrium, equation 43 (section B.1.b., Chapter II) is modified to give 4 K1) fc CLi ' KF = (13) [(1 + 8KDCLiff)l/2 - 111Cc — chLi] where ff = 1 - fC and KD is the dimerization constant. The 7Li NMR spectra chosen for deconvolution were selected so that large differences between Aft and Act were avoided. This was found to reduce the subsequent errors in the calculated Kp values. The results of these Calculations are given in Table 25. Averaged log KF values for the Li+-C221, Li+-C222, and Li+-02322 systems in basic melt are listed in Table 26 along with some results from previous studies in aqueous and nonaqueous solutions for comparison. In basic melt, the stability constants for the complexes increase in the order Li+-C2322 < Li+-C222 < Li+-0221. The larger value for C221 versus 0 C222 is reasonable since the cavity size of 0221 (2.2 A) is a better match 162 Table 25 The Fractiom of "Free" and Complexed Lithium Ion Obtained by Deconvolution of 7Li NMR Spectra in the Cryptde Lithium Ion Mole Ratio Studies in Basic Melt. Cryptate Complex Formation 0211 C222 Constants Calculated by Usilg Equation 4. Mole Ratio ff fc K1: (5’1) 0.594 .6502 .3498 245 .6605 .3395 226 .6615 .3385 225 0.716 .5197 .4803 394 .4200 .5800 494 .4210 .5790 491 .4493 .5507 406 1.00 .4158 .5842 309 .4523 .5477 255 .5098 .4902 189 0.757 .7021 .2979 107 .7003 .2997 108 0.791 .6344 .3656 149 .7160 .2840 91 .6244 .3756 158 0.842 .7046 .2954 89 .6738 .3263 106 .7119 .2881 85 0.876 .6492 .3508 114 .6749 .3251 99 Table 25 continued 163 Mole Ratio ff fc KP (_Lj’l) 0.6750 0.3250 99 1.01 0.4864 0.5136 208 0.6075 0.3925 113 0.5626 0.4374 142 1.14 0.6261 0.3739 85 0.6051 0.3949 94 0.5051 0.4949 150 0.6167 0.3833 89 0.439 0.9129 0.0871 35 0.9472 0.0528 19 0.9446 0.0554 20 0.635 0.8642 0.1358 39 0.9026 0.0974 26 0.8804 0.1096 30 0.740 0.7515 0.2485 79 0.7632 0.2368 73 164 Table 26 Lithium Cryptate Stability Constants“) in Basic Melt, Water, and Various Nonaqueaus Solvents Cryptand Solvent 0211 0221 0222 02322 H20 5.5 2.50 0.99 (b) -- MeOH 8.04 5.38 _ 2.6 2.19“” EtOH 8.47 5.38 2.3 -- AN 10 10.3 7.0 —- PC ' 12.44 9.60 6.94 -- NMP(°) 6.43 3.48 2.97 -- DMF 6.85 3.58 -- -- DMSO 5.84 2.77 1.0 —- PYR -- -- 2.94m -- Basic Melt -- 2.51 2.06 1.60 (10.15) (21:0.12) (i0.25) (a) Taken from reference 189. (b) Taken from reference 142. (c) NMP = N-methylpropionamide ((1) Taken from reference 191. 165 for the lithium ion (VLF = 0.86 X) than that of C222 (2.8 X). The smaller value for C2322 versus C222 is probably due to the reduced conformational flexibility of the former versus the latter cryptand. Cox 23.11: (190) have also observed, in various nonaqueous solutions, smaller stability constants for the C2322-M+ (M2+ = alkaline earth cations) cryptates than for the C222-M2+ cryptates. In methanol solutions, Cox g g. (191) also determined that the stability constant for the C222 complex of the lithium ion is ca. 0.4 log Kf units larger than that of the C2322-Li+ cryptate. From Table 26, it appears that the stability constants for the complexes in basic melt are generally smaller than those in aqueous or nonaqueous solutions. In addition, the change in the complex stability from the C222 to the 0221 complexes is either equal to, or less than (by 2 to 3 log K}: units) that found for the other solvents. As was found in the lithium-crown complexation studies (section C.1., Chapter III), it seems that the equilibrium between the monomer and dimer lithium chlorocomplexes tends to minimize the selectivity of the cryptand complexation of the lithium ion. 8.2. Potentiometry The observed changes in the cell potential as a function of C2322 titrant and the C2322/lithium ion mole ratio in the titration of a 1.0 mol% LiCl-basic melt solution with C2322 are shown in Figure 38. Data from this experiment are listed in Table 27. Recalling the discussion of the results for the similar titration using 1505 as the titrant (section 0.2., Chapter III), the titration curve in Figure 38 clearly indicates that chloride ions are released in the process of 02322 complexation of the lithium ion in basic melt. It is reasonable to expect an analogous response of the cell potential to titrations with C211, C221, or C222. Cryptand C2322 was chosen for this experiment since the precipitation of the C2322°LiAlCl4 complex provides a visual cue as to when the 1:1 cryptand/lithium ion mole Cfll 2011111111 (111') 166 45 ++ m * * ‘1] /I_ 1 5'0 100 250 outrun-2,22 11131111 (M) I 7/ I! I 0.5 150 1.5 [3.0 3.5 cnvriluo-zszz/tifion MOLE RAIIO Figure 38. Potentiometry: Ecell Versus 02322 Titrant (mg) and the C2322/Lithium Ion Mole Ratio. 167 Table 27 Potentiometric Titration Data: Observed Cell Potentials as a Function of C2322 Titrant (mg) and the 02322/Lithium Ion Mole Ratio 02322 02322/LP“) _ Aliq. # (mg) Mole Ratio lice" (mV)(b) 0 0.0 -- 43 1 9.7 0.13 43 2 19.4 0.259 43 3 29.1 0.388 42 4 38.8 0.518 43 5 48.5 0.647 41 6 58.2 0.777 40 7 67.9 0.906 39 8 77.6 1.04 38 9 87.3 1.17 34 10 97.0 1.29 33 11 106.7 1.42 36 12 116.4 1.55 36 13 126.1 1.68 36 14 135.8 1.81 36 15 145.5 1.94 36 16 155.2 2.07 35 18 174.6 2.33 36 24 232.8 3.11 37 26 252.2 3.37 37 (a) [Li+ 1 = 0.790 131; (b) 1 1 mv 168 ratio is reached (section 8.1.). As shown in Figure 38, the onset of the precipitation was observed to occur at about a mole ratio of 1.4:]. The slight increase in the cell potential for the 1.4:1 and higher mole ratios is probably not significant in light of the heterogeneous nature of the solution at the higher mole ratios. The heterogeneous equilibrium Li(02322)012‘ + AlCl4" :C2322-LiAlCl4(S) + 2Cl’ (14) is proposed to account for the behavior of the cell potential in the course of the titration, as well as the constancy of the chemical shifts of the C2322 complex signals with increasing C2322/lithium ion mole ratio. C. Characterization of the Solid Lithium Cryptate Complexes C.1. Elemental Analyses The results of the elementaI analyses of the assumed C2322-LiAlCl4 and C211-LiAlCl4 complexes performed by Galbraith Laboratories are shown in Table 28. Fair agreement between the actual and theoretical analyses for the C2322 LiAlCl4 complex was obtained. Less satisfactory agreement was obtained for the C211-LiAlCl4 complex, particularly for nitrogen (5.28 _vs. 6.04 wt%), oxygen (18.84 E. 13.79 wt%), and lithium (0.87 313. 1.50 wt%). However, the actual results are in better agreement with the theoretical composition based on the C211-LiAlCl4 stoichiometry than formulations such as 0211-LiCl (carbon: 52.96 wt%) or Cle-LiCl-BPCI (carbon: 55.52 wt%). Considerable difficulty was encountered in drying the crystalline solids isolated from basic melt solutions of 0221 and LiCl, and C222 with LiCl; traces of basic melt and benzene from the mother liquor clung tenaciously to the 169 82: $5.2: *2: oomvdm 3.8 2.2 2.2 2.: 8 3.1 3.5 :5 3.1 3. S; S... S; 3.: E 3.2 :2: . 2.2 :2: o 3.5 3.1 2.5 5:4 2 2.1 33 3.1 2.1 m 2.5.. 3.: 2.: 11.3 o 335 .85. A855 .5521 $55 .85. $55 :53 .5555 3023.28 4825.356 863550 33.50 1025.28 55 555.3558 55 .5 $5241 35555 55 co 5555 «N 030,—. 170 crystals, even after one week of pumping at _<_ 10'5 torr. Although this posed no problem for the election and mounting of single crystals for x-ray analysis, samples which were sufficiently dry for submission for elemental analysis could not be obtained. 0.2. Lithium-7 Magic Angle Spinning um}. The 7Li MASNMR spectra (spinning and static) for powder samples of LiCl, LiAlCl4, C2322-LiAlCl4, and C211-LiAlCl4 at 22°C are shown in Figures 39-42. Chemical shift and linewidth data for these spectra are given in Table 29. Solid state spectra could not be obtained for the (assumed) C221-LiAlCl4 and C222-LiAlCl4 complexes due to the drying problems described in the preceeding section. The classic Pake doublet (m = 1/2 m = -l/2 transition) was observed for LiCl in the static mode (Figure 39, top). According to Fyfe (192), for a nucleus with a spin of 3/2 experiencing large quadrupolar interactions in a glass or polycrystalline powder, the observed spacing of the doublet equals (25/9)A2 with A2 defined by A2 = 3. _L(X)2 (15) 64 v0 where x is the nuclear quadrupole coupling constant (= eZqQ/h). From Table 29, the observed splitting (5.5 kHz) yields a value of A2 = 2000 Hz. Substituting this value into equation 15, a coupling constant of 1.7 MHz is obtained for LiCl. This result is within an order of magnitude of the value for 7Li in lithium silicate glasses (910 kHz) obtained by Tokuhiro _e_t_ gl. (1 7 4). No splitting was observed in the static spectrum of LiAlCl4 (Figure 40, top), which indicates a smaller quadrupolar interaction for the 7Li nucleus in this compound. In this case (192), 171 Figure 39. Lithium-7 Solid State NMR Spectra: Static (top) and Magic Angle Spinning (02.7 kHz) (bottom) Spectra for Polycrystalline LiCl at 22°C (100 Scans). 1 kllz Figure 40. Lithium-7 Solid State NMR Spectra: Static (top) and Magic Angle Spinning (Ql.8 kHz) (bottom) Spectra for Polycrystalline LiAlCl4 at 22°C (100 Scans). Figure 41. 173 Lithium-7 Solid State NMR Spectra: Static (top) and Magic Angle Spinning (92.1 kHz) (bottom) Spectra for Polycrystalline 02322-LiAlCl4 at 22°C (20,000 Scans). Figure 42. 174 2 kHz Lithium—7 Solid State NMR Spectra: Static (top) and Magic Angle Spinning (Q0.8 kHz) (bottom) Spectra for Polycrystalline 0211-LiAlCl4 at 22°C (20,000 Scans). 175 Table 29 Lithium-7 Solid State NMR Results for Various Lithium Compounds Linewidth (Hz) Sample 6 (ppm) spinning static x (kHz) 0.015 M LiCl/D20 0.0 -- 19 -- LiCl -3.2 450 (q splitting: 1700 2.7 kHz 5.5 kHz LiAlCl4 -0.8 58 ((1 420 1.7 1.8 kHz C2322° +1.0 200 © 1600 6.4 LiAlCl4 2.1 kHz C211° +1.0 ca. 2000 ca. 2000 8. LiAlCl4 @ 1 kHz 176 Av 1/2 = A1 = (16) L 4 With AV1/2 = 420 Hz, a x value of 1.7 kHz is obtained for this sample. This very small value is reasonable in view of the known crystal structure of LiAlCl4 (space group p21 /c)9 which is made up of LiClg octahedra layers linked together by AlCl4 tetrahedra (193). The considerable narrowing effect of magic angle sample spinning is seen in the spectra for 02322:LiAlCl4 (Figure 41). In the spinning mode, the central transition is partially resolved from the broad background; this broadening, due to dipolar interactions, is not completely removed at the spinning rate of 2.1 kHz. By using equation 16 and Av 1/2 = 1600 Hz for the static spectrum, a coupling constant of 6.4 kHz is obtained for the complex. For the C211-LiAlCl4 sample, stable spinning rates of greater than 1 kHz could not be obtained. Thus, very little reduction in the dipolar broadening was observed (Figure 42). In the bottom spectrum, the central transition is barely discernable at this spinning rate. A coupling constant of ca. 8 kHz is obtained by using equation 16 and Av1/2 * 2000 Hz. The coupling constants for the 7Li nucleus in the two cryptate complexes are exceptionally small (cf. Table 14, Chapter III), indicating highly symmetric environments for the lithium ion in these, complexes. As is shown in the following section, this high symmetry is confirmed in the crystal structure of the 02322-LiAlCl4 complex. Evaluation of the differences in chemical shifts among the four compounds (Table 29) is difficult due to the lack of literature values for these or other lithium compounds in the solid state. In an unpublished work, Ellaboudy (194) reports chemical shifts of -2.8 ppm (LiCl), -l.l ppm (Lil), -0.8 ppm (Li+02111‘), and -3.5 ppm (Li+C211Na‘). From Table 29, it appears that the cryptands 177 effectively remove the shielding influence of the chlorine atoms in the AlCl4- ion on the 7Li nucleus; the shifts for LiCl and LiAlCl4 are more negative (by about 2 or 3 ppm) than those of the complexes. This shielding effect is understandable since the lithium ion is expected to reside within the ligand cavities. 0.3. The Crystal Structure of C2322-LiAlCl4 A single crystal of the 02322-LiAlCl4 complex was recovered from a. 5 mm NMR tube sample of basic melt containing 0.637 mol96 02322 and 1.00 mol96 LiCl. The crystal (0.6 x 0.6 x 1.0 mm) was mounted in a sealed 0.? mm Pyrex capillary tube for data collection. The crystal structure of this complex was determined by D.L. Ward, and data collected by using a Nicolet P3F four circle computer—controlled diffractometer. All data reduction routines (Enraf—Monius SDP program package) were performed on a VAX 11/750 computer. The crystallographic parameters and data collection conditions for this structure determination are listed in Table 30. The atomic numbering scheme (heavy atoms only) for the 02322 molecule is shown in Figure 43. A summary of all heavy atom bond distances and all bond' angles is given in Appendix 2. An abbreviated list of important bond angles and distances is given in Table 31. The structure of a single C2322-LiAlCl4 molecule is shown in Figure 44. In this perspective, the tetrahedral geometry of the AlCl4- ion is clearly observed. The large distance between the lithium ion and the nearest chlorine atom of the AlCl4‘ ion (5.90 X) indicates that the latter is not coordinated to the lithium ion. Two different views of the unit cell containing four complex molecules are shown in Figures 45 and 46. It can be seen that the cryptate ions are oriented in such a way that the bulky benzene rings on adjacent cryptates ‘4 .‘- u. n . 178 3b 2b 4b< >11) 5 4 6\ 3k 8 U 70 2 9 14 17 12 16 N 1 0 1g 10 18 11 . 15 19 26 21 240 20 0 \ / 25 22 23 Figure 43. Atomic Numbering Scheme for Heavy Atoms in the 02322 Molecule. 179 Table 30 Crystallographic Parameters and Data Collection Conditions for the Determination of the Structure of the 02322 -LiAlCl4 Cryptate Complex Space Group: P 21/n Cell Parameters: a = 11.099 :1: 0.002 X b = 11.796 2!: 0.002 X c = 22.345 1 0.005 R v = 2908.8 c 10 3.3 = 96.15 i: 0.02° z = 4(3) DC = 1.371 mg/m3 Data Collection: scan range = 4.5 to 55° scan speed - 1°/min scan width = 1.6 :1: A29- number of reflections used — 4571 (I > 30(1)) absorption correction - 4.74 cm‘1 class of reflections - hkl, hkl final R - 0.057 final Rw - 0.068 (a) Number of molecules in the unit cell. 180 Table 31 Some Important Bond Distances (X) and Bond Angles (Degrees) for the 02322 LlAlCl‘ Complex Atom 1 Atom 2 Bond Distance (3) All C11 2.13 Lil C11 5.90 Lil 013 2.20 Lil 016 2.37 Lil 021 2.29 Lil 024 2.20 Lil N1 2.97 Lil N10 2.75 Atom 1 Atom 2 Atom 3 Bond Algle (Degrees) C11 All C12 109.7 C11 All C13 109.8 C11 All C14 108.9 C12 All C13 109.4 C12 All C14 110.4 C13 A11 C14 108.6 C13 Lil 016 71.6 013 Lil 021 174.0 013 Lil 024 111.8 016 Lil . 021 105.6 016 Lil 024 82.6 021 Lil 024 72.5 181 .62 m 2: 082 8:0; 038...: 1 1023.230 2:. 3023.230 0.. 5.05m 350 9:. .3. 25$ 182 Q) I _V._V._ Figure 45. The Crystal Structure of 02322-LiAlC14: A View of the Unit Cell Along the _b Axis. 183 The Crystal Structure of 02322-LiAlCl4: A View of the Unit Cell Along the a Axis Figure 46. 184 are nearly parallel, thus minimizing steric interactions. In Figure 47 the oxygen and nitrogen atoms of the cryptand are labeled; lines from each oxygen to the lithium ion are drawn to emphasize the geometry of the lithium ion coordination. A least squares calculation of the deviation of the lithium ion from a series of six planes was performed, each plane defined by the positions of a set of oxygens, or oxygen and nitrogen atoms in the cryptand. The results of these calculations are given in Table 32. It appears that the lithium ion is octahedrally coordinated by the six oxygen atoms (max. deviation = -0.175 X from plane #5). The large Li-N distances (Li-N = 2.97 ii and Li-N10 = 2.75 3.) suggest that the nitrogen atoms do not participate in the lithium ion coordination. This is in contrast to the reported structure of the 0211-Lil complex (153), which has a mean Li-N bond distance of 2.28 R. In the 02322-LiAlCl4 complex, it appears that a line drawn to connect Ni, Li, and N10 is coincident with one of the three-fold axes which intersects a face of the LiOg octahedron. The Li-O bond distances range from 2.20 to 2.37 X in the complex. These values are only slightly longer than the mean Li-O distance of 2.13 X in the C211-Lil structure (153). Thus, despite the large difference in the size of the lithium ion (rLi+ = 0.86 3) versus the C2322 cavity size (dcngz = 2.8 X), and the supposed "stiffening" influence of the benzene ring, C2322 apparently possesses sufficient conformation flexibility to enable the coordination of the lithium ion within the cryptand cavity. D. Conclusiom The 7Li NMR data obtained in this study show that the chemical exchange between the "free" and cryptated lithium ions in basic melt solutions is slow at 40°C and a field strength of 42.28 kG. The NMR signals for the two sites 185 Figure 47. The Crystal Structure of 02322-LiAlCl4: A Closeup View of the Cryptated Lithium Ion. The Oxygen and Nitrogen Atoms are Labeled According to the Scheme in Figure 16. 186 Table 32 Least Squares Calculations: The Deviations (A) of the Lithium Ion from Coincidence with Planes Defined by Sets of Oxygen and Nitrogen Atoms in the 02322-LiAlCl4 Cryptate Complex Deviation ( X) Plane Set of Four Atoms 1 04, 013, 021, 024 - 0.002 t 0.010 2 07, 013, 016, 021 + 0.169 :t 0.010 3 04, 07, 016, 024 + 0.057 :1: 0.010 4 013, 021, N1, N10 + 0.062 i: 0.011 5 07, 016, N1, N10 - 0.175 t 0.011 6 04, 024, N1, N10 + 0.158 1: 0.010 187 are well resolved (AG ca. 2 ppm; Av “2 _<_ 20 Hz) for the systems which contain C211, C222, or 02322. For the lithium-0222 system, 40°C appears to be close to the coalescence temperature; the signals for the "free" and complexed lithium ion sites are broadened to the point of overlapping. The estimated decomplexation rate for this system (5 x 103 8‘1) is higher by factors of 103 and 106 than that observed for the lithium-C221 and lithium-€211 systems in pyridine (174), respectively. The apparently more facile decomplexation of the lithium ion from the C222 cryptate (compared to the C2322 cryptate) is attributed to the greater conformational flexibility of 0222 versus that of C2322. Potentiometry has been used to show that complexation of the lithium ion with C2322 occurs with the release of chloride ions in the basic melt. This is in contrast to the complexation of the lithium ion with 15C5 (section 0.2, Chapter 111), where retention of the chloride ions in the crown complex was indicated. Single crystals of lithium cryptate complexes have been isolated from basic melt solutions of LiCl with C211, 0221, C222, and C2322. The crystal structure of the 02322-LiAlCl4 complex has been determined. The results of this analysis indicate that the lithium ion is contained within the cryptand cavity in a nearly regular octahedral coordination by the oxygen atoms of the cryptand. The Li-N distances appear to be too long to conclude than the nitrogen atoms participate in the lithium ion coordination. CHAPTER V HEAVY METAL CHLOROCOMPLEX FORMATION IN THE A1013-BPCI SYSTEM A. Introduction In the previous studies of chlorocomplexation in the AlCl3-BPCI and AlCl3-ImCl molten salt systems (see Chapter I), electrochemical and UV-Vis spectrophotometric techniques were the principal methods of investigation. In only one of these studies (92) has vibrational spectroscopy been used to corroborate the structure of a chlorocomplex (NpClg3‘) inferred from UV-Vis spectrophotometric and electrochemical data. The lack of IR or Raman data for these systems is surprising considering the extent to which these methods have been applied in previous molten salt studies (195). No multinuclear N MR studies of chlorocomplexes in the A1013-BPCI system have been reported before, or since the work of Taulelle and Popov (58). For the reasons cited in section B.1.c.(3), Chapter 1, detection of NMR signals for most of the metal ions studied in this system is likely to be difficult. However, other metal ions exist which have NMR-active nuclei with more favorable NMR characteristics. Moreover, as is discussed herein, these metal ions have a marked tendency to form chlorocomplexes in ionic liquids which contain an excess of chloride ions. Therefore, the purpose of this study was to investigate chlorocomplexation of selected heavy metal ions in the A1013-BPCI molten salts by using vibrational spectroscopy (far-IR) and multinuclear NMR techniques. The metal ions selected for these studies were Cd2+, Hg“, Sn2+, Sn4"', 2112+, (30+, and Pb2+. B. Salvation of Heavy Metal Salts in Basic and Acidic A1013-BPCI Melts 8.1. Basic Melt Solutiom The heavy metal chlorides which were found to be soluble in basic melt are listed in Table 33. In this qualitative work, no attempt was made to determine thermodynamic solubility limits of these salts in this medium. Melt 188 189 Table 33 Heavy Metal Chlorides in Basic AlCl3-BPC1 Melt: Minimum Solubilities at 25°C Salt Solubility (Mol%) CdClz 3.0 SnClz 3.3 H8012 9.5 CuCl 6.7 ZnClZ 1.6 SnCl4 (a) (a) See text 190 solutions were prepared with metal chloride concentrations sufficient to enable far-IR and multinuclear N MR studies of these solutes. Both PbClz and Pb(NO3)2 were found to be insoluble in basic melt, even after six months of conditioning (see Chapter II, section A.1.c.(l)). In the case of Pb(NO3)2, the heterogeneous melt solution was observed to turn a bright yellow color over this conditioning period. This color change is similar to that observed for LiNO3 (which was soluble) in basic melt (see Chapter III, section 8.1.). It is suspected that exchange of nitrate ion from the lead salt for chloride ion from the melt occurred in this solution, producing the yellow melt color and leaving behind the insoluble PbC12 in the sample. The source of this yellow color is unknown; aqueous or nonaqueous solutions of nitrate ion are not, in general, colored. All salts in Table 33, were found to dissolve in basic melt within 24 hours with stirring. Only CuCl produced a color change (to dark orange) when dissolved in the melt. This result is in contrast to the observations of Laher and Hussey (81) who found no color change in the melt on dissolving CuCl in A1013-BPCI or AlCl3-ImCl melts. Evidence for the Cule chlorocomplex has been reported for other ambient temperature melts (25,132,313), as well as in nonaqueous solutions (204-206). From Table 33 it is seen that, in general, at 25°C the solubilities of these heavy metal salts are greater than than that of LiCl (ca. 2 mol%), or other lithium salts (_<_ 2 mol%). The concentration obtained for CdClz in basic melt is thought to be very near the solubility limit for this salt, since stirring was often required to redissolve transparent needle-like crystalline material which sometimes formed when the solutions were allowed to stand overnight. The identity of these crystals is unknown; attempts to isolate them from basic melt solutions were unsuccessful. From previous literature reports (119,196) the CdCl3" or CdCl42' 191 chlorocomplex ions were expected as the most likely cadmium species to exist in basic melt solutions of CdClz. Based on previous studies by Vanderzee and Rhodes (197), and Clarke and Solomons (198), the SnClg‘ complex was assumed to exist in SnClg-basic melt solutions. Chlorocomplexes of the Hg2+ ion have been observed in solutions and in the solid state (199-203). In light of the high solubility of HgClz in basic melt, it seemed likely that the formation of more than one complex for mercury in the melt was feasible. Reynolds gt _a_l_. (207) have recently inferred the existence of the ZnCl42‘ chlorocomplex in dilute ZnClz-basic AlCl3-ImCl melts at 30°C from observed variations in 1H NMR chemical shifts of the Im+ ion as functions of ZnClg concentration. The ZnCl42‘ species has been observed in several other previous solution and solid state studies (118,208-211). An unusual reaction was observed upon addition of SnCl4 to a stirred basic melt solution at room temperature. After adding 0.5213 g of SnCl4 to 5.6320 g of basic melt, a granular white precipitate was observed to form within 2 minutes. The resulting slurry was vacuum-filtered to remove the bulk melt, leaving a fairly dry white powder. This reaction appears to be analogous to that described by Cotton and Wilkinson (9) for the preparation of hexachloro ions of germanium and tin, 21101 or 2MIC1 + MC14 ->2H+ or 2M“ + MC152' (1) where M1+ is an alkali metal cation. Thus, for the SnCl4-basic melt mixture, 2BPCl + SnCl4 -D (BP)ZSnC16 (2) 192 where (BP)2SnC16 is assumed to be the solid adduct which was isolated from melt solution. This solid did not exhibit a sharp melting point. At 3 30°C, part of the solid (sealed in a capillary tube) melted, while the remaining solid ‘melted at ca. 100°C. Since the reported melting point of (BP)AlCl4 is 32°C (212), it is likely that the solid is a double salt. The results of elemental analyses of the solid by Galbraith Laboratories are given in Table 34. Considering that the percentage of hydrogen is larger than expected, and that the analyses do not sum to 100%, it is considered likely that the sample was contaminated with moisture. Since the sample was never exposed to the atmosphere prior to sealing under high vacuum (_g 10'5 torr), it is believed that the water contamination took place when the analyses were performed. Assuming that the missing 11.5% is due to oxygen from the water contaminant, the formula which is in best agreement with the reported analytical results is 4.5 (BP)AlCl4-(BP)2SnC16-l6H20. 8.2. Acidic Melt Solutions Of the salts listed in Table 33, only CdC12 was found to be soluble (at 3.95 mol%) in acidic melt at 25°C. Dispersions of the other salts (PbClz, SnClz, HgClZ, CuCl, and ZnClz) remained heterogeneous after six months of conditioning. It is believed that the solubility of CdClg in this medium results from the reaction of chloride ions from Cd012 with A12C17’ ions from the melt according to the reaction, .. 2+ _ CdC12(solid) + 2A12Cl7 —-)Cd + 4AlCl4 (3) 193 Table 34 Elemental Analyses of the Solid Adduct of San Isolated from Basic A1013-BPCI Melt Solution Theoretical Composition Actual Based on 4.5(8P)AlCl4- Element Composition“) (8P)ZSnClg-1GHzO c 29.38 31.18 H 6.02 5.01 N 3.93 4.04 Al 5.03 5.39 Sn 4.81 5.27 CI 39.36 37.76 0 -- 11.36 Total 88.52 100.01 (a) All values are given as wt% 194 C. Solution NMR Studies C.1. Cadmium-113 NMR A single 113Cd NMR resonance line was observed in all basic melt solutions of CdC12 at 40°C. The chemical shift of this signal is +466 ppm vs. 0.1 M Cd(ClO4)2 in water (Gobs = +373 ppm E. 0.5 _I\_/I_ CdClg in D20), and was observed to be independent of CdClz concentration in basic melt solutions. A typical 113Cd NMR spectrum for these solutions is shown in Figure 48.. Mennitt e_t El.- (213) have obtained the 113Cd CP/MAS NMR spectra for 27 solid complexes of the Cd2+ ion, to establish benchmarks for the shielding of this nucleus as a function of the number and type of donor atoms in various coordination geometries. These workers obtained chemical shifts for bis(tetraethylammonium) tetrachlorocadmate (6 = +483 ppm) and thiaminium tetrachlorocadmate (6 = +460 ppm). The similarity of these shifts to that observed for CdClz in basic melts strongly suggests that the CdCl42’ complex is the principal cadmium species in these solutions. The noted constancy of chemical shifts for the signals in CdClZ-basic melt solutions is attributable to the fact that none of these solutions had a ratio of melt chloride ion to CdClz of less than 2.5:1. Thus, a 113Cd NMR signal for the CdCl3‘ complex ( 6 = +296 ppm; (119)) was not observed. Several attempts were made to displace the chloride ions from the CdCl42" complex by the addition of crown ethers or cryptands to CdClz-basic melt solutions; ie., to affect macrocyclic complexation of the Cd2+ ion such as was done with the lithium ion in basic melt (see Chapters III and IV). No new 113Cd NMR signals were observed on additions of these ligands. However, an appreciable (ca. 10 to 3096) reduction in the S/N ratio for the 113Cd signal for the chlorocomplex was observed for these samples. These results are interpreted as indicating that some interaction of the ligands with the Cd2+ 195 .58 e... 8 .93. owes—0.00 w. a... 8 8.8m 9:. 3:5 33520 0.3 8 =6: Basia—02 038m 5 N.08 £6: 8.” .5588 as: 2753580 9:33 W ._. am? 8.? 8? u d d . u . - E E .77. 80+ .3. «9&5 196 ion is occurring in these solutions. Observation of 113Cd NMR signals for the cadmium macrocyclic complexes is apparently not possible due to fast multi-site chemical exchange between CdCl42', all intermediate chlorocadmium species, and the macrocyclic complexes. In acidic melt, a 113Cd NMR signal was observed at 6 = +117 ppm (+24 ppm is. 0.5 M CdClz/DZO; Figure 49). It is interesting to note that this shift position falls within the range which is loosely defined as the octahedral coordination region (ca. +100 ppm to -40 ppm gs. 0.1 M Cd(ClO4)2/H20) for 113C0 chemical shifts (214). This empirical correlation of 113Cd chemical shifts with coordination geometry is supported by the theoretical calculations of Nakatsuji and co-workers (215). They found that the diamagnetic and paramagnetic terms of the nuclear shielding constant for the Cd(H20)52+ ion (Oh symmetry) cancel, such that the chemical shift of this species is zero. With its 2+ charge and the presence of A12Cl7‘ ions in acidic melt, octahedral coordination of the cadmium ion by two or more A12Cl7' ions in this medium seems plausible. C.2. Tin-119 and Tin-117 NMR A single119Sn NMR resonance line was observed for basic melt solutions of SnClz at 25°C, with chemical shifts insensitive to SnClz concentration. For 3.29 mol% SnClz in basic melt, the chemical shift of the signal was +9.1 ppm downfield from neat SnCl4 (-l40.9 ppm 55 (CH3)4Sn primary standard), with a linewidth of 24 (11) Hz (Figure 50). The width of this line increased to 92 Hz at 40°C. The signal for 0.955 mol% SnClZ-basic melt solution was broader (75 Hz) than that observed for the 3.29 mol% SnC12 solutions. This indicates that fast chemical exchange among several tin species in solution is occurring. The ratios of melt chloride ion/SnC12 in these two samples is 3:1 for 3.29 mol% SnClz, and 10.5:1 for the 0.955 mol% SnC12 solutions. The 197 l l I I +30 .20 +10 0 8 (ppm) Figure 49. Cadmium-113 NMR Spectrum: 3.95 Mol‘X: CdClz in Acidic AlCla- BPCI melt at 40°C. Chemical Shifts are Scaled as in Figure 48. 198 l l l l 0000 _J; l l I I l' 080 020 610 l l l 1 l I l r -10 6‘ (ppm) 0 Figure 50. Tin-119 NMR SpeCtl'a: 3.29 M01% SnClZ (A) and 0.955 Mol% SnClz (B) in Basic A1013-BPCI Melt. 199 observed broadening at the. higher Cl‘(melt)/SnC12 ratio indicates possible formation of the SnCl42‘ chlorocomplex, or the polymerized (SnC12)n species. The 117 Sn NMR spectrum for the 3.29 mol% SnClz-basic melt sample is shown in Figure 51. Because of the slight receptivity advantage of the 119Sn nucleus (Rllgsn/R117Sn = 1.3), no further studies of the 117Sn nucleus were pursued. However, it is interesting to note that the linewidth for the 119Sn signal for this sample is ca. 1.1 times that of the 117Sn NMR signal (24 33. 22 Hz (:t 1 Hz) at 25°C). Assuming that the spin-lattice relaxation process is dominated by the intramolecular dipole-dipole mechanism (216), and further, that the motional narrowing limit (T1 = T2) obtains, 2 2 2 2 - obs. 1 _ 1 _ uoylys h S(S+l)1'c (4) V = w "' '- 1/2 "T2)s "T1 lzvzrgs Therefore, the ratio of the linewidths of the 119Sn and 117Sn NMR signals is proportional to the ratio of the square of the respective magnetogyric ratios as, 119 117s obs. _ Tobs. _ A Sn / Av n — 2 2 (5) T — -v -Y /Y / 2[119] 2[117] 1/2 1’2 1193" 1173" Using the magnetogyric ratios from Table 8 (Chapter II), a value of 1.1 is obtained from equation (5). Thus, it appears that the intramolecular dipolar mechanism does dominate the relaxation rates for both of these nuclei in this molten salt system. 200 o -10 5 (ppm) Figure 51. Tin-117 NMR Spectrum: 3.29 M01% Sn012 in Basic A1013-BPCI Melt. 201 0.3 Zinc-67 NMR Detection of this nucleus in ZnClz-basic melt solutions was very difficult due to its low receptivity (Rm-”130 = 0.665), and the sample configuration required in these experiments. Severe rf pulse attenuation was incurred in traversing the 10 mm dead space between the Helmholtz coil of the 20 mm probe and the 10 mm/5 mm (sample) coaxial NMR tube arrangement. The high concentration (1 M Zn(NO3)2 in D20) of the external reference solution further attenuated the pulse as well as the signals returning from the sample. By reducing the word size in the computer memory block from 12 to 6 bits (to prevent overflow of the A-D converter), and scanning for 48 hours (2 105 scans), a very weak 67Zn NMR signal was obtained for 1.56 mol% ZnClz in basic melt (Figure 52). The chemical shift of this signal is ca. +305 ppm downfield from the external reference solution. This result is in fair agreement with the value of +257 ppm for ZnCl42‘ in aqueous solution obtained by Maciel and co-workers (118). No further experiments were performed on this nucleus in basic melt because of the extremely long acquisition times, and the poor quality of spectra obtained. C.4. Mercury-199 NMR Mercury-199 NMR signals were obtained in nine HgClz-basic melt solutions at 25°C. Chemical shifts of these signals are listed in Table 35, and the chemical shift behavior as a function of HgClz concentration is depicted in Figure 53. A chemical shift range of ca. 250 ppm is spanned from 9.53 mol% HgClz to 0.77 mol% HgClg in the basic melt solutions. This concentration dependence of the chemical shift seems to indicate the presence of at least two complex sites for mercury in fast chemical exchange (one population-averaged NMR signal). An equilibrium which could account for this chemical shift behavior is, 202 I l : I +500 +400 +3'oo +200 +100 _130 8 (ppm) Figure 52. Zinc—67 NMR Spectrum: 1.56 M0196 Zn012 in Basic AlCl3—8PCI Melt. 203 Table 35 Mercury-199 NMR Chemical Shift Data for HgClz—Basic AlCl3-8PCI Melt Solutions Chemical 'ft 3“ M6196 HgClg (ppm)( 0.772 + 611 3.99 + 472 4.65 + 460 5.79 + 414 7.00 + 383 7.57 + 369 9.01 + 358 9.30 + 353 9.53 + 348 (a) Chemical shift uncertainty is estimated at i 3 ppm. 204 +3004 0 ‘1 . . O 0 +4004 0 E : ‘ - I: C 5'. : +500- 2 I ‘5‘ I. q 0 2 +600“ 0 I r r r I I I I fi 1 1 2 3 4 5 0 7 a 9 10 110111 11ch, Mercury-199 NMR: Chemical Shifts Versus Mol% HgClz in Basic Figure 53. A1013-BPCI Melts. 205 K HgCl3‘ + Cl‘ :4: HgCl42- (6) In view of the known Cl‘(melt)/HgC12 ratio for these solutions, it is likely that the downfield N MR signals correspond to the predominant population of the HgCl42‘ complex, and the upfield signals to the HgCl3‘ complex. 0.5. Copper-63 and Lead-207 NMR All attempts to detect 63Cu NMR signals in CuCl-basic melt solutions, and aqueous and nonaqueous solutions of CuCl were unsuccessful. Disproportionation of Cu” to Cu° and Cu2+ is suspected as the cause for no NMR signals for 1 M K3Ku(CN)4 (1 M CuCN with 3 M KCN) solutions in D20, acetonitrile, and pyridine, since these solutions turned black within 2 to 3 hours of preparation. The reason for a lack of 63Cu N MR signals in CuCl-basic melt solutions is not clear. The yellow color of these solutions suggests that oxidation of Cu+ may have occurred with reduction of the pyridinium ion in a reaction similar to that described in Chapter 11, section A.4.a. In any event, the 2+ oxidation state renders the 63Cu nucleus unobservable. No 207Pb NMR signals were observed for Pb012 or Pb(NO3)2 in basic or acidic melt mixtures, after a systematic search from +5000 to -5000 ppm E- 0.2 M Pb(NO3)2 in D20. Since no difficulty was encountered in obtaining a 207Pb NMR signal for the external reference solution, it seems clear that lead salts are virtually insoluble in basic or acidic AlCl3-BPCI melts. D. Far-IR Measurements of Heavy Metal Salt-Basic A1013-BPCI Melt Mixtures In the far-IR region (150-600 cm'l), the spectrum of pure basic melt is dominated by the v3(F2) and v4(F2) normal vibrational modes of the AlCl4' 206 ion (Figure 54). A summary of the results with band assignments (from Gale and Osteryoung, (53)), is shown in Table 36. The assignment of the 04(F2) and (184 cm'l) is made based on the Raman study of basic melt by Gale e_t a_l. (49). The v1(A1) band at 345 cm'1 (Figure 54, part B) is barely discernable from the background absorption, even with the larger spacer size. Aside from this weak band, the region between 200 cm’1 and 450 cm‘1 is essentially featureless, enabling observation of heavy metal-chlorine vibrational bands. The far-IR spectra of basic melt solutions of CdClz, ZnClz, CuCl, HgClz, and SnC12 are shown in Figure 55. Band frequencies and assignments from the literature are given in Table 37. In the Raman studies of Davies and Long (217) and Delwaulle (200), values of 260 cm‘1 and 250 cm‘1 were reported for the v 1(A1) mode of the CdCl42“ chlorocomplex in aqueous solutions. However, in a far-IR study by Adams e_t 31: (218), the band observed at 260 cm‘1 for CdC12 in thionyl chloride was assigned to the V3(F2) mode. While it is possible that ionic associations in basic melt solutions could produce a perturbation strong enough to enable observation of a v1(A1) band for CdCl42' in the far-IR (as was observed for the A1014“ ions), it is unlikely that this band would be as intense as the IR-active v 3(F2) mode. For this reason, the assignment made in Table 37, for the CdCl42' species is favored. The band due to a lattice-like vibration of the (CdC12)n polymeric species is expected to be at 240 cm"1 (217). No such band was seen in the CdClg-basic melt solution. The v 3(E') mode for CdCl3" is expected to appear at ca. 290 cm'1 (217). However, no such band was observed in the basic melt solution of CdClZ. Due to the very poor quality of spectra obtained below 150 cm‘l, the anticipated 04(F2) band for CdCl42‘ could not be observed. The frequency of the band observed in the ZnClg-basic melt solution is in good agreement with those identified for the ZnCl42‘ complex ion in previous ABSORBANCE 207 0.55-- 490 0.33-- 182 .. 527 0.11-- : l l l L I I l 1'— 550 0.55.- Hal 0 z ‘ a: 0351- a: O m m C 0.15" v 3 i 5 i 3 i i l i ; ‘r ; : ; f. 250 350 450 550 cm ‘1 Figure 54. Far—IR Spectrum (150 to 600 cm'l): Basic A1013-BPCI Melt; (A) - 0.05 mm Spacer (B) - 0.1 mm Spacer. 208 Table 36 Far—IR Bands and Assignments for the Normal Mode Vibrations of the Alle Ion in Basic A1013-BPCI Melt This Work Gale and Osteryoung“) Assignment 345 353 v 1(A1) -- 476 490 490 v 3(F2) 527 525 184 -- v4(F2) (a) Reference 48 . 209 248 405 aaaaaaaa 250 Figure 55. Far-IR Spectra (150 to 600 cm'l): Basic A1013-BPCI Melt Solutions of Heavy Metal Chlorides; (A) - 2.98 M01% CdClz, (8) - 1.56 M6196 211012, (C) - 6.66 M6196 CuCl, (D) — 2.37 M6196 HgClz, (E) - 3.29 M6196 SnClz. 210 8:3: va E. 2:05 3.: a.» ma M.” £05 83...; 2.. -3030 no a so -3050 fw V? as. 3... 8:0 4.85 c... 430% 3: as EN 3 30m: $5.: :5 :5 SN 3”0 -305 a: as S: a; 30.5 *2.” p... 3:08 3.: me me: he N20.00 4.3.: Seesaw 858m 08: .733 828 83: 8:38 .200 2:25 L0 8.6: 3202 3:08:92 0:: 35:03.0:— 0:3 "2.538 :5: 8.3.30? 05...: - 8:620 .35: 0:0: «a 883m :73: an 036,—. 211 studies (207-209). The v4(F2) mode for this species is expected to occur at ca. 130 cm"1 (209), and could not be measured for the reasons just given. Irish and co-workers (219) have assigned the Raman band at 230 cm'1 in ZnClz aqueous solutions to the bridge Zn-Cl stretching vibration of the (ZnClg)n polymeric species. Since no band was observed near this frequency for the ZnClg-basic melt solution, the existence of this polymeric ion in this solution is considered to be unlikely. The assignment of the 405 cm"1 band in the CuCl—basic melt solution to the v3( 2*) mode of the linear CuClz' ion is consistent with IR and Raman studies of CuCl in nonaqueous solutions (25,204). However, Axtell e_t a_l. (33) have noted that the only difference in the far-IR spectra for triethylphosphonium chloride (TEPCI)—CuCl mixtures at the 1:1 (Cule) and 1:2 (Cu2C13‘) mole ratios, is that the 405 cm‘l- band broadens slightly at the latter mole ratio versus the former one. The VZa/Zb modes (ca. 109 cm"1 (25)) are outside the accessible spectral window of this work. Two different chlorocomplexes of Hg2+ ion, HgCl3" and HgCl42‘, are possible for HgClz in basic melt. For the D3h structure of HgClg‘, three IR-active modes ( v 2(A"), v3(E'), v 4(E')) and three Raman-active modes ( v 1(A'), v 3(E'), v4(E')) are predicted (222). For the 03v geometry, all four fundamental vibrations are allowed in the IR and Raman spectra. In a Raman study of molten HgClz—(KCI or NH4Cl) mixtures by Janz and James (201), the v4(E') band was observed at 223 .cm"1 for 45 mol% HgClz-Ss mol96 KCl melt at 580°C. These authors favored the planar arrangement for the HgCl3‘ ion based on the fact that this structure would enable maximum separation of the three chlorine atoms in the complex. In addition, the v3(E') mode was observed for this melt at 270 cm‘l. This band (which is also IR-active) is not observed in the HgClz-basic melt solution. The v3(E') mode has been 212 observed at 263 cm'1 in the IR spectrum of Me3SHgCl3 by Biscarini _e_t_ a_l. (202). The reliability of the assignment for this vibration is excellent since the crystal structure of the compound was reported in this work, confirming the planar HgCl3' ion. Adams e_t .a_l. (218) have assigned the band at 228 cm‘1 in the far-IR spectrum of tetraethylammonium tetrachloromercurate to the v 3(F2) mode of the HgCl42' ion. Deacon and co-workers (199) observed this mode at 225 cm'l. Thus, it appears that the band observed at 224 cm'1 in the far-IR spectrum of 2.37 mol96 HgClz in basic melt is due to the v3(F2) mode of the HgCl42‘ complex. Only Raman spectroscopic data are available for comparison with the results obtained for SnC12 in basic melt. Clarke and Solomons (198) assigned Raman bands at 268 cm‘1 and 220 cm"1 to the v1(A1) and v3(E) modes, respectively, of the SnClg‘ ion, in 1:1 SnClg-KCI mixtures at 300 and 600°C. In ether extracts of aqueous acidified SnC12 solutions, Woodward and Taylor (221) obtained 297 cm"1 (v1(A1)) and 256 cm‘1 (v 3(E)) for the SnCl3‘ species. In both of these studies, the bands for the v2(A1) and v4(E) modes were observed below 150 cm‘l. In view of the diversity in band frequencies reported in these studies, the frequencies observed for the SnClz-basic melt solution (and their respective assignments) appear to be reasonable for the SnCl3‘ complex. The mid— and far-IR spectra of the solid adduct of SnCl4 isolated from basic melt solution (section B.1) were obtained in a KBr pellet. In the mid-IR region (550 to 3500 cm‘l), the spectrum retains virtually all bands attributable to the stretching and bending modes of the BP+ cation. These bands are shifted by as much as i 40 cm"1 in the SnCl4 adduct versus those observed for pure BPCI. The largest deviations are observed for one of the out-of-plane ring 213 bending modes (765 cm"1 for the tin adduct _v_s_. 804 cm'1 for BPCI), and the methylene group bending mode (676 cm'1 for the tin adduct v_s. 699 cm"1 for BPCI). Although the background absorption is stronger for the tin adduct, no new features are observed in this region compared to BPCI. In the far-IR region (200 to 515 cm'l), the S/N ratio for the spectrum of the SnCl4 adduct was poorer than that obtained for the heavy metal chloride-basic melt solutions. However, the v3(Fz) band at 496 cm'1 for the AlCl4' ion (490 cm‘1 in basic melt), and two new bands centered at 238 cm‘1 and 303 cm"1 were observed (Figure 56). Of the six normal modes of vibration for an octahedral XY6 molecule, only the v 3(F1u) and V4(F1u) modes are predicted to be active in the infrared (222). The vibrational bands which have been reported in previous studies of the SnClsz’ ion in the solid state are listed in Table 38 as well as those observed for the SnCl4 adduct. The assignment of the 238 cm'1 band to the normally IR-forbidden .v 2(Eg) mode is based on the supposition that in the solid state, the effect of the crystal lattice can perturb the normal mode vibrations so that the normal IR/Raman selection rules are violated. This effect has been observed previously (224) for an analogous tin compound ((NH4)2SnF6). In view of the width of the band at 303 cm‘l, and the generally poor resolution of the spectrum, it is possible that the v1(A1g) band (also supposedly IR-forbidden) also occurs near this frequency. E. Conclusions Based on the evidence obtained from these NMR and far-IR studies of basic melt solutions of heavy metal chlorides, the following conclusions are made. The NMR chemical shifts and far-IR band frequencies for CdC12 and ABSORBANCE 214 ‘F 00.04... 303 -0.20.. 238 -0.44 7 : 5 i 5 5 i 5 £ 5 3 § 5 g : - 3 . l . 200 275 350 425 560 WAVENUMBER (cm'1) Figure 56. Far-IR Spectrum (200 to 515 em-l): The SnCl4 Adduct Isolated from Basic A1013-BPCI Melt Solution. 215 583.80 c: 0033 3:5 A0: 0033 "mucus—0m 3: m3 00:0..80m A3 :22 -- i -- 2m ”2 .. seem 820 6.63. 30:0 8N .. .. e2 :2 -- 02” 30532;: EN -- $0 2: 8m «2 2:” 30522:: i -- a: mam -- 2:” 3052232: 2: HS at N: SN 08 30.55: 3539: Amman: A35: A359, Aunts: mg m: 0:509: E 3. E 3 .e 2: 5 8 5:05:m_8< 33m .58 9: 5 uoaseeesgo use—05 05 «a 38:55 :78.— 0.... 55a: an 030,—. 216 ZnClz-basic melt solutions clearly support the supposition that the CdCl42' and ZnCl42' complex ions are the predominant species formed from the parent MClz salts. The existence of (CdC12)n or (ZnC12)n polymeric species is considered to be very unlikely. The situation for CuCl-basic melt solutions is not as straightforward. It is likely that whatever its precise mechanism, the suspected charge transfer reaction is probably responsible for the inability to detect 63Cu NMR signals. The far-IR data indicate that either the Cule or Cu2C13' complex ions are possible in these solutions, although the former species is favored considering the ratio of free chloride ion to CuCl in the melt (see Table 37). A more detailed 199Hg N MR study is required to test the validity of the fast chemical exchange model for the HgCl3‘ and HgCl42‘ ions in basic melt solutions. The assignment of the 224 cm'1 band observed in the HgClz-basic melt solution to the HgCl42' complex is consistent with results reported in previous studies. The constancy of 119Sn NMR chemical shifts with SnClz concentration in basic melt solutions, and the reasonable agreement of far-IR band frequencies with results from previous studies indicate that the SnCl3‘ chlorocomplex is the predominant tin species in these solutions. The mid- and far-IR spectra of the SnCl4 adduct isolated from basic melt indicate that the BP", AlCl4', and SnC162" ions are the structural components of this material. Although the results of the elemental analyses were not completely satisfactory, the percentages of chlorine, tin, and aluminum in the sample are consistent with that expected for the AlCl4' and SnC16' ions. CHAPTER V1 SUGGESTIONS FOR FURTHER STUDIES A. Lithium Chlorocomplexes in Basic Melt Although it has been shown that the monomer-dimer (LiClg‘ §° LiZCl42‘) equilibrium model satisfactorily accounts for the observed concentration dependence of the 7Li chemical shifts in basic melt, more information regarding the structure of these species and the nature of the lithium-chlorine bonds is required. It is possible that the techniques of EXAFS (x-ray absorption fine structure spectroscopy) and XANES (x-ray absorption near edge structure spectroscopy) could be used to obtain this information. The structure of the MnBr32‘ in molten (Bu4N)2MnBr3 has been studied by using these methods (225). It has been shown that the BP” ion can be observed in the gas phase by using the FAB (Fast Atom Bombardment) mass spectrometry method for the analysis of the AlCl3-BPCI molten salt system (226). It is feasible that negative ions such as AlCl4‘, AIZCI7', and, more importantly, the lithium chlorocomplexes in basic melt, could be observed by using this technique in the negative ion detection mode. As a theoretical compliment to these experimental studies, a molecular dynamics calculation which models a dilute basic melt solution of LiCl would be useful to critically evaluate the coordination number of the lithium ion, and the distribution of the chloride ions (coordination geometry) about the lithium ion, which are implied in the monomer-dimer model. B. Macrocyclic Complexation of the Lithium Ion and Other Alkali Metal Ions A detailed study of the kinetics of complexation of the lithium ion with C222 in basic melt by the NMR technique is clearly feasible, and may also be possible for the Li+-C2322 system if the coalescence temperature for this 217 218 system is accessible. These studies would permit a quantitative measure of the effect of the benzene ring on the conformational flexibility of the C222 skeletal structure, through a comparison of the decomplexation rates for the Lit-0222 and Li+-C2322 cryptates. Considering the relative ease with which single crystals of the lithium cryptates were obtained from basic melt, it is feasible that the crown ether complexes of the lithium ion may be obtainable, as single crystals, by using the same method. In addition, crown ether or cryptate complexes of the sodium or cesium ions may be obtainable by first solubilizing the NaCl or CsCl salts in basic melt with the desired ligand, and then adding benzene to "salt out" the macrocyclic complexes. C. Heavy Metal Ion Chloracomplex Formation The qualitative results of this preliminary study demonstrate how vibrational spectroscopy and multinuclear N MR may be combined to identify discrete chlorocomplexes in the A1013-BPCI system. Additional far-IR studies (including the region below 150 cm‘l) and Raman spectroscopy would enable a more complete analysis of the vibrational modes of these complexes. The observed high (> 9 mol%) solubility of HgClZ in basic melt, and the sensitivity of 199Hg chemical shifts to Hg012 concentration in this medium may be used to obtain the formation constant for the HgCl42' ion. Far-IR studies at high and low HgClz concentrations could confirm the identity of the mercury chlorocomplexes assumed for the fast exchange modeling of the 199Hg NMR chemical shift data. The potentiometric technique used in the study of lithium chlorocomplexes in basic melt is certainly applicable to the heavy metal complexes, to confirm the chloride ion/metal ion stoichiometry in these species. In addition, the 219 standard potentiometric method (by using Cs, Hg, Sn, etc. working electrodes of the first kind) could be used to determine the formation constants for the MClx(“'X) complexes in basic melt. APPENDIC- Appendix 1 A. The Two-Site Past Exchange Model for the Determination of Equilibrium Constants The 7Li chemical shift data obtained from the studies of crown ether complexation of the lithium ion in basic melt were fitted, as a first approximation, to a simple two-site fast exchange model, M + L -—‘ ML (1) where formal charges are omitted. Then KF = CML / CM°CL (2) and 506s = XM‘SM + XML‘SML (3) From the derivation by Bodner gt a]: (227), it can be shown that Gobs = {(KFCMt - KfCLt - 1)+ [(KFCLt - KfCMt + 1)2 + 4Kfch1/2}- 5M - 5ML { ZKF } + 6ML (3) where CMt and CLt are the analytical concentrations of the metal ion and the crown ether, respectively. 220 221 In this expression, KF, 5M, and 5ML are the adjustable parameters whose final values are calculated by the KINFIT program, and CL+ is the independent variable. For the equilibrium between the monomer (M) chlorocomplexes of the lithium ion, KD = D/M2 The analytical concentration of the lithium ion (C Mt) is given by th=M+2D Solving (6) for D, and substituting into (7 ), CMt = M + 4KDM2 4KDM2 + M-th =0 Solving (9) and taking the positive root, -1 + (1 + schMtfl/Z 4K1) Dividing (7) by th and dimer (D) (5) (6) (7) (8) (9) (10) (11) 222 thus, XM = M/CMt. For fast exchange between the monomer and dimer chlorocomplexes of the lithium ion, Gobs = XMGM + XD 5D where 6 M and 6 D are the limiting chemical shifts of the respectively. From (11), XD = 1 - XM and (21) becomes XM (GM' 6D) + 61) obs = M( 5 M - 6D) Gobs = + 6 D CMt Substituting (10) for M into (14), [(1 + 8KDCMt)1/2 - 1] (6M - 6D) Gobs 7' + GD 4KDCMt (12) monomer and dimer, (13) (14) (15) In this expression, 5M, 5D and K9 are the adjustable parameters, and CMt is the independent variable. The (CMt, Gobs) data set is entered for fitting by equation (15). The SUBROUTINE EQN listings in the KINFIT program for the calculations using equations (4) an (15) are given below. 223 SUBROUTIhE EQN for the calculation of Li -crown complex formation constants: two-site fast exchange between free and complexed lithium ion. SUBROUTIBE EQN COMMON KOUNTJTAPEJTAPEJWTLARXIBERINDPIWVARWUBK,X,U,|TMAX. 1WTX,TEST.I,AV,RE$ID.IAR,EPS,ITYP,XX.RXTYP,DX1I,FOP,FO.FU.P.ZL,TO.E 2 IGVAL,XST.T.DT,L,M.JJJ,Y,DY,VECT.NCST,CONST,hDAT,JDAT,MOPT,LOPT, 3YYY,CO|\STS COMMON/FREDT/IMETH COMMON/POINT/KOPT,JOPT.XXX DIMENSION X(4.300),U(20),WTX(4,300).XX(4).FOP(300).FO(300),FU(300) 1,P(20,21),VECT(20,21).ZL(300).T0(20),EIGVAL(20),XST(300),Y(‘D). ZDY(10).CONSTS(50.B).M3$T(50).ISMIM50).RXTYP(50),DX1I(50)JRX(50) 3.MOPT(50).LOPT(50).YYY(50).CONST(B).XXX(15) , GO TO (2,3,4,5,1,7,8,9,10,11,12) ITYP 1 CONT IMJE ”APE-60 JTAPE-61 RETURN 7 CONT IMJE mUM-3 mVAR-Z RETURN 8 CONTIMJE RETURN 2 CONTIMJE U(2)-1.0E+02 1000 CONTIMJE A-U(2)*COl‘ST(1) B-U(2)‘XX(1) C-(U(3)—U(1))/(2.‘A) D-(B-A+1.)"2 CALC-((A-B-1.)+SQRT(D+4.*A))*C+U(1) |F(|MET H.hE.-1) GO TO 35 RETURN 35 CONT IMJE RESID-CALC-XX(2) RET URN 3 CONTIMJE RETUW 4 CONT IMJE RETURN 5 CONT IMJE _ |F(|METHJ)E.-1) GO TO 20 RETURN 20 CONTIMJE RETURN 9 CONT IMJE 224 RETURN I) CONT IMJE RETURN 11 CONT IMJE RETURN 12 CONT IMJE RETURN EIND 225 SUBROUTIIE EQN for the calculation of the lithium chlorocomplex dimerization constant: two—site fast exchange between the monomer and the dimer. SUBROUTIBE EQN COMMON KOUNTJTAPE,JTAPE,IWT.LAP,X|NCR.hDPT.NOVAR,NOUM(.X,U,ITMAX, 1WTX,TEST,I,AV,RESID,lAREPS,ITYP.XX,RXTYP.DX1I,FOP,FO,FU,P,ZL,TO,E 2|GVAL,XST.T,DT,L.M,JJJ,Y,DY,VECT.l\DST,CONST,hDAT,JDAT,MOPT,LOPT. 3YYY,CONSTS COMMON/FREDT/IMETH COMMON/POlNr/KOPT,JOPT.XXX DIMENSION X(4,300).U(20).WTX(4.300).XX(4),FOP(300).FO(300).FU(300) 1,P(20,21).VECT(20,21).ZL(300).T0(20),EIGVAL(20),XST(300).Y('O). 20Y(10),CONSTS(50,16).NCST(50).ISMlM50),RXTYP(50).DX1I(50).IRX(50) 3,MOPT(50).LOPT(50).YYY(50).CONST(16).XXX(15) GO TO (2,3.4.5.1,7,8.9.D.11,12) ITYP 1 CONT IMJE lTAPE-GO JT APE-61 RETURN 7 CONT IMJE NOUM(-3 NOVAR-Z RETURN 8 CONTIMJE RETURN 2 CONT IMJE U(1)-ABS(U(1)) ARG-1.0+8.0*U(1)*XX(1) lF(U(1).EQ.0.00) GO TO 55 ALPH-(-1.0+SQRT(ARG))/4.0*U(1)*XX(1)) CALC-ALPH*(U(2)-U(3))+U(3) GO TO 37 55 CALC-U(2) 37 CONTIMJE lF(lMETH.l‘E.-1) GO TO 35 RETURN 35 CONT lMJE RESIDaCALC—XXQ) RETURN 3 CONT IMJE RETURN 4 CONTIMJE RETURN 5 CONTIMJE HIMETH.|\E.—1) GO TO 20 RETURN 20 CONTIMJE RETURN 9 CONT IMJE 226 RETURN 10 CONT IMJE RETURN 11 CONT IMJE RETURN 12 CONT IMJE RETURN EDD 227 B. The Three-Site Fast Exchange Model for the Determination of Equilibrium Constants The three-site fast exchange model is given as K 2M & D (16) K M + L :11“. ML (17) where M is the Lile monomer, D is the LiZCl42" dimer, and K9 is the dimerization constant. In this case, Gobs = XM5M + XD5D + XML‘SML (18) The values for KD, 6M, and <5 L are entered as constants from the monomer-dimer equilibrium model (section A.). The adjustable parameters are KI: and 5ML: and CMt is the independent variable. The procedure for this calculation is an interative one, and is summarized as follows. For each concentration (CMt) equation (10) is used to calculate a value for the monomer in solution (M). Complexation of the monomer by the crown ether is then assumed, and a new value for M (M') is calculated by first defining B = KFCMt + KFM 4' 1 (19) 131 = 4KFZCMtM (20) then, 228 B - (32 - 131)“2 M' = (21) ZKF which is analogous to the quadratic root that appears in (13). The M' value is then entered into equation (6), and the difference between M' and M calculated. This process is continued until the charge in M is less than 10'6 _M_, where convergence is assumed. The SUBROUTINE EQN listing for this calculation is given below. 229 SUBROUTlhE EQN for the calculation of Li —crown complex formation constants; three-site fast exchange between monomer and dimer lithium chlorocomplexes, and the crown-complexed lithium ion. SUBROUTlhE EQN COMMON KOUNT,ITAPEJTAPEJWTLARXINCR,NOPT,NOVARJ)DUM<.X,U.ITMAX. 1WTX,TEST.l.AV,RESID.IAR.EPS,lTYP.XX,RXTYP.DX1|,FOP,FO,FU,P.ZL.TO,E 2lGVAL,XST,T,DT,L.M,JJJ,Y,DY,VECT.NCST,CONST,I‘DAT,JDAT,MOPT,LOPT, 3YYY,CONSTS COMMON/FREDT/IMETH COMMON/POINT/KOPT.JOPT.XXX DIMENSION X(4,300).U(20).WTX(4,300).XX(4),FOP(300),F0(300),FU(300) 1.P(20,21).VECT(20,21).ZL(300).T0(20),E|GVAL(20),XST(300).Y(10). 20Y(10).CONSTS(50.16).I‘CST(50).ISMIM50).RXTYP(50),DX1I(50).IRX(50) 3,MOPT(50).LOPT(50).YYY(50),CONST(16),XXX(15) GO TO (2,3.4,5,1,7,8.9,10,11,12) ITYP 1 CONT IMJE lTAPE-GO JT APE-61 RETURN 7 CONT IMJE NOUM(-2 NOVAR-Z RETURN 8 CONT IMJE RETURN 2 CONT IMJE U(1)-ABS(U(I)) CN--I.+SQRT(1+8.‘CONST(1)‘CONST(2)) CM-CN/(4.*CONST(2)) CD-(CONST(1)—CM)/2. IF(XX(1).EQ.0.00) GO TO 1500 2000 CONTINUE B-U(1)‘XX(1)+U(1)’CM+10 Bl-4.0*(U(1)"2.)’XX(1)’CM 824B-SQRT((B‘*2.)—B1))/2.‘U(1)) FREEL-XX(1)-82 FREED—CM—BZ lF(FREED.LT.0.00)FREED-0.0 C-2.‘CONST(2)*FREED+1. CHC“*2.)-4.“(CONST(2))‘((CONST(2))*(FREED“2.)-CD) FCHANG-(C-SQRT1C1))/ 2.’CONST(2)) CD-CD+FCHANG FREEDsFREED—FCHANG FCHAMS-ABSFCHANG) IF(FCHANG.LT.0.000001) GO TO 1000 CM-FREEDHXXUH‘REEL) GO TO 2000 230 1000 CONTIMJE XM-FREED/CONST(1) XD-(2.*CD)/CONST(1) XCI-(U(1)*FREEL‘FREED)/CONST(1) CALC-COI‘IST(3)‘XM+CONST(4)‘XD+U(2)*XCI GO TO 36 1500 XM-CM/CONST(1) XD-(2.*CD)/CONST(1) CALC-XM‘COBSTBHXD‘CONSTM) 36 CONTIMJE lF(lMETH.hE.—1) GO TO 35 RETURN 35 CONT IMJE RESlD-CALC-XX(2) RETURN 3 CONT IMJE RETURN 4 CONTIMJE RETURN 5 CONT IMJE lF(lMETHJ\E-1) GO TO 20 RETURN 20 CONT IMJE RETURN 9 CONT IMJE RETURN 10 CONT IMJE RETURN 11 CONT IMJE RETURN 12 CONT IMJE RETURN END 231 APPENDIX 2 A. Crystallographic data for the C2322-LiAlCl4 Complex 1. Bond distances and angles In the first two tables which follow, the bond distances (in Angstroms) and bond angles (in degrees) which were calculated in the least squares refinement of the crystal structure of the C2322-LiAlCl4 complex, are listed. The values in parentheses are the estimated standard deviations in the bond . distances and bond angles. 2. Least squares planes The following calculations were performed to evaluate the site symmetry of the lithium ion in the cryptand cavity with respect to the oxygen and nitrogen donor atoms. The reader is referred to Figure 47 and Table 31. . In this procedure, a set of four donor atoms (combinations of oxygens or oxygens and nitrogens) are selected which roughly describe a plane in the cryptand cavity. The computer program then calculates the "best" plane of these atoms by using a least squares routine and an equation of the form Ax+By+Cz+D=0 (1) where A,B,C, and D are variable parameters, and x,y, and z are the orthogonalized atom coordinates. The program then calculates the distance between the calculated plane and the lithium ion. This procedure is repeated for the other five possible sets of donor atoms. The details of these calculations, and the resulting dihedral angles between the calculated planes are given in the folowing table. 232 Table of Bond Distance: <1n Angstroms) for the C2228 Conplox of L1th1un Totrachloroaluuinate Aton1 Aton2 D1stanco 011 A11 2.131(2) 012 A11 2.120(2) 013 A11 2.125(2) 014 A11 2.121(2) 04 L11 2.457(11) 07 L11 2.492(11) 013 L11 2.200(11) 016 L11 2.371(11) 021 L11 2.291(11) 024 L11 2.195(11) N1 L11 2.980(11) N10 L11 2.729(11) 04 C3 1.400(5) 04 05 1.383(6) 07 C6 1.380(7) 07 08 1.403(6) 013 C12 1.403(7) 013 014 1.412(6) 016 C15 1.409(6) 016 017 1.375(7) 021 020 1.478(8) 021 022 1.411(8) 024 023 1.392(7) 024 025 1.460(7) N1 02 1.461(7) N1 018 1.489(7) N1 019 1.455(7) N10 09 1.446(8) N10 011 1.465(7) N10 026 1.448(7) 02 03 1.524(7) 013 023 1.405(9) 018 C6 1.385(8) 02B 038 1.335(9) 03B 04B 1.394(8) 04B 05 1.393(7) 05 06 1.359(7) 08 C9 1.489(9) 011 012 '1.524(8) 014 015 1.516(8) C17 C18 1.546(8) 019 020 1.453(8) 022 023 1.426(10) 025 026 1.450(8) 233 Table of Bond Distances (Continued) for the 02228 Complex of L1th1um Tetrechloroaluminate Atom1 Atom2 Distance C2 H20 0.950(5) 02 H2b 0.950(5) 03 H30 0.950(5) 03 H3b 0.950(5) C18 H18 0.950(7) 028 828 0.950(6) C38 H38 0.950(6) 048 H48 0.950(5) 08 H80 0.950(6) 08 Heb 0.950(6) C9 H90 0.950(6) 09 H9b 0.950(7) 011 H110 0.950(5) 011 H11b 0.950(6) 012 H120 0.950(6) 012 H12b 0.950(6) 014 H140 0.950(5) 014 H14b 0.950(6) C15 H150 0.950(5) 015 H15b 0.950(5) 017 H170 0.950(6) 017 H17b 0.950(6) 018 H180 0.950(6) 018 H18b 0.950(6) 019 H190 0.950(6) 019 H19b 0.950(6) 020 H200 0.950(6) 020 H20b 0.950(7) 022 H220 0.950(6) 022 H22b 0.950(6) 023 H230 0.950(7) 023 H23b 0.950(7) 025 H250 0.950(5) 025 H25b 0.950(6) 026 8260 0.950(6) 026 H26b 0.950(6) Numbers in parentheses are estimated standard deviations in the least s19n1£1¢0nt digits. 234 Table of 80nd Angles (in Degrees) for the 02228 Complex of Lithium Tetrachloroaluninate Atoml Atom2 Atom3 Angle 011 All 012 109.7(1) 011 All 013 109.8(1) 011 All 014 108.9(1) 012 All 013 109.4(1) 012 All 014 110.4(1) Cl3 All 014 108.6(1) 03 _04 Lil 113.1(4) 05 04 Lil 119.4(4) 06 07 Lil 118.1(4) C8 07 Lil 116.3(4) 012 013 L11 117.1(4) 014 013 Lil 115.1(4) 015 016 Lil 111.0(4) 017 016 Lil 120.1(4) 020 021 Lil 121.1(4) 022 021 Lil 111.2(4) 023 024 Lil 115.1(5) C25 024 Lil 116.4(4) 02 N1 Lil 106.9(4) 018 N1 Lil 106.6(4) 019 N1 Lil 103.0(4) 09 N10 Lil 110.7(4) 011 N10 Lil 102.6(3) 026 N10 Lil 103.0(4) 04 Lil 07 61.3(3) 04 Lil 013 82.1(4) 04 Lil 016 106.0(4) 04 Lil 021 93.8(4) 04 Lil 024 165.6(5) 04 Lil N1 63.1(3) 04 Lil N10 113.1(4) 07 Lil 013 97.9(4) 07 Lil 016 165.2(5) 07 Lil 021 83.8(4) 07 Lil 024 111.5(4) 07 Lil N1 112.6(4) 07 Lil N10 63.8(3) 013 Lil 016 71.6(3) 013 Lil 021 174.0(5) 013 Lil 024 111.8(5) 013 Lil N1 109.2(4) 013 Lil N10 70.6(3) 016 Lil 021 105.6(4) 016 Lil 024 82.6(4) 016 L11 N1 63.4(3) 235 Tabla of 80nd Angles (Continued) for the 02228 Complex of Lithium Tetrachloroaluninate Atoml Atom2 Atom3 Angle 016 Lil .N10 119.7(4) 021 Lil 024 72.5(4) 021 L11 N1 65.0(3) 021 Lil N10 115.2(4) 024 Lil N1 112.9(4) 024 Lil N10 70.4(3) N1 Lil N10 176.1(5) 03 04 05 119.5(4) 06 07 C8 121.9(4) 012 013 014 111.6(4) 015 016 017 116.8(4) 020 021 022 112.8(5) 023 024 025 113.7(4) 02 N1 018 111.7(4) 02 N1 019 113.5(4) 018 N1 019 114.3(4) 09 N10 011 111.6(5) 09 N10 026 114.7(4) 011 N10 026 113.1(5) N1 02 03 109.2(4) 04 03 02 112.2(4) 028 018 06 118.0(6) 018 028 038 121.5(6) 028 038 048 120.6(6) 038 048 05 118.3(5) 04 05 048 124.0(4) 04 05 06 115.1(4) 048 05 C6 120.9(5) 07 06 018 124.6(5) 07 06 05 114.7(4) 018 06 05 120.6(5) 07 08 C9 106.3(5) N10 09 08 113.9(5) N10 011 012 110.3(5) 013 012 011 111.1(5) 013 014 015 106.1(4) 016 ‘ 015 014 107.4(4) 016 017 018 113.4(5) N1 018 017 107.5(4) N1 019 020 112.1(5) 021 020 019 112.6(5) 021 022 023 110.1(6) 024 023 022 110.5(5) 024 025 026 112.0(5) N10 926 C25 114.3(4) 236 Table of 80nd Angles (Continued) for the 02228 Complex of Lithium Tetrachloroaluminato Atoml Atom2 Atom3 Angle N1 02 H20 110.3(4) N1 02 H2b 108.6(4) 03 02 H20 111.1(4) 03 02 H2b 108.2(4) H20 02 H2b 109.5(5) 04 03 H30 109.3(4) 04 C3 H3b 109.2(4) 02 C3 H30 108.5(4) C2 03 H3b 108.0(4) H30 03 H3b 109.5(5) 028 018 H18 121.3(6) C6 018 H18 120.7(6) 018 028 H28 118.5(6) 038 028 H28 119.9(6) 028 038 H38 119.7(6) 048 C38 H38 119.7(6) C38 C48 H48 120.8(5) 05 048 H48 120.9(5) 07 08 H80 110.2(6) 07 08 H8b 110.9(5) C9 C8 H80 110.4(6) 09 C8 H8b 109.5(6) H80 08 H8b 109.5(6) N10 09 H90 108.2(6) N10 09 H9b 107.9(5) 08 C9 H90 109.2(6) 08 C9 H9b 108.0(6) H90 09 H9b 109.5(6) N10 011 H110 109.3(4) N10 011 Hllb 109.0(5) 012 011 H110 110.2(6) 012 011 Hllb 108.6(4) H110 011 Hllb 109.5(6) 013 012 H120 109.7(5) 013 012 H12b 109.0(6) 011 012 H120 108.8(6) 011 012 H12b 108.7(5) H120 012 H12b 109.5(6) 013 014 H140 109.8(5) 013 014 H14b 111.2(5) 015 014 H140 109.4(5) 015 014 H14b 110.8(5) H140 014 H14b 109.5(6) 016 015 H150 109.6(5) 016 015 H15b 109.7(5) 014 015 H150 110.1(5) 014 015 H15b 110.6(5) 237 Table of Bond Angles (Continued) for the 02228 Complex of Lithium Tetrachloroaluninate Atoml Atom2 Atom3 Angle H150 015 H15b 109.5(5) 016 017 H170 107.5(6) 016 017 H17b 110.1(5) 018 017 H170 107.2(5) 018 017 H17b 109.0(6) H170 017 H17b 109.5(6) N1 018 H180 110.1(5) N1 018 H18b 109.2(5) 017 018 H180 110.8(5) 017 018 H18b 109.8(6) H180 018 H18b 109.5(5) N1 019 H190 108.6(5) N1 019 H19b 109.3(5) 020 019 H190 108.0(5) 020 019 H19b 109.4(6) H190 019, H19b 109.5(6) 021 020 H200 108.4(5) 021 020 H20b 107.7(5) 019 ‘020 H200 109.6(6) 019 C20 H20b 109.0(6) H200 020 H20b 109.5(6) 021 022 H220 110.2(6) 021 022 H22b 108.7(6) 023 022 H220 111.6(6) 023 022 H22b 106.6(6) H220 C22 H22b 109.5(7) 024 023 H230 110.5(6) 024 023 H23b 108.3(6) 022 023 H230 111.2(6) 022 023 H23b 106.8(6) H230 023 H23b 109.5(7) 024 025 H250 108.9(5) 024 025 H25b 107.4(5) 026 025 H250 110.3(5) 026 025 H25b 108.7(5) H250 025 H25b 109.5(6) N10 026 H260 107.5(5) N10 026 H26b 109.3(5) 025 C26 H260 107.3(5) 025 C26 H26b 108.9(5) H260 026 H26b 109.5(5) Number-Lin parentheses are estimated standard deviations in the least significant digits. 238 Table of Least-Squares Planes in the 02228 Complex of Lithium Tetrachloroaluminate The equation of the plane is of the fora: AIx 0 BIy 0 CI: - D I 0 where A, 8, 0 G D are constants and x. y 8 z are orthogonalized coordinates. Plane No. 1 A I -0.8889. 8 I -0.4152. 0 I -0.1935, 0 I -9.8441 Chi Squared I 1995. Atom x y 2 Distance Esd ------------- Atoms in Plane------------- 04 6.3798 6.6327 7.7298 -0.077 0.003 013 7.4904 4.9806 5.4008 0.073 0.003 021 7.0483 3.8733 9.7239 0.089 0.004 024 8.3126 2.4439 7.8781 -0.084 0.004 --------------- Other Atoss-------------- Lil 7.3839 4.3999 7.5196 -0.002 0.010 07 8.7676 6.2508 8.4516 -2.180 0.004 016 5.8216 3.0914 6.3071 2.165 0.003 N1 4.5487 4.5234 8.4270 2.292 0.004 N10 9.9938 4.4683 6.7264 -2.197 0.004 Plane No. 2 A I 0.7595. 8 I -0.6442, 0 I -0.0907. D I 1.9221 Chi Squared I 1126. Atom x y 2 Distance Esd ------------- Atoms in Plane------------- 07 8.7676 6.2508 8.4516 -0.057 0.004 013 7.4904 4.9806 ,5.4008 0.068 0.003 016 5.8216 3.0914 6.3071 -0.065 0.004 021 7.0483 3.8733 9.7239 0.053 0.004 --------------- Other Atoms-------------- Lil 7.3839 4.3999 7.5196 0.169 0.010 04 6.3798 6.6327 7.7298 -2.051 0.003 024 8.3126 2.4439 7.8781 2.102 0.004 N1 4.5487 4.5234 8.4270 -2.146 0.004 N10 9.9938 4.4683 6.7264 2.179 0.004 Plane Plane Plane No. No. No. Table of Least-Squares Planes (Continued) 239 in the 02228 Complex of Lithium Tetrachloroaluminate 3 4 5 Atom O4 016 024 L11 013 021 N10 A s Atom Atom O7 016 N10 L11 O4 013 021 024 -0.0896, B I -0.2142. 8 I 0.4598, 8 I 0.1727, 0 I -0.8711. 0 I -2.4519 Chi Squared I 10353. x y 2 Distance Esd ------------- Atoms in Plane------------- 6.3798 6.6327 7.7298 -0.203 0.003 8.7676 6.2508 8.4516 0.201 0.004 5.8216 3.0914 6.3071 0.169 0.004 8.3126 2.4439 7.8781 -0.166 0.004 --------------- Other Atoms-------------- 7.3839 4.3999 7.5196 0.057 0.010 7.4904 4.9806 5.4008 2.051 0.004 7.0483 3.8733 9.7239 -2.109 0.004 4.5487 . 4.5234 8.4270 -2.016 0.004 9.9938 4.4683 6.7264 1.959 0.004 -0.9626, 0 I -0.2557. D I -6.8820 Chi Squared I 299. x y 2 Distance Esd ------------- Atoss in Plane------------- 7.4904 4.9806 5.4008 0.035 0.004 7.0483 3.8733 9.7239 0.035 0.004 4.5487 4.5234 8.4270 -0.035 0.004 9.9938 4.4683 6.7264 -0.035 0.004 --------------- Other Atoms-------------- 7.3839 4.3999 7.5196 0.062 0.011 6.3798 6.6327 7.7298 -2.051 0.004 8.7676 6.2508 8.4516 I2.082 0.004 5.8216 3.0914 6.3071 1.771 0.004 8.3126 2.4439 7.8781 1.770 0.004 0.6773. 0 I -0.7039, D I -3.7l93 Chi Squared I 3784. x y 2 Distance Esd ------------- Atoms in Plane------------- 8.7676 6.2508 8.4516 0.126 0.004 5.8216 3.0914 6.3071 0.127 0.004 4.5487 4.5234 8.4270 -0.123 0.004 9.9938 4.4683 6.7264 -0.130 0.004 --------------- Other Atoms-------------- 7.3839 4.3999 7.5196 -0.175 0.011 6.3798 6.6327 7.7298 1.404 0.004 7.4904 4.9806 5.4008 1.687 0.004 7.0483 3.8733 9.7239 -2.012 0.004 8.3126 2.4439 7.8781 -1.951 0.004 Plane No. 240 Table of Least-Squares Planes (Continued) in the 02228 Complex of Lithium Tetrachloroaluminate 6 A. Atom O4 024 N1 N10 L11 013 016 021 -0.2953, 6.3798 8.3126 4.5487 9.9938 7.3839 8.7676 7.4904 5.8216 7.0483 Dihedral Angles Between Planes: Plane usswwwnwbnupuwu Plane a~m