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Synthesis, characterization and magnetic properties of some transition metal diorganophosphinate and… Xia, Shihua 1997

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SYNTHESIS, CHARACTERIZATION AND MAGNETIC PROPERTIES OF SOME TRANSITION METAL DIORGANOPHO SPHINATE AND DIMETHYLARSINATE COMPLEXES by Shihua Xia M.Sc., Hangzhou University, 1987 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (Department of Chemistry) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA September 1997 © Shihua Xia, 1997 |n presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver, Canada Date DE-6 (2/88) ABSTRACT Several divalent transition metal diorganophosphinate and dimethylarsinate complexes have been synthesized and characterized using physical methods such as thermal analysis, X-ray crystallography, electronic and vibrational spectroscopy and magnetic susceptibility measurements. Metal monophenylphosphinate complexes containing the neutral donor molecules methylformamide, monophenylphosphinic acid and dimethylsulfoxide have also been prepared and characterized. Six binary copper(II) phosphinates are shown by indirect evidence to have linear chain structures. Cu[(C6F5)2P02]2, Cu[(C6H5)(C6F5)P02]2 and Cu[(CH3)(C2H5)P02]2 exhibit antiferromagnetic exchange between metal centers while Cu{CF3[(CF2)3CH2CH2P02]2P02}2 and Cu{[CF3(CF2)3CH2CH2P02]2P02}2 (Forms I and II) exhibit ferromagnetic behaviour. A single crystal X-ray study of {Cu3[(CH3)2P02]6}x has revealed trimetallic copper(II) units linked to form a linear chain polymer. Both intra-trimer and inter-trimer antiferromagnetic interactions are present in this compound. All binary manganese(II) phosphinates studied are antiferromagnetic. Mn[(CH3)2P02]2 (Form II), Mn[n-(C8H17)2P02]2, Mn[(C6F5)2P02]2, Mn{[CF3(CF2)3CH2CH2]2P02}2 and Mn{[CF3(CF2)5CH2CH2]2P02}2 exhibit very weak exchange while relatively stronger antiferromagnetic coupling is present in Mn[(CH3)2P02]2 (Form I), Mn[(C2H5)(CH3)P02]2 and Mn[(CH3)2As02]2. These results have been correlated with structures proposed for these compounds on the basis of indirect evidence. Single crystal X-ray diffraction studies revealed that {(DMF)3Mn[//-(C6F5)2P02}2]3}2Mn is a linear trimetallic compound with ii manganese(II) ions linked by triple phosphinate bridges. The compound exhibits weak antiferromagnetic behaviour. Weak antiferromagnetism was observed for the linear chain cobalt(II) phosphinates, Co[(CH3)2P02]2, Co[(CH3)(C2H5)P02]2, Co[(C6F5)2P02]2, Co{[CF3(CF2)3CH2CH2]2P02}2 and Co{[CF3(CF2)5CH2CH2]2P02}2. The arsinate complex, Co[(CH3)2As02]2, which exhibits ferromagnetic behaviour is believed to have an extended sheet structure. Ni[(C6H5)2P02]2 and Ni[(C6F5)2P02]2 are proposed to have linear chain structures and exhibit antiferromagnetic behaviour. Ni[(CH3)2P02]2, Ni[(CH3)(C2H5)P02]2, Ni{[CF3(CF2)5CH2CH2]2P02}2 and Ni[(CH3)2As02]2, on the other hand, are proposed to have extended sheet structures. Magnetic studies on these latter materials revealed ferromagnetic behaviour. A number of monophenylphosphinate adduct polymers were studied and found to have linear chain polymeric structures and to exhibit antiferromagnetic behaviour. These compounds have the compositions Mn[(CH3)2SO]2[H(C6H5)P02]2, M[H(C6H5)P02H]2[H(C6H5)P02]2 (M = Co or Ni) and M(HCONHCH3)2[H(C6H5)P02]2 (M = CoorNi). Co(H20)2(HCOO)2 and Co(HCONH2)2(HCOO)2 are shown by single crystal X-ray diffraction studies to have polymeric structures. The compounds exhibit antiferromagnetism at high temperatures. Spin-canting results in weak ferromagnetism and long range order at low temperatures in these complexes. iii TABLE OF CONTENTS Abstract ii Table of Contents iv List of Tables xv List of Figures xviii List of Symbol and Abreviations xxvii Acknowledgments xxx Chapter 1 Introduction 1 1.1 Low-dimensional Materials and Their Magnetic Properties 1 1.2 Aspects of Physical Methods Used in Compound Characterization 10 1.2.1 Thermal Analysis 11 1.2.2 Infrared Spectroscopy 13 1.2.3 Electronic Spectroscopy 15 1.2.4 Powder X-ray Diffraction 20 1.2.5 Single Crystal X-ray Diffraction 21 1.2.6 Magnetic Susceptibility Studies 22 1.3 Objectives and Organization of the Thesis 27 References 28 iv Chapter 2 Copper(II) Phosphinates 35 2.1 Introduction 35 2.2 Results and Discussion 36 2.2.1 Synthesis and Thermal Properties 36 2.2.2 Single Crystal X-ray Diffraction 42 2.2.2.1 Structure of Copper(II) Dimethylphosphinate {Cu3[(CH3)2P02]6}x 42 2.2.3 X-ray Powder Diffraction 45 2.2.4 Infrared Spectroscopy 47 2.2.5 Electronic Spectroscopy 52 2.2.6 EPR Spectra 55 2.2.7 Magnetic Properties and Magneto-structural Correlations : 57 2.2.7.1 Copper(II) Dimethylpho sphinate {Cu3[(CH3)2P02]6}x 57 2.2.7.2 Copper(II) Methylethylphosphinate Cu[(CH3)(C2H5)P02]2 63 2.2.7.3 Copper(II) Bis(perflurophenyl)phosphinate Cu[(C6F5)2P02]2 67 2.2.7.4 Copper(II) Phenylperfluorophenylpho sphinate Cu[(C6H5)(C6F5)P02]2 72 2.2.7.5 Copper(II) Bis(perfluoro-n-butylethyl)phosphinate Copper(II) Bis(perfluoro-n-hexylethyl) v phosphinate (Form I) and Copper(II) Bis(perfluoro-n-hexylethyl)phosphinate (Form II); Cu{ [CF3(CF2)5CH2CH2]2P02}2, Cu{[CF3(CF2)3CH2CH2]2P02}2 (Form I) and Cu{[CF3(CF2)5CH2CH2]2P02}2 (Form II) 73 2.3 Summary and Conclusions 80 References 81 Chapter 3 Manganese(II) Phosphinate Complexes and Manganese(II) Dimethylarsinate 84 3.1 Introduction 84 3.2 Results and Discussion 86 3.2.1 Synthesis 86 3.2.2 Thermal Analysis 89 3.2.3 Single Crystal X-ray Diffraction 94 3.2.3.1 Structure of Manganese(II) Dimethylphosphinate (Form II) 94 3.2.3.2 Structure of Mn(DMSO)2[H(C6H5)P02]2 96 3.2.3.3 Structure of {DMF)3Mn[//-(C6F5)2P02]3}2Mn 99 3.2.4 X-ray Powder Diffraction 102 3.2.5 Infrared Spectroscopy 105 3.2.6 Magnetic Properties 107 3.3 Summary and Conclusions 120 References 121 vi Chapter 4 Cobalt(II) Phosphinate Complexes and Cobalt(II) Dimethylarsinate 123 4.1 Introduction 123 4.2 Results and Discussion 125 4.2.1 Synthesis and Thermal Properties 125 4.2.2 Single Crystal X-ray Diffraction Study of Co[(CH3)2P02]2 131 4.2.2.1 Structure of Cobalt(II) Dimethylphosphinate Co[(CH3)2P02]2 131 4.2.3 X-ray Powder Diffraction 133 4.2.4 Infrared Spectroscopy 136 4.2.5 Electronic Spectroscopy 142 4.2.6 Magnetic Properties and Magneto-structural Correlations 148 4.2.6.1 Tetrahedral Complexes 148 4.2.6.2 Octahedral Complexes and a Five-coordinate Compound.. 156 4.3 Summary and Conclusions 171 References 172 Chapter 5 Nickel(II) Phosphinate Complexes and Nickel(II) Dimethylarsinate 175 5.1 Introduction 175 5.2 Results and Discussion 177 vii 5.2.1 Synthesis and Thermal Properties 177 5.2.2 X-ray Powder Diffraction 184 5.2.3 Infrared Spectroscopy 187 5.2.4 Electronic Spectroscopy 193 5.2.5 Magnetic Properties and Magneto-structural Correlations 198 5.2.5.1 Octahedral Complexes and a Five-Coordinate Compound 198 5.2.5.2 Tetrahedral Complexes 214 5.3 Summary and Conclusions... 218 References 219 Chapter 6 Miscellaneous Compounds 222 6.1 Poly-diaquabis(//-formato)cobalt(II) and Poly-bis(formamide)bis(//-formato)cobalt(II); Co(H20)2(HCOO)2 and Co(HCONH2)2(HCOO)2 222 6.1.1 Results and Discussion 223 6.1.1.1 Syntheses and Thermal Properties 223 6.1.1.2 Single Crystal X-ray Diffraction 224 6.1.1.2.1 Structure of Co(H20)2(HCOO)2 224 6.1.1.2.2 Structure of Co(HCONH2)(HCOO)2 226 6.1.1.3 Magnetic Properties 230 6.2 {Co[n-C8F17)P03](DMF)(H20)2}x 240 References 243 viii Chapter 7 Experimental 244 7.1 Physical Experimental Techniques 244 7.1.1 Elemental Analysis 244 7.1.2 Thermal Analysis 244 7.1.3 Infrared Spectroscopy 245 7.1.4 Electronic Spectroscopy 245 7.1.5 Powder X-ray Diffraction 246 7.1.6 Single Crystal X-ray Crystallography 246 7.1.7 Magnetic Susceptibility 247 7.1.8 Melting Point Determination 248 7.1.9 Electron Paramagnetic Resonance Spectroscopy (EPR) 249 7.2 Syntheses 250 7.2.1 General Comments 250 7.2.2 Materials 251 7.2.3 Copper(II) Compounds 252 7.2.3.1 Poly-{ [hexakis(/i-dimethylphosphinato)] tricopper(II)]}, {Cu3[(CH3)2P02]6}x 252 7.2.3.2 Bis(methylethylphosphinato)copper(II), Cu[(CH3)(C2H5)P02]2 252 7.2.3.3 Bis[bis(perfluorophenyl)phosphinato]copper(II), Cu[(C6F5)2P02]2 253 7.2.3.4 Bis(phenylperfluorophenylphosphinato)copper(II), Cu[(C 6H 5)(C 6F 5)P0 2], 253 7.2.3.5 Bis{bis[(perfluoro-n-butyl)ethyl]phosphinato]}, copper(II) Cu{[CF3(CF2)3CH2CH2]2P02}2 254 7.2.3.6 Bis {bis[(perfluoro-n-hexyl)ethyl]phosphinato]} copper(II), Form I Cu{[CF3(CF.2)5CH2CH2]2P02}2, Form 1 254 7.2.3.7 Bis{bis[(perfluoro-n-hexyl)ethyl]phosphinato]}, copper(II), Form II Cu{[CF3(CF2)5CH2CH2]2P02}2, Form II 255 7.2.4 Manganese(II) Compounds. 255 7.2.4.1 Bis(dimethylphosphinato)manganese(II), Form I, Mn[(CH3)2P02]2 256 7.2.4.2 Bis(dimethylphosphinato)manganese(II), Form II, Mn[(CH3)2P02]2 256 7.2.4.3 Bis(methylethylphosphinato)manganese(II), Mn[(CH3)(C2H5)P02]2 257 7.2.4.4 Bis{bis[(perfluoro-n-hexyl)ethyl]phosphinato]}, Manganese(II) Mn{[CF3(CF2)5CH2CH2]2P02}2 257 7.2.4.5 Bis[(di-n-octyl)phosphinato]manganese(II), Mn[(n-C8Hi7)2P02]2 258 x 7.2.4.6 Bis{di[(perfluoro-n-butyl)ethyl]phosphinato]}, Mn{ [CF 3(CF 2) ?CH 2CH 2] 2P0 2 }2 258 7.2.4.7 Bis[(dimethylarsinato)manganese(II), Mn[(CH3)2As02]2 259 7.2.4.8 Poly-bis(dimethylsulfoxide) bis(//-monophenylphosphinato)manganese(II), Mn(DMSO)2[H(C6H5)P02]2 259 7.2.4.9 Bis(perfluorodiphenylphosphinato)manganese(II) Mn[(C6F5)2P02]2 260 7.2.4.10 {(DMF)3Mn[//-(C6F5)2P02]3}2Mn 260 7.2.5 Nickel(II) Compounds 261 7.2.5.1 Bis(monophenylphosphinic acid) bis(monophenylphosphinato)nickel(II), Ni[H(C6H5)P02H]2[H(C6H5)P02]2 261 7.2.5.2 Bis(N-methylformamide) bis(monophenylphosphinato)nickel(II), Ni(HCONHCH3)2[H(C6H5)P02]2 262 7.2.5.3 Bis(dimethylphosphinato)nickel(II), Ni[(CH3)2P02]2 263 7.2.5.4 Bis(methylethylphosphinato)nickel(II), Ni[(CH3)(C2H5)2P02]2 263 7.2.5.5 Bis[(dimethylarsinato)nickel(II), Ni[(CH3)2As02]2 264 xi 7.2.5.6 Bis[bis(perfluorophenyl)phosphinato]nickel(II), Ni[(C6F5)2P02]2 264 7.2.5.7 Bis[bis(perfluorophenyl)phosphinato]nickel(II) monohydrate, Ni[(C6F5)2P02]2 • H 2 0 265 7.2.5.8 Bis(diphenylphosphinato)nickel(II), Ni[(C6H5)2P02]2 265 7.2.5.9 Bis{bis[(perfluoro-n-hexyl)ethyl]phosphinato]} nickel(II), Ni{[CF3(CF2)5CH2CH2]2P02}2 265 7.2.6 Cobalt(II) Compounds 266 7.2.6.1 Bis(dimethylphosphinato)cobalt(II), Co[(CH3)2P02]2 266 7.2.6.2 Bis(methylethylphosphinato)cobalt(II), Co[(CH3)(C2H5)P02]2 267 7.2.6.3 Bis [(dimethylar sinato)cobalt(II), Co[(CH3)2As02]2 267 7.2.6.4 Bis(monophenylphosphinic acid) bis(monophenylphosphinato)cobalt(II), Co[H(C6H5)P02H]2[H(C6H5)P02]2 268 7.2.6.5 Bis(N-methylformamide) bis(monophenylphosphinato)cobalt(II), Co(HCONHCH3)2[H(C6H5)P02]2 269 7.2.6.6 Bis[bis(perfluorophenyl)phosphinato]cobalt(II), Xll Co[(C6F5)2P02]2 269 7.2.6.7 Bis[bis(perfluorophenyl)phosphinato]cobalt(II) monohydrate, Co[(C6F5)2P02]2 • H 2 0 270 7.2.6.8 Bis{bis[(perfluoro-n-butyl)ethyl]phosphinato]} cobalt(II), Co{[CF3(CF2)3CH2CH2]2P02}2 270 7.2.6.9 Bis{bis[(perfluoro-n-hexyl)ethyl]phosphinato]} cobalt(II), Co{[CF3(CF2)5CH2CH2]2P02}2 270 7.2.7 Miscellaneous Compounds 271 7.2.7.1 Poly-diaquabis(//-formato)cobalt(II), Co(H20)2(HCOO)2 271 7.2.7.2 Poly-bis(formamide)bis(//-formato)cobalt(II), Co(HCONH2)2(HCOO)2 272 7.2.7.3 {Co[n-C8F17)P03](DMF)(H20)2}x 273 References 273 Chapter 8 Summary and Suggestions for Further Study 275 8.1 Summary 275 8.2 Suggestions for Further Study 281 References 283 x i i i Appendixes I Single Crystal X-ray Diffraction Data 284 II Magnetic Susceptibility Results 288 xiv LIST OF TABLES Table Page 2.1 Thermal parameters for copper(II) phosphinates 39 2.2 Selected bond lengths (A) and angles (deg) for {Cu3[(CH3)2P02]6}x 43 2.3 Selected infrared data for copper(II) phosphinates 48 2.4 Electronic spectra data for copper(II) phosphinates 58 2.5 EPR spectral data for copper(II) phosphinates. 55 2.6 Magnetic parameters for copper(II) complexes 67 2.7 Magnetic parameters for copper(II) phosphinates.......... 77 3.1 DSC thermal parameters for manganese(II) phosphinates 92 3.2 Selected bond lengths (A) and angles (deg) for Mn[(CH3)2P02]2 (Form II) 95 3.3 Selected bond lengths (A) and angles (deg) for Mn(DMSO)2[H(C6H5)P02]2 97 3.4 Selected bond lengths (A) and angles (°) for {(DMF)3MnI//-(Cf,F02PO2]3}2Mn 100 3.5 Selected infrared data (cm"1) for manganese(II) phosphinates 107 3.6 Magnetic parameters for manganese(II) phosphinate complexes 116 3.7 Magnetic parameters and bond distances of Mn-O-P-O-Mn for MnL2(H(C6H5)P02]2 complexes 117 4.1 Thermal parameters for cobalt(II) phosphinates 129 4.2 Selected bond lengths (A) and angles (deg) for Co[(CH3)2P02]2 132 xv 4.3 Selected infrared data (cm"1) for nickel(II) phosphinates 139 4.4 Electronic spectra data for cobalt(II) complexes 144 4.5 Magnetic parameters for cobalt(II) phosphinate complexes 152 4.6 Magnetic parameter for cobalt(II) phosphinate complexes. 167 5.1 Thermal parameters for nickel(II) complexes 181 5.2 Selected infrared data (cm"1) for nickel(II) phosphinates 190 5.3 Electronic spectra data for nickel(II) complexes 195 5.4 Magnetic parameters for nickel(II) complexes 206 5.5 Experimental magnetization for nickel(II) binary complexes 212 5.6 Magnetic parameters for nickel(II) phosphinate complexes 215 6.1 Selected bond lengths (A) and angles (deg) for Co(HCONH2)2(HCOO)2 227 6.2 Selected bond lengths (A) and angles (deg) for {Co[n-C8F17)P03](DMF)(H20)2}x 241 8.1 Classification of the compounds 277 Appendix I Single crystal X-ray diffraction data 284 1-1 Crystallographic data for {Co[(n-C8F17)P03](DMF)(H20)2}x 284 1-2 Crystallographic data for {Cu3[(CH3)2P02]6}x 284 1-3 Crystallographic data for [Co(HCOO)2(HCONH2)2]x 285 1-4 Crystallographic data for {[Mn[CH3)2P02]2}x 285 1-5 Crystallographic data for {[Co[CH3)2P02]2}x 286 1-6 Crystallographic data for xvi {[HCON(CH3)2]3Mn[//-(C6F5)2P02]3}2Mn 286 I- 7 Crystallographic data for {Mn[(CH3)2SO]2(H(C6H5)P02]2}x 287 Appendix II Magnetic susceptibility data 288 II- 1 Magnetic data for copper(II) phosphinates 288 II-2 Magnetic data for manganese(II) phosphinates 293 II-3 Magnetic data for nickel(II) phosphinates 297 II-4 Magnetic data for cobalt(II) phosphinates 302 II-5 Magnetic data for miscellaneous compounds 302 xvii LIST OF FIGURES Figure Page 1.1 Structures of (A) Zn[(C6H5)(n-C4H9)P02]2 and (B) Cu[(n-C6H13)2P02]2 5 1.2 The linear polymeric chain structure of Mn(CH3CONH2)2[H(C6H5)P02]2 8 1.3 RRTO2" bonding modes and possible polymeric structures 16 2.1 TGA thermogram of Cu{ [CF3(CF2)3CH2CH2]2P02}2 40 2.2 DSC thermograms for (a) Cu{[CF3(CF2)3CH2CH2]2P02}2, (b) Cu{[CF3(CF2)5CH2CH2]2P02}2 (Form I) and (c) Cu{[CF3(CF2)5CH2CH2]2P02}2 (Form II) 41 2.3 Stereoview of a section of the chain and atom numbering scheme for {Cu 3[(CH3)2P02]6}x 44 2.4 View of the trimetallic unit for {Cu 3[(CH3)2P02]6}x 45 2.5 X-ray powder diffraction patterns for a) Cu3[(CH3)2P02]6, b) Cu[(CH3)(C2H5)P02]2, c) Cu[(C6F5)2P02]2, d) Cu[(C6H5)(C6F5)P02]2, e) Cu{[CF3(CF2)3CH2CH2]2P02}2, f) Cu{[CF3(CF2)5CH2CH2]2P02}2 (Form I) and g) Cu{[CF3(CF2)5CH2CH2]2P02}2 (Form II) 46 2.6 Infrared spectra of (a) Cu[(CH3)2P02]2 and (b) Cu[(CH3)(C2H5)P02]2 49 2.7 Infrared spectra of (a) Cu[(C6F5)2P02]2 and xviii (b) Cu[(C6H5)(C6F5)P02]2 50 2.8 Infrared spectra of (a) Cu{[CF3(CF2)5CH2CH2]2P02}2 (Form I) and (b) Cu{ [CF3(CF2)5CH2CH2]2P02}2 (Form II) 51 2.9 Electronic spectra of Cu[(C6F5)2P02]2 and Cu[(CH3)(C2H5)P02]2 54 2.10 EPR spectra for (a) Cu[C6H5)2P02]2, (b) Cu[(C6F5)2P02]2 and (c) Cu[(C6H5)(C6F5)P02]2 56 2.11 Magnetic moment (per mole of trimetallic unit) versus temperature for {Cu3[(CH)3P02]6}x 61 2.12 Magnetic moment versus temperature plot for compound Cu[(CH3)(C2H5)P02]2 64 2.13 Magnetic moment versus temperature plots for (a) Cu[(C6F5)2P02]2 and (b) Cu[(C6H5)(C6F5)P02]2 70 2.14 Magnetic susceptibility plot for Cu[(C6F5)2P02]2 71 2.15 Magnetic moments versus temperature plots for (a) Cu{[CF3(CF2)3CH2CH2]2P02}2, (b) Cu{[CF3(CF2)5CH2CH2]2P02}2 (Form I), (c) Cu{[CF3(CF2)5CH2CH2]2P02}2 (Form II), 10 kOe and (d) Cu{ [CF3(CF2)5CH2CH2]2P02}2 (Form II), 50 kOe 74 2.16 Magnetic moments versus temperature plots for Cu{[CF3(CF2)3CH2CH2]2P02}2 78 2.17 Magnetic moments versus temperature plots for Cu{[CF3(CF2)5CH2CH2]2P02}2 (Form I) 79 x ix 3.1 DSC thermograms of Mn(DMSO)2[H(C6H5)P02]2 and (b) {(DMF)3Mn[/i-(C6F5)2P02]2}2Mn 93 3.2 TGA thermograms of (a) Mn(DMSO)2[H(C6H5)P02]2 and (b) {(DMF)3Mn[|a-(C6F5)2P02]2}2Mn 93 3.3 Stereo view of a portion of the chain of Mn[(CH3)2P02]2 (Form II) 95 3.4 Atom labeling scheme of Mn(DMSO)2[H(C6H5)P02]2 98 3.5 Stereoview of a section of polymeric chain of Mn(DMSO)2[H(C6H5)P02]2 98 3.6 View of {(pMF)3Mn[//-(C6F5)2P02]3}2Mn showing the numbering scheme and coordination about the manganese atom: 101 3.7 Trinuclear manganese structure of {(DMF)3Mn[//-(C6F5)2P02]3}2Mn 101 . 3.8(A) X-ray powder diffraction patterns for Mn[(DMSO)2[H(C6H5)P02]2 103 3.8(B) X-ray powder diffraction patterns for (a) Mn[(CH3)(C2H5)P02]2, (b) Mn[(CH3)2P02]2 (Form I), (c) Mn[(CH3)2P02]2 (Form II), (d) Mn[(C6F5)2P02]2, (e) Mn[(CH3)2As02]2 and (f) {(DMF)3Mn[//-(C6F5)2P02}2]3}2Mn 104 3.9 JR. spectra of (a) Mn(DMSO)2[H(C6H5)P02]2 and (b) {(DMF)3Mn[//-(C6F5)2P02]3}2Mn 108 x x 3.10 Magnetic moment versus temperature plots for (a) Mn[(CH3)2As02]2, (b) Mn[(CH3)2P02]2 (Form I), (c) Mn[(CH3)2P02]2 (Form II), (d) Mn[(DMSO)2[H(C6H5)P02]2, (e) Mn[(C6F5)2P02]2, (f) Mn[(CH3)(C2H5)P02]2, (g) Mn{[CF3(CF2)5CH2CH2]2P02}2, (h) Mn([CF3(CF2)3CH2CH2]2P02}2, (i) Mn[(n-C8Hi7)2P02]2 and (j) {(DMF)3Mn[u.-(C6F5)2P02]3}2Mn 110 3.11 Magnetic susceptibility versus temperature plots for (a) Mn[(CH3)2As02]2, (b) Mn[(CH3)2P02]2 (Form I), (c) Mn[(CH3)2P02]2 (Form II), (d) Mn[(DMSO)2[H(C6H5)P02]2, (e) Mn[(C6F5)2P02]2, (!) Mn[(CH3)(C2H5)P02]2, (g) Mn{[CF3(CF2)5CH2CH2]2P02}2, (h) Mn([CF3(CF2)3CH2CH2]2P02}2, (i) Mn[(n-C8Hi7)2P02]2 and (j) {(DMF)3Mn[^-(C6F5)2P02}2]3}2Mn.) I l l 3.12 Magnetic susceptibility data versus temperature plots for (a) Mn[(CH3)2P02]2 (Form I), (b) Mn[(CH3)2P02]2 (Form II), (c) Mn[n-(C8H17)2P02]2 and (d) Mn(DMSO)2[H(C6H5)P02]2 115 3.13 Plots of magnetic data (per mole of manganese ion) versus temperature for manganese trinuclear complex {(DMF)3Mn[//-(C6l-5)2P02}2]3 }2Mn 119 4.1 DSC thermograms of (a) Co[(C 6F 5) 2P0 2]2} 2 and (b) Co(HCONHCH3)2[H(C6H5)P02]2 130 xxi 4.2 TGA thermograms of (a) Co[(C6F5)2P02]2 and (b) Co(HCONHCH:,)2|H(C6H5)P02]2 130 4.3 Atom numbering scheme for Co[(CH3)2P02]2 132 4.4 Stereoview of the geometry about manganese for Co[(CH3)2P02]2. 133 4.5(A) X-ray powder diffraction patterns for Co(HCONHCH3)2[H(C6H5)P02]2 and Co [H(C6H5)P02H]2[H(C6H5)P02]2 135 4.5(B) X-ray powder diffraction patterns for (a) Co[(CH3)2P02]2, (b) Co[(CH3)(C2H5)P02]2, (c) Co[(CH3)2As02]2, (d) Co[(C6F5)2P02]2 and (e) Co[(C6F5)2P02]2 • H 2 0 136 4.6 IR spectra of Co[(CH3)2P02]2 (top) and Co[(CH3)2As02]2 (bottom) 140 4.7 IR spectra of Co(HCONHCH3)2[H(C6H5)P02]2 and Co(H(C6H5)P02H]2[H(C6H5)P02]2 141 4.8 Electronic spectra for (a) Co[(CH3)2P02]2 and (b) Co[H(C6H5)P02H]2[H(C6H5)P02]2 146 4.9 Electronic spectrum of Co[(C6F5)2P02]2*H20 147 4.10 A linear chain polymeric structure with a square-pyramidal geometry around the metal centers proposed for Co[(C6F5)2P02]2#H20 147 4.11 Magnetic moment versus temperature plots for Co[(CH3)2P02]2, Co[(CH3)(C2H5)P02]2, Co[(C6F5)2P02]2, Co{ [CF3(CF2)3CH2CH2]2P02}2 and Co{[CF3(CF2)5CH2CH2]2P02}2 153 xxii 4.12 Magnetic susceptibility versus temperature plots for (a) Co[(CH3)2P02]2, (b) Co[(CH3)(C2H5)P02]2, (c) Co[(C6F5)2P02]2 and d) Co{[CF3(CF2)3CH2CH2]2P02}2 154 4.13 Magnetic data versus temperature plots for Co{[CF3(CF2)5CH2CH2]2P02}2 155 4.14 Magnetic moment versus temperature plots for (a) Co[(H(C6H5)P02H]2[H(C6H5)P02]2, (b) Co(HCONHCH3)2[H(C6H5)P02]2 and (c) Co[(C 6 F 5 ) 2 P0 2 ] 2 «H 2 0 157 4.15 Magnetic moment versus temperature plot for Co [(CH3)2As02]2 158 4.16 Partial energy level diagram for octahedral cobalt(II) 158 4.17 Magnetic susceptibility versus temperature plot and magnetic moment versus temperature plot for Co[(H(C6H5)P02H]2[H(C6H5)P02]2 (zero-field splitting model) ; 160 4.18 Magnetic susceptibility versus temperature plot and magnetic moment versus temperature plot for Co[(H(C6H5)P02H]2[H(C6H5)P02]2 162 4.19 Magnetic susceptibility versus temperature plot and magnetic moment versus temperature plot for Co(HCONHCH3)2[H(C6H5)P02]2 164 4.20 Magnetic susceptibility versus temperature plot and magnetic moment versus temperature plot for Co[(C6F 5) 2P0 2] 2«H 20 168 xxiii 4.21 Magnetic susceptibility versus temperature plots for Co[(CH3)2As02]2 169 4.22 Magnetization versus field plots for Co[(CH3)2As02]2 at various temperatures 170 5.1 DSC thermograms of (a) Ni[(CH3)2P02]2}2 and (b) Ni(HCONHCH3)2[H(C6H5)P02]2 183 5.2 TGA thermograms of (a) Ni[(CH3)2P02]2}2 and (b) Ni(HCONHCH3)2[H(C6H5)P02]2 183 5.3 (A) X-ray powder diffraction patterns for Ni[H(C6H5)P02H]2[H(C6H5)P02]2 and Ni(HCONHCH3)2[H(C6H5)P02]2 185 5.3 (B) X-ray powder diffraction patterns for (a) Ni[(CH3)2P02]2, (b) Ni[(CH3)(C2H5)P02]2, (c) Ni[(CH3)2As02]2 (Form II), (d) Ni[(C6F5)2P02]2 and (e) Ni[(C 6 F 5 ) 2 P0 2 ] 2 »H 2 0 186 5.4(a) IR spectrum of Ni[H(C6H5)P02H]2[H(C6H5)P02]2 191 5 4(b) IR spectra of Ni[(CH3)2P02]2 and Ni[(CH3)2As02]2 192 5.5 Electronic spectra for (a) Ni[(C6F5)2P02]2, (b) Ni[(CH3)(C2H5)P02]2 (c) Ni[H(C6H5)P02H]2[H(C6H5)P02]2 197 5.6 Magnetic moment versus temperature plots for (a) Ni(H(C6H5)P02H]2[H(C6H5)P02]2, (b) Ni(HCONHCH3)2[H(C6H5)P02]2 and (c) Ni[(C 6 F 5 ) 2 P0 2 ] 2 «H 2 0. . . 199 5.7 Magnetic susceptibility versus temperature plot Ni(H(C6H5)P02H]2[H(C6H5)P02]2 200 xxiv 5.8 Magnetic susceptibility versus temperature plots for (a) Ni(HCONHCH3)2[H(C6H5)P02]2 and (b) Ni[(C6F5)2P02]2»H20... 202 5.9 Magnetic moment versus temperature plots for (a) Ni[(CH3)2P02]2, (b) Ni[(CH3)(C2H5)P02]2, (c) Ni[(CH3)2As02]2 and (d) Ni{[CF3(CF2)5CH2CH2]2P02}2 at various fields 204 5.10 Magnetization versus field plot for Ni{[CF3(CF2)5CH2CH2]2P02}2 at various temperatures 207 5.11 Sheet polymeric structure proposed for Ni[H(C6H5)PC»2]2 210 5.12 Magnetization versus field plot for Ni{[CF3(CF2)5CH2CH2]2P02}2... 213 5.13 Magnetic moment versus temperature plots for Ni[(C6F5)2P02]2 and Ni[(C6H5)2P02]2 216 5.14 Magnetic susceptibility versus temperature plots for Ni[(C6F5)2P02]2 and Ni[(C6H5)2P02]2. 217 6.1 Configuration of formate anion in complexes 223 6.2 A portion of the polymeric structure of Co(H20)2(HCOO)2 225 6.3 Atom labeling scheme of Co(HCONH2)2(HCOO)2 227 6.4 A section of the polymeric sheet of Co(HCONH2)2(HCOO)2 228 6.5 A portion of network three-dimensional for Co(HCONH2)2(HCOO)2 229 6.6 Magnetic moment versus temperature plots for Co(H20)2(HCOO)2 at different fields 232 XXV 6.7 Magnetic moment versus temperature plots for Co(HCONH2)2(HCOO)2 at different fields 233 6.8 Magnetic susceptibility versus temperature plots for Co(HCONH2)2(HCOO)2 at different fields as shown in the diagram 234 6.9 Magnetic susceptibility versus temperature plots for Co(H20)2(HCOO)2 at different fields 23 5 6.10 Magnetization versus temperature plot at different fields for Co(HCONH2)2(HCOO)2 236 6.11 Magnetization versus magnetic field plot at various temperatures for Co(HCONH2)2(HCOO)2 237 6.12 Hysteresis loop for Co(HCONH2)2(HCOO)2 23 8 6.13 Magnetic data versus temperature plots for Co(HCONH2)2(HCOO)2 at 50,000 G 239 6.14 A section of the polymeric structure of {Co[n-C8F17)P03](DMF)(H20)2}x with atom labeling scheme 242 xxvi LIST OF ABBREVIATIONS AND SYMBOLS a angle A Angstrom Anal. analysis arb. arbitrary anti. antisymmetric B interelectron repulsion (Racah) parameter B magnetic induction P angle br broad u.B or B. M. Bohr Magneton Calcd. calculated cm"1 wavenumber(s) d crystal interplanar spacing D dimensional parameter D axial zero-field splitting parameter deg or ° degree(s) DMF dimethylformamide DMP 2,2-dimethoxypropane DSC differential scanning calorimetry °C degree Celsius AH change in enthalpy ESR electron spin resonance Dq ligand field splitting parameter EtOH ethanol g Lande splitting factor g gram(s) xxvii G Gauss K Kelvin h hour(s) or Planck's constant H or H magnetic field J exchange coupling constant k Boltzmann's constant X magnetic susceptibility Xg gram magnetic susceptibility XM molar magnetic susceptibility M magnetization m medium MeOH methanol mg milligram(s) min minute(s) ml milliliter(s) mmol millimole(s) mol mole(s) N Avogadro's number nm nanometer(s) V stretching vibrational frequency M bridging obs. Observed P density s strong S total electron spin sh shoulder SQUID Superconducting Quantum Interference Device T temperature TGA Thermal Gravimetric Analysis TIP. Temperature Independent Paramagnetism xxviii w weak TJ.B.C. University of British Columbia Vis visible V S M vibrating sample magnetometer ~ approximately < less than > greater than A difference between xxix ACKNOWLEDGMENTS I would like to express my sincerest thanks to my research supervisor, Dr. R. C. Thompson, for his support, guidance and patience during the course of this work. I am extremely grateful to Dr. K. W. Oliver for her supply of some ligands. I would also like to thank the members of my guidance committee, Drs. A. Storr, J. Trotter and K. Mitchell for the constructive criticism they provided during the final preparation of this dissertation. The research described in this thesis would have been rendered painstakingly slow if it were not for the expert assistance of the staff in the electronics, glassblowing, and mechanical shops. Many thanks go to Dr. S. J. Rettig for the crystal structure determinations, Dr. F. G. Herring for running the ESR spectra for several copper(II) samples and Mr. P. Borda for his micro-analytical services. I also thank my colleagues, both present and past, Drs. T. Otieno, M. Ehlert and Mr. D. Summers for their invaluable help in various aspects of this work. Finally, I extend my special thanks to my wife X. Y. Sun, my daughter, L. L. Xia and my sons, B. S. H. Xia and C. S. C. Xia, for their enduring support and encouragement during the course of this work. xxx Chapter 1 Introduction 1.1. Low-dimensional Materials and Their Magnetic Properties Physical space permits the existence of three orders of dimensionality. From a chemical point of view we add zero-dimensional (0-D) compounds which are molecular species having local connectivity only. 1-D and 2-D compounds possess extended connectivity in one or two spatial directions, in other words, they are chains or sheets, respectively. 3-D compounds possess extended connectivity in three spatial directions. Low-dimensional materials deal with 1-D and 2-D compounds and the compounds which are described in this thesis primarily concern such materials. The solid state properties of low-dimensional materials have long been of interest to both physicists and chemists. Of particular interest are their magnetic and optical as well as structural and chemical properties (1-7). The types of compounds which have been studied range from organic compounds to inorganic coordination polymers. Organic polymers such as polyacetylene can be used as semiconductors (8). Inorganic polymers which are a sub-branch of low-dimensional materials have a long history of investigation. In fact, many of the compounds that were studied extensively in the 1970s were first prepared over one hundred years before. For example, the first linear-chain inorganic polymer, K 2Pt(CN)4Clo.3»xH 20, was first synthesized in the middle of the nineteenth century (9). It was found to possess a high conductivity although its structure was not known until it was solved by X-ray diffraction studies in the late 1960s (10). A common feature of inorganic polymers is that metal ions are bridged by intervening groups 1 and are more closely spaced in some directions than others. Metals in paramagnetic ground states may be involved. In such examples, the bridging ligands may influence the magnetic properties of the complexes and give rise to magnetic exchange via the so-called super-exchange mechanism. Some of the studies on magneto-structural correlations of low-dimensional complexes, carried out in our laboratory and elsewhere, are reviewed below. Pyrazine (pyz), 1,4-diazine, and its substituted derivatives are able to link metal ions through two nitrogen atoms. Complexes involving these ligands are typically chain or sheet polymers which exhibit magnetic exchange interactions. For example, in CuL(NC<3)2 (where L is pyrazine, chloropyrazine, methylpyrazine, 2,5- and 2,6-dimethylpyrazine and phenazine), the variation in the magnitude of antiferromagnetic coupling between different complexes correlates with the energy of the 7 1 - 7 1 * transition of the particular pyrazine ligand. This is correlated with the presence of an exchange mechanism primarily involving the pyrazine 7t-system (11,12). Dimeric copper(II) carboxylates were among the first complexes to be investigated thoroughly in terms of magnetic interactions and how they relate to the structure of the complex (13-15). The compounds are very strongly coupled antiferromagnetically (with \J\, the magnetic coupling constant defined later in equation [1.15], around 300 cm"1). In comparison, oxygen or halogen bridged dinuclear copper(II) complexes exhibit J values which may be much smaller (on the order of a few cm"1) and can be positive or negative, depending on the bridging Cu-X-Cu angle and on the out-of-plane bond distance (6, 17). Crawford et al. (18) prepared a series of planar bis-//-hydroxo copper(II) dimers and 2 found that the exchange coupling varies linearly with the Cu-O-Cu angle and that the exchange changes from ferromagnetic to antiferromagnetic as the bridging angle is increased. Iron(II) sulfonate compounds, Fe(RS03)2, where R is F, CF 3, CH 3 or p-CH3C6H4, have polymeric layered structures (19, 20) similar to that of Ca(CH3S03)2 (21), in which each RS03" acts as a tridentate bridging ligand to three different metal centers. In this structure, each metal is in an approximately octahedral environment of oxygen atoms and each oxygen atom is from a different sulfonate group. It was found that the magnitude of magnetic exchange in these Fe(RS03)2 compounds is not simply related to electronic or steric effects associated with the substituents on the sulfonate group. Different magnetic properties observed for these complexes arise more from differences in the detailed molecular geometries of the complexes. Long-range magnetic ordering is seen in 0-Fe(CH3S03)2 and the super-exchange in this material as well as in the other complexes mentioned above is believed to be via the O-S-0 bridging unit (22). In metal pyrazolates, M[(pz)2]x, or substituted pyrazolates, M[(pz*)2]x, the anions, pz and pz*, serve as links between metal centers. The X-ray crystal structure of Cu[(pz)2]x (23) reveals an infinite double pyrazolate bridged polymeric chain in which each Cu atom has a D2 symmetry and distorted tetrahedral geometry. The TC system of the ligands is believed to provide the pathway for magnetic exchange. Strong antiferromagnetic exchange (\J\ ranges from 78 to 105 cm"1) was observed in these complexes (23, 24). Magnetic studies showed that the magnitude of exchange is not related to ligand basicities, but is determined by structural differences which affect the overlap between the Tc-orbital 3 system and the metal's magnetic orbital. Relatively weak exchange coupling was observed in related cobalt(II) pyrazolates. On the basis of indirect spectroscopic evidence these complexes were proposed to have polymeric one-dimensional chain structures, similar to the copper structures (25). Poly-(metal phosphinates), M(RR'P02)2, are a class of compounds in which metal ions are bridged by phosphinate ligands. Research on these and related systems forms the basis of this thesis. Oliver and Du from our research group (26, 27) have previously reviewed early research on these complexes including their structures, magnetic properties and other chemical and physical properties. U02[(n-C4H9)2P02]2 appears to be the first compound shown to contain bridging phosphinate ligands (28, 29). Two different types of structures have been observed in poly-(metal phosphinates) as shown by single crystal X-ray diffraction or X-ray fiber studies. One type is a linear chain structure involving a bridging system in which chains of metal atoms are linked alternately by single and triple phosphinate anions as observed in Zn[(C6H5)(n-C4H9)P02]2 (Figure 1.1 A) (30, 31). A similar structure was reported for Zn[(n-C4H9)2P02]2 (32) and Zn[(n-C4H9)(n-C6Hi3)P02]2 (33). These particular structures were determined by X-ray fiber studies and have never been confirmed by single crystal X-ray diffraction. Most of the complexes prepared to date adopt the second type of structure in which linear chains of metal ions are linked by double phosphinate bridges (34-41). The polymeric structure of one of these complexes, Cu[(n-C6H13)2P02]2 is shown in Figure L I B . 4 A B Figure 1.1. Structures of (A) Zn[(C6H5)(n-C4H9)P02]2, (B) CuKn-CeH^POzfc, taken from references 30 and 37. Phosphinate ligands have the ability to form inorganic coordination polymers which are stable to high temperatures and have plastic properties (42). These are desirable properties in industry and the early studies of metal phosphinates concentrated on finding materials which might be of such commercial use (43). Magnetic properties have been extensively investigated since the middle of the 1970s when magnetic interaction via O-P-0 bridges was found to be present in metal phosphinates (26-27, 35, 44-45). Oliver (26) prepared a series of copper(II) diorganophosphinates, Cu(R-2P02)2, where R is an alkyl group, and found that when R is n-octyl, n-decyl or n-dodecyl, the complexes can be obtained in two different polymorphs, so called, a- and P-forms. Other compounds which do not show polymorphism are the ethyl derivative whose structure has the a-form and the butyl and 5 hexyl derivatives which have the P-form structure (46). The two forms exhibit different magnetic behaviours with the former showing antiferromagnetic exchange interactions (with \J\ ranging from ~ 25 to ~ 30 cm"1) and the latter being ferromagnetic (with \J\ approximately 2 cm"1). These differences in magnetic properties were ascribed to different degrees of distortion in the CuCU chromophore leading to differences in the overlap between the copper(II) magnetic orbital and the oxygen orbitals of the O-P-0 bridges. Cu[(C6H5)2P02]2 has the same basic double phosphinate bridged infinite chain structure as the other copper(II) phosphinates; however, the Cu0 4 chromophore in this case is square planar (39) instead of the flattened tetrahedral geometry found in the other copper(II) phosphinates (35-37). Magnetic susceptibility studies down to 2.0 K revealed the presence of weak ferromagnetic exchange in the compound (47). Other metal diphenylphosphinates, M[(C6H5)2P02]2 (M = Co(II) or Mn(II)) have been obtained and shown to exhibit polymorphism. Two forms, the so-called 3- and y- forms, were observed for each (41). Single crystal X-ray studies showed the structures of the y- forms to consist of infinite linear chains, formed by metal ions in nearly regular tetrahedral environments, joined by bridging phosphinate ligands. Both p- and y- forms of both the Co(II) and Mn(II) compounds are weakly antiferromagnetic materials with \J\ less than 1 cm"1. A series of metal monophenylphosphinates, M[H(C6H5)P02]2 (where M is Co(II), Mn(II), Ni(II), Cd(II) or Cu(II)) were prepared by Du (27). All were suggested to be polymeric materials as indicated by indirect spectroscopic evidence and magnetic studies. One of the complexes, Co[H(C6H5)P02]2, was obtained in three structural forms. Two of them exhibit antiferromagnetism, while the third form exhibits ferromagnetic, field 6 dependent behaviour. On the basis of electronic spectroscopy studies all three forms appear to have tetrahedral metal centers. The other metal monophenylphosphinates studied by Du were concluded to have octahedrally-coordinated metal centers which are cross-linked to form sheet polymers, however, importantly, no single crystal X-ray diffraction determined structures are available for these compounds. The manganese and copper compounds are weakly antiferromagnetic, while the nickel compound exhibits ferromagnetic, field dependent, behaviour. Polymeric materials with the empirical formula ML2(RR'P02)2 (where L is a neutral ligand) are called "adduct polymers". They have linear chain structures in which phosphinate bridged metal ions are coordinated by additional neutral ligands. Du and others prepared a series of adduct polymers, ML2[H(C6H5)P02]2, where M is Mn(II), Co(II) or Ni(II) and L is pyridine (py), pyz, H 20 or HCONH 2 (27, 48, 49). It was found that regardless of metal involved, the strength of antiferromagnetic coupling in these complexes increases in the order L = py < pyz < H 20 < HCONH 2. Structures of the manganese complexes, MnLzfHtCeHs^POzk (where L = H(C 6H5)P0 2H, CH 3CONH 2, H20, HCONH2), determined by single crystal X-ray diffraction techniques, revealed infinite linear chains with metal ions double-bridged by phosphinates, and neutral ligands coordinated axially to complete an octahedral chromophore for the metal ions. A representative structure of Mn(CH3CONH2)2[H(C6H5)P02]2 is shown in Figure 1.2. The structures of some related cobalt complexes were also confirmed by X-ray studies. All the manganese(II) adduct polymers exhibit weak antiferromagnetic coupling. Moreover, it was found that symmetry of O-P-0 bridges played an important role in the strength of 7 magnetic exchange. Whether or not the O-P-0 bridges are symmetrical significantly affects the strength of the magnetic coupling between metal centers. Specifically the magnitude of the magnetic coupling is enhanced by symmetrically bridging O-P-0 units and short Mn-O-P-O-Mn pathways for exchange. Figure 1.2. Stereoview of the linear polymeric chain structure of Mn(CH3CONH2)2[H(C6H5)P02]2, taken from reference 48. Other work on phosphinates of manganese(II) carried out in our laboratory includes a study of doping cadmium into the polymeric structure of manganese(II) monophenylphosphinate (27, 50, 51). It was found that the incorporation of diamagnetic 8 cadmium atoms into the polymer chain had the effect of breaking the infinite chain into finite segments and generating paramagnetic impurities in odd numbered segments. As the extent of doping is increased the average chain length decreases. In addition, the value of \J] was found to decrease (from 3.00 to 2.00 cm"1) as the average chain length decreases. Several conclusions on how magnetic exchange relates to structure have been drawn from the work described above. The combination of single crystal X-ray structure determinations and magnetic susceptibility measurements is important if meaningful conclusions are to be made. Moreover, magnetic susceptibility measurements have to be made at low temperatures in order to probe the weak exchange interactions often observed in these coordination polymers which involve multi-atom bridges between metal centers. It should be noted that molecular magnetism has been a very active field of research since the discovery of the ferromagnetic transition in the organometallic donor-acceptor salt decamethylferrocenium tetracyanoethenide, [Fe(Me5C5)2][TCNE] (52-56). The spins associated with both donor and acceptor units in this compound are strongly coupled along the chains in a ferromagnetic fashion (J = 26 cm"1). The ferromagnetic chains are also weakly coupled inter-molecularly, again in a ferromagnetic fashion. This results in bulk ferromagnetic properties with a spontaneous magnetization below the Tc (Curie temperature) of 4.8 K. Other decamethylmetallocenium charge-transfer salts ordering ferromagnetically have also been reported. These are [Mn(Me5C5)2][TCNE] (57) with a Tc = 8.8 K and [Cr(Me5C5)2][TCNE] (58, 59) with a Tc = 3.1 K. 9 Molecular magnetic materials based on purely organic molecules carrying stable radicals have also been prepared and studied. P-nitrophenyl nitronyl nitroxide radical exhibits a ferromagnetic transition (Tc = 0.60 K) and four crystallographic phases of this compound have been characterized (60-63). Recently, charge-transfer compounds involving the TEMPO (2,2,6,6-tetramethylpiperidinyloxy) radical (or its derivatives) as donors and TCNQF 4 (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquionodimethane) as an acceptor have been prepared and characterized (64). Both ferromagnetic and antiferromagnetic interactions are found in these materials. 1.2. Aspects of Physical Methods Used in Compound Characterization Since the main thrust of this thesis deals with magneto-structural correlations in polymeric systems, the focal points were the measurements of magnetic susceptibilities and the determination of the structure(s) of the complexes. In some cases the structures of the complexes could be solved by single crystal X-ray diffraction methods. This provided details of bond lengths and angles and established the exact nature of the bridging systems. However, most of the complexes were only obtained in microcrystalline powder form and, for these, indirect methods were used to obtain structural information. The technique of X-ray powder diffraction is useful to identify polymorphism and isomorphism. Also, a range of spectroscopic tools were found to be very helpful. UV-Vis-NIR spectroscopy was used to establish the nature of the metal chromophore in compounds of Co(II), Ni(II) and Cu(II). Infrared spectroscopy also provided information on the coordination of neutral and anionic ligands through the analysis of the number of diagnostic bands and their frequencies. The correlation between the spectra and the structures was important; the 10 results obtained for complexes of known structures were used to probe the nature of the chromophore or assess the nature of the ligand coordination modes in complexes of unknown structure. The thermal properties of the complexes prepared were measured by DSC (Differential Scanning Calorimetry) and TGA (Thermal Gravimetric Analysis). These techniques were used to determine the thermal stability of the complexes and to yield information on enthalpies of the thermal processes, including melting, polymorphism, phase transitions, and decomposition. C, H, N elemental analyses were obtained routinely as an important means of determining the stoichiometry and purity of the complexes synthesized. The remainder of this chapter will give a brief introduction to some of the techniques mentioned above. Attention is focused on the kind of information that each method provides and, where possible, examples are given when the particular technique has been used in earlier work. 1.2.1. Thermal Analysis Two thermal analysis techniques were employed in this work. Thermogravimetric analysis (TGA) records the change of weight of a sample as a function of either temperature or time, while differential scanning calorimetry (DSC), measures the enthalpy changes that occur in a sample as a function of either temperature or time. Earlier work involving thermal analysis of metal phosphinates showed their stabilities to be greatly reduced by the introduction of phosphinates containing long chain alkyl groups. For instance, Cr[(CH 3 ) (C6H 5)P0 2 ]3 undergoes its major weight loss, under nitrogen, at 480 °C; however, replacement of one methylphenyl phosphinate ligand with a di-n-hexylphosphinate ligand reduces that temperature to 265 °C (65). This phenomenon 11 has been attributed to the greater ease of oxidation of the longer alkyl chains. Phenyl groups on the phosphorus can stabilize the complexes. The thermal stability of binary metal diphenylphosphinates, M[(C6H5)2P02]2 (M = Co, Zn or Mn), show initial weight loss at temperatures of about 500 °C (41, 66, 67), while the corresponding dimethyl phosphinates, decompose at temperatures below 350 °C (68), and the monophenylphosphinates at temperatures below 300 °C (26, 27, 51). DSC studies can also provide important information. The shape of the DSC melting curve (whether it exhibits a broad or a sharp melting curve) for a sample can give an indication of the distribution of molecular weights present in a given sample; the narrower the distribution, the sharper the melting point. The DSC technique can also be used to investigate the phenomenon of polymorphism which is often seen in bivalent metal phosphinates. Different forms for the same complex normally have a different DSC thermogram and conversion of one polymorph into another can be studied by this DSC technique. Several factors may cause a given polymer to exist in different forms, for example, i) the compound crystallizes in slightly different ways, yielding the same basic polymeric structure but a different unit cell, ii) there may be differences in the orientation of the organic groups attached to phosphorus, yielding different polymeric structures and iii) there may be differences in the coordination number or geometry of the metal from one form to another. For example, nickel(II) di-n-butyl and di-n-octyl phosphinates, can be obtained in different forms (69, 70). Direct preparation gives octahedral compounds containing unsymmetrically bridged phosphinate ligands; however, upon melting, the octahedral compounds can be converted into tetrahedral ones containing symmetrically 12 bridged phosphinates. In some cases, different preparative routes yield different forms for a given polymer. In the preparation of cobalt(II) methylphenylphosphinate, different solvents can produce different forms of the compound. P-Co[(CH3)(C6H5)P02]2 (66), which melts at 210 °C, is obtained in ethanol, while y-Co[(CH3)(C6H5)P02]2, which melts at 226 °C, is obtained in benzene. Cu(R2P02)2 (R = n-C8Hi7, n-Ci0H2i or n-Ci2H25), exist in two forms. The a-forms, have higher melting points (120 to 130 °C) and are obtained by direct synthesis in solution, while the P-forms, which have lower melting points (90 to 100 °C), are obtained by conversion from the corresponding a-forms on melting the sample (46). 1.2.2. Infrared Spectroscopy Infrared spectroscopy probes molecular vibrations and can provide information about the coordination mode(s) of the ligands in complexes, the stereochemistry around the metal, and the strength of metal-ligand interactions (71-73). Phosphinate ligands, RR'P02", considered in this work have a maximum free ion symmetry of C2v A total of nine fundamental vibrations are expected (4 Ai, 1 A 2 , 2 Bi, 2 B2) for the C2PO2" part of the ligand; none of these are degenerate (74-76) and only one of them, the A 2 (torsion) mode, is infrared inactive. The appearance of this mode is not very useful in assigning coordination details since it appears around 300 cm-1. Infrared spectroscopy has proven to be a useful tool in the characterization of metal phosphinate polymers, despite the fact the ligand has low symmetry in its free anion state. Most of the earlier studies have used P02 symmetric and antisymmetric stretching modes (69, 70, 74, 77-82) as guides in assigning structural details of the complexes. Coordination through oxygen results in a decrease in 13 the frequency of the antisymmetric PO2 stretch and an increase in the frequency of the symmetric stretch, when compared to the free anion (the K or Na salt of the acid). Also, larger frequency shifts were observed for bidentate coordination than those for monodentate coordination (71, 74-76, 82-89). The frequency difference between the symmetric and antisymmetric PO2 stretches, A = v a n t i . - v s y m . , has been used to indicate the coordination mode of the phosphinate and hence the geometry about the metal (73, 79). Similar studies involving C 0 2 stretching frequencies in carboxylate complexes have been reported (90). Coordination number and stereochemistry of the metal involved and the nature of the substituents on phosphorus are some of the factors in determining the binding manner of phosphinate ligands. Some of the possible symmetric, unsymmetric and bridging coordination modes are shown in Figure 1.3 (69, 70, 91). Symmetric bonding (I - IV, Figure 1.3) is expected to yield smaller antisymmetric-symmetric stretching frequency separations than unsymmetric bonding (V - VTTI). Structures I X - X I show polymer structures involving symmetric bonding modes with tetrahedral metal centers. A is around 70 cm"1 for symmetric P 0 2 bonding as in the types IX and X , examples of which have been confirmed by X-ray crystallography. The antisymmetric and symmetric P0 2 stretching vibrations fall into the frequency ranges, 1150 to 1100 and 1065 to 1025 cm"1, respectively for these systems. Metal phosphinates with unsymmetric P 0 2 bonding, are characterized by values of A that are much larger than those encountered in symmetric bonding, ranging up to 120 cm"1. The frequencies are typically about 1100 cm"1 for 14 antisymmetric P0 2 stretching and about 990 cm"1 for symmetric P0 2 stretching, respectively. Polymorphism is common in phosphinate coordination polymers and infrared spectroscopy has been used to identify different polymorphs in addition to the X-ray powder diffraction technique. For example some copper(II) phosphinates have been synthesized in a- and P-forms (46). IR spectra showed the value of A to be almost the same for the two forms. However, examination of the PC 2 stretching region revealed significant difference between a- and P-forms. The former showed a broad, medium intensity band corresponding to the antisymmetric PC 2 stretching frequency in the 770-775 cm"1 region.. Conversely, in the P form, this band occurs at about 805 cm'1 and is significantly narrower. 1.2.3. Electronic Spectroscopy For "free" transition metal ions, the five d-orbitals are degenerate. The degeneracy is lifted when the metal ions are coordinated to ligands; different coordination geometries causing the d-orbital to be split differently in terms of orbital energies and their sequence. These energies and sequences may be determined through UV-Vis-NIR spectroscopy and in so doing the nature of the metal chromophore of the metals may be deduced. In the present work, UV-Vis-NIR spectroscopy was found to be very useful in the characterization of nickel(II), cobalt(II) and, to a lesser extent, copper(II) complexes. No electronic spectra were obtained for the manganese complexes studied here. Spin-free manganese(II) complexes have a 6A ground state and electronic transitions are formally 15 Examples of symmetric POi bonding: \ / \ / V \ / / P \ / P \ n / p \ n / p \ ^ I 1 M M A m m 0 . m I II III IV Examples of unsymmetric PO7 bonding: V / V \/ P^  \ / > c >C X ^ o M M M V VI VII VIII Possible polymer structures: Symmetric: \/ \ / \ / \ / / P \ .1' \ . / ° ^ M ^ O — P — O - M LX X Figure 1.3. RR'PCV bonding modes and possible polymeric structures, taken from references 69 and 26. (Continued on the next page). 16 Unsymmetric: V V °i 0 : i ( o i 0 . 1 . 0 0 . 1 Q o 1 o 1 I / O I / O 1 0 1 -p ^ p — ° ^ I XIII XIV O. \ / . O - P — O . \ / O — P — 0 \ ! Jd JM' *M' ~M' 1 1 \ / : I \ / 1 1 O . 1 ^O—P—O. 1 / O — P — 0 \ 1 J V L J V L O I O—P^—O I O—P^ — 1 o XV Figure 1.3. (Continued), RR 'P0 2 " bonding modes and possible polymeric structures, taken from references 69 and 26. 17 spin forbidden, resulting in very low intensity bands. Consequently structural information is difficult to obtain from an examination of the electronic spectra of high spin manganese(II) complexes, particularly when dealing with solid state powders as was done in this work. Cobalt(II) is a d7 ion; the ground state is 4F when in the "free ion" state. The higher electronic state with the same spin multiplicity is 4P. B0 (free ion electron repulsion parameter or Racah parameter) and \ 0 (free ion spin-orbit coupling parameter) are 971 and 172 cm"1, respectively (95). In the presence of an octahedral or tetrahedral ligand field, the free ion ground term is split to 4A2(g), 4T2(g), and 4Ti(g) terms and the 4P becomes 4Ti(g) (P) term. In an octahedral ligand field, the ground term is 4TIg. The three spin-allowed transitions one would expect to see in the electronic spectra are to the 4T2g, 4A2g, and 4Tig (P) excited states. In practice, usually only two relatively strong bands are observed due to 4Tig -> 4T2g (vi) and 4Tlg -> 4T/g (P) (v3); the 4T!g -> 4A2g (v2) transition is much weaker because it is formally a two-electron transition: t2g eg t2g eg . The energies are given in terms of the ligand field parameters Dq and B in equations [1.1], [1.2] and [1.3] below (93). vi = 5Dq - 7.5B + 1/2 (225B2 + l00Dq2 +l80DqB)m [1.1] v 2 = 15D9 - 7.5B + 1/2 (22552 + \00Dq2 +\S0DqB)m [1.2] v3 = 1/2 (22552 + \00Dq2 +\80DqB)m [1.3] For tetrahedral cobalt(II), the ground state term is 4A2. The three spin-allowed transitions are % "> 4T2 (vi), % ^ % (F) (v2) and 4A2 ^ 4T, (P) (v3). Because of its 18 low energy, V i generally occurs in the near-infrared or infrared regions and is often not reported. The relations between transition energies and Dq and B are given below (80). V i = 10A, [1.4] v 2 = \5Dq + 7.5B - 1/2 (225B2 + 100£>?2 - \80DqB)112 [1.5] v3 = l5Dq + 7.5B + 1/2 (225B2 + 100D2 - 180A,B)m [1.6] The values of Dq and B can be calculated for tetrahedral cobalt(II) by the following equations (94): 340 Dq2 - 18(v2 + v3) Dq +v2 v3 = 0 [1.7] B= (v2 + v3 -30 A , ) / 15 [1.8] Nickel(II) has a d8 electronic configuration. In the "free ion", the ground state is 3F with a higher 3P state. The values of B0 and X0 are 1080 and 172 cm"1, repectively. In the presence of an octahedral or tetrahedral ligand field, the free ion ground term is split into 3A2(gj, 3T2(g), and 3Ti(g) terms and the 3P term becomes a 3Ti(g> (P) term. In an octahedral field, three transitions are expected in the electronic spectrum. These are 3A2g 3T2g (vi) , 3A2g 3Tig (v2), and 3A2g -> 3Tig (P) (v3). The transition energies as functions of Dq and B can be calculated as in the cobalt(II) tetrahedral case or by using V i as \QDq, and then calculating B from v2 and v3. Tetrahedral nickel(II) phosphinate complexes are relatively rare compared to octahedral complexes although several have been prepared here and elsewhere. The free-ion 3F ground term in tetrahedral fields is split into three states, the order of the energy states is the inverse of the order spliting in an octahedral field. Hence, 19 in the electronic spectrum, the three expected transitions are 3T, (F) -> 3T2 (vi) , -> 3A2 (v 2 ) , and 3T\ (P) (v3). Dq and B may be obtained by use of equations [1.1], [1.2] and [1.3]. It should be noted that in tetrahedral complexes of Co(II) and Ni(II), the relaxation of symmetry restrictions on band intensities results in much more intense ligand field bands than observed in octahedral complexes. In addition, in tetrahedral complexes, bands are often split by spin-orbit coupling to such an extent that an unambiguous assignment of the transitions is sometimes impossible. Copper(II), having a d9 configuration should, theoretically, give rise to a simple, spin-allowed, one band spectrum in either octahedral or tetrahedral ligand field, since the splitting of the 2D free ion term, upon complexation, produces 2T2(g) and 2E(g) terms only. In reality, copper(II) is usually found in low symmetry environments (i.e., less than cubic), by virtue of the Jahn-Teller effect, often making detailed correlations of stereochemistry and spectra very difficult. Practically all copper(II) complexes are blue or. green, the color arising from the presence of a broad absorption band typically in the 600 ~ 900 nm region of the spectrum. 1.2.4. Powder X-ray Diffraction The powder X-ray diffraction method was very useful in this work since it could be used to determine whether an unknown compound is isomorphous with a compound with a known structure. 20 1.2.5. Single Crystal X-ray Diffraction Single-crystal X-ray crystallography (95-98) provides the most powerful method available for the direct determination of structures of complexes. The technique yields not only unit cell parameters but also allows for the determination of the atomic coordinates from which bond lengths and angles can be calculated. Thus the combination of the detailed structural information available by this technique with results of cryogenic magnetic susceptibility studies gives us the best foundation for understanding magneto-structural correlations in our systems. Unfortunately, it is often very difficult to obtain suitable single crystals of inorganic polymeric complexes suitable for X-ray diffraction work. In most cases, polycrystalline or X-ray amorphous compounds are obtained; thus, spectroscopic methods have played an important role to indirectly obtain structural information. Early work on metal phosphinates and their structures as determined by single crystal X-ray crystallography was summarized in section 1.1. Two types of phosphinate bridging have been reported: (i) alternate single-triple phosphinate bridges, (ii) double phosphinate bridges. The coordination around the metal ions has been shown to adopt a tetrahedral, square planar or octahedral geometry. In adduct complexes of metal phosphinates, polymeric linear chains are present consisting of metal ions linked by double-bridged phosphinate ligands and coordinated axially by additional neutral ligands, producing an octahedral coordination around the metal ions. In the present work another type of bridge involving triple bridging phosphinates has been observed in a manganese trimetallic complex. In the present work, also, a novel form of phosphinate bridging in which the 21 phosphinate ligand binds to one metal through one of its oxygens and to two different metals through the other oxygen was observed in copper(II) dimethylphosphinate. This work will be discussed in later chapters. 1.2.6. Magnetic Susceptibility Studies Magnetic susceptibility studies involve the measurement and analysis of the response of a material to the presence of a magnetic field. Many general reviews are available which describe various experimental techniques (99-104), methods of theoretical analysis (104-108), and surveys of literature reports (52, 109-113). Traditionally magnetic susceptibility measurements on transition metal complexes have been made on monometallic complexes and have been used for structural elucidation through the correlation of the magnitude of the effective magnetic moment with the metal's oxidation state and stereochemistry. In contrast, the work described in this thesis is directed towards obtaining a better understanding of the magnetic properties of extended polymetallic systems, the structures of which are elucidated by other techniques. At the simplest level, all matter may be divided into two categories, diamagnetic and paramagnetic. Diamagnetism is characterized by all electron spins paired in the molecule. The magnetic susceptibility of such systems is negative and is of the order of 1 x 10"6 cm3 mol"1. Paramagnetism is characterized by unpaired electron spins in the molecule and positive susceptibilities of the order of 10"3 cm3 mol"1 or higher depending on the system. If there are no interactions between spins of neighboring paramagnetic ions, the system is called "magnetically dilute", and it exhibits single ion susceptibilities. In the presence of 22 interactions between spins of neighboring paramagnetic ions, the system is called "magnetically concentrated" and behaviours other than that of single ion behaviours are observed. Two common forms of interaction are: (i) ferromagnetic, when the spins orient themselves parallel to one another and (ii) antiferromagnetic (or sometimes ferrimagnetic when a system has alternating ions each with different spin), when the spins orient themselves antiparallel to one another (114). The present work is aimed at studying the correlation between structure and magnetism in magnetically concentrated systems, specifically those systems in which transition metal ions in paramagnetic ground states are bridged by phosphinate ligands. The following gives a brief description of the magnetic properties to be expected of magnetically dilute complexes of manganese(II), cobalt(II), nickel(II) and copper(II). The spin-free manganese(II) ion has five unpaired electrons, with 6Ai(g) as the electronic ground state in octahedral or tetrahedral geometry. The g value is isotropic at about 2.00. Zero-field splitting is usually very small and the ground state is well isolated from higher energy levels. In a magnetically dilute system, the magnetic moment is the spin-only value of 5.92 u,B and is independent of temperature. Any deviation from this (except possibly at very low temperature) is indicative of magnetic coupling. Cobalt(II) has a d7 electron configuration. For the high-spin situation, the ground state for an octahedral crystal field is 4Ttg and an important orbital contribution to the magnetic moment is expected. The moment at room temperature is typically around 5.2 u,B, falling as the temperature decreases. This temperature dependence makes the identification and 23 interpretation of magnetic exchange effects in octahedral complexes rather difficult. This matter is dealt with in more detail at appropriate points later in this thesis. In a tetrahedral ligand field, a 4A2 ground state results. Since there is no orbital angular momentum associated with this term to first order, the moment is expected to be close to, but slightly higher than, the spin-only value and to be temperature independent except possibly at low temperatures where zero-field splitting effects become important. In octahedral ligand fields, the ground term of nickel(II) complexes is 3A2g and, as for tetrahedral cobalt(II) described above, the magnetic moment is expected to be slightly higher than the spin-only value and to be temperature independent except possibly at low temperatures. In tetrahedral ligand fields, the nickel(II) ion has a sTi ground state and would be expected to exhibit a temperature dependent magnetic moment as described above for octahedral cobalt(II). Copper(II) ion has a d9 electron configuration. For an octahedral copper(II) complex, a 2Eg ground state results and its moment is expected to be close to but slightly higher than the spin-only value and to be independent of temperature. Tetrahedral compounds would have a 2T2 ground state, which would be expected to result in an orbital contribution to the moment. Copper(II) complexes tend to be distorted and generally exhibit temperature independent moments slightly larger than the spin-only value. A temperature dependent moment usually indicates the presence of magnetic exchange in copper complexes. Methods used for magnetic susceptibility measurements can be divided into two basic categories: force methods and induction methods. The commonly used techniques involving force methods are the Gouy and Faraday techniques (115-118). These methods 24 are based on the fact that when a material is placed in an inhomogeneous magnetic field it experiences a force into the region of higher field for paramagnetic samples and away from the region of higher field for diamagnetic samples. Induction methods, on the other hand, are based on the principle that materials placed in an applied field produce an induced field which in turn induces a voltage change in an induction detection coil. This voltage change detected by the instrument is proportional to the magnetic susceptibility of the material. Two instruments based on induction methods were used in this work, a Vibrating Sample Magnetometer (VSM) and a Superconducting Quantum Interference Device (SQUID) Magnetometer (117). The principles involved in magnetic measurements are briefly described below. When a substance is placed in a magnetic field, H, the field within the substance, B which is different from the applied field, H, will be expressed as: where I is the intensity of magnetization. The ratio of B/H is the magnetic permeability and I/H, K, is the magnetic susceptibility per unit volume: In practice, magnetic susceptibility is usually expressed per unit mass, %s, or per mole, X M : B = H + 4TCI [1.9] B/H = 1 + 4%K [1.10] [111] XM = Xg M.W. [1.12] 25 where p is the density of the sample and M.W. is the molecular weight of the sample. The effective moment can be calculated as follows: u e f f=(3k/Np 2) 1 / 2(XMT) 1 / 2 [1.13] where N is Avogadro's number, P is the Bohr magneton and k is Boltzman's constant. Substituting values of constants into equation [1.13] yields, u e f f= 2.828 ( X M T ) 1 / 2 [1.14] For magnetically concentrated systems, the magnetic interaction between paramagnetic centers may be estimated by a theoretical model. If the total spins for the neighboring paramagnetic ions are S; and Sj, the interactions may be represented by the spin Hamiltonian (108): H = -2 [a S iz Sjz + b (Six Sjx + S iy Sjy)] ( i* j) [1.15] where J is the exchange constant and its magnitude is a measure of the strength of the interaction. The parameters a and b are the parallel and perpendicular anisotropy parameters, respectively, and can vary independently between the values of zero and one. In the limiting case when a = b = 1, the Heisenberg model for magnetic exchange is obtained; this is the case for most of the complexes studied in this work. If a = 1 and b = 0, the Ising model for magnetic exchange is obtained whereas the limit in which a = 0 and b = 1 gives the X-Y model for magnetic exchange (108). Data collected in magnetic measurements are analyzed according to appropriate models and J values are obtained. More detail concerning this procedure is given at appropriate places in the thesis. 26 1.3. Objectives and Organization of the Thesis The objectives of this work are (i) to extend the earlier work in our laboratory on transition metal (Cu, Ni, Co, Mn) phosphinate complexes to include other phosphinates such as fluorinated derivatives, (ii) to extend the study of "adduct polymers" of monophenylphosphinate using neutral ligands such as HCONHCH 3, DMSO and H(C6H5)P02H. A major goal is to explore magneto-structural correlations for the complexes under investigation. A general introduction which includes a description of the historical development of metal phosphinate chemistry was given in this chapter, along with a description of how a variety of physical techniques may be used to characterize coordination complexes. Binary transition-metal phosphinates with the general formula of M(RR'P02)2, where M = Mn, Ni, Co, Cu; R, R' = CH 3 , C 2 H 5 , C 6 H 5 , C 6F 5 , n-C 8 H n , CF 3(CF 2) 3CH 2CH 2 and CF 3(CF 2) 5CH 2CH 2 were prepared in the present study. Chapters 2, 3, 4 and 5 are organized to discuss the complexes of copper, manganese, cobalt and nickel, respectively. Each chapter begins with a description of the experimental procedures used for the preparation of the compounds. Following this, the results of compound characterization studies are presented and interpreted. In some cases, the structures were clearly identified by single crystal X-ray structure determinations; in the absence of such conclusive evidence, the proposed structures based upon spectroscopic evidence and X-ray powder diffraction studies are presented. In all cases the magnetic properties were investigated over the temperature range 4-80 K (some studies were made over the temperature range 1.8 K to 300 K) and magneto-structural correlations are discussed. Chapter 6 will describe 27 research on some miscellaneous compounds, while experimental details are presented in Chapter 7. 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Carlin, Magnetochemistry, Springer-Verlag, Berlin, Heidelberg, 1986. 34 Chapter 2 Copper(II) Phosphinates 2.1. Introduction There have been earlier studies on copper(II) phosphinates in our lab and elsewhere. Several crystal structures of this type of complex have been solved (1-4), revealing linear chain polymeric structures with metal ions linked by double-bridged phosphinate anions. Both flattened tetrahedral (1-3) and square planar (4) chromophores around the metal ions have been observed. These materials exhibit either ferromagnetic or antiferromagnetic exchange interactions. Variable temperature magnetic behavior of most of these compounds agreed well with that predicated by theory for extended chains of S = 1/2 metal ions (5). Copper(II) dimethylphosphinate was one of the exceptional compounds studied in the earlier work (6), its variable temperature susceptibilities being at variance from theory for linear chain structures which most copper(II) phosphinates have. In the present work this compound was obtained in crystalline form suitable for single crystal X-ray diffraction studies. With the help of the detailed structure, its magnetic susceptibilities have been analyzed successfully by an appropriate model. It has been shown (7-9) that the electronegativity of substituents on bridging atom(s) affects the magnitude of J in exchange coupled systems by causing changes in the electron density present in the bridge. In order to examine the influence of fluorinated substituents on phosphinate ligands, acting as bridging units, on magnetic properties, complexes of Cu{[n-CF3(CF2)3CH2CH2]2P02}2 and Cu([n-CF3(CF2)5CH2CH2]2P02}2 were synthesized and studied. Comparisons are made with the corresponding perhydro-derivatives, Cu[(n-35 C6Hi3)2PO]2 and Cu[(n-C8Hi7)2PO]2 which had been studied and reported before (3, 10). Cu[(C6H5)2P02]2, which structural studies show it has a linear chain structure with square planar Q1O4 chromophores (4), exhibits ferromagnetic behaviour (11). It was shown (11) that this geometry provides only a c orbital pathway and this was considered to be the cause of the observed ferromagnetism. Two related fluorinated phenyl compounds, Cu[(C6F5)2P02]2 and Cu[(C6H5)(C6F5)P02]2, were obtained in the present work and were studied with the objective of examining the effect of fluorination on the magnetic properties of copper(II) diphenylphosphinate. The mixed substituent compound, Cu[(CH3)(C2H5)P02]2, has been synthesized and characterized here. Previous studies indicated that the longer is the alkyl group attached to phosphorus, the stronger is the antiferromagnetic coupling. For example, Cu[(C2H5)2P02]2 (3) has \J\ = 1.27 cm"1 while \J\ values for Cu[(n-C8H i7)2PO]2 and Cu[(n-Ci0H2i)2PO]2 are 25 and 29 cm"1, respectively (10). If Cu[(CH3)(C2H5)P02]2 follows this trend, it should exhibit very weak antiferromagnetic behaviour with \J\ less than 1.3 cm"1. 2.2. Results and Discussion 2.2.1. Syntheses and Thermal Properties Detailed descriptions of the synthetic procedures used to obtain the binary copper(II) phosphinates are given in Chapter 7. The general methods are summarized in the equations below. Usually the appropriate phosphinic acid was first partially neutralized with a base (triethylamine or sodium hydroxide), and the appropriate copper(II) salt was added to the solution, resulting in a precipitate from a solution of acetone, diethyl ether, or water. 36 Acetone 3x Cu(N03)2.3H20 + 6x (CH 3) 2P0 2H + 6x (C 2H 5) 3N p M p • {Cu3[(CH3)2P02]6}x+ 9 H 2 0 + 6x [(C2H5)3NH+][N03~] [2.1] Diethyl Ether Cu(CH3COO)2-H20 + 2(C6H5)(C6F5)P02H [2.2] Cu[(C6H5)(C6F5)P02]2 + H 2 0 + 2CH 3COOH H 2 0 Cu(C104)2.6H20 + (C6F 5)2P 0 2 K Cu[(C6F5)2P02]2 + 6H 20 + 2KC104 P " 3 ! Cu(N03)2 -3H 20 + 2[(CF3(CF2)3CH2CH2]2P 0 2 H + 2NaOH H20/Ethanol — - Cu{[CF3(CF2)3CH2CH2]2P 0 2} 2 + 5H20 + 2NaN03 [2.4] Cu[(CH3)(C2H5)P02]2 was obtained by the method described in equation [2.1]. Cu{[n-CF3(CF2)5CH2CH2]2P02}2 (Form I) was prepared as described in equation [2.4] and Form II of the compound was obtained by heating Form I at 115 °C for several hours. The results of thermal analyses are given in Table 2.1 and the DSC thermograms for Cu{[n-CF3(CF2)3CH2CH2]2P02}2 and both forms of Cu{[n-CF3(CF2)5CH2CH2]2P02}2 are shown in Figure 2.2. A representative TGA curve for Cu{[n-CF3(CF2)3CH2CH2]2P02}2 is shown in Figure 2.1. As shown in Table 2.1, all seven compounds are thermally stable to at least 270 °C. The fluorinated octyl and hexyl derivatives (which begin to decompose at temperatures around 310 °C) are more stable than the corresponding perhydro-derivatives (which decompose at around 260 °C) (6). However, Cu[(C6H5)2P02]2 (11) and Cu[(C6F5)2P02]2 have almost the same thermal stability. They decompose at 320 and 325 °C, respectively while the mixed phenyl/perfluorophenyl copper(II) complex decomposes 37 at 287 °C. The DSC thermograms of the copper(II) complexes show exothermic decomposition peaks. Exceptions are the two fluorinated octyl copper(II) complexes (Form I and Form II) which exhibit endothermic peaks on decomposition (Figure 2.2). DSC studies on copper(II) dimethylphosphinate reveal an endothermic peak at 251 °C. After heating the sample to 270 °C, followed by cooling to room temperature and then reheating to 270 °C, the endothermic peak at 251 °C reappears. This is termed reversible behaviour in Table 2.1. Such phenomena are usually associated with melting or phase transitions. Features designated as irreversible in Table 2.1 are those which did not reappear after cooling to room temperature and reheating. For example, DSC thermograms of Form I of Cu{[CF3(CF2)5CH2CH2]2P02}2 show an endothermic peak at 100 °C. After heating a sample to 130 °C, cooling to room temperature and then reheating, the event at 100 °C does not reappear. This behaviour suggests the existence of an irreversible phase transition. DSC studies showed the first thermal event for Cu{[CF3(CF2)5CH2CH2]2P02}2 at 100 °C is irreversible (Table 2.1), indicating that another form of this compound exists. This form, termed Form II, can be obtained by heating Form I to a temperature above the transition temperature of 100 °C. 38 Table 2.1. Thermal parameters for copper(II) phosphinates. Complexes Temp. (°C) AH (k/mol"1) Comments {Cu3[(CH3)2P02]6}s 251 295 147 Endothermic, R Exothermic* Cu[(CH3)(C2H5)P02]2 84 212 270 10 6 Endothermic, I Endothermic, R Exothermic Cu[(C6F5)2P02]2 Cu[(C6H5)(C6F5)P02]2 252 325 267 287 50 Endothermic, R Exothermic* Endothermic, R Exothermic* Cu([CF3(CF2)3CH2CH2]2P02}2 92 123 336 40 25 Endothermic, R Endothermic, R Exothermic* Cu{[CF3(CF2)5CH2CH2]2P02}2 (Form I) 100 158 310 60 43 Endothermic, I Endothermic, R Endotheric* Cu{[CF3(CF2)5CH2CH2]2P02}2 158 (Form II) 310 42 Endothermic, R Endothermic" a R is Reversible, see text for definition. Compound begins to decompose. I is Irreversible, see text for definition. This peak reappeared when the sample temperature for several days (see text). was rerun after it had been kept at room 39 Cu{[CF3(CF2)3CH2CH2]2P02}2 has a similar DSC curve to that of the Form I complex of Cu{[CF3(CF2)5CH2CH2]2P02}2 below 200 °C, both having two endothermic peaks. When a sample of the former compound is heated to 110 °C, cooled to room temperature and then reheated to 110 °C the peak at 92 °C does not appear, again suggesting the presence of a second form of this compound. However, when allowed to stand at room temperature for extended periods of time the 92 °C event reappears (at least partially). This suggests the second form of this compound is not thermodynamically stable and reverts slowly at room temperature to the initial form. Indeed, the second form of this compound has never been obtained in a pure form in this work. 120 100 80 6s 60 +-» 1-*— bp '5 40 20 0 0 100 200 300 400 500 600 700 800 Temperature (°C) Figure 2.1. TGA thermogram of Cu{[CF3(CF2)3CH2CH2]2P02}2. 40 Temperature C Q Figure 2.2. DSC thermograms for (a) Cu{[CF3(CF2)3CH2CH2]2P02}2 (b) Cu{[CF3(CF2)5CH2CH2]2P02}2 (Form I) (c) Cu{[CF3(CF2)5CH2CH2]2P02}2 (Form II) 41 2.2.2. Single Crystal X-ray Diffraction 2.2.2.1. Structure of copper(II) dimethylphosphinate, {CusKCFts^ PCbJelx All X-ray determined structures of binary diorganophosphinates of copper(II) reported to date have revealed linear chains with metal ions doubly bridged by phosphinate groups. In this respect, the structure of copper(II) dimethylphosphinate is unique consisting of trimetallic units linked in extended chains. Crystallographic data for {Cu3[(CH3)2P02]6}x are given in the Appendix and some bond distances and angles are given in Table 2.2. Figure 2.3 shows a section of a chain with trimetallic units linked via phosphinate 0(2) atoms to Cu(2) atoms on neighbouring units. Figure 2.4 gives details of the structure of the trimetallic unit which has exact C2 symmetry with Cu(l) located on the two-fold axis. The unique Cu(l) is in a distorted square planar environment of oxygens from four different bridging phosphinate groups. These groups, in pairs, link the unique copper to the other two copper ions, Cu(2). The two phosphinate groups in a pair are different. One, containing P(2), is only involved in the single intra-trimer bridging interaction, while the other, containing P(l), is also involved, via 0(2), in inter-trimer bridging to a Cu(2) atom of a neighbouring trimer. The form of coordination shown by the latter phosphinate in which it bridges three metals is rare although it has been reported previously (12). The two Cu(2) atoms in a given trimetallic unit are bridged by two identical phosphinate groups (containing P(3)). Because of their involvement in the inter-trimetallic interactions each Cu(2) atom is bonded to five oxygens in a distorted square pyramidal environment. The extent of the distortion is clear from an examination of bond lengths and angles (Table 2.2). Of particular note are the Cu(2)-0 bond lengths. The four distances forming the base of the pyramid are on average 1.948(8) A, comparable to the average of the Cu(l)-0 42 distances (1.924(4) A) and the average Cu-0 distances in Cu[(C2H5)2P02]2 (2) and Cu[(C6H13)2P02]2 (3) (1.918(1) A and 1.907(3) A, respectively), while the axial Cu(2)-0(2) distance is, at 2.505(2) A, considerably longer. Table 2.2. Selected bond lengths (A) and angles (deg) for {Cu3[(CH3)2P02]6}x* Bond lengths Cu(l)-0(1) 1.918(2) Cu(l)—0(3) 1.929(2) Cu(2)—0(2) 1.965(2) Cu(2)—0(2)a 2.505(2) Cu(2)—0(4) 1.938(2) Cu(2)—0(5) 1.932(2) Cu(2>—0(6)b 1.955(2) Bond angles O(l ) -Cu(l ) -O(l ) 4 162.5(1) 0(1)—Cu(l)—0(3) 92.89(8) 0(1)—Cu(l)—0(3)* 89.89(8) 0(3)—Cu(l)—0(3) 161.6(1) 0(2)—Cu(2>-0(2)fl 73.46(7) 0(2)—Cu(2)—0(4) 93.17(8) 0(2)—Cu(2)—0(5) 170.39(8) 0(2)—Cu(2)—0(6)* 93.77(8) 0(2)"—Cu(2)—0(4) 104.10(8) 0(2)°—Cu(2)—0(5) 97.07(7) 0(2f—Cu(2>—0(6)* ' 103.86(7) 0(4)—Cu(2)—0(5) 87.53(8) 0(4)—Cu(2)—0(6)* 152.03(9) 0(5)—Cu(2)—0(6)0 90.04(8) * Superscripts refer to symmetry operations: a 1 - x, 1 - y, -z; b 1 - x, y, 1/2 - z. 43 Figure 2.3. Stereoview of a section of the chain and atom numbering scheme for {Cu3[(CH3)2P02]6}x; 33% probability thermal ellipsoids are shown. 44 Figure 2.4. View of the trimetallic unit for {Cu3[(CH3)2P02]6} x. 33% probability thermal ellipsoids are shown. 2.2.3. X-ray Powder Diffraction Diffraction patterns for all the compounds described in this Chapter are given in Figure 2.5. The patterns indicate that Cu[(C6F5)2P02]2 and Cu[(C6H5)(C6F5)P02]2 are isomorphous. No other examples of isomorphism are indicated in the powder diffraction patterns of the other complexes. Importantly, the X-ray powder diffraction patterns of Form I and Form II of Cu{[CF3(CF2)5CH2CH2]2P02}2 are distinct. 45 a JL«..-...,,. A. »,„ ss i-= J ^ X w - A AA. II i I I I | | I | ! I I I I I I • I I •• I I I I I I I I • I I I I I I I I I I I I I 1 I I I I I I I I I I I I I 5 10 15 20 25 30 35 40 45 50 55 60 2 0 Figure 2.5. X-ray powder diffraction patterns for a) {Cu3[(CH3)2P02]6}x, b) Cu[(CH3)(C2H5)P02]2, c) Cu[(C 6F 5) 2P0 2] 2, d) Cu[(C 6H 5)(C 6F 5)P0 2] 2, e) Cu{[CF 3(CF 2) 3CH 2CH 2] 2P0 2} 2, f) Cu{[CF 3(CF 2) 5CH 2CH 2] 2P0 2} 2 (Form I) and g) Cu{ [CF 3(CF 2) 5CH 2CH 2] 2P0 2} 2 (Form II). 46 2.2.4. Infrared Spectroscopy Infrared spectroscopy was routinely used in this work as the initial test of product purity. We will concentrate here on the P 0 2 stretching vibrations of the phosphinate ligands. The infrared data for these vibrations are listed in Table 2.3 and the spectra over the frequency range 400 to 1800 cm"1 for all the copper(II) complexes except Cu{[CF3(CF2)3CH2CH2]2P02}2 are shown in Figures 2.6 to 2.8. According to previous studies (13-15), the difference between the antisymmetric and symmetric P 0 2 stretching frequencies, A (vP0 2 anti. - VPO2 sym.), can be used to judge the bond type of the O-P-0 bridges in the complexes. Thus some structural information may be obtained. The infrared spectrum of copper(II) dimethylphosphinate shows that there are two types of O-P-0 bridges as evidenced by two antisymmetric and two symmetric stretches at 1159, 1108 and 1055, 1032 cm"1, respectively (see Figure 2.6). The separations between the bands, A, are 104 and 76 cm"1, with the former falling into the range expected for nonequivalent P-0 bonds and the latter for equivalent P-0 bonds (11, 16, 17). Three types of O-P-0 bridges were also observed in the detailed structure determined by single crystal X-ray diffraction studies. The difference in P-0 bond lengths is 0.008 (4) A in the 0(l)-P(l)-0(2) bridge and 0.015(4) A in the 0(3)-P(2)-0(4) bridge. More than one type of phosphinate may also be present in Cu[(C6H5)(C6F5)P02]2 as evidenced by its infrared spectrum (Table 2.3). The infrared spectra of other copper(II) complexes studied in this work have relatively small A values, indicating that they have symmetric O-P-0 units, similar to those in copper(II) phosphinates studied by others (2, 3, 11). Because of the complexity of the 47 spectra in the 900-1300 cm"1 region no attempt was made to assign PO2 stretching frequencies in the case of the fluorinated octyl and hexyl derivatives. Table 2.3. Selected infrared data (cm"1) for copper(II) phosphinates*. Complexes v(P02 anti.) v(P02 sym.) A^m"1) {Cu3[(CH3)2P02]6}x 1159vs 1055vs 104 1108vs 1032vs 76 Cu[(CH3)(C2H5)P02]2 1108vs 1052vs 56 Cu[(C6F5)2P02]2 1179vs 1119vs 60 Cu[(C6H5)(C6F5)P02]2 1136s 1054s 82 1101s 1027m 74 Here and elsewhere in this thesis: vs, very strong; s, strong; m, medium; w, weak; vw, very weak; sh, shoulder and b, broad. 48 Peaks due to Nujol are marked by asterisks. 49 Wavenumber (cm*1) Figure 2.7. Infrared spectra of (a) CuKCgFs^POzk and (b) Cu[(C6H5)(C6F5)P02]2. Peaks due to Nujol are marked by asterisks. 50 Wavenumber (cm") Figure 2.8. Infrared spectra of (a) Cu{[CF3(CF2)5CH2CH2]2P02}2 (Form I) and (b) Cu{[CF3(CF2)5CH2CH2]2P02}2 (Form II). Peaks due to Nujol are marked by asterisks. 51 2.2.5. Electronic Spectroscopy All the copper(II) phosphinates prepared in this work are blue in color except for form II of Cu{[CF3(CF2)5CH2CH2]2P02}2 which is green. The electronic spectra of the complexes were measured over the range 400 nm to 2000 nm and absorption maxima are listed in Table 2.4. Representative spectra are shown in Figure 2.9. Table 2.4. Electronic spectra data for copper(II) phosphinates. Complexes Peak maximum (nm) (cm1 in brackets) {Cu3[(CH3)2P02]6}x Cu[(CH3)(C2H5)P02]2 Cu[(C6F5)2P02]2 Cu[(C6H5)(C6F5)P02]2 Cu{ [CF3(CF2)3CH2CH2]2P02}2 Cu{ [CF3(CF2)5CH2CH2]2P02}2 (Form I) Cu{ [CF3(CF2)5CH2CH2]2P02}2 (Form II) 790br(12, 700) 795br(12, 600) 600 (16, 700), 680sh (14, 700) 850sh(ll, 800) 780s (12, 800), 970sh (10, 300) 580s (17, 200), 640sh (15, 600) 840sh(ll, 900) 580s (17, 200), 636sh (15, 700) 800sh (12, 500) 800s (12, 500), 920sh (10, 900) 52 Previously studied copper(II) dialkylphosphinates, which have compressed tetrahedral geometries (D2d symmetry), are characterized by broad absorption maxima in the 11, 400 to 12, 300 cm"1 region with shoulders around 13, 200 to 14, 400 cm"1 (11). These bands have been assigned to the 2B2 ~> 2Ah 2E transition (these two transitions are too close to be resolved) with the shoulder assigned to the 2B2 -> 2Bi transition (2, 3). Four of the complexes studied here, copper(II) dimethylphosphinate, methylethylphosphinate, phenylperfluorophenylphosphinate and fluorinated-n-octylphosphinate (Form II), show peak maxima in the 12, 500 to 12, 800 cm"1 region, suggesting that they may also have compressed tetrahedral chromophore geometry; although, unlike the previously studied complexes, none shows resolved shoulders at higher frequencies. Interestingly, the structure of the dimethylphosphinate derivative reveals that only a third of the copper(II) ions have the suggested compressed tetrahedral geometry while two thirds of the copper(II) ions have distorted square pyramidal geometries. Clearly the broad band centered at 12, 700 cm"1, which is observed in the electronic spectrum of this compound, arises from the overlap of several transitions arising from copper ions in two different highly distorted environments. The other three complexes, copper(II) bis(perfluorophenyl)phosphinate, fluorinated-n-hexylphosphinate and fluorinated-n-octylphosphinate (Form I), are all characterized by a principal absorption band at relatively high energy (ranging from 16, 700 to 17, 200 cm"1), with two shoulders at lower frequencies. These spectra are quite different from those described above but show remarkable similarity to the reported spectra of copper(II) diphenylphosphinate (11). This compound, which has square planar chromophore 53 geometry, exhibits band maxima at 11, 500, 14, 900 cm"1 and 16, 400 cm"1 (assigned to 2B2 -> 2Ai, 2Bi and 2E transitions, respectively). This suggests that the three compounds considered here may either have square planar Cu0 4 chromophores, or also distorted tetrahedral geometries which are more compressed than those of the other four complexes. 400 600 800 1000 1200 1400 1600 1800 2000 Wavelength (nm) Figure 2.9. Electronic spectra of Cu[(C6F5)2P02]2 and Cu[(CH3)(C2H5)P02]2. 54 2.2.6. EPR Spectra The g values obtained for these complexes are presented in Table 2.5. Cu[C6H5)2P02]2 exhibits a normal axial symmetry spectrum (g[{ » gi > 2.04), indicative of a dx2.y2 ground state for Cu(II) ion (18). This result is consistent with square-planar Cu0 4 chromophores as determined by single crystal X-ray diffraction studies (4). The complexes containing phosphinate with fiuorinated substituents, CulXCeFs^PC^k and Cu[(C6H5)(C6F5)P02]2, exhibit similar EPR spectra, with broad, asymmetrical, and only partly resolved, resonances (Figure 2.10). The assignments as axial spectra given in Table 2.5 should be considered tentative. These compounds clearly do not have square planar Cu0 4 chromophores of the type seen in Cu[(C6H5)2P02]2- The EPR spectra do suggest however that the chromophores are similar for the two fiuorinated compounds. Table 2.5. EPR spectral data for copper(II) phosphinates". Compound g\\ g± gb Cu[C6H5)2P02]2 2.381 2.047 2.158 Cu[(C6F5)2P02]2 2.256 2.077 2.137 Cu[(C6H5)(C6F5)P02]2 2.218 .2.078 2.125 a Data collected at ~ 120 K. Error in g values, + 0.003. * g (isotropic value) = (g\\ + 2 g±) I 3. 55 Figure 2.10. EPR spectra for (a) CurCsHj^PC^, (b) Cu[(C«F5)2P02]2 and (c) Cu[(C6Hj)(C6F5)P02]2. dA/dH = first derivative of absorption curve. 56 2.2.7. Magnetic Properties and Magneto-structural Correlations Magnetic susceptibility and magnetic moment data for all seven copper(II) phosphinates discussed in this chapter are given in the Appendix. Different compounds with similar magnetic behaviors are grouped together for convenience of discussion. 2.2.7.1. Copper(II) Dimethylphosphinate, {Cu 3[(CH3) 2P0 2]6}x Copper(II) dimethylphosphinate was prepared and studied before and its magnetic data had been fitted to a linear chain model for antiferromagnetic exchange (6). A good fit to theory was obtained with J= -8.5 cm"1, g = 2.19 but with a high paramagnetic impurity (P = 21.7%). This suggested that the assumption that the compound has a linear chain structure was incorrect. The structure of this compound determined in this work and described in Section 2.2.2.1 reveals trimetallic units linked to form extended chains. Compounds containing trimetallic units belong to an interesting class of copper(II) compounds, the structures of which involve linear or triangular trimetallic units. Studies on such systems have revealed magnetic properties ranging from ferromagnetic behavior, as in the recently reported u.3-C032" triangular array complex, (u3-C03)[Cu3(Medpt)3(C104)3](C104) (where Medpt is bis(3-aminopropyl)methylamine) (19), to antiferromagnetic behaviour in a number of complexes. Examples of the latter are the imidazolate-bridged triangular [L3Cu3(Im)3](C104)3 (where L is l,4,7-trimethyl-l,4,7-triazacyclodonane and Im is imidazolate) (20), several reported triangular // 3 -X complexes (21) and the linear trimetallic [Cu(pdz)3(N03)3]2Cu (where pdz is pyridazine) (22). The structure of copper(II) dimethylphosphinate is particularly interesting in that it involves 57 triangular bis(/i-dimethylphosphinato)copper(II) units linked in extended chains. This creates the possibility of additional exchange interactions propagated along the chain. Magnetic susceptibilities were previously measured over the temperature range 4.2 to 80 K using a vibrating sample magnetometer and 80 to 300 K using Gouy equipment (6). These magnetic moment data (per mole of trimetallic unit) are plotted versus temperature in Figure 2.11. Assuming isotropic Heisenberg exchange and the equivalence of g values for an isosceles triangle (ABA) arrangement of three S = 1/2 metal centers the expression for the magnetic susceptibility is (23, 24): Ng2$2 exp(-2 J I k T) + exp(-2 J'/kT) + 10 exp( J I kT) 4kT exp(-2 J I kT) + exp(-2 J'/kT) + 2 exp( J I kT) where J is the exchange integral between the unique copper(II) (compressed tetrahedral ligand chromophore in this compound, see Figure 2.3) and the other two copper(II) ions and J is the exchange integral between the two equivalent copper(II) ions (square pyramidal chromophore in this case), P is the Bohr magneton, k the Boltzman constant, T the temperature in Kelvin, and g the Lande splitting factor. Computer fits were made to the susceptibility data with J and J as the fitting parameters. The best fit was considered to be that set of fitting parameters which gave the minimum value of the deviation, that is, the minimum value of F where F is given by equation [2.6]. F = 1 2~ n X Xcalc. Xobs. j n i=l Xobs. Y2 [2.6] 58 In equation [2.6], n is the number of data points, and x'obs. and x'caic are the experimental and theoretical susceptibilities, respectively. In examining fits of experimental susceptibility to equation [2.5] we fixed g at the value 2.22, determined by EPR (25), and allowed J and J to vary. While reasonable fits between experiment and theory could be obtained the individual J and J had unacceptably high error limits, in effect making the two parameters indistinguishable. Accordingly, we modified equation [2.5] putting J = J. The best fit to this modified equation was obtained with J = -7.4 ±0.3 cm"1 and F = 0.059. There is good agreement between experiment and theory above about 30 K using this model; however, significant deviation occurs in the low temperature region. This is demonstrated most clearly by the magnetic moments plot, shown by the dotted line in the inset in Figure 2.11. The experimental moments at low temperature are significantly less than those calculated by theory, suggesting the presence of an additional source of antiferromagnetic coupling. This most likely arises from coupling between adjacent trimetallic units via the 0(2) oxygen (see Figure 2.3). This oxygen occupies a short-bonded (1.965(2) basal position of one copper and a long-bonded (2.505(2) axial position of the other metal. Such a molecular arrangement is unlikely to result in strong magnetic coupling and we accordingly examined the possibility of allowing for this exchange by employing a molecular field correction to the susceptibilities (26). The expression for this is: 59 where X M ' is the corrected molar susceptibility, z is the number of nearest interacting units, , / m f is the molecular field exchange coupling constant and XM is the susceptibility calculated with equation [2.5], modified by putting J = J. Using the two variable parameters only, J, and z /mf, we obtained a good fit to the data over the whole temperature range studied with the values / = -5.9 ± 0.1 cm"1 and ZJM = -0.27 ± 0.02 cm"1 (F= 0.021 ). These calculated data are shown as solid lines in Figure 2.11. This analysis of the magnetic data seems reasonable particularly since the molecular field correction is less than 10% of the magnitude of J (26). 60 3.5 3.0 09 =L 2.5 ss QJ = © S 2.0 ca WD e s S 1.5 1.0 1.5 I i i i i I i i i i i ' ' I I I ' ' ' ' I i ' ' ' l 0 ^ I l l l l I l l I l I l l l l I l l l l I I I I I I I I I I I l_ 0 50 100 150 200 250 300 Temperature (K) 10 15 20 25 30 35 Figure 2.11. Plot of magnetic moment (per mole of trimetallic unit) versus temperature for {Cu3[(CH)3P02]6}x- The solid lines are calculated from theory employing a single intra-trimer exchange constant plus a molecular field correction as described in the text. The dotted lines are calculated from equation [2.5] as described in the text. 61 Within the trimetallic units there are three potential pathways for exchange, all involving double phosphinate bridges. The phosphinates containing P(l) and P(2) link the two five-coordinate copper ions to the four-coordinate copper and the two phosphinates containing P(3) link the five-coordinate metal ions to each other. Analysis of our data permits the determination of a single intra-trimetallic exchange constant linking all three metals. Presumably the exchange couplings by the three pathways are not significantly different from each other and J for each is close in magnitude to the value obtained from our fit. The intra-trimetallic phosphinate bridges observed in the title compound are not significantly different in terms of bond angles or lengths from those reported previously for antiferromagnetically coupled linear chain copper(II) dialkylphosphinates. The exchange coupling constants in these polymers range from J= -1.3 cm"1 in the ethyl derivative (3) to J= -29 cm"1 in the dodecyl derivative (10). Hence the value J = -5.9 cm"1 obtained for the copper(II) dimethylphosphinate can be considered typical for copper(II) ions exchanging antiferromagnetically via double phosphinate bridges. It was previously noted that the magnitude of exchange does not correlate with bonding parameters associated with the bridging phosphinates but that the chromophore geometry may play a significant role in determining the nature of the exchange (3, 11). The present work shows, however, no significant change in the magnitude of exchange on going from the linear chain polymers where all metal centers are four-coordinate to the title compound where two out of three metal centers are five-coordinate. Two potential pathways for inter-trimetallic exchange involve (i) the Cu(2) ions in different units linked by 0(2) and (ii) the Cu(l) from one unit linked via the P(l) 62 containing phosphinate bridge to a Cu(2) in a neighbouring unit. The first, being the shorter pathway, would be expected to dominate; however, exchange via either should be weak since both involve the long (2.505(2) A) Cu-0 link. Adding to the expectation that exchange via this link will be weak is the fact it is orthogonal to the presumed magnetic orbital, d x 2. y 2 , in the basal plane. Comparisons with related systems are not possible since the form of phosphinate coordination seen here in which one oxygen (0(2)) is bonded to two metal ions has not been previously reported for a magnetically and structurally characterized copper(II) compound. 2.2.7.2. Copper(II) Methylethylphosphinate, Cu[(CH3)(C2H5)P02]2 The structures of both copper(II) diethylphosphinate (3) and copper(II) dimethylphosphinate (present work) are known from X-ray diffraction studies; the former having an extended linear chain structure (Figure 1.5, FX), the latter having a structure consisting of trimetallic units linked in chains. Although we have not been able to obtain crystals of the mixed substituent (methylethyl) derivative, some evidence that its structure involves simple double phosphinate bridged chains comes from its infrared spectra which show only two bands in the P-0 stretching region (at 1108 cm"1 and 1052 cm"1) like that of the diethyl derivative (at 1110 cm"1 and 1049 cm"1) (2) rather than four bands as reported here for the dimethyl derivative. Further evidence for a linear chain structure comes from the magnetic properties, discussed below, which show behaviour consistent with a linear chain. 63 The magnetic moment versus temperature plot is depicted in Figure 2.12. As the temperature is lowered, the moment decreases, indicating antiferromagnetic coupling present in the compound. The magnetic behaviour was analyzed according to three 2.0 1.9 PS S 1.8 E o '•0 ea S3 1.7 h 1.6 1.5 i i I i i i i I i i i r I i i i i I i i i i i ' ' ' ' I i i i i I i i i i I i 0 10 20 30 40 50 60 70 80 90 Temperature (K) Figure 2.12. Magnetic moment versus temperature plot for Cu[(CH3)(C2H5)P02]2 64 isotropic Heisenberg models (5, 2) for exchange coupled linear chains with S = 1/2. According to the Bonner and Fisher (27) model as developed by Hall (28, 29) (and hereafter called the Hall model), the susceptibility is given by the polynomial expression: Ng^p2 0.25+0.14995X"1+0.30094X -2 % M kT 1+1.9862X"1+0.68854X"1+6.0626X3 t 2 ' 8 ] where X = kT /14 According to the Wagner-Friedberg model (30) (termed WFG model hereafter), the magnetic susceptibility, XM , is given by the following equation: Ng2p2SQS + l) 1 + U 3kT 1 - U KM 1 -T1 I T T L • J where U = Coth(K-l/K) and K = 2JS(S+l)/kT, S is 1/2, for copper(II). In the third model, Hiller et al. (31) generated a series of coefficients to reproduce Weng's numerical results (32) for the magnetic susceptibilities. According to this model (which we termed Weng model): N g 2 p 2 A + B X 2 % M ~ kT 1 + C X + D X 3 [ 2 1 0 ] In this equation, for S =1/2, A =0.2500, B = 0.18297, C = 1.5467, D = 3.4443 and X = J/kT. In all three models, g, J, k and P have the same meanings as defined in section 2.2.7.1. The experimental results for copper(II) methylethylphosphinate were analyzed using the three models with fits made to the experimental susceptibility data and with J and g as variable parameters. The best fit to the experimental susceptibility data was the 65 one which minimized the function F, defined in equation [2.6]. Values of g and J for the best fit using the three models are given in Table 2.6. All three models gave good fits, supporting the conclusion that the compound has a linear chain structure. The value of the exchange coupling constant, J = -0.48 cm"1 (Hall model) is very small compared to that obtained for copper(II) diethylphosphinate where J = -1.27 cm"1 (3) and copper(II) dimethylphosphinate where the intra-trimetallic exchange constant J = -5.9 cm"1. Interestingly, comparing only linear chain antiferromagnetically coupled dialkylphosphinates of copper(II), earlier work had shown that the strength of the exchange increased with increasing length of the alkyl substituents. In the copper(II) dialkylphosphinates, Cu(R.2P02)2, where R is ethyl, octyl, decyl, dodecyl, the values of |J| are 1.27, 25, 29 and 29 cm"1, respectively (3, 10). The value of |J| = 0.48 cm"1 for copper(II) methylethylphosphinate obtained here fits the trend. Lack of detailed structural information (X-ray structure of only the ethyl derivative is available) prevents a detailed discussion of factors determining this trend; however, it seems most likely that steric factors, rather than electronic factors associated with the substituents, are affecting the detailed geometries of the phosphinate pathways for exchange and hence the value of \J\. 66 Table 2.6. Magnetic parameters for copper(II) complexes. Complexes Model° -/(cm"1) g PC Cu[(CH3)(C2H5)P02]2 Hall 0.48 2.18 0.014 d Weng 0.42 2.18 0.014 d WGF 0.56 2.12 0.015 d Cu[(C6F5)2P02]2 Hall 6.32 2.26 0.019 0.026 Weng 6.32 2.25 0.014 0.049 WFG 8.52 2.28 0.017 0.012 a Models are described in the text. The function F is defined in equation [2.6]. P is the fraction of paramagnetic impurity and is defined in equation [2.11]. ^P is set to zero. 2.2.7.3. Copper(II) Bis[bis(perfluorophenyl)phosphinate], Cu[(C6F5)2P02]2 Copper(II) diphenylphosphinate has a linear chain double phosphinate bridged structure and to date is the only example of such a structure in which the copper(II) centers have square planar Cu0 4 chromophores (4). Magnetic studies on this compound revealed ferromagnetic exchange interaction and it was suggested at the time that ferromagnetism may be a characteristic feature of this coordination geometry in extended chain copper(II) phosphinates (11). It was of interest therefore to examine the effects on both structure and magnetism of substituting perfluorophenyl substituents for the perhydrophenyl groups on phosphorus. In the absence of single crystal X-ray diffraction data (sample could not be obtained in single crystal form suitable for such studies) the 67 structure of the bis(perfluorophenyl)phosphinate derivative must be inferred from indirect information. The best evidence for a linear chain structure for copper(II) bis(perfluorophenyl)phosphinate comes from the magnetic studies. The magnetic moment versus temperature plot shown in Figure 2.13 indicates the moment drops with decreasing temperature, suggesting antiferromagnetic behaviour. Its susceptibility data were analyzed according to all three linear chain models. Good fits to the experimental data have been obtained. The plot of susceptibility data versus temperature is shown in Figure 2.14. The solid line in the figure was calculated employing the Hall model with the best fit parameters given in Table 2.6. This result supports the assumption that Cu[(C6F5)2P02]2 has a linear chain structure. The infrared spectrum of the compound (see Figure 2.7) is consistent with only one type of bridging phosphinate and relatively symmetric O-P-0 bridges. The electronic spectrum is consistent with either a square planar or a highly compressed tetrahedral Cu04 chromophore geometry. Further information on the chromophore comes from the EPR spectrum. This is shown in Figure 2.10 where it is compared to that of the perhydro-analogue. Whereas the perhydro-derivative shows a typical two-g spectrum expected for square planar geometry the spectrum of the perfluoro-derivative is different, with only one broad peak showing some splitting. We conclude that the chromophore geometry is highly compressed tetrahedral rather than square planar and that may be the main cause of the change in the magnetic behavior from ferromagnetism in the perhydro-derivative to antiferromagnetism in the perfluoro-derivative. 68 As can be seen in Figure 2.14 the magnetic susceptibility exhibits a maximum at 10 K, then increases at lower temperatures, indicating some paramagnetic impurity is present in the bulk sample. To correct for the paramagnetic impurity, the susceptibility was calculated according to equation [2.11]. Xcalc. = (1 " P)Xchain + PXpara. [2.11] In this equation, Xchain is the susceptibility calculated according to one of the chain models, Xpara. is the susceptibility for paramagnetic impurity and P is the fraction of metal ions making up the paramagnetic component. The paramagnetic component, P, is assumed to follow Curie Law given by: — L [2.121 A para. 31cT J where g is assumed to have the same value as in the bulk of the polymer, and other parameters have the same definitions as described above. Combining equations [2.11], [2.12] and the appropriate chain model, J and P were obtained and these values are listed in Table 2.6. 69 2.5 2.0 g 1.5 S 1.0 0.5 0.0 A A A o o o o A § A . A A A OA 0 o o o o o o o o o A * A A A A A A A A o o o o o o o o o o A A A a » A A A A A A — O — A o A A O A O A - ° A o a A °A* A b OA A f i I i i i i I i i i i I i i i i 1 i i i i 1 0 50 100 150 200 250 300 Temperature (K) Figure 2.13. Magnetic moment versus temperature plots for (a) Cu[(C 6F 5) 2P0 2] 2 and (b) Cu[(C6H5)(C6F5)P02]2. 70 Figure 2.14. Magnetic susceptibility versus temperature plots for Cu[(C6F5)2P02]2, circles are experimental and lines are calculated from Hall model (see text). 71 2.2.7.4. Copper(II) Bis(phenylperfluorophenylphosphinate), Cu[(C6H5)(C6F5)P02]2 The mixed substituent complex, Cu[(C6H5)(C6F5)P02]2, has a different structure from that of Cu[(C6F5)2P02]2- IR spectra suggest that the two compounds have different types of O-P-0 bridges. The electronic spectra are also quite different (see section 2.2.5), indicating a less compressed tetrahedral chromophore geometry in Cu[(C6H5)(C6Fs)P02]2 compared to that of the bis(perfluorophenyl)phosphinate compound. The magnetic properties of this compound are also unique. The magnetic moment at room temperature is 1.56 U B , a value which is low for magnetic dilute copper(II), suggesting antiferromagnetic exchange. As the temperature is lowered (Figure 2.13), the moment rises to a maximum value of 1.79 u B at 60 K then drops to about 0.55 u,B at 1.83 K. Such behavior cannot be fitted to linear chain antiferromagnetic or ferromagnetic models. Qualitatively the results suggest a system in which the exchange constant is temperature dependent. Comparing the magnitude of the moment to that observed for the bis(perfluorophenyl) derivative over the temperature range, the exchange appears to be stronger for the mixed substituents complex at room temperature then decreases in magnitude due perhaps to structural change, down to 40 K at which temperature and below it is of the same order of magnitude as that of the bis(perfluorophenyl)phosphinate derivative. Without a detailed knowledge of the structure, further speculation on the cause of this unique magnetic behavior is inappropriate. More studies are needed and more sample is also required. 72 2.2.7.5. Copper(II) Bis(perfluoro-n-butylethyl)phosphinate, Copper(II) Bis(perfluoro-n-hexylethyl)phosphinate (Form I) and Copper(II) Bis(perfluoro-n-hexylethyl)phosphinate (Form II), Cu{[CF3(CF2)3CH2CH2]2P02}2, Cu{[CF3(CF2)5CH2CH2]2P02}2 (Form I) and Cu{[CF3(CF2)5CH2CH2]2P02}2 (Form II) Studies on copper(II) (di-n-hexyl)phosphinate and copper(II) (di-n-octyl)phosphinate revealed the former to exhibit linear chain ferromagnetism and the latter to exist in two structural forms — the ot-form which is a linear chain antiferromagnet and the P-form which is a linear chain ferromagnet (10). In the present work we have examined partially fiuorinated analogues of both of these compounds with a view to determine the effects of fluorination on both structure and magnetism. Copper(II) bis(perfluorobutylethyl)phosphinate is the analogue of copper(II) di(n-hexyl)phosphinate and like the perhydro-compound it exhibits magnetic behavior indicative of ferromagnetic coupling. The plot of magnetic moment versus temperature is shown in Figure 2.15. The magnetic moment at room temperature is 2.09 u.B, a value in excess of that normally observed for magnetically dilute copper(II). Below about 120 K the moment rises to a maximum of 2.72 u.B at 3 K and then decreases when the temperature is lowered further. The decrease at the lowest temperatures is a consequence of magnetic saturation effects. Baker et al. (33) developed a polynomial expression for ferromagnetic S = 1/2 chains. The expression is given below as equation [2.13], where K = J/2kT. —12/3 1 + 5.7980K + 16.9027K2 + 29.3769K3 + 29.8330K4 + 14.0369K5 1 + 2.7980K + 7.0087K2 + 8.6539K3 + 4.5743K4 [ 2 ' 1 3 ] Ng 2p 2 4kT 73 e £ ° (a) D (b) A (c) * (d) B O B g » B B B B 8 B 8 8 B ^ O f i f i B f i B e f i B X D D D D Q D D D D D D D D D 50 100 150 200 250 Temperature (K) 300 Figure 2.16. Magnetic moment versus temperature plots for: (a) Cu{ [CF3(CF2)5CH2CH2]2P02}2 (Form I), (b) Cu{[CF3(CF2)3CH2CH2]2P02}2, (c) Cu{[CF3(CF2)jCH2CH2]2P02}2 (Form U), 10 kOe, (d) Cu{[CF3(CF2)5CH2CH2]2P02}2 (Form II), 50 kOe. 74 Fitting the experimental susceptibility data over the entire temperature range studied to this equation gives the best fit shown in Figure 2.16 with the parameters shown in Table 2.7. The magnitude of J is somewhat smaller than that observed for the perhydro analogue (1.8 versus 2.6 cm"1, Table 2.7). Close comparison of the experimental data and the theoretical curve reveals the experimental moments show a small but smooth decrease in value from 300 K to ~ 120 K before showing the increase in magnitude expected for a ferromagnetic substance. Although the decrease in moment is not significantly greater than experimental error the smooth trend suggests it is significant. Moreover the effect is seen more dramatically in the related compound (Cu{[CF3(CF2)5CH2CH2]2P02}2) (see later). This behavior cannot be modeled by the theory. In addition, the g value, given by the best fit, is 2.34, a value anomalously high for copper(II). Exploring the possibility that J is temperature dependent for this compound, decreasing slightly with decreasing temperature as a consequence of small structure changes, we attempted fits of the magnetic data to the low temperature region only (from 3 K to 120 K). This low temperature fit was obtained with better agreement between experiment and theory. The fitting parameters are listed in the Table 2.7 and the calculated curve is shown in the inset of Figure 2.17. The value of J is 2.5 cm"1 and g is 2.30 for the fit over the low temperature region. Interestingly, this coupling constant is close to the value for the corresponding perhydro-derivative. These results suggest that there is some "fluxionality" to the solid state structure of this compound in the high temperature region and that at low temperatures the structure "freezes" to one that approximates perhydro-derivative. 75 Copper(II) bis(perfluorohexylethyl)phosphinate is the analogue of copper(II) di(n-octyl)phosphinate. Like the perhydro derivative which exists in a- and |3-fofms (10), the fluorinated derivative also exhibits polymorphism. The form labeled Form I in this work exhibits magnetic behaviour very similar to that of copper(II) bis(perfluorobutylethyl)phosphinates. The magnetic moment versus temperature behaviour (Figure 2.15) indicates ferromagnetic interaction as for the perfluorobutylethyl derivative, however, in this case the initial decrease in moment below 300 K is more steep and the moment levels off at a temperature of ~70 K before showing an increase at lower temperatures. Examining fits to theory over the entire temperature range generates a J value of 1.1 cm"1 (Table 2.7), significantly smaller than that of the perhydro-derivative (J = 1.8 cm"1, see Reference 10). Again, however, the anomalously high g value (2.42) and the inability to model the decreasing moment below 300 K suggests a temperature dependent J for this compound. Accordingly as before we attempted to fit the low temperature data only and the result is plotted in the inset of Figure 2.17. As shown in Figure 2.17 and by the F value in Table 2.7, the latter fit is much better than the fit over the entire temperature range. This constant J below 70 K indicates that there is no significant fluxionality in this temperature region. The J value obtained from this low temperature fit is 2.33 cm"1, slightly higher than that of the corresponding perhydro-derivative as described above. As described above, fluxionality in the solid state structure at high temperatures is one possible explanation for the interesting magnetic properties of this compound. 76 The magnetic moment of Form II of copper bis(perfluoro-n-hexylethyl)phosphinate at room temperature and in an applied field of 10, 000 G is 5.9 u.B, a totally unexpected and unprecedented value. The moment versus temperature plot is shown in Figure 2.15. The magnetization at 300 K is 140 cm3 G mol"1, far below the saturation value of 5585 cm3 G mol"1 (for S = 1/2, see chapter 4). When the sample is run at a higher field of 50,000 G, this anomaly disappears and the magnetic properties behave the same as the Form I compound. This result indicates that additional ferromagnetic coupling exists in the Form II compound between the chains at high temperatures, causing a big magnetic moment. The inter-chain interaction is destroyed when a sample of the Form II compound is placed in a very high field and this compound exhibits normal magnetic behaviour as the Form I compound. Table 2.7. Magnetic parameters for copper(II) phosphinates. Compound /(cm"1)" gb F Cu{[CF3(CF2)3CH2CH2]2P02}2 1.8 2.34 0.051 c 2.5 2.30 0.023 p-Cu[(n-C6H13)2P02]/ 2.6 2.16 0.013 Cu{ [CF3(CF2)5CH2CH2]2P02}2 1.1 2.41 0.070 (Form I) d 2.3 2.29 0.019 P-Cu[(n-C8H17)2P02]2e 1.8 2.24 0.017 b Here and elsewhere in this thesis J and g are considered to be significant to within ±10% and ±2%, respectively (6). 0 Fit was made over temperatures ranging from 3 K to 120 K. d Fit was made over temperatures ranging from 3 K to 70 K. °'e Taken from references 3 and 10, respectively. 77 4.0 3.6 =? 3.2 S3 a o 2.8 a WD ^ 2.4 2.0. 4.0 3.6 h -o o e e © J I i i i i I i i i i I i i— i— i—L i . . . . i . 20 40 60 80 100 Temperature (K) o o o o o o o Q Q Q 120 1.6 _l I I I I I I I I I 1—1 I I I I l_ 0 50 100 150 200 Temperature (K) 250 300 Figure 2.16. Magnetic moment versus temperature plot for Cu{[CF3(CF2)3CH2CH2]2P02}2- Circles are experimental data, lines are calculated from the Baker model (equation 2.13). The inset shows the result of fitting the low temperature data only. 78 S3 ii E o 4.0 3.6 1 3.2 '•0 = 93 2.8 1.6 « A e o CD 4.0 3.6 h 3.2 2.8 2.4 2.0 1.6 M M © 0 '•<»—©-I 1 I I I I I I I I I 1 I I I 1 I I I I I 0 10 20 30 40 50 60 70 Temperature (K) § o o o o o o c j T ^ 0 0 0 o o o •o Q Q o o o o o o H I -1 1 1 1 1 1 1 1 i 1 1 1 1 1 1 1—i— 0 50 100 150 200 Temperature (K) 250 300 Figure 2.17. Magnetic moment versus temperature plot for Cu{[CF3(CF2)5CH2CH2]2P02}2. Circles are experimental data, lines are calculated from the Baker model (equation 2.13). The inset shows the result of fitting the low temperature data only. 79 2.3. Summary and Conclusions Seven copper(II) dialkylphosphinate complexes have been synthesized and characterized. All are considered to have linear chain polymeric structures with compressed tetrahedral chromophores with the exception of copper(II) dimethylphosphinate. Single crystal X-ray diffraction studies on the latter reveal trimetallic units linked to form chains. There are two different chromophores in each trimetallic unit, one copper(II) being pyramidal, the other two distorted tetrahedral. Intra-trimetallic antiferromagnetic coupling occurs with J = -5.9 cm"1, a value typical for a phosphinate bridged copper(II) system. In addition there is weak inter-trimetallic interaction (zJ^ = -0.27 cm"1). Both the structure adopted and the magnetic properties of this compound are unique for a binary copper(II) phosphinate. Due to the lack of the detailed structures for the other copper(II) complexes, magneto-structural correlations involving them are of necessity somewhat tentative. Comparison of Cu[(C6F5)2P02]2 with the previously studied perhydro-derivative led to the conclusion that the dramatic difference in the nature of the magnetic exchange in these compounds (antiferromagnetic for the former versus ferromagnetic for the latter) is a consequence of a change in the Cu04 chromophore from square planar to distorted tetrahedral. It is tempting to suggest that the latter chromophore is favored by the more weakly coordinating perfluorophenyl phosphinate ligand. The mixed substituents complex, Cu[(C6H5)(C6F5)P02]2, exhibits unique magnetic properties which cannot be modeled at this point. More work to elucidate the structure of this compound is required. 80 The mixed ligand complex, Cu[(CH3)(C2H5)P02]2, is antiferromagnetic and the magnitude of the exchange coupling constant fits the trend observed for antiferromagnetically coupled n-alkylphosphinates of copper(II). Cu{[CF3(CF2)3CH2CH2]2P02}2 and Cu{[CF3(CF2)5CH2CH2]2P02}2 (Form I) show interesting magnetic properties which indicate the presence of solid state fluxionality at high temperatures and that the structures of these compounds freeze to one that approximates that of the perhydro- analogues at low temperatures. The magnetic properties of Cu{[CF3(CF2)5CH2CH2]2P02}2 (Form II) are unprecedented and at this point unexplained, more work is required here. REFERENCES 1. R. Cini, P. Colamarino, P. L. Orioli, L. S. Smith, P. R. Newman, H. D. Gillman and P. Nannellli, Inorg. Chem. 16, 3223 (1977). 2. K. W. Oliver, S. J. Rettig, R. C. Thompson and J. Trotter, Can. J. Chem. 60, 2017 (1982). 3. J. S. Haynes, K. W. Oliver, S. J. Rettig, R. C. Thompson and J. Trotter, Can. J. Chem. 62, 891 (1984). 4. A. Bino and L. Sissman, Inorg. Chim. Acta, 128, L21 (1987). 5. W E . Hatfield, W. E. Estes, W. E. Marsh, M. W. Pickens, L. W. Ter Haar and R. R. Weller, Extended Linear Chain Compounds, J. S. Miller, Ed. Plenum, New York, London, Vol. 3, 1983. 6. K. W. Oliver, Ph. D Dissertation, University of British Columbia, B. C. Canada, 1984. 7. M. Melnik, Coord. Chem. Rev. 42, 259 (1982). 81 8. P. J. Hay, J. C. Thibeault and R. Hoffman, J. Am. Chem. Soc. 97, 4884 (1975). 9. D. J. Hodgson, Prog. Inorg. Chem. 19, 173 (1975). 10. J. S. Haynes, K. W. Oliver and R. C. Thompson, Can. J. Chem. 63, 1111 (1985). 1.1. J.-L. Du, K. W. Oliver and R. C. Thompson, Inorg. Chim. Acta, 141, 19 (1988). 12. J.-L. Du, S. J. Rettig and R. C. Thompson and J. Trotter, Acta Crystallogr. Sect. C, 48, 1394 (1992). 13. K. Dehnicke and A. F. Shihada, Structure and Bonding, 28, 52 (1976). 14. H. D. Gillman, Inorg. Chem. 13, 1921 (1974). 15. H. D. Gillman and J. L. Eichelberger, Inorg. Chem. 15, 840 (1976). 16. H. D. Gillman, Inorg. Chem. 11, 3124 (1972). 17. E. I. Matrosov, K. A. Andrianov, I. Ra. Manevich and Yr. A. Buslaev. Izv. Akad. Nauk SSSR, Neorg. Mater. 1, 464 (1965); Eng. Translation: Inorg. Mater. (USSR), 1, 428 (1965). 18. B. J. Hathaway and D. E. Billing, Coord. Chem. Rev. 5, 143 (1970). 19. A. Escuer, R. Vicente,, E. Pefialba, X. Solans and M. Font-Bardia, Inorg. Chem. 35, 248 (1996). 20. P. Chaudhuri, I. Karpenstein, M. Winter, C. Butzlaff, E. Bill, A. X. Trautwein, U. Florke and H.-J. Haupt, J. Chem. Soc. Chem. Commun. 321 (1992). 21. See reference 8 in P. Chaudhuri, I. Karpenstein, M. Winter, C. Butzlaff, E. Bill, A. X. Trautwein, U. Florke and H.-J. Haupt, J. Chem. Soc. Chem. Commun. 321 (1992). 22. T. Otieno, S. J. Rettig, R. C. Thompson and J. Trotter, Inorg. Chem. 34, 1718 (1995). 23. D. B. Brown, J. R. Wasson, J. W. Hall and W. E. Hatfield, Inorg. Chem. 16, 2526(1977) 24. B. N. Figgis and D. J. Martin, J. Chem. Soc. Dalton Trans. 2174 (1972). 25. J.-L. Du and R. C. Thompson, unpublished work. 82 26. C. J. O'Connor, Prog. Inorg. Chem. 29, 203 (1982). 27. J. C. Bonner and M. E. Fisher, Phys. Rev. 135, A460 (1964). 28. W. E. Estes, W. E. Hatfield, J. A. C. van OoiJen and J. ReediJk, J. Chem. Soc. Dalton Trans. 2121 (1980). 29. J. W. Hall, Ph. D. Dissertation, University of North Carolina, 1977. 30. G. R. Wagner and S. A. Friedberg. Phys. Lett. 9, 11 (1964). 31. W. Hiller, J. Strahle, A. Datz, M. Hanack, W. E. Hatfield, L. W. terHaar and P. Giitlich, J. Am. Chem. Soc. 106, 329 (1984). 32. C. H. Weng, Ph. D. Dissertation, Carnegie-Mellon University, Pittsburgh, P. A. U.S.A. 1968. 33. G. A. Baker, Jr., G. S. Rushbooke and H. E. Gilbert, Phys. Rev. 135, A1271 (1964). 83 Chapter 3 Manganese(II) Phosphinate Complexes and Manganese (II) Dimethylarsinate 3.1. Introduction Manganese(II) phosphinate complexes which have been reported may be classified into two categories, (i) binary complexes with the formula Mn(RR'P02)2 and, (ii) adduct polymeric complexes with the formula MnL2(RR'P02)2, where R and R' are H, or alkyl or aryl groups and L refers to neutral ligands generally with oxygen or nitrogen donors. Two different coordination geometries, tetrahedral and octahedral, were reported previously for the binary manganese compounds. Polymeric chain structures in which metal ions are linked by double phosphinate bridges are formed for compounds with tetrahedral manganese centers. This kind of structure was confirmed by single crystal X-ray diffraction studies on the y form of Mn[(C6H5)2P02]2 (1) The P form of this compound is considered to have a similar linear chain structure with, it is assumed, small differences in the detailed coordination geometry around the manganese center. Both compounds are weakly antiferromagnetic with the y form of Mn[(C6H5)2P02]2 showing stronger magnetic coupling between metal centers compared to the P form. For compounds with octahedral manganese centers, sheet polymer structures have been proposed (See diagram XV, Figure 1.5). There have been no crystal structures reported so far on this type of binary manganese complex; however, Mn[H(C6H5)P02]2 and Mn[(CH3)2P02]2 (Form I) were suggested to have this structure based on evidence obtained from DSC data and JR spectra (2, 3). MnKn-CgHn^POVU (4) was also proposed to have octahedral coordination 84 about the metal; however, this conclusion is not supported by the results of the current work which suggests that this compound is a linear chain polymer with tetrahedral metal centers. Compounds with composition MnL2[H(C6H5)P02]2 in which metal ions are linked to form linear chains by double phosphinate bridges are also known (3, 5, 6). In these complexes, four oxygen atoms from four different phosphinate anions are coordinated to one metal, forming a square planar Mn0 4 chromophore. Additionally, the metal is axially coordinated by L groups, resulting in an octahedral MnCUO^ chromophore. Structures of compounds with formula MnL2[H(C6H5)P02]2, where L = H 20, HCONH 2, H(C 6H 5)P0 2H and CH3CONH2, have been determined by single crystal X-ray diffraction studies (3, 5, 6). All these complexes are antiferromagnetic and their exchange coupling constants range from -0.51 cm"1 for the L = HCONH 2 complex to -0.13 cm"1 for the L = H(C 6H 5)P0 2H complex. Magneto-structural correlations involving these complexes revealed that two factors may determine the strength of magnetic coupling. A short Mn-O-P-O-Mn path length and a symmetric O-P-O bridging unit favor the magnetic exchange. The syntheses and characterization of ten manganese compounds will be reported in this chapter. Mn[(CH3)2P02]2 exists in two forms (referred to as Form I and Form II in this thesis). Form I exhibits much stronger antiferromagnetic coupling than that of Form II. The synthesis and magnetic properties of Form I were reported before (3). However, Form II had not been observed previously. We were able to obtain Form II as crystals suitable for single crystal X-ray diffraction studies. Interestingly, this form can also be obtained by conversion from Form I by heating to 220 °C. In addition, Form II converts 85 back to Form I when it is kept in DMF solvent for about one month in the open atmosphere. A manganese(II) bis(perfluorophenyl)phosphinate trimetallic complex, which contains triple bridging phosphinate units, has also been obtained in this work and studied by single crystal X-ray diffraction. Studies show that the magnitude of the magnetic exchange in this complex is comparable to Mn[(C6F5)2P02]2, a compound which contains the same phosphinate bridging units but only two groups between each metal. As a continuation of the work of Du et al. on manganese(II) monophenylphosphinate adduct polymers, Mn(DMSO)2[H(C6H5)P02]2 was synthesized and studied here. Four other binary manganese(II) phosphinate complexes, Mn(RR'P02)2, (R = R' = n-CgHn, CF3(CF2)3CH2CH2 or CF3(CF2)5CH2CH2; R = CH 3 , R' = C 2H 5) were also synthesized and studied in the current work. Finally, to examine the potential of O-As-0 bridges in mediating magnetic exchange between metal centers manganese(II) dimethylarsinate was synthesized and studied. Comparisons are made with the analogous dimethylphosphinate compound. 3.2. Results and Discussion 3.2.1. Synthesis Detailed descriptions of the synthetic procedures used to obtain the manganese(II) complexes are given in Chapter 7. Two forms of manganese(II) dimethylphosphinate were synthesized. The synthesis and magnetic properties of Form I were reported previously (3). In the present work, a different but more convenient method was employed to obtain the Form I compound. In this synthesis, manganese perchlorate hexahydrate was used to 86 react with partially neutralized dimethylphosphinic acid to produce a precipitate in acetone solvent (equation 3.1). Form II can be obtained by heating Form I to 220 °C for 4 hours. Form I is a pinkish powder while form II is a light green compound. Crystals of the Form II compound, suitable for X-ray diffraction studies, were obtained by reaction of dimethylphosphinic acid with manganese dichloride tetrahydrate in DMF (equation 3.2). Acetone Mn(C104)2 • 6 H 2 0 + 2 (CH 3) 2P0 2H + 2 N(C 2H 5) 3 Mn[(CH3)2P02]2 (Form I) + 2 [(C2H5)3NH ] [C104"] + 6 H 2 0 Mn[(CH3)2P02]2 (Form H) [3.1] 220 °C 4 hrs DMF MnCl2 •- 4 H 2 0 + 2 (CH 3) 2P0 2H + 2 DMF-Mn[(CH3)2P02]2 (Form II) (Crystal) + 4 H 2 0 + 2 pMFH+][Cf] [3.2] A similar method to that used for the synthesis of Mn[(CH3)2P02]2 (Form I) was applied to the preparation of Mn[(CH3)2As02]2 except that ethanol was used as solvent in this latter preparation. A pinkish precipitate of manganese(II) methylethylphosphinate was formed immediately after mixing a manganese(II) acetate solution with a methylethylphosphinic acid solution in ethanol (equation 3.3). Ethanol Mn(CH 3COO) 2-4H 20 + 2 (CH3)(C2H5)P02H ' Mn[(CH3)(C2H5)P02]2 + 4 H 2 0 + 2 CH 3COOH [3.3] Manganese(II) bis(perfluorophenyl)phosphinate was synthesized by a similar method to that described by equation [3.3]. However, this compound is very air sensitive, hence, all 87 the preparation procedures were conducted in a dinitrogen filled glove box. In addition, diethyl ether was used as solvent since no precipitate formed if other organic solvents such as ethanol or acetone were used. In attempting to grow crystals of Mn[(C6F5)2P02]2, we obtained instead a trimetallic compound with the formulation {(DMF)3Mn[//-(C6F5)2P02]3}2Mn (see equation [3.4]). X-ray studies revealed that there are 4.5 molecules of lattice water per mole of the manganese complex. However, the elemental analysis and IR studies showed no water in the bulk material. To obtain the bulk material the crystals were washed with acetone and allowed to air dry and this procedure likely resulted in the loss of lattice water. DMF 3 MnCl 2-4H 20 + 6 (CgF^PC^H-H^O + 12 DMF • {(DMF)3Mn[// -(C6F5)2P02]3}2Mn+18H20 + 6 [DMFH+][Cf] [3.4] (Crystal) Mn{[n-CF3(CF2)3CH2CH2]2P02}2 was prepared as a powder by the same method as that described in equation [3.4]. Mn{[n-CF3(CF2)5CH2CH2]2P02}2 and Mn[(n-CgHi7)2P02]2 were synthesized according to equation [3.5]. It was difficult to dissolve both the acid and the manganese salt starting materials in a single solvent; hence mixed solvents of ethanol (or methanol) and water were used in the preparation of both compounds. H20/Methanol Mn(C104)2 -6H20 + 2 n-(C8H17)2P02H + 2 NaOH — • Mn[n-(C8H1 7)2P02]2 + 2 NaC104 + 8 H 2 0 [3.5] 88 Two common methods (6-8) have been employed to synthesize adduct polymer materials. One method involves mixing metal phosphinates with appropriate neutral ligands in an organic solvent. The second method, normally used to get crystals suitable for X-ray studies, involves mixing solutions of metal salts with an appropriate acid in a solvent such as water, DMF, HCONH 2, or acetone, then adding neutral ligands (ligand and solvent may be the same reagents) to the above mixed solutions and allowing the resulting solutions to stand for a period of time. Representative preparations using the above described methods are presented in equations [3.6] and [3.7]. Crystals of compound Mn(DMSO)2[H(C6H5)P02]2 were obtained by the same method shown in equation [3.7]. Here DMSO was used both as a solvent and as the neutral ligand. Mn[H(C6H5)P02]2 + 2 L S o l V e n t » MnL2[H(C6H5)P02]2 [3.6] where L is a neutral ligand such as DMF, HCONH 2 or H 2 0. Solvent MnX2 'iM20 + 2 H(C 6H 5)P0 2H + 2 B + 2 L • MnL 2 p(C 6 H 5 )P0 2 ] 2 + 2 [BH+][X] + nH 2 0 [3.7] where X is Cl or CIO4 , B is a base and L is neutral ligand. 3.2.2. Thermal Analysis The results of the thermal analyses are summarized in Table 3.1. All DSC peaks observed are endothermic with the exception of the highest temperature events observed for complexes containing bis(perfluorophenyl)phosphinate ligands. These events are exothermic. Studies showed that the two forms of Mn[(CH3)2P02]2 have similar DSC curves except for an extra endothermic event at 193 °C (Table 3.1) in the thermogram for 89 Form I. This event is irreversible and there is no weight loss associated with it, implying that a phase transition has occurred. The event is ascribed to the conversion of Form I to Form II at 193 °C. With the help of this observation, large amounts of Form II were obtained by heating the Form I material at a temperature above 193 °C. Manganese dimethylphosphinate (Form II) is very stable thermally; it decomposes at temperatures above 500 °C. At 328 °C, a reversible endothermic event corresponding to the melting of the sample occurs. The DSC studies on Mn[(CH3)(C2H5)P02]2 reveal two reversible events at 149 and 172 °C corresponding to the melting and a possible phase transition, respectively. The compound is only slightly less stable thermally than the dimethyl derivative; it decomposes above 420 °C. Interestingly, Mn[(CH3)2As02]2 is significantly less stable thermally than the dimethylphosphinate analogue. In the DSC thermogram of this material there are no thermal events up to 314 °C above which temperature the compound decomposes. Mn[(C6F5)2P02]2 melts at 344 °C before it decomposes at 496 °C, its stability being comparable to that of the corresponding perhydro-diphenyl derivative (1). The DSC thermogram of {(DMF)3Mn[//-(C6F5)2P02]3}2Mn shows three endothermic peaks over the range 25 to 600 °C (Figure 3.1). TGA studies show that there is a 15.2% weight loss over the temperature range 100 °C to 170 °C, corresponding to the loss of all six DMF molecules in this complex (Six DMF molecules are theoretically 14.7% of the total weight of the molecule, Figure 3.2). Combining the results of DSC and TGA studies, the first event at 144 °C on the DSC curve may be assigned to the dissociation of DMF molecules and the second event at 194 °C to their evaporation. Interestingly, the third endothermic 90 peak at 346 °C at which the compound melts is almost the same as that for Mn[(C6F5)2P02]2, and the decomposition temperatures are same for both compounds. Clearly the product after loss of DMF is Mn[(CeF5)2P02]2. Further proof of this was obtained by investigation of the residue by heating the compound to 250 °C. This revealed that the residue has the same IR spectra, DSC thermogram and X-ray powder diffraction pattern as that of Mn[(C6F5)2P02]2. Previous studies on adduct manganese monophenylphosphinate complexes showed that neutral ligands are lost during the heating process prior to decomposition (8). Similar thermal behavior was found for Mn(PMSO)2[H(C6H5)P02]2. An endothermic event at 76 °C may be assigned to the dissociation of DMSO molecules and a second event at 196 °C to the evaporation of DMSO. TGA studies confirmed this assignment by showing a weight loss of 31.2 % over the temperature range 74 to 181 °C (compared to theoretical 31.7%) (Figure 3.2). The reversible event in the DSC curve at 270 °C may be due to the melting of Mn[H(C6H5)P02]2 which was formed after losing the DMSO molecules. DSC studies in air on Mn[(C6Hi3)2P02]2 revealed an endothermic event at 129 °C, possibly due to melting, and an exothermic event at 189 °C due to decomposition (1). The partially fiuorinated derivative, Mn{[CF3(CF2)3CH2CH2]2P02}2 melts and decomposes at the higher temperatures of 210 °C and 295 °C, respectively, under a nitrogen atmosphere. As shown in Table 3.1, DSC thermograms of Mn{[CF3(CF2)5CH2CH2]2P02}2 show that there are two endothermic events at 141 and 182 °C prior to decomposition above 230 °C. Under the same conditions, the perhydro-derivative melts at 122 °C, and decomposes at a much higher temperature of 420 °C. 91 Table 3.1. DSC thermal parameters for manganese(II) phosphinates. Complexes Temp. (°C) AH (kJ mol"1) Comments Mn[(CH3)2P02]2 (Form I) 193 13 Irreversible 326 20 Reversible 500 Begin to decompose Mn[(CH3)2P02]2 (Form II) 328 21 Reversible 500 Begin to decompose Mn[(CH3)2As02]2 314 Begin to decompose Mn[(CH3)(C2H5)P02]2 149 37 Reversible 172 0.34 Reversible 420 Begin to decompose Mn[(C6F5)2P02]2 344 41 Reversible 496 Begin, to decompose Mn[(n-C8H17)2P02]2 122 58 Reversible 420 Begin to decompose Mn[CF3(CF2)3CH2CH2]2P02}2 210 26 Reversible, 295 Begin to decompose Mn{ [CF3(CF2)5CH2CH2]2P02}2 141 27 Reversible 182 27 Reversible 230 Begin to decompose {(DMF)3Mn[^-(C6F5)2P02}2]3}2Mn 144 130 Irreversible 194 195 Irreversible 346 117 Reversible 495 Begin to decompose Mn(DMSO)2[H(C6H5)P02]2 76 40 Irreversible 196 74 Irreversible 270 47 Reversible 338 Begin to decompose 92 Figure 3.1. DSC thermograms of (a) Mn(DMSO)2[H(C6H5)P02]2 and (b) {(DMF)3Mn[//-(C6F5)2P02]2}2Mn. 0 100 200 300 400 500 600 700 800 Temperature (°C) Figure 3.2. TGA thermograms of (a) Mn(DMSO)2[H(C6H5)P02]2 and (b) {(DMF)3Mn[/i-(C6F5)2P02]2}2Mn. 93 3.2.3. Single Crystal X-ray Diffraction 3.2.3.1. Structure of manganese(II) dimethylphosphinate (Form II) Crystallographic data for Mn[(CH3)2P02]2 (Form II) are given in the Appendix and some bond distances and angles are given in Table 3.2. A stereoview of a portion of the polymer chain is shown in Figure 3.3. This figure also gives the atom numbering scheme. The structure of Mn[(CH3)2P02]2 (Form II) consists of fused eight-membered rings, each ring consisting of two manganese ions bridged by two phosphinate groups and all the rings are connected to form a polymeric linear chain, propagating along the crystallographic b axis. The coordination about each manganese is approximately tetrahedral with O—Mn—O bond angles ranging from 104.99(9) to 113.15(7)°. These are very similar to those seen in the y form of manganese(II) diphenylphosphinate, which range from 103.2(1) to 114.7(1)° (1). The Mn--Mn distance along the chain of Mn[(CH3)2P02]2 (Form II) is 4.4485(1) A which is very close to the values seen for y-Mn[(C6H5)2P02]2, which are 4.471(1) and 4.446(1) A. The distance for the Mn-O-P-O-Mn pathway, which has been claimed to be an important factor in determining the strength of magnetic coupling between neighbouring metal ions (6), is 7.038(8) A for the dimethylphosphinate derivative compared to 7.053 (12) A for the diphenyl derivative. 94 Table 3.2. Selected bond lengths (A) and angles (deg) for Mn[(CH3)2P02]2 (Form II)*. Bond lengths Mn(l)—0(1) 2.013(2) Mn(l)—0(2)° 2.014(2) P(l)—O(l) 1.505(2) P(l)—0(2) 1.506(2) Bond angles 0(l)-^vln(l)—0(l)b 104.99(9) 0( l ) -^vln( l )—0(2)° 107.60(7) 0(l)-^ln(l>-0(2)C 113.15(7) 0(2)°—Mn(l)—0(2) C 110.3(1) * Superscripts refer to symmetry operations: ° x, 1 - y, V2 - z; b -x, y, V2 - z; ° -x, 1 - y, -z. Figure 3.3. Stereoview of a portion of the chain of Mn[(CH3)2P02]2 (Form II). 33% probability thermal ellipsoids are shown. The atom numbering scheme is also shown. 95 3.2.3.2. Structure of Mn(DMSO)2[H(C6H5)P02]2 Crystallographic data for Mn(DMSO)2[H(C6H5)P02]2 are given in the Appendix and some bond distances and angles are given in Table 3.3. The atom numbering scheme and a stereoscopic view of a portion of the polymeric chain are shown in Figure 3.4 and Figure 3.5, respectively. The crystal structures of MnL2[H(C6H5)P02]2 where L = H 20, HCONH 2, CH 3CONH 2, H(C 6H 5)P0 2H have been reported (3, 5, 6). These complexes have the double phosphinate bridged chain structure with axially coordinated neutral ligands. The metal chromophores have distorted octahedral geometries with a square planar Mn0 4 formed by the manganese ion and four oxygen atoms from four different phosphinate anions. Two other oxygen atoms from neutral ligands L coordinate axially to the metal, completing a distorted octahedral Mn0 40 2' chromophore. The same geometry about the manganese ion is observed for the current DMSO derivative. The average Mn-0 bond lengths for the complexes described above range from 2.170(4) to 2.184(4) A while the Mn-O' bond lengths range from 2.231(1) to 2.247(2) A. In comparison with the previously reported structures, the DMSO derivative has a slightly longer Mn-0 bond length (2.192(4) A) and a very similar Mn-O' bond length (2.247(2) (A)). In addition, the P-0 bond length is typical for these types of complexes. 96 Table 3.3. Selected bond lengths (A) and angles (deg) for Mn(DMSO)2[H(C6H5)P02]2a Bond lengths Mn(l)—0(1) 2.160(2) Mn(l)—0(2)' 2.224(2) Mn(l)—0(3) 2.247(2) S(l)—0(3) 1.508(2) P(l)—0(1) 1.508(2) P(l)—0(2) 1.505(2) 0(1)—Mn(l)—0(1)" 180.0 0(1)—Mn(l)—0(2)* 92.94(6) 0(1)—Mn(l)—0(3)" 87.97(6) 0(2)'—Mn(l)—0(3) 90.68(6) 0(3)—Mn(l)—0(3)" 180.0 angles 0(1)—Mn(l)—0(2)' 87.06(6) 0(1)—Mn(l)—0(3) 92.03(6) 0(2)'—Mn(l)—0(2)* 180.0 0(2)'—Mn(l)—0(3)" 89.32(6) a Superscripts refer to symmetry operations: ' 1 + x, y, z; " 1 - x, 1 - y, 1 - z; * -x, -1 - y, 1 - z . 97 Figure 3.4. Atom labeling scheme of Mn(DMSO)2[H(C6H5)P02]2, 33% probability thermal ellipsoids are shown. Figure 3.5. Stereoview of a section of polymeric chain of Mn(DMSO)2[H(C6H5)P02]2, 33% probability thermal ellipsoids are shown. 98 3.2.3.3. Structure of {(DMF)3Mn[//-(C6F5)2P02]3}2Mn Crystallographic data for Mn{(DMF)3Mn[^(C6F5)2P02]3}2Mn are given in the Appendix and some bond distances and angles are given in Table 3.4. The atom numbering scheme is shown in Figure 3.6 while the stereo view of the trimetallic manganese complex is given in Figure 3.7. The structure of this complex was solved by direct methods. The molecule has exact S6 symmetry. Triply-bridged complexes involving phosphinate anions and manganese(II) ions are rare. Betz et al. (9) reported a class of metalphosphinates containing both bridging formamide and phosphinate ligands, where the metals were copper(II), manganese(II) or cobalt(II). For the manganese complex, Mn(HCONH2)2[(CH3)(C6H5)P02]2.HCONH2, the manganese ions are bridged by double phosphinate units as in the binary phosphinates and additionally by one formamide molecule. Complexes which may contain triply-bridged phosphinate units are the trivalent transition metal complexes such as chromium(III) phosphinate complexes. However, no structures have been reported on such complexes. The trimetallic manganese complex studied here is the first metal phosphinate complex to have been characterized by single crystal X-ray diffraction studies which has triple phosphinate bridges between metals. In this trimetallic compound, the central manganese is coordinated by all six phosphinate ligands via their oxygen atoms, forming a rather regular octahedral Mn0 6 chromophore. The 0-Mn(l)-0 bond angles are in the range 89.6(2) to 180.0°. The two terminal manganese atoms are equivalent to each other, each atom being coordinated by three bridging phosphinate ligands and three DMF molecules via oxygen atoms, resulting in slightly distorted octahedral MnChCV chromophores. The 0-Mn(2)-0 bond angles are in the range 88.1(3) to 171.3(3)°. The internal phosphinate bond parameters in the 99 compound are typical for the metal phosphinate compounds (1, 3, 5). The Mn(l)-0(2) and Mn(l)-0(1) bond lengths are 2.149(6) A and 2.126(6) A, respectively, -0.1 A longer than those in Y-Mn[(C6H5)2P02]2 (1). Table 3.4. Selected bond lengths (A) and angles (°) for {(DMF)3Mn[//-(C6F5)2P02]3}2Mn*. Bond lengths Mn(l)—0(2) Mn(2>—0(3) P(l)-0(2) 2.149(6) 2.198(9) 1.496(6) Mn(2)—0(1) P(l)-0(1) 0(3)—C(13) 2.126(6) 1.500(6) 1.13(2) Bond angles 0(2)—Mh(l)—0(2) 89.6(2) 0(2)—Mn(l)—0(2)c 90.4(2) 0(1)—Mn(2)—0(3) 88.1(3) 0(1)—Mn(2)—Q(3)d 93.6(3) 0(2)—Mn(l)—0(2)" 180.0 0(1)—Mn(2)—0(1)" 94.5(2) 0(1)—Mn(2)—0(3)° 171.3(3) 0(3)—Mn(2)—0(3)" 83.4(4) * Superscripts refer to symmetry operations: ° -y, x - y, z; b -x, -y, -z; C y, -x + y, -z; -x +y, -x, z. 100 Figure 3.6. View of {(DMF)3Mn|>(C6F5)2P02]3} 2M11 showing the numbering scheme and coordination about the manganese atom. 33% probability thermal ellipsoids are shown. 04 and 05 are from the lattice water. Figure 3.7. Trinuclear manganese structure of {(DMF)3Mn[/i-(C6F5)2P02]3hMn. 33% probability thermal ellipsoids are shown. 101 3.2.4. X-ray Powder Diffraction Diffraction patterns for some of the manganese(II) compounds studied in this work are given in Figures 3.8(A) and 3.8(B). Mn[(CH3)2P02]2 (Form II) is isomorphous and isostructural with Co[(CH3)2P02]2. The latter will be discussed in Chapter 4. This manganese compound has a different X-ray powder pattern from that of the Form I compound. As shown in Figure 3.8 (B), Form I of Mn[(CH3)2P02]2 is isomorphous with Mn[(CH3)(C2H5)P02]2. This suggests that these two compounds may have the same structure. In fact, both compounds exhibit similar magnetic behavior as will be discussed in section 3.2.6. The powder diffraction patterns obtained for Mn[(CH3)2As02]2 and Mn[(C6F5)2P02]2 were of poorer quality than those of the other complexes, a consequence perhaps of their moisture sensitive nature. All other compounds have their own unique X-ray powder diffraction patterns as shown in Figure 3.8. Since the amount of sample was not enough, the X-ray powder patterns for Mn{[CF3(CF2)3CH2CH2]2P02}2 and Mn{[CF3(CF2)5CH2CH2]2P02}2 were not obtained. Also, an X-ray powder diffraction pattern could not be obtained for Mn[n-(C8Hi7)2P02]2 because a gel like material was obtained when the powder was mixed with organic solvents. 102 Figure 3.8 (A). X-ray powder diffraction pattern of Mn[(DMSO)2[H(C6H5)P02]2 103 S3 P -O < S3 J J U . > A . . . g I — I — I — I — I • 'I ' I 1 1 1 1 1 I • • • • I • • I • I • I • • I • • • • I I • ' 5 10 15 20 25 30 35 40 45 50 55 60 2 0 Figure 3.8 (B). X-ray powder diffraction patterns for (a) Mn[(CH3)(C2H5)P02]2, (b) Mn[(CH3)2P02]2 (Form I), c) Mn[(CH3)2P02]2 (Form II), (d) Mn[(C6F5)2P02]2, (e) Mn[(CH3)2As02]2 and (f) {(DMF)3Mn[//-(C6F5)2P02]3}2Mn. 104 3.2.5. Infrared Spectroscopy Infrared bands observed for the manganese(II) complexes over the 200 to 4000 cm"1 range are given in the Appendix. We will concentrate here on the P0 2 stretches of the bridging ligands. The infrared data for these vibrations are listed in Table 3.5 and the spectra over the 400 to 1800 cm"1 region for {(DMF^MnL^CeFs^PC^hkhMn and Mn[(DMSO)2[H(C6H5)P02]2 are shown as examples in Figure 3.10. The absorptions appearing in the 950-1200 cm"1 region are readily assigned to the antisymmetric and symmetric P0 2 stretches of coordinated phosphinate groups (10-14). As discussed in Chapter 2, the value of A (vP02 anti. - vP0 2 sym.) may be used to obtain structural information. Form II of Mn[(CH3)2P02]2 has a A of 58 cm'1, this small value suggesting the compound has symmetric O-P-0 bridges. This result is consistent with the X-ray crystal data which show this compound has very symmetric O-P-0 bridges. The same conclusion may also be drawn for Mn(DMSO)2[H(C6H5)P02]2 (60 cm"1 in the table). A large separation between the antisymmetric and symmetric P0 2 stretching frequencies was observed for Mn[(C6F5)2P02]2. Since there have been no previous reports on P0 2 stretches of the fiuorinated phenylphosphinates and due to the lack of detailed structural information, it is impossible to draw any conclusions about the nature of the O-P-0 bridge at this stage. However, it should be noted that the value of 107 cm"1 is slighter bigger than that of Y-Mn[(C6H5)2P02]2 (A value of 94 cm"1) (1), a linear chain polymer with tetrahedral metal centers as determined by single crystal X-ray diffraction studies. Mn[(n-C8Hi7)2P02]2 has a A value of 80 cm"1 and may contain relatively symmetric O-P-0 105 bridges. The fluorinated hexyl and octyl derivatives have numerous bands in the 950-1200 cm"1 region. No attempt was made to identify the PO2 stretches for these compounds. Mn[(CH3)2As02]2, Mn[(CH3)(C2H5)P02]2 and Form I of Mn[(CH3)2P02]2 are pink in color, indicating that they may contain octahedral chromophores (15). Magnetic studies on these compounds, to be presented below, support this conclusion. The X-ray powder diffraction studies showed that the latter two phosphinates are isomorphous, further supporting the probable structural similarity in the two compounds. The A values of Mn[(CH3)(C2H5)P02]2 and Mn[(CH3)2P02]2 (Form I) are 91 and 87 cm'1, respectively. These values suggest relatively symmetrical O-P-0 bridges, a finding somewhat surprising in view of the postulated structure in which one oxygen of a given phosphinate bonds to two metals and the other to only one metal. Without X-ray determined structures for these octahedral complexes, nothing more can be concluded concerning this. The S-0 stretching frequency for non-coordinated DMSO is in the range 1055 to 1100 cm"1. This vibration is typically shifted to lower frequencies in the range 910 to 960 cm"1 in coordinated DMSO (16). This is the case for Mn(DMSO)2[H(C6H5)P02]2. The S-0 vibration shifts to 961 cm"1 in the complex. Single crystal X-ray structure analysis shows that this complex has very symmetric O-P-0 bridges (Section 3.2.3.2) and the A value observed for this compound (Table 3.5) is consistent with this. The C-0 stretching frequency for non-coordinated DMF is at 1670 cm"1 (17). This vibration is at 1672 cm"1 for {(DMF)3Mn[//-(C6F5)2P02]3}2Mn, showing almost no shift from the free ligand. 106 Table 3.5. Selected infrared data (cm1) for manganese(II) phosphinates. Complexes v(P02 anti.) v(P02 sym.) A(cm"1) Mn[(CH3)2P02]2 (Form I) 1119vs 1032vs 87 Mn[(CH3)2P02]2 (Form II) 1124vs 1066vs 58 Mn[(CH3)(C2H5)P02]2 1118vs 1027vs 91 Mn[(C6F5)2P02]2 1226vs 1119vs 107 Mn[(n-C8H17)2P02]2 1140vs 1069vs 80 {(DMF)3Mn[//-(C6F5)2P02]3}2Mn 1140vs 1103s 37 Mn(DMSO)2[H(C6H5)P02]2 1130vs 1070vs 60 3.2.6. Magnetic Properties Magnetic susceptibility and magnetic moment data for all the ten manganese(II) phosphinates studied here are given in the Appendix. The effective magnetic moment expected for the 6A!(g) ground state for octahedral or tetrahedral manganese(II) in the absence of magnetic interactions is the spin-only moment of 5.92 u.B. Any magnetic moment below this value except at very low temperatures where effects of weak zero field splitting may occur indicates that there is antiferromagnetic exchange coupling in the complex. All of the compounds studied here exhibit antiferromagnetic behavior as shown by the magnetic moment versus temperature plots (Figure 3.10). Some of the complexes exhibit maxima in their %M versus temperature plots (Figure 3.11), behaviour typical for antiferromagnetic complexes. For the other complexes the maxima presumably occur 107 (V cw e es c E 1800 1600 1400 1200 1000 800 600 400 Wavenumber (cm*1) Figure 3.9. IR spectra of (a) Mn(DMSO)2[H(C6H5)P02l2 and (b) {(DMF)3Mn|>-(C6F5)2P02]3}2Mn. Peaks due to the Nujol are marked with asterisks. 108 below the temperature range accessible to our equipment. Mn[(CH3)2P02]2 (Form II) and Mn(DMSO)2[H(C6H5)P02]2, are shown by X-ray diffraction studies to have extended linear chain structures (Section 3 .2.3) and it is assumed that the other manganese(II) complexes, with the exception of the trimetallic compound, have similar structures. Hence the magnetic data of these complexes were analyzed according to linear chain models. The magnetic data for the trimetallic complex were fitted to a published model for such complexes and this will be described below. For linear chain manganese(II) complexes which exhibit antiferromagnetic exchange behaviour, two theoretical models are available for data analysis. According to the Wagner-Friedberg model (18), the magnetic susceptibility, X H IS given by equation [2.9]. A second model, referred to here as the Weng model, is described by equation [2.10]. In this equation, for S = 5/2, the parameters are A = 2 .9167, B = 208 .04 , C = 15.543 and D = 2707.2 (19, 20). The experimental data were analyzed using both models with fits made to the susceptibility data and with J as a variable parameter and g fixed at 2 .00. The best fit to the experimental susceptibility data was obtained by adjusting J until the function, F, defined by equation [2.6], is minimized. 109 I I I I I 1 I I I I I I I 1 I I I I I I I I L . 0 20 40 60 80 Temperature (K) Figure 3.10. Magnetic moment versus temperature plots for (a) Mn[(CH3)2As02]2, (b) Mn[(CH 3) 2P0 2]2 (Form I), (c) Mn[(CH 3 ) 2 P0 2 ] 2 (Form II), (d) Mn[(DMSO) 2 [H(C 6 H 5 )P0 2 ] 2 , (e) Mn[(C 6 F 5 ) 2 P0 2 ] 2 , (f) Mn[(CH 3 )(C 2 H 5 )P0 2 ] 2 , (g) Mn{[CF 3 (CF 2 ) 5 CH 2 CH 2 ] 2 P0 2 } 2 , (h) Mn{[CF 3 (CF 2 ) 3 CH 2 CH 2 ] 2 P0 2 } 2 , (i) Mn[(n-C 8 Hi 7 ) 2 P0 2 ] 2 and (j) {(DMF) 3Mn[//-(C 6F 5) 2P02] 3}2Mn. 110 0.8 0.6 0.4 0.2 • • A O O • A 0 • a b c d e f g h i j A 4 * ^ * I _L L_ _L _L_ a 5 & & l_ J 0 10 20 30 40 50 60 Temperature (K) 70 80 90 Figure 3.11. Magnetic susceptibility versus temperature plots for (a) Mn[(CH3)2As02]2; (b) Mn[(CH3)2P02]2 (Form I); (c) Mn[(CH3)2P02]2 (Form II); (d) Mn[(DMSO)2[H(C6H5)P02]2; (e) Mn[(C6F5)2P02]2; (f) Mn[(CH3)(C2H5)P02]2; (g) Mn{[CF3(CF2)5CH2CH2]2P02}2; (h) Mn{[CF3(CF2)3CH2CH2]2P02}2; (i) Mn[(n-C8H17)2P02]2; (j) {(DMF)3Mn[//-(C6F5)2P02]3}2Mn, 111 Representative plots of magnetic susceptibility versus temperature are shown in Figure 3.12. In this figure, the data points are experimental and the lines are theoretical, calculated using the best fit values of J obtained from the models. The magnetic parameters obtained are listed in Table 3.6. Mn[(CH3)(C2H5)P02]2 and Mn[(CH3)2P02]2 (Form I) both have exchange coupling constants |J| above 2.5 cm"1. The other compounds have much smaller \J\ values, all of which are below 0.55 cm"1. We postulate that there are two types of complexes which contain different manganese chromophores, one with a distorted octahedral Mn06 chromophore and the other with a tetrahedral MnCU chromophore. This suggestion is supported by IR spectroscopy and by the colors of the compounds. Compounds with MnC>6 chromophore are pink or white while four coordinated MnCu compounds are usually yellow-green (4, 15). Mn[(CH3)(C2H5)P02]2 and Mn[(CH3)2P02]2 (Form I) are pink and likely contain octahedral chromophores. Based on the metal coordination, two possible structures are proposed for the binary manganese complexes. Complexes with Mn0 6 chromophore must have one kind of oxygen which can coordinate two different metal ions, resulting in a sheet polymer (see diagram XV, Figure 1.5). This type of coordination was observed in the crystal structures of Cd(H20)Cl[H(C6H5)P02] (8) and {^[(CH^PCbMx (see section 2.2.2.1). Complexes with Mn04 chromophores are more common and this type of chromophore will lead to a linear chain structure (see diagram IX, Figure 1.5). Mn[(CH3)2P02]2 (Form II) (see section 3.2.3.1) and y-Mn[(C6H5)2P02]2 (1) have been proven to have this linear chain structure by single crystal X-ray diffraction studies. Most copper phosphinate complexes also have this type of structure (9, 11, 12). For complexes having linear chain structures, Mn-O-P-O-Mn is the only possible pathway to mediate magnetic exchange, while for 112 complexes having a sheet structure, both Mn-O-P-O-Mn and Mn-O-Mn could provide magnetic coupling pathways. In the sheet polymers, the much shorter Mn-O-Mn path length would provide a more efficient pathway for exchange than the extended Mn-O-P-O-Mn path. This would explain why Mn[(CH3)(C2H5)P02]2 and Mn[(CH3)2P02]2 (Form I), which are postulated to have sheet polymeric structures, exhibit much stronger antiferromagnetic exchange. We were unable to fit the magnetic data for Mn[(CH3)2As02]2 to either the WFG or the Weng models. However, visual inspection of its ueff versus temperature plot (Figure 3.10) compared to those of Mn[(CH3)(C2H5)P02]2 and Mn[(CH3)2P02]2 (Form I) indicates that the coupling is strong in this compound also. Comparing the values of |J| observed for Mn[(C6F5)2P02]2, Mn{[CF3(CF2)3CH2CH2]2P02}2 and Mn{[CF3(CF2)5CH2CH2]2P02}2 (Table 3.6) with \J\ values for the perhydro analogues we note that in each case the value is higher for the fluorinated analogue. This may reflect stronger phosphinate-manganese bonding in the case of the fluorinated derivatives. Manganese(II) is a relatively hard Lewis acid (reference to Hard/Soft acid base theory) and since fluorinated phosphinates may be expected to be "harder" than perhydro-phosphinates stronger bonding with these acids might be expected. All manganese adduct polymers reported so far have linear chain structures as shown, in most cases, by single crystal X-ray diffraction studies (3, 5, 6). Magnetic studies showed that these complexes exhibit weak antiferromagnetic behavior with coupling constants less than 0.51 cm"1. The structure of the DMSO adduct compound showed that 113 the O-P-0 bridge is very symmetric in this compound. Interestingly, although the coupling constant is smaller than that of the HCONH 2 derivative the DMSO adduct polymer has a very similar Mn-O-P-O-Mn pathlength for exchange. Table 3.7 lists the total Mn-O-P-O-Mn distances and exchange coupling constants for some of manganese adduct complexes reported. This suggests that relative pathlength alone will not provide a guide to expected strength of exchange. The much weaker exchange observed in the H(CeH5)P02H complex was explained in reference (6) as arising from very unsymmetrical O-P-0 bridges, the latter resulting from H-bonding effects. Combined with the previous work, the magnitude of exchange in the Mn(L)2[H(C6H5)P02]2 complexes appears to increase in the order L = py < H(C 6H 5)P0 2H < H C O N H C H 3 < CH3CONH2 < DMSO ~ H 2 0 < HCONH 2. The relative position of the complex containing the N-bonded ligands (the pyridine complex) versus those containing O-bonded ligands may be explained on the basis of relative basicities towards metal ions. The greater basicity of pyridine towards metal ions results in weaker bonding between the metal and the bridging phosphinate ligands in the complex and leads to weaker exchange. The conclusion, previously drawn by Du (1), that short M-O-P-O-M and symmetric O-P-0 bridging results in stronger magnetic exchange also holds in the complexes studied here. 114 Temperature (K) Temperature (K) ^ 0.4 Temperature (K) Temperature (K) Figure 3.12. Magnetic susceptibility versus temperature plots for (a) Mn[(CH3)2P02]2 (Form I), (b) Mn[(CH3)2P02]2 (Form II), (c) Mn[n-(C8H17)2P02]2 and (d) Mn(DMSO)2[H(C6H5)PC>2]2 • Lines were calculated using the Wagner-Friedberg model and the parameters are given in Table 3.6. 115 Table 3.6. Magnetic parameters"' for manganese(II) phosphinate complexes. Complexes -J(cm'l)C Mn[(CH3)2P02]2 (Form I) 2.77 (2.98) 0.054 (0.071) Mn[(CH3)2P02]2 (Form II) 0.17(0.18) 0.0074 (0.019) Mn[(CH3)(C2H5)P02]2 2.58 (2.77) 0.021 (0.027) Mn[(C6F5)2P02]2 0.35 (0.37) 0.045 (0.034) Y-Mn[(C6H5)2P02]2e 0.17(0.17) 0.013 (0.017) Mn[(n-C6H13)2P02]2/ 0.29 (0.32) 0.021 (0.033) Mn[(n-C8H17)2P02]2 0.28 (0.30) 0.013 (0.0070) Mn{ [CF3(CF2)3CH2CH2]2P02}2 0.42 (0.45) 0.040 (0.028) Mn{ [CF3(CF2)5CH2CH2]2P02}2 0.50 (0.54) 0.048 (0.035) {(DMF)3Mn[//-(C6F5)2P02}2]3}2Mng 0.13 0.014 Mn(DMSO)2[H(C6H5)P02]2 0.30 (0.32) 0.020 (0.0076) a The data outside the brackets were obtained using the Weng model (19, 20) and those inside the brackets were obtained using the Wagner-Friedberg model (18). * g was fixed at 2.00. J is considered to be significant to within ±10% d The function F is defined in equation [2.6]. e'f Taken from references 1 and 8, respectively. The parameters were obtained by using the model described by equation [3.7]. 116 Table 3.7. Magnetic parameters and Mn-O-P-O-Mn bond distances for MnL2(H(C6H5)P02]2 complexes. Compound (L) Mn-O-P-O-Mn (A) HCONH 2* 7.38(1) 0.51(1) H 20* 7.41(1) 0.33(1) DMSOC 7.40(1) 0.32(1) CH 3CONH 2* 7.43(1) 0.30(1) H(C6H5)P02HZ' 7.43(1) 0.13(1) a All/values were obtained using the Wagner-Friedberg model (18). Data were taken from references 6 and 8. This work. As described earlier in section in 3.2.3.3, {(DMF)3Mn[//-(C6F 5)2P0 2]3}2Mn contains a linear trimetallic unit. Magnetic coupling among these three manganese ions exists but is very weak as shown by its magnetic moment which decreases very slowly with temperature in the very low temperature region (Figure 3.10). The only compound reported earlier which has a similar structure to this one is Mn3(Ettrz)6(H20)6(CF3S03)6 (where Ettrz is 4-ethyl-l,2,4-triazole) (21). This compound had been characterized both structurally and magnetically. In this compound, the central manganese ion is linked to the other two terminal manganese ions by Ettrz ligands via N atoms and all the manganese ions are octahedrally coordinated. The magnetic susceptibility data were analyzed according to the following equation (21): 117 XM = [N^pVpkT)] x [(105 + 2040e25x + 1860e10x + 1365e20x + 858e15x + 495e4x + 252ex + 252e5x + 858e"3x + 495e"4x + 498e"14x + 252e"23x + 252e"13x + 252e"5x + 105e"30x + 108e"20x + 105e"12x + 105e"6x + 105e"2x + 30e"25x + 30e"17x + 30e"llx + 30e"7x) / (12 + 32e25x + 48e10x + 28e20x + 24e7x + 24e15x + 20e4x + 16ex + 16e5x + 24e"3x + 20e"4x + 24e'14x + 16e"23x + 16e"13x +16e"5x + 12e"30x + 16e"20x + 12e"12x + 12e"6x + 12e"2x + 8e"25x + 8e"17x + 8e"llx + 8e"7x)] [3.7] where x = J/(kT) and XM is the susceptibility per mole of manganese(II). The magnetic susceptibility data for {(DMF)3Mn[//-(C6F5)2P02]3}2Mn were analyzed according to equation [3.7]. The fit was very good as can be seen by the small F value (Table 3.6) and as seen visually in Figure 3.13. This manganese complex exhibits very weak antiferromagnetic behavior indicated by the very small \J\ value. The exchange coupling constant (-0.13 cm"1) is smaller than that reported for the related triazole derivative (-0.6 cm"1) and is also smaller than that obtained for Mn[(C6F5)2P02]2- It might be expected that the more bridging phosphinates the stronger the exchange (as seen in some copper complexes); however, this is not the case here. In comparing the trimetallic complex with Mn[(C6F5)2P02]2 it is important to note that the former has octahedral Mn0 6 chromophores while the latter likely has tetrahedral Mn0 4 chromophores. For steric reasons, this will almost certainly lead to longer Mn-0 bonds in the trimetallic species and this is likely the cause of weaker exchange. 118 Figure 3.13. Plots of magnetic data (per mole of manganese ion) versus temperature for {(DMF)3Mn[//-(C6F5)2P02]3}2Mn. Symbols are experimental data while the lines are calculated using the model described in equation [3.7]. Magnetic moment error bars represent +1% error. Parameters are given in Table 3.6. 119 3.3. Summary and Conclusions All manganese(II) complexes discussed in this Chapter exhibit antiferromagnetic behaviour. Analysis of the magnetic data of {(DMF^MnO-tCeFs^PCbkhMn revealed weaker exchange in this triple phosphinate bridged complex (\J\ = 0.13 cm"1) than in the double phosphinate bridged complex Mn[(C6F5)2P02]2 (M = 0.37 cm"1). Steric factors associated with Mn06 versus Mn04 chromophores were involved to explain this result. The exchange coupling in Mn[(C6F5)2P02]2 is stronger than that in y-MnlXCeHs^PC^k (M = 0.17 cm"1) but comparable to that in 3-Mn[(C6H5)2P02]2 (M = 0.36 cm"1) (1). The other two fluorinated derivatives, MnlfCFstCFz^CFfcCHzkPC^h and Mn{[CF3(CF2)5CH2CH2]2P02}2, both exhibit stronger antiferromagnetic coupling than their perhydro-analogues. Stronger metal ligand interactions in complexes containing the "harder" fluorinated phosphinates were suggested to account for these results. Magnetic susceptibility data of other complexes were analyzed according to linear chain models. Reasonable fits were obtained for all complexes except for Mn[(CH3)2As02]2- The magnetic data of this arsinate complex could not be fitted to either the Weng or Wagner-Friedberg models; however, it was determined that the strength of antiferromagnetic coupling in this compound is comparable to that of Mn[(CH3)2P02]2 (Form I) and Mn[(CH3)(C2H5)P02]2- Unfortunately, without a detailed X-ray structure of the arsinate complex no reasonable explanation of the details of its magnetic behaviour can be offered. The binary phosphinate complexes can be classified into two categories according to their coupling constants, one having weaker antiferromagnetic exchange than the other. These results were explained by structural considerations, one class of compounds having 120 octahedral and the other tetrahedral metal centers. Different pathways for exchange involving the two structural types were proposed. Continuing the work of Du et al. (1), a DMSO adduct polymer has been obtained and characterized both magnetically and structurally. This compound exhibits weak antiferromagnetic behaviour, the magnitude of \J\ being consistent with previously reported magneto-structural correlations involving such complexes. Combined with the work done by Du et al. (1), the magnitude of exchange in the Mn(L)2[H(C6H5)P02]2 complexes increases in the order L = py < H(C 6H5)P0 2H < HCONHCH 3 < CH 3CONH 2 < DMSO ~ H 20 < HCONH2. REFERENCES 1. J.-L. Du, S. J. Rettig, R. C. Thompson and J. Trotter, Can. J. Chem. 69, 277 (1991). 2. J.-L. Du and R. C. Thompson, Can. J. Chem. 67, 1239 (1989). 3. W. V. Cicha, J. S. Haynes, K. W. Oliver, S. J. Rettig, R. C. Thompson and J. Trotter, Can. J. Chem. 63, 1055 (1985). 4. H. D. Gillman, Inorg. Chem. 13, 1921 (1974). 5. P. Betz, A. Bino, J.-L. Du, L. S. M. Lo and R. C. Thompson, Inorg. Chim. Acta, 170, 45 (1990). 6. J.-L. Du, S. J. Rettig, R. C. Thompson, J. Trotter, P. Betz and A. Bino, Can. J. Chem. 70, 732 (1992). 7. K. W. Oliver, Ph. D Dissertation, University of British Columbia, B. C. Canada, 1984. 8. J.-L. Du, Ph. D Dissertation, University of British Columbia, B. C. Canada, 1991. 9. P. Betz and A. Bino, Inorg. Chim. Acta, 149, 171 (1988). 121 10. R. A. Nyquist, J. Mol. Struct. 2, 111 (1968). 11. K. W. Oliver, S. J. Rettig, R. C. Thompson and J. Trotter, Can. J. Chem. 60, 2017 (1982). 12. J. S. Haynes, K. W. Oliver, S. J. Rettig, R. C. Thompson and J. Trotter, Can. J. Chem. 62, 891 (1984). 13. J.-L. Du, K. W. Oliver and R. C. Thompson, Inorg. Chim. Acta, 141, 19 (1988). 14. K. Dehnicke and A. F. Shihada, Structure and Bonding, 28, 52 (1976). 15. F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, 4th Ed., Interscience, New York, 1988. 16. K. Nakamoto, Infrared Spectra of Inorganic and Coordination Compounds, 2nd Ed., 1970, John Wiley & Sons, Inc., New York. 17. D. Dolphin and A. Wick, Tabulation of Infrared Spectra Data, John-Wiley & Sons, New York, 1977. 18. G. R. Wagner and S. A. Friedberg. Phys. Lett. 9, 11 (1964). 19. W. Hiller, J. Strahle, A. Datz, M. Hanack, W. E. Hatfield, L. W. terHaar and P. Gutlich, J. Am. Chem. Soc. 106, 329 (1984). 20. C. H. Weng, Ph. D. Dissertation, Carnegie-Mellon University, Pittsburgh, P. A. U.S.A. 1968. 21. G. Vos, J. G. Haasnoot, G. C. Verschoor and J. Reedijk, Inorg. Chim. Acta, 105, 31 (1985). 122 Chapter 4 C o b a 11 (11) Phosphinate Complexes and C o b alt (II) Dimethylarsinate 4.1. Introduction Du (1) made a series of cobalt(II) monophenylphosphinate adduct polymers of the type CoL2[H(C6H5)P02]2, where L = H20, HCONH 2, pyridine (py) and pyrazine (pyz). Among these complexes, Co(HCONH2)2[H(C6H5)2P02]2 was studied by single crystal X-ray diffraction and found to be isostructural with the manganese(II) analogue (2, 3). Both compounds have a linear chain structure with metal ions linked by doubly-bridged phosphinate ligand and axially coordinated by HCONH 2 via oxygen. On the basis of indirect evidence the other complexes were assigned analogous structures with the exception of the pyz derivative which was suggested to have a sheet polymeric structure (1). The strength of antiferromagnetic exchange coupling for CoL2[H(C6H5)P02]2 complexes appears to increase in the order L = py < pyz < H 20 < HCONH 2. It was suggested that the greater basicity of pyridine and pyrazine towards cobalt(II) may result in weaker bonding between cobalt and the bridging phosphinate in these complexes, and hence weaker exchange. To extend this previous work, Co[H(C6H5)P02H]2[H(C6H5)P02]2 and Co(HCONHCH3)2[H(C6H5)P02]2 were prepared and studied here. Cobalt(II) diphenylphosphinate, like the manganese analogue, has been reported to exist in two forms (4). Designated P and y; the two forms both have tetrahedral metal centers. y-Co[(C6H5)2P02]2 has been studied by single crystal X-ray diffraction (4), 123 confirming that the cobalt(II) ions are four-coordinate and linked by double bridging phosphinate ligands to form a linear chain structure. Both P- and y-forms are antiferromagnetic materials with the y-form having the stronger magnetic coupling. In the present work, the related perfluorophenyl derivative, Co[(C6F5)2P02]2, has been prepared and studied. Only one form of Co[(C6F5)2P02]2 was observed and magnetic studies have revealed antiferromagnetic behavior for this compound also. The monohydrate of Co[(C6F5)2P02]2 was also obtained and studied in this work. In the present work, cobalt(II) dimethylphosphinate was obtained in crystalline form suitable for single crystal X-ray diffraction studies. The compound is isomorphous and also isostructural with the manganese(II) analogue (Form II) described in Chapter 3. For comparison, Co[(CH3)(C2H5)P02]2 and Co[(CH3)2As02]2 were synthesized and studied here. While the effect of changing from dimethyl to methylethyl phosphinate had little affect on structure or magnetism, changing phosphorus for arsenic resulted in a significant change in magnetic properties. In Co[(CH3)2As02]2, the metal ions are octahedrally coordinated and the compound exhibits ferromagnetic behaviour in contrast to the phosphinate analogue which has tetrahedrally coordinated metals and exhibits antiferromagnetic behaviour. Co[(n-C6Hi3)2P02]2 and Co[(n-CgHi7)2P02]2 were synthesized and studied previously in our research group (5, 6). Both compounds exist in two forms, designated I and II. Studies showed that both Form I compounds contain only one type of phosphinate ligand while the Form II compounds contain two types of phosphinate ligands. Both Form I compounds and Form II of the di-n-hexylphosphinate were found to contain distorted 124 tetrahedral chromophores while a distorted octahedral chromophore had been suggested to be present in the di-n-octylphosphinate Form II compound. All four compounds exhibit antiferromagnetic behaviour with the Form I compounds exhibiting stronger magnetic couplings. For comparison with these earlier studies and to explore the effect of increasing the electronegativity of the substituents on phosphorus the partially fluorinated hexyl and octyl derivatives, Co{[CF3(CF2)3CH2CH2]2P02}2 and Co{[CF3(CF2)5CH2CH2]2P02}2 were prepared and studied here. 4.2. Results and Discussion 4.2.1. Syntheses and Thermal Properties Detailed descriptions of the synthetic procedures are given in Chapter 7. A total of nine cobalt(II) complexes, including five binary phosphinates, one binary arsinate and three adduct polymers, were synthesized in this work. The synthetic routes are summarized in the equations below. Crystals of Co[(CH3)2P02]2, suitable for single crystal X-ray diffraction studies, were obtained by using a route similar to that described in equation [4.1] except that a different solvent, namely, DMF, was used here. The synthetic route to Co[(CH3)(C2H5)P02]2 is described by equation [4.2]. Acetone and ethanol were also tested as potential solvents for this reaction but were not found to yield the required precipitate. Cobalt(II) bis(perfluorophenyl)phosphinate was synthesized in two steps. A pink powder was obtained by evaporation after stirring an aqueous solution of cobalt(II) chloride hexahydrate and potassium bis(perfluorophenyl)phosphinate for about two hours. Extraction of this pink powder with acetone and evaporation of the extractants afford the purple product, Co[(C6F5)2P02]2 (see equation [4.3]). As shown by equation [4.4], the 125 synthesis of Co[(CH3)2As02]2 was achieved by mixing cobalt(II) perchlorate hexahydrate with partially neutralized dimethylarsinic acid in ethanol. Co[(C6F5)2P02]2»H20 can be obtained by the route shown in equation [4.5], in which cobalt(II) acetate tetrahydrate reacts with the monohydrate of bis(perfluorophenyl)phosphinic acid in diethyl ether. As shown in equations [4.6] and [4.7], Co{[CF3(CF2)3CH2CH2]2P02}2 can be obtained by the reaction of cobalt(II) chloride hexahydrate with bis(perfluorobutylethyl)phosphinic acid in DMF, and Co{[CF3(CF2)5CH2CH2]2P02}2 can be prepared by mixing cobalt(II) nitrate hexahydrate with partially neutralized bis(perfluorohexylethyl)phosphinic acid. The cobalt(II) monophenylphosphinate adduct complexes were synthesized by using a conventional method in which cobalt(II) monophenylphosphinate is mixed with neutral ligand in an appropriate solvent and stirred for several hours. A representative reaction is shown by equation [4.8]. .Acetone CoCl 2 • 6H 20 +2 (CH 3) 2P0 2H + 2 (C 2H 5) 3N 2,2-DMP Co[(CH3)2P02]2 + 2 [(C2H5)3NH+][Cr] + 6 H 2 0 [ 4 i l ] Co(CH3COO)2 • 4H 20 +2 (CH3)(C2H5)P02H E t h e r ,. Co[(CH3)(C2H5)P02]2 + CH 3COOH + 4 H 2 0 [ 4 2 ] H 2 0 CoCl2-6 H 2 0 +2 (C6F5)2P02K -Co[(C 6F 5) 2P0 2] 2 + 6H20 + 2 KC1 [4.3] Extracted by acetone ^ , N Ethanol Co(C104)2 • 6 H 2 0 +2 (CH 3) 2As0 2H + 2 (C 2H 5) 3N 2 2 _ D M p * Co[(CH3)2As02]2 + 2 [(C2H5)3NH+][C104"] + 6 H 2 0 [ 4 4 ] 126 Diethyl Ether Co(CH3COO)2-4 H 2 0 + 2 (C 6 F 5 ) 2 P0 2 H-H 2 0 » Co[(C 6F 5) 2P0 2] 2 -H 2 0 + 4 H 2 0 + 2 CH 3COOH [4.5] DMF CoCl 2- 6 H 2 0 +2 [CF 3(CF 2) 3CH 2CH 2] 2P0 2H 2 2 , D M p * Co{[CF 3(CF 2) 3CH 2CH 2] 2P0 2} 2 + 6 H 2 0 +2 HC1 [4.6] Ethanol/H20 Co(N0 3) 2 • 6 H 2 0 +2 [CF 3(CF 2) 5CH 2CH 2] 2P0 2H + 2 NaOH -Co{[CF 3(CF 2) 5CH 2CH 2] 2P0 2} 2 +6H 20+2NaN0 3 [4.7] Acetone Co[H(C6H5)P02]2 + 2 H(C 6H 5)P0 2H Co[H(C6H5)P02H]2[H(C6H5)P02]2 [4.8] The thermal analysis studies are summarized in Table 4.1 and representative DSC and TGA curves are shown in Figures 4.1 and 4.2. Thermal analysis revealed that all of the binary cobalt(II) phosphinates studied here, except Co[(CH3)(C2H5)P02]2 and Co[(CH3)2As02]2, undergo a single endothermic event due to melting before the onset of exothermic decomposition at temperatures ranging from 420 °C to 443 °C. Co[(CH3)2P02]2 and Co[(C6F5)2P02]2 melt at the relatively high temperatures at 353 °C and 344 °C, respectively. Compounds with long alkyl group substituents on phosphorus such as Co{[CF3(CF2)3CH2CH2]2P02}2 and Co{[CF3(CF2)5CH2CH2]2P02}2, however, melt at the relatively lower temperatures of 195 °C and 175 °C, respectively. All four compounds undergo exothermic decomposition at temperatures over 400 °C. In comparison, the perhydro-octyl derivative decomposes at much lower temperatures. For example, Form I and Form II of Co[(n-C8Hi7)2P02]2 decompose at 221 °C and 240 °C, respectively (5). At 113 °C, Form His converted to Form I. No melting is observed in 127 either form of this compound. Co[(CH3)(C2H5)P02]2 exhibits two endothermic events at about 58 °C and 174 °C, possibly due to phase transitions, and begins to decompose at around 450 °C, a temperature close to the decomposition temperature of the dimethylphosphinate derivative. Cobalt(II) dimethylarsinate undergoes exothermic decomposition at about 288 °C without melting or undergoing any other thermal events at lower temperatures. This compound is much less thermally stable compared to the phosphinate analogue, Co[(CH3)2P02]2, which decomposes thermally at 443 °C. As shown in Table 4.1, Co[(C 6F 5) 2P0 2] 2 .H 20 losses one mole of water at 118 °C, melts at 343 °C and undergoes exothermic decomposition beginning at about 450 °C. Its thermal properties after losing the water molecule are similar to those of Co[(C6F5)2P02]2, indicating that the monohydrate compound may be converted to its anhydrous form by heating to ~118 °C. In fact, this route was used to obtain bulk samples of the anhydrous compound. Thermal analysis indicates that Co(HCONHCH 3) 2[H(C 6H 5)P0 2] 2 loses both molecules of HCONHCH 3 at about 92 °C. This is followed by an endothermic event at -206 °C, an exothermic decomposition at ~352 °C and another endothermic event at ~561 °C. Similar thermal behaviour was reported for the corresponding manganese derivative (3). In the case of Co[H(C6H5)P02H]2[H(C6H5)P02]2, TGA studies show no clear-cut loss of H(C 6 H 5 )P0 2 H ligands. At a temperature of about 180 °C, slightly more than one mole of H(C 6 H 5 )P0 2 H is lost. At a temperature of 290 °C, this compound undergoes further weight loss but the total weight loss at this temperature is less than expected for two 128 molecules of H(C6H5)P02H. The gradual weight loss may be attributable to partial decomposition of the H(C6H5)P02H ligand. Table 4.1. Thermal parameters for Cobalt(II) phosphinates. Complexes Peak Temp. AH (°C) (kJ mol-1) % Weight Loss Calcd.a Obs. Co[(CH3)2P02]2 353 18 443* Co[(CH3)(C2H5)P02]2 58 3 174 8 450* Co[(CH3)2As02]2 288* Co[(C6F5)2P02]2 344 39 439* Co{ [CF3(CF2)3CH2CH2]2P02}2 195 28 420* Co{[CF3(CF2)5CH2CH2]2P02}2 175 52 425* Co[(C6F5)2P02]2.H20 118 65 343 34 450* Co(HCONHCH3)2[H(C6H5)P02]2 92 48 206 117 352* 48 561 25 Co[H(C6H5)P02H]2[H(C6H5)P02]2 128 55 180 290* 570 2.1 25.7 22.7C 2.3 25.3 9.0 17.7 30 9 20 " Calculated for loss of all neutral ligands. * Onset of exothermic decomposition (°C). All other events are endothermic. c Calculated for loss of one molecule ofH(C6H5)P02H]2. 129 CD +-» O T3 100 200 300 400 Temperature (oC) 500 600 Figure 4.1. DSC thermograms of (a) Co[ (C 6 F 5 ) 2 P0 2 ] 2 and (b) Co(HCONHCH 3 )2 [H(C 6 H 5 )P0 2 ] 2 . 0 100 200 300 400 500 600 700 800 Temperature (°C) Figure 4.2. T G A thermograms of (a) Co[ (C 6 F 5 ) 2 P0 2 ] 2 and (b) Co(HCONHCH 3 ) 2 [H(C 6 H 5 )P0 2 ] 2 . 130 4.2.2. Single Crystal X-ray Diffraction Study of Co[(CH3)2P02]2 4.2.2.1. Structure of cobalt(II) dimethylphosphinate, Co[(CH3)2P02]2 Crystallographic data for Co[(CH3)2P02]2 are given in the Appendix and some bond distances and angles are listed in Table 4.2. The atom numbering scheme is illustrated in Figure 4.3 while a stereoview of the geometry around the cobalt ion is shown in Figure 4.4. The crystal structure of Co[(CH3)2P02]2, which is isostructural with the manganese analogue described in chapter 3, consists of fused eight-membered rings, each ring consisting of two cobalt ions bridged by two phosphinate groups. The rings are connected to form polymeric linear chains, propagating along the crystallographic b axis. The coordination about each cobalt is approximately tetrahedral with O — C o — O bond angles ranging from 103.12(8) to 112.4(1)°. These angles are very close to the bond angles of the y forms of the cobalt(II) and manganese(II) diphenylphosphinate complexes, which range from 104.81(8) to 117.77(9)° and from 103.2(1) to 114.7(1)°, respectively (4). The total Co-O-P-O-Co distance, which is considered an important factor in determining the strength of magnetic coupling between neighbouring metal ions, is 6.905(4) A for Co[(CH3)2P02]2. This is slightly shorter than the M-O-P-O-M distances of 7.038(8) A in Mn[(CH3)2P02]2 (Form II) (described in Chapter 3) and 6.936(8) A in y-Co[(C6H5)2P02]2 (4). 131 Table 4.2. Selected bond lengths (A) and angles (deg) for Co[(CH3)2P02]2*. Bond lengths Co(l>—O(l) 1.949(1) Co(l)—0(2)° 1.943(1) P(l)—O(l) 1.505(1) P(l)—0(2) 1.508(1) Bond angles 0(1)—Co(l)—O(l)6 103.12(8) 0(1)—Co(l)—0(2)° 108.30(6) 0(1)—Co(l)—0(2)C 112.17(6) 0(2)°—Co(l>—0(2) c 112.4(1) * Superscripts refer to symmetry operations: ° x, 1 - y, 1/2 + z; * 1 - x, y, 3/2 - z; ° 1 - x, - y, 1 - z. Figure 4.3. Atom numbering scheme for Co[(CH3)2P02]2; 33% probability thermal ellipsoids are shown for non-hydrogen atoms. 132 Figure 4.4. Stereoview of the geometry about cobalt for Co[(CH3)2P02]2. 33% probability thermal ellipsoids are shown for non-hydrogen atoms. 4.2.3. X-ray Powder Diffraction Diffraction patterns are given in Figure 4.5, Due to the lack of sufficient sample, powder diffraction patterns were not obtained for the partially fiuorinated octyl and hexyl derivatives. Co[(CH3)2P02]2 is isomorphous and isostructural with Mn[(CH3)2P02]2 (Form II) discussed earlier. These compounds have similar IR spectra and similar magnetic properties. Cobalt(U) methylethylphosphinate is not isomorphous with the dimethyl analogue indicated by the powder diffraction patterns; however, both compounds have tetrahedral metal chromophores as evidenced by their electronic spectra and probably have similar structures based on similar vibrational spectra. Cobalt(U) bis(perfluorophenyl)phosphinate monohydrate is isomorphous with the nickel(II) 133 derivative (to be described in Chapter 5). The X-ray powder patterns of Co(HCONHCH3)2[H(C6H5)P02]2 and Co[H(C6H5)P02H]2[H(C6H5)P02]2 reveal that they are isomorphous with the corresponding manganese derivatives (3) and the corresponding nickel(II) derivatives (Chapter 5). Co[(CH3)2As02]2 and Co[(C6F5)2P02]2 have unique diffraction patterns with that of the former, involving very broad peaks, suggesting a high degree of amorphism. in •*» 'S • . c u < t/3 B ii CtfHCONHCHsMHCtHsPOih JU Co(HC«H$P02Hh(HC6H5P02h JLLJL I , • • • I • • , • I • • t i I • • • • I • • • • I • • • • I i • • i I i i 5 10 15 20 25 30 35 40 45 50 55 60 2 © Figure 4 5 X-ray powder diffraction patterns for Co(HCONHCH3)2[H(C6H5)P02]2 and Co[H(C6H5)P02H]2[H(C6H5)P02]2 (Continued on the next page). 134 •A ' 1 J 1 *- • * • — » > n w»^. j r L l | L I • • • • I • • • • I 1 • • ' 1 ' • • • I • • ' • • I I I ' ' I — I . . . . I — I 5 10 15 20 25 30 35 40 45 50 55 60 2 0 Figure 4.5. (Continued) X-ray powder diffraction patterns for (a) Co[(CH3)2P02]2; (b) Co[(CH3)(C2H5)P02]2; (c) Co[(CH3)2As02]2; (d) Co[(C6F5)2P02]2 and (e) Co[(C6F5)2P02]2 • H 20. 135 4.2.4. Infrared Spectroscopy Some selected infrared data are listed in Table 4.3 and some selected spectra are shown in Figures 4.6 and 4.7. The absorptions appearing in the 950-1200 cm"1 region are readily assigned to the antisymmetric and symmetric P0 2 stretches of coordinated phosphinate groups (7-12). The vibrational spectra of Co{[CF3(CF2)3CH2CH2]2P02}2 and Co{[CF3(CF2)5CH2CH2]2P02}2 show numerous peaks in this region and no attempt was made to assign these peaks and or to identify the P0 2 stretches. The P0 2 stretching frequencies and A values (A = v(P02 anti.) - v(P02 sym.)) for several compounds are given in Table 4.3. The A values of 55 and 66 cm"1 respectively for Co[(CH3)2P02]2 and Co[(CH3)(C2H5)P02]2 suggest the presence of equivalent P-0 bonds in these complexes. X-ray studies on the dimethyl compound support this conclusion. Co(HCONHCH3)2[H(C6H5)P02]2 has a A value of 94 cm"1 which is in the range of symmetric O-P-0 bonds and this is supported by other examples. y-Co[(C6H5)2P02]2 and y-Mn[(C6H5)2P02]2 have A values of 86 and 94 cm"1 and symmetrical O-P-0 bridging units were confirmed in these materials by single crystal X-ray diffraction studies (4). Usually, antisymmetric and symmetric PO2 stretching frequencies will shift from "free ion" values, to lower and higher frequencies, respectively, in coordination complexes (12-21). The infrared spectrum of (C6F5)2P02K shows two strong absorptions at 1255 cm"1 and 1111 cm"1 which are tentatively assigned to the antisymmetric and symmetric P0 2 136 stretching frequencies. The frequencies of these bands are shifted to 1225 cm"1 and 1122 cm"1 on coordination to cobalt(II). It should be noted these assignments of P 0 2 stretches for compounds containing the bis(perfluorophenyl)phosphinate ligand are tentative. The A values observed for Co[(C6F5)2P02]2 and Co[(C 6F 5) 2P0 2] 2 .H 20 are 103 and 101 cm"1, respectively. In the absence of detailed structural information on complexes of this phosphinate ligand it is not possible to correlate these A values with the nature of O-P-0 bridge. Frequencies in the range 2200-2500 cm"1 may be assigned to P-H stretches for monophenylphosphinic acid and its salts (13, 16, 22-26). In the HCONHCH 3 adduct complex, only one broad band around 2390 cm"1 was observed in the infrared spectrum, suggesting that only one type of phosphinate anion is present in this complex. This is consistent with the conclusion drawn from the analysis of the PO2 stretching frequencies described above. More than one type of phosphinate unit in Co[H(C6H5)P02H]2[H(C6H5)P02]2 results in the presence of several bands in the P 0 2 stretching region for this compound. As expected more than one P-H band is also observed in the 2339-2424 cm"1 region for this compound. Single crystal X-ray diffraction studies have shown that, in phosphinate adduct polymers, amide ligands such as HCONH 2 and CH 3CONH 2 are bonded to the metal through the oxygen atom (2, 3). A carbonyl stretching frequency, lower compared to that in the free state, is expected and has been observed. For example, the C=0 stretching frequencies are shifted from 1680 cm'1 (free HCONH2) to 1674 cm"1 in Mn(HCONH 2) 2[H(C 6H 5)P0 2] 2 and from 1680 cm"1 (free CH3CONH2) to 1653 cm"1 in 137 Mn(CH3CONH2)2[H(C6H5)P02]2. For the HCONHCH 3 ligand, a similar shift from 1663 cm"1 (free) to 1657 cm"1 (coordinated) has also been observed (3). In the IR spectrum of the currently studied compound, Co(HCONHCH3)2[H(C6Hs)P02]2, the C=0 band is shifted to 1649 cm"1. A broad band at 3220 cm"1 in Co(HCONHCH3)2[H(C6H5)P02]2 can be assigned to the N-H stretching frequency (27, 28). As in the manganese(II) analogue, the N-H stretching frequency for Co(HCONHCH3)2[H(C6H5)P02]2 is not shifted relative to that in free HCONHCH 3. Very sharp bands at 3583 and 3522 cm"1 in the infrared spectrum of Co[(C6F5)2P02]2.H20 may be assigned to the O-H stretching frequencies of water. This assignment was supported by a deuterium test in which the H 2 0 molecules were substituted by D 20. The two bands shift to 2664 cm"1 and 2576 cm"1, respectively. This compares with calculated values of 2607 and 2563 cm"1. These values were obtained using equation [4.9] (29) and by assuming the force constants are the same for O-H and O-D vibrations. (where v is frequency of vibration, K is the force constant for the vibration, and u. is the reduced mass (which can be calculated by 1/u. = 1/mi + l/m2, and mi and m2 are the masses of the two nuclei)). The assignment of bands to As0 2 symmetric and antisymmetric stretches (Table 4.3) should be considered tentative. The fact they occur at significantly lower frequencies than [4.9] 138 PO2 stretches is of course expected considering the larger mass of arsenic compared to phosphorus. Table 4.3. Selected infrared data (cm"1) for cobalt(II) complexes. Complexes v(P02 anti.) v(P02 sym.) A^m"1)" Co[(CH3)2P02]2 1118vs 1063vs 55 Co[(CH3)(C2H5)2P02]2 1120vs 1054s 66 Co[(CH3)2As02]2Z' 899sh, 845vs 788vs 84 Co[(C6F5)2P02]2 1225vs 1122s 103 Co[(C6F5)2P02]2.H20 1219vs 1118s 101 Co(HCONHCH3)2[H(C6H5)P02]2 1133vs 1045vs 94 Co(H(C6H5)P02H]2[H(C6H5)P02]2 1109-1176 1071-1022 c a A = v(P02 anti.) - v(P02 sym.). Refers to As0 2 stretches. A value can not be calculated for this compound. 139 Figure 4.6. JJR spectra of Co[(CH3)2P02]2 (top) and CoKCH^AsO^ (bottom). Peaks due to Nujol are marked by asterisks. 140 Wavenumber (cm") Figure 4 7 IR spectra of CofHCONHCHaOTC^PO^ (top) and Ftgure 4.7. ^ ^ ^ o ^ ^ ^ O P O , ] , (bottom). Peaks due to Nujol are marked by asterisks. 141 4.2.5. Electronic Spectroscopy The binary phosphinates Co[(CH3)2P02]2, Co[(CH3)(C2H5)P02]2, Co[(C6F5)2P02]2, Co{[CF3(CF2)3CH2CH2]2P02}2 and Co{[CF3(CF2)5CH2CH2]2P02}2 are blue in color while the arsinate, Co[(CH3)2As02]2, is pink. The adduct complexes Co(HCONHCH3)2[H(C6H5)P02]2, Co[(H(C6H5)P02H]2[H(C6H5)P02]2 and Co[(C6F 5) 2P0 2] 2»H 20 are also pink in colour. Representative electronic spectra for these complexes over the range 300 nm to 2000 nm are shown in Figure 4.8 and band positions and assignments are given in Table 4.4. Due to lack of sufficient sample the electronic spectrum of Co{[(CF3(CF2)5CH2CH2]2P02}2 was not obtained. A blue color is consistent with the compound having a tetrahedral or distorted tetrahedral ligand/metal chromophore while a pink color is consistent with the compounds having an octahedral or distorted octahedral ligand/metal chromophore (30, 31). Single crystal X-ray diffraction studies have shown that Co[(CH3)2P02]2 is a linear chain polymer with tetrahedrally coordinated cobalt(II) centers. The color and electronic spectrum of this compound is consistent with this structure. Electronic spectroscopy studies indicate that all of the blue compounds have similar spectra comparable to that of the tetrahedral cobalt(II) anion, CoCL2" (31), suggesting that they all have structures similar to that of Co[(CH3)2P02]2. Although the electronic spectrum of Co{[(CF3(CF2)5CH2CH2]2P02}2 is unavailable, its color and magnetic properties (described latter in this chapter) suggest that it also has this same structure. The Ligand Field splitting parameters, Dg, and the interelectron repulsion (Racah) parameters, B, were obtained from equations [1.5] and [1.6] (see Chapter 1) and are given in Table 4.4. The Dq 142 values are in the range 364 to 375 cm"1 and the B values are from 804 to 825 cm"1 for these complexes (compared to Dq = 320 cm" and B = 730 cm" 1 for CoCl/"). All of the pink complexes (except Co[(C6F5)2P02]2»H20) have similar electronic spectra to that obtained for Co(HCONH2)2[(H(C6H5)P02]2. This latter complex contains a distorted octahedral Co040'2 chromophore as determined by single crystal X-ray diffraction studies (1, 2). Calculated Dq values range from 823 to 851 cm"1 and are close to the value of 915 cm"1 reported for Co(H 20)6 2 + (31). B values obtained for these complexes are in the range 804 to 825 cm"1, compared to the value of 845 cm"1 for Co(H20)62+. Included in this group of compounds is Co[(CH3)2As02]2 and hence the electronic spectrum shows that the cobalt(II) ions are octahedrally coordinated in this complex also. Octahedral geometry around the cobalt(II) ion requires that one oxygen atom from one arsinate or phosphinate anion must coordinate to two different cobalt(II) ions, leading to a sheet polymer as discussed in Chapter 1. The adduct complexes have linear chain structures in which cobalt(II) ions are linked by double phosphinate bridges and are axially coordinated by neutral ligands via oxygen to complete the octahedral coordination about cobalt. Such structures have been confirmed by X-ray diffraction studies for manganese and cobalt complexes (2, 3). The electronic spectrum (as shown in Figure 4.9) of Co[(C6F5)2P02]2»H20 is very similar to that of P-Co(paphy)2Cl2 (paphy is l,3-bis(2'-pyridyl)-2,3-diaza-l-propene) (32) which is known to have approximate square-pyramidal symmetry, and differs from those of the other pink complexes studied here. This compound may be proposed to have a linear chain structure with metal ions linked by double phosphinate bridges, and 143 coordinated axially by the water molecules, forming a square-pyramidal geometry (see Figure 4.10 for its proposed structure). Table 4.4. Electronic spectra data for cobalt(II) complexes. Complexes Band Position (nm) (cm"1 in brackets) Assignment" (cm 1) B (cm"1) Co[(CH 3 ) 2 P0 2 ] 2 560sh (17, 900)1 b 590sh (16, 900)j 634s (15, 800J/ 1380w (7, 25"6)7 b 1540w (6, 490)1 1710w (5, 850)] ' j , (P) <r- % 4T, (F) <- % 374 804 Co[(CH 3 )(C 2 H 5 )P0 2 ] 2 560sh(17, 900)1 b 585sh(17, 100))-635s (15, 700y 1380w (7, 25(5)) * 1560w (6, 410)V 1710w (5, 850)) 4T, (P) <- 4A2 "T, (F) <- 4A2 373 812 Co[(C 6 F 5 ) 2 P0 2 ] 2 555sh(18, 000)] * 580sh(17, 2 0 0 K 595sh (16, 800) 630s (15, 900jy 1400w (7, 140)) b 1600w (6, 250)1 1730w(5, 780)) 4Tj(P)<^4A2 4T,(F)^4A2 364 821 Co {[CF 3 (CF 2 ) 3 CH 2 CH 2 ] 2 P0 2 ] }2 550sh(18, 200)) 6 580sh (17, 200)V 625s (16, 000)J 900w( l l , 100) 1340w (7, 460)) 6 1540w (6, 490)f 4T, (P) <- % c 4T, (F) <- 4A2 375 825 Table continued overleaf. 144 Table 4.4 (continued) Complexes Band Position (nm) Assignment" Dq B (cm"1 in brackets) (cm_1) (cm"1) Co[(CH3)2As02]2 490sh (20,400)? h 4Tlg (P) <- 4T!g(F) 851 788 545s (18, 300)J 630sh (15, 900) 4A2g (F) <- 4TIg (F) 1250w (8, 000) 4T2g (F) <- 4Tlg (F) Co[(C6F5)2P02]2.H20 445s (22, 500) d 490s (20, 400) 540s (18, 500) 620sh(16, 100) 1200m (8, 300) 1725w(5, 800) 500sh (20,000)7 6 823 873 525sh (19, 000)L 4Tlg (P) <- 4T!g(F) 540s(18, 500}J 650sh (15, 400) 4A2g (F) <- 4T,g (F) 1200w (8, 3307) h 4T2g (F) <- 4Tlg (F) 1390w (7, 190)} f 475sh(21, 1007) b 836 919 495sh (20, 200) K 4T,g (P) <- 4Tlg (F) 540s (18, 500JJ 640sh (15, 600) 4A2g (F) <- 4Tlg (F) 1200w (8,330))* 4T2g(F)<r- 4Tlg (F) 1390w(7, 190) | a Based on (approximate) tetrahedral and octahedral symmetries. 6 Centers of gravity of these bands were used for calculating Dq. c Possibly due to a spin-forbidden transition (33). d No attempt was made to assign these bands. e Co(HCONHCH3)2[H(C6H5)P02]2. /Co[(H(C6H5)P02H]2[H(C6H5)P02]2. 145 400 600 800 1000 1200 1400 1600 1800 2000 Wavelength (nm) Figure 4.8. Electronic spectra for (a) Co[(CH3)2P02]2 and (b) Co[H(C6H5)P02H]2[H(C6H5)P02]2. I I I I I I I I I I I I I I I I I 1 I I I I I I I I I I I I I I I I I I ' I I I I I 400 600 800 1000 1200 1400 1600 1800 2000 Wavelength (nm) Figure 4.9. Electronic Spectrum of Co[(C6F5)2P02]2«H20. Figure 4.10. A linear chain polymeric structure with a square-pyramidal geometry around the metal centers proposed for Co[(C6F5)2P02]2»H20 147 4.2.6. Magnetic Properties and Magneto-structural Correlations The discussion of the magnetic properties of these complexes is divided into two sections. One section considers five binary cobalt(II) phosphinate complexes, Co[(CH3)2P02]2, Co[(CH3)(C2H5)P02]2, Co[(C6F5)2P02]2, Co{[CF3(CF2)3CH2CH2]2P02]}2 and Co{[CF3(CF2)5CH2CH2]2P02]}2, all of them considered to contain tetrahedral or a pseudo-tetrahedral geometry about cobalt. The second section will be devoted to the adduct polymers, Co(HCONHCH3)2[H(C6H5)P02]2, Co[H(C6H5)P02H]2[H(C6H5)P02]2 and to Co[(C6F5)2P02]2.H20 and will include the binary arsinate complex, Co[(CH3)2As02]2. All of these latter complexes are considered to involve pseudo-octahedral cobalt(II) centers except Co[(C6F 5) 2P0 2] 2»H 20 which is proposed to have square-pyramidal cobalt centers. 4.2.6.1. Tetrahedral Complexes When the cobalt(II) ion is in a tetrahedral environment, the ground electronic state is an orbital singlet 4A2 state. Even in a distorted tetrahedral environment the ground state will be orbitally non-degenerate. Hence, the magnetic moment of a tetrahedral cobalt(II) complex is expected to be temperature independent over a wide range of temperature with possibly some decrease in moment at the lowest temperatures due to the effects of zero-field splitting (34). Magnetic susceptibilities measured on the VSM magnetometer over the temperature range of 82 K to 2 K for Co[(CH3)2P02]2 and Co[(C6F5)2P02]2, 82 K to 4 K for Co{CF3(CF2)3CH2CH2P02}2 and Co[(CH3)(C2H5)P02]2, and on the SQUID 148 magnetometer over the temperature range of 300 K to 1.86 K for Co{CF3(CF2)5CH2CH2]2P02}2 are all given in the Appendix, together with calculated values of u.eff. Magnetic moment versus temperature plots for all the above compounds are shown in Figure 4.11. The magnetic moment decreases with decreasing temperature for all five compounds. To examine the possibility of this being caused by zero-field splitting we examined fits of the magnetic susceptibilities to the model (34) described in equation [4.10]. l + 9e-2* r 4 + f ( 1 - C " 2 ' > X l l _ C 4 ( l + e-2 x)' X l 4(l + e- 2 x) [ 4 1 0 ] where x = £>/kT, C = Ng^/kT and the powder magnetic susceptibility is % = (xn + 2x±)/3. All attempts gave very poor agreement between experiment and theory and it was concluded that zero-field splitting effects alone cannot account for the magnetic behaviour of these complexes. The strong temperature dependence of ueff suggests the presence of antiferromagnetic exchange interactions for all five compounds. Assuming the temperature variation of the moment arises primarily from antiferromagnetic coupling, the susceptibility data were fitted to the WFG (35) and Weng (36, 37), S = 3/2 models for linear chains. There is little difference in the quality of fit using these two models, the fit being reasonable for both models for all compounds except for Co{[CF3(CF2)5CH2CH2]2P02}2- This complex will be discussed later in this section. Values of the best fit magnetic parameters are given in Table 4.5 and the best fit magnetic susceptibility curves using the WFG model are shown in Figure 4.12. As shown in Table 149 4.5, magnetic exchange constants for these cobalt(II) complexes are comparable to that obtained for Y-CO[(C6H 5) 2P0 2 ]2 (-J = 0.60 cm"1 for WFG model) which has a linear chain structure with tetrahedrally coordinated cobalt centers as determined by single crystal X-ray diffraction studies (4). This result suggests that the substituents on the phosphorus atoms have no major effect on the strength of magnetic exchange, however, a difference in the magnitude of magnetic exchange between non-fluorinated and fluorinated compounds exists. Magnetic exchange coupling decreases on going from a perhydro-derivative to the fluorinated analogue. For example, the absolute value of the coupling constant drops from 0.60 cm"1 for y-Co[(C 6H 5) 2P0 2] 2 to about 0.37 cm"1 for the perfluorophenyl analogue. Form I compounds of cobalt(II) di-n-hexyl- and di-n-octyl-phosphinate (6), which have the same metal/ligand chromophore as the partially fluorinated derivatives studied here, have \J\ values of 3.2 cm"1 and 2.7 cm"1, respectively, these values dropping to around 0.7 cm"1 for the corresponding fluorinated complexes as shown in Table 4.5. From the above investigation, the conclusion may be drawn that the "harder" fluorinated phosphinates form weaker bonds to cobalt(II) than the "softer" perhydro-analogues resulting in weaker magnetic coupling in the case of the fluorinated derivatives. Recall that in the discussion on manganese(II) derivatives (Chapter 3) the "harder" acid manganese(II) appeared to form stronger bonds with the harder fluorinated phosphinates leading to stronger magnetic coupling in that case. As shown in Figure 4.11, Co{[CF3(CF2)5CH2CH2]2P02}2 has a moment of 5.01 u B at about 300 K. This value is a bit higher than that expected for a tetrahedral Co(II) ion (38). The moment decreases with decreasing temperature, indicating the compound exhibits 150 antiferromagnetic behaviour. Fits of the magnetic data to theory for antiferromagnetic coupling in linear chains measured over the full temperature range are poor as indicated by the F values and plots shown in Table 4.5 and Figure 4.13, respectively. Fits of the magnetic data over the low temperature range of 80 K to 1.86 K are better as shown in Table 4.5 and Figure 4.13. The parameter values obtained for the low temperature fits are also reasonable in view of the similarity to the values obtained for the other complexes studied here. Also compared to other complexes, this is the only compound which has magnetic data measured to 300 K. The agreement with theory is as good as for the other complexes at temperatures below 82 K. We are not sure why the agreement is not good over the whole temperature region studied but it may result from minor structural changes resulting from changing interchain interactions (called solid state fluxionality in Chapter 2) over the wide range of temperatures studied. 151 Table 4.5. Magnetic parameters" for cobalt(II) phosphinate complexes. Complexes -J (cm-1) g F° Co[(CH3)2P02]2 0.46 (0.50) 2.41 (2.40) 0.035 (0.003) Co[(CH3)(C2H5)P02]2 0.56 (0.59) 2.33 (2.31) 0.007 (0.006) Co[(C6F5)2P02]2 0.34(0.37) 2.28 (2.28) 0.044 (0.019) Co{ [CF3(CF2)3CH2CH2]2P02}2 0.67 (0.71) 2.39 (2.37) 0.009 (0.007) Co{ [CF3(CF2)5CH2CH2]2P02}2 0^.65 (0.73) 0^.59 (0.66) 2.46 (2.45) 2.37(2.37) 0.055 (0.053) 0.011 (0.0007) a The data outside the brackets were obtained using the Weng model (36, 37) and those inside the brackets were obtained using the Wagner-Friedberg model (35). Values of J and g are considered accurate to ±10% and ±2%, respectively. The function F is defined in equation [2.6]. Fits over temperature range of 1.86-300 K. f Fits over low temperature region ranging from 1.86 to 80 K. 152 pa =L ¥ 4 a S © fl J WD 88 5 T - « O O ° ° ° • o « fi A • V A - o. A n 4 ) A3* O 5 i o s 2 r j i i I_I i i i i i i i i i _ • i i i I i i i i L 0 50 100 150 200 250 300 Temperature (K) 1_J I L _ J I I I I I 1 1 I I I 1 1 1 1 I I I I 1 I I I I I I I I I 1 I I I I I I I I I L _L 0 10 20 30 40 50 60 70 80 90 Temperature (K) Figure 4.11. Magnetic moment versus temperature plots for Co[(CH3)2P02]2 (circle), Co[(CH3)(C2H5)P02]2 (square), Co[(C6F5)2P02]2 (triangle), Co{[CF3(CF2)3CH2CH2]2P02}2 (hexagon) and for Co{[CF3(CF2)5CH2CH2]2P02}2 (solid dots). The inset shows data obtained for the last compound over the temperature region 2-300 K. 153 Figure 4.12. Magnetic susceptibility versus temperature plots for: (a) Co[(CH3)2P02]2; (b) Co[(CH3)(C2H5)P02]2; (c) Co[(C6F5)2P02]2; d) Co{[CF3(CF2)3CH2CH2]2P02}2. Lines are calculated using the WFG model and the parameters are given in Table 4.5. 154 0 50 100 150 200 250 300 Temperature (K) Temperature (K) i i i i I i i i i I i i i i I i i i i I i i i i I i i i i 0 50 100 150 200 250 300 Temperature (K) Figure 4.13. Magnetic data versus temperature plots for Co{[CF3(CF2)5CH2CH2]2P02}2-Circles are experimental data while lines are calculated from the WFG model (35) and the parameters are given in Table 4.5. Plots over the low temperature region of 1.86 to 80 K are shown in insets. The solid lines are calculated for the whole temperature range from 1.86 to 300 K while the dash line are calculated by using only the data points in the low temperature region from 1.86 to 80 K. 155 4.2.6.2. Octahedral Complexes and a Five-coordinate Compound Magnetic susceptibility and magnetic moment data for Co(HCONHCH3)2[H(C6H5)P02]2, Co[H(C6H5)P02H]2[H(C6H5)P02]2, Co[(C6F5)2P02]2.H20 and Co[(CH3)2As02]2 are recorded in the Appendix. Magnetic moment versus temperature plots (measured at 7,501 G) for the three phosphinate complexes are given in Figure 4.14, and moment versus temperature plots for Co[(CH3)2As02]2 obtained at various fields are given in Figure 4.15. The electronic ground state for high-spin cobalt(II) in an octahedral environment is 4Tig. This state is split in an axial field to yield, for axial elongation, a 4A2g ground state as shown in Figure 4.16 where the effect of zero-field splitting on the 4A2g ground state is also depicted (39). The analysis of the magnetic properties of an isolated cobalt(II) ion, in an axially distorted octahedral field, can therefore be expected to be complicated as the properties are affected by a number of factors including electron derealization, spin-orbit coupling, extent of distortion and mixing of excited states into the ground state. These factors may be termed "single ion effects". The complexes studied here are polymeric leading to the possibility that the cobalt(II) ions are not isolated but are, in fact, exchange coupled. Because of single ion effects interpretation of magnetic exchange in such complexes can be rather difficult. The magnetic properties of each of the complexes are discussed separately below. 156 5.0 4.5 4.0 pa *s 3.5 ••a c u ss (WO 3.0 2.5 2.0 1.5 1.0 - • • 5 fi rn • ° fi 8 ft • 1 o B - ° 0 J A i o a 7 O A : ° A D • b — A O A c • — • - • - • - • t i i i 1 i i i i 1 i i i i 1 i i i i 1 i i i i i i i i 1 i • i i i i i i , , , , 0 10 20 30 40 50 60 70 80 90 Temperature (K) Figure 4.14. Magnetic moment versus temperature plots for (a) Co[(H(C6H5)P02H]2[H(C6H5)P02]2, (b) Co(HCONHCH3)2[H(C6H5)P02]2 and (c) Co[(C6F5)2P02]2.H20. 157 14 12 10 1 1 1 1 1 1 • H=2549 G • • H=5251G - D • ? • o H=7501G - » f ; » A H=9225 G - OA 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 V O A Q V O AOv AO , , , 1 , , , , 1 , , , , 1 , , , , 0 10 20 30 40 50 60 70 80 90 Temperature (K) Figure 4.15. Magnetic moment versus temperature plot for Co[(CH3)2As02]2 A2g s JL^r'. y* 4. A r - M s = -3/2 A2g 1 J - K ' . 2D Ms = 11/2 Free ion Octahedral Axial field Zero-field field splitting 158 Co[(H(C6H5)P02H]2[H(C6H5)P02]2 The magnetic moment of this compound decreases with decreasing temperature from 4.5 U B at 82 K to 3.3 U B at 4.2 K. Magnetic susceptibility and magnetic moment values calculated from theory for zero-field splitting of the ground 4A2g stage (equation [4.10], reference 34) are compared with experiment in Figure 4.17. The curves shown in the figure are calculated with the best fit values of the parameters D = 31 cm"1 and g = 2.28 (F = 0.055). Better fits to the experimental data were obtained employing low temperature data only. This is expected since the zero-field splitting model may be expected to work best at low temperatures. This gave best fit values of D = 15 cm"1, g = 2.12 (F = 0.025). These attempts at analyzing the magnetic data have shown that zero-field splitting effects alone cannot account for the observed behaviour. The magnetic properties of Co[(H(C6H5)P02H]2[H(C6H5)P02]2 may also be accounted for on the basis of weak antiferromagnetic coupling between metal centers. As described earlier, Co[(H(C6H5)P02H]2[H(C6H5)P02]2 is proposed to have a linear chain polymeric structure; hence, the WFG (35) and Weng (36, 37) one-dimensional exchange models were used in attempting to analyze the magnetic data. The problem of analyzing for antiferromagnetic coupling in the presence of the other factors affecting the magnetic properties of pseudo-octahedral cobalt(II) complexes, discussed above, is simplified if the assumption is made that the distortion from Of, symmetry is sufficiently strong that the splitting of the 4Tlg term leaves a well isolated 4A2g orbital singlet as the ground state (39). Thermal population of excited states is ignored in this case. Under this assumption the 159 Figure 4.17. Magnetic susceptibility versus temperature plot (top) and magnetic moment versus temperature plot (bottom) for Co[(H(C6H5)P02H]2[H(C6H5)P02]2. Circles are the experimental data while the solid lines are calculated from the zero-field splitting model (34) by using the all data point; the dashed lines are calculated by using only the data points in the range 4.4 to 31 K. 160 magnetic properties of this compound may be analyzed according to the WFG model (35) with S = 3/2 or according to the Weng model with the coefficients generated by Hill et al. (36, 37) for S = 3/2. The best fit parameters utilizing these models are given in Table 4.6. The best fit curve using the WFG model is shown in Figure 4.18. There is a discrepancy between the general shapes of the experimental and calculated curves; moreover the deviation of the g value (~2.26) from the spin-only value (2.00) shows that the orbital contribution to the susceptibility cannot be totally "quenched" as is assumed by the model. An alternative approach to the interpretation of the magnetic data for a six-coordinate cobalt(II) ion, particularly at low temperatures, is to consider that spin-orbit coupling splits the 4Tig term in such a way that the lowest level, a Kramers' doublet, is the only thermally occupied level. Under this assumption one needs to consider an effective spin, S' = 1/2 (40). The best fit parameters using the WFG and Weng models for S'= 1/2 are given in Table 4.5. As indicated by the F values the fits are no better than for the S = 3/2 models. In treating this cobalt(II) system as an effective spin S'= 1/2, thermal population of the excited states above the ground Kramers doublet is ignored, hence the model fits would be expected to work best at the lowest temperatures. We therefore examined fits to the low temperature data only (2 to 30 K) using both WFG and Weng with S' = Ml models. The fits over this limited temperature range are better for both models and the representative fitting curve for the WFG model is shown in Figure 4.18. As described above, the fits of the magnetic data of Co[(H(C6H5)P02H]2[H(C6H5)P02]2 to zero-field splitting and one-dimensional chain 161 Figure 4.18. Magnetic susceptibility versus temperature plot (top) and magnetic moment versus temperature plot (bottom) for Co[(H(C6H5)P02H]2[H(C6H5)P02]2. Circles are the experimental data while the solid lines are calculated from the WFG S = 3/2 model (35) by using the all data point; the dashed lines are calculated from the WFG S 1/2 model by using only the data points in the range 4.4 to 31 K. 162 models are similar. In both cases the fits over the whole temperature range studied are poor while each model generates similar fits to the low temperature data. In summary one can conclude that any antiferromagnetic coupling present in this compound must be very weak. Co(HCONHCH3)2[H(C6H5)P02]2 As shown in Figure 4.19, the magnetic susceptibility versus temperature plot for Co(HCONHCH3)2[H(C6H5)P02]2 exhibits a maximum at about 4 K, indicative of significant antiferromagnetic exchange in this complex. The data were analyzed employing linear chain models as described for Co[(H(C6H5)P02H]2[H(C6H5)P02]2 and the corresponding parameters are given in Table 4.6. Plots of magnetic susceptibility versus temperature for the HCONHCH 3 complex are compared with theory in Figure 4.19. In this case much better agreement between experiment and theory was obtained for both fits to all data as well as for fits to the low temperature data only. It is clear that the magnetic exchange is significantly stronger than that in the H(C6H5)P02H complex. In view of the complexities involved in analyzing the magnetic properties of distorted octahedral cobalt(II) systems like the above two adduct complexes one should not place too much reliance on the significance of the actual values of the exchange constants. Du (1) determined exchange coupling constants for several cobalt(II) adduct polymers and combined with the values for the two new complexes studied here, the exchange coupling 163 Figure 4.19. Magnetic susceptibility versus temperature plot (top) and magnetic moment versus temperature plot (bottom) for Co(HCONHCH3)2[H(C6H5)P02]2. Circles are the experimental data while the solid lines are calculated from WFG S = 3/2 model (35) using the all data points; the dashed lines are calculated from the WFG S = 1/2 model using only the data points in the range 2.2 to 31 K. 164 appears to increase in the order L = py < pyz ~ H(C 6H 5)P0 2H < H 2 0 < HCONHCH 3 < HCONH2 for CoL2[H(C6H5)P02]2 complexes. This order was previously found for analogous manganese(II) complexes (3). The relative positions of the complexes containing N-bonded ligands versus those containing O-bonded ligands may be explained on the basis of relative basicities towards metal ions. The greater basicity of pyridine and pyrazine towards metal ions result in weaker bonding between the metal and the bridging phosphinate ligands in these complexes and hence weaker exchange. Co[(C6F5)2P02]2.H20 X-ray powder diffraction studies have shown that this compound is isomorphous with the nickel(II) analogue to be discussed in Chapter 5. Both compounds are proposed to have square-pyramidal metal chromophores. The proposed structure is given in Figure 4.10. As shown in Figure 4.14, the magnetic moment of Co[(C6F5)2P02]2.H20 decreases with decreasing temperature from 4.5 | i B at 82 K to 2.99 U.B at 4.2 K, indicating the presence of antiferromagnetic behaviour. The magnetic data have been analyzed as for Co[(H(C6H5)P02H]2[H(C6H5)P02]2 and the corresponding parameters are given in Table 4.6. Plots of magnetic susceptibility versus temperature for Co[(C6F5)2P02]2»H20 are compared with theory in Figure 4.20. In this case agreement between experiment and theory appears to be a little better for the low temperature data fitted to the WFG S' = 1/2 model. The magnetic exchange in this compound appears to be a little stronger than that in the H(C 6H 5)P0 2H adduct complex. 165 Co[(CH3)2As02]2 As shown in Figure 4.15, the magnetic moment of Co[(CH3)2As02]2 increases with decreasing temperature, indicating ferromagnetic coupling in this complex. The magnetic moment reaches a maximum at about 10 K, then decreases when the temperature is further lowered due to the effects of magnetic saturation. This saturation effect is more clearly seen in Figure 4.21 in which the magnetic susceptibility is seen to approach a constant value at low temperatures and the susceptibility becomes field dependent below 10 K. Theoretically, magnetization saturation, M, a t , can be calculated by the expression (40): MS!A = SNgB [4.11] where N is Avogadro's number, g is the Lande splitting factor, B is the electron Bohr magneton and S is the total spin of the paramagnetic ion. For high spin cobalt(II), the theoretical saturation magnetization is 16755 cm3 G mol"1 (calculated from equation [4.11] for S = 3/2 and g = 2). Because of the zero-field splitting, the saturation magnetization can be as small as 5585 cm3 G mol"1 (for S = 1/2) at low temperatures. At a field of 2549 G and a temperature of 4.2 K, the experimental magnetization of Co[(CH3)2As02]2 is 8220 cm3 G mol"1. At a field of 50000 G and a temperature of 2 K, the magnetization is 11930 cm3 G mol"1, suggesting that the cobalt(II) ion in this complex has a S = 3/2 ground electronic state and at the experimental conditions studied, its magnetization has not reached saturation. As shown in Figure 4.22, at low temperature and high field the magnetization of Co[(CH3)2As02]2 approaches saturation. 166 Co[(CH3)2As02]2 contains an octahedral chromophore and is proposed to have a sheet polymeric structure as shown in Figure 1.5 (Chapter 1). Magnetic interactions (for d7-d7) via Co-O-Co 90° pathways result in ferromagnetic exchange (41). Table 4.6. Magnetic parameter for cobalt(II) phosphinate complexes. Models* Complexes" WFG Weng WFG Weng WFG C WengC s 3/2 3/2 1/2 1/2 1/2 1/2 g 2.26 2.27 5.04 5.03 4.74 4.74 J (cm1) 0.41 0.39 2.04 1.62 1.42 1.20 F 0.069 0.065 0.069 0.073 0.025 0.027 (b) S 3/2 3/2 1/2 1/2 1/2 1/2 g 2.36 2.36 5.27 5.17 5.02 4.84 J (cm1) 0.84 0.74 4.20 2.84 3.77 2.50 F 0.053 0.060 0.053 0.075 0.018 0.029 (c) S 3/2 • 3/2 1/2 1/2 1/2 1/2 g 2.24 2.25 5.00 4.97 4.61 4.59 J (cm"1) 0.55 0.51 2.74 2.06 1.83 1.48 F 0.086 0.081 0.086 0.096 0.033 0.039 a (a) Co[(H(C6H5)P02H]2[H(C6H5)P02]2, (b) Co(HCONHCH3)2[H(C6H5)P02]2 and (c) Co[(C6F5)2P02]2.H20. See text for details about the models used. c Data are fitted to the magnetic data obtained below 31 K. All other fits were made to data over the whole temperature range. d Values of J and g are considered accurate to ±2% and ±1%, respectively. The function F is defined in equation [2.6]. 167 Figure 4.20. Magnetic susceptibility versus temperature plot (top) and magnetic moment versus temperature plot (bottom) for Co[(C6F5)2P02]2.H20. Circles are the experimental data while the solid lines are calculated from the WFG S = 3/2 model (35) by using the all data points; the dashed lines are calculated from the WFG S = 1/2 model using only the data points in the range 4.2 to 30 K. 168 4 o = S n. CJ Ul 3 CJ CJ = (90 • • • • o H=2549 G H=5251 G H=7501 G H=9225 G • • O _J I I I I I I I 1 I I I I I I I I I I i , 7, P i a , ° , V i ° , A 9v Q A P V . A Q • • • 0 0 10 20 30 40 50 60 70 80 90 Temperature (K) Figure 4.21. Magnetic susceptibility versus temperature plots for Co[(CH3)2As02]2 at various fields as indicated in the plots. 169 14000 12000 -3 10000 o 9 8000 6000 4000 2000 r-, O Q & O 5 o 2 o o 8 0 A o o • * rt ° A o O 0 o ° 2 K D 4 K A 8 K o 10 K 0 20 K o o _l I I 1_ I I I . J_ _1 I I L_ _ L _ L 10000 20000 30000 40000 Field (Gauss) 50000 60000 Figure 4.22. Magnetization versus field plots for Co[(CH3)2As02]2 at various temperatures. 170 4.3. Summary and Conclusions Single crystal X-ray studies on Co[(CH3)2P02]2 showed that the complex is a linear chain polymer with tetrahedrally coordinated cobalt(II) ions linked by double phosphinate bridges. Electronic spectroscopy studies reveal that four other binary complexes, namely, Co[(CH3)(C2H5)P02]2, Co[(C6F5)2P02]2, Co([CF3(CF2)3CH2CH2]2P02]}2 and Co{[CF3(CF2)5CH2CH2]2P02]}2 also have tetrahedral metal/ligand chromophores and probably have similar linear chain polymeric structures. All of these complexes exhibit antiferromagnetic behavior and the magnetic data were successfully analyzed employing two linear chain S = 3/2 models. Studies showed that the antiferromagnetic exchange coupling increases from Co[(CH3)2P02]2 (0.50 cm"1) to Co[(CH3)(C2H5)P02]2 (0.59 cm"1), a result consistent with the findings for related copper(II) phosphinates (41). The fluorinated complexes exhibit weaker antiferromagnetic coupling than the corresponding perhydro-derivatives and this has been interpreted as the result of weaker Co-ligand bonds in the case of the fluorinated ligands. In contrast to the binary cobalt(II) phosphinates, Co[(CH3)2As02]2 has distorted octahedral metal centers and a sheet polymeric structure. Magnetic exchange interactions via the Co-O-Co pathway have been suggested as the cause of the overall ferromagnetic behaviour of this compound. Three cobalt(II) adduct complexes, Co[H(C6H5)P02H]2[H(C6H5)P02]2, Co(HCONHCH3)2[H(C6H5)P02]2 and Co[(C6F5)2P02]2.H20 have been prepared and studied in this work. The two monophenylphosphinates represent an extension of the work of Du (1). It was found that the H(C6H5)P02H adduct complex exhibits no significant 171 magnetic exchange behavior while the HCONHCH 3 adduct complex exhibits significant antiferromagnetic coupling. Combined with the work of Du (1), the magnitude of exchange in CoL2[H(C6H5)P02]2 phosphinate bridged complexes, appears to increase in the order L = py ~ H(C 6H 5)P0 2H < pyz < H 2 0 < HCONHCH 3 < HCONH 2. This order was previously observed in analogous manganese(II) complexes (3). Co[(C6F5)2P02]2.H20 is suggested to have a linear chain polymeric structure with water molecules bonding axially, leading to a square-pyramidal geometry around the cobalt(II) ions. There is evidence for antiferromagnetic exchange in this compound and the data have been analyzed employing linear-chain models. REFERENCES 1. J.-L. Du, Ph. D Dissertation, University of British Columbia, B. C. Canada, 1991. 2. P. Betz, A. Bino, J.-L. Du, L. S.-M. Lo and R. C. Thompson, Inorg. Chim. Acta, 170, 45 (1990). 3. J.-L. Du, S. J. Rettig, R. C. Thompson, J. Trotter, P. Betz and A. Bino, Can. J. Chem. 70, 732 (1992). 4. J.-L. Du, S. J. Rettig, R. C. Thompson and J. Trotter, Can. J. Chem. 69, 277 (1991). 5. P. B. Banks, B. Sc. Thesis, University of British Columbia, B. C. Canada, 1986. 6. - D. G. Nygard, B. Sc. Thesis, University of British Columbia, B. C. Canada, 1990. 7. H. D. Gillman, Inorg. Chem. 11, 3124 (1972). 8. R. A. Nyquist, J. Mol. Struct. 2, 111 (1968). 172 9. K. W. Oliver, S. J. Rettig, R. C. Thompson and J. Trotter, Can. J. Chem. 60, 2017 (1982). 10. J. S. Haynes, K. W. Oliver, S. J. Rettig, R. C. Thompson and J. Trotter, Can. J. Chem. 62, 891 (1984). 11. J. L. Du, K. W. Oliver and R. C. Thompson, Inorg. Chim. Acta, 141, 19 (1988). 12. K. Dehnicke and A. F. Shihada, Structure and Bonding, 28, 52 (1976). 13. D: E. C. Corbridge and E. J. Lowe, J. Chem. Soc. 493 (1954). 14. D. E. C. Corbridge and E. J. Lowe, J. Chem. Soc. 4555 (1954). 15. L. C. Thomas and R. A. Chittendon, Spectrochim. Acta, 26A, 781 (1970). 16. M. Tsuboi, J. Am. Chem. Soc. 79, 1351 (1957). 17. J. R. Ferraro, J. Inorg. Nucl. Chem. 24, 475 (1962). 18. E. A. Robinson, Can. J. Chem. 41, 173 (1963). 19. E. A. Robinson, Can. J. Chem. 41, 302 C1963). 20. L. C. Thomas and R. A. Chittendon, Spetrochim. Acta, 20, 467 (1964). 21. L. C. Thomas and R. A. Chittendon, Spetrochim. Acta, 20, 489 (1964). 22. N. C. Johnson and W. E. Rull, Inorg. Chim. Acta, 27, 191 (1978). 23. L. W. Daasch and D. C. Smith, Anal. Chem., 23, 853 (1951). 24. D. E. C. Corbridge, Topics in Phosphorus Chem., 6, 235 (1969). 25. L. S. Mayants and E. I. Matrosov, Izvest. Akad. Nauk. SSSR, Neorg. Mat, 1, 546 (1965). 26. J. Sala-Pala, R. Kergoat and J. E. Duerchais, C. R. Acad. Sci. Paris, Ser. C, 274, 595 (1972). 27. D. Dolphin and A. Wick, Tabulation of Infrared Spectra Data, John-Wiley & Sons, New York, 1977. 28. D. Welti, Infrared Vapor Spectra, Heyden & Son Ltd., 1970. 173 29. K, Nakamoto, Infrared Spectra of Inorganic and Coordination Compounds, 2nd Ed., 1970, John Wiley & Sons, Inc., New York. 30. F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, 5th Ed., Interscience, New York, 1988. 31. B.N. Figgis, Introduction to Ligand Fields, Interscience Publishers, a division of John Wiley & Sons, New York, 1966. 32. A. B. P. Lever, Inorganic Electronic Spectroscopy, 2nd Ed. Elsevier Publishing Company, New York, 1984. Also see reference: I. G. Dance, M. Gerloch, J. Lewis, F. S. Stephens and F. Lions, Nature, 210, 298 (1966) 33. J. Taylor and R. C. Thompson, Can. J. Chem. 49, 511 (1971). 34. C. J. O'Connor, Prog. Inorg. Chem. 29, 203 (1982). 35. G. R. Wagner and S. A. Friedberg. Phys. Lett. 9, 11 (1964). 36. W. Hiller, J. Strahle, A. Datz, M. Hanack, W. E. Hatfield, L. W. terHaar and P. Giitlich, J. Am. Chem. Soc. 106, 329 (1984). 37. C. H. Weng, Ph. D. Dissertation, Carnegie-Mellon University, Pittsburgh, P. A. U.S.A. 1968. 38. A. Earnshaw, Magnetochemistry, Academic Press, London and New York, 1968. 39. E. A. Boudreaux and L. N. Mulay, Theory and Application of Molecular Paramagnetism. John Wiley & Sons, New York, 1976. 40. R. L. Carlin, Magnetochemistry, Berlin Heidelberg, Springer-Verlag, 1986. 41. J. S. Haynes, K. W. Oliver and R. C. Thompson, Can. J. Chem. 63, 1111 (1985). 174 Chapter 5 Nickel(II) Phosphinate Complexes and Ni c ke I (II) Dimethylarsinate 5.1. Introduction A series of nickel(II) monophenylphosphinate adduct polymers of the type NiL2[H(C6H5)2P02]2, where L = H20, HCONH 2, pyridine (py) and pyrazine (pyz), was synthesized and studied earlier by Du (1). Although none of the complexes were obtained in crystalline form suitable for single crystal X-ray diffraction studies, electronic spectral and vibrational spectral analyses and X-ray powder diffraction studies were used to obtain structural information. It was concluded that these complexes have linear chain polymeric structures, with metal ions linked by double phosphinate units and axially coordinated by L via oxygen or nitrogen atoms, completing distorted octahedral NiC^O^ or N1O4N2 chromophores. These nickel(II) complexes appear to be isomorphous with their cobalt(II) and manganese(II) analogues (1). The nickel complexes exhibit antiferromagnetic coupling between the metal centers and as for the cobalt(II) complexes, the strength of the coupling increases as a function of L in the order py < pyz < H 20 < HCONH 2. To expand the series of nickel(II) monophenylphosphinate adduct polymers, the new complexes, Ni(HCONHCH3)2[H(C6H5)P02]2 and Ni[H(C6H5)P02H]2[H(C6H5)P02]2 were prepared and studied in this work. Both complexes were found to be isomorphous with the cobalt(II) analogues described in Chapter 4 and, like their cobalt analogues, to exhibit antiferromagnetic behaviour. 175 Previous studies have shown that two forms of binary nickel(II) diaryl- or dialkyl-phosphinate complexes exist. In one form the compounds are yellow in color and have octahedral nickel coordination geometry. Such a geometry inevitably involves one phosphinate oxygen atom coordinating two different metal ions, resulting in a sheet polymer as discussed in Chapter 1. Some examples of this form include Ni[H(C6H5)P02]2 (1) and Ni[(n-C8Hi7)2P02]2 (2, 3). Magnetic studies have shown that these complexes exhibit ferromagnetic behavior. Three complexes, Ni[(CH3)2P02]2, Ni[(CH3)(C2H5)P02]2 and Ni{[CF3(CF2)5CH2CH2]2P02}2 obtained and studied in this work, are classified in this group. In addition, Ni[(CH3)2As02]2, also prepared and studied here as a comparison with the dimethylphosphinate analogue, appears to have a structure involving octahedral centers. All four nickel(II) complexes studied here are yellow, have distorted octahedral metal geometries and exhibit ferromagnetic behavior. Binary nickel(II) phosphinates of the second form have structures involving tetrahedral coordination around the metal centers. These complexes are purple. Examples of this type of polymer from the work of others include Ni[(/-C4H9)2P02]2, Ni[(n-C4H9)2P02]2 and Ni[(n-C8Hi7)2P02]2 (3, 4). Studies have shown that these three complexes exhibit polymorphism. All three complexes may be obtained in both yellow and purple forms, the latter obtained by simply heating the corresponding yellow form. The structures of the purple nickel complexes are proposed to be analogous to the structures of Mn[(CH3)2P02]2 (Form II) and Co[(CH3)2P02]2, both of which have been determined by single crystal X-ray diffraction studies (described in Chapters 3 and 4). The structure involves tetrahedral metal centers linked in extended chains by double bridging 176 phosphinates. Two purple complexes, Ni[(C6H5)2P02]2 and [Ni[(C6F5)2P02]2, were synthesized and studied in this work. These complexes were found to exhibit antiferromagnetic behaviour, in contrast to the ferromagnetic behaviour of the yellow form complexes. The monohydrate of [Ni[(C6F5)2P02]2 was also obtained and studied in this work. 5.2. Results and Discussion 5.2.1. Syntheses and Thermal Properties Detailed descriptions of the synthetic procedures are given in Chapter 7. A total of nine nickel(II) phosphinate complexes, including six binary and three adduct compounds, has been synthesized. The synthetic routes are summarized in the equations below. Ni[(CH3)2P02]2 and Ni[(CH3)(C2H5)P02]2 were obtained as described in equation [5.1] except that different solvents were used in the individual preparations. For the former, ethanol was used as solvent while in the latter case diethyl ether was used for reasons described in the preparation of the cobalt analogue (see Chapter 4). The preparation of Ni[(CH3)2As02]2 is described in equation [5.2]. In this reaction the nickel(II) salt was mixed with dimethylarsinic acid which had been partially neutralized by an organic base. In only a few minutes of stirring the reaction mixture a yellow precipitate formed. Care must be taken to handle this moisture sensitive compound. Ni{[CF3(CF2)5CH2CH2]2P02}2 was synthesized by mixing the nickel(II) salt with bis(perfluoro-n-hexylethyl)phosphinic acid which was partially neutralized with sodium hydroxide in aqueous solution (equation [5.4]. Ni([H(C6H5)P02H]2[H(C6H5)P02]2 can be prepared by two different synthetic routes detailed in equations [5.6] and [5.7]. Ni(HCONHCH3)2[H(C6H5)P02]2 was 177 synthesized employing analogous procedures. Both compounds are light green in colour. Ni[(C6F5)2P02]2 was obtained after heating its monohydrate at 290 °C for about 4 h (equation [5.5]). NiKCeFs^PC^k'HbO is a green powder and stable in the air while the anhydrous complex is very air sensitive. We experienced some difficulties in synthesizing Ni[(C6H5)2P02]2. Reactions done in solution in various solvents, including acetone and ethanol, did not yield a precipitate. Hence a solid state reaction was tried, in which nickel(II) carbonate mixed with diphenylphosphinic acid was heated in a furnace in a stream of dinitrogen (see equation [5.3]). The final product was extracted with acetone. Later studies showed that this compound to be very hygroscopic; hence, the handling of this compound was conducted in a dinitrogen glove box. Ethanol Ni(CH 3COO) 2-4H 20 + 2(CH 3) 2P0 2H Ni[(CH3)2P02]2 +2CH 3 COOH + 4H 2 0 [5.1] Ethanol Ni(C104)2 • 6 H 2 0 +2 (CH 3) 2As0 2H + 2 (C 2H 5) 3N 2 2 _ D M p " Ni[(CH3)2As02]2 + 2 [(C2H5)3NH+][C104"] + 6 H 2 0 [ 5 2 ] 250 °C, N 2 NiC0 3 + 2 (C 6H 5) 2P0 2H — Ni[(C6H5)2P02]2 + C 0 2 + H 2 0 [5.3] H 2 0 Ni(N03)2 • 6 H 2 0 +2 [CF 3(CF 2) 5CH 2CH 2] 2P0 2H + 2 NaOH— •Ni{[CF3(CF2)5CH2CH2]2P02}2 + 8 H 2 0 +2 NaN0 3 [5.4] 178 Ni(CH3COO)2 • 4 H 2 0 + 2 ( C ^ P C ^ F ! • H 2 0 D i e t h y 1 E t h e r , Ni[(C 6F 5) 2P0 2] 2-H 20+ 6 H 2 0 + 2 CH 3COOH N 2 3—»- Ni[(C6F5)2P02]2 + H 2 0 [5.5] 290 C Acetone Ni[H(C6H5)P02]2 + 2 H(C 6H 5)P0 2H Ni[H(C6H5)P02H]2[H(C6H5)P02]2 [5.6] Ni(N03)2 -6 H 2 0 + 4 H(C 6H 5)P0 2H + 2 (C 2H 5) 3N 2 2 p M p • Ni[H(C6H5)P02H]2[H(C6H5)P02]2 + 2 [(C2H5)3NH+][N03"] + 6 H 2 0 [5.7] The results of thermal analyses are given in Table 5.1 and representative DSC and TGA curves are shown in Figures 5.1 and 5.2. Thermal analysis by DSC and TGA revealed that nickel(II) dimethylphosphinate and dimethylarsinate experience no other thermal events prior to exothermic decomposition. The thermal stability of the arsinate compound (decomposition starts at 310 °C) is significantly lower than that of the phosphinate (decomposition starts at about 410 °C). This had been observed for the cobalt(II) analogues (Chapter 4). Ni[(CH3)(C2H5)P02]2 melts at 342 °C before it decomposes at 385 °C. This decomposition temperature is slightly lower than that of the dimethyl derivative (410 °C). This is consistent with the earlier finding that the longer is the alkyl group attached to the phosphorus atom, the lower is the decomposition temperature (5-7). As shown in Table 5.1, Ni[(C6H5)2P02]2 decomposes at 450 °C, 55 °C higher than nickel(II) bis(perfluorophenyl)phosphinate. The DSC curve for Ni[(C6H5)2P02]2 shows that prior to the decomposition there are three small endothermic 179 peaks with enthalpies less than 5 kJ per mole. These may possibly be due to various phase transitions. Ni[(C6F5)2P02]2.H20, like the cobalt analogue, loses a molecule of water before melting and decomposition. Interestingly the temperature at which the water is lost is significantly higher in the nickel complex (229 °C) than in the cobalt complex (118 °C). The two nickel(II) monophenylphosphinate adduct complexes exhibit similar thermal events to those of the corresponding cobalt compounds (see Chapter 4). Ni(HCONHCH3)2[H(C6H5)P02]2 loses both molecules of HCONHCH 3 at 145 °C, then exhibits another endothermic peak around 205 °C possibly due to the melting of residual Ni[H(C6H5)P02]2. Decomposition begins at around 327 °C. Ni[H(C6H5)P02H]2[H(C6H5)P02]2, however, loses only one molecule of H(C 6H 5)P0 2H up to about 230 °C at which temperature exothermic decomposition begins. This complex then experiences gradual weight loss up to about 540 °C with weight losses amounting to an additional 40%. Ni{[CF3(CF2)5CH2CH2]2P02}2 decomposes at around 236 °C following two small endothermic events at about 86 °C and 161°C. These endothermic events may involve phase transitions. More importantly, it was observed with the help of a melting apparatus (described in Chapter 7) that this yellow compound begins to transform at ~ 86 °C into a purple form. This indicates that the second, purple, form of this compound may be obtained by heating and hence, like the perhydro- analogue (2, 3), polymorphism is exhibited in this partially fiuorinated octyl derivative. Because of the shortage of sample, no further investigation of this phenomenon was possible. The thermal stability of this partially fiuorinated nickel(II) compound is lower than that of the 180 perhydro-derivative, Ni[(n-CgHn)2P02]2, which decomposes at about 300 °C as determined in this work. Table 5.1. Thermal parameters for nickel(II) complexes. Complexes Peak Temp. (°C) A H (kJ mole"1) Ni[(CH3)2P02]2 410° Ni[(CH3)(C2H5)P02]2 342 59 385* Ni[(CH3)2As02]2 310* Ni[(C6F5)2P02]2 314 33 395* Ni[(C 6H5)2P02]2 160 2 318 5 334 4 450C Ni{ [CF3(CF2)5CH2CH2]2P02}2 86 5 161 0.3 236* Table 5.1 continued overleaf. 181 Table 5.1 (Continued) Complexes Peak Temp. (°C) A H (kJ mole"1) % Weight Loss Calcd. Obs. Ni [ (C 6 F 5 ) 2 P0 2 ] 2 .H 2 0 229 99 2.ld 2.5 308 36 398* Ni(HCONHCH 3 ) 2 [H(C 6 H 5 )P0 2 ] 2 145 45 25. ld 25.2 205 73 327* 40 25.3 516 27 Ni[H(C 6 H 5 )P0 2 H] 2 [H(C 6 H 5 )P0 2 ] 2 175 71 230* 84 22.7* 22.0 310 8.1 540 32 a Decomposition starts and complicated events are observed. This event is exothermic and accompanied by weight loss. All other events are endothermic unless otherwise specified. Onset of endothermic decomposition. d Calculated for loss of all neutral ligands. Calculated for loss of one molecule of H(CeH 5)P0 2H. 182 X a b J _ J I 1 L-l 1 I I I I I I I I 1 L _ J I I I I I I I I I I 1_ 0 100 200 300 400 500 600 Temperature (°C) Figure 5.1. DSC thermograms of (a) Ni[(CH3)2P02]2 and (b) Ni(HCONHCH3)2[H(C6H5)P02]2. 0 100 200 300 400 500 600 700 800 Temperature (°C) Figure 5.2. TGA thermograms of (a) Ni[(CH3)2P02]2}2 and (b) Ni(HCONHCH3)2[H(C6H5)P02]2 183 5.2.2. X-ray Powder Diffraction Ni[(C6H5)2P02]2 is very hygroscopic and instantly changes color when a sample is exposed to the air. For this reason, no X-ray powder diffraction experiment could be performed on this compound. In addition, the amount of Ni{[CF3(CF2)5CH2CH2]2P02}2 available for study was not sufficient to obtain an X-ray powder diffractogram. Diffraction patterns for the remaining seven nickel(II) compounds studied here are given in Figures 5.3(a) and 5.3(b). As evidenced from the powder patterns shown in Figures 5.3(a) and 5.3(b), no two nickel compounds studied here appear to be isomorphous with each other except Ni[(CH3)2P02]2 and Ni[(CH3)(C2H5)P02]2. As described in Chapter 4, the X-ray powder pattern for Ni[(C6F5)2P02]2-H20 is very similar to that for ColXCsFs^PC^k'FfcO, indicating that these two compounds are isomorphous and likely isostructural with each other. They may have the same linear chain structure with five-coordinate metal centers. The X-ray powder patterns of Ni(HCONHCH3)2[H(C6H5)P02]2 and Ni[H(C6H5)P02H]2[H(C6H5)P02]2 reveal that they are isomorphous with their manganese analogues reported elsewhere (7) and also with the analogous cobalt(II) complexes (discussed in Chapter 4). The structure of Mn[H(C6H5)P02H]2[H(C6H5)P02]2, determined by single crystal X-ray diffraction studies (7), involves linear polymeric chains with octahedrally coordinated metal ions linked by double phosphinate bridges. Two axially coordinated monophenylphosphinic acid molecules complete the coordination sphere of the metal. A similar structure was suggested for Mn(HCONHCH3)2[H(C6H5)P02]2 based on indirect evidence. The two nickel(II) monophenylphosphinate adduct compounds 184 studied here likely have the same structure as the manganese(II) analogues as indicated by indirect evidence to be presented below. e .e %m < (0i e Ni(HC«H)P02H)3(HC«HsP02)2 J _JL_I_L1JUJI oj** JUL. Ni(HCONHCH3)i(HC*H$P02)j r r y W & i I'l'l I l I l | I iTt ' l ' l -r . I I I I I I'l I I I I I 10 20 30 40 50 60 2 0 Figure 5 3(a) X-ray powder diffraction patterns for K . t H ^ P O ^ ^ C G W P O . h Figure 5.3W. ^ ™ K ^ c o r a a ^ < ^ ^ (bottom). 185 Figure 5.3(b). X-ray powder diffraction patterns for (a) Ni[(CH3)2P02]2; (b) Ni[(CH3)(C2H5)P02]2; (c) Ni[(CH3)2As02]2; (d) Ni[(C6F5)2P02]2; and (e) Ni[(C6F5)2P02]2.H20. 186 5.2.3. Infrared Spectroscopy Some selected infrared data are listed in Table 5.2 and some representative spectra are shown in Figures 5.4(a) and 5.4(b). Absorption bands appearing in the 950-1200 cm"1 region are readily assigned to the antisymmetric and symmetric PO2 stretches of coordinated phosphinate groups. However, Ni{[CF3(CF2)5CH2CH2]2P02}2 has numerous peaks in this region (observed also in the copper(II) analogue described in Chapter 2), hence, no attempt was made to assign the peaks in this region for this compound. The PO2 stretching frequencies and A values (A = v(P02 anti.) - v(P02 sym.)) (3, 4, 8) for some compounds studied here are given in Table 5.2. The X-ray powder diffraction studies show that Ni[(CH3)2P02]2 and Ni[(CH3)(C2H5)P02]2 are isomorphous each other. Moreover, electronic spectral studies indicate that both compounds have octahedral metal chromophores and infrared spectra show the compounds have almost the same A values (91 and 94 cm"1, respectively). These results suggest the two compounds are also isostructural. Ni[(C6Hs)2P02]2 has a A value of 86 cm"1, within the range of symmetric O-P-0 bridges. For comparison, the previous reported y-forms of Co[(C6H5)2P02]2 and Mn[(C6H5)2P02]2 have A values of 86 and 94 cm"1, respectively, and symmetrical O-P-0 bridging units as confirmed by single crystal X-ray diffraction studies (9). Mn[H(C6H5)P02H]2[H(C6H5)P02]2, on the other hand, has a A value of 118 cm"1 and 187 unsymmetrical O-P-0 bridges as confirmed by single crystal X-ray diffraction studies (7). Ni(HCONHCH3)2[H(C6H5)P02]2 exhibits a A value of 94 cm"1, indicating it has relatively symmetric O-P-0 bridging groups. The numerous peaks in the P0 2 stretching region observed for the H(C 6H5)P0 2H adduct complex are consistent with the presence of more than one type of phosphinate in this complex. The A values observed for Ni[(C6F5)2P02]2 and Ni[(C6F5)2P02]2'H20 are 99 and 123 cm"1, respectively. In the absence of detailed structural information on complexes of this phosphinate ligand it is not possible to correlate these A values with the nature of O-P-0 bridge. However, one can conclude that Ni[(C6F5)2P02]2 niay contain more symmetric O-P-0 bridges than the corresponding monohydrate compound. Tentative assignments for v(As02 anti.) and v(As02 sym.) in the compound Ni[(CH3)2As02]2 are given in Table 5.2. These frequencies appear to be in the correct region when compared with the PO2 stretching vibrations of the phosphinate analogue, Ni[(CH3)2P02]2 (Table 5.2). The larger mass of As compared to P is expected to lead to lower frequencies. For example, employing the P0 2 stretching frequencies and equation [4.9] (10) given in Chapter 4 the As02 frequencies are calculated to be 995 and 913 cm"1. The bands close to these in the observed spectrum of Ni[(CH3)2As02]2 are those listed in Table 5.2. Frequencies in the range of 2200-2500 cm"1 may be assigned to the P-H stretches for monophenylphosphinic acid or its salts (11-17). For the HCONHCH 3 adduct complex, only one band around 2400 cm"1 was observed in the infrared spectrum, suggesting only 188 one type of phosphinate anion present in the complex. More than one type of phosphinate unit is present in Ni[H(C6H5)P02H]2[H(C6H5)P02]2 and, as expected, this leads to more than one observed band in the P-H stretching region of this compound. Single crystal X-ray diffraction studies have shown that amide ligands such as HCONH2 and CH3CONH2 are bonded to the metal through the oxygen atom in adduct phosphinate polymers involving these ligands (7, 18) and a lower carbonyl stretching frequency (compared to that of the free ligand) is expected and observed. For example, the C=0 stretching frequencies are shifted from 1680 cm"1 (free HCONH2) to 1674 cm'1 in Mn(HCONH2)2[H(C6H5)P02]2 and from 1680 cm"1 (free CH3CONH2) to 1653 cm"1 in Mn(CH3CONH2)2[H(C6H5)P02]2. For the HCONHCH 3 ligand, a similar shift from 1663 cm"1 (free ligand) to 1657 cm"1 (coordinated ligand) was also observed (7). In the IR spectrum of the currently studied compound Ni(HCONHCH3)2[H(C6H5)P02]2, this C=0 band is shifted to 1648 cm"1. Moreover, a broad band at 3203 cm"1 can be assigned to the N-H stretching frequency of the amide (19, 20). This N-H band has been shifted to lower frequency compared to 3220 cm"1 (free HCONHCH3). An analogous shift was not observed in the manganese(II) analogue reported earlier (7). Very sharp bands at 3555 and 3499 cm"1 in the infrared spectrum of Ni[(C6F5)2P02]2»H20 may be assigned to the O-H stretching vibrations of the water molecules. This assignment of bands for Ni[(C6F5)2P02]2»H20 is consistent with a similar assignment for the cobalt(II) analogue for which the assignment was confirmed by the D 20 test described in Chapter 4. 189 Table 5.2. Selected infrared data (cm1) for nickel(II) complexes. Complexes v(P02 anti.) v(P02 sym.) Atcrrf1) Ni[(CH3)2P02]2 1112vs 1021vs 91 Ni[(CH3)(C2H5)2P02]2 1112vs 1018s 94 Ni[(CH3)2As02]2* 861vs 794s 97 Ni[(C6H5)2P02]2 1132vs 1046s 86 Ni[(C6F5)2P02]2 1237vs 1114s 123 Ni[(C6F5)2P02]2.H20 1210vs 1118s, 1105s 99C Ni(HCONHCH3)2[H(C6H5)P02]2 1134vs, 1147vs 1047vs 94^ Ni(H(C6H5)P02H]2[H(C6H5)P02]2 1171-lllOvs 1023-1072s e a A = v(P02 anti.) - v(P02 sym.). The IR bands listed are for v(As02 anti.) and v(As02 sym.). An average v(P02 sym.) was taken in calculating the A value. d An average v(P02 anti.) was taken in calculating the A value. A value can not be calculated in this compound. 190 T 1 1 1 1 1 Figure 5.4(a). IR spectrum of Ni[H(C6Hj)P02H]2[H(C6H5)P02]2. Peaks due to Nujol are marked by asterisks. 191 Figure 5.4(b). JR spectra of NiKCHj^PO^ (top) and Ki[(CH3)2As02)2 (bottom). Peaks due to Nujol are marked by asterisks. 192 5.2.4. Electronic Spectroscopy The binary compounds Ni[(CH3)2P02]2, Ni[(CH3)(C2H5)P02]2, Ni[(CH3)2As02]2 and Ni{[(CF3(CF2)5CH2CH2]2P02]}2 are yellow in color while Ni[(C6H5)2P02]2 and Ni[(C6F5)2P02]2 are purple. All the adduct complexes, Ni[(C6F5)2P02]2.H20, Ni(HCONHCH3)2[H(C6H5)P02]2 and Ni[(H(C6H5)P02H]2[H(C6H5)P02]2, are light green. Representative electronic spectra for these complexes over the range 300 nm to 2000 nm are shown in Figure 5.5 and band positions and assignments are given in Table 5.3. The X-ray powder diffraction studies have shown that Ni[(C 6 F 5 ) 2 P0 2 ] 2 «H 2 0 is isomorphous with its cobalt analogue, indicating both complexes may have a similar structure. The electronic spectrum of this monohydrate nickel(II) compound is similar to that of a five-coordinate nickel(II) complex with a square-pyramidal symmetry (21). The linear chain structure proposed earlier for the cobalt analogue (Figure 4.10) is also proposed for Ni[(C6F5)2P02]2.H20. The electronic spectra observed for the yellow binary nickel(II) complexes and light green monophenylphosphinate adduct compounds are similar to that observed for the octahedral cation Ni(H20)62 + (22). Assuming octahedral symmetries, the ligand field splitting Dq parameters and Racah B parameters were obtained from equations [1.5] and [1.6] given in Chapter 1 and are listed in Table 5.3. The Dq values range from 745 to 770 cm"1, close to the value of 850 cm"1 for Ni(H 20) 6 2 + (21). The B values range from 867 to 900 cm"1, also close to the value of 905 cm"1 for Ni(H20)6 2 +. 193 The purple binary complexes have similar electronic spectra to that of the tetrahedral nickel compound NiCl2[(C6H5)3AsO]2 (22). The Dq and B values (Table 5.3) for these two complexes were determined from equations [1.1] and [1.3]. The Dq and B of NiCl2[(C6H5)3AsO]2 are 420 cm"1 and 850 cm"1, close to the values for the two purple nickel (II) complexes studied in this work. While all spin allowed transitions were observed for the octahedral complexes, only two of the three spin allowed ligands were observed for these tetrahedral complexes. The lowest energy bands for these complexes, corresponding to the 3T2 <— 3Tj (F) transition, were not observed. The calculated energies for these transitions are 2610 nm (3,830 cm"1) and 2710 nm (3,690 cm"1) for Ni[(C6F5)2P02]2 and Ni[(C6F5)2P02]2, respectively. Other unassigned transitions likely result from the spin-forbidden transitions. The higher is the value of B the more ionic is the bonding. It is concluded that Ni[(C6F5)2P02]2 has a more ionic bonding than its perhydro-derivative. The same conclusion is obtained for the cobalt analogue. Important conclusions may be drawn from the above observations. Nickel(II) adduct complexes and the yellow binary complexes have octahedral nickel(II) chromophores. Such a coordination geometry for the adduct complexes can be explained by a structure in which the nickel(II) ions are linked by double bridged phosphinate units with axially coordinated neutral ligands. This structure has been confirmed for the manganese and cobalt adduct complexes (7, 18). As for the yellow binary nickel(II) complexes, the octahedral geometry requires one oxygen atom from each phosphinate anion (or arsinate anion) to bond to two different metal ions, thus leading to a sheet polymer as illustrated in 194 Figure 1.5 in Chapter 1. Because of the limited amount of Ni{[(CF3(CF2)5CH2CH2]2P02]}2 available for study the electronic spectrum of the compound was not obtained. This compound, however, is yellow and it exhibits similar magnetic behaviour (described below) to the other yellow nickel(II) complexes. Hence, an analogous sheet polymeric structure is also proposed for this compound. The two purple complexes, Ni[(C6F5)2P02]2 and Ni[(C6H5)2P02]2, have tetrahedrally coordinated metal centers and likely have linear chain structures similar to those of the Form II polymorphs of Mn[(CH3)2P02]2 and Co[(CH3)2P02]2 (see Chapter 3 and Chapter 4). Table 5.3. Electronic spectra of nickel(II) complexes. Complexes Band Position (nm) (cm"1 in brackets) Assignment (cm"1) B (cm"1) Ni[(CH3)2P02]2 434s(23, 000) 695m (14, 400) 795m (12, 600) 1340w (7, 460) 3Tlg (P) <- 3A2g a 3Tlg (F) <- 3A2g 3T2g <- 3A2g 753 867 Ni[(CH3)(C2H5)P02]2 432s(23, 100) 695m (14, 400) 800m (12, 500) 1350w (7, 410) 3Tlg (P) <- 3A2g a 3Tlg (F) <- 3A2g 3T2g <- 3A2g 745 883 Ni[(CH3)2As02]2 428s(23, 400) 705m (14, 200) 792m (12, 600) 1215w (8, 230) 3Tlg (P) <- 3A2g a 3Tlg (F) <- %g 3T2g <- 3A2g 750 900 Ni[(C6F5)2P02]2.H20 400s (25, 000) 800m (12, 500) 1195w (8, 370) 1725w (5, 800) b Table 5.3 continued overleaf. 195 Table 5.3. (Continued). Complexes Band Position (nm) (cm-1 in brackets) Assignment (cm"1) B (cm"1) c 418s(23, 900) 678m (14, 700) 773m (12, 900) 1200w (8, 300) 3Tlg (P) <- 3A2g 3TIg (F) <- 3A2g 3T2g <- 3A2g 770 913 d 415s (24, 100) 680m (14, 700) 785m (12, 700) 1260w (7, 900) 3TIg (P) <- 3A2g a 3Tlg (F) <- 3A2g 3T2g <- 3A2g 754 945 Ni[(C6F5)2P02]2 510sh(19, 600j e 575s (17, 400) L 615sh(16,300j) 748m (13, 400) 1195w (8, 370) 3T, (P) <- 3Tj (F) a 3A2 <- 3T, (F) 464 962 Ni[(C6H5)2P02]2 600s (16, 700) 762m (13, 100) 1220w (8, 200) 3TJ(P)^3TJ(F) a 3A2+-3Tj(F) 451 922 a Possibly due to the spin-forbidden transitions. b No attempt was made to assign these transitions. cNi(HCONHCH3)2[H(C6H5)P02]2 and d Ni[H(C6H5)P02H]2[H(C6H5)P02]2. e Center of gravity of the bands was used for calculating Dq. 196 I 1 I I I 1 I I I I 1 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I L 400 600 800 1000 1200 1400 1600 1800 2000 Wavelength (nm) Figure 5.5. Electronic spectra for (a) Ni[(C6F5)2P02]2, (b) Ni[(CH3)(C2H5)P02]2 and (c)Ni[H(C6H5)P02H]2[H(C6H5)P02]2. 197 5.2.5. Magnetic Properties and Magneto-structural Correlations Magnetic susceptibility and magnetic moment data for all nine nickel(II) complexes studied here are given in the Appendix. Electronic spectral studies have shown that the nickel complexes, except Ni[(C6F5)2P02]2*H20, can be separated into two groups, those with octahedral and those with tetrahedral coordination geometries. Ni[(C 6 F 5 ) 2 P0 2 ] 2 »H 2 0 appears to have a five-coordinate square-pyramidal geometry and is included in the octahedral group since it is also an adduct compound and has similar magnetic properties to those of the compounds in the group. The magnetic properties of the complexes of each group are described separately below. 5.2.5.1. Octahedral Complexes and A Five-coordinate Compound Since the ground state for an octahedral Ni(II) ion is 3A2g, the magnetic moment for such a system in the absence of magnetic concentration effects is expected to be temperature independent except at very low temperatures where zero-field splitting effects may result in a decrease in moment (23, 24). Magnetic moment versus temperature plots are shown in Figure 5.6 for the three adduct complexes and in Figure 5.7 for the four binary complexes. The magnetic moments of the adduct complexes decrease with decreasing temperature. This is particularly noticeable for Ni[(C6F 5) 2P0 2] 2»H 20 and Ni(HCONHCH3)2[H(C6H5)P02]2 where the decrease in the moment is much bigger than that of Ni[(H(C6H5)P02H]2[H(C6H5)P02]2. These results suggest relatively strong antiferromagnetic interactions in the first two complexes and weak antiferromagnetic exchange in the last. In contrast, all four of the binary nickel phosphinates which have octahedral metal centers have magnetic moments which increase with decreasing 198 temperature, indicating ferromagnetic behavior. The magnetic properties of these seven complexes will now be discussed separately in some detail. pa 3.5 3.0 2.5 S a 2.0 o c u sa 1 5 M C 3 1.0 0.5 - o ° ° ° ° ° _ o _ a ° ° ; S s s n a - d * ° a A A b 1 A ° C - A A _* i i i i 1 i i i i I i i i i I i i i i i i i i i i i i i i i i i i i i i i i i i i i i i 0 10 20 30 40 50 60 70 80 90 Temperature (K) Figure 5.6. Magnetic moment versus temperature plots for (a)Ni[(H(C6H5)P02H]2[H(C6H5)P02]2, (b) Ni(HCONHCH 3) 2[H(C 6H 5)P0 2] 2 and (c) Ni[(C 6F 5) 2P0 2] 2 .H 20. 199 6.0 ^ 5.5 g 5.0 S | 4.5 | 4.0 s w ^ « 3.5 3.0 : O 2549 G :o • 5251 G I D A 7501 G & o 9225 G " i i i i 1 i i i A , 1 A A A A A A A , , ! , , , , ! , , 20 40 60 80 Temperature (K) « e B © (J fi W) A 7501 G O 9225 G * * "l 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 20 40 60 80 Temperature (K) = 4 o o 2549 G A 7501 G 9225 G 1 1 1 1 1 1 1 1 > 111 111 111 111 i 0 20 40 60 80 Temperature (K) a =1 fi 4 S o ••B 3 fl W) es 0 10000G toccoocoxoaoaxj 11111111111111111111111111111 0 50 100 150 200 250 300 Temperature (K) Figure 5.7. Magnetic moment versus temperature plots for nickel(II) complexes at various fields as labeled in the graphs: (a) Ni[(CH3)2P02]2, (b) Ni[(CH3)(C2H5)P02]2, (c) Ni[(CH3)2As02]2 and (d) Ni{[CF3(CF2)5CH2CH2]2P02}2. 200 Ni[(H(C6H5)P02H]2[H(C6H5)P02]2 The magnetic moment (Figure 5.6) is ~3.2 u.B over the range 82 to 25 K, a value of the order expected for octahedral nickel(II). Below 25 K the moment decreases to ~3.0 \iB at 4 K. If there is any magnetic exchange present in this complex, it must be very weak. The magnetic data were fitted to two linear chain models, the WFG (25) and Weng (26, 27) models described in Chapter 2. Good agreement between experiment and theory was obtained with both models. The best fit parameters obtained using the WFG model are J--0.17 cm-1 and g = 2.26 (F = 0.010), while those using the Weng model are J= -0.14 cm"1 andg= 2.26 (F= 0.010). Since the magnetic moment for this complex decreases significantly only at very low temperatures it is possible that this temperature dependence arises from zero-field splitting effects alone. Consequently, the susceptibility data were analyzed assuming no exchange but employing a model which incorporates the effects of zero-field splitting. The axial zero-field splitting parameter D and the g value were found by a least-squares fit of the temperature dependence of the molar magnetic susceptibility to the zero-field splitting S = 1 model (23). The best fit parameters obtained employing this model are D = 4.6 cm'1 and g = 2.24 (F = 0.013). The best fit magnetic susceptibility data for both WFG and zero-field splitting models along with the experimental data for this complex are shown in Figure 5.8. Both zero-field splitting model and linear chain exchange models can successfully account for the magnetic data obtained for Ni[(H(C6H5)P02H]2[H(C6H5)P02]2, indicating that magnetic exchange coupling, if present, is very weak in this complex. 201 0.30 0oo r i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i I 0 10 20 30 40 50 60 70 80 90 Temperature (K) 0.30 0 oo ' 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 1 1 1 1 i 0 10 20 30 40 50 60 70 80 90 Temperature (K) Figure 5.8. Magnetic susceptibility versus temperature plot for Ni[(H(C6H5)P02H]2[H(C6H5)P02]2. Solid line is calculated employing the zero-field splitting model (top) and WFG Model (bottom), as described in the text. 202 Ni(HCONHCH3)2[H(C6H5)P02]2 This complex exhibits a temperature dependent magnetic moment, with values decreasing from approximately 3.1 u,B at 82 K to ~1.1 UB at 2.2 K, a behaviour characteristic of an antiferromagnetically coupled nickel(II) system. The effect of magnetic concentration in Ni(HCONHCH3)2[H(C6H5)P02]2 is more clearly seen in the magnetic susceptibility versus temperature plot shown in Figure 5.9. XM exhibits a maximum at ~6 K. In accordance with the proposed polymeric structure of this compound, the magnetic data were analyzed employing one-dimensional WFG and Weng models for S = 1 systems (25-27). The parameters obtained from the best fit of the magnetic susceptibility data for this complex to these models are given in Table 5.4. Excellent agreement between experimental and calculated susceptibilities were obtained for both models. The susceptibility data are plotted against temperature in Figure 5.9 where the solid line is calculated from the WFG model using the best fit parameters. 203 Figure 5.9. Magnetic susceptibility versus temperature plot for Ni(HCONHCH3)2[H(C6H5)P02]2. Line was calculated using the WFG, S=l, model and the best fit parameters are given in Table 5.3. 204 Ni[(C6F5)2P02]2.H20 The electronic spectrum of Ni[(C6F5)2P02]2.H20 suggests that the nickel(II) centers are square-pyramidal. Assuming a linear chain polymeric structure with five-coordinate metal/ligand geometry as shown in Figure 4 . 10 for the cobalt analogue, one-dimensional linear chain antiferromagnetic models were used to analyze the magnetic data. The magnetic moment versus temperature plot for this complex is shown in Figure 5.6. This complex exhibits almost the same magnetic behaviour as Ni(HCONHCH3)2[H(C6H5)P02]2 described above. Its magnetic moment has a value of ~3.1 UB at 82 K and it decreases to ~1 .7 UB at 4.4 K. This indicates relatively strong antiferromagnetic behaviour. The magnetic susceptibility data were analyzed according to the two one-dimensional WFG and Weng models for S = 1 systems (25-27) . The parameters obtained from the best fits are given in Table 5.4. The susceptibility data are plotted against temperature in Figure 5 .10 where the solid line is calculated from the WFG model using the best fit parameters. Reasonably good agreement was obtained between experiment and theory as seen visually and from F values. From the similar variations of magnetic moment with temperature for the complexes, Ni[(CeF5)2P02]2.H20 and Ni(HCONHCH3)2[H(C6H5)P02]2, similar magnetic susceptibility behaviour may also be expected. In Figure 5.9, it can be seen that XM for Ni(HCONHCH3)2[H(C6H5)P02]2 reaches a maximum at ~6 K, a characteristic property of antiferromagnetic materials, while no maximum is observed in the XM versus temperature plot for Ni[(C6F 5) 2P0 2] 2»H 20 down to a temperature ~4.4 K. The possibility that paramagnetic impurity is contributing to the susceptibility of Ni[(C6F5)2P02]2.H20, particularly at low temperatures, resulting in a 205 masking of the susceptibility maximum was considered. If a contribution from paramagnetic impurity is incorporated into the Weng and WFG models another set of magnetic parameters for each model can be obtained. These parameters are also listed in Table 5.4. Obviously, this fit (see dash line in Figure 5.10) is better compared to the fit without impurity contribution. The large amount of paramagnetic impurity which this analysis gives (as high as over 10%) suggests that Ni[(C6F5)2P02]2«H20 contains large amounts of either monomelic or oligomeric species. Table 5.4. Magnetic parameters" for nickel(II) phosphinate complexes. Complexes J (cm"1) b g F° p(%y* Ni[H(C6H5)P02H]2[H(C6H5)P02]2 0.14(0.17) 2.26 (2.26) 0.010(0.010) Ni(HCONHCH3)2[H(C6H5)P02]2 1.6(2.0) 2.29 (2.31) 0.022 (0.014) Ni[(C6F5)2P02]2.H2Oe 1.5(1.7) 2.2 (2.2) 2.27 (2.27) 2.32 (2.30) 0.044 (0.024) 0.010 (0.006) 14 (10) a The data outside the brackets were obtained using the Weng model (26, 27) and those inside the brackets were obtained using the WFG model (25). b Values of J and g are considered accurate to ±10% and ±2% respectively. The function F is defined in equation [2.6]. ^P is the fraction of paramagnetic impurity calculated as described in equation [2.11] First set of parameters ignores paramagnetic impurity and the second set includes paramagnetic impurity (see text). 206 0.09 Q r i i i i i i i i i i i i i i i i i i i i i i i i i i i i, i i i i i i i i i i i i i i i i i 0 10 20 30 40 50 60 70 80 90 Temperature (K) Figure 5.10. Magnetic susceptibility versus temperature plots for Ni[(C6F5)2P02]2»H20. Solid lines were calculated using the WFG, S=l, model. The dash line was calculated using the W F G model and incorporating a correction for paramagnetic impurity. The lines were calculated using the best fit parameters given in Table 5.4. 207 As compared with the work done by Du (1), the magnitude of exchange for the HCONHCH3 adduct complex is larger than that for the aqua adduct complex but smaller than that of the HCONH 2 analogue. While the H(C 6H 5)P0 2H adduct compound has a magnetic exchange coupling strength comparable to its pyridine analogue, magnetic data for both compounds can be analyzed with the zero-field splitting models, suggesting that negligible magnetic exchange coupling is present in each compound. Overall, combined with the work done previously by Du (1), the magnitude of exchange in the monophenylphosphinate bridged adduct polymers with the formula Ni(L)2[H(C6H5)P02]2 appears to increase in the order L = py ~ H(C 6H 5)P0 2H < pyz < H 2 0 < HCONHCH3 < HCONH 2. This order was also seen in the related manganese(II) analogue (7). The relative positions of the complexes containing N-bonded ligands versus those containing O-bonded ligands may be explained on the basis of relative basicities towards metal ions. The greater basicities of pyridine and pyrazine towards metal ions result in weaker bonding between the metal and the bridging phosphinate ligands in these complexes and hence weaker exchange. Symmetric O-P-0 bridges and short Ni-O-P-O-Ni distances may account for the order of magnetic exchange in the other adduct complexes as described in Chapter 4 for the corresponding cobalt complexes. Ni[(CH3)2P02]2, Ni[(CH3)(C2H5)P02]2, Ni[(CH3)2As02]2 and Ni{[CF3(CF2)5CH2CH2]2P02}2 Earlier studies (1) reported Ni[[H(C6H5)P02]2 as a yellow complex which on the basis of indirect evidence was suggested to have a sheet polymeric structure with double phosphinate bridged chains cross-linked as shown in Figure 5.11. In this proposed 208 structure, one oxygen from a phosphinate anion coordinates to one metal while the other binds to two different metal ions to complete octahedral coordination geometry around each metal. This type of coordination has been observed in the crystal structures of Cd(H20)Cl[H(C6H5)P02] (28) and {Cu3[(CH3)2P02]6}x (29). In this type of bridging, chains of metal ions are linked by only one oxygen atom. The relatively short M-O-M pathway that results can lead to stronger magnetic exchange coupling than is possible with the usual, much longer M-O-P-O-M pathway. This was discussed in the chapter on the manganese complexes (Chapter 3). For instance, Form I of Mn[(CH3)2P02]2 which was suggested to be a sheet polymer exhibits a much stronger exchange coupling {-J = 2.98 cm"1) than the Form II complex which is a linear chain polymeric material. In the latter complex, only the Mn-O-P-O-Mn pathway is available for magnetic exchange and the value of -J for this complex is 0.18 cm"1. Interestingly, magnetic studies on Ni[H(C6H5)P02]2, a compound believed to have this structure, revealed a magnetic moment which increases with decreasing temperature, behaviour indicative of ferromagnetic exchange (1). The present work, to be described below, shows that this phenomenon is characteristic of octahedrally coordinated binary nickel(II) phosphinates. 209 Figure 5.11. Sheet polymeric structure proposed for Ni[H(C6H5)P02]2. All the complexes considered here are proposed to have the polymeric structure represented by Figure 5.11. Magnetic moment versus temperature plots at various fields for all four complexes are shown in Figure 5.7. The magnetic data for Ni{[CF3(CF2)5CH2CH2]2P02}2 were obtained using the SQUID magnetometer while data for other three complexes were obtained using the VSM magnetometer. All four complexes exhibit ferromagnetic behaviour, their magnetic moments increasing with decreasing temperature. Field dependent behaviour is also seen. In high applied field, the moments reach a maximum value and then decrease at very low temperature due to the effects of magnetic saturation. This saturation is more clearly seen from the magnetization versus field plots for Ni{[CF3(CF2)5CH2CH2]2P02}2 shown in Figure 5.12. These plots show that magnetization at temperatures below 10 K and at fields higher than 25,000 Gauss gradually approaches saturation. Theoretically, the magnetization saturation, M s a t , can be calculated (24) by using the expression: Msal = SNgB [5.10] 210 where N is Avogadro's number, g is the Lande splitting factor, /? is the electron Bohr magneton and S is the total spin of the paramagnetic ion. For the Ni(II) ion, the theoretical saturated magnetization is 11,170 cm3 G mole-1 (calculated from equation [5.10] for S = 1 and g taken as 2). Table 5.5 gives magnetization values at low temperatures and different fields for each of the complexes. The data show that none has reached saturation under current measurement conditions. Most measurements were done at relatively low fields (below 10,000 G); the data for Ni{[(CF3(CF2)5CH2CH2]2P02]}2 at 2 K and 50,000 G, however, show close to saturation behaviour (9,550 versus 11,170 cm3 Gmole"1). The ferromagnetic couplings in these binary nickel(II) complexes can be accounted for by considering the Ni-O-Ni magnetic exchange pathway involved in the sheet polymeric structure. The magnetic orbitals for octahedral Ni(II) ions are (dx2_y2y (d z 2)\ A superexchange pathway via Ni-O-Ni with a 90 ° angle at oxygen may be described as involving a d x 2 -y2| |p y ±p z | |d z 2 mechanism (30). The orthogonal p y l p z step in the path leads to ferromagnetic exchange. 211 Table 5.5. Experimental magnetization for nickel(II) binary complexes*. Complexes Field (G) Temp. (K) Magnetization (cm3 G mole"1) Ni[(CH3)2P02]2 2549 4.3 2970 7501 2.5 6850 9225 2.4 7260 Ni[(CH3)(C2H5)P02]2 7501 2.3 7470 9225 2.1 8070 Ni[(CH3)2As02]2 2549 4.5 1920 5251 4.5 3730 7501 4.4 4740 9225 2.5 6720 Ni{ [(CF3(CF2)5CH2CH2]2P02] }2 50000 2.0 9550 50000 4.0 9150 50000 8.0 7610 50000 10 6710 50000 20 3580 * All the measurements were made using of VSM magnetometer except those for Ni{[(CF3(CF2)5CH2CH2]2P02}2 for which the SQUID magnetometer was used. It should be noted that in none of the ferromagnetic nickel(II) systems was there any evidence for long range magnetic ordering under the experimental conditions employed. In the magnetization plots for Ni{[(CF3(CF2)5CH2CH2]2P02}2, for example (Figure 5.12), all of the plots including the one obtained at 2 K go through zero magnetization at zero applied field. This is in contrast, for example, to the behaviour of Co(HCONH2)2(HCOO)2, a system to be discussed in the next chapter. This material is ferromagnetic and undergoes long range magnetic ordering at temperatures below 9 K resulting in a net magnetization at zero applied field and temperatures below 9 K. 212 12000 10000 o S 8000 o B o 6000 es •J fl (5X1 « 4000 2000 0 2 K o ° ° o ° o n A o n A o n A O • A • A O A O A O V • A o A o A O A O 8 K o 10 K A O A O o o o 20 K A o A O o o o " o A O § 0 " ° . J I I I I I I I I I I I I I I I I I I 1 I I I I I I L . 0 10000 20000 30000 40000 50000 60000 Field (Gauss) Figure 5.12. Magnetization versus field plot for NiltCFsCCFa^C^CFkkPOzh at various temperatures as labeled in the graph. 213 5.2.5.2. Tetrahedral complexes Ni[(C6F5)2P02]2 and Ni[(C6H5)2P02]2 are different from the other binary nickel(II) complexes in that they are purple in color and contain tetrahedral metal chromophores as determined by electronic spectral studies. For tetrahedral nickel(II) complexes, the ground electronic term is 3Tj. The magnetic properties in such a case are effected by a number of factors including electron derealization, spin-orbit coupling and mixing of excited states into the ground state (31). The magnetic moment versus temperature plots for the two compounds given in Figure 5.13 reveal the similarity in the magnetic properties of these two compounds. The strong temperature dependence suggests antiferromagnetic couplings and assuming linear chain polymeric structures the susceptibilities were analyzed by the linear-chain WFG and Weng models as before (Figure 5.14 and Table 5.6). The agreement between experiment and theory is not satisfactory. An important contributing factor to this is no doubt that the models do not take into account the single ion effects mentioned above. Nonetheless, we attempted fits assuming paramagnetic impurity and while the fits are better (solid lines in Figure 5.14) the relatively large values of P(%) (see Table 5.6) raise some doubt about the validity of this procedure. The main conclusion one can draw from this is that there is probably weak antiferromagnetic exchange in these complexes and that the strength of the exchange is comparable in the two complexes. The Ni-O-P-O-Ni pathway leads to antiferromagnetic exchange, in contrast to the Ni-O-Ni pathway which leads to ferromagnetic exchange. The question as to why Ni[(C6H5)2P02]2 and Ni[(C6F5)2P02]2 have tetrahedral chromophores while the other binary nickel(II) phosphinates have octahedral 214 chromophores remains. Since the perfluoro- and perhydro- derivatives have the same basic structure one can conclude that electronic effects are not important. It seems that steric effects dominate, two relatively bulky substituents on phosphorus favoring the sterically less crowded tetrahedral geometry over the octahedral geometry. Table 5.6. Magnetic parameters" for nickel(II) phosphinate complexes. Complexes •%/ (cm'1) g F° Vd Ni[(C6F5)2P02]2 Fitl 1.66(2.04) 2.30 (2.34) 0.10(0.073) Fit 2 2.45 (2.78) 2.43 (2.44) 0.049 (0.035) 0.062 (0.048) Ni[(C6H5)2P02]2 Fitl 2.10(2.50) 2.46(2.49) 0.087(0.065) Fit 2 3.54(3.91) 2.62 (2.64) 0.027 (0.016) 0.11 (0.093) a The data outside the brackets were obtained using the Weng model (26, 27) and those inside the brackets were obtained using the WFG model (25). In fit 1, P was set to zero. In fit 2, P was employed as a variable parameter. Values of J and g are considered accurate to ±10% and ±2%, respectively. The function F is defined in equation [2.6]. ^P is the fraction of paramagnetic impurity calculated as described in equation [2.11]. 215 4 aa = c u E o CJ c u a CQ A O A A O A A O A ° A) A A O A ° N i [ ( C 6 F 5 ) 2 P 0 2 ] 2 * N i [ ( C 6 H 5 ) 2 P 0 2 ] 2 6? A o 8 J—I I 1 I I I I I—I I I I I I I I I I I i i i i L_l i i i I i i i l_J i i i i I i i 1_1 . . . . I 0 10 20 30 40 50 60 70 80 90 Temperature (K) Figure 5.13. Magnetic moment versus temperature plots for (a) Ni[(C6F5)2P02]2 and (b)Ni[(C 6 H 5 ) 2 P0 2 ] 2 216 « 0.024 c WO ^ 0.012 N i [ ( C 6 F 5 ) 2 P 0 2 ] 2 _ l I I I I I I L . I . J I I I I I I I I L 20 40 60 Temperature (K) 80 0.08 H "E 0.06 u • PI g- 0.04 3 H 0.02 N i [ ( C 6 H 5 ) 2 P 0 2 ] 2 _ l I I I I I I I I I I 1 I I I I I I ' I I L 20 40 60 Temperature (K) 80 Figure 5.14. Magnetic susceptibility versus temperature plots for Ni[(C6F5)2P02]2 (above) and Ni[(C6H5)2P02]2 (below) Lines were calculated employing WFG model (25) with best fit parameters shown Table 5.5. The dotted lines were calculated assuming no paramagnetic impurity and the solid lines were calculated employing paramagnetic impurity as a variable parameter. 217 5.3. Summary and Conclusions Six nickel(II) binary complexes, Ni[(CH3)2P02]2, Ni[(CH3)(C2H5)P02]2, Ni[(CH3)2As02]2, Ni{[(CF3(CF2)5CH2CH2]2P02}2, Ni[(C6H5)2P02]2 and Ni[(C6F5)2P02]2 have been synthesized and characterized in this work. These complexes may be classified into two groups according to their coordination geometries and magnetic properties. The first group, which consists of the first four complexes, is characterized by octahedrally coordinated metal centers. These compounds are proposed to have sheet polymeric structures and are found to exhibit ferromagnetic behaviour, a behaviour similar to that reported previously for Ni[H(C6H5)P02]2 (1) and Ni[(n-C8Hi7)2P02]2 (2). This magnetic property may be attributed to the Ni-O-Ni exchange pathway as depicted in Figure 5.11. The second group includes nickel(II) diphenylphosphinate and its perfluoro-derivative. These two complexes are purple in color and involve tetrahedrally coordinated metal centers. Their structures are proposed to be similar to those of Mn[(CH3)2P02]2 (Form II) and Co[(CH3)2P02]2 described in Chapters 3 and 4, respectively. Magnetic studies reveal weak antiferromagnetic exchange interactions propagated by Ni-O-P-O-Ni pathways in these compounds. In addition, three nickel(II) adduct complexes, Ni[(H(C6H5)P02H]2[H(C6H5)P02]2, Ni(HCONHCH3)2[H(C6H5)P02]2 and Ni^CeFs^POsh.TfcO have been prepared and studied in this work. The first two monophenylphosphinates represent an extension of the work of Du (1). It was found that the H(CeH5)P02H adduct complex exhibits very weak antiferromagnetic behaviour while the HCONHCH 3 adduct complex exhibits a much stronger antiferromagnetic coupling. Combined with the work done by Du (1), the 218 magnitude of exchange in the phosphinate bridged adduct complexes, Ni(L)2[H(C6H5)P02]2, appears to increase in the order L = py ~ H(C 6H 5)P0 2H < pyz < H 2 0 < HCONHCH3 < HCONH 2. This order was observed in the analogous manganese(II) complexes (7). Ni[(C6F5)2P02]2.H20 is proposed to have a linear chain polymeric structure with water molecule bonding axially to the nickel(II) ions, forming a square-pyramidal geometry around the metal. The compound exhibits antiferromagnetism, the strength of which is comparable to that of the HCONHCH 3 adduct polymer. REFERENCES 1. J.-L. Du, Ph. D Dissertation, University of British Columbia, B. C. Canada, 1991. 2. J. R. D. Peers, B. Sc. Thesis, University of British Columbia, B. C. Canada, 1987. 3. H. D. Gillman, Inorg. Chem. 13, 1921 (1974). 4. H. D. Gillman and J. L. Eichelberger, Inorg. Chem. 15, 840 (1976). 5. B. P. Block, Inorg. Macromol. Rev. 1, 115 (1970). 6. P. Nannelli, B. P. Block, J. P. King, A. J. Saraceno, O. S. Sprout Jr., N. D. Peschko and G. H. Dahl, J. Poly. Sci.: Poly. Chem. Ed, 11, 2691 (1973) 7. J.-L. Du, S. J. Rettig, R. C. Thompson, J. Trotter, P. Betz and A. Bino, Can. J. Chem. 70, 732 (1992). 8. K. Dehnicke and A. F. Shihada, Structure and Bonding, 28, 52 (1976). 9. J.-L. Du, S. J. Rettig, R. C. Thompson and J. Trotter, Can. J. Chem. 69, 277 (1991). 219 10. K. Nakamoto, Infrared Spectra of Inorganic and Coordination Compounds, T Ed., 1970, John Wiley & Sons, Inc., New York. 11. N. C. Johnson and W. E. Rull, Inorg. Chim. Acta, 27, 191 (1978). 12. D. E. C. Corbridge and E. J. Lowe, J. Chem. Soc, 494 (1954). 13. T. Tsuboi, J. Am. Chem. Soc, 79, 1351 (1957). 14. L. W. Daasch and D. C. Smith, Anal. Chem., 23, 853 (1951). 15. D. E. C. Corbridge, Topics in Phosphorus Chem., 6, 235 (1969). 16. L. S. Mayants and E. I. Matrosov, Izvest. Akad. Nauk. SSSR, Neorg. Mat., 1, 546 (1965). 17. J. Sala-Pala, R. Kergoat and J. E. Duerchais, C. R. Acad. Sci. Paris, Ser. C, 274, 595 (1972). 18. P. Betz, A. Bino, J.-L. Du, L. S.-M. Lo and R. C. Thompson, Inorg. Chim. Acta, 170, 45 (1990). 19. D. Dolphin and A. Wick, Tabulation of Infrared Spectra Data, John-Wiley & Sons, New York, 1977. 20. D. Welti, Infrared Vapor Spectra, Heyden & Son Ltd., 1970. 21. A. B. P. Lever, Inorganic Electronic Spectroscopy, 2nd Ed., New York, 1984. 22. B. N. Figgis, Introduction to Ligand Fields, Interscience Publishers, a division of John Wiley & Sons, New York, 1966. 23. C. J. O'Connor, Prog. Inorg. Chem. 29, 203 (1982). 24. R. L. Carlin, Magentochemistry, Berlin Heidelberg, Springer-Verlag, 1986. 25. G. R. Wagner and S. A. Friedberg. Phys. Lett. 9, 11 (1964). 26. W. Hiller, J. Strahle, A. Datz, M. Hanack, W. E. Hatfield, L. W. terHaar and P. Gutlich, J. Am. Chem. Soc. 106, 329 (1984). 27. C. H. Weng, Ph. D. Dissertation, Carnegie-Mellon University, Pittsburgh, P. A. U.S.A. 1968. 220 28. J.-L. Du, S. J. Rettig, R. C. Thompson and J. Trotter, Acta Cryst. C49, 1035 (1993). 29. K. W. Oliver, S. J. Rettig, R. C. Thompson, J. Trotter and S. H. Xia, Inorg. Chem. 36, 2465 (1997). 30. A. P. Ginsberg, Inorg. Chim. Acta, C45, (1971). 31. E. A. Boudreaux and L. N. Mulay, Theory and Applications of Molecular Paramagnetism, John Wiley & Sons, New York, 1976. 221 Chapter 6 Miscellaneous Compounds 6.1. Poly-diaquabis(//-formato)cobalt(II) and Poly-bis(formamide)bis(//-formato)cobalt(n); Co(H20)2(HCOO)2 and Co(HCONH2)2(HCOO)2 In attempting to prepare adduct polymers of compositions Co(HCONH2)2[(C6F5)2P02]2 and Co(HCONH2)2[(CH3)(C2H5)P02]2, two formate complexes of compositions Co(H20)2(HCOO)2 and Co(HCONH2)2(HCOO)2 were obtained instead. These compounds were obtained in crystalline form suitable for single crystal X-ray diffraction studies. As for phosphinate and arsinate ligands, formate anions can bridge metal centers. Syn-syn bridging (Figure 6.1) can lead to the formation of dimetallic species while syn-anti or anti-anti generates polymeric materials (1-4). Magnetic studies have also shown the formate ligand to be an efficient mediator of magnetic exchange (5-7). Examples of such system are the aqua complexes M(H20)2(HCOO)2 (where M = Co, Ni, Mn(II), Cu(II) and Mg(II)). (1-4). The X-ray studies on the two formates prepared revealed interesting polymeric structures and prompted us to examine the magnetic properties of these materials for magnetic exchange effects. Structural and magnetic data are listed in the Appendix. 222 M i i ,0 M (X X> (1 JO i y i i y 1 A 1 M M M < O — M syn-syn anti-anti syn-anti Figure 6.1. Configurations of formate ions in complexes. 6.1.1. Results and Discussion 6.1.1.1. Syntheses and Thermal Properties Detailed procedures followed in obtaining Co(H20)2(HCOO)2 and Co(HCONH2)2(HCOO)2 are given in Chapter 7. The powder forms of the two compounds were prepared by direct synthesis by routes summarized in equations [6.1] and [6.2]. In the preparation of the crystals, the formate ions were formed serendipitously by the slow hydrolysis of formamide. This process has been reported before in the syntheses of copper(II) formate derivatives (8, 9). .Acetone Co(C104)2 • 6 H 2 0 + 2 HCOOH + 2 (C 2H 5) 3N Co(H20)2(HCOO)2 + 2 [(C2H5)3NH ][C104"] + 4 H 2 0 [6.1] Co(C104)2 -6 H 2 0 + 2 HCOOH + 4 HCONH 2 Acetone^ Co(HCONH2)2(HCOO)2 + 2 [HCONH3+][C104 ] + 6 H 2 0 [6.2] 223 Thermal studies revealed that both water molecules in Co(H20)2(HCOO)2 are lost over the range 108 to 167 °C; further decomposition occurs over the range 281 to 348 °C. Co(HCONH2)2(HCOO)2 loses two HCONH 2 molecules over the range 157 to 233 °C and further decomposition takes place from 276 °C to 354 °C. No further thermal events were observed on heating the two compounds to about 800 °C. 6.1.1.2. Single Crystal X-ray Diffraction 6.1.1.2.1. Structure of Co(H20)2(HCOO)2 The structure of Co(H20)2(HCOO)2 solved in this work is same as that reported by Kaufman et. el. (1). A portion of the polymeric structure is shown in Figure 6.2. Two types of cobalt(II) ions are found, both involving coordination by six oxygen atoms in an octahedral arrangement. One of the cobalt octahedra contains oxygen atoms from six different formate ions. The second cobalt ion is surrounded by four water molecules and an oxygen atom from each of two formate ions. The two different octahedra are bridged by one of the formate ions and by hydrogen bonds. This network extends in a three-dimensional manner throughout the crystal structure. Both anti-anti and syn-anti configurations are observed in this structure. Formates used to bridge the cobalt(II) ions which are coordinated to six formates have the anti-anti configuration while the formates used to bridge different cobalt(II) ions have the syn-anti configuration. 224 225 6.1.1.2.2. Structure of Co(HCONH2)2(HCOO)2 There have been no previous reports on this compound. Crystallographic data for Co(HCONH2)2(HCOO)2 are given in the Appendix. The labeling scheme and a portion of the polymeric structure are shown in Figures 6.3 and 6.4, respectively. In addition, a portion of the three-dimensional network is shown in Figure 6.5. The nitrogens are disordered as shown in Figure 6.3. For clarity, only N(l) is shown in the representations of the structures shown in Figures 6.4 and 6.5. Selected bond lengths and angles are listed in Table 6.1. In Co(HCONH2)2(HCOO)2, all cobalt(II) ions are in the same octahedral environment, each cobalt(II) ion being coordinated by four formate anions and two formamide molecules. Formamide molecules are coordinated in a frans-fashion. Each cobalt(II) ion is linked with four other cobalt(II) ions by four formate ligands, adopting the anti-anti configuration. This results in a two-dimensional sheet polymeric structure. Hydrogen bonds present between formate anions and formamide molecules link the sheets together generating a three-dimensional lattice. Co-O(l) and Co-0(2) (oxygen atoms are from formate anions) bond lengths are 2.082(1) A and 2.085(1) A, respectively, close to the values observed in Co(H20)2(HCOO)2 (which are 2.065(2) A and 2.095 (2) A). The Co-0(3) (formamide) bond length is 2.122(2) A, slightly shorter than that observed in Co(HCONH2)2[H(C6H5)P02]2 (which is 2.179 (3) A) (10). 226 Table 6.1. Selected bond lengths (A) and angles (deg) for Co(HCONH2)2(HCOO)2*. Bond lengths Co(l)—0(1) 2.082(1) Co(l)—0(2)* 2.085(1) Co(l)—0(3) 2.122(2) 0(1)—C(l) 1.242(2) 0(2>—C(l) 1.242(2) 0(3>—C(2) 1.224(2) Bond angles o(i)-<:o(i)-o(i)H 0(1)—Co(l>—0(2)c 0( l ) -Co( l )—0(3)° 0(2)*—Co(l)-0(3) 0(3)—Co(l)—0(3)a Co(\)d—0(2>—C(l) 180.0 O(l)-Co(l>-0(2)* 92.75(5) 87.26(5) 0(l)-Co(l>-0(3) 90.97(7) 89.03(7) 0(2)*-<:o(l)-0(2)c 180.0 91.57(6) 0(2)*-€o(l)—0(3)° 88.43(6) 180.0 Co(l>-0(l)-C(l) 124.6(1) 123.6(1) Co(l)—0(3)—C(2) 123.7(2) * Superscripts refer to symmetry operations: ° 1/2 - x, 1/2 - y, 1 - z; 1/2 - x, -1/2 + y, 1/2 - z; ° x, 1 - y, 1/2 + z /x , 1 - y, -1/2 + z. C o O - ) C o O ) " B " -orr> oo) woo OH*) Figure 6.3. Atom labeling scheme of Co(HCONH2)2(HCOO)2, 33% probability thermal ellipsoids for non-hydrogen atoms are shown. 227 Figure 6.4. A section of the polymeric sheet of Co(HCONH2)2(HCOO)2. 33% probability thermal ellipsoids for non-hydrogen atoms are shown. 228 A portion of network three-dimensional for Co(HCONH2)2(HCOO)2. 33% probability thermal ellipsoids for non-hydrogen atoms are shown. 229 6.1.1.2. Magnetic Properties Magnetic susceptibility and magnetic moment data for Co(H20)2(HCOO)2 and Co(HCONH2)2(HCOO)2 are given in the Appendix. Neither compound has been subjected to detailed magnetic studies previously. Magnetic moment versus temperature plots for Co(H20)2(HCOO)2 and Co(HCONH2)2(HCOO)2 are shown in Figures 6.6 and 6.7, respectively. For both compounds the magnetic moment decreases with decreasing temperature, then shows an abrupt increase (at 8 K for Co(H20)2(HCOO)2 and at 9 K for Co(HCONH2)2(HCOO)2) and then drops again with decreasing temperature in the lowest temperature range. The magnetic behaviours for the two complexes may be explained as follows. Both compounds exhibit antiferromagnetic behaviour in the high temperature range. This can be more clearly seen in the magnetic susceptibility versus temperature plot for Co(HCONH2)2(HCOO)2 (Figure 6.8), in which an incipient maximum in the 9-18 K region is seen. Although no maximum is observed for Co(H20)2(HCOO)2 as shown in Figure 6.9, antiferromagnetic behaviour may be assumed for this compound also on the basis of the decreasing moment with decreasing temperature observed in the high temperature region. The sharp increase in moment may be ascribed to spin-canting, which results in weak ferromagnetism (11,12) as schematized in the following diagram. 230 / \ / \ / \ \ / \ / \ / Diagram to show the spin-canting interaction. The weak ferromagnetism caused by the spin-canting behaviour for Co(HCONH2)2(HCOO)2 was further supported by magnetization versus temperature and field plots as shown in Figures 6.10 and 6.11, respectively. Magnetization is not zero at temperatures below 10 K in zero applied field, indicating that the spins are spontaneously aligned and produce a net moment. The magnetic phase transition is also seen in the magnetic moment plot (Figure 6.9). Upon cycling the field between 55,000 G and - 55,000 G at 4.8 K a hysteresis loop is obtained with a remnant magnetization of 350 cm3 G mole"1 and a coersive field of 1,770 G, which are obtained from half of the vertical length at zero applied field and half of the horizontal length at zero magnetization, respectively (Figure 6.12). Antiferromagnetic coupling between metal centers via formate ligands within the extended 2-D sheets leads to a canted spin structure of the type depicted in the above diagram. Below 9 K three-dimensional magnetic ordering of the uncompensated spins occurs by ferromagnetic coupling via the H-bonding network linking the sheets. That applied fields may significantly affect magnetic ordering is clearly shown in Figure 6.9. As the applied field is increased from 2550 to 9225 G the magnetic moment anomaly at 9 K virtually disappears (Figure 6.9) due to disruption of the interlayer exchange. Susceptibility and moment plots versus temperature at 50,000 G (Figure 6. 13) 231 reveal no magnetic anomaly. The line shown in the figure was calculated from theory for a square lattice 2-D array of cobalt(II) ions with g = 2.43 and - J = 0.90 cm'1. CQ e c u s o V cu s w> ^  « 3 1 A A A AD O 0 O o A ^ fi O • B A C P ft A H=2549 G ° H=5251 G D H=7501 G 2 I—1—>—1—1—I—1—1—'—'—I ' ' ' i I—i—i—i—i—L_i i i i l_i i i i i i i i i I i i i i I i i i i 0 10 20 30 40 50 60 70 80 90 Temperature (K) Figure 6.6. Magnetic moment versus temperature plots for Co(H20)2(HCOO)2 at different fields. 232 r 3 i -• -A A D -A • O A • • • A • ° A • A A • - 0 o H=2549 G H=5251G A H=7501G oh ti - ° o p OA -> • • H=9225 G H=2549 G o A -_o A i i i i 1 i > i i 1 i i i i 1 i i i i 1 i i i i 1 i i i > i i i i > i i i i i i i i i i 0 10 20 30 40 50 60 70 80 90 Temperature (K) Figure 6.7. Magnetic moment versus temperature plots for Co(HCONH2)2(HCOO)2 at different fields (solid symbols are the data obtained from the crystals and open symbols are the data obtained from the powder samples). 233 0.14 •S 0.12 S Xi ••e a . <u u S CJ cu B bX) cd 0.10 0.08 0.06 0.04 0.02 ° H=2549 G ° H=5251 G A H=7501 G ° H=9225 G O A • A O A • A L ° A _1 I I I I I I I I 1 I 1 L_ 0 20 40 60 Temperature (K) 80 Figure 6.8. Magnetic susceptibility versus temperature plots for Co(HCONH2)2(HCOO)2 at different fields as shown in the diagram. 234 0.6 s 0.5 0.4 he* O A ho. 'V g- 0.3 3 u £ 0.2 WD S3 0.1 0.0 A H=2549 G ° H=5251 G ° H=7501 G O A a A _ l I I I I I I I I I I I I I I I L . J i i i i \ i i i i I i i i i L A • 0 10 20 30 40 50 60 70 80 90 Temperature (K) Figure 6.9. Magnetic susceptibility versus temperature plots for Co(H20)2(HCOO)2 at different fields. 235 800 600 CU "© E o s e © S3 'J CU WD 93 s 400 200 0 o H = 0 G • £ o O A fi ° H=2549 G o H=5251 G A H=7501 G • H=9225 G : « 4 Q X a O ° 0 A 0 o A o O r . A • • o o A • A ^ A O O 6 o , i 1 i i i i 1 i i i i 0 20 40 60 Temperature (K) 80 100 Figure 6.10. Magnetization versus temperature plot at different fields for Co(HCONH2)2(HCOO)2. 236 5000 4000 o E O s c _© « N T5 e C9 3000 2000 1000 a • o o o 8 g ° o ° 20 K D 10 K A 8K v 4.8 K O 2K 2 V o • 6 v o • A • A • A 8 • A A o 8 j i i — 1 _ J I I L. _l I I L. _1 I I L. 10000 20000 30000 40000 50000 Field (G) Figure 6.11. Magnetization versus magnetic field plot at various temperatures for Co(HCONH2)2(HCOO)2. 237 6000 © s o S e o ••a cu c CQ 4000 2000 0 -2000 -4000 • • B1 0 s • I I I I I ' I 1 I I I I I I I I 1 1 I I I I I 1 I I 0 20000 40000 -6000 -60000 -40000 -20000 60000 Field (G) Figure 6.12. Hysteresis loop for Co(HCONH 2 ) 2 (HCOO) 2 . 238 0.10 A A A A A A A A A A A A A A A A A _ 0.00 0 2 £ P o o o p i —1 I I I I I I I 1 I 1 L _L J I I I I I I I I 1 I I L 09 fl CU 3 1 CU c u fl (5D 93 - 2 - 1 0 50 100 150 200 250 300 Temperature (K) Figure 6.13. Magnetic data versus temperature plots for Co(HCONH2)2(HCOO)2 at 50, 000 G. Circles are the experimental susceptibility data and triangles are experimental moment data and line is calculated using Lines model (13). The structure of Co(HCONH2)2(HCOO)2 has led to a relatively simple and plausible description of the magnetic properties of the compound. The rather more complex three-dimensional covalent lattice of Co(H20)2(HCOO)2 does not lead to an obvious description of how spin-canting and overall ferromagnetism occur in this material. 239 6.2. {Co[(n-C 8F 1 7)P0 3](DMF)(H 20) 2} x Phosphonate anions, RP032", have three oxygen atoms which may be used to coordinate to metal ions. For divalent transition metal ions, complexes with composition of M(RP03) may be prepared. The possibility of generating 3-D polymeric structures employing such anions and the possibility that such materials could exhibit strong exchange interactions via M-O-P-O-M pathways led to a preliminary investigation of a cobalt(II) phosphonate. A preparative reaction involving perfluoro-n-octylphosphonic acid and cobalt(II) was examined. Crystals of {Co[(n-C8Fi7)P03](DMF)(H20)2}x were obtained over a period of three months after mixing an aqueous solution of cobalt(II) chloride hexahydrate with a DMF solution of perfluoro-n-octylphosphonic acid. Details are given in Chapter 7. The product turned out to be a mixture of materials from which the crystals were taken. For this reason no other physical characterization was performed except the crystal structure. Crystallographic data for {Co[(n-C8Fi7)P03](DMF)(H20)2}x are given in the Appendix. A section of the polymeric structure with the numbering scheme is shown in Figure 6.14 and selected bond lengths and bond angles are listed in Table 6.2. As seen in Figure 6.14, each cobalt(II) is six-coordinate, bonded to two molecules of water in a cis-configuration, one molecule DMF and three phosphonate anions. Each phosphonate ligand coordinates three different cobalt(II) ions via its three oxygen atoms and every cobalt(II) ion is surrounded by six neighbouring cobalt atoms, leading to a mesh-like sheet polymer. Bond lengths for the three P-0 bonds in each phosphonate ligand are 1.512(4) A, 1.499(4) A and 1.516(4) A, comparable to the P-0 bond length (1.510(1) A) in y-Co[(C6H5)2P02]2 240 (13). Co-0 (phosphonate) bond lengths are in the range 2.107(4) to 2.122(4) A, longer than those (in the range 1.950(3) to 1.963(3) A) observed in y-Co[(C6H5)2P02]2. This latter compound is weakly antiferromagnetic (\J\ = 0.60 cm"1). Since the cobalt(II) ions in {Co[(n-C8Fi7)P03](DMF)(H20)2}x are bridged by phosphonate ligands which are similar to diphenylphosphinate ligands, {Co[(n-C8Fi7)P03](DMF)(H20)2}x is expected to exhibit magnetically concentrated behaviour. Table 6.2. Selected bond lengths (A) and angles (deg) for {Co[(n-C8Fi7)P03](DMF)(H20)2}x*. Bond lengths Co(l)-0(l) 2.115(4) Co(l)—0(2)° 2.107(4) Co(l)—0(3)* 2.122(4) C o ( l>-0(4) 1.149(4) Co(l)—0(5) 2.112(4) Co(l)—0(6) 1.126(4) P(l)-0(1) 1.512(4) P(l)-0(2) 1.499(4) P(l)-0(3) 1.516(4) Bond angles 0(1)—Co(l)—0(2)° 100.5(2) 0(1)—Co(l)—0(3)* 170.9(2) 0 ( l ) - C o ( l M ) ( 4 ) 88.7(2) 0(1)—Co(l)—0(5) 87.3(2) 0(1)—Co(l)—0(6) 89.8(2) 0(2)°—Co(l)—0(3) 85.5(2) 0(2)°—Co(l)—0(4) 92.4(2) 0(2)a—Co(l)—0(5) 169.9(2) 0(2)a—Co(l)—0(6) 84.5(2) 0(3)*—Co(l)—0(4) 84.1(2) 0(3)*—Co(l)—0(6) 84.5(2) 0(3)*—Co(l>—0(6) 97.7(2) 0(4)—Co(l)—0(5) 94.4(2) 0(4)—Co(l)—0(6) 176.2(2) 0(5)—Co(l)—0(6) 89.1(2) * Superscripts refer to symmetry operations: a -1 + x, y, z; 1 - x, 1/2 + y, 1 - z; ° 1 + x, y , z / l - x , l/2 + y , l - z . 241 A section of the polymeric structure of {Co[(n-CgFn)P03](DMF)(H20)2}x with atom labeling shown in the diagram. 242 REFERENCES 1. A. Kaufman, C. Afshar, M. Rossi, D. E. Zacharias and J. P. Glusker, Inorg. Chem. 4, 191 (1993). 2. K. Krogmann and R. Mattes, Z Kristallogr. 18, 291 (1963). 3. K. Osaki, Y. Nakai and T. Watanabe, J. Phys. Soc. Jpn. 19, 717 (1964). 4. M. Bukowska-Strzyzewska, Acta Crystallogr. 19, 357 (1965). 5. M. Gerloch, Prog. Inorg. Chem. 26, 1 (1979). 6. B. N. Figgis and R. L. Martin, J. Chem. Soc. 3837 (1956). 7. J. J. Girard, O. Kahn and M. Verdaguer, Inorg. Chem. 19, 274 (1980) 8. G. A. Nifontova, O. S. Filipenko, A. S. Astokhova, I. P. Lavrent'ev and L. O. Atovmyan, Koord. Khim. 16, 218 (1990). (Eng. Trans.) 16, 121 (1990). 9. A. K. Chulkevich, I. P. Lavrent'ev, A. P. Moravskii, M. L. Khidekel', V. I. Ponomarev, O. S. Filipenko and L. O. Atovmyan, Koord. Khim. 12, 470 (1986). (Eng. Trans.) 12, 285 (1986). 10. P. Betz, A. Bino, J.-L. Du, L. S.-M. Lo and R. C. Thompson, Inorg. Chim. Acta, 170, 45 (1990). 11. R. L. Carlin, Magnetochemistry, Berlin Heidelberg, Springer-Verlag, 1986. 12. O. Kahn, Molecular Magnetism, VCH Publications, Inc. New York, 1993. 13. J.-L. Du, S. J. Rettig, R. C. Thompson and J. Trotter, Can. J. Chem. 69, 277 (1991). 243 Chapter 7 Experimental 7.1. Physical Experimental Techniques 7.1.1. Elemental Analysis All carbon, hydrogen and nitrogen analyses were performed by Mr. Peter Borda of this department using a Carlo Erba Model 110 elemental analyzer. Elemental analyses are considered to have an absolute accuracy of ±0.30%. For the complexes containing fluorinated ligands, oxidants such as Pb 30 4 were used to help the decomposition of the sample. 7.1.2. Thermal Studies Differential Scanning Calorimetry (DSC) and thermogravimetric analysis (TGA) were performed utilizing a TA Instruments TA 2000 system, consisting of a TA Instruments DSC 91 OS standard cell and a TA Instruments TGA 51 thermogravimetric analyzer. For DSC studies, finely ground powdered samples of approximately 5 mg were accurately weighed into aluminum pans and sealed hermetically with a sample encapsulating presser. The sample was heated from 25 °C to 600 °C at a rate of 10 °C/min and purged with dinitrogen gas at a flow-rate of 40 cc/min. The temperature was calibrated with pure indium (m.p. = 156.61 °C), tin (m.p. = 231.97 °C) and zinc (m.p. = 419.58 °C). Heating flow calibration was achieved using accurately weighed samples of indium (AH = 28.4 J/g). Both calibrations were checked periodically. The temperature and enthalpy of a particular thermal event were obtained from the maximum (or minimum) in 244 the DSC curve and the integrated area above (or underneath) the curve, respectively. Temperature and enthalpy are considered to be accurate to ±1 °C and ±1%, respectively. For TGA studies, samples of approximately 10 mg were put into a platinum pan and heated from 25 °C to 800 °C at a rate of 10 °C/min and purged with dinitrogen at a flow-rate of 100 cc/min. The TGA 51 system recorded the weight changes against the temperature. The accuracy of the weight loss is about ±1%. 7.1.3. Infrared Spectroscopy Infrared spectra, over the range 4000 cm"1 to 200 cm"1, were recorded on samples mulled in Nujol sandwiched between KRS-5 plates (58% Til, 42% TIBr, Harshaw Chemical Co.). For moisture sensitive compounds, the plates were sealed with plastic tape. A Bomen MB 102 Fourier-transform Infrared Spectrophotometer (FTIR) was used. The instrument was calibrated at 907 and 1061 cm"1 with polystyrene film. The recorded frequencies are considered accurate to ±3 cm"1 for broad peaks and ±1 cm"1 for sharp peaks. 7.1.4. Electronic Spectroscopy A Varian Cary 5 UV-Vis-NIR Spectrophotometer, operating over the range 200 to 3,000 nm (3,300 to 50,000 cm"1) was used to record the electronic spectra. The samples were mulled in Nujol and sandwiched between quartz glass plates. Another plate containing only Nujol was used as reference. Bands observed in the electronic spectra were usually broad, hence spectral frequencies are considered accurate only to ±200 cm"1. 245 7.1.5. Powder X-ray Diffraction X-ray powder diffraction data were recorded in the range 29 = 4 to 60° on a Rigaku Rotating Anode Powder X-ray Diffractometer using Cu Koc (k = 1.54718 A ) radiation. The peak finding program was provided by Rigaku. Samples were prepared by grinding compounds with n-octane to make a slurry, applying the slurry to a glass slide, then allowing the n-octane to evaporate. 7.1.6. Single Crystal X-ray Crystallography Single crystal X-ray diffraction structural determinations were performed by Dr. S. J. Rettig of this department. The data used to solve crystal structures of complexes were collected on a Rigaku AFC6S Diffractometer using Cu Ka (k = 1.54718 A ) or Mo Ka (X = 0.71069 A ) radiation with a graphite monochromator at temperature of 294 K. The takeoff angle was 6.0° and the aperture has a size of 6.0 x 6.0 mm at a distance of 285 mm from the crystal. The final unit-cell parameters were obtained by least squares on the setting angles for 25 reflections. The intensities of three standard reflections, measured every 200 reflections throughout the data collections, should show only small random fluctuation. The data were processed according to the software package (1), corrected for Lorentz and polarization effects and for absorption (based on azimuthal scans for three reflections. Two methods, direct method or Patterson method (2, 3), were used to solve the structures in this work. Non-hydrogen atoms were refined with anisotropic thermal parameters. A correction for secondary extinction was applied sometimes. Neutral atom scattering factors for all atoms 246 and anomalous dispersion corrections for the non-hydrogen atoms were taken from the International tables for X-ray crystallography (4, 5). 7.1.7. Magnetic Susceptibility Two different kinds of apparatus were used for the magnetic susceptibility measurements. Measurements over the temperature range 2 to 80 K were made using a Princeton Applied Research Model 155 Vibrating Sample Magnetometer (VSM) (6). Magnetic fields of 2549, 5251, 7501, 9225 and 9625 G were employed with this instrument. Magnetic fields were estimated to an accuracy of 0.5% and measured using a F. W. Bell model 620 gaussmeter. Accurately weighed samples of approximately 80 mg, contained in Kel-F capsules, were attached to Kel-F holder with epoxy resin. Ultra-pure nickel metal was used to calibrate the instrument. Temperature measurement was achieved with a chromel versus Au-0.02% Fe thermocouple (7). The thermocouple was calibrated by using the known susceptibility versus temperature behavior of tetramethyldiammonium tetrachlorocuprate(II) and checked with mercury(II) tetrathiocyanatocobaltate(II) (8). The temperature was estimated to be accurate to ±1% from the scatter in the data points of four separate calibrations. The accuracy of the magnetic susceptibility values as measured by this technique is estimated to be in the ±1% range. The maximum field available with this instruments is 10,000 G. The other apparatus used to measure magnetic susceptibilities over the temperature range 1.7 to 400 K was a Quantum Design MPMS SQUID magnetometer (9). The temperature was measured using a Ge resistance thermometer in the range of 1.7-40 K and a Pt resistance thermometer in the range 40-400 K. Temperature measurement was 247 calibrated using an external Pt resistance thermometer and is accurate to within 0.1%. Except for variable field measurements, all samples were measured in an applied field of 10,000 G. Susceptibility measurements were calibrated using ultrapure Ni, Pd and Bi standards and are accurate to within ±1%. Samples of about 30 mg were loaded in a PVC plastic sample holder (made in the mechanical engineering shop of this department). The maximum field for this instrument is 55,000 G. Corrections were made for the background signal produced by the holders for both techniques. Magnetic susceptibilities were corrected for the diamagnetism of all atoms (10-12). The corrections used, in units of 10"6 cm3 mol'1, are: Cu 2 +, -11; Ni 2 +, -11; Mn 2 +, -14; Co 2 +, -12; (n-C6H13)2P02-, -166; (C 6H 5)HP0 2\ -78; (C6H5)2P02', -127; (n-C 8H 1 7) 2P0 2-, -210; (C6F5)2P02-, -161; [CF3(CF2)3CH2CH2]2P02-, -227; [CF3(CF2)5CH2CH2]2P02-, -298; H 20, -12; (CH3)2SO, -61; HCONHCH 3, -32; HCONH(CH3)2, -36. The molar magnetic susceptibilities were also corrected for the temperature independent paramagnetism (T.I.P) of 60 x 10'6 cm3mol'1 for Cu(II), of 230 x 10"6 cm3 mol'1 for octahedral Ni(II) and of 560 x 10"6 cm3 mol'1 for tetrahedral Co(II) (10-15). 7.1.8. Melting Point Determination Melting points of compounds were determined by using a Gallenkamp melting point apparatus. The thermometer was calibrated by the indium standard (m.p. = 156.6 °C), the accuracy was within ±1 °C. 248 7.1.9. Electron Paramagnetic Resonance Spectroscopy (EPR) The ERP spectra of the copper(II) complexes studied in this work were measured by Dr. F. G. Herring in the Chemistry Department at the University of British Columbia. Powder samples for EPR studies were packed into quartz glass tubes of ~3.0 mm internal diameter to a height of ~5-10 mm. The spectra were recorded on a Bruker ECS 106 ERP spectrometer. The instrument was equipped with a 50 kHz field modulation. The field sweep was calibrated by Bruker, and the calibration checked with peroxylamine disulphonate (Fremy's salt). The X-band frequency (-9.8 GHz) was monitored with a EIP model 625A CW microwave counter. Measurements were performed at 120 K on a Bruker ER 4112VT cryostat system. 249 7.2. Syntheses 7.2.1. General Comments The synthetic methods used to make the compounds are classified into two types, one for the adduct polymers and the other for the binary compounds. The methods employed in the synthesis of adduct polymers were described before (16-18) for the preparation of transition metal monophenylphosphinate derivatives. Either transition metal salts were reacted, in the presence of neutral ligands (L), with monophenylphosphinic acid which had been partially neutralized by base (see equation [7.1]), or neutral ligands (L) were reacted directly with the binary metal monophenylphosphinate (equation [7.2]). M X 2 + 2H(C6H5)P02H +2L ** ML 2[H(C 6H 5) 2P0 2] 2 + 2HX [7.1] M[H(C6H5)P02]2 +2L • MI^[H(C6H5)2P02]2 [7.2] The binary phosphinates were synthesized by use of routes reported before (18), modified in some cases. Some reported methods are rather exotic. Zn[(C6Hs)2P02]2, for example, was synthesized through the interfacial polymerization of an aqueous solution of zinc(II) acetate with a benzene solution of diphenylphosphinic acid (19). Also, several metal methylphenylphosphinates were obtained through the high temperature reaction of the appropriate metal halide with an excess of methyl methylphenylphosphinate (20). However, the more conventional syntheses generally involve the reaction between a metal salt and either the phosphinic acid or a salt of the acid, in an appropriate solvent or mixture of solvents (18) [7.3]: 250 -B3.se M X 2 + 2RR ,P02H *- M[H(C 6H 5) 2P0 2] 2 + 2HX [7.3] Some of the compounds discussed here were sensitive to water vapor and were handled only in the absence of moisture. This was typically done by utilizing Schlenk techniques and handling the compounds in an inert dinitrogen atmosphere dry box (D. L. Herring Corporation Dri-Lab (Model He-43) equipped with a dry-train (Model He-93)). The yields in these synthetic reactions varied from nearly quantitative to -30% of theory. In some syntheses the dehydrating reagent DMP (2,2'-dimethoxypropane) was used to eliminate any water from starting materials or products. 7.2.2. Materials Most of the chemicals used were commercially available reagent grade and were used as received (Table 7.1). Di-n-hexylphosphinic acid, di-n-octylphosphinic acid, dimethylphosphinic acid, bis(perfluorophenyl)phosphinic acid monohydrate , potassium bis(perfluorophenyl)phosphinate, bis[(perfluoro-n-hexyl)ethyl]phosphinic acid and bis[(perfluoro-n-butyl)ethyl]phosphinic acid were synthesized by K. W. Oliver (also see some relevant references 21-25), the methylethylphosphinic acid was provided by G. Haegele, perfluoro-n-octylphosphonic acid and phenylperfluorophenylphosphinic acid were provided by R. Schmutzler. 251 7.2.3. Copper(II) Compounds 7.2.3.1. Poly{ [hexakis(//-dimethylpho sphinato)]tricopper(II)} {Cu 3[(CH 3) 2P0 2] 6}x. A solution of copper(II) nitrate trihydrate (0.725 g, 3.00 mmol) in 50 mL acetone and 5 mL DMP was added to a solution of dimethylphosphinic acid (0.658 g, 7.00 mmol) (neutralized with 0.83 mL triethylamine) in 50 mL acetone. A blue precipitate formed after the addition of about one third of the copper salt. After all of the copper salt was added the mixture was further stirred for 3 days. The precipitate was collected on a sintered glass filter and washed with acetone. After drying in vacuo at 100 °C for about 4 h the final product (yield 88%) was obtained as a blue powder. Anal, calcd. for Cu 3Ci 2H 3 6Oi 2P6: C 19.25, H 4.85; found: C 19.15, H 4.91. Blue crystals suitable for single crystal X-ray diffraction studies were formed after 3 weeks by mixing copper(II) dichloride dihydrate (0.085 g, 0.50 mmol) in 10 mL DMF with dimethylphosphinic acid (0.188 g, 2.00 mmol, neutralized by 0.14 mL triethylamine) in 10 mL DMF. IR spectra, X-ray powder diffraction, DSC studies and elemental analyses showed that the crystals were the same compound as the powder form synthesized as described above. 7.2.3.2. Bis(methylethylphosphinato)copper(II) Cu[(CH3)(C2H5)P02]2 A solution of methylethylphosphinic acid (0.900 g, 8.00 mmol) in 50 mL acetone and 5 mL DMP was partially neutralized with 1.1 mL of triethylamine. Copper(II) perchlorate hexahydrate (1.46 g, 4.00 mmol) was dissolved in 30 mL acetone and 5 mL DMP and the 252 solution was added dropwise with stirring to the above acid solution. The clear blue solution obtained after the addition of all the copper salt was stirred for 3 d. A blue precipitate which was formed during this period of time was collected on a sintered glass filter in an atmosphere of dinitrogen, washed with acetone and dried in vacuo at room temperature for 4 h. The product was a blue powder (yield 27%). Anal, calcd. for CuC6H1604P2: C 25.95, H 5.81; found: C 26.09, H 5.90. 7.2.3.3. Bis[bis(perfluorophenyl)phosphinato]copper(II) Cu[(C6F5)2P02]2 Potassium bis(perfluorophenyl)phosphinate (0.872 g, 2.00 mmol) was dissolved in 5 mL of H 20. To this solution was added dropwise with stirring a solution of copper(II) perchlorate hexahydrate (0.290 g, 0.800 mmol) in 5 mL H 20. The clear blue solution which was obtained after the addition of all of the copper salt was stirred for another 10 h. A blue solid obtained after the evaporation of water under vacuum at 80°C was extracted with 4 x 100 mL of acetone. The acetone extractants were combined and allowed to evaporate under vacuum. The residue after the evaporation of all the solvent was dried in vacuo at 60 °C for 5 h. The final product was obtained as a pale blue powder (yield 36%). Anal, calcd. for CuC 2 4F 2 0O4P 2: C 33.61; found: C 33.63. 7.2.3.4. Bis(phenylperfluorophenylphosphinato)copper(II) Cu[(C6H5)(C6F5)P02]2 Phenylperfluorophenylphosphinic acid (0.235 g , 0.75 mmol) was dissolved in 30 mL diethyl ether. To this acid solution was added copper acetate monohydrate (0.050 g, 0.25 mmol). A clear blue solution was formed after stirring the mixture for 30 min. Further 253 stirring resulted in the precipitation of a blue powder. The precipitate was collected on a sintered glass and washed with acetone in a dinitrogen atmosphere, and then dried in vacuo at room temperature for 2 h. (yield 60%). Anal, calcd. for CUC24F10H10O4P2: C 41.91, H 1.47; found: C 41.71, H 1.57. 7.2.3.5. Bis{bis[(perfluoro-n-butyl)ethyl]phosphinato}copper(II) Cu{ [CF3(CF2)3CH2CH2]2P02}2 Bis[(perfluoro-n-butyl)ethyl]phosphinic acid (0.558 g, 1.00 mmol) was dissolved in 100 mL EtOH : H 2 0 (50:50 V/V) and then neutralized by 0.90 ml 1.00 M sodium hydroxide. To this sodium salt solution was added slowly with stirring copper(II) nitrate trihydrate (0.125 g, 0.500 mmol) in 20 mL H 20. A precipitate appeared after about half of the copper(II) salt was added. After all of the copper(II) salt was added the mixture was stirred for another 2 d . The precipitate was collected on a sintered glass, washed with ethanol, then water, then ethanol again, and then left to dry in the air overnight (yield 46 %). Anal, calcd. for CuC2 4Hi6F3 604P2: C 24.48, H 1.37; found: C 24.80, H 1.43. 7.2.3.6. Bis{bis[(perfluoro-n-hexyl)ethyl]phosphinato}copper(II), form I Cu{[CF3(CF2)5CH2CH2]2P02}2, form I Bis[(perfluoro-n-hexyl)ethyl]phosphinic acid (0.758 g, 1.00 mmol) was dissolved in 100 mL ethanol. The solution was partially neutralized by 1.80 mL 0.500 M sodium hydroxide. Undissolved material was removed by filtration. To the filtrate was added, with stirring, copper nitrate trihydrate (0.121 g, 0.500 mmol) in 20 mL ethanol. After about one third of the total copper(II) salt was added, a blue precipitate formed. After adding all the copper (II) salt, the mixture was stirred for 1 d. The precipitate was collected on a 254 sintered glass, washed with ethanol, then water, and then ethanol again. The final product was a pale blue powder (yield 68 %). Anal, calcd. for CuC3 2Hi6F5 2C>4P2: C 24.36, H 1.02; found: C 24.32, H 1.00. 7.2.3.7. Bis{bis[(perfluoro-n-hexyl)ethyl]phosphinato}copper(II), form II Cu{[CF3(CF2)5CH2CH2]2P02}2, form II The DSC thermogram of form I of bis{bis[(perfluoro-n-hexyl)ethyl]phosphinato}copper(II) prepared as above shows two thermal events over the temperature range of 35 to about 200 °C. The first event at 101 °C was observed to be irreversible, indicating that another form of this compound (called form II) could be obtained. A powder sample of bis{bis[(perfluoro-n-hexyl)ethyl]phosphinato}copper(II) (form I) was heated in an oil bath at 115 °C for 4 h, then cooled to room temperature, and reheated at 115 °C for 2 h. During this period of time, the original pale blue powder changed into a pale green powder. The conversion was quantitative and purity was checked by DSC (no event at 101 °C was observed). Anal, calcd. for CuC32H16F5204P2: C 24.36, H 1.02; found: C 24.22, H 1.09. 7.2.4. Manganese(II) Compounds 7.2.4.1. Bis(dimethylphosphinato)manganese(II), Form I Mn[(CH3)2P02]2, form I The synthesis and magnetic properties of this compound were reported previously (22). In the present work, a different method was employed to obtain the same compound, identified by the results of elemental analysis, IR spectra and magnetic studies. 255 Dimethylphosphinic acid (0.476 g, 5.00 mmol) was dissolved in 50 mL acetone and was partially neutralized by 0.57 mL of triethylamine. To this acid solution was added dropwise, with stirring, manganese(II) perchlorate hexahydrate (0.723 g, 2.00 mmol) dissolved in 30 mL of acetone and 5 mL of DMP. A white precipitate appeared after only a few drops of the manganese salt was added. The mixture was stirred for 1 d and the precipitate was collected on a sintered glass, and washed with acetone. A pink powder was obtained after the product was dried in vacuo at room temperature for 6 h (yield 65%). Anal, calcd. for M11C4H12O4P2: C 19.93, H 5.02; found: C 19.94, H 5.01. 7.2.4.2. Poly-bis(dimethylphosphinato)manganese(II), Form II Mn[(CH3)2P02]2, form II In the course of DSC studies on Mn[(CH3)2P02]2 (Form I), a second form of the compound (Form II) was identified. A sample of manganese dimethylphosphinate, Form I, was put into a furnace and heated to 220 °C in a stream of dinitrogen gas for 4 h. The pink color of original material changed to pale green. The yield was quantitative, and IR and DSC studies indicated there was no Form I impurity in the final product. Anal, calcd. for MnC4Hi204P2: C 19.93, H 5.02; found: C 19.79, H 4.98. Crystals of Mn[(CH3)2P02]2, Form II, suitable for the single crystal X-ray diffraction studies were obtained as follows. Manganese dichloride tetrahydrate (0.198 g, 1.00 mmol) was dissolved in 10 mL DMF. Dimethylphosphinic acid (0.188 g, 2.00 mmol) was dissolved in 10 mL DMF. A clear solution obtained after mixing the above two solutions and was allowed to stand over a period of 4 weeks and pale greenish crystals deposited. 256 The IR spectra, X-ray powder diffraction, and DSC thermogram confirmed the crystals are the same compound as that obtained by heating form I of MnlXCFL^PO^h-7.2.4.3. Bis(methylethylphosphinato)manganese(II) Mn[(CH3)(C2H5)P02]2 Manganese acetate tetrahydrate (0.980 g, 4.00 mmol) was dissolved in 100 mL of ethanol and the solution was added slowly, with stirring, to a solution of methylethylphosphinic acid (1.081 g, 10.0 mmol) in 100 mL ethanol. The mixture became cloudy after about half of the manganese salt was added. More precipitate formed after all of the manganese salt had been added. The mixture was stirred for 24 h. The precipitate was collected on a sintered glass, washed with ethanol and left to air dry for one night. The dried product was a pale pink powder (yield 94%). Anal, calcd. for MnCeHieC^: C 26.78, H 5.99; found: C 26.87, H 6.00. 7.2.4.4. Bis {bis[(perfluoro-n-hexyl)ethyl]phosphinato} manganese(II) Mn{ [CF3(CF2)5CH2CH2]2P02}2 Bis[(perfluoro-n-hexyl)ethyl]phosphinic acid (0.758 g, 1.00 mmol) was dissolved in 100 mL of ethanol and the solution was partially neutralized with 1.80 mL 0.500 M aqueous sodium hydroxide (0.900 mmol). This sodium salt solution was filtered to remove any insoluble materials. To the filtrate was added, dropwise with stirring, manganese perchlorate hexahydrate (0.198 g, 0.500 mmol) dissolved in 20 mL of H20. A fluffy white precipitate formed immediately and the resulting mixture was stirred for another 2 d. The precipitate was collected on a sintered glass, washed with water, then with ethanol, and 257 then left to air dry (yield 45%). Anal, calcd. for MnC32F52Hi604P2: C 24.49, H 1.03; found: C 24.63, H 1.10. 7.2.4.5. Bis{di-n-octylphosphinato}manganese(II) Mn[(n-C8H17)2P02]2 Di-n-octylphosphinic acid (2.08 g, 7.16 mmol) was dissolved in 200 mL of methanol and the solution was partially neutralized by a solution of sodium hydroxide (0.250 g, 6.25 mmol) in 20 mL of H20. To this solution was added, dropwise with stirring, manganese perchlorate hexahydrate (1.296g, 03.58 mmol) dissolved in 100 mL of methanol. A white precipitate formed immediately and after all of the manganese salt solution was added, the mixture was stirred for another 10 h. The precipitate was collected on a sintered glass, washed with water, and then with methanol, and then left to air dry (yield 80%). Anal, calcd. for MnC32H6804P2: C 60.64, H 10.82; found: C 60.81, H 10.92. 7.2.4.6. Bis{bis(perfluoro-n-butyl)ethyl]phosphinato}manganese(II) Mn{ [CF3(CF2)3CH2CH2]2P02}2 Bis[(perfluoro-n-butyl)ethyl]phosphinic acid (0.268 g, 0.48 mmol) was dissolved in 5 mL DMF. To this solution was added manganese dichloride tetrahydrate (0.047 g, 0.24 mmol) in 5 mL DMF/5 mL DMP. A white precipitate formed immediately and the mixture was stirred for 6 h. The precipitate was collected on a sintered glass, washed with acetone, and left to air dry (yield 56%). Anal, calcd. for MnC24F36H1604P2: C 24.65, H 1.38; found: C 24.86, H 1.19. 258 1.2 Al. Bis(dimethylarsinato)manganese(II) Mn[(CH3)2As02]2 Dimethylarsinic acid (0.552 g, 4.00 mmol) was dissolved in 50 mL ethanol/2 mL DMP and was partially neutralized by 0.28 mL of triethylamine. A solution of manganese(II) perchlorate hexahydrate (0.723 g, 2.00 mmol) in 30 mL of ethanol/2 ml DMP was added slowly, with stirring, to the above solution. A brownish precipitate formed immediately after a few drops of the manganese salt was added. After all of the manganese salt was added the mixture was stirred for 12 h . The precipitate was collected on a sintered glass funnel under an atmosphere of dinitrogen gas, washed with ethanol, and dried in vacuo at room temperature for 5 h (yield 82%). Anal, calcd. for MnC4Hi2As204: C 14.61, H 3.68; found: C 14.49, H 3.65. 7.2.4.8. Poly-bis(dimethylsulfoxide)bis(Ju-monophenylphosphinato)manganese(II) Mn[(CH3)2SO]2[H(C6H5)P02]2 Monophenylphosphinic acid (0.560 g, 4.00 mmol) was dissolved in 10 mL DMSO, and was partially neutralized by 0.54 mL triethylamine. Manganese dichloride tetrahydrate (0.394 g, 2.00 mmol) was dissolved in 20 mL DMSO/5 mL DMP. The clear solution obtained after the above two solutions were mixed was allowed to stand. A crop of white crystals formed after 4 d. The crystals were collected on a sintered glass in a dinitrogen atmosphere, washed with DMSO and then with diethyl ether, and dried in vacuo at room temperature for 2 h (yield 50%). Anal, calcd. for MnCi6H2406P2S2: C 38.95, H 4.90; found: C 38.78, H 5.07. 259 7.2.4.9. Bis[bis(perfluorophenyl)phosphinato]manganese(II) Mn[(C6F5)2P02]2 Manganese acetate tetrahydrate (0.245 g, 1.00 mmol) was mixed with bis(perfluorophenyl)phosphinic acid monohydrate (1.248 g, 3.00 mmol) in 50 mL diethyl ether. A clear colorless solution was obtained after stirring the mixture for about 2 h and a white precipitate formed during a period of -20 h. The precipitate was collected in a dinitrogen atmosphere, washed with acetone and dried in vacuo at room temperature for 4 h. The white powder obtained was found to be a moisture sensitive compound (yield 54%). Anal, calcd. for MnC 2 4F 2 0O4P 2: C 33.95; found: C 33.84. 7.2.4.10. {(DMF)3Mn[//-(C6F5)2P02]3}2Mn In an attempt to grow crystals of Mn[(CeF5)2P02]2, a compound with the formulation of {(DMF)3Mn[//-(C6F5)2P02]3}2Mn was obtained instead. This compound was characterized by single crystal X-ray crystallography. Bis(perfluorophenyl)phosphinic acid monohydrate (0.333 g, 0.800 mmol) was dissolved in 10 mL DMF and manganese(II) chloride tetrahydrate (0.0396 g, 0.200 mmol) was dissolved in 5 mL DMF. A clear colorless solution was obtained after mixing the above two solutions. Two months later, colorless crystals were obtained, and some crystals were retrieved for the X-ray studies while the bulk of the crystals were collected on a sintered glass in an atmosphere of dinitrogen and washed with acetone, air dried and used in other studies. This bulk material was analyzed for C, H and N. Anal, calcd. for Mn3C9oH42F6oN6o018P6: C 36.20, H 1.42, N 2.81; found: C 36.68, H 1.55, N 3.05. The X-ray studies on the crystal revealed the presence of 4.5 molecules of lattice water. Neither 260 the elemental analysis nor IR studies showed the presence of water in the bulk material. It is assumed that the lattice water was removed in the washing procedure. 7.2.5. Nickel(II) Compounds 7.2.5.1. Bis(monophenylphosphinic acid)bis(monophenylphosphinato)nickel(II) Ni[H(C6H5)2P02H]2[H(C6H5)P02]2 This compound was synthesized by two different methods. Monophenylphosphinic acid (2.00 g, 14.0 mmol) was dissolved in 50 mL acetone/10 mL DMP. To this solution was added nickel(II) monophenylphosphinate (0.35 g, 1.00 mmol) which was prepared according to the method described in reference (18). The mixture was allowed to stir for 3 h. During this period of time, the yellow solid changed to a green solid. The product was collected on a sintered glass, washed with acetone and left to air dry for 12 h (yield 80%). Anal, calcd. for NiC^eOgP^ C 46.12, H 4.19; found: C 46.02, H 4.29. Another synthetic method employed nickel(II) nitrate hexahydrate and monophenylphosphinic acid. Monophenylphosphinic acid (2.00 g, 14.0 mmol) was dissolved in 50 mL acetone and partially neutralized by 0.30 mL triethylamine. This solution was mixed with a solution of nickel nitrate hexahydrate in 20 mL acetone/5 mL DMP, resulting in the formation of a clear yellow solution. A greenish precipitate formed overnight in the solution. The product was collected on a sintered glass, washed with acetone and dried in air for 12 h. The final product was a pale green powder (yield 73%). Anal, calcd. for N^^gOgP^ C 46.12, H 4.19; found: C 46.10, H 4.14. 261 7.2.5.2. Bis(N-methylfomarmde)bis(m Ni(HCONHCH3)2[H(C6H5)P02]2 This compound was synthesized by two different routes. JR spectroscopy and X-ray powder diffraction studies showed the compounds obtained in the two different ways to be identical. Monophenylphosphinic acid (0.568 g, 4.00 mmol) was dissolved in 20 mL acetone/5 mL DMP, and the solution was partially neutralized with 0.56 mL triethylamine. Nickel nitrate hexahydrate (0.582 g, 2.00 mmol) in a mixture of 10 mL acetone/10 mL N-methylformamide/5 mL DMP was added slowly with stirring to the above acid solution. A pale green precipitate formed after stirring for 2 d. This was collected under a dinitrogen atmosphere, washed with a mixture of N-methylformamide and diethyl ether (50:50 V/V) and then dried in vacuo at room temperature for 4 h. The final product was a pale greenish powder (yield 43%). Anal, calcd. for NiCi 6H 2 2N 20 6P 2: C 41.87, H 4.83, N 6.10; found: C 41.58, H 5.02, N 6.01. An alternative way to obtain the compound involved mixing nickel(II) monophenylphosphinate (13) (0.620 g, 2.00 mmol) with 8 mL N-methylformamide in 5 mL DMP/10 mL acetone. The original yellow color changed to a pale green after the mixture was stirred for 3 d. The product was collected on a sintered glass in dinitrogen, washed with a mixture of N-methylformamide and diethyl ether (50:50 V/V) and dried in vacuo at room temperature for 2 h (yield 68%). NiCi 6H 2 2N 20 6P 2: C 41.87, H 4.83, N 6.10; found: C 41.68, H 4.92, N 6.18. 262 7.2.5.3. Bis(dimethylphosphinato)nickel(II) Ni[(CH3)2P02]2 Dimethylphosphinic acid (0.376 g, 4.00 mmol) was dissolved in 100 mL ethanol. Nickel(II) acetate tetrahydrate (0.497 g, 2.00 mmol) dissolved in 200 mL of ethanol was added dropwise, with stirring, to the above solution. The yellow solution obtained was stirred for 3 d. The solution was flash evaporated to about 30 mL, resulting in the formation of a yellow slurry. The slurry, left in a beaker overnight, produced more precipitate. The precipitate was collected, and washed with a small amount of cold ethanol and then with acetone. A yellow powder was obtained after drying in vacuo at 130 °C for 4 h (yield 74%). Anal, calcd. for N i C ^ C u P ^ C 19.63, H 4.94; found: C 19.65, H 4.96. 7.2.5.4. Bis(methylethylphosphinato)nickel(II) Ni[(CH3)(C2H5)P02]2 Methylethylphosphinic acid (1.297 g, 12.0 mmol) in 50 mL of diethyl ether was mixed with nickel(II) acetate tetrahydrate (0.995 g, 4.00 mmol). After stirring for 30 min, the mixture gave a clear yellow solution. A yellow precipitate formed after further stirring for about 3 h. This mixture was stirred for another 10 h, after which time it was allowed to evaporate under vacuum at room temperature. The solid obtained after the evaporation of the diethyl ether solvent was heated for 4 h at 120 °C under vacuum. The yellow solid was washed with acetone and dried in vacuo at room temperature for 4 h (yield 69%). Anal, calcd. for NiC6Hi604P2: C 26.41, H 5.91; found: C 26.59, H 5.92. 263 7.2.5.5. Bis(dimethylarsinato)nickel(II) Ni[(CH3)2As02]2 Dimethylarsinic acid (0.826 g, 6.00 mmol) was dissolved in 50 mL ethanol and partially neutralized by 0.60 mL of triethylamine. Nickel(II) perchlorate hexahydrate (0.731 g, 2.00 mmol) was dissolved in 20 mL of ethanol/5 ml DMP and this solution was added slowly, with stirring, to the above acid solution. A yellow precipitate formed after half of the nickel salt was added. After all of the nickel salt was added, the mixture was stirred for 2 d. The precipitate was collected on a sintered glass funnel under an atmosphere of dinitrogen gas, washed with ethanol and dried in vacuo at room temperature for 6 h (yield 71%). Anal, calcd. for NiCoHnAszCv C 14.44, H 3.64; found: C 14.24, H 3.78. 7.2.5.6. Bis(perfluorophenylphosphinato)nickel(II) Ni[(C6F5)2P02]2 Bis(perfluorophenyl)phosphinic acid monohydrate (0.624 g, 1.50 mmol) was dissolved in 50 mL of diethyl ether and mixed with nickel(II) acetate tetrahydrate (0.124 g, 0.50 mmol). The mixture became clear after stirring for 1 h. A pale green precipitate formed over a period of about 1 d. The precipitate was collected and washed with acetone. The pale green powder obtained was then placed in a furnace in a stream of dinitrogen gas and was heated at 290 °C for 6 h. The final product was a blue powder and was very moisture sensitive ( yield 77%). Anal, calcd. for N ^ ^ o C ^ : C 33.80; found: C 33.40. 264 7.2.5.7. Bis[bis(perfluorophenyl)phosphinato]nickel(II) monohydrate Ni[(C6F5)2P02]2.H20 Bis(perfluorophenyl)phosphinic acid monohydrate (0.624 g, 1.50 mmol) was dissolved in 50 mL of diethyl ether and mixed with nickel(II) acetate tetrahydrate (0.124 g, 0.50 mmol). The mixture became clear after stirring for 1 h. A pale green precipitate formed over a period of about 1 d. The precipitate was collected and washed with acetone and then dried in air for one night. The product was a pale green powder (yield 83%). Anal, calcd. for NiC 2 4 F 2 0 H 2 O 5 P 2 : C 33.10, H 0.23; found: C 32.90, H 0.37. 7.2.5.8. Bi s(diphenylpho sphinato)nickel(II) Ni[(C6H5)2P02]2 Diphenylphosphinic acid (1.09 g, 5.00 mmol) was mixed with nickel carbonate (0.178 g, 1.50 mmol) and ground to a fine powder. The mixture was heated in a furnace at 250 °C for 4 h. During this period of time, the color changed from the original pale green to blue. The mixture cooled to room temperature, ground to powder again and heated again at 250 °C for 2 h. 4 x 50 mL of acetone were used to extract the product. All the acetone extractants were combined and the acetone was removed by a rotary evaporator. The final product was a blue powder and very moisture sensitive (yield 36%). Anal, calcd. for NiC24H 1 0 O4P 2 : C 58.46, H 4.09; found: C 58.19, H 4.15. 7.2.5.9. Bis {bis[(perfluoro-n-hexyl)ethyl]phosphinato} nickel(II) Ni{[CF3(CF2)5CH2CH2]2P02}2 Bis[(perfluoro-n-hexyl)ethyl]phosphinic acid (0.379 g, 0.500 mmol) was dissolved in 60 mL ethanol and was partially neutralized by 0.50 M aqueous sodium hydroxide (0.90 265 mL, 0.45 mmol). Insoluble materials were removed by filtration. To the filtrate was added nickel(II) nitrate hexahydrate (0.0727 g, 0.250 mmol) in 10 mL H 2 0 and the mixture was stirred for 2 d. The clear yellow solution obtained was evaporated to dryness in a rotary evaporator. The residue was washed with a small amount of cold water and then ethanol and dried in vacuo at room temperature for 4 h. The final product is a yellow powder (yield 46 %). Anal, calcd. for NiC 3 2Hi6F 5 20 4P 2: C 24.43, H 1.03; found: C 24.13, H 1.18. 7.2.6. Cobalt(II) Compounds 7.2.6.1. Poly-bis(dimethylphosphinato)cobalt(II) Co[(CH3)2P02]2 Dimethylphosphinic acid (0.470 g, 5.00 mmol) was dissolved in 50 mL of acetone, and was partially neutralized with 0.57 mL triethylamine. To this solution was added slowly, with stirring, cobalt dichloride hexahydrate (0.476 g, 2.00 mmol) dissolved in 50 mL acetone/5 mL DMP. A blue precipitate formed after half of the cobalt salt had been added. The mixture was left stirring overnight. The precipitate was collected on a sintered glass, washed with acetone, and dried in vacuo at room temperature for 4 h. The final product was obtained as a blue powder (yield 75%). Anal, calcd. for CoC4Hi2C»4P2: C 19.61, H 4.94; found: C 19.83, H 4.96. Crystals suitable for the single crystal X-ray diffraction studies were obtained as follows. Cobalt(II) dichloride tetrahydrate (0.238 g, 1.00 mmol) dissolved in 10 mL DMF was mixed with dimethylphosphinic acid (0.188 g, 2.00 mmol) dissolved in 10 mL DMF containing 0.14 mL triethylamine. This resulted in a clear blue solution which was allowed to stand. A purple precipitate formed after 2 d and this was removed by filtration. The 266 blue filtrate was kept in a beaker covered with parafilm. Purple crystals were obtained after 5 weeks. Elemental analysis and IR, and X-ray powder diffraction studies showed the crystals and powder obtained here as well as the powder obtained in the preparation described above are the same compound. 7.2.6.2. Bis(methylethylphosphinato)cobalt(II) Co[(CH3)(C2H5)P02]2 Methylethylphosphinic acid (1.297 g, 12.0 mmol) in 50 mL of diethyl ether was mixed with cobalt(II) acetate tetrahydrate (1.00 g, 4.00 mmol) and the mixture was stirred for 2 h, resulting in a clear blue solution. A purple precipitate formed after further stirring for about 10 h. This mixture was stirred for another 2 d and the solvent was then removed under vacuum at room temperature. The solid obtained was heated at 120 °C under vacuum for 6 h. This gave a purple solid which was then washed with diethyl ether and dried in vacuo at room temperature for 4 h (yield 60%). Anal, calcd. for CoC6Hi604P2: C 26.39, H 5.91; found: C 26.45, H 5.94. 7.2.6.3. Bis(dimethylarsinato)cobalt(II) Co[(CH3)2As02]2 Dimethylarsinic acid (1.38 g, 10.0 mmol) was dissolved in 50 mL ethanol/5 mL DMP and partially neutralized by 0.84 mL of triethylamine. To this solution was added, slowly with stirring, cobalt(II) perchlorate hexahydrate (0.732 g, 2.00 mmol) in 20 mL of ethanol/5 ml DMP. A pink precipitate formed after a few drops of the cobalt salt was added. After adding all of the cobalt salt the mixture was stirred for 2 d. The precipitate was collected on a sintered glass funnel under an atmosphere of dinitrogen gas, then 267 washed with ethanol and then dried in vacuo at room temperature for 10 h (yield 47%). Anal, calcd. for CoC4Hi 2As 20 4: C 14.43, H 3.68; found: C 14.02, H 3.63. 7.2.6.4. Bis(monophenylphosphinic acid)bis(monophenylphosphinato)cobalt(II) Co[H(C6H5)2P02H]2[H(C6H5)P02]2 This compound was synthesized by two different methods. Monophenylphosphinic acid (2.00 g, 14.0 mmol) was dissolved in 50 mL acetone/10 mL DMP. To this solution was added cobalt(II) monophosphinate (0.35 g, 1.00 mmol) which was prepared according to a previously described procedure (18). The mixture was allowed to stir for 3 h. During this period of time a purple solid originally present in the mixture became pink. The product was collected on a sintered glass, washed with acetone and left to air dry for 12 h (yield 70%). Anal, calcd. for CoC 2 4H 2 6 0 8 P 4 : C 46.10, H 4.19; found: C 46.02, H 4.29. A second method of synthesis of the compound involved the use of cobalt(II) monophenylphosphinate dihydrate. Monophenylphosphinic acid (2.13 g, 15.0 mmol) was dissolved in 50 mL acetone/10 mL DMP. Cobalt(II) monophenylphosphinate dihydrate (0.377 g, 1.00 mmol) was dissolved in 50 mL acetone. A clear reddish solution was obtained after mixing the above two solutions. A pink precipitate formed after stirring the solution for about 30 min. The product was collected on a sintered glass, then washed with acetone and then dried under vacuum at room temperature for about 4 h (yield 60%). Anal, calcd. for CoC 2 4H 2 6 0 8 P 4 : C 46.10, H 4.19; found: C 46.22, H 4.09. 268 7.2.6.5. Bis(N-methylformamide)bis(monophenylphospWnato)cobalt(II) Co(HCONHCH3)2[H(C6H5)P02]2 Cobalt(II) monophenylphosphinate (18) (0.682 g, 2.00 mmol) was mixed with 15 mL N-methylformamide and 5 mL DMP. The mixture was stirred for one day. During this period of time, the color of the solids present in the mixture changed from purple to pink. The product was collected on a sintered glass in a dinitrogen atmosphere, then washed with a mixture of N-methylformamide and diethyl ether (30:70 V/V), and dried in vacuo at room temperature for 4 h (yield 70%). Anal, calcd. for C0C16H22N2O6P2: C 41.85, H 4.83, N 6.10; found: C 41.68, H 4.97, N 6.15. 7.2.6.6. Bis[bis(perfluorophenyl)phosphinato]cobalt(II) Co[(C6F5)2P02]2 Potassium bis(perfluorophenyl)phosphinate (0.872 g, 2.00 mmol) in 20 mL of H 2 0 was mixed with cobalt(II) perchloride hexahydrate (0.290 g, 0.80 mmol) in 10 mL H 2 0 and the mixture was stirred for 2 d. The resulting reddish solution was taken to dryness in a rotary evaporator and the red flakes left in the flask were extracted by acetone. The acetone extractant ((C6F5)2P02K formed is insoluble in acetone) was allowed to evaporate in the fume hood and a red powder was obtained. Drying of the red powder in vacuo at 100 °C for 4 h gave a blue powder (yield 60%). Anal, calcd. for C0C24F20O4P2: C 33.79; found: C 33.96. 269 7.2.6.7. Bis[bis(perfluorophenyl)phosphinato]cobalt(II) monohydrate Co[(C6F5)2P02]2.H20 Cobalt(II) acetate tetrahydrate (0.125 g, 0.500 mmol) was mixed with bis(perfluorophenyl)phosphinic acid monohydrate in 50 mL diethyl ether. A blue solution was obtained after stirring the mixture for about 30 min and a red precipitate formed after further stirring for another 3 h. The product was collected on a sintered glass, then washed with acetone and then left to air dry. The final product was a red powder (yield 95%). Anal, calcd. for CoC 2 4F 2 0H 2O 5P 2: C 33.09, H 0.23; found: C 33.27, H 0.20. 7.2.6.8. Bis{bis[(perfluoro-n-butyl)ethyl]phosphinato}cobalt(II) Co{ [CF3(CF2)3CH2CH2]2P02}2 Bis[(perfluoro-n-butyl)ethyl]phosphinic acid (0.268 g, 0.480 mmol) was dissolved in 5 mL DMF containing 0.20 mL triethylamine. Cobalt(II) chloride hexahydrate (0.0571 g, 0.24 mmol) was dissolved in 5 mL DMF/5 mL DMP. A blue precipitate formed immediately after the two solutions were mixed. After the mixture was stirred for 6 h, the precipitate was collected on a sintered glass and washed with acetone. After drying in air for 1 d, the product was obtained as a blue powder (yield 56%). Anal, calcd. for CoC 2 4Hi 6F 3 604P 2: C 24.57, H 1.37; found: C 24.82, H 1.23. 7.2.6.9. Bis {bis[(perfluoro-n-hexyl)ethyl]phosphinato} cobalt(II) Co{ [CF3(CF2)5CH2CH2]2P02}2 Bis[(perfluoro-n-hexyl)ethyl]phosphinic acid (0.379 g, 0.500 mmol) was dissolved in 75 mL ethanol and was neutralized partially by 0.50 M sodium hydroxide (0.90 mL, 0.45 mmol). Insoluble materials were removed by filtration. To the clear filtrate was added, 270 with stirring, cobalt(II) nitrate hexahydrate (0.0728 g, 0.250 mmol) in 10 mL H 20. A blue precipitate formed after half of the cobalt salt was added. After all of the cobalt salt was added, the mixture was left stirring for 1 d. The precipitate was filtered on a sintered glass, then washed with ethanol then water, and then ethanol again. After drying in the air overnight, the final product was obtained as a blue powder (yield 71%). Anal, calcd. for CoC32Hi6F5204P2: C 24.43, H 1.03; found: C 24.16, H 0.97. 7.2.7. Miscellaneous Compounds 7.2.7.1. Poly-diaquabis(//-formato)cobalt(II) Co(H20)2(HCOO)2 Cobalt (II) perchlorate hexahydrate (1.46 g, 4.00 mmol) in 100 mL acetone was added to a 2 mL aqueous solution of partially neutralized (1.14 mL triethylamine) formic acid (0.40 mL, 8.0 mmol). After a few drops of the cobalt salt was added, a red precipitate formed. Precipitation continued as more cobalt salt was added. After all the cobalt salt was added, the mixture was stirred for one day . The red precipitate was collected on a sintered glass, and washed with water and then acetone and then left to air dry for about one day (yield 91 %). Anal, calcd. for CoQHgOs: C 12.98, H 3.27; found: C 13.06, H 3.12. Crystals suitable for single crystal X-ray diffraction studies were obtained from the attempt to prepare an adduct polymer of the formula, Co(HCONH2)2[(C6F5)2P02]2. Cobalt acetate tetrahydrate (0.125 g, 0.500 mmol) was mixed with perfluorodiphenylphosphinic acid monohydrate (0.624 g, 1.50 mmol) in 50 mL acetone. A clear blue solution was obtained after stirring the mixture for 1 h. A red precipitate formed 271 immediately after 5 mL formamide was added to the solution. The precipitate was removed by filtration and the clear blue solution was allowed to stand in the fume hood. Red crystals formed after three months and during this period of time the solution changed from blue to pale red. The red crystals were shown by X-ray diffraction to be Co(H20)2(HCOO)2. 7.2.7.2. Poly-bis(formamide)bis(//-formato)cobalt(II) Co(HCONH2)2(HCOO)2 To a mixture of 4 mL formic acid and 10 mL formamide was added cobalt perchlorate hexahydrate (0.732 g, 2.00 mmol) in 50 mL acetone. The solution was stirred and a red precipitate formed after 3 days. The precipitate was collected on a sintered glass under an atmosphere of dinitrogen, then washed with acetone and then dried in vacuo at room temperature for 4 h (yield 87%). Anal, calcd. for CoC4H8N206: C 20.10, H 3.37, N 11.72; found: C 19.99, H 3.40, N 11.24. In an attempt to grow crystals of, Co(HCONH2)2[(CH3)(C2H5)P02]2, suitable for single crystal X-ray diffraction studies, red crystals of composition Co(HCONH2)2(HCOO)2 were obtained. The solvent acid, methylethylphosphinc acid (1.30 g, 12.0 mmol), was mixed with cobalt acetate tetrahydrate (0.996 g, 4.00 mmol). Stirring the mixture resulted in the formation of a clear blue solution after one hour. A red solution formed after 10 mL formamide was added. Red crystals formed after the red solution was allowed to stand in the fume hood for about three months. Anal, calcd. for CoC4H 8N 20 6: C 20.10, H 3.37, N 11.72; found: C 20.22, H 3.37, N 11.62 272 7.2.7.3. {Co[(n-C8F17)P03](DMF)(H20)2}x A solution of cobalt(II) chloride hexahydrate (0.238 g, 1.00 mmol) in 10 mL H 2 0 was added to perfluoro-n-octylphosphonic acid (0.500 g, 1.00 mmol) in 10 mL DMF/5 mL DMP. The clear blue solution which was obtained was allowed to stand in the fume hood. Red crystals formed during a period of three months. REFERENCES 1. teXsan: Crystal Structure Analysis Package, Molecular Structure Corporation, The Woodlands, Texas, U. S. A. 1985 and 1992. 2. PATTY: P. T. Beurskens, G. Beurskens, W. P. Bosman, S. Garcia-Granda, R. O. Gould, J. M. M. Smits and C. Smykalla, The DIRDIFProgram System, Technical Report of the Crystallography Laboratory, University of Nijmegen, The Netherlands, 1992. 3. SIR92: A. Altomare, M. Cascarano, C. Giacovazzo and A. Guagliardi, J. Appl. Cryst. 26, 343 (1993). 4. International Tables for X-ray Crystallography. Vol. IV. 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Springer-Verlag, Berlin, Vol. 8, Chap. 1, 1978. 13. C. J. O'Connor, Prog. Inorg. Chem. 29, 203 (1982). 14. R. L. Carlin and A. J. van Duyneveldt, Magnetic Properties of Transition Metal Compounds, Spring-Verlag, New York, 1977. 15. R. L. Carlin, Magnetochemistry, Spring-Verlag, New York, 1986. 16. J.-L. Du, S. J. Rettig, R. C. Thompson and J. Trotter, Can. J. Chem. 70, 732 (1992). 17. P. Betz, A. Bino, J.-L. Du, S.-M. Lo and R. C. Thompson, Inorg. Chim. Acta, 170, 45 (1990). 18. J.-L. Du, Ph. D. Dissertation, The University of British Columbia, Vancouver, B. C. Canada, 1991. 19. S. H. Rose and B. P. Block, J. Polymer Sci. 4, 573 (1966). 20. B. P. Block, S. H. Rose, C. W. Shaumann, E. S. Roth and J. Simkin, J. Am. Chem. Soc. 84, 3200 (1962). 21. C M . Mikulski, J. Unruh, R. Rabin, F. J. Iaconianni, L. L. Pytlewski and N. M. Karayannis, Inorg. Chim. Acta, 44, L77 (1980). 22. K. W. Oliver, S. J. Rettig, R. C. Thompson, J. Trotter and S. H. Xia, J. Fluoro. Chem. (In press). 23. W. V. Cicha, J. S. Haynes, K. W. Oliver, S. J. Rettig, R. C. Thompson and J. Trotter, Can. J. Chem. 63(5), 1055 (1985). 24. K. W. Oliver and R. C. Thompson, The University of British Columbia, Vancouver, B. C. Canada, unpublished results. 25. G. M. Kosolapoff and J. S. Powell, J. Chem. Soc. 3535 (1950). 26. D. F. Peppard, G. W. Mason and S. Lewey, J. Inorg. Nucl. Chem. 27, 2065 (1965). 274 Chapter 8 Summary and Suggestions for Further Study 8.1. Summary The present study involved the synthesis and characterization of several metal phosphinate and arsinate compounds most, but not all, of which are polymeric. An extensive investigation of the spectral, magnetic and other properties of these compounds in the solid state was carried out in an attempt to study magneto-structural correlations and in so doing, increase our understanding of metal phosphinate and arsinate chemistry and magnetic exchange phenomena in general. Structures of compounds isolated in the form of X-ray quality crystals have been determined by single crystal X-ray diffraction. Structures of the remainder of the compounds have been proposed on the basis of indirect evidence provided by other physical methods of characterization, particularly electronic and vibrational spectroscopy. Although new dimethylarsinate compounds of the transition metals have been characterized structurally and magnetically in this work, the lack of X-ray determined structures for these compounds prevented the anticipated detailed comparison with known dimethylphosphinate analogues. Comparison of structures and magnetic properties of coordination polymers containing fluorinated phosphinate ligands with analogues containing perhydro-phosphinate ligands revealed relatively small differences for most metals. Copper is somewhat of an exception to this, however. The bis(perfluorophenyl)phosphinate of copper(II) is an antiferromagnetic system while the perhydro-analogue is ferromagnetic. In the case of the 275 long alkyl chain derivatives the fluorinated phosphinate compounds exhibit temperature dependent lvalues due to solid state fluxionality, a phenomenon not seen in the perhydro-analogues. These observations may be explained by postulating that one effect of fluorination of the phosphinate ligands is to alter the detailed Cu04 chromophore geometry. It has been shown in previous work that relatively small changes in the copper chromophore can alter the magnetic properties in copper(II) phosphinate complexes. The remainder of this chapter provides a summary of the characterization of individual compounds studied in this work. For the purpose of this summary, the compounds studied here have been divided into groups based on elemental composition and structural considerations (Table 8.1). Group 1: ML2[H(C6H5)P02]2 Adduct Polymers The complexes in this group contain octahedral metal centers with M040'2 chromophores. Single crystal X-ray diffraction studies revealed that the DMSO complex is a linear chain polymer with metal centers linked by double phosphinate bridging units and axially coordinated by DMSO ligands through the oxygen atom. Indirect methods showed that the other complexes in this group have similar structures. All five of the complexes in this group exhibit antiferromagnetic behaviour. The HCONHCH 3 complexes show stronger magnetic coupling than the H(C 6H5)P0 2H complexes. Combined with the work done by Du (1), the magnitude of exchange in the ML2[H(C6H5)P02]2 (M = Co(II) and Ni(II)) complexes appears to increase in the order L = py ~ H(C6H5)P02H < pyz < H 20 < HCONHCH3 < HCONH2. The magnitude of exchange in the MnL2[H(C6H5)P02]2 2 7 6 Table 8.1. Classification of the compounds. Group 1: ML2[H(C6H5)P02]2 adduct polymers (IA) L = DMSO, M = Mn(II). (IB) L = HCONHCH3 with M = Co(II) and Ni(II). (IC) L = H(C 6H5)P0 2H with M = Co(II) and Ni(II). Group 2: Manganese(II) compounds (2A) Mn[(CH3)2P02]2 (Form II), Mn[(C6F5)2P02]2, Mn[(n-C8H17)2P02]2. Mn{[CF3(CF2)3CH2CH2]2P02}2 and Mn{[CF3(CF2)5CH2CH2]2P02}2. (2B) Mn[(CH3)2P02]2 (Form I), Mn[(CH3)(C2H5)P02]2 and Mn[(CH3)2As02]2. (2C) {(DMF)3Mn[//-(C6F5)2P02}2]3}2Mn. Group 3: Copper(II) compounds (3 A) Cu[(CH3)(C2H5)P02]2, Cu[(C6F5)2P02]2 and Cu[(C6H5)(C6F5)P02]2. (3B) Cu{[CF3(CF2)3CH2CH2]2P02}2 and Cu{[CF3(CF2)5CH2CH2]2P02}2. (3C) {CU3[(CH3)2P02]6}x. Group 4: Cobalt(II) compounds (4A) Co[(CH3)2P02]2, Co[(CH3)(C2H5)P02]2, Co[(C6F5)2P02]2, Co{[CF3(CF2)3CH2CH2]2P02}2 and Cu{[CF3(CF2)5CH2CH2]2P02}2. (4B) Co[(CH3)2As02]2. Group 5: Nickel(II) compounds (5 A) Ni[(C6F5)2P02]2 andNi[(C6H5)2P02]2. (5B) Ni[(CH3)2P02]2, Ni[(CH3)(C2H5)P02]2, Ni[(CH3)2As02]2, and Ni{[CF3(CF2)5CH2CH2]2P02}2. Group 6: Ni[(C6F5)2P02]2.H20 and Co[(C6F5)2P02]2.H20. Group 7: Miscellaneous compounds Co(H20)2(HCOO)2, Co(HCONH2)2(HCOO)2, and{Co[(n-C8F17)P03](DMF)(H20)2}x. 277 complexes appears to increase in the order L = py < H(C6H5)P02H < HCONHCH 3 < CH3CONH2 < DMSO ~ H 20 < HCONH2. The conclusions previously drawn by Du (1) that shorter M-O-P-O-M pathways and more symmetric O-P-0 bridges result in stronger magnetic exchange also appear to hold in the complexes studied here. Group 2: Manganese(II) Compounds The compounds in this group are divided into three sub-groups with the first two groups involving polymeric binary metal phosphinates and one arsinate and the third involving a trimetallic compound. The compounds in sub-group 2A are considered to have tetrahedral metal centers with structures similar to those of Y-Mn[(C6H5)2P02]2 (2) and Mn[(CH3)2P02]2 (Form II) (this work), in which metal centers are linked by double phosphinate bridges, resulting in linear chain polymers. These complexes show very weak antiferromagnetic coupling with \J] values ranging from 0.18 to 0.54 cm"1. Compared to their perhydro-derivatives, the partially fluorinated complexes exhibit slightly stronger magnetic coupling. For instance, Mn[(n-C6H13)2P02]2 has a \J\ of 0.29 cm"1 (1) while Mn{[CF3(CF2)3CH2CH2]2P02}2 has a \J] of 0.45 cm"1. The same phenomenon occurs with the octyl derivatives. The complexes in sub-group 2B are proposed to have octahedral metal centers and two-dimensional sheet structures. They exhibit much stronger antiferromagnetic coupling than that shown by tetrahedral complexes of group 2A. The additional Mn-O-Mn exchange pathway which is much shorter than the usual Mn-O-P-O-Mn pathway is suggested to be responsible for the increase in magnitude of the exchange. 278 {(DMF)3Mn[//-(C6F5)2P02}2]3}2 is the first structurally characterized metal(II) phosphinate complex to exhibit a structure in which pairs of metal ions are bridged by three phosphinate groups. Interestingly, this compound exhibits weaker antiferromagnetic coupling than does Mn[(C6F5)P02]2, a compound which contains double phosphinate bridges. It appears that the number of bridges may not necessarily be important in determining the strength of magnetic coupling. In the trimetallic complex the overall length of the Mn-O-P-O-Mn pathway is long and this may be responsible for the fact that the exchange is weak. Group 3: Copper(H) Compounds Compounds in the 3A and 3B sub-groups are considered to have distorted tetrahedral metal centers. However, compounds in the 3A sub-group exhibit antiferromagnetic behaviour while the complexes in the 3B sub-groups exhibit ferromagnetic behaviour. As found previously in studies on poly-copper(II) dialkylphosphinates (3) relatively minor structural differences appear to alter significantly the nature of the exchange in these linear chain copper(II) complexes. A single crystal X-ray diffraction study of {Cu3[(CH3)2P02]6}x revealed a novel structure in which trimetallic units are linked to form a chain polymer. Two different chromophores exist in this structure, one involving distorted tetrahedral coordination about copper, the other square pyramidal coordination. With the detailed structure available, the magnetic properties of this material were successfully analyzed employing a copper(II) trimer model (4, 5) with a molecular field correction (6). 279 Group 4: Cobalt(II) compounds Binary cobalt(II) complexes in this sub-group 4A have tetrahedral metal centers. Single crystal X-ray studies on Co[(CH3)2P02]2 reveal the compound to have a linear chain polymeric structure with double bridging phosphinates. Based on indirect evidence the other complexes in this sub-group are considered to have similar structures. All the compounds in this sub-group exhibit antiferromagnetic coupling QJ] less than 0.73 cm"1). Co[(CH3)2As02]2 has octahedral metal centers and is considered on the basis of indirect evidence to be a sheet polymer. It exhibits ferromagnetic coupling. The Co-O-Co pathway is suggested to be responsible for this ferromagnetism. Group 5: Nickel(II) Compounds Compounds in sub-group 5 A have tetrahedral metal centers and are considered on the basis of indirect evidence to be linear chain polymers. They exhibit antiferromagnetic behaviour and the magnetic data have been analyzed according to linear chain models. The strength of magnetic exchange present in the two compounds is comparable in spite of the large electronegativity difference in the phosphorus substituents. Compounds in sub-group 5B have octahedral metal centers and are considered on the basis of indirect evidence to have extended sheet structures. They exhibit ferromagnetic behaviour. 280 Group 6: Ni[(C6F5)2P02]2.H20 and Co[(C 6F 5) 2P0 2] 2.H 20 These two complexes are suggested to have square pyramidal metal/ligand chromophores and extended linear chain structures on the basis of indirect evidence. Both exhibit antiferromagnetic interactions. Group 7: Miscellaneous Compounds Single crystal X-ray diffraction studies on Co(H20)2(HCOO)2, Co(HCONH2)2(HCOO)2 and {Co[n-C8F17)P03](DMF)(H20)2}x reveal that all three complexes have polymeric structures. Magnetic studies on the two cobalt(II) formates revealed that antiferromagnetic interactions with spin canting lead to weak ferromagnetism and a net magnetic moment at low temperatures in zero applied field. 8.2. Suggestions for Further Study One area of interest would be the further investigation of polymorphism in metal phosphinates. Previous studies have shown that polymorphism is present in copper(II) phosphinates (3), different forms exhibiting unique magnetic properties. For example, the a-forms of copper(II) dialkylphosphinates exhibit antiferromagnetic behaviour while the P-forms exhibit ferromagnetic behaviour. In the current work, manganese(II) dimethylphosphinate was found to exist in two forms. Form II of the compound is a linear chain polymer with very weak antiferromagnetic coupling, while Form I, which exhibits much stronger antiferromagnetic coupling, is proposed to be a sheet polymer. Another example of polymorphism from the present work involves Ni{[CF3(CF2)5CH2CH2]P02}2. Heated to 125 °C, this compound is converted from a yellow form to a purple compound. 281 It seems that for manganese(II) complexes, polymorphism is seen in phosphinates with shorter alkyl groups, while for other metal(II) (Co(II), Ni(II) and Cu(II)) complexes in phosphinates with longer alkyl groups. More metal phosphinates containing different length alkyl groups need to be synthesized and studied to confirm this trend and provide a better understanding of the phenomenon. In particular, more X-ray determined structures of different polymorphs are needed. In the current work, it was found that fluorinated manganese(II) derivatives exhibit stronger antiferromagnetic coupling than their perhydro analogues while for cobalt(II) derivatives the fluorinated complexes exhibit weaker exchange interactions. To investigate further the influence of the electronegativity of substituents on magnetic properties, new phosphinate ligands containing substituents of different electronegativity, such as those containing different halo- atoms, need to be synthesized and their complexes studied. Single crystal X-ray determined structures remain an important goal in this work. Such studies would lead to better magneto-structural correlations. To date, no crystal structures have been reported on binary metal phosphinates thought to have extended sheet structures. Such compounds have revealed very interesting magnetic properties. For instance, the manganese(II) phosphinates with sheet structure exhibit much stronger antiferromagnetic coupling than that exhibited by manganese(II) phosphinates with linear chain structure. Also the cobalt(II) and nickel(II) compounds which have sheet structures exhibit ferromagnetic coupling interactions, in contrast to the linear chain polymers which exhibit antiferromagnetic behaviour. It has been suggested the magnetic exchange in the sheet polymers is dominated by the short M-O-M pathway in the proposed structures. X-282 ray determined structures should provide a much clear picture of how these different magnetic properties are related to structure. Studies to date have revealed that the phosphinate ligands, R2P02", are capable of bridging metal centers to form 1-D linear chains or 2-D sheet polymers only. Phosphonate, RP03 2- ligands, on the other hand, may be capable of generating 3-D structures. The one phosphonate complex studied here, {Co[(n-C8Fi7)P03](DMF)(H20)2}x, has a 2-D extended lattice but the potential for 3-D bridging is clearly there. Further studies on phosphonate complexes should be made. Studies on these compounds may reveal interesting magnetic properties. REFERENCES 1. J.-L. Du, Ph. D Dissertation, University of British Columbia, B. C. Canada, 1991. 2. J-L. Du, S. J. Rettig, R. C. Thompson and J. Trotter, Can. J. Chem. 69, 277 (1991). 3. J. S. Haynes, K. W. Oliver and R. C. Thompson, Can. J. Chem. 63, 1111 (1985). 4. D. B. Brown, J. R. Wasson, J. W. Hall and W. E. Hatfield, Inorg. Chem. 16, 2526(1977) 5. B. N. Figgis and D. J. Martin, J. Chem. Soc. Dalton Trans. 2174 (1972). 6. C. J. O'Connor, Prog. Inorg. Chem. 29, 203 (1982). 283 APPENDIX I SINGLE CRYSTAL X-RAY DIFFRACTION DATA TABLE 1-1. Crystallographic data for {Co[(n-C8Fi7)P03](DMF)(H20)2}x (CnHnCoFnNOcP)* Crystal system Monoclinic Space group P2, a, A 5.502(4) b, A 9.046(5) c,k 21.087(3) P, deg 91.99(3) v , A 3 1048.9(8) z 2 Pc g cm-3 2.109 F(000) 654.00 Crystal colour and habit violet plate Crystal Size, mm 0.08x0.20x0.40 R 0.046 Rw 0.042 TABLE 1-2. Crystallographic data for {Cu3[(CH3)2P02]6}x (Ci 2H 3 6Cu 30 1 2P 6)* Crystal system Monoclinic Space group C2/c a, A 10.957(1) b, A 18.300(1) c,A 14.907(1) P, deg 108.973(9) V , A 3 2826.7(5) z 4 Pc, g cm-3 1.76 F(000) 1524 Crystal colour and habit blue prism Crystal Size, mm 0.30x0.40x0.50 R 0.030 R w 0.029 284 TABLE 1-3. Crystallographic data for [Co(HCOO)2(HCONH2)2]x (C4H8CoN206)* Crystal system Monoclinic Space group C2/c a, A 12.772(1) b, A 8.354(1) c,k 8.243(1) P, deg 93.19(1) v , A 3 878.2(2) z 4 pc, g cm"3 1.808 F(000) 484 Crystal colour and habit pink prism Crystal Size, mm 0.25x0.30x0.35 R 0.030 Rw 0.031 TABLE 1-4. Crystallographic data for {[Mn[CH3)2P02]2}x (C4H12MnC»4P2)* Crystal system Monoclinic Space group C2/c a, A 12.012(2) b,A 11.545(1) c,k 8.774(1) 3, deg 124.773(8) v , A 3 999.5(2) z 4 Pc g cm"3 1.602 F(000) 492.00 Crystal colour and habit Colorless prism Crystal Size, mm 0.20x0.40x0.55 R 0.040 Rw 0.039 285 TABLE 1-5. Crystallographic data for {[Co[CH3)2P02]2}x* (C4H12C004P2) Crystal system Monoclinic Space group C2/c a, A 11.852(1) A, A 11.451(2) c,A 8.605(1) P,deg 124.635(8) v , A 3 960.8(3) z 4 Pc g cm"3 1.694 F(000) 500 Crystal colour and habit Purple prism Crystal Size, mm 0.20x0.30x0.45 R 0.032 Rw 0.029 TABLE 1-6. Crystallographic data for {[HCON(CH3)2]3Mn[|i-(C6F5)2P02]3}2Mn (C 9 0 H 5 1 F 6 0 Mn 3 N 6 O 2 2 . 5 0 P6)* Crystal system Space group a, A c,A v , A 3 z Pc g cm"3 F(000) Crystal colour and habit Crystal Size, mm R Rw Trigonal R3c 21.958(2) 41.612(8) 17374(4) 6 1.759 9108.00 Colorless, irregular 0.30x0.40x0.45 0.046 0.046 286 T A B L E 1-7. Crystallographic data for {Mn[(CH3)2SO]2(H(C6H5)P02]2}x / (C 1 6 H 2 4Mn0 6 P 2 S 2 ) Crystal system Monoclinic Space group P2i/c a, A 5.7102(9) b, A 8.253(1) c,k 22.2395(9) 3, deg 95.542(9) v , A 3 1043.2(2) z 2 Pc g cm-3 1.571 F(000) 510 Crystal colour and habit Colorless prism Crystal Size, mm 0.20x0.30x0.35 R 0.038 Rw 0.036 287 APPENDIX II MAGNETIC SUSCEPTIBILITY RESULTS" TABLE II-1. Magnetic data for copper(II) phosphinates {Cu3[(CH3)2P02]6}x f c Cu[(CH3)(C2H5)P02]2 Cu[(C6F5)2P02]2 GouyandVSM VSM SQUID Temp. XM |J.eff Temp. XM M-eff Temp. XM U-eff 4.20 88.9 1.73 4.32 86.6 1.73 2.00 17.0 0.52 4.91 81.0 1.78 6.00 65.0 1.77 3.00 16.1 0.62 5.29 76.8 1.80 9.76 40.8 1.78 4.00 15.8 0.71 6.21 69.2 1.85 15.4 26.8 1.81 5.00 15.8 0.79 7.07 64.3 1.91 20.5 20.5 1.83 6.00 16.0 0.88 9.10 56.4 2.03 25.5 16.7 1.84 8.00 16.3 1.02 10.9 52.0 2.13 29.9 14.2 1.85 10.0 16.4 1.15 12.7 48.8 2.22 40.7 10.5 1.85 12.0 16.2 1.25 14.6 45.9 2.32 48.3 8.97 1.86 15.0 15.1 1.35 16.6 43.2 2.40 55.3 7.96 1.88 20.0 13.9 1.49 18.8 41.1 2.48 60.7 7.27 1.88 25.0 12.4 1.58 20.8 38.9 2.54 65.9 6.75 1.89 30.0 11.2 1.64 22.4 37.1 2.58 70.2 6.31 1.88 40.0 9.14 1.71 24.8 35.4 2.65 74.2 6..00 1.89 50.0 7.70 1.75 27.8 33.0 2.71 81.6 5.50 1.89 60.0 6.62 1.78 30.8 31.0 2.76 70.0 5.81 1.80 33.4 29.4 2.80 80.0 5.16 1.82 40.2 25.9 2.88 90.0 4.64 1.83 43.4 24.5 2.92 100.0 4.24 1.84 48.6 22.5 2.96 110.0 3.88 1.85 60.3 18.9 3.02 120.0 3.59 1.86 69.9 16.8 3.06 130.0 3.34 1.86 80.6 14.7 3.08 140.0 3.12 1.87 Continued on the next page. a Here and elsewhere is this thesis temperatures are in K; molar susceptibility (XM) are in 10'3 cm3 mol"1; magnetic moments (|ieff) are in B.M.; measurements were normally made at 7, 501 G for VSM method and 10, 000 G for SQUID method unless otherwise stated. b Data taken from K. W. Oliver, Ph. D. Dissertation, The University of British Columbia, 1984. 288 Continued. {Cu3[(CH3)2P02]6}x (Continued) Temp. X M Ueff 90.2 13.3 3 .10 98.0 12.3 3.11 110 11.3 3 .15 128 9.75 3 .16 131 9.66 3 .18 152 8.25 3 .16 154 8.25 3 .19 177 7 .20 3 .19 179 7 .20 3.21 201 6 .27 3 .17 205 6 .27 3 .20 2 2 6 5.64 3 .19 2 2 9 5.61 3 .20 2 5 0 5.07 3 .19 2 5 4 5.07 3.21 275 4 .62 3 .19 278 4 .62 3.21 301 4.23 3 .19 304 4.23 3.21 Cu[(C6F5)2P02]2 (Continued) Temp. X M M-eff 150.0 2 .94 1.88 160.0 2 .77 1.88 170.0 2.63 1.89 180.0 2 .49 1.89 190.0 2 .39 1.90 200 .0 2 .28 1.91 210 .0 2 .18 1.91 220 .0 2 .09 1.92 230 .0 2.01 1.92 240 .0 1.94 1.93 250 .0 1.87 1.94 260 .0 1.81 1.94 270 .0 1.75 1.94 280 .0 1.70 1.95 290 .0 1.65 1.95 300.0 1.60 1.96 Cu[(C6H5)(C6F5)P02]2 Cu{ [CF3(CF2)3CH2CH2]2P02}2 SQUID SQUID Temp. X M Ueff Temp. X M M-eff 1.83 20.6 0.55 2 .00 440 2.65 2 .00 19.8 0 .56 3.00 3 0 9 2 .72 3.00 15.4 0.61 4 .00 223 2 .67 4 .00 12.7 0.64 5.00 167 2.58 5.01 10.7 0.66 6.00 132 2 .52 6.00 9.6 0.68 8.00 91.4 2 .42 7 .00 9.0 0.71 10.0 68.7 2 .34 8.00 8.8 0.75 12.0 54.8 2 .29 Continued on the next page. 2 8 9 Continued. Cu[(C 6H 5)(C 6F 5)P0 2] 2 (Continued) Temp. X M M-eff 8.99 8.7 0 .79 9.99 8.8 0.84 10.99 9 .00 0.89 11.99 9.2 0.94 12.99 9.4 0 .99 15.00 9.9 1.09 17.00 12.0 1.18 20 .00 10.5 1.30 22.01 10.6 1.37 25.01 10.6 1.46 30.03 10.3 1.57 35.03 9.80 1.66 39 .99 9.21 1.72 45 .00 8.62 1.76 50 .00 8.01 1.79 60 .00 6.71 1.79 70 .00 5 .52 1.76 80 .00 4 .69 1.73 90 .00 4 .09 1.71 100.0 3.64 1.71 110.0 3.28 1.70 120.0 3 .00 1.70 130.0 2.75 1.69 140.0 2 .54 1.68 150.0 2 .35 1.68 160.0 2 .18 1.67 170.0 2.03 1.66 180.0 1.89 1.65 190.0 1.77 1.64 200 .0 1.66 1.62 210.0 1.55 1.62 220.0 1.46 1.60 230.0 1.38 1.59 240.0 1.30 1.58 260.0 1.18 1.56 270.0 1.13 1.56 300.0 1.02 1.56 Continued on the next page. Cu{ [CF 3(CF 2)3CH 2CH 2] 2P0 2}2 (Continued) Temp. XM M-eff 15.0 41.5 2.23 20 .0 29.6 2 .18 25.0 22.8 2 .14 30.0 18.1 2 .08 40 .0 13.6 2 .09 50.0 10.7 2 .07 60.0 8.75 2 .05 70.0 7.36 2.03 80.0 6.40 2 .02 90.0 5.66 2 .02 100.0 5.10 2 .02 110.0 4.51 2.01 120.0 4 .22 2.01 130.0 3.93 2 .02 140.0 3.65 2 .02 150.0 3.43 2.03 160.0 3.21 2.03 170.0 3 .02 2.03 180.0 2.88 2 .04 190.0 2 .74 2 .04 200.0 2.61 2 .04 210.0 2 .49 2 .04 220 .0 2 .38 2 .04 230 .0 2 .29 2.05 240 .0 2.21 2 .06 250 .0 2 .13 2 .06 260 .0 2.05 2 .07 270 .0 1.99 2 .07 280 .0 1.93 2.08 290 .0 1.87 2.08 300.0 1.81 2 .09 2 9 0 Continued. Cu{[CF3(CF2)5CH2CH2]2P0 2}2 (Form I) Cu{ [CF3(CF2)5CH2CH2]2P02}2 (Form II) SQUID 10, 000 G SQUID 50, 000 G Temp. X M u.eff Temp. XM Heff Temp. X M Heff 1.86 4 4 6 2 .58 2 .00 4 0 7 2.55 2 .00 113 1.34 2 .00 4 2 6 2.61 3.00 2 9 2 2.65 3 .00 109 1.62 3.00 3 0 0 2.68 4 .00 2 1 6 2.63 4 .00 103 1.81 4 .00 2 1 4 2 .62 5.00 166 2 .57 5.00 93 .9 1.94 5.00 161 2 .54 6.00 134 2 .54 6.00 85.1 2 .02 6.00 128 2 .47 7.00 112 2 .50 7 .00 76.6 2 .07 7.00 105 2 .42 7.99 97.1 2 .49 8.00 68 .9 2 .10 7.99 88.2 2 .37 8.99 85.5 2.48 9.00 62 .0 2 .11 8.99 75.8 2.33 9.99 76.5 2 .47 9.99 56.1 2 .12 9.99 66.4 2 .30 11.0 69.5 2 .47 11.0 51.1 2 .12 11.0 58.8 2 .27 12.0 63.8 2 .47 12.0 46.6 2 .12 12.0 52.8 2 .25 13.0 59.1 2.48 13.0 42 .9 2 .11 13.0 47.8 2.23 15.0 51.8 2 .49 15.0 36.8 2 . 1 0 15.0 40.1 2 . 1 9 17.0 46.6 2 .52 17.0 32.1 2 .09 17.0 34.5 2 . 1 6 20.0 40 .9 2 .56 20 .0 26 .9 2 .07 20.0 28.4 2 .13 22.0 38.0 2 .59 22 .0 24.3 2 .07 22.0 25.4 2 .12 25.0 34.8 2 .64 25 .0 21.1 2.05 25.0 22 .0 2 .10 30.0 31.0 2.73 30.0 17.4 2 .04 30.0 17.9 2.08 35.0 28.3 2 .82 35.0 14.8 2.03 35.0 15.2 2 .06 40 .0 26.4 2.91 40 .0 12.9 2.03 40.0 13.1 2.05 45 .0 24 .9 2 .99 45 .0 11.4 2.03 45.0 11.7 2.05 50.0 23.8 3.08 50.0 10.2 2 .02 50.0 10.5 2 .04 60.0 22.0 3.25 60.0 8.53 2 .02 60.0 8.64 2 .04 70.0 20 .7 3.40 70 .0 7.33 2.03 70.0 7.40 2 .04 80.0 19.7 3.55 80.0 6.44 2.03 80.0 6.48 2 .04 90.0 19.1 3.70 90.0 5.76 2 .04 90.0 5.77 2 .05 100.0 18.4 3.84 100.0 5.22 2 .04 100.0 5.22 2 .05 110.0 18.0 3.98 110.0 4 .79 2.05 110.0 4 .77 2 .06 120.0 17.6 4 .11 120.0 4.43 2 .06 120.0 4 .40 2 .07 130.0 17.3 4 .24 130.0 4 .13 2 .07 130.0 4 .09 2 .08 140.0 17.0 4 .37 140.0 3.88 2.08 140.0 3.83 2 .08 150.0 16.7 4.48 150.0 3 .66 2 .09 Continued on the next page. 291 Continued. Cu{ [CF3(CF2)5CH2CH2]2P02}2 (Form I) Cu{ [CF3(CF2)5CH2CH2]2P02}2 (Form II) (Continued) 10, 000 G (Continued) 50, 000 G Temp. X M Ueff Temp. X M Ueff Temp. X M M-eff 150.0 3.61 2 .09 160.0 16.5 4 .60 160.0 3.46 2 . 1 0 160.0 3 .40 2 . 1 0 170.0 16.4 4 .72 170.0 3 .29 2 .11 170.0 3.23 2 .11 180.0 16.2 4.83 180.0 3 .15 2 .13 180.0 3 .07 2 . 1 2 190.0 16.0 4.93 190.0 3 .02 2 .14 190.0 2.93 2 .13 200 .0 15.9 5.04 200 .0 2 .90 2 .15 200.0 2.81 2 . 1 4 210 .0 15.7 5.13 210 .0 2 .80 2 . 1 7 210.0 2 .70 2 .15 220 .0 15.6 5.23 220 .0 2 .72 2 .19 220.0 2 .60 2 . 1 6 230 .0 15.4 5.33 230 .0 2.63 2 .20 230 .0 2 .50 2 . 1 7 240 .0 15.2 5.41 240 .0 2 .55 2.21 240.0 2 .42 2 .18 250 .0 15.1 5.50 250 .0 2.48 2 .22 250 .0 2 .40 2 . 1 9 260 .0 15.0 5 .59 260 .0 2 .40 2 .24 260.0 2 .26 2 . 1 9 270 .0 14.9 5.68 270 .0 2 .33 2 .24 270.0 2 .19 2 .20 280 .0 14.8 5.76 280 .0 2 .26 2.25 280.0 2 .13 2.21 290.0 14.7 5.84 290 .0 2 .21 2 .26 290.0 2 .07 2 .22 300.0 14.6 5.92 300.0 2 .14 2 .26 300.0 2 .02 2.23 2 9 2 TABLE II-2. Magnetic data for manganese(II) compounds Mn[(CH3)2P02]2 (Form I) VSM Temp. X M M-eff 4.55 25.7 0 .97 6.01 26.5 1.13 10.0 30.1 1.55 15.7 33.0 2.03 21.1 35.1 2.43 26.0 36.3 2 .74 30.5 36.7 2 .99 40.7 36 .9 3.46 48.3 36.2 3.74 55.3 35.2 3.95 60.7 34.2 4 .08 65.9 33.5 4 .20 70.3 32.7 4 .29 74.6 32 .0 4 .37 82.1 30.6 4 .48 Mn[(CH3)2As02]2 Temp. X M Meff 4.20 91.0 1.75 6.04 85.5 2.03 9.70 77.8 2 .46 15.1 71.7 2 .94 20.4 66.7 3 .30 Continued on the next page. Mn[(CH3)2P02]2 (Form VSM Temp. XM M-eff 4 .20 53.1 4 .22 5.48 47.5 4 .56 6.64 42.5 4.75 7.80 38.3 4 .88 10.1 31.9 5.08 12.3 27.4 5.18 14.5 24.0 5.27 16.9 21.1 5.34 18.7 19.4 5.38 21.6 17.1 5.44 25.1 15.2 5.51 27.7 13.9 5.55 30.0 13.0 5.57 33.5 11.6 5.58 36.3 10.8 5.60 40.6 9.76 5.62 47 .9 8.38 5.67 54.9 7.47 5.72 60.4 6.81 5.73 65.5 6.35 5.77 69.9 5.99 5.79 74.1 5.63 5.78 81.8 5 .12 5.79 Mn[(C6F5)2P02]2 Temp. X M M-eff 2 . 1 2 266 2 .13 2 .50 269 2 .32 2 .89 274 2 .52 3 .20 275 2.65 3.46 277 2 .77 293 Mn[(CH3)(C2H5)P02]2 VSM Temp. X M M-eff 4 .32 30.3 1.02 6 .50 31.4 1.28 10.3 33 .2 1.66 15.5 35.6 2 . 1 0 20 .9 37.4 2 .50 25.8 38.1 2 .80 30.3 38.4 3.05 40 .6 38.1 3 .52 48.3 37 .0 3.78 55.2 36 .0 3.99 60.7 34 .9 4 . 1 2 65.8 34.0 4.23 70.3 33.3 4 .32 74.5 32.5 4 .40 81.8 30 .9 4 .50 Mn[(n-C8H17)2P02]2 Temp. XM Meff 2.08 3 3 4 2 .36 2 .40 345 2 .57 3.54 353 3 .16 3.89 353 3.31 4 .11 353 3.41 Continued. Mn[(CH3)2As02]2 Mn[(C6F5)2P02]2 Mn[(n-C8H17)2P02]2 (Continued) (Continued) (Continued) Temp. XM M*ff Temp. XM Heff Temp. XM M*ff 25.8 62.7 3.60 4 .11 278 3.02 4 .20 353 3.41 30.9 58.7 3.81 4 .40 2 8 0 3 .14 4 .88 3 4 6 3.67 40.5 52.4 4 .13 5.05 277 3.34 6.04 3 3 0 3.99 48.0 48 .2 4 .31 6.04 271 3.62 6.72 3 2 0 4 .15 55.0 45 .0 4.45 6.96 266 3.84 8.96 283 4 .50 60.6 42 .4 4 .54 7.60 2 6 2 3.99 12.5 2 3 6 4 .84 65.7 40 .4 4.61 11.8 2 2 2 4 .57 14.6 2 1 3 4 .97 70.2 38.8 4 .68 13.2 206 4.65 17.8 185 5.12 74.4 37.3 4 .72 17.0 181 4.95 20.8 164 5.23 81.8 34.9 4 .79 18.7 168 5.00 22 .9 153 5.30 22.3 150 5.18 27.5 132 5.39 23.0 147 5.20 30.4 122 5.44 27 .0 132 5.34 40.4 94.3 5.52 27.7 128 5.33 48.1 81.2 5.59 30.5 120 5.41 54.9 72.5 5.64 41 .0 95.4 5.59 60.7 66.6 5.69 48.5 83.6 5.70 65.7 62.0 5.71 55.5 75.6 5.79 70.0 58.4 5.72 60.9 70.0 5.84 74.2 55.4 5.73 66.0 65.4 5.88 81.2 50.7 5.74 69.9 62.4 5.91 Mn{[CF3(CF2)3CH2CH2]2P02}2 Mn{[CF3(CF2)5CH2CH2]2P02}2 VSM SQUID Temp. XM Mef Temp. XM |J.eff 2 . 1 2 2 2 7 1.96 1.86 181 1.64 3.00 2 2 9 2.35 2 .00 181 1.70 3.54 231 2 .56 3.00 183 2 .09 4 .20 2 3 2 2 .79 4 .00 186 2 .44 4 .27 2 3 2 2.81 5.00 189 2.75 5.09 231 3.07 6.00 190 3.02 5 .17 231 3.09 7 .00 189 3.26 6.08 2 2 7 3.32 8.00 188 3.46 6.38 2 2 6 3.391 9.00 185 3.65 7 .52 2 2 0 3.64 9.99 181 3.81 Continued on the next page. 294 Continued Mn{ [CF 3(CF 2)3CH 2CH 2] 2P02} 2 (Continued) Temp. X M Heff 9.70 205 3.99 12.1 188 4 .27 14.4 175 4.48 16.5 161 4.61 18.6 151 4.73 21.4 139 4 .87 24.8 126 5.00 27.6 118 5.09 30.1 110 5.15 36.0 95.9 5.25 40.6 87.6 5.33 47 .9 76.7 5.42 54.3 69.1 5.48 60.6 63 .7 5.55 65.6 59.5 5.59 70.0 56.2 5.61 74.0 53.5 5.63 81.7 49.1 5.67 Continued on the next page. Mn{ [CF 3 (CF 2 ) 5 CH 2 CH 2 ] 2 P0 2 } 2 (Contined) Temp. X M l^ eff 11.0 177 3.95 12.0 173 4 .07 13.0 169 4 . 1 9 15.0 160 4 .38 17.0 151 4 .54 20.0 139 4 .72 22.0 132 4 .82 25.0 123 4 .95 30.0 109 5.11 35.0 97.9 5.24 40.0 88.9 5.33 45 .0 81.3 5.41 50.0 74.6 5.46 60.0 64.3 5.56 70.0 56.6 5.63 80.0 50.6 5.69 90.0 45.8 5.74 100.0 41.8 5.78 110.0 37.9 5.82 120.0 35.1 5.85 130.0 33.2 5.88 140.0 31.1 5.90 150.0 29.1 5.91 160.0 27 .4 5.93 170.0 25 .9 5.94 180.0 24.5 5.94 190.0 22.6 5.94 200 .0 21.5 5.94 210 .0 20.4 5.94 220 .0 20 .0 5.94 230 .0 19.1 5.93 240 .0 18.3 5.92 250 .0 17.5 5.92 260 .0 16.8 5.91 270 .0 16.2 5.91 280 .0 15.6 5.91 290 .0 15.1 5.92 300.0 14.6 5.92 295 Continued {(DMF) 3Mn[//-(C 6F 5) 2P0 2] 3} 2Mri Mn(DMSO) 2 [H(C 6 H 5 )P0 2 ] 2 V S M V S M Temp. XM Heff Temp. XM Heff 4 .20 724 4.93 2 .20 3 1 9 2 .37 5.00 6 3 4 5.03 2 .50 3 2 2 2 .54 5.28 6 1 0 5.08 2 .80 325 2 .70 6 .12 544 5 .16 3.00 3 2 7 2 .80 6.88 495 5.22 3 .29 3 2 9 2 .94 8.04 4 3 4 5.28 3.64 331 3 .10 10.3 3 5 4 5.39 4 .11 331 3 .30 12.3 3 0 0 5.43 4 .24 3 2 9 3 .34 14.7 2 5 9 5.51 4 .89 325 3 .57 16.8 2 2 9 5.53 5.06 3 2 6 3.63 18.9 205 5.57 6.13 311 3.90 20.7 188 5.58 6.20 313 3.94 23.0 171 5.60 7 .30 293 4 . 1 4 25.1 158 5.63 11.0 2 4 6 4 .66 27.7 145 5.66 16.5 191 5.02 30.0 133 5.65 21.8 157 5.23 33.7 120 5.67 26.9 133 5.35 40.6 100 5.71 31.2 118 5.43 55.0 76.0 5.78 • 40.8 93.5 5.54 65.7 64.1 5.80 48.3 81.0 5.59 74.0 57.0 5.81 55.3 72.7 5.68 81.1 52.2 5.82 60.8 66.7 5.71 65.9 62.0 5.72 70.3 58.6 5.76 74.4 55.6 5.77 81.6 51.0 5.77 \ 296 TABLE II-3. Magnetic data for nickel(II) compounds Ni[(CH3)2P02]2 VSM Temp. X M M-eff 2.50 729 3.82 2.90 710 4.06 3.40 669 4.27 4.10 603 4.45 4.47 511 4.27 4.98 514 4.53 6.30 404 4.51 7.80 310 4.40 11.2 188 4.10 16.7 109 3.82 4.42 632 4.73 6.50 407 4.60 10.4 212 4.19 15.9 118 3.87 21.1 81.3 3.70 26.2 62.8 3.63 30.6 51.4 3.55 40.7 36.7 3.46 48.3 30.2 3.41 55.1 26.1 3.39 Continued on the next page. Ni[(CH3)(C2H5)P02]2 VSM Temp. XM Meff 9225 G 2.12 875 3.85 2.32 863 4.00 3.00 818 4.43 3.30 781 4.54 3.90 721 4.74 4.81 623 4.90 6.25 477 4.88 8.98 295 4.60 18.9 105 3.97 23.8 76.9 3.82 28.9 60.2 3.73 36.4 44.7 3.61 44.6 35.7 3.57 51.4 30.1 3.52 58.0 26.5 3.51 63.3 24.0 3.49 67.8 22.2 3.47 76.3 19.5 3.45 7501 G 2.32 996 4.30 2.70 956 4.54 3.00 936 4.74 3.20 881 4.75 3.54 836 4.87 4.28 746 5.05 5.24 611 5.06 6.32 497 5.01 5.80 564 5.11 9.86 266 4.58 297 Ni[(CH3)2As02]2 VSM Temp. X M Meff 2.40 786 3.89 2.50 791 3.98 2.90 773 4.23 3.30 747 4.44 4.19 721 4.91 4.32 685 4.87 5.88 549 5.08 10.0 271 4.66 15.9 140 4.21 20.9 95.7 4.00 25.9 71.7 3.85 30.3 58.4 3.76 40.5 40.2 3.61 48.10 32.7 3.55 55.0 28.1 3.52 60.5 24.4 3.44 65.6 22.7 3.45 70.1 20.9 3.43 74.3 19.6 3.41 81.7 17.5 3.38 2.50 913 4.27 2.80 902 4.50 3.11 881 4.68 3.54 827 4.84 4.47 751 5.18 4.58 734 5.18 5.80 594 5.25 6.17 562 5.27 10.1 274 4.70 15.8 142 4.23 Continued Ni[(CH3)2P02]2 (Continued) Temp. X M Meff 60.8 23.4 3 .37 65.8 21.5 3 .36 70.3 19.9 3.35 74.6 18.8 3 .34 82.0 16.8 3 .32 4 .47 7 0 9 5.04 7.58 335 4 .51 11.2 190 4 .13 16.6 111 3.84 4 .47 751 5.18 6 .50 4 4 2 4 .79 10.3 2 1 4 4 .20 15.8 119 3.88 21.1 83.3 3.75 26.0 64.4 3.66 30.7 52.6 3 .60 Continued on the next page. Ni[(CH3)(C2H5)P02]2 (Continued) Temp. X M Meff 15.6 137 4 .13 20.9 94.2 3.96 25.8 70.6 3.81 30.5 57.0 3.73 40.3 40.4 3.61 47.8 33.1 3 .56 54.4 28.6 3.53 60.4 25.4 3.51 65.4 23.2 3.48 70.1 21.5 3.47 74.3 20.1 3.46 81.7 18.0 3.43 5251 G 2549 G Ni[(CH3)2As02]2 (Continued) Temp. X M Meff 20.9 96.2 4.01 26 .0 71.8 3.87 30.8 57.5 3.76 40 .7 40.1 3.61 48 .2 32 .7 3.55 55.1 28.1 3.52 60.8 24 .9 3.48 65.8 22.8 3.46 70.3 21.1 3.45 74.6 19.6 3.42 82.2 17.5 3.40 4 . 3 2 1166 6.35 7.28 4 5 4 5.14 11.0 2 3 6 4 .56 17.0 127 4 .15 21.8 90.8 3.98 27 .0 68.8 3.86 31.6 55.1 3.73 40.6 40.3 3.62 48 .2 33.5 3 .59 54.9 29 .0 3 .57 60.6 25 .9 3.55 65.8 23 .7 3.53 73.6 20 .9 3 .50 81.9 16.9 3.33 298 Continued. Ni[(C 6 F 5 ) 2 P0 2 ] 2 V S M Temp. XM !leff 2.20 74.3 1.14 2.88 73.5 1.30 3.12 73.1 1.35 3.63 72.0 1.45 4.20 71.2 1.55 4.50 70.4 1.59 6.04 67.3 1.80 6.65 65.7 1.87 7.93 62.9 2.00 10.3 56.3 2.15 12.6 54.3 2.33 14.5 51.2 2.44 17.8 46.8 2.58 20.9 43.1 2.68 23.2 40.8 2.75 25.9 38.3 2.82 27.6 36.9 2.85 30.2 34.9 2.90 40.8 28.6 3.05 48.4 25.3 3.13 55.3 23.1 3.19 60.7 21.4 3.23 70.3 19.1 3.28 81.6 17.0 3.33 Ni[(C 6 F 5 ) 2 P0 2 >H 2 0 V S M Temp. XM M f^f 4.38 85.1 1.73 6.13 78.4 1.96 7.38 74.7 2.10 11.0 63.8 2.37 14.5 55.3 2.53 18.9 47.8 2.66 21.7 43.0 2.73 24.9 39.3 2.79 27.6 36.6 2.84 30.3 34.1 2.87 40.9 26.8 2.96 48.5 23.4 3.01 55.4 21.1 3.05 61.0 19.4 3.08 66.1 18.0 3.09 70.5 17.0 3.09 74.6 16.1 3.10 81.6 14.8 3.11 Ni[(C 6 H 5 ) 2 P0 2 ] 2 V S M Temp. XM 4.20 74.7 1.58 5.05 70.9 1.69 6.32 67.5 1.85 7.59 64.2 1.97 8.70 61.7 2.07 10.4 58.8 2.21 12.3 55.3 2.33 14.6 52.0 2.46 17.0 48.9 2.58 18.7 46.9 2.65 22.1 43.6 2.78 24.9 41.0 2.86 27.8 38.7 2.93 29.8 37.1 2.97 33.3 34.7 3.04 36.1 33.0 3.09 40.4 30.8 3.16 47.9 27.6 3.25 54.8 25.2 3.32 65.5 22.0 3.40 73.9 19.9 3.43 81.6 18.5 3.47 Ni[H(C 6 H 5 )P0 2 H] 2 [H(C 6 H 5 )P0 2 ] 2 V S M Temp. XM Heff 4.33 254 2.97 7.76 152 3.07 11.1 109 3.11 Ni(HCONHCH 3 ) 2 [H(C 6 H 5 )P0 2 ] 2 V S M Temp. XM lleff 2.20 62.7 1.05 2.30 63.2 1.08 2.50 63.9 1.13 Continued on the next page. 299 Continued. Ni[(C 6H 5)P0 2H] 2[H(C 6H 5)P0 2] 2 (Continued) Temp. XM lleff 16.9 72.8 3 .14 22.0 56.5 3.15 26.8 46 .4 3.15 32.3 39.6 3 .20 41.2 29 .9 3 .14 48.5 25.6 3 .15 55.4 22.6 3 .16 61.0 20.6 3 .17 66.1 19.1 3 .18 70.6 18.1 3 .20 74.6 17.1 3 .19 81.9 15.6 3 .20 Ni(HCONHCH 3 ) 2 [H(C 6 H 5)P0 2] 2 (Continued) Temp. XM U.eff 2 .90 65.4 1.23 3.64 67.7 1.40 4.25 68.4 1.52 4 .34 69.5 1.55 5.46 71.1 1.76 5.96 71.2 1.84 6.91 70 .9 1.98 7 .32 69.4 2 .02 8.11 69.1 2 . 1 2 11.2 62 .0 2 .36 16.0 53.2 2.61 16.8 50.9 2.61 21.7 43 .2 2 .74 27.1 37.0 2.83 31.0 33.3 2 .87 40.8 26 .7 2.95 48.3 23 .2 2 .99 55.3 20 .9 3.04 60.9 19.2 3 .06 65.8 18.1 3 .09 70.3 17.2 3.11 74.3 16.3 3.11 81.8 15.0 3.13 Ni{ [CF 3 (CF 2 ) 5 CH 2 CH 2] 2P0 2} 2 SQUID Temp. XM 1.86 551 2 .86 2 .00 545 2 .95 3.00 493 3.44 4 .00 4 2 2 3.68 5.00 355 3.77 6.00 2 9 7 3 .77 7.00 2 5 2 3.76 Continued on the next page. 3 0 0 Continued. Ni{ [CF 3 (CF 2 ) 5 CH 2 CH 2 ] 2 P0 2 } 2 (Continued) 7.99 217 3.72 9.00 189 3.69 9.99 167 3.65 11.0 149 3.62 12.0 134 3.59 13.0 122 3.56 15.0 102 3.51 17.0 88.2 3.46 20.0 72.5 3.40 22.0 64.6 3.37 25.0 55.5 3.33 30.0 45.0 3.29 35.0 37.7 3.25 40.0 32.3 3.22 45.0 28.3 3.19 50.0 25.1 3.17 60.0 20.6 3.14 70.0 17.5 3.13 80.0 15.2 3.11 90.0 13.4 3.11 100 12.0 3.10 110 10.9 3.10 120 10.0 3.09 130 9.18 3.09 140 8.52 3.09 150 7.94 3.09 160 7.43 3.08 170 6.98 3.08 180 6.58 3.08 190 6.22 3.07 200 5.89 3.07 210 5.60 3.07 220 5.33 3.06 240 4.83 3.04 250 4.62 3.04 260 4.42 3.03 280 4.08 3.02 290 3.94 3.02 300 3.81 3.02 301 TABLE II-4. Magnetic data for cobalt(II) compounds Co[(CH3)2P02]2 Co[(CH3)(C2H5)P02]2 Co[(CH3)2As02]2 VSM VSM VSM Temp. XM Ueff Temp. XM Meff Temp. X M Meff 2 .12 298 2.25 4 .38 2 3 2 2.85 9225 G 2 .30 305 2 .37 6.24 208 3 .22 2 .50 305 2 .47 10.1 164 3.64 5.84 9 7 9 6.76 2 .80 304 2.61 15.1 125 3.89 6.86 9 6 2 7.27 3 .20 2 9 7 2 .76 20.7 98.5 4.03 8.44 9 2 0 7.88 3.90 2 8 7 2 .99 27.1 79.5 4 .15 10.2 836 8.25 4 .98 2 6 9 3.28 30.3 71.8 4 . 1 7 11.4 7 6 9 8.37 6 .50 221 3 .39 40.7 54.9 4.23 12.6 685 8.31 10.2 183 3.87 48.2 47 .2 4 .26 13.0 6 7 9 8.38 16.3 141 4 .29 55.1 42.3 4 .32 13.5 635 8.26 21.1 114 4 .38 60.7 38.7 4 .33 14.3 571 8.09 26.0 90 .0 4 .33 65.8 35.9 4 .35 15.0 538 8.02 30.8 79.1 4.41 70.2 33.8 4 .36 16.0 4 8 4 7.87 40.8 60.4 4 .44 74.5 32.0 4 .36 17.5 4 2 9 7.75 48.4 51.4 4 .46 81.9 29.2 4 .37 20.7 3 1 5 7.21 55.0 45 .9 4 .49 25.3 223 6.71 60.8 42 .0 4 .52 27.4 194 6.51 65.9 38.8 4 .52 30.2 166 6.32 70.3 36.6 4.53 32.0 150 6 .20 74.6 34.6 4 .54 36.5 123 5.99 82.1 32.0 4 .58 51.8 63.6 72.6 80.0 77.2 60.7 51.8 46.3 5.65 5.56 5.48 5.44 Continued on the next page. 302 Continued. Co[(CH 3 ) 2 As0 2 ] 2 (Continued) Temp XM Temp. XM Temp. X M 7501 G 5251 G 2549 G 4.38 1204 6.49 4 .20 1661 7.47 4 .20 3225 10.4 5.84 1174 7.40 5.84 1617 8.69 4 .70 3164 10.9 6.30 1168 7.67 6.86 1558 9.25 5.64 3058 11.7 6.86 1148 7.93 7.86 1492 9.68 6.72 2 8 1 5 12.3 7.40 1132 8.18 9.88 1263 9.99 7 .56 2 6 1 7 12.6 10.2 9 6 2 8.85 10.2 1204 9.90 9 .36 1933 12.0 11.2 889 8.93 11.4 1034 9 .17 10.2 1658 11.6 11.4 870 8.90 12.6 865 9.33 11.1 1389 11.1 12.6 755 8.72 13.1 835 9.34 12.2 1077 10.3 13.5 688 8.60 13.5 769 9.09 13.4 9 0 9 9.85 14.3 631 8.48 14.3 676 8.79 14.4 7 6 0 9.34 14.4 6 1 6 8.39 15.0 6 1 9 8.60 18.6 4 1 8 7.88 15.0 575 8.29 16.0 535 8.27 23 .0 2 7 6 7 .12 16.0 5 1 0 8.07 27 .0 205 6.66 18.5 386 7 .56 30.5 167 6.38 21.7 285 7.03 25.0 223 6.67 27.5 189 6.45 30.6 159 6 .24 36.6 123 5.99 40 .9 105 5.86 48.5 83.7 5.70 55.4 71.7 5.64 60.9 63.4 5.55 66.1 57.7 5.52 70.1 54.0 5.50 74.4 50.4 5.47 81.5 45.1 5.42 Continued on the next page. 303 Continued. Co[(C 6F 5)2P0 2] 2 V S M Temp. XM Meff 2 .12 4 0 0 2 .60 2 .50 3 8 0 2 .76 2 .89 351 2.85 3.72 3 1 7 3.07 4 .24 305 3.22 4 .99 275 3.31 6 .10 245 3.21 6.96 2 2 6 3.55 10.4 171 3.77 15.8 126 3.99 21 .0 101 4 .11 25 .9 84.4 4 .18 30.5 73.2 4 .22 40.8 56.2 4 .28 48.3 48 .2 4 .31 55.1 43 .0 4 .35 60.8 39 .2 4 .36 65.8 36.5 4 .38 70.4 34.4 4 .40 74.5 32.5 4 .40 81.8 29.8 4.41 Co[H(C 6 H 5 )P0 2 H] 2 [H(C 6 H 5 )P0 2 ] 2 V S M Temp. XM M-eff 4.40 3 0 9 3 .30 5.79 2 5 6 3.44 10.2 164 3.65 16.0 113 3.80 20.8 90 .9 3.88 27.4 72 .9 3 .99 Continued on the next page. Co[(C 6 F 5 ) 2 P0 2 >H 2 0 V S M Temp. XM Meff 4 .20 2 6 4 2 .98 6.44 203 3.24 9.94 148 3.43 15.5 104 3 .59 20.8 83.7 3.73 25.8 71.6 3 .84 30.0 64 .0 3 .92 40.8 51.1 40.8 48 .2 45.4 4 .18 55.2 41.3 4 .27 60.7 38.5 4 .32 65.8 36.3 4 .37 70.3 34.6 4.41 74.5 33.3 4.45 82.1 30 .9 4 . 5 0 Co(HCONHCH 3) 2[H(C 6H 5)P02]2 V S M Temp. XM Meff 2 .20 162 1.67 2 .40 165 1.78 2 .70 170 1.92 3.20 175 2 . 1 2 3 .80 178 2.33 4 .40 178 2 .50 304 Continued. Co[H(C 6H 5)P0 2H] 2[H(C 6H 5)P0 2] 2 (Continued) Temp. XM M-eff 31.0 66.3 4 . 1 6 40.8 52.7 4.21 48.3 46 .4 4.23 55.1 42 .2 4.31 60.8 39.2 . 4 .37 65.9 36.9 4.41 70.3 35.2 4.45 74.4 33.6 4 .47 81.9 31 .2 4 .52 Co(HCONHCH 3 ) 2 [H(C 6 H 5)P0 2] 2 (Continued) Temp. XM M-eff 5.06 175 2 .66 6.24 168 2 .90 9.94 137 3 .30 15.9 103 3.61 21.5 85.6 3.83 27.1 71.5 3 .94 31.0 64.8 4 .01 40.8 53.2 4 . 1 7 48.3 47.3 4 .27 55.2 43.3 4 .37 60.9 40.5 4 .44 65.9 38.3 4 .49 70.4 36.6 4 .54 74.4 35.1 4 .57 81.8 32.8 4.63 Co{ [CF 3 (CF 2 ) 3 CH 2 CH 2] 2P0 2] 2 V S M Temp. XM Meff 4 .20 205 2 .62 5.09 201 2 .86 6.47 191 3 .15 7.55 182 3 .32 10.15 159 3 .59 11.85 145 3.70 14.30 129 3.85 16.45 118 3.93 18.65 108 4.01 21.85 95.4 4.08 24 .75 86.9 4 .15 27 .45 79.1 4 .17 30 .30 74.2 4 .24 36 .20 62.5 4.25 Continued on the next page. Co{[CF 3 (CF 2 ) 5 CH 2 CH 2] 2P0 2] 2 SQUID Temp. XM ' Heff 1.86 2 1 1 1.77 2 .00 2 1 3 1.84 3.00 2 2 2 2.31 4 .00 2 2 2 2 .67 5.00 2 1 7 2 .94 6.00 208 3 .16 7.00 197 3 .32 8.00 187 3.46 8.99 177 3.56 10.00 167 3.65 10.99 158 3.73 11.99 150 3 .79 12.99 142 3.84 15.00 129 3.93 305 Continued. Co {[CF3(CF 2) 3CH 2CH 2] 2P0 2] 2 (Continued) 40.60 56.8 4.29 48.10 48.9 4.34 54.40 43.8 4.37 60.56 40.2 4.41 65.48 37.5 4.43 70.00 35.4 4.45 74.13 33.5 4.46 81.61 30.8 4.48 Co{[CF 3 (CF 2 ) 5 CH 2 CH 2 ] 2 P0 2 ] 2 (Continued) 17.00 118 4.00 20.01 104 4.07 22.02 96.1 4.11 25.01 86.5 4.16 30.02 74.3 4.22 35.02 65.1 4.27 39.99 57.9 4.30 45.00 52.2 4.33 50.00 47.6 4.36 60.00 40.5 4.41 70.00 35.3 4.45 80.00 31.4 4.48 90.00 28.3 4.51 99.99 25.8 4.54 110.0 23.8 4.57 120.0 22.1 4.60 130.0 20.6 4.63 140.0 19.3 4.65 150.0 18.2 4.68 160.0 17.3 4.70 170.0 16.4 4.72 180.0 15.7 4.75 190.0 15.0 4.77 200.0 14.4 4.79 210.0 13.8 4.82 220.0 13.3 4.84 230.0 12.8 4.86 240.0 12.4 4.88 250.0 12.0 4.91 260.0 11.7 4.92 270.0 11.3 4.94 280.0 11.0 4.97 290.0 10.7 4.99 300.0 10.5 5.01 306 T A B L E II-5. Magnetic data for miscellaneous compounds Temp. XM Meff 2549 G 2.20 567 3 .16 2 .40 528 3 .19 2 .79 501 3.34 3 .30 4 7 7 3.55 4 .07 441 3.82 4 .79 4 2 6 4 .04 5.09 3 9 2 4 .00 5.34 3 6 2 3.94 5.64 325 3.83 5.92 2 9 2 3.72 6.42 2 4 9 3.58 7.08 2 1 8 3.51 7.93 190 3.47 8.76 173 3.48 9.84 156 3.51 10.6 145 3.51 11.7 134 3.55 12.6 127 3 .59 15.2 110 3 .66 18.3 96.4 3.76 20.5 88.3 3.80 24.2 78.2 3.89 26.9 71.9 3.93 30.2 65.3 3.97 31.6 63.9 4 .02 32.5 61.4 4 .00 37.5 55.5 4 .08 54.9 42 .4 4 .31 63.8 38.1 4.41 74.4 33 .9 4 .49 78.3 32.6 4 .52 Continued on the next page. Co(H 20) 2(HCOO) 2 V S M Temp. XM M e f f 5251 G 2 .20 498 2 .96 2 .40 4 8 0 3.04 2 .89 4 3 9 3 .18 3 .39 401 3 .30 4 .20 362 3.49 4 .50 351 3.56 4.85 3 3 4 3.60 5.42 298 3.60 5.54 295 3.61 5.56 285 3.56 5.85 266 3.53 6.38 2 3 6 3.47 6.79 2 1 8 3.44 7 .30 201 3.43 7.72 191 3.43 8.04 181 3.42 8.57 171 3.43 9.06 163 3.44 9.46 157 3.45 9.96 152 3.48 10.9 140 3 .50 11.9 130 3 .52 13.1 122 3 .57 13.8 117 3.60 14.6 112 3.62 15.7 106 3.65 16.5 102 3.68 18.5 93.8 3.73 21.6 83.7 3.80 24.7 76.0 3.88 27.8 69.7 3.94 29.8 65.9 3.96 32.4 62.0 4.01 40.7 52.3 4 . 1 2 48.1 46.5 4.23 Temp. XM Meff 7501 G 4 .20 335 3.35 4 .85 308 3.46 5.09 293 3.46 5.34 2 8 4 3.48 5.85 2 5 6 3.46 6.24 2 3 7 3.44 6.58 2 2 9 3.47 6.84 2 1 7 3.45 7.23 205 3.44 7.67 194 3.45 8.30 179 3.45 8.96 167 3.46 10.00 151 3.48 10.62 144 3.50 10.93 141 3.51 11.46 136 3.53 12.05 130 3.54 12.95 123 3 .57 13.30 120 3 .57 13.75 117 3 .59 15.15 109 3.63 17.20 99.0 3.69 19.35 89.9 3.73 22 .65 80.3 3.81 24 .80 74.7 3.85 26 .95 70.3 3.89 28 .05 68.3 3.91 31.65 62.2 3.97 4 7 . 9 0 46 .0 4 .20 65 .28 36.5 4 .36 73 .82 33.5 4 .44 81 .11 31.1 4 .49 307 Continued. Co(HCONH 2 ) 2 (HCOO) 2 V S M Temp. XM Heff Temp. XM Heff 2549 G * 5251 G* 2 .12 145 1.57 6.98 94.5 2 .30 2 .99 145 1.86 7.38 95.0 2 .37 3.45 144 2 .00 7.74 94.6 2 .42 4 .67 145 2.33 8.17 92.5 2.46 5.77 145 2 .59 8.37 91.3 2 .47 4 .20 145 2.21 8.50 88.8 2.46 4.63 145 2 .32 8.70 85.1 2.43 5.29 145 2.48 8.82 81.7 2 .40 5.70 145 2 .57 8.89 78.4 2 .36 6.24 145 2 .69 9.00 76.8 2 .35 6.72 144 2 .79 9 .14 74.3 2.33 7.23 143 2 .87 9.26 72.2 2.31 7.67 140 2.93 9.38 71.0 2.31 7.86 137 2 .94 9.56 70.2 2 .32 8.30 130 2 .94 9.82 68.9 2.33 8.50 120.6 2 .86 10.31 68.5 2 .38 8.70 107.0 2.73 11.85 67.3 2 .52 8.90 90.4 2 .54 13.95 66.1 2 .72 9.07 81.0 2 .42 17.25 61.1 2 .90 9 .20 75.7 2 .36 20.85 57.0 3.08 9 .39 72.7 2 .34 23 .70 53.6 3 .19 10.0 69.2 2 .35 28 .70 49.5 3 .37 11.3 68.0 2.48 29.85 48.2 3 .39 13.6 66.1 2 .68 37 .80 43.1 3.61 16.9 62.1 2 .90 52 .60 35.7 3.88 18.8 59.7 3 .00 64.21 31.7 4 .04 Continued on the next page. Temp. XM Meff 7501 G * 2 . 1 2 75.7 1.13 3.09 75.7 1.37 3.64 75.7 1.48 4.43 76.3 1.64 4 .20 76.0 1.60 5 .19 77.2 1.79 5.34 77.5 1.82 5.78 78.4 1.90 6.64 79.8 2 .06 6.65 80.1 2 .06 7 .10 81.3 2 .15 7.48 82.2 2 .22 7.98 82.5 2 .29 8.44 81.9 2 .35 8.63 80.4 2 .36 8.83 78.7 2 .36 9.00 76.4 2 .34 9 .14 73.8 2 .32 9 .20 73.5 2 .33 9 .32 71.4 2.31 9.64 70.0 2 .32 9.70 69.7 2.33 12.00 67.4 2 .54 14 .10 65.4 2 .72 16.15 62.8 2.85 18.35 60.5 2.98 21.7 56.4 3.13 24.8 5 2 . 9 . 3.24 27.3 50.6 3 .32 30.0 48.3 3.40 33.1 45.6 3.47 36.0 43.6 3.54 40.5 41 .2 3.65 308 Continued. Co(HCONH 2 ) 2 (HCOO) 2 (Continued) 48.0 37.4 3.79 55.0 35.0 3.92 60.5 33.0 3.99 65.5 31.5 4 .06 70.1 30.3 4 . 1 2 74.0 29.4 4 .17 81.7 27 .7 4.25 Temp. X M Meff Temp. XM M-eff 9225 G 2549 G 4.47 86.7 1.76 4 .39 111 2.49 5.09 86.2 1.87 4.93 176 2.63 6.38 86.0 2 .09 5.34 175 2.73 7 .10 86.5 2 .22 5.85 173 2.85 7.98 87.1 2 .36 6.72 170 3.02 8.70 85.7 2 .44 7 .17 168 3.11 8.96 84.4 2.46 7.60 163 3 .15 9 .20 82.0 2.46 8.04 157 3 .18 9 .57 78.6 2.45 8.70 136 3.08 10.1 75.6 2 .47 9.00 119 2.93 10.9 73.2 2.53 9 .14 105 2 .78 11.7 71.9 2 .59 9.26 96.2 2 .67 14.2 68.4 2 .78 9.46 93.0 2.65 17.5 63.4 2 .98 9.50 86.8 2 .57 19.6 60.5 3.08 9.65 84.0 2 .55 9.82 79.8 2 .50 10.0 77.9 2 .50 10.4 75.7 2.51 13.7 70.1 2.78 16.7 65.4 2 .96 19.1 62.2 3 .09 22.4 58.0 3.23 25 .0 54.9 3 .32 27.6 52.5 3.41 30.4 50.1 3.49 * Data were collected on the crystal sample of Co(HCONH 2 ) 2 (HCOO) 2 . Other data were collected on the powder sample. Continued on the next page. 309 Continued. Co(HCONH 2 ) 2 (HCOO) 2 (Continued) Temp. XM Meff 2549 G 34.0 41.4 3.59 36.5 45.5 3.65 40.9 42.7 3.74 48.4 39.1 3.89 60.7 34.7 4.11 70.3 32.0 4.24 81.6 29.2 4.37 Magnetization data for Co(HCONH 2 ) 2 (HCOO) 2 (SQUID) Magnetization (cm3 G mol"1) Field (G) 2 K 4.8 K 8 K 10K 20 K 10 279 273 220 1.06 0.15 50 283 284 220 4.56 2.93 100 289 290 227 8.95 6.43 500 332 317 257 44.0 34.4 1000 379 349 293 87.7 69.1 1500 424 380 329 131 103 2000 466 411 363 174 138 2500 508 442 398 218 173 5000 706 599 571 433 344 7500 889 756 742 647 518 10000 1070 916 915 857 689 15000 1380 1230 1260 1270 1030 20000 1674 1530 1600 1680 1370 25000 1949 1830 1960 2090 1710 30000 2223 2140 2320 2500 2060 35000 2494 2440 2700 2910 2400 40000 2770 2760 3100 3330 2750 45000 3060 3090 3520 3750 3090 50000 3370 3440 3960 4160 3420 55000 3710 3830 4400 4580 3760 310 Magnetization data for hysteresis run for Co(HCONH 2 ) 2 (HCOO) 2 (SQUID) Field up (G) M a g * Field down (G) Mag. Field up (G) Mag. 0 -272 55000 3740 -55000 -3750 10 -267 50000 3360 -50000 -3380 20 -261 40000 2700 -40000 -2710 50 -244 30000 2100 -30000 -2120 100 -232 20000 1530 -20000 -1540 250 -217 10000 945 -10000 -953 500 -193 7500 794 -7500 -801 750 -170 5000 638 -5000 -645 1000 -150 4000 577 -4000 -582 2000 -48.1 3000 514 -3000 -519 3000 110 2000 451 -2000 -455 4000 266 1000 386 -1000 -391 5000 400 750 371 -750 -375 7500 660 500 355 -500 -358 10000 856 400 347 -400 -351 20000 1480 300 341 -300 -345 30000 2060 200 335 -200 -338 40000 2670 100 327 -100 -330 50000 3350 75 325 -75 -329 55000 3740 50 323 -50 -327 40 322 -40 -325 30 321 -30 -324 20 318 -20 -322 10 312 -10 -315 0 303 0 -307 -10 294 10 -298 -20 286 20 -289 -30 280 30 -283 -40 275 40 -279 -50 272 50 -275 -75 265 75 -269 -100 260 100 -264 -200 247 200 -252 -300 237 300 -243 -400 226 400 -234 -500 216 500 -225 -750 191 750 -202 * Abbreviation for magnetization. Continued on the next page. 311 Continued. Magnetization data for hysteresis run for Co(HCONH 2 ) 2 (HCOO) 2 (Continued) Field up (G) Mag.* Field down (G) Mag. Field up (G) Mag. -1000 170 1000 -175 -2000 48.0 2000 -45.5 -3000 -122 3000 127 -4000 -282 4000 288 -5000 -419 5000 427 -7500 -685 7500 695 -10000 -886 10000 896 -20000 -1530 20000 1540 -30000 -2110 30000 2120 -40000 -2709 40000 2720 -50000 -3370 50000 3380 -55000 -3750 55000 3750 Magnetic data collected at 50, 000 G for Co(HCONH 2 ) 2 (HCOO) 2 (SQUID) Temp. XM Meff Temp. XM u e f f Temp. XM M-eff 2.00 66.6 1.03 19.0 68.9 3.24 140 20.5 4.79 3.00 66.7 1.27 20.0 67.5 3.29 145 19.4 4.83 4.00 67.3 1.47 22.0 64.6 3.37 160 18.4 4.85 5.00 68.5 1.65 25.0 60.7 3.48 170 17.4 4.87 6.00 70.7 1.84 30.0 55.2 3.64 180 16.6 4.88 7.00 74.3 2.04 35.0 50.8 3.77 190 15.8 4.90 7.99 78.8 2.24 40.0 47.1 3.88 200 15.1 4.91 8.99 81.5 2.42 45.0 43.9 3.98 210 14.5 4.93 9.99 82.1 2.56 50.0 41.2 4.06 220 13.9 4.95 11.0 81.2 2.67 60.0 36.8 4.20 230 13.4 4.97 12.0 80.0 2.77 70.0 33.4 4.32 240 13.0 4.99 13.0 78.5 2.86 80.0 30.5 4.42 250 12.5 5.01 14.0 77.0 2.94 90.0 28.2 4.51 260 12.1 5.02 15.0 75.4 3.01 100 26.2 4.58 270 11.7 5.03 16.0 73.7 3.07 110 24.5 4.64 280 11.4 5.04 17.0 72.1 3.13 120 23.1 4.71 290 11.0 5.06 18.0 70.4 3.18 130 21.7 4.75 300 10.7 5.07 312 

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