THE SYNTHESIS, CHARACTEREZATION AND ELECTRONIC PRQPERTIES 0F ‘ SOME ALKYLAMBNOFLUOROPHOSPHINE COMPLEXES 0F COBALT (ll) HAUDES Thesis for the Degree of Ph. D. MECHIGAN STATE UNWERSITY THOMAS EDWARD NOWLIN 1971 ,,,,,,,,,,,, -\§m4uwm:At 4. WW ¢ ._ {4' ‘3 him in State U r:. {varsity 6'“ . .. w“"rx3rr£ i5 gJ:.A{il\41[\J. This is to certify that the thesis entitled The Synthesis, Characterization and Electronic Properties of Some Alkylaminofluorophosphine Complexes of Cobalt(II) Halides presented by Thomas Edward Nowlin has been accepted towards fulfillment . of the requirements for t 4’ Ph-D- degree mm .r ’ \1"C,J9\_ Major professor Date 7fldf}; /77/ 0-7639 BINDERY INC. - av emnsns "”31. males] . . 1‘ a» ABSTRACT THE SYNTHESIS. CHARACTERIZATION AND ELECTRONIC PROPERTIES OF SOME ALKYLAMINOFLUOROPHOSPHINE COMPLEXES OF COBALT(II) HALIDES BY Thomas Edward Nowlin Pentacoordinate complexes of the type CoLsxz (where L is an alkylaminofluorophosphine and x is Cl, Br, I) were obtained from the interaction of anhydrous coba1t(II) halides with dimethylaminodifluorophosphine, (CH3)2NPF2(apf2), or bis(dimethylamino)fluorophosphine, [(CH3)2N)2PF(a2pffl. The pentacoordinate complexes Co(apf2)312, Co(apf2)3Br2, and Co(a2pf)312 have been characterized both by analytical and magnetic moment data and by visible and electron-spin resonance spectral data. Although the complexes Co(a2pf)3C12 and Co(a2pf)3Br2 were not isolated, magntic moment and spectroscopic data strongly suggest their existence in solution. -When the complex Co(a2pf)312 is dissolved in either methylene chloride or benzene, an equilibrium is established between the pentacoordinate low-spin complex and a four-coordinate high-spin complex of the type Co(a2pf)212. Formation con- stants Kf, AHO, and A50 values were obtained for the Thomas Edward Nowlin equilibrium. Similar results were obtained for the analogous CoClz and CoBr2 complexes. The electronic properties of these complexes are discussed and correlated with the thermodynamic stability constants (Kf). THE SYNTHESIS, CHARACTERIZATION AND ELECTRONIC PROPERTIES OF SOME ALKYLAMINOFLUOROPHOSPHINE COMPLEXES OF COBALT(II) HALIDES BY Thomas Edward Nowlin A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Chemistry 1971 To Margaret ii ACKNOWLEDGMENTS The author is indebted to Professor Kim Cohn for the helpful guidance and assistance offered during this in- vestigation and during the preparation of this thesis. He is also grateful to Dr. S. Subramanian for assist- ance in interpretation of the esr spectra. Finally, the author is grateful to his fellow graduate students whose suggestions and friendship were invaluable to the comple- tion of this degree. iii TABLE OF CONTENTS Page INTRODUCTION 0 O O O O O O O O O O O O O O O o O O 1 HISTORICAL INTRODUCTION . . . . . . . . . . . . . . 3 Synthesis of Pentacoordinate Cobalt(II) Complexes 3 Solution Equilibrium Studies Involving Cobalt(II) Complexes . . . . . . . . . . . . . . . . . Electron Spin Resonance (esr) Studies of Cobalt(II) Complexes . . . . . . . . . . . . 7 EXPERIMENTAL . . . . . . . . . . . . . . . . . . . 9 General Procedure . . . . . . . . . . . . . . 9 Materials . . . . . . . . . . . . . . . . . . 10 Magnetic Moment Measurements . . . . . . . . . 12 Measurement of Equilibrium Constants . . . . . 13 Measurement of the Esr Spectra . . . . . . . . 17 Infrared and Optical Spectra . . . . . . . . . 18 Preparation of the Complexes . . . . . . . . . 19 Attempts to Prepare Complexes with the Ligand tris(dimethylamino)phosphine . . . . . . . . 24 iv TABLE OF CONTENTS (Cont.) Page RESULTS AND DISCUSSION . . . . . . . . . . . . . . 29 (A) Characterization of Dimethylaminodifluoro- phosphine Cobalt(II) Complexes . . . . 29 (B) Characterization of the bis(dimethylamino)- fluorophosphine Complexes . . . . . . . 40 (C) Electron Spin Resonance Spectra of the Complexes . . . . . . . . . . . . . . . 71 BIBLIOGRAPIIY . C O 0 O . O O O O O O O O O O O O O 99 10. LIST OF TABLES Anal tical data for complexes isolated with trisfdimethylamino)phosphine, [(CH3)2N]3P . . Summary of the infrared spectra of Co(apf2)312 and Co apf233r2 (C-H and P-F regions) . . . . Magnetic moments of the complexes Co(apf2)3Iz and Co(apf2)3Br2, solutions contain excess ligand . . . . . . . . . . . . . . . . . . . Summary of the visible spectra of Co(apf2)3Iz and C0(apf2 )3Br2 o o o o o o o o o o o o o 0 Concentration dependence of solution magnetic moments when Co(a2pf)313 was dissolved in either CH2C12 0r COHG o o o o o o o o o o o o Equilibrium constants Ks, AH0 and A§° values 1 of a solution which wa .49 x 10' :1 with respect to Co(a2pf)312 and 0.36M_with re- spect to azpf . . . . . . . . . . . . . . . . Temperature dependence of the solution magnetic moments and the equilibrium constants calcu- lated for the solutions obtained when C0C12 or CoBrz were allowed to interact with excess ligand in methylene chloride . . . . . . . ESR parameters of Co(a2pf)3xz and Co(apf2)3x2 in methylene chloride solution at room temperature 298 K and 77 K . . . . . . . . . g_values calculated from the room temperature esr spectra of pol crystalline samples of Co(a2pf)312 and Co dpp)33r3 (this work) and related compounds . . . . . . . . . . . . . . Summary of the visible spectra of the complexes Co(apf2)3X2 (X . Br, I) and Co(a2pf)3xg (X = .Cl, Br, I) mulled in Nujol and dissolved in~ CHQClz I o o c o, o o o o o o o o . o o o o o o 0 vi Page 37 39 41 48 56 57 73 80 87 LIST OF TABLES (Cont.) TABLE 11. 12. 13. Page Observed and calculated gfvalues for the complexes Co(apf2)3X2 (X = Br, I) . . . . . . 95 State and transition energies calculated for the Co(apf2)3X2 (X = Br, I) complexes, three- vacancy configurations . . . . . . . . . . . 96 Single—electron d-orbital energies for the Co(apf2)3X2 (X = Br, I) complexes . . . . . . 98 vii LIST OF FIGURES FIGURE 1. 2. 10. 11. Nmr spectra of Co(apf2)312 dissolved in methylene chloride and excess ligand . . . . Infrared spectrum of the complex isolated when ACOBrz was allowed to interact with [(CH3)2N]3P Infrared spectra (3100-2700 cm-l) of (A) CH3)2NPF3, neat, gas phase (10 mm pressure), B) Co(apf2)3Br2, Fluorolube mull . . . . . Infrared spectrum (2000-625 cm-l) of Co(apf2)313, Nujol mull . . . . . . . . . . . Infrared spectrum (2000-625 cm-l) of CO(apf2 )3Br2 ' NUjOl [(1111]. o o o o o o o o o o Visible Spectra (mull and solution) of Co(apf2)312 and Co(apf2)3Br2, solution spectra obtained in excess ligand . . . . . . . . . . Infrared spectra of (A) neat azpf and (B)_ Co(a2pf)312 (Fluorolube mull 3100-2700 cm 1, Nujol mull 1600-250 cm 1) . . . . . . . . . . Visible spectra of (A) solid Co azpf 312 and (B) 2.98 x 10 3M'solution of Co aapf 312 dissolved in CH2C12 (path length 10.0 mm) . . Temperature dependence of the visible spectra exhibited by a solution which was 1.49 x 10 2M in Co(a2pf)312 and 0.36M_in azpf, 500-800 mu (path length 1.0 mm) . . . . . . . . . . . . Temperature dependence of the visible spectra of a 5.0 x 10 3M'solution of Co(a2pf)312 and 0.121;: in azpf, 550-350 ml (path length 1.0 mm) Visible spectra 25° of solutions_containing a CoClz concentration of 1.48 x 10 3M, with the concentration of azpf increasing from ap roxi- mately 0.05 to 0.15M, 1-4, respectively path length 1.0 mm) . . . . . . . . . . . . . . . viii Page 15 27 32 34 36 43 45 50 53 55 59 LIST 0 FIGURE 12. 13. 14. 15. 16. 17.' 18. 19. 20. F FIGURES (Cont.) Visible spectra temperature dependence of a 3.52 x 10 2M solution of COC12 in excess azpf, 450-850 mu.TPath length 1.0 mm) . . . . . . . Visible spectra temperature dependence of a 1.0 x 10 21\_a_solution of CoClz in excess azpf, 325-550 mu (path length 1.0 mm) . . . . . . . Visible Spectra temperature dependence of a 2.34 x 10 3M solution of CoBrz in excess azpf, 500-850 mu (path length 1.0 mm) . . . . . . . Visible spectra temperature dependence of a 7.80 x 10 3M solution of CoBrz in excess a2pf, 300-550 mu (path length 1.0 mm) . . . . . . . Typical room temperature esr solution spectrum of CoL3x2 (L = azpf or apfa, x = Cl, Br, or I) in methylene chloride and excess ligand . . . Room temperature esr spectrum of a polycrys— talline sample of Co(a2pf)312 . . . . . . . . Room temperature esr spectrum of a polycrys- talline sample of Co(dpp)3Br2 . . . . . . . . Frozen solution Spectrum (77 K) of Co(a2pf)312 in excess a2pf and CH2C12 . . . . . . . . . . .Frozen solution spectrum (77 K) of Co(apf2)312 in excess apfz and CH2C12 . . . . . . . . . . ix Page 62 64 66 68 75 77 79 83 85 INTRODUCTION There have been several recent investigations on the factors which influence the ability of transition metals such as cobalt(II) and nickel(II) to form pentacoordinate complexes.1"9 Steric and electronic effects, in addition to the nature of the coordinated anions, have been examined. Some investigators have suggested that electronic factors1:2 may be more important than steric factors in stabilizing pentacooridnate cobalt(II) and nickel(II) com- plexes. Specifically, steric interactions3 have been in- voked to rationalize the fact that bulky tertiary phOSphines such as (C3H5)3P do not form stable pentacoordinate cobalt- (II) complexes. However, coskran gt 31.4 concluded from results obtained on spectral studies with phosphite ligands that the importance of steric factors has been overempha- sized. Turco and coworkers"”9 have considered the role of the anion in stabilizing pentacoordinate cobalt(II) complexes. They proposed that a "strong field" anion was required for the formation of complexes of the type CoL3X2, where L is a neutral donor atom and X is a coordinated anion. For example, the “strong field" pseudohalogen anions CN- and SCN- have been used to prepare Co[PC2H5(CBH5)2]3(CN)2, 1 2 C0[P(C2H5)2CSH5]3(CN)2'5’6 and C°[P(C2Hs)3]2(SCN)2-7-9 They also reported that similar low-Spin pentacoordinate com- plexes do not form when the anion is Cl-, Br-, 1', or NCO-. No quantitative information has been reported on the role the halogens play in stabilizing the pentacoordinate complex. The present investigation was undertaken to obtain in- formation on how the electronic effects of the anions (Cl-, Br-, I-) and of the ligands influence the formation of pentacoordinate cobalt(II) complexes. I evaluated these effects with monodentate ligands in order to eliminate any possibility that the geometry of the resulting complex was controlled by steric requirements imposed by multidentate ligands. Numerous pentacoordinate complexes of cobalt(II) with polydentate ligands have been examined. The relative thermodynamic stability of four and five coordinate complexes of the type Co(a2pf)2X2 and Co(a2pf)3X2 (where X is Cl, Br or I) have been determined. These data are discussed and correlated with the electronic pro- perties as indicated from the electron Spin resonance spec- tral data obtained for these complexes. HISTORICAL INTRODUCTION A survey of the previous work reported for pentaco- ordinate low-spin cobalt(II) complexes will be discussed in three parts. First, synthesis of pentacoordinate low- spin complexes will be reviewed. Second, a summary of the equilibria investigations that have been reported for cobalt(II) complexes is given. Finally, the electron spin resonance studies that have involved pentacoordinate co- balt(II) complexes will be presented. Synthesis of Pentacoordinate Cobalt(II) Complexes Pentacoordinate complexes of cobalt(II) which contain coordinated anions and neutral ligands attached to the metal have been reported for various types of chelating ligands. The first pentacoordinate complex of this type was reported in 1960 by Issleib and Wenschush.10 When excess diphenylphosphine (dpp) was allowed to interact with anhy- drous cobalt(II) bromide in either dichloromethane or benzene a brown crystalline solid, Co(dpp)3Br2, (Ueff 2.01 B.M.) was isolated. Recently, it has been shown by a single crystal X-ray diffraction study11 that the structure of this pentacoordinate complex is intermediate between a 3 4 trigonal bipyramidal and square pyramidal configuration, the two possible idealized pentacoordinate structure types. The axial site is occupied by one of the three phOSphorus donor atoms. Until this present investigation, no other pentacoordinate complex of the type COL3X2 where L is a monodentate ligand and »X a halogen had been reported, although Rigo and coworkers had reported a series of com- plexes of the type CoL3(CN)2 where L is diethylphenyl- phosphine P(C2H5)2C3H5, and ethyldiphenylphosphine PC2H5(C6H5)2'5'6 Other pentacoordinate ionic complexes of the type (CoL2X)Y where L is a bidentate ligand, X a coordinated anion and Y a non-coordinating anion such as perchlorate or another halogen atom have been reported. These include ditertiary phoSphine complexes of the type Co[¢2P(CH2)2P¢2]2X2 in which X is Cl, Br, and 1.12 Dyer and Meek reported the preparation of similar complexes which incorporated the ligands diphenyl(g-methylthiOphenyl)phOSphine (Se) S-CH3 -P¢2 and diphenyl(9-diphenylarsinophenyl)phosphine AS¢2 Other pentacoordinate complexes of cobalt(II) which contained 8-dimethylarsinoquinoline @9 CH3, AS\CH3 as the ligand have been prepared.14 PentaCoordinate complexes of the type CoLXz where L are tridentate ligands have been prepared as part of a sys- tematic investigation that was undertaken to determine the effect various sets of donor atoms have on determining the spin-multiplicity of the ground state of cobalt(II). For example, the ligands bis-(2-diphenylphosphinoethyl) R-amine, ¢2P(CH2)2-N-(CH2)2P¢2 (R = H or CH3)15 and 2,6-di(B-di- I R phenylphosphinoethyl)pyridine (a PNP donor atom set) yield low-spin complexes.16 Finally, quadridentate ligandsl7:19 such as P(gf ¢2PC6H4)3(QP) have been employed in the preparation of low- spin complexes of the type (CoLX) where L is a quadri- dentate ligand and X and Y are coordinated and non-co- ordinated anions, respectively. There is a complete review of tri- and quadridentate ligands which have been used to prepare pentacoordinate complexes.20 Solution Equilibrium Studies Involving Cobalt(II) Complexes There are various types of equilibria involving high- and low-Spin cobalt(II) complexes in non-coordinating 6 solvents. A series of investigations by Everett and Holm’n-23 has suggested a structural equilibrium which involves strictly four coordinate cobalt(II) complexes in which the two forms are interconnected by a torsional deformation. This equi- librium may be represented as: Planar (low spin) > tetrahedral (high spin). A similar equilibrium in which the high and low-Spin species are both pentacoordinate has been suggested recently. Nelson and Kelly suggested the following interconversion 24 square pyramidal __3_ trigonal bipyramidal . (low spin) (high spin) The existence of high-Spin, low-spin solution equi- librium in which a configurational change is involved has been reported for Co[P(C2H5)3]2(SCN)2.8 The high spin form has been identified as a monomeric Species with a tetra- hedral configuration about the cobalt(II). The low-spin species is dimeric in solution, and it has been suggested that the cobalt atoms are linked by SCN bridges to give a pentacoordinate Species. This type of equilibrium can be expressed as: 2[Co[P(C2H5)3]2(NCS)2] ¢__: [CO[P(C2H5)3]2(NCS)2]& tetrahedral high-spin low-spin dimer A Similar type of equilibrium which involved only monomeric species has also been reported, and may be ex- pressed as: C0112 (NCS ) 2 + L > COL3 (NCS ) 2 tetrahedral high-spin low-spin-monomer The ligands employed in this study were P(C2H5)2C6H5 and PC2H5(C6H5)2. This latter equilibrium is analogous to the one I investigated in the present study, however, I was able to study the role of the halogen in stabilizing the pentacoordinate species. In all previous work it was noted that halocomplexes of the type Co(PR3)2X2 (R is ethyl or phenyl) did not Show any tendency to coordinate a third phosphine molecule. Electron Spin Resonance Studies (esr) of Cobalt(II) Complexes There have been relatively few reports of esr studies on five coordinate low-spin cobalt(II) complexes and, con- sequently, the electronic properties of this type of complex are not well known. Horrocks and coworkers12 reported that the esr Spectra of the polycrystalline complexes, Co[(C6H5)2PCH2CH2P(C6H5)2]2X2 (where X is a coordinated and a non-coordinating halogen, Cl, Br or I), Showed three distinct 'g values. This obser- vation indicates that the symmetry has been reduced from idealized C4; to sz' The electronic ground state sug- gested was |(£§)(£})(xzi§2)> (vacancy configuration) and the energies of the one-electron d-orbitals were estimated using the observed optical data and the interelectronic interaction energies calculated for the low-spin d7 sys- tem. No cobalt or ligand hyperfine interaction was observed 8 in the esr spectra of these complexes. There has been only one other esr investigation of pentacoordinate cobalt complexes. Genser reported25 esr results obtained from a bis-dithiodiketone complex. The fifth coordination site was occupied by a neutral phoSphite ligand. It should be pointed out that it is not clear if this complex Should be considered as a cobalt(II) 3d7 deriv- ative with two monovalent bidentate ligands. ‘It may be thought of as a cobalt(IV) derivative with two divalent ligands. Hence, the conclusions about the electronic prOperties of this complex may not be useful in compari- sons with other cobalt(II) low-Spin complexes. No esr results have been reported for complexes of the type CoL3X2 (where L is a monodentate neutral ligand and X is a coordinated anion). Most of the known complexes of this type are dissociated in solution (in contrast to the numerous dissociatively stable pentacoordinate complexes prepared with polydentate ligands). EXPERIMENTAL General Procedure The cobalt(II) complexes of dimethylaminodifluoro- phosphine, (CH3)2NPF2(apf2), and bis(dimethylamino)fluoro- phOSphine, [(CH3)§M2PF(a2pf), are sensitive to air. How- ever, solutiOns of these complexes could be stored in methylene chloride or benzene for serveral hours in a glove bag filled with dry nitrogen without any observable changes in their spectral and magnetic properties. Therefore, these solutions were prepared under an atmOSphere of dry nitrogen in a glove bag just prior to use. Solid materials which contained apfz were handled in an atmosphere of dry nitro- gen in a dry box. The complexes Co(apf2)3X2 (X = Br, I) were prepared by use of standard vacuum techniques. A com- plete description of these techniques and a diagram of a suitable vacuum line can be found in "The Synthesis and Characterization of Inorganic Compounds," William L. Jolly, Prentice-Hall (1970), pages 139-181. The complex Co(a2pf)312 was prepared under a nitrogen atmosphere and was handled in a glove bag that contained phosphorus pentoxide as a desiccant. Elemental analyses were carried out by Galbraith Laboratories, Inc. (Knoxville, Tennessee) or Spang Labora- tories (Ann Arbor, Michigan). 9 10 Materials Anhydrous cobalt(II) fluoride, chloride, and iodide were used as obtained from Alfa Inorganics (Beverly, Massa- chusetts). Anhydrous cobalt(II) bromide was used as ob- tained from Research Inorganic Chemical (Sun Valley, Cali- fornia). . The solvents employed in this research (methylene chloride, benzene and pentane) were dried by refluxing over calcium hydride for at least twenty-four hours and were then distilled just prior to use. The ligand apfz was prepared from dimethylamino- dichlorophOSphine.26 The identity of the ligand was established by comparison of its infrared spectrum with a previously reported spectrum;27 by its vapor pressure of 93.7 mm at 0°, and by its nmr spectral data (Olppm(TMS) -2.69, JPH 9.6, JFH 3.8). Bis(dimethylamino)fluorophosphine, a2pf, was prepared by the reaction: (CH3)2NPF2 + [(CH3)2N]3P-——> 2[(CH3)2N]2PF In a typical experiment a 58.5 9 sample (0.52 mol) of dimethylaminodifluorophosphine and an 89.2 9 sample (0.55 mol) of tfis(dimethylamino)phOSphine were combined. This mixture (approximately 140 ml) was added to a 200 cc "monel" bomb. The bomb was sealed and maintained for three days at 155° in an oil bath. The bomb was opened after it had cooled to 23°. The contents (nmr spectral data 11 indicated that approximately 75% of this mixture was azpf) was transferred to a glass vessel equipped with a stopcock. Impurities were removed by (a) fractional distillation. The product distilled at 50°/50 mm (b) trap to trap dis- tillation in vacuo from -22° to -49° to -78°. The product remained in the -45° trap, (c) gas chromatography. The details of the gas chromatography experiment have been pre- viously described.28 The identity of the ligand was estab- lished from nmr spectral data (O,ppm(TMS)-2.5, JPH 8.8, JFH 3.0).29 The ligand purified by gas chromatography exhibited an nmr spectrum in which no absorptions attri- butable to either (CH3)2NPF3 or [(CH3)2N]3P were observed, and was used for the final preparative work and the equi- librium studies. The nmr of the ligand purified by both of the other methods indicated slight traces (less than 5%) of [(CH3)2N]3P in the product and was used in prelim- inary investigations. Tris(dimethylamino)phosphine [(CH3)2N]3P was prepared by a modification of a previously reported method3° as fol- lows: Six moles of dimethylamine was added dropwise to an ether solution which contained one mole of phosphorus tri- chloride. The reaction was carried out at ~78? Ether was removed by distillation, 35°/760 mm. Tris(dimethylamino)- phosphine was distilled, 47°/10 mm. The identity of the product was established by nmr spectral data (O,ppm(TMS) -2.43; JPH 8.9).3i 12 Magnetic Moment Measurements Magnetic susceptibilities of solids were measured by the Guoy method by use of an apparatus described by Vander Vennen.32 In this work the low temperature dewar apparatus was modified to allow a constant stream of helium to pass over the sample tube. This gas flow prevented water from condensing on the sample tube at low temperatures and also protected the sample from hydrolysis. The magnetic moment was measured at room temperature and at -196°. In those cases where a large change occurred, the moment at -78° was also determined. The nmr method of Evans33 was used to obtain the solu- tion magnetic susceptibilities over a range of temperatures. The magnetic resonance Spectra were obtained by the use of a Varian A-60 analytical spectrometer equipped with a Model V-6040 Varian variable temperature controller. Temperatures were determined by measuring the chemical shift34 difference for methanol (low temperatures) or ethylene glycol (ele- vated temperatures). The nmr tubes which were used have been described.35 These were sealed to avoid air oxidation of the solution. The separation of the "paramagnetic" and "diamagnetic" signals (Av) was measured by using both TMS and methylene chloride as the internal standards. Identical results were obtained within experimental error in both cases which indicates that the frequency 13 separations used to calculate the magnetic moments are due solely to bulk susceptibility differences and contain no contribution from isotropic contact shifts. The frequency separations (Av) are related to the molar susceptibility of the complex by: 3Av mw 2W(60 x 20°)c XI“: where mw is the molecular weight of the paramagnetic complex, 60 x 106 is the frequency of the proton resonance, and c is the concentration of complex (paramagentic solute) in gml-l. Figure 1 Shows a typical nmr spectra recorded from a solution that contained Co(apf2)3I2. As the temperature was lowered two effects were observed. First, the increased broaining'of the resonance line which arises from protons in the paramagnetic environment and, secondly, an increase in frequency separation. Concentrated solutions were not used because the broadening of the paramagnetic resonance line reduced the precision. It was found that with the con- centration used in this work (approximately 10-2 M or c = 0.02 gml-1) the broadening of resonance lines was not severe and the peak separation was measured easily. Measurement of Equilibrium Constants These measurements were carried out by a modification of a method described by Everett and Holm.21 The solutions used contained a large excess of ligand. For example, a 14 Figure 1. Nmr spectra of Co(apf2)312 dissolved in methylene chloride and excess ligand. 15 'H m... diam": _ “o Pommoonofic Figure 1. 16 typical solution was prepared by adding a 0.0097 g (0.075 mmol) sample of anhydrous QoClz to a 0.3121 g (2.259 mmol) sample of azpf contained in a 2.00 ml volumetric flask. The solution of CoClz and azpf was then diluted with methylene chloride so that the total volume was 2.00 ml. To obtain the formation constant, Kf, for the equi- librium COLzXz + L < > COL3X2 high spin- low Spin- tetrahedral pentacoordinate the magnetic moment of the solution was measured, and Kf was calculated by a modification of the basic equation where Nt and Nf are the mole fractions of the tetra- hedral and five-coordinate species, respectively (Nt + Nf = 1), and L is the concentration of the free ligand. The expression for the equilibrium constant is given by 2 _ 2 K _ ut uobs 1 f — 2 uobs - uf (L) where ut and uf are the limiting moments of the tetra- hedral and five coordinate complexes, respectively. The value of ut was estimated from known moments of similar phosphine cobalt(II) complexes (X = Cl, 4.40 B.M.; X = Br, 4.45 B.M.; x = I, 4.50 B.M.).8 17 The limiting value of uf was estimated to be 2.0 B.M. for the bromide and chloride complexes and determined as 2.10 B.M. for the iodide complex. The value of L was as- sumed to remain constant and equal to the initial ligand concentration. Because the ratio of ligand to metal ion was greater than 30:1 in every measurement, and because the amount of ligand involved in establishing the equilibrium is small, the error associated with this assumption is about an order of magneitude less than the standard error in Kf. The uncertainity in the solution susceptibility measurements allowed us to estimate the standard error of K to be i20%. f The AH° values were obtained from plots of In K .33 f l/T by measuring the equilibrium constants at four or five different temperatures selected in the range 2 to 40° at approximately 6° intervals. Equilibrium results could be obtained only in methylene chloride or benzene. Either poor solubility of the complexes in other weakly coordinating solvenuaor reactivity of the ligand with the solvents pre- cluded the use of other solvents. Measurement of the esr Spectra Both the room temperature (23°) and the frozen solu- tion (-196°) esr spectra were obtained in methylene chloride solutflxs made approximately 10-2M in complex. These solu- tions were prepared by allowing an excess of ligand to interact with the appropriate cobalt(II) halide. All esr spectra were recorded as first derivative curves by use of 18 a Varian E-4 spectrometer with the magnet regulated by a fieldial. The spectra were determined at frequencies which ranged from 9.2 to 9.5 KHz and were recorded on an x-y re- corder with the x-axis pr0portional to the magnetic field strength. A three millimeter diameter quartz tube approxi- mately twelve inches in length was used as a sample con- tainer. Values of g_ were determined from the measured klyston frequency (vk) and the field strength Ho by the expression k ‘ hv - where h - o 9 - EEO . - 0.714489 sec Gauss B" h is Planck's constant and B is the Bohr magneton. Infrared and Optical Spectra Either a Perkin-Elmer 237B or 457 spectrophotometer was employed to obtain ir spectra. The solid materials were examined as Nujol and Fluorolube mulls between cesium iodide plates. For volatile materials a gas cell with a 7.5 cm path length and KBr windows was used. Solu- tion and mull electronic Spectra were obtained by use of either a Cary 14 or a Unicam model SP 820- series 2 double beam spectrophotometer. Solutions which were examined con- tained the Complex plus excess ligand in methylene chloride. while the reference solution contained an equivalent amount of ligand, but no metal salt. Mull spectra were obtained 36 by using Nujol mulls between quartz plates. Solution 19 temperatures were controlled to 10.2° by the use of a thermo- stated cell compartment. Preparation of the Complexes Dibromotris(dimethylaminodifluorophosphine)cobalt(II) C0(apf2)33r2 In a typical reaction a 1.8 g (8.3 mmol) sample of anhydrous cobalt(II) bromide was transferred to a 50 ml flask which was equipped with a standard taper joint and a magnetic stirrer. The flask was evacuated and a 6.90 g (61.1 mmol) sample of apfz was condensed into the flask at -196°. The mixture was warmed to room temperature and the resulting dark green solution was stirred with a magnetic stirrer for twelve hours. At the end of this time the re- action mixture was opened to the vacuum pumping system (while the stirring was continued) for about one-half hour, and the unreacted apfz (3.90 g; 34.5 mmol) was collected in a -196° trap. In a number of separate experiments the mole ratio (apfz/COBrz) of the dark green solid which re- mained in the reaction flask varied from 2.98 to 3.18. Shorter reaction times (three to four hours) did not seem to affect the composition of the reaction product. Since the complex has a small apfz dissociation pressure at room temperature, it was stored in a closed container under a nitrogen atmosphere. Aggl; calculated for C5H13COF3BraN3P3: C, 12.93; H, 3.23; N, 7.54; Br, 28.70. Found: C, 12.65; H, 3.13; N, 7.59; Br, 28.59. 20 Because of the limited solubility of the CoBr2 complex in organic solvents, the value of the molecular weight was obtained by determining the vapor pressure lowering of apf2 when CoBr2 is dissolved in it. A mercury differential manometer of a type previously described was employed.37 Molecular weight determinations were made on solutions which contained 10.9% and 10.7% CoBr2 by weight in excess apfz. If the two sets of data are averaged and the complex is assumed to be only Co(apf2)3Br3, the calculated molecular weight is 630 i 100 g/mol (theory: 558 g/mol). Diiodotris(dimethylaminodifluorophosphine)cobalt(II)— C°(an2)312 In a typical experiment, a 2.50 g (7.98 mmol) sample of anhydrous cobalt(II) iodide was transferred in a dry box to a 50 ml flask which was equipped with a stopcock, stand- ard taper joints and a magnetic stirrer. The flask was evacuated and a 5.10 g (45.1 mmol) sample of apfz was con- densed into the bulb at -196°. The mixture was warmed to room temperature, approximately 30 ml of methylene chloride was added, and the solution was stirred for two hours. The reaction mixture was then transferred to a glove bag which had been purged with dry nitrogen several times, and was filtered through a sintered glass filter to remove un- reacted C012. The filtrate, which contained excess ligand, methylene chloride and complex was distilled in vacuo to remove the excess ligand and methylene chloride. The dark 21 brown solid residue was then dried in vacuo for about one- half hour. 5231, calculated for C6H13C0F512N3P3: C, 11.04; H, 2.76; I, 38.93: N, 6.44. Found: C, 11.03: H, 2.76; I, 39.88; N, 5.88. Formation of a small variable amount of PF3 from re- action of C012 with apfz prevented molecular weight deter- minations of the CoIz complex by the method cited pre- viously. Dissociation of the complex, similar to that ob- served for Co(apf2)3Br2, prevented molecular weight deter- minations in other solvents. However, the hyperfine interaction of one unpaired electron with a single 59Co (I - 7/2) nucleus observed in the esr frozen solution spec— trum of this complex strongly suggests that it is monomeric. This esr Spectrum and that of related complexes will be discussed later. The green solution of CoBr2 in excess apfz turned blue when a small amount of 1,2-dimethoxyethane, tetrahydrofuran, acetone, triethylamine, trimethylamine, or dioxane was added. This color change suggests that any of these neutral molecules is a better ligand toward CoBr2 than apfz, or alternatively, that they allow formation of CoX42' ions. The addition of dimethylsulfoxide to the green solution of CoBr2 in apfz yielded an almost colorless solution, again indicative that some sort of reaction, presumably displace- ment, occurs. The green solution turned pink when absolute ethanol was added. A brown solution of C012 in apfz 22 underwent similar ligand displacement reactions. No at- tempt was made to isolate any of the species formed. How- ever, when the weakly coordinating solvent methylene chlor- ide was employed, the solution optical and magnetic properties were identical to those observed when excess apfz was used as the solvent. Hence, these complexes could be studied in solution by making use of either methylene chloride in excess ligand or neat ligand as sol- vent. I found that these complexes can be kept in a solu- tion of methylene chloride and apfz if the mole ratio of ligand to cobaltous halide is greater than approximately four to one. Other workers5I1°r38 have observed that dis- sociative processes occur with five-coordinate cobalt(II) complexes which contain phosphine ligands and have made use of excess phosphine ligand to stabilize the complexes in solution. The Systems CoCl2 and CoP2 in (CH3)2NPF2 A reaction identical to the one described for the CoBrz-apfz system was employed. No absorption of apfz or any observable color change was found for interactions of the ligand with C0C12 or Con. Diiodotris[bis(dimethylamino)fluorOphosphine]cobalt(II)- Co(a2pf)3I2 A 0.32 g sample of anhydrous cobalt(II) iodide (1.0 mmol) was added to approximately 20 ml of thiophene-free benzene containing 0.75 g (5.4 mmol) of 23 bis(dimethylamino)fluorophosphine. The brown solution which resulted was refluxed in a nitrogen atmosphere for approxi- mately one-half hour, and then cooled. Pentane (10 ml) was added to promote precipitation, and the solution was fil- tered. The filtrate was concentrated to one-fourth the original volume by distillation in vacuo and pentane (10 ml) was again added. A dark brown solid slowly precipitated when the solution was cooled. 5231; calculated for C12H36C0F312N6P3: C, 19.83: H, 4.95; P, 12.82; N, 11.56: I, 34.91. Found: C, 19.82; H, 4.87; P, 12.63; N, 11.31; I, 34.62. U 2.10 B.M. Molecular eff weight found 610, theory 727 (Galbraith Laboratories, Knox- ville, Tennessee). The molecular weight supports the con- tention that the complex dissociates in solution. The solid complex shows no spectral or color changes when stored under nitrogen. Dibromotris(diphenylphosphine)gobalt(II) The complex Co[(C5H5)2PH]3Br2 was prepared by the method reported by Issleib and Wenschul.1° This complex was characterized by infrared and visible spectral data. It was included in the esr study because it has been shown by a single crystal X-ray diffraction study to be a penta- coordinate species. The structure lies intermediate be- tween a square pyramid and trigonal'bipyramfi6111.- 24 Attempts to Prepare Complexes with the Ligand Tris(di- methylamino)phosphine, [(CH3)2N]3P Attempts to prepare complexes of the type CoL3X2 (where L is [(CH3)3N]3P and X is Br, I) were unsuccessful. The reactions were attempted by allowing an anhydrous cobalt(II) halide in a mixture of methylene chloride and ligand to re- flux three hours. The ligand to cobalt ratio was slightly greater than three to one. The reaction mixture was allowed to cool to 23° and anhydrous ether was added to the blue- green solutions to promote precipitation. After the mixture has been maintained at -78° for four hours blue crystals can be recovered by filtration. Analytical data are reported in Table 1. These data indicate that the N-P bond was cleaved in the reaction and that a decomposition product in which nitrogen acts as the donor atom was isolated. The elemental analyses of these decomposition products indicate that four coordinate di- methylamine adducts of the cobalt(II) halides were isolated. In addition, the visible spectra of the complexes mulled in Nujol or dissolved in acetone are similar to the spectra of four coordinate tetrahedral cobalt(II) complexes.39 The infrared spectrum of the complex isolated with CoBrz is given in Figure 2. Examination of the visible and esr spectra and solution magnetic moments of freshly prepared solutions of anhydrous cobalt(II) halides (Cl, Br, I) dissolved in [(CH3)2N]3P and 25 Table 1. Analytical data for complexes isolated with tris- (dimethylamino)phOSphine, [(CH3)2N]3P a Calculated for CoBr 1 2 3 2 CO[(CH3)2NH]2X2 C 15.71(2.00) 16.09(1.97) 15.64(2.07) 15.55(2.00) H 4.52(6.96) 4.68(6.88) 4.93(7.80) 4.53(7.00) N 9.09(1.oo) 9.55(1.oo) 8.81(1.00) 9.07(1.00) P None None ---- ---- C012 C 12.14(2.03) 12.32(2.04) ---- 11.92(2.oo) H 3.58(7.16) 3.48(6.96) ---- 3.48(7.00) N 6.98(1.00) 7.02(1.00) ---- 6.95(1.oo) P None None ---- ---- aResults were obtained on three different samples. Atom ratios in parentheses. b Results were obtained on two different samples. 26 .mm—Z«Aamov_ nufi3 uomuoucfl on COBOHHM mmB NHmou cm£3 Coumaomfl xOHmEoo mnu mo Esnuoomm OOHMHMCH .N Onsmflm 27 com com— .N Tasman ¢ C°(an2 )2 + apfz occurs in solution.5 However, this equilibrium probably favors the pentacoordinate low-spin species with the 39 Table 3. Magnetic moments of the complexes Co(apf3)312 and Co(apf3)3Bra, solutions contain excess ligand. Tem Complex Phase Method (°K§ ‘ueff(§’M') Co(apfa)3Br2 solid Guoy 293 2.27(10.10) 195 2.29 solution in , CH3C13 Evans 308 ' 2.00(i0.06) 265 1.98 238 2.00 217 1.99 Co(apf2)312 solid Guoy 297 2.42(10.10) 195 2.30 solution in CH3C12 Evans 309 2.46(i0.06) 263 2.49 233 2.47 206 2.45 40 concentration of the four coordinate high-spin species relatively small and undetectable by the methods used in this work. Optig§l<§pectra Visible results are presented in Table 4 and Figure 6. The fact that the visible spectra of both solid Co(apf2)312 and Co(apf2)3Br3 are almost identical with the solution spectra suggests that the structures of the solids dis- solved in excess ligand are unchanged. All solution spectra were independent of temperature. All observed transitions and intensities of the Co(apf2)3xz complexes (where X is I or Br) are consistent with a low-spin pentacoordinate structure. .Other pentacoordinate low-spin cobalt(II) complexes exhibit absorptions similar to those which are observed for Co(apf2)312 and Co(apf2)3Br2.5'12'13'2°I4£5 The true geometry of these pentacoordinate complexes prob- ably is intermediate between a trigonal-bipyramidal and a square-pyramidal configuration. (B) Characterization of the bis(dimethylamine)fluorophos- phine Complexes The complex Co(a2pf)312 was characterized by analytical and magnetic moment data and by visible, infrartd, and ear spectral data. The infrared Spectra of this complex and the ligand, azpf, are shown in Figure 7. Examination of this figure 41, .U0>H0mno uoc cofluwmsmnu mflzso .umoasozm u gnu .pmopm «mazennmov mmooxmn .ulEO SA sumsoam>mzo .nmm.na Accsvnmc.ne .ccs.ee Accvvemm.ve c Acnvmms.eu c Aosmvame.Hm cce.ee ucm.mm onsvmcv.cn Acccsvsmc.nu Acnvcco.nn Hess um AoSHeVAancHn.nm pascamo um nes.nn Hess H Acceaveca.em «Hesse H A .3. ecoseom x .nnmnA«MQMVOO was «HnAnmmmvoo mo mnuommm manfimw> can no mumsfism .v magma 42 .sofi “Hmflfi unwaom saom ADV .«Hnaummmvoo pcmucoausHom Amy .Oflaom mmmvoo "moxoameoo axnnnmmmvoo mo muuoomm OHAH a mfl> .m ousmwm 43 .m ounmflm A55 59.0.92: one coo cos con one coo co... co... one _ cos one .1 I I. _ u q . _ _ . o I I ‘ 0 I I. I I \ \ I I I I. CON 5 I .\ It: a 1 < [III I L GOV III \\ z o . L a. ’l“\ ' ( I. \ I \ 4 COO w a .t o I O 4 w: I J I 1 com , , n , . coo. II ‘1 I J In. / (I .I/ l ocu— I — m 11 - _ p b _ 83 N. n— m. on «a mm .s x a... 44 OAfi'EU . t SE OQSHOHOSHMV u Hos Honoz .20 oosm ooem He «mmmmmmmwow Amv cam mm m pom: Adv mo muuoomm UOHMHmGH .b Ousmflm .b ousmfim («U oov coo com )000— pl. oou— Defip coo- ocuu . coca 45 rid id — A, q A) 5 4| ,4. Al l grills/Mi % C . 46 Stungly sweets that'the structure of the ligand is essentially unchanged in the complex. When the complex is dissolved in either methylene chloride or benzene an equilibrium is estab- lished between the low-spin, pentacoordinate complex and a high-spin, pseudotetrahedral, four-coordinate complex of the type Co(a3pf)2I2. Similar results were obtained for analo- gous CoClz and CoBr2 complexes, even though I was unable to isolate the Species that contained the chloride or bromide anions. On the basis of extensive magnetic and spectral data I suggest that similar equilibria involve these anions. These equilibria may be represented by Co(a2pf)2x2 + azpf 4__:.C°(32Pf)sxz (1) The Equilibrium Involving the Cobalt(II)_Iodide Complex A brown crystalline pentacoordinate, low-spin complex of the type Co(a2pf)3I2 can be obtained when C012 and azpf are allowed to interact in benzene. The visible spectrum and magnetic moment of this complex are almost identical to those of similar monomeric pentacoordinate cobalt(II) complexes.5r1°r1313°v‘5 When this complex is dissolved in methylene chloride or benzene, the magnetic moment increases and the visible spectrum undergoes a change which is sug- gestive of the formation of a new species. «'1; was able to establish equilibrium (1) by measuring the concentration dependence of the solution magnetic moments when Co(a2pf)312 is dissolved in methylene chloride 47 or benzene. These results (Table 5) are easily rationalized by the equilibrium shown in (1). As the initial concentra- tion of Co(a2pf)3Iz is decreased from 2.16 x 10-2! to 0.30 x 10-2M_the effective moment of Species in solution increases from 3.42 B.M. to 4.36 B.M., a change which is consistent with an increase in the ratio of the four-coordinate, high spin complex to the pentacoordinate, low-spin complex. Further support for equation (1)-is obtained by (A) examining the effect of the additiOn of excess azpf on the solution magnetic moment and (B) a comparison of the visible spectra of Co(a2pf)3I2 dissolved in methylene chloride and mulled in Nujol. The magnetic moment of a solution that was 1.49 x 10'?! in Co(a2pf)312 was 3.68 B.M. (Table 5). The addition of a 0.51 mmol sample of azpf to a solution that was also made 1.49 x 10-2M_in Co(a2pf)312 lowered the magnetic moment to 3.24 B.M. These results are consistent with a shift in (1) as the concentration of free ligand is increased. Figure 8 shows the visible spectra obtained from a sample of Co(a2pf)3I2 mulled in Nujol and dissolved in methylene chloride. Examination of this figure clearly shows that the visible Spectrum undergoes a change which is suggestive of the formation of a new Species. In fact, the position, intensity and band shape in the 500-800 mu regiOn in the spectrum of a 2.98 x 10-3M_Solution of the complex in CH2C12 is typical of the v3[‘A2 > 4T1(P)] transition 48 Table 5. Concentration dependence of solution magnetic moments when Co(a2pf)312 was dissolved in either CH2C12 or C3113. Initial-Concentration ”eff at 312 K SOlvent OfLfioiaigflala (B.M.) r 0.06 2.16 3.42 CH2C12 1.77 3.53 CH2C12 .1.49 3.68 CH2C12 1.08 3.78 CH2C12 0.75 3.98 CH2C12 0.30 4.36 CH2c12 1.93 3.41 CBHB 1.38 3.49 CeHe 1.29 3:62 CeHa 49 .seanoaasvoo chaos “no as. Asa a rescue chase «House as possesses «Hnnmmamvoo mo GOHDSHom.mnIoH x mm.N Aav mo manommm manwmfl> .m onsmwm 50 (mass Mangqle) "mu one .m Tasman 1:. £98.96; o8 onk cos one con onn con one 8.. . one A q T - q u d u q .. oo. n =3:- 1 con .. o8 m .23... < L oov M 1 w a. misused .. con .. con 51 found in high-Spin four-coordinate pseudotetrahedral cobalt- (II) complexes.39 The magnetic moment of the solution (approximately 4.36, Table 5) supports the contention that the high-Spin Species predominates in this solution. In addition to the above data, the visible spectra of the solution which was 1.49 x 10-3M_in Co(a2pf)312 and 0.36 Miin free ligand (azpf) were obtained at a number of different temperatures. The spectra are presented in Figures 9 and 10. Because all cobalt(II) species absorb in the visible region, the presence of isobestic points at 600 and 550 mu indicate only two species are in solution. These spectra underwent reversible changes. The temperature de- pendence of the magnetic moments and the equilibrium con- stant (Kf), AH°, and AS° values for this solution are pre- sented in Table 6. Table 6 also presents data for the complex dissolved in benzene. Equilibria Involving the CoBrz and CoClz Complexes Although we were unable to isolate the pentacoordinate complexes of CoClz and CoBrz with aapf, analogous temperature and concentration dependence of the visible spectra and the solution magnetic moments indicates an equilibrium identical to that observed for Co(a2pf)312 occurs in these solutions (Table 7). When the concentration of COC12 is held constant and that of the ligand is increased from approximately 0.05M to 0.15M, Beer's law does not hold (Figure 11). Isobestic 52 I Ass on“. rescue candy as oowuoon .ndas ca zon.o can aHnAndacvoo cs zeros x oe.e has conga conusHOn m an Covanfinxm muuommm manfimfl> mnu mo mocopcmmmo OusumuomEmB .m onsmflm 53 .m onsmwm aE sauce—963 con 000 con - - d emu /_// cm... od v.0 «.0 ON 54 Figure 10. Temperaturg dependence of the visible spectra of a 5.0 x 10 3M solution of Co(a2pf)312 and 0.1211 in azpf, 550-350 mu (path length 1.0 mm)- 55 2.0 - 12 - 0.8 -- 0.4 - 1 15° 24° 37° 4 0.0 350 450 wavelength mu Figure 10. 550 56 Table 6. Equilibrium constants Kf, AH° and AS° values of a solution which was 1.49 x 10-2g_with respect to Co(a2pf)312 and 0.36! with reSpect to azpf. a a V b -AH° neff(B.M.) Kf - 0 Solvent T(K) (kcal/mol) AS CH2C12 315 3.24 4.17 3.6 8.5 CH2C12 301 3.05 5.74 CH2C12 293 2.q9 6.36 CGHG 320 3.54 4.53 CBHB 313 3.35 6.25 6.8 18.2 C3H3 309 3.24 7.50 CGHG 301 3.12 9.17 aSolution moments 10.08 B.M. $0.06. bError in measurements estimated to be 120%. 57 Table 7. Temperature dependence of the solution magnetic moments and the equilibrium constants calculated for the solutions obtained when CoCla or CoBrz were allowed to interact with excess ligand in methylene chloride. ggiid: T K ”eff(B'M') Kr kcdi§mole AS~ aCool2 319 4.11 0.19 312 4.04 0.25 305 3.96 0.31 300 3.89 0.38 6.0 22 291 3.77 0.50 282 3.68 0.61 bCool2 319 3.98 0.33 309 3.87 0.44 303 3.77 0.56 6.0 21 297 3.68 0.67 cCool2 316 3.93 0.27 310 3.87 0.32 303 3.78 0.39 5.4 20 296 3.69 0.48 aCoBr2 314 3.21 1.51 307 3.11 1.78 301 3.04 2.01 4.3 13 295 2.96 2.31 287 2.85 2.83 281 2.75 3.43 aSolutions were 0.37M in Cox; and a concentration of free ligand adjusted to I20M_in CH3C12. bFree ligand concentration adjusted to 0'2!- cFree ligand concentration adjusted to 1.25M, 58 _ . I. . EB o.H numcoH aumm wao>fluoommou .vIH .2ma.o ou.Mo.o maoumfifixoum m Eoum mcflmmouocw mm m mo cowumuucoocoo on» nufl3 .zutoH x w¢.H mo SOAUMHO Icoosoo «HOOD m mcflswmusoo msofiusaom mo emu um muuoomm manfimfl> .HH cusses 59 .HH ousmwm 3: 596.053 . mu oak one 090 ooh con 0% a d _ q _ omv UK We“? 0mm fl/ p V / 1,1/ N \NW\\ — Vd I .x//// _. n v v 05.1 «All N V o— I 9.. 1 .F 60 points were observed at 610 and 560 mu. This indicates that two species are in solution. The temperature dependence of the visible spectra exhibited by solutions of CoCla and CoBr; in excess azpf and methylene chloride also establish that only two species are involved in the equilibrium. The spectra for the CoClz solutions are presented in Figures 12 and 13. As in the case of Co(a2pf)3I2, the spectra underwent reversible changes over the temperature range investigated. Isobestic points at 610 and 560 mu.were observed for the solution which con- tained C0012. This observation indicates the presence of only two complexes. This is substantiated by comparing Figures 11 and 12. Identical isobestic points were ob- tained from both the Beer's law and temperature dependence studies. (I did not observe isobestic points in the Spectrum of solutions which contained CoBr2 in excess azpf (Figures 14 and 15). I was able to establish the presence of only two absorbing species by the use of a recently described pro- cedure. Three arbitrary wavelengths are chosen from the visible spectrum shown in Figures 14 and 15. .These wave- lengths were chosen in regions that exhibit the greatest temperature dependence (i.e. 412, 480 and 690 mu). A plot of absorbance ratios of the general form (AZTJ AaTJ ) A1T1 ' A1T1 where A2T1 represents the absorbance at one of the 61 .heE o.“ numGOH gummy 18 ommlomv .wmum mmmoxo SA «HOOD mo cofiusaom SquH 2 an.” 6 mo mocoocwmoo ousumuomfiou mnuommm OHQHmfl> .me choose 62 .NH Ousmwm :8 565.253 one com com ooo oon - a T - o.o o.o ofi 63 Figure 13. Vigible spectra temperature dependence of a 1.0 x 10 2M'solution of CoC12 in excess aapf, 325-550mu (path length 1.0 mm). 64 2.0 1.6 - -50 .40 1.2 - 50 0.0 l J l I 325 350 400 450 500 wavelength mu Figure 13. 550 65 .hBE o.n sumsoa gummy 1E ommloom .mmnm mmooxo an «Hmoo mo coflusHom z. IOH x vM.N 6 mo mosoocomoo ousumuomeou wuuoomm wanwmfl> .vH ousmflm 66 .vH ousmwm 3: 385.963 com com ooo . q _ on. so o.o ‘o u.— 0; od 67 .hBE o.fi gumsoa nummv :8 ommloom .mmam mmooxo an «Hmou mo coflusHou Eaten x ow.b 0 mo mocmpsomoo ousumuomfiou mnuoomm manamfl> . ma 0563 68 .mH Ousmflm as. £93.95; 93 con one. cow onn nan co... _ q _ 1 _ o.o .W/ i so .nu .. o.o _ on. 1 S .9 on 1 3 on own oN 69 wavelengths at temperature T1 was made. In this manner one set of coordinates is calculated for each temperature and a plot of these absorbance ratios is constructed. The straight line that resulted indicated that only two species are in equilibrium. This method was also used to confirm the existence of two absorbing species in the case of the C012 and CoClz complexes. An examination of the visible spectra and magnetic moment data obtained for solutions in which the high-Spin species predominate again provides compelling evidence for the presence of a tetrahedral cobalt(II) ion as the high- spin component involved in equilibrium (1). The visible spectrum of a CoCl, solution at 25° (Figure 12) exhibits a maximum at 636 mu and shoulders at 590, 670 and 710 mu. The position and intensity of those bands are character- istic of the v3[4A2‘——> 4T1(p)] absorption of a tetra- hedral, high-spin cobalt(II) complex.39 The magnetic moment of this solution is 3.89 B.M., a value which sup- ports the contention that the cobalt(II) solution species is predominantly high-Spin (Table 7). As the temperature is lowered, the changes in the visible spectra, as well as magnetic moment data, Show that the concentration of the pentacoordinate low-spin cobalt(II) species increases. The intensity of the v3 band is I markedly reduced as the temperature is lowered. at 15° the shoulders at 590, 670 and 710 mu begin to collapse while the maximum at 636 mu begins to lose intensity as a new 70 maximum at 660 mu attributable to the low-spin species forms. These changes progress as the temperature is lowered and at -10° the shoulders at 590, 670 and 710 mu are no longer discernible while the original maximum at 636 mu has lost intensity and is now distinguishable only as a shoulder. The new maximum at 660 mu which I assign to a transition involving the low-Spin, pentacoordinate species is now even more pronounced. It Should also be noted that the absorb- ance in the 400-500 mu region also gained intensity as the temperature is lowered. Absorbance in this region is par- ticularly characteristic of low-Spin, pentacoordinate cobalt(II) complexes.5r13'13'3°v45'47 The changes in the spectra are almost identical to changes which occur in solu- tions ofCo(a2pf)312. Further support for the existence of a low-spin, penta- coordinate cobalt(II) complex can be seen by comparison of the esr spectra of the frozen solutions (77 K) of these complexes with the spectra of the monomeric complexes of Co(apf2)3X2 (X = Br, I) and Co(dpp)3Br2. The esr spectra of these complexes will be discussed in Part C of this thesis. The equilibrium constant (Kf) as well as AH° and A80 values are presented in Table 7. If one assumes no error in the limiting moments estimated for the high and low-spin Species involved in equilibrium (1), the thermodynamic stability of the pentacoordinate complexes relative to the four-coordinate complexes as measured by the equilibrium 71 constant (Kf) increases in the order I > Br > C1. This ordering, which is opposite to what one would expect on the grounds of ligand field stabilization energies, has been discussed2° in terms of the "softness“ or polariz- ability of the atoms as measured by the values of the overall nucleophilic reactivity constant n° 4° of the donor atoms in the complex. AS° values are all negative and notably large in some cases. This magnitude is to be ex- pected Since the equilibria involve a change in cOOrdina- tion number between neutral species in relatively weakly coordinating solvents. (C) Electron Spin Resonance Spectra of the Complexes There have been relatively few reports of esr studies on pentacoordinate, low-spin cobalt(II) complexes”:25 and, consequently, the electronic properties of this type of complex are not well understood. In this part of the manuscript, I report the results of esr studies on the low-spin complexes, Co(apf2)3xz, Co(a2pf)3X2 and Co(dpp)3Br2. It will be shown that the unpaired-electron orbital of the complexes consists of predominantly 3d22 character plus a small amount of 8 character. However, the s orbital gives a significant positive contribution to the metal hyperfine interaction. The direct mixing and the con- sequent positive isotropic coupling constant is symmetry al- lowed with both the 4s and 3d22 orbitals belonging to 72 the totally symmetric a1 representation under the sz point group, the assumed symmetry for these complexes. The covalency of these complexes will be discussed in terms of 'spin-delocalization and the isotropic contribution to the metal hyperfine interaction. A satisfactory correlation between the measured electronic spectral, magnetic and esr data is found. The electronic ground state suggested is [(x2 3 y3)(x2 : y2)(;3)> (vacancy configuration). The energies of the one electron d-orbitals were estimated for the pentacoordinate complexes involving apfz by use of the observed dptical spectra and the interelectronic interaction energies calculated for the low-spin d7 system. Quantitative handling of the optical spectra of the complexes of azpf is prevented due to the presence of a substantial concentration of tetrahedral high-spin complex. However, the strikingly similar esr and optical spectra of the azpf complexes and (the apfz complexes suggest that the pentacoordinate low-Spin complexes formed with both ligands are quite similar. At room temperature the ear Spectra of all solutions showed only a broad structureless feature from which gav values were calculated. These are reported in Table 8. A typical room temperature Spectrum is shown in Figure 16. The room temperature esr spectra of polycrystalline samples of Co(a2pf)312 and Co(dpp)sBr2 are Shown in Figures 17 and‘ 18, respectively. The g_ values obtained for these and related compounds are presented in Table 9. The observation 73 .COHmOH HmHDoHUGOQHom 0:» mo £u©H3 on» m\H Eouw UOUMEHUEO mosam> Honuo .mGonOH HMHSOHCGOQHOQ manwtfiomno maamHuumm some oochuno moxoagoo OOHUOH mo 05.2.5 Hoasoapsomuomo .mmsmm n.0H pmumEHumo Honump .Onsumummeou EOOH um muuommm Hmo :oHusHom Eoum hauoouflo noon >mmo H _ _ n >6 ,- .A mm + mvfl.n ma .moo.o+ msoHusHom cououm Eonm pmcflfinouop osHm> SH woumfieumo Houumm on He o.nn n.sm no Hno.o omn.o oaH.m HmH.m mso.u Hov.n Haas Ho on me n.nn n.om HS nno.o osn.o nnH.m osH.m oso.m Hon.m Haas on an as n.on o.on Hm sno.o nHo.o osH.m HSH.N ooo.m Hun.m Hush H so Hn n.on o.nn on ono.o oHs.o suH.m ooH.~ etc.“ man.« sees us on so u- o.ne moH eeo.o ons.o HcH.m HsH.m sHH.n mm~.u ands H, HMHOQflCfi Omflaw _ _0 4'4 _ _4~ MN UH >mm >00 ._IO _ _m UCMEHQ QWHH o o .Mmbb paw ousumuomEOu Eoou.um COHDDHOm OUHHOHSO Osoamnumfi CH moxmamaoo xnfinmmovoo pom «Nmnwmnmvoo mo muouoEMHmm mmm .m magma 74 .UsmmHH mmooxo cam OUHHOHnO osmamsuoe CH “H Ho .Hm .HU u N .«mmm no mass M Av «anou mo Esnuoomm soHusHom Hmo ousumuomfiou Boon HMOHmmB .nH ousmHn 75 oH ousmHs Sm T : man—mo 00M 76 .«Hnammamvoo mo cameos OGHHHmumauomHom C no Enuuoomm Hmo ousumuomsou Boom .SH ousmHm 77 .ba OHDmHm a : singed com H.. manned 78 .«Hmnammovoo mo OHmEmm OSHHHmummuomHom o no Bouuoomm Hmo Ousumuomfiou Boom .nH ossmHn 79 .wH OusmHm T : .26 con «smeasoo 80 Table 9. g'values calculated from the room temperature esr spectra of polycrystalline samples of Co(a2pf)3Ig and Co(dpp)sBr3 (this work) and related compounds. Complex 91 92 93 9(av)a Co(dpp)3Br2b 2.339 2.092 2.045 2.159f Co(a2pf)312c 2.249 2.147 2.080 2.159 Co(dpe)3Br3d 2.258 2.075 2.037 2.123 Co(dpe),cl.,d 2.257 2.056 2.041 2.128 aAccurate to $0.005. bDiphenylphOSphine. cbis(dimethylamino)fluorophosphine. dbis( d irphenylphosphine )ethane , reference 12 . e 1 gav = §'(91 + 92 + 93)- fThe room temperature spectrum of Co(dpp)sBr2 in CH2C12 yields a gav value of 2.152 -- Figure 16. 81 of three distinct g. values for the compounds in Table 9 indicates that the symmetry is CZV.12 The esr spectra of polycrystalline samples of Co(apf2)3Br2 and Co(apf2)312 were poorly resolved and ac- curate g_ values could not be obtained. When solutions of these complexes were frozen to 77K the 59Co (I = 7/2) hyperfine structure was resolved in the parallel band of all samples with the solutions containing Co(apf2)3I2 giving partially resolved perpendicular bands. Phosphorus hyperfine 31F (I = 1/2) lines were resolved in the parallel region of all Solutions except for the solution containing Co(apf2)312 in which only the cobalt hyperfine structure was resolved. Typical frozen solution spectra (77K) are shown in Figures 19 and 20. Of the 16 lines expected in the "parallel" band due to metal and ligand coupling, typically ten to thirteen lines were resolved, the rest being obscured by the overlapping "perpendicular" band. In the frozen solution Spectrum of Co(apf2)312 in excess ligand and methylene chloride, in which phosphorus hyperfine lines were not resolved, twelve of the Sixteen combined "parallel" and "perpendicular" features were observed. No cobalt or ligand hyperfine structure was observed in the spectra of any of the poly- crystalline solid complexes either at room temperature or - 77K. The visible spectra of the complexes CoL3X2 (when L is azpf, X is Cl, Br or I; and when L is apfz, X is 82 oNHUNmU.@CM NQNM mmooxo CH «Hnammumvoo mo Axbbv Esuuoomm GOHUSHOE cououm .oH ousmflm 83 . 3 9.53m «— nan «Boo I Mono 8. 84 oflHUNmU ”Gm «Nam mmooxm CH «Hnaummmvoo mo Axhbv Esuuoomm SOHusHom cououm .om ouamHs 85 «.mmaocoo .om ousmHs : .266 cc. a 7...: 86 Br or I) in both solution and mull are shown in Figures 6 and 8-ISC The band positions and molar extinction coef- ficients are presented in detail in Table 10. 59Co Hyperfine Interaction For the complexes studied in the frozen state, the esr Spectra were characterized by axially symmetric g- and A-. tensors, and the hyperfine structure attributable to an interacting 59Co nucleus was best resolved in the "parallel" icomponent of the spectra. In contrast to the observation ‘that three distinct g-tensor components were resolved in the polycrystalline solids (Table 8), only two g-tensor com- ponents could be resolved in the frozen solution spectra. These observations can be rationalized by suggesting that the broadening of the perpendicular region, which arises from the closeness of the magnitude of the g, and g3 tensor components together with the additional 59Co hyperfine broadening, prevents resolution of the g2 and 93 tensor com- ponents in the "perpendicular“ band. A comparison of the gav values calculated from the spectra of the polycrystalline solids and frozen solutions supports this contention (Table 8). The experimental hyperfine coupling constants consist of dipolar hyperfine coupling between the unpaired electron in the cobalt d- orbital and the nucleus and isotrOpic coupling (A. ) due to the presence of unpaired electron lso density in cobalt S- orbitals. These have the tensor form 87 .HmHoz n-oH.>Houmsnxonmmm «H000 mo soflumnusoocooo .Hmaoz ca maoumEonummm «Hmoo ”I no coaumuusoocoo .Hoaoz OH x o.” «HnAwmumvoo mo coaumuusoocooo .«HOan was osmmHH o «- mo mmooxo so SH «x00 moonomscm msfl>aommflc an OOHMQOHQ mcowusHomn .HIEU CH sumcoao>mzo -- cnflonevoomvH How-VooansnAoonvoNNSH snaonvvoHSHm AoooHvoonnm Hoes EAH0amo oHo -- cnfiomnvoeoeH «ovovonannmonnvoonoH cnxoooVo-oHa AooovooHea Hons SAHoamo ohm III- r-II oNoma omwom gm ooewu III- «mam Hana H -- AoenvonnH cevooneHrnAoonvonnnH anoannnoH HomovooHuu Hues «Hesse H oooo .-- .nwnnH cu.onsHm ca ooonu -- ands HHss Hm Aonvoooo cnfloosvnmoeH nonsvnman AoanVn-on equSHHvonnnn -- ands «Hesse Hm .oooo .-- .ooseH .cnooH momma nssnu ands HHss H. Honvmoon cnxonnvannH “convene-H Honeymocom AoooHvooonm AooHHvooHom anus «Hesse H mauve . ommmuco>Hom x0 .aHOamo. CH pO>Homme tam Hoflsz SH COHHSE mmxoameoo How AH .Hm .HO 0 xv «xnhmmumvoo pom AH .Hm u xv uanmmmmvoo mOxOHmEoo can no muuoomm OHQHmH> on» no mHmEESm. .oa magma _ 88 (All, -Bl, - i) + (Aiso' Aiso' Aiso) in the parallel (z) and the perpendicular (x, y) directions. .The values Of AiSO and the dipolar contribution are indicated in Table 8. The large positive values of A180 are consistent with a direct transfer of electron-density from the cobalt d-or- bital which is occupied by the unpaired electron to the cobalt 4s-orbital. If we assume sz symmetry for All of the above pentacoordinate complexes, only the 3dzz and 3d orbitals belong to the totally symmetric a1 re- xz-yz presentation and can mix directly with cobalt S-orbitals leading to a transfer of spin-density into the cobalt 4s-orbital. .Examination of the esr spectra and the esr parameters calculated from the spectra, supports the 3d22 orbital as the orbital which is occupied by the unpaired electron. The fact that both cobalt hyperfine, and phosphorus hyper- fine from a single phosphorus atom were resolved only in the parallel (z) direction and not the x, y direction suggests that the 3dx2_ orbital is not the orbital of the ya unpaired electron. This is supported by the relative magnitudes of the g_ tensor values (gll > gl) and the relative magnitudes between the observed "parallel" and "perpendicu- lar" cobalt hyperfine (ACo > A On the other hand, ll “l" under the same symmetry the remaining cobalt d-orbitals belong to other representations (dy z' xz’ y a2) and as such direct participation of these orbitals with the 4s-orbital that form the molecular orbital of the 89 unpaired electron is symmetry forbidden. The ordering of the cobalt d orbitals under sz symmetry can be quali- tatively represented as: C - d7 strong field case 2v dx2_y2 a1 dz: +— a1 ° '-—+t—“ a2 The monomeric nature of these complexes is clearly Shown by the hyperfine interaction of an unpaired electron with a single 59Co nucleus. The fact that the cobalt hyper- fine is split into a doublet by a single phosphorus atom suggests that the axial site of these square pyramidal complexes is occupied by only one of the three donor phos- phorus atoms. Spin Densities of the Cobalt d322_r2 and 4s orbitals The values of the spin density on cobalt daza (fd) were calculated by setting an upper limit for the direct di- polar anisotropic contribution to the hyperfine coupling value IA'W of approximately 52 gauss.“9 The spin max densities of the cobalt 4s orbital (fs) were calculated by using a hyperfine interaction for unit occupancy of a cobalt 4s orbital as 1308 gauss.5° Values of f8 and fd are given in Table 8. 90 Phosphorus Hyperfine Structure and Probable Spin Density_ The resolution of phosphorus hyperfine structure only in the'parallel"band and not in the"perpendicular"band indi- cates a reasonably high anisotropic 31p hyperfine tensor. Assuming a perpendicular coupling constant of about 10 gauss I' estimate the unpaired electron has about 6-10% spin density in the phosphorus Sp3 hybrid orbital. There could be considerable back-bonding between the ligand phosphorus outer d orbitals, which are lowered in energy by the presence of the electron withdrawing fluorine atoms, and the cobalt d-orbitals. Covalency of the Metal-Ligand Bond Consideration of the total Cobalt hyperfine interac- tion for the complexes studied.(Table 8) indicates that there is more delocalization in aapf complexes than in apfz complexes. This suggests that the former complexes are more covalent.51 If one considers the cobalt hyperfine interaction of the complexes involving the same phosphine ligand, but different halides, then one would predict by use of the same arguments that the covalency of the com- plexes decreases in the order C1 > Br > I. The same conclusions regarding covalency can be reached if one considers the trend in the metal isotropic coupling constant. Other workers have suggested that the fractional 3 character Should in large part be determined by the relative energy separation between the S and d 91 orbitals and, consequently, may depend on the nature of the axial ligand. AS the cobalt-phosphorus bond becomes more Covalent one would expect the energy separation of the s and d orbitals to increase (larger effective nuclear charge on cobalt) and therefore would expect the isotropic contribution to the metal hyperfine coupling to decrease. These arguments lead to the same prediction in covalency as do the total cobalt hyperfine interaction considerations. Electronic Factors On the basis of simplified force constant calculations, it has been suggested that apfz has more v-accepting ability (through a dw'dv interaction) than aapf52 in molybdenum carbonyl complexes of the type LnM°(CO)6-n' where L is apfz and aapf and n= 2. On the other hand, it may be reasonably suggested that azpf is a better 0 donor than apfz. This argument is based on the observation that there appears to be a donation of the lone pair of electrons on nitrogen to the empty d-orbitals of phosphorus. This dona— tion makes the electrons on phosphorus more available.53 From the data obtained in this study, together with the ex- pectations which can be reasonably made on o and r bond character in the Co-P bond, it appears that the degree of covalency in a bond in which both 0- and w-bonding may be important, is determined primarily by the o-bond. The observed trend showing the Co(a2pf)312 complexes to possess a greater degree of covalency than the 92 Co(apf2)312 complexes may be related further to the tendency of these two phosphines to form pentacoordinate complexes. It has been previously shown that when Co(a2pf)312 is dissolved in methylene chloride and excess aapf and equi- librium (1) is established with a significant amount of high-spin four-coordinate complex in solution (K 8 0.17 at 27°). On the other-hand, when Co(apf2)312 is dissolved in methylene chloride and excess apfz no significant concentra- tion of high-spin four-coordinate [(Co(apf2)12] is detected. Hence, the tendency towards pentacoordination seems to be greater for the apfz complexes than for the azpf complexes. The identical results are obtained with the analogous bromide complexes CoLaBrz (L = apfz and azpf). The role the anion plays in determining the covalency of the complexes has been discussed above and is C1 > Br > I. The trend away from bond covalency towards increased stability of the pentacoordinate complexes, as found in the case of the phosphines, is found also for the anions. The stability of the Co(a2pf)3X2 complexes has been determined to be I > Br > C1 while in the present study the bond covalency for these Co(a2pf)3X2 complexes is C1 > Br > I. g_Tensor Values and Optical Spectra The observed relation between the magnitude of the g tensor components is in agreement with the criterion for the unpaired electron to be in the 3dzz orbital. The trend in 9'. and 91. is consistent with the 93 spectrochemical series. ,As the halogen becomes a better ligand 9" values increase and gi values decrease. This suggests a decrease in the mixing of the ‘3dzz and 3dx2 levels as their relative energy separation in- -y2 creases. The change in the optical absorption maxima as well as 9" and gl and the electronegativity of the halogen are all measures of the relative energy separation of the higher lying 31 orbitals. The large number of transitions in the higher energy region of the visible spectra and the observation of three distinct g-values indicate that the geometry of the complexes can be best represented under a C2v point group. The most reasonable geometry for these pentacoordinate complexes is a square pyramid with the basal plane defined by two phosphorus and two halogen atoms with the apex occupied by the third phosphorus atom. ,{I define a coordinate system where the (z) direction consists of the axial Co-P bond and the y axis lies in a plane which bisects the basal atoms. The best agreement between esr and electronic spectra is con- sistent with the ground state vacancy configuration of [(x2 : y2)(x2 : y3)(;2)>. In this case the expression for the principle g-tensor components are: gxx ’ 2 {ZA/[E(I(X2-y2)(x2—y2)(xz)>) (2) + _ + -‘E(|(x2-y2)(x3-y2)(22)>)]} 94 = _ + - + gyy 2 {23/[E(|(x2-y2)(xz-y2)(yz)>) (3) + - + - E(I(X2-Y2)(X2-Y2)(22)>)]} - + ,- + 922 ’ 2 '{ZA/[E(|(zz)(22)> . ('4) + - + - E (I (XL-y”) (xz-yz) (zz)>)]} Arbitrarily, we assign 91 as and 92 = g and YY 93 = gxx' g values were calculated (Table 11) according 922 to equations 2-4 by using a spin orbit coupling constant (A) of 500 cm-1, 95% of the free ion value. Only three of the seven possible one electron transition excited states contribute to the g values. These excited states are given in the second term of equations 2-4, while the third term represents the prOposed ground state. The remaining transi- tion energies in the electronic Spectra of the complexes involving dimethylaminodifluorophosphine were calculated as described previously.12 Briefly, the coulomb and ex- change integrals representing the interelectronic inter- action energies involved in each of the eight (including ground state) electronic configurations are found tabulated for d-—orbitals in terms of Condon-Shortley parameters F0, F2 and F4.54 The values of these interaction energies for the various states and the calculated transition ener— gies are given in Table 12:. By reducing the Condon-Shortley and Spin orbit coupling constant from the free ion values. one accounts for the mixing of metal and ligand orbitals in 95 Table 11. Observed and calculated g-values for the com- plexes Co(apf3)3X3 (X 3 Br, I). Observeda Calculated b c X 91 92:93 9av 91 92 .93 9 av Br 2.328 2.076 2.160 2.290 2.040 2.064 2.131 I 2.288 2.117 2.174 2.310 2.043 2.069 2.174 aError estimated from values determined using the frozen solution spectra 1 0.009. bDue to the broad structureless nature of the perpendicular band only one perpendicular value is observed (see text). CThe gav values obtained from the room temperature solution spectra are given in Table 8. Hones-w non.nm oon.nn nnn.on onn.nm omn.nu noe.ms .Anmvxas-axVAaH-axv_ 43+ use} mm + - + Home .on-w mos.on noc.om oso.ns nso.Hn n-c.Hn ons.on .AasVAauvAas-axv_ anew-«HNH- mm + -, .+ AonsN-V mos.sH nos.sH eso.on nms.nH nms.nH on.mn AANxVAas-axVAam-axv_ esm+asn-osn + - + Home .on-w -- ovo.nH ooH.s- -- on.SH nom.oe .AuxVAanVAsm-axv_ ease-asmH- an + - + “w “omen-w an.nH an.nH eHn.om nmo.sH nwo.sH osH.wm iAaH-avaaNVAmNVL .snn+amo- on + - Hoseo+ -- noe.s noo.om -- nno.n ooo.Hm iAsvaas-axvxam-axv_ ease-ammH+ on + - + Home .ou-w «on.n moo.n cem.nn ooo.o ooo.o nmo.nn AASRVAANVAas-axv_ anew-asmH- an . + - + homom- oumum o bmH.mH oumum o nwo.¢n AA«NVA«>-«vanm-nxv_ Hem-H.5- EP .66 .8 + - + .ONQO .ooamo .ooamo- w 2. - w ..omno N N mEHOB coHuomuoucH coaumnsmflwcoo OaconuoOHououcH osmom>v oumum l4 .mcowumusofimcoo aocmom>loougu may .mmonmEoo AH .Hm n XV axnaummmvou on» How ooumasoamo mOHmHoco GOHUHmcmuu ocm oumum .NH magma 97 a molecular orbital formulation. Good agreement between the observed and calculated transition energies is obtained for the states used in determining the one-electron orbital energies which are given in Table 13. As mentioned earlier, the quantitative handling of the optical spectra of the complexes of bis(dimethylamino)fluorophosphine is disabled by the complexity of the optical Spectra arising presumably by the presence of a substantial concentration of tetra- hedral high-Spin complex. 98 Table 13. Single-electron d-orbital energies for the Co(apf3)3X2 (X = Br, I) complexes.a Orbital x = I x = Br x3-y2 39,853 42,465 32 26,696 28,380 xy 19,161 21,465 xz . 8,904 9,655 yzb 0 0 a . . 1 Energies in cm . bAssigned arbitrarily as the lowest lying orbital. BIBLIOGRPAHY 10. 11. 12. 13. BIBLIOGRAPHY Benner, G. S. and D. W. Meek, Inorg. Chem., 6, 1399 (1967). "' Workman, M. 0., G. Dyer and D. W. Meek, Inorg. Chem., 6“ 1543 (1967) and references cited therein. Chastarn, B. B., E. A. Rick, R. L. Pruett and H. B. Gray, J. Amer. 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