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The synthesis and characterization of copper(II) phosphinate coordination polymers Oliver, Katherine Wells 1984

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THE SYNTHESIS AND CHARACTERIZATION OF COPPER(II) PHOSPHINATE COORDINATION POLYMERS by KATHERINE WELLS OLIVER B.Sc, The University of B r i t i s h Columbia, 1978 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES Department of Chemistry We accept this thesis as conforming to the required standard The University of B r i t i s h Columbia July, 1984 © Katherine Wells O l i v e r , 1984 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements fo r an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I further agree that permission f o r extensive copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or p u b l i c a t i o n of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of _>(YV\STR>f The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 >E-6 (3/81) i i Abstract. A number of disu b s t i t u t e d and monosubstituted copper(II) phosphi-nate coordination polymers, {Cu[R 2P0 2]2^ x a n ^ {Cu[R(H)P0 2l2) x» r e s p e c t i -vely, where R i s an a l k y l or a phenyl group, has been prepared and characterized. The p h y s i c a l , e l e c t r o n i c and magnetic properties of these systems were investigated using physical methods such as thermal ana l y s i s , v i b r a t i o n a l and e l e c t r o n i c spectroscopy, and magnetic suscep-t i b i l i t y measurements. The e f f e c t that the d i f f e r e n t substituents on phosphorus had on the structures and the properties was examined. The p o s s i b i l i t y of magnetic exchange propagated through the three-atom O-P-0 bridge made the i n v e s t i g a t i o n of magneto-structural co r r e l a t i o n s of p a r t i c u l a r i n t e r e s t . The series of compounds containing s t r a i g h t chain a l k y l groups, of one to twelve carbon atoms, were found to e x i s t i n two forms, l a b e l l e d a and |3; i n some cases, derivatives were i s o l a t e d i n both forms. X-ray crystallography showed that the structures of both forms consisted of i n f i n i t e l i n e a r chains of eight—membered rings, formed by two copper atoms i n fla t t e n e d tetrahedral environments, joined by two bridging phosphinate ligands. The s t r u c t u r a l differences between the two isomers were associated with d i f f e r e n t degrees of d i s t o r t i o n of the CuO^ chromophore from regular tetrahedral geometry, and with d i f f e r e n t orientations of the a l k y l groups on phosphorus. These s t r u c t u r a l differences were manifested i n the thermal, spectral and magnetic properties, making the two isomer groups distinguishable on t h i s b a s i s . Magnetic exchange was found i n both forms; the a-isomers exhibited antiferromagnetic exchange with values of the exchange parameter, J , i i i ranging from ca. -1 to -30 cm - 1, while the (3-isomers showed weak f e r r o -magnetism with J approximately +2 cm"*-. This behavior was discussed i n r e l a t i o n to the known s t r u c t u r a l differences between the two forms. The copper(II) phosphinate polymers containing branched chain a l k y l groups were proposed to be l i n e a r polymers, while the diphenyl derivative was postulated to be crosslinked, on the basis of t h e i r properties. S i m i l a r l y , the monosubstituted compounds were proposed to be crosslinked. A l l -these derivatives probably contain four-coordinate copper(II) atoms, from a consideration of the v i b r a t i o n a l and e l e c t r o n i c spectra, with degrees of d i s t o r t i o n from regular tetrahedral geometry s i m i l a r to that found i n the di-n-alkylphosphinates. The exception to this was the diphenyl compound, which was postulated to have a more flattened' CuC^ chromophore than the l a t t e r d e r i v a t i v e s . This unique structure was suggested to a r i s e as a r e s u l t of the s t e r i c requirements of the bulky phenyl substituents and the e f f e c t of this on the crosslinked structure. No evidence for or against magnetic exchange was found i n these compounds over the temperature range studied. i v Table of Contents. Page Abstract i i Table of Contents i v L i s t of Tables v i i i L i s t of Figures ' x L i s t of Abbreviations and Symbols x i i Acknowledgements x i i i Chapter 1 Introduction 1 1.1 Phosphinate Coordination Polymers 1 1.2 Methods of Characterization 7 1.2.1 Physical Characterization: S o l u b i l i t i e s and Thermal Analysis 7 1.2.2 Infrared Spectroscopy 13 1.2.3 E l e c t r o n i c Spectroscopy 24 1.2.4 Magnetic S u s c e p t i b i l i t y 28 1.2.5 X-ray Crystallography 33 1.2.6 Proposed Structures of Some Divalent F i r s t 39 Row T r a n s i t i o n Metal Phosphinates Chapter 2 Results and Discussion 42 2.1 Diorganophosphinate Derivatives, [Cu(R 2P0 2) 21 X, 42 Containing Straight Chain A l k y l Groups 2.1.1 Introduction 42 2.1.2 C r y s t a l and Molecular Structures of C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 and C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 42 2.1.3 Synthesis, S o l u b i l i t i e s and Thermal Properties 55 2.1.4 Infrared Spectra 79 2.1.5 E l e c t r o n i c Spectra 97 V Table of Contents, (contd) Page 2.1.6 Magnetic Properties 112 2.2 Diorganophosphinate Derivatives, [Cu(R 2P0 2)2 l x » Containing Branched Chain A l k y l Groups or Phenyl Groups 2.2.1 Introduction 141 2.2.2 Synthesis, S o l u b i l i t i e s and Thermal 141 Properties 2.2.3 Infrared Spectra 149 2.2.4 E l e c t r o n i c Spectra 157 2.2.5 Magnetic Properties 162 2.3 Monoorganophosphinate Derivatives, [Cu(R(H)P0 2) 2] x» 163 Containing Straight Chain, A l k y l Groups or Phenyl Groups 2.3.1 Introduction 163 2.3.2 Synthesis, S o l u b i l i t i e s and Thermal 163 Properties 2.3.3 Infrared Spectra 168 2.3.4 E l e c t r o n i c Spectra 177 2.3.5 Magnetic Properties 178 Chapter 3 Summary, Conclusions and Suggestions for Further Work 180 Chapter 4 Experimental 184 4.1 Methods of Characterization 184 4.1.1 Elemental Analysis 184 4.1.2 Thermal Studies 184 4.1.3 Infrared Spectroscopy 184 4.1.4 E l e c t r o n i c Spectroscopy 184 4.1.5 Magnetic S u s c e p t i b i l i t y Measurements 185 4.1.6 X-ray Crystallography 186 v i Table of Contents, (contd) Page 4.2 Synthesis of Phosphinic Acids 187 4.2.1 Introduction 187 4.2.2 Materials 188 4.2.3 Dimethylphosphinic Acid, (CH^PO^H 190 4.2.4 Diethylphosphinic Acid, (C 2H 5) 2P0 2H 195 4.2.5 Di-n-butylphosphinic Acid, (n-C^Hg) 2P0 2H 197 4.2.6 Di-n-octylphosphinic Acid, ( n - C 8 _ 1 7 ) 2 P 0 2 H 199 4.2.7 Di-n-hexylphosphinic Acid, (n-C 6H 1 3) 2P0 2H 201 4.2.8 Di-n-decylphosphinic Acid, (n-C l f JH 2 1) 2P0 2H 203 4.2.9 Di-n-dodecylphosphinic Acid, ( n - C 1 2 H 2 5 ) 2 P 0 2 H 204 4.2.10 Di-i-propylphosphinic Acid, ( i - C 3 _ 7 ) 2 P 0 2 H 205 4.2.11 Di-t-butylphosphinic Acid, (t-C^Hg) 2P0 2H 207 4.3 Synthesis of Copper(II) Phosphinate Polymers 210 4.3.1 Introduction 210 4.3.2 Materials 211 4.3.3 Copper(II) Dimethylphosphinate, 212 C u [ ( C H 3 ) 2 P 0 2 ] 2 4.3.4 Copper(II) Diethylphosphinate, 216 C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 4.3.5 Copper(II) Di-n-butylphosphinate, 218 Cu[(n-C l tH 9) 2P0 2] 2 4.3.6 Copper(II) Di-n-hexylphosphinate, 219 C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 4.3.7 a-Forms of the n-o c t y l , n-decyl and 220 n-dodecyl Derivatives 4.3.7.1 a-Copper(II) Di-n-octylphosphinate, 221 a - C u [ ( n - C 8 H 1 7 ) 2 P 0 2 ] 2 Table of Contents* (contd) 4.3.7.2 a-Copper(II) Di-n-decylphosphinate, a - C u [ ( n - C 1 0 H 2 1 ) 2 P O 2 ] 2 4.3.7.3 ot-Copper(II) Di-n-dodecylphosphinate, a-Cu [ ( n-C x2H 2 5 ) 2P0 2 ] 2 4.3.8 8-Forms of the n- o c t y l , n-decyl and n-dodecyl Derivatives 4.3.8.1 p-Copper(II) Di-n-octylphosphinate, 8 - C u [ ( n - C 8 H 1 7 ) 2 P 0 2 ] 2 4.3.8.2 B-Copper(II) Di-n-decylphosphinate, 8 - C u [ ( n - C 1 0 H 2 1 ) 2 P O 2 ] 2 4.3.8.3 B-Copper(II) Di-n-dodecylphosphinate, 8 - C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 4.3.9 Copper(II) Di-i-propylphosphinate, C u [ ( i - C 3 H 7 ) 2 P 0 2 ] 2 4.3.10 Copper(II) Di-t-butylphosphinate, C u [ ( t - C l f H 9 ) 2 P 0 2 ] 2 4.3.11 Copper(II) Diphenylphosphinate, C u [ ( C 6 H 5 ) 2 P 0 2 ] 2 4.3.12 Copper(II) Mono-n-hexylphosphinate, C u [ ( n - C 6 H 1 3 ) ( H ) P 0 2 ] 2 4.3.13 Copper(II) Mono-n-decylphosphinate, C u [ ( n - C 1 0 H 2 1 ) ( H ) P O 2 ] 2 4.3.14 Copper(II) Monophenylphosphinate, C u [ ( C 6 H 5 ) ( H ) P 0 2 ] 2 References Appendices Appendix 1. Complete S t r u c t u r a l Parameters for cc-Cu[(C 2H 5) 2P0 2] 2 and B-Cu[(n-C 6H 1 3) 2P0 2] 2 Appendix 2. Unassigned Infrared Absorptions Appendix 3. Magnetic S u s c e p t i b i l i t y Data v i i i L i s t of Tables. Page 2.1.2.1 Crystallographic Data for Copper(II) D i e t h y l - and 45 Di-n-hexylphosphinate 2.1.2.2 Selected Bond Lengths 47 2.1.2.3 Selected Bond Angles 48 2.1.2.4 Interannular Torsion Angles 50 2.1.3.1 S o l u b i l i t i e s of Copper(II) Di-n-alkylphosphinates 58 2.1.3.2 D.S.C. Studies on Copper(II) Di-n-alkylphosphinates 62 2.1.4.1 Infrared Bands Associated with P-0 Stretching 80 2.1.4.2 Infrared Bands Associated with Cu-0 Stretching 89 2.1.4.3 Infrared Bands Associated with P-C Stretching 92 2.1.4.4 Infrared Bands i n the 600 cm"1 - 400 cm - 1 Region 95 2.1.5.1 E l e c t r o n i c Spectra of Copper(II) D i - n - a l k y l - 98 phosphinates 2.1.5.2 Possible Assignments for the E l e c t r o n i c "Spectrum of 104 C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 a n d C a l c u l a t i o n of the Cry s t a l F i e l d Parameters 2.1.5.3 Calculated and Observed T r a n s i t i o n Energies for 110 P-Cu[(n-C HH 9) 2P0 2] 2 and p - C u [ ( n - C 6 _ 1 3 ) 2 P 0 2 ] 2 : Dq = 1665 cm-* and Cp = 1800 cm"1 2.1.6.1 Magnetic Parameters 117 2.2.2.1 S o l u b i l i t i e s of Copper(II) D i - i - p r o p y l - , D i - t - b u t y l - , 142 and Diphenylphosphinate 2.2.3.1 Infrared Bands Associated with P-0 Stretching 150 2.2.3.2 Infrared Bands Associated with Cu-0 Stretching 152 2.2.3.3 Infrared Bands Associated with P-C Stretching 154 2.2.3.4 Infrared Bands Associated with C 2P0 2 Bending 155 2.2.3.5 Infrared Bands Associated with the Internal 156 Vibrations of the i-Pr o p y l , t-Butyl, and Phenyl Groups ix L i s t of Tables, (contd) Page 2.2.4.1 E l e c t r o n i c Spectra of Copper(II) D i - i - p r o p y l - , 158 D i - t - b u t y l - , and Diphenylphosphinate 2.2.5.1 Magnetic Moments at ca. 300K and 80K 163 2.3.2.1 D.S.C. Studies on Copper(II) Monosubstituted 167 Phosphinates 2.3.3.1 Infrared Bands Associated with P-0 Stretching 171 2.3.3.2 Infrared Bands Associated with Cu-0 Stretching 174 2.3.3.3 Infrared Bands Associated with P-H Stretching 174 2.3.3.4 Infrared Bands Associated with P-C Stretching 174 2.3.3.5 Infrared Bands Associated with (C)(H)P0 2 Bending 176 2.3.3.6 Infrared Bands Associated with the Internal 176 Vibrations of the Phenyl Group i n Cu[(C gH 5)(H)-P O 2 ] 2 2.3.4.1 E l e c t r o n i c Spectra of Copper(II) Monosubstituted * 177 • Phosphinates 2.3.5.1 Magnetic Moments at ca. 300K and 80K 179 4.2.2.1 Reagents, P u r i t i e s and Suppliers 189 X L i s t of Figures. Page 1.2.2.1 R 2P0 2~ Bonding Modes and Possible Polymer 18 Structures 1.2.5.1 Structures of Some Metal(II) Phosphinates 35 2.1.2.1 Polymeric Structures of C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 and 43 C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 2.1.2.2 Atom numbering and coordination around copper 46 for C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 and C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 2.1.2.3 Chain Packing i n C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 53 2.1.2.4 Chain Packing i n C u [ ( n - C g H 1 3 ) 2 P 0 2 ] 2 54 2.1.3.1 Thermograms of the a- and 6-isomers 67 2.1.3.2 Thermal Behavior of the Methyl, E t h y l , n-Butyl, 71 and n-Hexyl Derivatives 2.1.3.3 Thermal Behavior of C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 74 2.1.3.4 Polymorphism i n C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 7 6 2.1.4.1 Infrared Spectra of a) a - C u [ ( C 2 H 5 ) 2 P ° 2 ] 2 and 84 b) B - C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 2.1.4.2 Infrared Spectrum of o-Cu[(CH 3) 2P0 2] 2 86 2.1.4.3 Infrared Spectra of the a- and p-forms of 93 C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 2.1.5.1 E l e c t r o n i c Spectra of C u [ ( n - C 1 Q H 2 1 ) 2 P 0 2 ] 2 99 2.1.5.2 The D i s t o r t i o n Angle a 102 2.1.5.3 Energy Level Diagram for Dq = 1665 cm - 1 and 109 Dq = 1800 cm - 1 2.1.6.1 I l l u s t r a t i o n of the Estimated Accuracy of J (± 10%) 119 2.1.6.2 I l l u s t r a t i o n of the Estimated Accuracy of g (± 2%) 120 2.1.6.3 Magnetic Moments Versus Temperature for 121 a) oe-Cu[(CH3) 2P0 2] 2 and b) a-Cu[ (C 2H 5) 2P0 2] 2 x i L i s t of Figures, (contd) 2.1.6.4 Magnetic Moments Versus Temperature for a - C u [ ( n - C 8 H 1 7 ) 2 P 0 2 ] 2 2.1.6.5 Magnetic Moments Versus Temperature for a - C u [ ( n - C 1 Q H 2 1 ) 2 P 0 2 ] 2 2.1.6.6 Magnetic Moments Versus Temperature for a) a ' - C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 and b) a - C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 2.1.6.7 Magnetic Moments Versus Temperature for a) B-CutCn-C^Hg) 2P0 2] 2 and b) B - C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 2.1.6.8 Magnetic Moments Versus Temperature for a) p - C u [ ( n - C 8 H 1 7 ) 2 P 0 2 ] 2 and b) B - C u [ ( n - C 1 0 H 2 1 ) 2 P O 2 ] 2 2.1.6.9 Magnetic Moments Versus Temperature for B - C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 2 . 1 . 6 . 1 0 Magnetic S u s c e p t i b i l i t y Versus Temperature for a - C u [ ( n - C 8 H 1 7 ) 2 P 0 2 ] 2 2 . 1 . 6 . 1 1 Magnetic S u s c e p t i b i l i t y Versus Temperature for a - C u [ ( n - C 1 0 H 2 1 ) 2 P O 2 ] 2 2 . 1 . 6 . 1 2 Magnetic S u s c e p t i b i l i t y Versus Temperature for a - C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 2.2.2.1 D.S.C. Curve of C u [ ( i - C 3 H 7 ) 2 P 0 2 ] 2 2.2.2.2 D.S.C. Curves of a) C u [ ( C g H 5 ) 2 P 0 2 ] 2 and b) C u [ ( t - C l t H 9 ) 2 P 0 2 ] 2 2.2.3.1 Infrared Spectra of a) C u [ ( i - C 3 H 7 ) 2 P 0 2 ] 2 and b) C u [ ( C 6 H 5 ) 2 P 0 2 ] 2 2.2.4.1 E l e c t r o n i c Spectrum of C u [ ( C 6 H 5 ) 2 P 0 2 ] 2 2.3.2.1 Thermograms of the Copper(II) Monoalkyl-phosphinates 2.3.2*2 Thermograms of Copper(II) Monophenylphosphinate 2.3.3.1 Infrared Spectrum of C u [ ( n - C 1 0 H 2 1 ) ( H ) P 0 2 ] 2 x i i L i s t of Abbreviations and Symbols. Anal, c a l c d . : Analysis calculated cm - 1 nm : r e c i p r o c a l centimeter : nanometer l i t . R.T. m.p. : l i t e r a t u r e : room temperature; T, temperature : melting point i n t Et Me is o : normal t e r t i a r y ethyl : methyl B.M. g k N Bohr magneton, ((3) : Lande" s p l i t t i n g factor Boltzmann constant Avogadro's number gram s u s c e p t i b i l i t y molar s u s c e p t i b i l i t y \ wavelength A o c t frequency d - o r b i t a l s p l i t t i n g i n a tetrahedral d - o r b i t a l s p l i t t i n g i n an octahedral f i e l d f i e l d Throughout t h i s thesis C u [ ( R ) 2 P 0 2 ] 2 l f l used, for convenience, instead of {Cu[(R) 2P0 2] 2}„. No s t r u c t u r a l implications are intended. x i i i Acknowledgements. I would l i k e to express my sincerest thanks to my supervisor, Dr. R.C. Thompson, for the support, guidance, and understanding he provided during the course of t h i s work. I am extremely g r a t e f u l to J.S. Haynes, for running many of my samples on the magnetometer, and for assistance with the rest; and to D.H. Jones, for his invaluable help with the computer f i t t i n g of the magnetic data. I am indebted to Dr. S.J. Rettig for the extra e f f o r t he put into the determination of the two c r y s t a l structures i n this work, without which many questions would have remained unanswered. Many thanks go to the s t a f f , f a c u l t y and graduate students of the Department for the i r help, discussions and good humor, which made the work enjoyable. I am indebted to the U.B.C. Graduate Scholarship Committee and NSERC for scholarship awards. F i n a l l y , I would l i k e to thank T i l l y Schreinders for her expert preparation of this manuscript. - 1 -CHAPTER 1 INTRODUCTION 1.1 Phosphinate Coordination Polymers. There Is a long and r i c h h i s t o r y of chemistry involving phos--(x-1) phorus containing ligands of the type, PO . The side group G can be hydrogen, a halide, or any of a wide v a r i e t y of organic groups, such as an a l k y l or alkoxy group. The int e r a c t i o n s of these ligands with metals ranging from sodium to thorium have been studied. The compounds prepared have u t i l i z e d neutral donor ligands such as the phosphine oxides, R3PO, (R i s an a l k y l or a r y l group, or a halide) (1-8), f i r s t incorporated i n a metal complex i n 1861 (9), and the phosphoryl esters, (RO)3PO or (RO)-,_x(R)xPO (9-11). Anionic ligands have included the monoacidic phosphates, (RO) 2P0 2~, and phosphonates, (RO)(R)P0 2~, (9,12-17); the phosphinates R 2P0 2~, R(H)P0 2~, and X 2P0 2~ (X i s F, CI or Br), and the hypophosphite anion, H 2P0 2~ (18-27). D i a c i d i c and t r i a c i d i c ligands such as RP0 3 2~ and P0 4 3~, res p e c t i v e l y , have also been investigated (28-34). Changes i n the atom that coordinates to the metal, from oxygen to, for example, s u l f u r , selenium, or nitrogen (9,21,23,35,36), further expand the range of phosphorus containing ligands. Of primary i n t e r e s t to us i n t h i s work are the phosphinate ligands which, i n t h e i r a b i l i t y to form inorganic coordination polymers (37), have received much attention i n recent years. The f i r s t metal phosphinate compounds were reported i n the l a t e 1800's (38), but t h e i r polymeric nature was not confirmed u n t i l 1959, - 2 -when preliminary v i s c o s i t y data for UC^Un-C^Hg) 2P0 2] 2 were published (39). Since that time research has been l a r g e l y directed to the forma-t i o n of thermally stable polymers with p l a s t i c properties, that would, hopefully, be of some commercial, p r a c t i c a l use. The phosphinate ligands thought most l i k e l y to accomplish t h i s goal were the d i s u b s t i t u -ted d e r i v a t i v e s , containing a r y l or a l k y l groups (or a mixture, i . e . , RR'P02~) (20). There are several reasons for this choice; i ) the three atom bridge i s considered to have p o t e n t i a l i n the formation of f l e x i b l e polymers, i i ) the donor atoms are oxygen, r e s u l t i n g i n greater oxidative s t a b i l i t y than i f they were, for example, su l f u r (21) and there are only two donor atoms per bridge to prevent branching, i i i ) the phosphorus atom i s protected from chemical attack by the organic side groups, which also give-the best h y d r o l y t i c s t a b i l i t y , and i v ) the charge i s -1, permitting the ready design of neutral chains. The modifications i n the polymeric properties of these materials (such as the amount of cross-l i n k i n g present, the c r y s t a l l i n i t y , the glass t r a n s i t i o n , melting and decomposition temperatures, the v i s c o s i t y , t e n s i l e strength, percent elongation, s o l u b i l i t i e s and molecular weights (40,41)) with changing the substituents on phosphorus and with d i f f e r e n t metals, have been the main focus of much of the research (19,20,22,42-64). At the same time, c h a r a c t e r i z a t i o n of these compounds, aimed at c l a s s i f y i n g them by s t r u c t u r a l type and r e l a t i n g these structures to the R groups on phosphorus, was ongoing (18,21,56,65-68). The knowledge of the structures was expected to aid i n the explanation of the polymeric properties, and to enable researchers to design and synthesize polymers with good p l a s t i c properties and thermal s t a b i l i t y , by the ju d i c i o u s - 3 -choice of the metal and of the phosphinate ligand. By the very nature of the materials, s t r u c t u r a l c h a r a c t e r i z a t i o n has been primarily accom-plished by i n d i r e c t methods such as thermal analysis, s o l u b i l i t i e s , s p e ctral techniques ( v i b r a t i o n a l and e l e c t r o n i c ) and at times, magnetic s u s c e p t i b i l i t y measurements (65-71). However, i n some cases single c r y s t a l s were obtained (usually with considerable d i f f i c u l t y ) (53,55,72-74). The r e s u l t s of the X-ray s t r u c t u r a l determinations, together with data gathered from X-ray f i b e r and powder photographs (47,53-55,65,67, 68,75,76), have helped to c l a r i f y the r e l a t i o n s h i p of the substituents on phosphorus to the polymer structure for a number of z i n c ( I I ) , c o b a l t ( I I ) and beryllium(II) phosphinates. Two d i s t i n c t polymer s t r u c -tures were found, both inv o l v i n g tetrahedral metal centers and symmetric phosphinate bridging, but having metals joined by ei t h e r double or a l t e r n a t i n g s i n g l e - t r i p l e b r i d g e s 1 . The f l e x i b i l i t y of the compounds has been at t r i b u t e d to the f l e x i b i l i t y inherent i n the eight-membered rin g of the backbone (46) or to the presence of the s i n g l e , u n r e s t r i c t e d bridge between t r i p l e bridged units (72). This f l e x i b i l i t y can then be moderated through the choice of the R groups (refer to Section 1.2.1). Research involving metal compounds of the phosphates, (RO^PO^ -* and phosphonates, (RO)(R)P0 2~, rather than focussing on t h e i r polyme-r i c p r o p e r t i e s 2 , has been directed towards i d e n t i f y i n g i n t e r e s t i n g s p e c t r a l and magnetic properties a r i s i n g from the presence of a metal i n See Section 1.1.5 for a complete discussion of the structures. They are not proposed to be of p o t e n t i a l commercial use; the presence of RO groups leads to reduced thermal and oxidative s t a b i l i t y . - 4 -the backbone of these inorganic polymers (9,12-17). Subnormal room temperature magnetic moments have been found (9) for complexes contain-ing a wide var i e t y of metals and t h i s phenomenon i s explained as being due to superexchange v i a the O-P-0 bridging u n i t s . The presence or absence of magnetic exchange i n these compounds has been related to the nature of the substituents on phosphorus, as have some of the characte-r i s t i c i n f r a r e d stretching frequencies (see Section 1.2.2). Recently, the d i r e c t i o n of the research on phosphinate polymers has s h i f t e d i n t h i s d i r e c t i o n , towards the recognition of these compounds as i n t e r e s t i n g t r a n s i t i o n metal coordination complexes i n the c l a s s i c a l sense. The awakened i n t e r e s t i n the microscopic, rather than the macroscopic, properties of the phosphinates containing magnetic centers has resulted i n an i n v e s t i g a t i o n of the p o s s i b i l i t y of magnetic exchange ef f e c t s In these materials using techniques such as 3 1 P N.M.R. (73), E.S.R., s p e c i f i c heat, and variable temperature magnetic s u s c e p t i b i l i t y measurements (78-85). In addition, Mikulski et_ a l . (18,86,87) have p a r t i a l l y characterized a large number of methylphenylphosphinates, u t i l i z i n g i n f r a r e d spectroscopy and room temperature magnetic moments. However, the number of compounds that have been completely c h a r a c t e r i -zed, including analysis of the physical properties, i n f r a r e d spectra, e l e c t r o n i c spectra and p a r t i c u l a r l y , v ariable temperature magnetic measurements, i s r e l a t i v e l y small. For example, the variable temperatu-re work of Scott and coworkers (78-84), has been directed p r i n c i p a l l y to the chromium trisphosphinates, C r [ ( C H 3 ) ( C 6 H 5 ) P 0 2 ] 2 [ ( n - C Q H 1 7 ) 2 P 0 2 ] and C r [ ( C H 3 ) ( C 6 H 5 ) P 0 2 ] 2 ( 0 H ) , and to C o [ ( C H 3 ) ( C 6 H 5 ) P 0 2 ] 2 . Examinations of - 5 -M [ R 2P0 2] 2 complexes, where M(II) = Mn, Fe, Co, Ni or Cu, and R i s a v a r i e t y of a l k y l and/or a r y l groups (78,80), yielded some evidence for magnetic exchange; however, the low temperature data have not been f u l l y analyzed. I t was t h i s dearth of f u l l c h aracterization that prompted our own group to undertake the i n v e s t i g a t i o n of phosphinate compounds, with the aim of discovering possible c o r r e l a t i o n s between the substituents on phosphorus and the p h y s i c a l , s t r u c t u r a l , e l e c t r o n i c , and magnetic properties of the coordination polymers. A better understanding of the microscopic properties, i t was f e l t , might be of value i n explaining some of the unique c h a r a c t e r i s t i c s of these compounds, for example, the a n t i s t a t i c properties of some chromium(III) phosphinates (20,63). The copper(II) phosphinates reported i n the present work were s p e c i f i c a l l y investigated for several reasons. R e l a t i v e l y few of these compounds have been prepared (18,38,66-68,88), and characterization has been extremely cursory, usually involving only the l i s t i n g of P0 2 stretching frequencies, absorptions i n the e l e c t r o n i c spectra and, perhaps, a room temperature magnetic moment. For the d i - n - o c t y l d e r i v a -t i v e (66), these data are interpreted as being "consistent with a v a r i e -ty of structures including square planar, d i s t o r t e d octahedral, and eight-coordinate". The d i - t - b u t y l compound (67) was proposed to contain d i s t o r t e d tetrahedral metal centers, with c r o s s l i n k i n g phosphinate bridges, on the basis of i t s i n s o l u b i l i t y and isomorphism with the analogous cobalt(II) and z i n c ( I I ) polymers. I n i t i a l l y , the di-n-butyl derivative was proposed to have the same structure as the d i - n - o c t y l complex. However, a c r y s t a l structure determination (89) proved that the di-n-butylphosphinate contained d i s t o r t e d tetrahedral copper atoms - 6 -and symmetric, double bridging phosphinate groups 1. The lack of understanding of these compounds on a molecular l e v e l (for example, the coordination number and geometry of the metal and the nature and extent of the phosphinate bridging) prompted us to undertake the synthesis and more complete characterization of a range of copper(II) diorganophos-phinates 2, containing straight chain a l k y l , branched a l k y l and phenyl substituents on phosphorus, as well as some monosubstituted phosphina-tes. It was hoped that c o r r e l a t i o n s could be made between, as mentioned e a r l i e r , the substituents on phosphorus and the properties (p h y s i c a l , spectral and magnetic) of the compounds. Given the p o s s i b i l i t y of magnetic exchange through the three atom O-P-0 bridge, already shown to ex i s t for some chromium(III) and cobalt ( I I ) phosphinates (83,85), we were p a r t i c u l a r l y interested i n e s t a b l i s h i n g magneto-structural corre-l a t i o n s . Copper(II) was then a good candidate for t h i s ; the magnetic behaviour i s s i m p l i f i e d because the d 9 configuration r e s u l t s i n only one unpaired e l e c t r o n 3 , and copper i s known to exhibit magnetic exchange i n many compounds, involving a wide v a r i e t y of ligands (see, for example, references 90-93). From the examination of a seri e s of r e l a t e d compounds we hoped to e s t a b l i s h the means by which we could, perhaps, be able to predict the magnetic properties expected i n an as-yet-unsynthe-size d compound, and, hence, control the magnitude and sign of the Refer to Section 2.1.2. This necessarily involved the preparation of a number of phosphinic acids, which were either p r o h i b i t i v e l y expensive or not commercially a v a i l a b l e . These syntheses are described i n Chapter 4. 3 Refer to Section 1.2.4. - 7 -exchange, a so-called "tunable exchange" (94). This goal has been accomplished to some extent, and a discussion of the res u l t s of t h i s work i s to be found i n Chapter 2, where the compounds discussed have been grouped into three sections, depending on the substituents on phosphorus. With the above b r i e f introduction to the topic, i t may be opportune to comment on the contents of the remainder of Chapter 1. The discussion under Section 1.2, Methods of Characterization, focuses on the techniques used i n t h i s work; the information a v a i l a b l e from them, how they have been u t i l i z e d i n the study of phosphinate compounds i n the past, and/or t h e i r a p p l i c a b i l i t y to the study of the copper(II) com-pounds. This Chapter then ends with a summary of the structures proposed previously for some divalent f i r s t row t r a n s i t i o n metal phos-phinates, on the basis of the information garnered from these charac-t e r i z a t i o n methods. 1.2 Methods of Characterization. 1.2.1 Physical Characterization; S o l u b i l i t i e s and Thermal Ana l y s i s . S o l u b i l i t y studies and thermal analysis ( d i f f e r e n t i a l scanning calorimetry (D.S.C.) or thermogravimetric analysis (T.G.A.)) have been used widely i n the study of metal phosphinate polymers to help charac-t e r i z e the systems under i n v e s t i g a t i o n , and i d e n t i f y the e f f e c t s that d i f f e r e n t R groups have on the physical properties. The s o l u b i l i t i e s i n non-coordinating solvents have been used extensively (22,48,49,52-54,56, - 8 -61,66-68,95) to draw conclusions about the nature of the polymer, that i s , whether i t i s predominantly a l i n e a r polymer, expected to be soluble i n such solvents, or a crosslinked polymer, expected to be insoluble i n non-coordinating solvents but to gel In aromatic solvents such as toluene and chlorobenzene (66,96). On t h i s basis then, for example, the zinc(II) and cobalt ( I I ) di-l-methylbutylphosphinates (67) are proposed to be l i n e a r polymers, while the d i - t - b u t y l and diphenyl analogues are crosslinked. S i m i l a r l y , a wide v a r i e t y of aluminum trisphosphinates (52) are thought to be e s s e n t i a l l y l i n e a r , with perhaps a small amount of c r o s s l i n k i n g but less than i s found i n the chromium(III) hydroxo-bridged bisphosphinates, Cr[RR'P0 2] 2(0H) where R = methyl and R' = phenyl or R = R' = n-octyl (61). In addition, the e f f e c t s on polymer s o l u b i l i t y of changing the R groups on phosphorus have been investigated (20,48,49,55), with the emphasis being, pri m a r i l y , on developing more tractable polymers. Reductions i n c r y s t a l l i n i t y as a r e s u l t of introducing randomness into the polymer, either through the use of "mixed" phosphinate ligands (22) ( i . e . , two d i f f e r e n t R groups per phosphorus) or through copolymeriza-t i o n (the use of two or more d i f f e r e n t phosphinate ligands) has been found (20,49,55) to produce more soluble polymers 1. For example, i n the copolymers, M [ ( n - C 4 H g ) 2 P 0 2 ] 2 _ x [ ( C 6 H 5 ) 2 P 0 2 ] x , where M = Zn(II) or Co(II) (55), decreasing the proportion of the diphenylphosphinate present increases the s o l u b i l i t y , so that copolymers richer i n d i - n -That i s , more soluble i n common organic (non-coordinating) solvents. - 9 -butylphosphinate have the same s o l u b i l i t i e s as the homopolymers, M [ ( n - C 4 H 9 ) 2 P 0 2 ] 2 (67). This e f f e c t has also been investigated by T.G.A. (20,22,46,48, 49), which indicates that the reduction i n c r y s t a l l i n i t y r e s u l t s i n polymers that are more f u s i b l e and f l e x i b l e than the corresponding homologs (41). So, for example, while the z i n c ( I I ) and c o b a l t ( I I ) dimethyl- and diphenylphosphinates (48,49) are high melting (the dimethyl derivatives melt at approximately 340°C) or i n f u s i b l e (the diphenyl derivatives are i n f u s i b l e to above 450°C), insoluble polymers, the methylphenylphosphinates are soluble i n benzene and chloroform and soften or melt at 90°C and 210°C, for the zinc and cobalt compounds, re s p e c t i v e l y . The 1:1 hybrid copolymer, Zn[(n-C i tH 9) 2P0 2] [(n-C 8H 1 7) 2P0 2] (46), which remains amorphous i n d e f i n i t e l y a f t e r melting at 150°C, can be fabricated into films and shaped a r t i c l e s that are transparent, very f l e x i b l e and exhibit good leathery recovery. The objects hold t h e i r shape at 100°C and remain f l e x i b l e when immersed i n dry i c e . On the other hand, the amorphous form of zinc di-n-butylphosphinate becomes b r i t t l e at only -40°C and gradually turns c r y s t a l l i n e with standing at room temperature, while the d i - n - o c t y l derivative cannot be obtained i n an amorphous form since i t decomposes before i t melts (46). Of more relevance to our own work i s the use of thermal a n a l y s i s , p a r t i c u l a r l y D.S.C., i n examining the thermal properties of these poly-meric materials and the e f f e c t s , on these properties, of changing the substituents on phosphorus. T.G.A. i s used routinely to determine thermal s t a b i l i t y under varied conditions, e.g., i n nitrogen or moist a i r atmospheres, and under isothermal heating (21,22,48,49,56). Thermal - 10 -s t a b i l i t y has been found (22) to be greatly reduced by the introduction of phosphinates containing long chain a l k y l groups. Hence, chromium tris(methylphenylphosphinate) undergoes i t s major weight l o s s , under nitrogen, at 480°C, but replacing one methylphenyl ligand with a d i - n -hexylphosphinate reduces that temperature to 265°C. This phenomenon has been attributed to the greater ease of oxidation of the longer a l k y l chains (20,22). The thermal s t a b i l i t y of phosphinate polymers, p a r t i c u -l a r l y of some bivalent metal diphenylphosphinates, M ( I I ) [ ( C 6 H 5 ) 2 P 0 2 ] 2 , (for example, the cobalt ( I I ) and z i n c ( I I ) compounds, mentioned e a r l i e r , show i n i t i a l weight loss temperatures of j u s t under 500°C (48,49)), has f u e l l e d much of the i n t e r e s t i n these compounds as p o t e n t i a l l y useful polymers (20). The observed s t a b i l i t y has been at t r i b u t e d p a r t i a l l y (49) to the necessity of breaking two bonds i n order to rupture the polymer backbone of a double bridged structure. After the f i r s t bond has been thermally cleaved, the atoms are s t i l l near the metal and the second bond must be broken, before the f i r s t reforms, to e f f e c t decompo-s i t i o n of the material. In addition, the polymer backbone i s s t a b i l i z e d by the chelation energy (97) imparted by each metal being involved i n two eight-membered rings, so that the polymer may be viewed as an i n t e r -locking chelate system (49). The search for more thermally stable poly-mers then e x p l o i t s t h i s chelation energy 1, i n combination with the choice of a metal that w i l l form f a i r l y i o n i c bonds to the ligand, r e s u l t i n g i n greater thermal s t a b i l i t y (21,98,99). For example, recent work (68) has been directed at the s t a b i l i z a t i o n of the polymer through chelation of the side groups on phosphorus, to the metal. - 11 -D i f f e r e n t i a l scanning calorimetry plays an important role i n Investigating the thermal properties of phosphinate polymers, y i e l d i n g information on the r e v e r s i b i l i t y and energies of melting and phase t r a n s i t i o n s , and decomposition patterns and energies (19,21,45,48,49, 53,55,56,65,67,100). Variations i n these properties, for a given metal, with d i f f e r e n t substituents on the phosphinate ligand, have been a t t r i -buted p a r t i a l l y to the a b i l i t y of the longer a l k y l chains to s h i e l d the polymer backbone from polar i n t e r c h a i n interactions (22,46,53,55,101) more e f f e c t i v e l y than methyl or phenyl groups (72), thereby causing a reduction i n melting points by decreasing the heat of fusion. (This point i s discussed i n d e t a i l i n Chapter 2.) The shape of the D.S.C. melting curve, that i s , whether a compound exhibits a broad or a sharp melting curve, can be accounted for by the d i s t r i b u t i o n of molecular weights present i n a given sample (102); the narrower the d i s t r i b u t i o n , the sharper the melting point. One of the most i n t e r e s t i n g properties that can be investigated using D.S.C. i s the polymorphism that i s common i n many of the bivalent metal phosphinate polymers (19,48,49,53,55,65-67,74,100). The d i f f e r e n -ces between the forms of a given polymer may be caused by; i ) changes i n the coordination number of the metal (65,67), necessarily implying d i f -ferent modes of coordination of the phosphinate ligand i n the d i f f e r e n t forms, i i ) changes i n the orientations of the organic groups attached to phosphorus (48,49,53,55,67,100), or i i i ) i n some cases, compounds crys-t a l l i z e i n s l i g h t l y d i f f e r e n t ways, y i e l d i n g the same basic polymer structure but d i f f e r e n t unit c e l l s (74). Polymorphism most frequently occurs as a r e s u l t of side group o r i e n t a t i o n changes. One form may generally be converted into another by heating and/or d i s s o l v i n g i n an appropriate solvent, and the conversion may be rev e r s i b l e or i r r e v e r s i -b l e . The n i c k e l ( I I ) d i - n - b u t y l - and di-n-octylphosphinates (67), for example, are i s o l a t e d from the preparative mixture as octahedral com-pounds containing unsymmetrically bridging phosphinate ligands; how-ever, melting (at 218°C and 196°C, res p e c t i v e l y ) i r r e v e r s i b l y converts both to polymers containing tetrahedral metal centers and symmetric phosphinate bridging. Frequently, d i f f e r e n t preparative routes w i l l y i e l d d i f f e r e n t isomers (48,49,65), or a mixture of isomers may be produced from a single synthetic method (55,74). Cobalt(II) methyl-phenylphosphinate (49), when prepared i n ethanol, i s a c r y s t a l l i n e s o l i d ( l a b e l l e d p-Co[(CH 3)(C 6H 5)P0 2] 2 ) , insoluble i n common organic solvents and with a melting point of 210-211°C. With benzene as the preparative solvent, the product i s a second c r y s t a l l i n e form, (Y-Co[(CH 3)(C 6H 5)P0 2] 2), also i n s o l u b l e , but which melts at 226-227°C and has a d i s t i n c t l y d i f f e r e n t X-ray d i f f r a c t i o n pattern than the p-form. Both isomers give the same soluble amorphous form when melted and then cooled, and this conversion i s i r r e v e r s i b l e . The behavior of the zinc analogue (48) i s somewhat more complex. When the synthesis i s ca r r i e d out i n ethanol, the amorphous a-form i s i s o l a t e d . This compound Is soluble i n benzene, s l i g h t l y soluble i n water, insoluble i n other common non-aromatic solvents, and softens at ca. 90°C to a viscous melt. Occasionally, the same preparation, i n ethanol or In benzene, y i e l d s a second form, frequently i n addition to the a-form, that i s insoluble i n water, chloroform and benzene. This form, l a b e l l e d the p-form, i s c r y s t a l l i n e and melts at 209-211°C to give, when cooled, the a-form. - 13 -I n t e r e s t i n g l y , low molecular weight samples of the a-form convert, on standing, to a second c r y s t a l l i n e form, the Y ~ l s o m e r » while the higher molecular weight samples remain amorphous. The Y ~ f o r m I s reconverted to the a-form with melting at 200-205°C. Polymorphism has been encountered i n copper phosphinate polymers (66); the d i - n - o c t y l d e r i v a t i v e i s o l a t e d from so l u t i o n melts at 120°C to y i e l d , upon cooling, a second modification, with a d i f f e r e n t X-ray powder pattern than the f i r s t , which melts at 81°C. This conversion i s i r r e v e r s i b l e . In the course of our work we have found polymorphism i n the copper di-n-alkylphosphinates and the study of the properties of the d i f f e r e n t forms constitutes the major portion of t h i s t h e s i s . 1.2.2 Infrared Spectroscopy. The value of in f r a r e d spectroscopy i n inorganic chemistry has long been recognized for the information It provides (from the numbers and positions of absorptions) about the coordination mode(s) of the ligand, and hence the stereochemistry around the metal, and the strength of the metal-ligand i n t e r a c t i o n (103,104). For ligands with high symmetry i n the non-coordinated ("free") state, i n f r a r e d spectroscopy can, i n some cases, d i s t i n g u i s h between possible coordination modes, for example, monodentate versus bidentate, through the appearance of previously i n f r a r e d inactive bands and/or the s p l i t t i n g of degenerate - 14 -v i b r a t i o n s , due to the lowering of the ligand's symmetry upon coordi-n a t i o n 1 . This applies to tetrahedral ions such as s u l f a t e (105) and perchlorate (106-110) and substituted sulfates ( C ^ v symmetry) of the type XS0 3~, where X = F, CF 3, CH 3 or p-CH3C6H^, the l a t t e r studied extensively by many research groups (111-115), including our own (116-121). With, for example, the s u l f a t e anion, monodentate coordination reduces the symmetry from Tj to C ^ , and bidentate coordination further reduces the symmetry to ^2V* n e n c e these two bonding modes are d i s t i n -guishable on the basis of the number of bands present i n the i n f r a r e d spectrum. This c r i t e r i o n cannot be used to decide between bidentate bridging and bidentate chelation, however, since the symmetry of the anion i s the same (^2V) I Q both cases; here the frequencies of the absorptions become the deciding f a c t o r . I t i s not always as s t r a i g h t -forward as i n the case of s u l f a t e coordination; the i n f r a r e d spectra of complexes of the n i t r a t e ion (105,107,109,110,122) are of less value i n s t r u c t u r a l determination, as both unidentate and bidentate coordination r e s u l t i n a reduction of the anion symmetry from to n e n c e t n e mode of coordination cannot be determined by simply counting the number of bands. The frequencies of the absorptions are not as useful i n d i s -tinguishing between the modes of coordination, since they depend not only on the bonding geometry but also on the strength of the Interaction (104) (that i s , a unidentate ligand strongly coordinated to a metal may Care must be taken, of course, i n i n t e r p r e t i n g these phenomena In s o l i d state spectra, since e f f e c t s such as s i t e symmetry and factor group s p l i t t i n g can r e s u l t i n the appearance of extra bands (103). - 15 -give r i s e to stretching frequencies associated with the non-coordinated N=0 that are lower than those associated with a bidentate N0 3~ group that i s less strongly bound (more I o n i c ) ) . Comparison of the numbers and frequencies of the i n f r a r e d absorp-tions of a ligand i n the "free" state and i n a complex can also y i e l d Information on the degree of coordination, i . e . , non-coordinated, "semi-coordinated" (weak metal-ligand i n t e r a c t i o n and, hence, only s l i g h t perturbation of the free ion symmetry), or coordinated (stronger metal-ligand i n t e r a c t i o n ) (108,110,118). Where a ligand i s coordinated, the strength of the i n t e r a c t i o n has been related to the degree of s p l i t t i n g seen i n the degenerate modes (for example, ClO^ - (109); FS0 3~ (118); EF 6 (E = As or P) (123)). For a ligand which has r e l a t i v e l y low free state symmetry, the infrared spectra of i t s complexes do not generally y i e l d as much s t r u c t u r a l information, since there may be no degenerate modes and, hence, no s p l i t t i n g upon coordination. This i s the case with, for example, carboxylates (RC0 2~) and p-diketonates (O-C(R)-C(R')-C(R")=0~), where the maximum free ion symmetry i s C..^ , and s t r u c t u r a l inferences must come from the p o s i t i o n s , rather than the number, of bands. The i n t e r p r e t a t i o n of i n f r a r e d spectra i s not always as simple or straightforward as described above, although that type of analysis i s invaluable i n systems involving highly symmetric ligands. Generally, factors such as v i b r a t i o n a l coupling between groups In the same molecule ( p a r t i c u l a r l y i n compounds with chelating or bridging ligands, as i n the present case) and the coupling of l a t t i c e modes with i n t e r n a l modes (23, 103,124,125), serve to increase the complexity of a given spectrum so that i n t e r p r e t i o n becomes d i f f i c u l t . The phosphinate ligands considered - 16 -i n t h i s work have a maximum free ion symmetry of for the C 2P0 2 portion of the symmetrically disubstituted species ( i . e . , RRP0 2~), and nine fundamentals are expected (4A^, 1A 2, 26^, 2B 2), none of which are degenerate (23,126,127) and only one of which, the A 2 (torsion) mode, i s in f r a r e d i n a c t i v e . (The a c t i v a t i o n of this l a t t e r mode i s not expected to be of much value i n assigning s t r u c t u r a l d e t a i l as i t appears around 300 cm - 1, and may be masked by metal-oxygen modes, l a t t i c e v i b r a t i o n s and i n t e r n a l ligand v i b r a t i o n s . ) The polymeric nature of these comple-xes, involving double phosphinate bridges between adjacent copper atoms (Section 2.1.2), may be expected to r e s u l t i n s i g n i f i c a n t coupling between the v i b r a t i o n a l modes (23,103,125), i n analogy to, for example, chelating acetylacetonate (124,128-130) or oxalate (131) compounds, for which normal coordinate analysis i s used to a s s i s t i n the assignment. We have adopted the terminology of Nyquist (127) and have, i n the assignment of the spectra, not attempted to separate, for example, the P0 2 and PC 2 bending modes, pr e f e r r i n g to i d e n t i f y the frequency ranges where the C 2P0 2 bending modes occur. On the other hand, we have assigned symmetric and asymmetric stretches for the P-0 and P-C groups, as these modes can be rather r e a d i l y i d e n t i f i e d by comparison to the spectra of the free acid or the sodium s a l t (when avai l a b l e ) and by comparison with l i t e r a t u r e data for a wide range of related phosphorus compounds (7,8,11,16,21,23,26,27,30-32,34,50,56, 65-67,69,71,126,127, 132-146). In some cases, the bands a r i s i n g from the organic groups attached to phosphorus have been assigned; however, these bands are usually very numerous and of l i t t l e diagnostic value, hence no attempt has been made to assign a l l of them i n the present work. - 17 -Although the free anion symmetry i s f a i r l y low, as mentioned, inf r a r e d spectroscopy has proven to be a useful t o o l In the c h a r a c t e r i -zation of the copper(II) phosphinate polymers prepared i n this study. Most in f r a r e d analyses of divalent t r a n s i t i o n metal phosphinates c o n t a i -ning a l k y l substituents on phosphorus have concentrated on the phospho-rus-oxygen symmetric and asymmetric stretching modes (16,23,50,56, 65-67,136,145). This i s not s u r p r i s i n g i f one considers the information available from an examination of the number and frequencies of these absorptions. Coordination through oxygen re s u l t s i n a decrease i n the frequency of the asymmetric P0 2 s t r e t c h and an increase i n the frequency of the symmetric s t r e t c h , when compared to the free anion (the acid or a s a l t (K or Na) of the a c i d 1 ) frequencies, with bidentate coordination causing larger frequency s h i f t s than monodentate coordination (23, 30-32,34,103,126,127,136-138,140,142). This i s comparable to s h i f t s seen i n carboxylic acid C0 2 stretching frequencies upon coordination (149) and, i n analogy to those ligands, attempts have been made (66,67) to correlate the frequency diff e r e n c e between the asymmetric and symmetric stretches, A = v -v (23,136), to the coordination mode asy. sym. ' of the phosphinate and hence to the geometry about the metal. Some of the possible symmetric, unsymmetric and bridging coordination modes are shown i n Figure 1.2.2.1 (66,67). The manner i n which the phosphinate binds w i l l depend on a number of factors such as; i ) the preferred coordination number and stereochemistry of the metal involved, and, i i ) The spectra of i o n i c s a l t s are preferred as intermolecular hydrogen-bonding i n the acids can cause s h i f t s i n v a s y . p 0 2 a i u * vsym. P 02 (136, 140,147,148). - 18 -Figure 1.2.2.1. R 2P0 2~ Bonding Modes and Possible Polymer Structures. Examples of symmetric P 0 2 bonding = o'Pxo M o in A A M M M \ / MM MM III IV Examples of unsymmetric P 0 2 bonding: o'p*o \ M \ / M M C T P N O / / \ M M M VI VII VIII Possible polymer structures1 Symmetric' x°X°x ' NON V N • \ / M-O-P-O-M' No / \ ' C K M X ) " / XI / Un symmetric: c r p v c r p s ' o * o - p XII XIII I x o • O i o vJL "P ' - p I 2P M - 19 -the substituents on phosphorus, which can introduce s t e r i c r e s t r i c t i o n s on the type of phosphinate bonding pos s i b l e . A knowledge of these e f f e c t s , combined with the i n f r a r e d spectra, physical properties such as s o l u b i l i t i e s and thermal properties, and, where possible, e l e c t r o n i c and magnetic data, then forms the basis from which probable structures are assigned, as indicated i n the Introduction to t h i s t h e s i s . Symme-t r i c bonding (each oxygen of the phosphinate bonded to the metal(s) i n an equivalent manner, r e s u l t i n g i n two equivalent PO bonds) of the type I-IV (Figure 1.2.2.1) i s expected to have smaller asymmetric-symmetric stretching frequency separations than unsymmetric bonding (types V-VIII) which involves non-equivalent PO bonds. Structures IX-XI show polymer structures involving symmetric bonding modes with tetrahedral metal c e n t e r s 1 . Structures IX and X are not expected to be d i s t i n g u i s h a b l e on the basis of t h e i r i n f r a r e d spectra as they have very si m i l a r bridging, although there i s the p o s s i b i l i t y of m u l t i p l i c i t y i n the bands due to the s l i g h t l y d i f f e r e n t environments of the phosphinate groups i n X. For both of these structures, which have been confirmed by X-ray crystallography, as mentioned e a r l i e r , A i s around 70 cm - 1 (66,67), and the asymmetric and symmetric P0 2 stretching vibrations f a l l into the frequency ranges, 1150 - 1100 and 1065 - 1025 cm"1, r e s p e c t i v e l y , as expected for symmetrically bonded phosphinates with a l k y l groups on phosphorus (34). Structure XI i s proposed for those metal phosphinates Unlike the dichlorophosphinate, C1 2P0 2~ (23), the ligands considered here appear to have no tendency to chelate (20), probably due to the 0P0 angle s t r a i n that would be present i n a four-membered ring (17, 23). - 20 -containing bulky a l k y l groups, for example, t e r t i a r y butyl groups (67). The i n s o l u b i l i t y of these compounds i n common organic solvents (see Section 1.2.1), coupled with A values of 85-95 cm - 1 (v : 1140 - 1100 asy. cm - 1; : 1050 - 1020 cm - 1), a r i s i n g from the le s s symmetric arrangement of the ligands around the d i s t o r t e d tetrahedral metal centers, have resulted i n the formulation of the crosslinked structure shown. Octahedral complexes with symmetric phosphinate bonding, proba-bly involving a combination of modes I-IV, for divalent metals, are also possible and would be predicted to have at least four P0 2 stretching frequencies (two for each d i f f e r e n t l y bonded phosphinate group). In f a c t , the spectra of compounds proposed to have this structure show only three absorptions due to P0 2 stretching (65-67), perhaps implying an accidental degeneracy of the asymmetric stre t c h of the phosphinate group involved i n bonding to more than two metals ( I I I or IV) with the symme-t r i c stretch of the ligand bonded only to one (type I) or two (type II) metals. The highest and middle frequencies observed correspond quite well to the asymmetric and symmetric stretching frequencies, respective-l y , of structures IX and X, r e s u l t i n g i n a A of about 70 cm - 1, while the middle and lower frequencies, with A ca. 50 cm - 1, f a l l into the range, 1065 - 1010 cm - 1, expected for the asymmetric and symmetric stretching frequencies of P0 bonds with much more reduced double bond character as a r e s u l t of each oxygen bonding to more than one metal. Metal phosphinates with unsymmetric P0 2 bonding, modes V-VIII, Figure 1.2.2.1, and octahedral metal centers are characterized by values of A that are much larger than those encountered i n symmetric bonding, ranging up to 120 cm - 1, as anticipated for non-equivalent PO bonds (66, - 21 -67). The frequencies, ca. 1110 cm - 1 for v&3y P0 2 and ca. 990 cm - 1 for Vsym indicate again the reduced PO double bond character expected i n this type of structure ( c f . XII and XIII of Figure). I t i s more d i f f i c u l t to postulate t h i s unsymmetrical bonding i n a compound with a tetrahedral metal center, due to problems i n s a t i s f y i n g both coordina-t i o n number and charge n e u t r a l i t y ; a combination of mode V and one (or both) of VII or VIII would be required. As there are no examples of a l k y l substituted phosphinates acting as s t r i c t l y monodentate ligands with t r a n s i t i o n metals (except as polymer chain terminating groups), t h i s appears u n l i k e l y and t h i s structure has not been proposed for any metal phosphinates. (Bridging v i a mode VI would r e s u l t i n four-coordi-nate metal centers and unsymmetric bonding; however, i t i s not obvious why a phosphinate would adopt this type of coordination unless, perhaps, i t was bridging two d i f f e r e n t metals, or had two d i f f e r e n t substituents on phosphorus, causing s t e r i c r e s t r i c t i o n s severe enough to r e s u l t i n non-equivalent bonding.) The s h i f t s i n the positions of the P0 2 stretching absorptions, from the free ion values, have been related not only to structure, as described above, but also to the strength and type (covalent or i o n i c ) of the metal-ligand i n t e r a c t i o n (16,21,32,69,136). This i n t e r a c t i o n w i l l depend on the ligand f i e l d strength of the ligand which w i l l be affected by the a ligand to metal i n t e r a c t i o n ( b a s i c i t y of the anion) and the d(n)-p(it) metal to oxygen backbonding (12,16,17); these e f f e c t s , i n turn, depend on the nature of the substituents on phospho-rus. A great deal of research has been ca r r i e d out i n an e f f o r t to understand and to predict the substituents' e f f e c t s on the strength - 22 -and type of the i n t e r a c t i o n , and, hence, on the PO stretching frequen-cies of phosphorus compounds containing oxygen. It i s generally recog-nized that more electronegative groups r e s u l t i n greater metal-to-ligand n backbonding (12,16,17) and i n higher PO stretching frequencies (23,132,137,138,150,151). This e l e c t r o n e g a t i v i t y has been parameterized as the "phosphorus inductive or u constants" (34,140) or as the Hammett (or Hammett-Kabachnik) substituent constants, modified by Kabachnik (152,153) to apply to phosphorus acids, for which the Hammett a c i d i t y function holds (154). The P0 2 asymmetric stretching frequencies, for some t r i - and tetravalent coordination compounds involving phosphate ( ( R 0 ) 2 P 0 2 ~ ) 1 and phosphonate ((R0)(R)P0 2~) 1 ligands, have been correlated with So (<r= Hammett-Kabachnik constant) (12,16,17). This c o r r e l a t i o n r e s u l t s i n a l i n e a r r e l a t i o n s h i p , v a g v increasing, for a given metal, as the substituents on phosphorus become more e l e c t r o -negative. Mikulski et a l . (12,16) have, for the t r i v a l e n t compounds, related the primarily M-0 stretching frequency to Zo and found a compli-cated, non-linear c o r r e l a t i o n when 3d metals were involved but a reaso-nably l i n e a r one when non-transition metals were involved. In the l a t t -er case, where no d electrons are available for M-L backbonding, the strength of the M-0 i n t e r a c t i o n i s governed mainly by the coordinating s t r e n g t h 2 of the ligand ( i . e . , b a s i c i t y ; electron-releasing substituents R = a l k y l or a r y l . S t e r i c factors w i l l also play a r o l e i n determining the strength of the i n t e r a c t i o n . - 23 -( a l k y l or a r a l k y l ) on phosphorus r e s u l t i n g i n a better a donor ligand and hence a higher vM-O). On the other hand, the M-0 strength for 3d metals depends on a combination of; i ) the b a s i c i t y of the ligand, enhanced, as mentioned above, by electron-releasing groups, i i ) the amount of d(Tt)-p(it) M-L backbonding, enhanced by electron-sink groups (alkoxy or aryloxy) which reduce the electron density of the P0 2 moiety and, hence, promote M •*• 0 backbonding, and, i i i ) the s t e r i c e f f e c t s of the ligand which can i n h i b i t n backbonding (17). Although s i m i l a r comparisons have not been attempted for divalent metals, an examination of the P0 2 and M-0 stretching frequencies may y i e l d information on the strength of the metal-oxygen i n t e r a c t i o n s i n the compounds under discus-sion i n t h i s work. F i n a l l y , as discussed i n Section 1.2.1, i t has long been recognized that many phosphinate coordination polymers are polymorphic (48,49,55,74) e x i s t i n g , for example, i n d i f f e r e n t forms i n the i n i t i a l l y prepared s o l i d state and i n the s o l i d recovered a f t e r d i s s o l u t i o n i n , and evapo-r a t i o n of, an appropriate solvent, or a f t e r melting. Examination of the i n f r a r e d spectra, again s p e c i f i c a l l y the P0 2 stretching region, has allowed workers to postulate whether the s t r u c t u r a l differences are related to backbone rearrangements (usually some observable d i f f e r e n c e in I.R.) (65-67,100) or side group reorientations (no change i n vP0 2 region of I.R.) (55,66). Outside of the region associated with the P0 2 stretching v i b r a t i o n s , the i n f r a r e d spectra of these compounds have been v i r t u a l l y ignored. We have found, i n the spectra of the d i f f e r e n t isomers of the copper(II) di-n-alkylphosphinates, s i g n i f i c a n t changes i n absorptions not associated with the P0 2 stretching v i b r a t i o n s , that have - 24 -been very useful i n d i s t i n g u i s h i n g one isomer from another, and i n predicting t h e i r e l e c t r o n i c and magnetic properties. This i s discussed i n Chapter 2. 1.2.3. E l e c t r o n i c Spectroscopy. The study of the absorptions a r i s i n g from t r a n s i t i o n s between the e l e c t r o n i c energy l e v e l s of a metal ion i n a ligand f i e l d Is a v i t a l t o o l i n the inference of s t r u c t u r a l d e t a i l s of the complex under inves-t i g a t i o n . The i n t e r p r e t a t i o n of the e l e c t r o n i c spectrum can y i e l d information on the environment of the metal ion, for example, the coor-dination number, and the geometry of the chromophore. The a p p l i c a t i o n of C r y s t a l F i e l d Theory (C.F.T.), Ligand F i e l d Theory (L.F.T.), or Mole-cular O r b i t a l Theory ( i n those cases where there i s s i g n i f i c a n t metal-ligand o r b i t a l overlap), to predict and interpret spectra (and magnetic properties) i s well-documented (155-165) and w i l l not be expanded on here. Copper(II), having a d 9 configuration, should, t h e o r e t i c a l l y , give r i s e to a simple, spin-allowed, one band spectrum i n either an octahedral or tetrahedral ligand f i e l d , since the s p l i t t i n g of the 2D free ion term, upon complexation, produces a 2^2(g) a n d- a n 2^(g) t e r m only, with no other terms of the same m u l t i p l i c i t y (164). In r e a l i t y , one almost never finds copper(II) i n a cubic f i e l d due to Jahn-Teller d i s t o r t i o n s i n octahedral coordination (159,163,166), and to the non-s p h e r i c a l symmetry of the C u 2 + ion, considered to be responsible for the compression seen i n tetrahedral copper compounds (163,167). The r e l a t i o n s h i p between the e l e c t r o n i c properties of copper and the stereo-- 25 -chemistry of the ligand f i e l d i s f a i r l y complicated. This arises from the va r i e t y of coordination numbers (four, f i v e and s i x are the most common (104,167,168)), and geometries (for example, tetrahedral, octa-hedral, square planar, square pyramidal, and t r i g o n a l bipyramidal, most with at least some d i s t o r t i o n (164,168,169)), that copper can adopt i n i t s compounds* The c o r r e l a t i o n of copper stereochemistry to the e l e c -t r o n i c spectra of the compound has been the subject of numerous reports and reviews (170-176). For example, an increase i n tetragonal d i s t o r -t i o n , from octahedral towards square planar, for a series of copper(II) tetra-amine complexes (177), has been related to increased e l e c t r o n i c t r a n s i t i o n energies for the d^2 d„2 y2 t r a n s i t i o n , and, to a lesser extent, for the d -*• d 2_ 2 t r a n s i t i o n . Shorter in-plane copper-ligand bond lengths (R_), and a decrease i n the tetragonality f a c t o r , T = Rg/R^ (110,168), where i s the copper-ligand distance along the tetragonal a x i s 1 , also accompany increasing d i s t o r t i o n . Similar c r i t e r i a were found to apply to a series of copper compounds with a (^10^X2 chromophore, where X = CI, Cu (at a distance of 7.56 A) or 0 (178). In addition, a c o r r e l a t i o n was found to exist between the highest energy e l e c t r o n i c absorption and the square of the highest copper-nitrogen stretching frequency, for the tetra-amines, Cu(NH 3) 4X 2, where X 2 = (N0 2) 2» P t C l ^ , (SCN) 2, C l 2 , B r 2 , C0 3, C ^ , for example (172), and for a series of Cu(N-N) 2X 2 compounds, where N-N i s ethylene-diamine, 1,3-propylenediamine, or the symmetric or asymmetric N-substi-1 A correction (177) must be applied to this bond length i f the a x i a l ligands are not the same as the in-plane ligands. - 26 -tuted dimethyl- or diethylethylenediamine, and X i s CI, Br, I, NCS, BF^, N0 3 or ClO^ (179). The complexes with the highest e l e c t r o n i c t r a n s i t i o n energy also had the highest Cu-N stretching frequencies, as a r e s u l t of the increase i n the in-plane f i e l d strength (and, hence bond strength) a r i s i n g from increasing tetragonal d i s t o r t i o n . Square pyramidal geomet-ry i s characterized by two s t r u c t u r a l parameters; the out-of-plane copper-ligand bond length and the distance (p) by which the copper atom i s l i f t e d out of the plane of the four in-plane ligands (169), the two distances being, generally, inversely proportional. Increased d i s t o r -t i o n away from the parent square planar geometry r e s u l t s i n a lowering of the energy of the d 2 d 2 2 d t r a n s i t i o n , a greater out-of-plane z x —y , xy s h i f t and a shorter value. As indicated i n the above examples, then, c o r r e l a t i o n s can be made between the stereochemistry and structure of the copper(II) complex and the e l e c t r o n i c spectra, a change from square planar to tetragonal octahedral or to square pyramidal geometry r e s u l t -ing i n a decrease i n the energy of the d 2 + d 2_ 2>d t r a n s i t i o n , the frequency reduction being less i n the l a t t e r case (169). Correlations of t his type require knowledge of the c r y s t a l structures of as many of the compounds i n a given series as possible, i n order to confirm that the spectral changes are as a r e s u l t of s t r u c t u r a l changes. The corre-l a t i o n s then form the base from which, hopefully, predictions may be made about unknown structures from an examination of t h e i r e l e c t r o n i c spectra, i n combination with other physical measurements (173). Complexes of the type discussed above, with an e s s e n t i a l l y square planar coordination and zero, one, or two ligands at some distance, usually longer than R , away from the copper atom, have been - 27 -the most extensively studied i n the search for s t r u c t u r a l - e l e c t r o n i c c o r r e l a t i o n s (e.g., references 180-185). Tetrahedral coordination, usually f l a t t e n e d , occurs r e l a t i v e l y less frequently (186), and has been studied less thoroughly. E l e c t r o n i c t r a n s i t i o n energies w i l l be lower than those of corresponding octahedral or square planar compounds (155-163). For example, compounds containing the CuX^ 2 - anion where X = Br or CI, have been well investigated (161,164,187-191). With large cations ( C s +, for example) the chromophore i s approximately (157) and t r a n s i t i o n s occur at ca. 9000 and 6000 cm - 1, whereas with smaller cations the copper i s i n a square planar environment and e l e c t r o n i c t r a n s i t i o n s occur at ca. 13,000 and 10,500 cm - 1 (191). The e l e c t r o n i c spectra of the cesium s a l t s of the t e t r a c h l o r i d e and the tetrabromide, for which the c r y s t a l structures are known (192,193), have been assigned (187,188) and the c r y s t a l f i e l d parameters, Dq and Cp, have been deter-mined (161). T r a n s i t i o n energies are, then, related to the d i s t o r t i o n (from regular tetrahedral coordination) angle, a, as defined by Gerloch and Slade (161). We have adopted t h i s approach i n discussing the e l e c -t r o n i c spectra of the copper(II) phosphinates under consideration here (see Chapter 2). As mentioned i n the Introduction, the published data on copper phosphinates are sparse and, where reported (66-68,85), the e l e c t r o n i c spectra have not been assigned or interpreted, beyond, i n some cases, a reference to the spectra as being consistent with a propo-sed structure. For example, the absorptions at 13,800 and 25,000 cm - 1 for the N-phenylaminomethyl d e r i v a t i v e , Cu[(C 6H 5NHCH 2) 2P0 2] 2 (68), were ci t e d as support for the proposed tetragonally d i s t o r t e d octahedral coordination. We have met with some success i n c o r r e l a t i n g the - 28 -e l e c t r o n i c spectra to the s t r u c t u r a l and magnetic properties, as well as to the i n f r a r e d spectra, of the copper(II) compounds prepared i n t h i s study. 1.2.4 Magnetic S u s c e p t i b i l i t y . The importance of the magnetic properties of the t r a n s i t i o n elements i n probing the ground state of the metals i s well known (156-160,162,189,194-196). Information on the type of ground state (and, hence, metal coordination number and stereochemistry) and the e f f e c t s of spin-or b i t coupling, lower than cubic ligand f i e l d components and electron d e r e a l i z a t i o n are av a i l a b l e from the magnitude of the e f f e c -t i v e magnetic moment (u ) and i t dependence on temperature. The err. theory of magnetic s u s c e p t i b i l i t y i s presented i n d e t a i l elsewhere (see, for example, references 160,196-203). As with the e l e c t r o n i c spectra, for copper(II) s t r u c t u r a l e l u c i d a t i o n from magnetic data i s not a simple matter because, i n the absence of magnetic exchange, the magnetic moments of copper complexes l i e i n the 1.75-2.20 B.M. range and are e s s e n t i a l l y independent of temperature, regardless of stereochemistry (104,203), although "tetrahedral" copper compounds should have moments at the higher end of the range (189). This invariance of the moment to stereochemistry arises due to a lack of any f i r s t - o r d e r o r b i t a l c o n t r i -bution to the moment i n copper(II) compounds. "Octahedral" complexes would have a "non-magnetic" (204) 2 E ground state and would be expected to have moments close to the spin-only value (u =1.73 B.M.) and s • o. independent of temperature. Tetrahedral compounds, i f regular, would have a 2 T 2 ground state, which would be expected to y i e l d an o r b i t a l - 29 -contribution to the moment; however, the spin-orbit coupling constant, \, of copper Is quite large (\q (free ion value) = -830 cm"1 (160)) and would s p l i t the 2 T 2 state into two components separated by an amount larger than kT (ca. 200 cm - 1 at room temperature). There would be mini-mal thermal population of the upper state at normal temperatures (or lower) and only a small temperature dependence to the moment. Copper i s not found i n a regular tetrahedral geometry i n any event so that d i s t o r -t i o n removes the degeneracy of the 2 T 2 ground state, s p l i t t i n g i t into a 2 B 2 and an 2E state, from which there i s again no o r b i t a l c o n t r i b u t i o n . Spin-orbit coupling gives r i s e to a mixing i n of an o r b i t a l l y degenerate excited state thereby r e s u l t i n g i n a second-order o r b i t a l c ontribution to the moment and values of u that are larger than the spin only e r r . value. (Any electron d e r e a l i z a t i o n w i l l reduce X^, r e s u l t i n g i n moments closer to \i , for copper(II).) With 10 Dq 1 being smaller i n s. o. the "tetrahedral" compounds, the i r moments tend to be somewhat higher than i s the case for six-coordinate copper (or square planar copper) complexes. The separation of the mixed-in l e v e l s from the ground state i s , however, large enough such that there i s no thermal population at room temperature and the moment i s temperature independent. Compared to some other t r a n s i t i o n metals, then, copper stereo-chemistry, i n magnetically d i l u t e compounds, i s not re a d i l y d i s c e r n i b l e on the basis of magnetic moments. Study of the s u s c e p t i b i l i t y , p a r t i c u -l a r l y over a range of temperatures, does provide evidence of any magne-t i c exchange present i n the compound, a phenomenon very common to More c o r r e c t l y , the energy diffe r e n c e between the ground state and the state being mixed i n . - 30 -complexes containing two or more copper atoms. Dimers (205-221) such as the much studied copper carboxylates (86,222-226), trimers and other c l u s t e r s (167,228-231) and l i n e a r and two-dimensional chain complexes (81,231-238) have been found to exhibit both ferromagnetic and a n t i f e r -romagnetic exchange interactions (239), the l a t t e r being more common. In some cases, a single system may show both types of i n t e r a c t i o n (236, 237) representing d i f f e r i n g i n t r a - and interchain exchange, or may have two values of the exchange parameter, J , i n d i c a t i n g d i f f e r i n g i n t e r -actions within the compound i t s e l f (231,238). For example, the s t r u c -ture of the complex Cu 2L[CH 3COO] 2»2CH 3OH, where L 2 - i s the hexadentate anion of N,N'-bis(2-((o-hydroxybenzhydrylidene)amino)ethyl)-l,2-ethane-diamine (238), i s such that the 1,2-ethanediamine portion of L 2 ~ bridges two copper atoms of the dinuclear u n i t s , which are then linked by Cu 20 2 bridging units i n v o l v i n g the coordinated oxygen atoms of the acetate anions. The J values then alternate between -7.88 cm - 1 for the exchange through the Cu-N-C-C-N-Cu portions of the molecule, and -1.50 cm - 1 for the exchange through the oxygen bridges of the C u 2 0 2 moieties. The observed i n t e r a c t i o n varies from weak p a r a l l e l spin alignment (89,240-242) to complete spin p a i r i n g , r e s u l t i n g i n e s s e n t i a l l y diamag-net i c compounds (243,244). Magneto-structural c o r r e l a t i o n s emphasize the importance of such factors as copper stereochemistry (relates to the effectiveness of metal-ligand o r b i t a l overlap), the geometry of the bridging ligands and the type of substituents on the bridge, as well as - 31 -the nature of any non-bridging ligands present, i n determining the magnitude and the sign of the exchange (86-90,228-231,233-251).1 The th e o r e t i c a l aspects of the mechanisms of exchange and the models used to inte r p r e t and f i t the experimental data for copper (and other metal) compounds e x h i b i t i n g spin-spin i n t e r a c t i o n s , have been the subjects of extensive investigations (85,194,202,203,228,246,252-262). The f i t t i n g techniques and a discussion on possible exchange mechanisms, as related to the copper(II) di-n-alkylphosphinates, are presented i n Chapter 2, Section 2.1.6. As indicated i n the Introduction, magnetic exchange, propagated through the three atom O-P-O bridges, has been reported i n some metal phosphinates (18,77-80,87). The most thoroughly studied chromium compounds have been found to exhibit antiferromagnetic behavior, with the values of the coupling parameters, -1.74 cm - 1 for C r [ ( C H 3 ) ( C 6 H 5 ) -P 0 2 ] 2 (82,83,85) and -1.20 cm"1 for Cr ( 0 H ) [ ( C H 3 ) ( C 6 H 5 ) P 0 2 ] 2 , being I n d i -cative of a f a i r l y weak i n t e r a c t i o n . A sim i l a r value of J (-2.44 cm"1) was found for the chromium dimer, C r [ ( C 6 H 5 ) 2 P 0 2 ] 2 [ a c a c ] ^ (acac = acetylacetonate) (81). The cobalt n-butyl d e r i v a t i v e , Co[(n-C 1 +H 9) 2P0 2] 2 (77), behaves as a c l a s s i c a l Heisenberg antiferromagnetic chain at temperatures above ca. 20K (J = -2.15 cm - 1); below t h i s temperature an antisymmetric exchange occurs between adjacent cobalt atoms, giving r i s e to a weak ferromagnetism and an increase i n the s u s c e p t i b i l i t y (84). In addition to the above phosphinates, exchange in t e r a c t i o n s have also been observed i n some of the phosphates, (R0) 2P0 2~, and phosphonates, Refer to Section 2.1.6. - 32 -(RO)RP0 2~, of the t r i v a l e n t metals F e ( I I I ) , C r ( I I I ) , V ( I I I ) , and T i ( I I I ) , which have subnormal room temperature magnetic moments (9,12, 16). I t was found that increasing the bulkiness of the ligand decreased the i n t e r a c t i o n so, for example, C r [ ( C H 3 0 ) 2 P 0 2 ] 3 has a moment of 2.56 B.M. but t h i s increases to 3.89 B.M. upon replacing the methoxy group with a butoxy group (12). This has been at t r i b u t e d (9) to d i s t o r t i o n s from regular octahedral symmetry i n the polymers with the b u l k i e r ligands causing the observed decreased demagnetization. Metal phenyl-phosphonates, M[C 6H 5P0 3]'H 20, where M i s Mn, Fe, Co, Ni, and Cu (28), revealed antiferromagnetic i n t e r a c t i o n only i n the manganese polymer, which had a Weiss constant of -42. This contradicted an e a r l i e r report (29) which at t r i b u t e d the temperature dependence of the magnetic moments of the n i c k e l and cobalt monohydrates (as well as the anhydrous n i c k e l compound) to antiferromagnetic exchange. However, the l a t e r report (28) considered this temperature dependence to be due to an o r b i t a l contribu-t i o n to the moment. The few copper(II) phosphinates, for which magnetic data have been reported, have room temperature magnetic moments t y p i c a l of magne-t i c a l l y d i l u t e copper compounds, for example, C u [ ( n - C g H 1 7 ) 2 P 0 2 ] 2 , 2.01 B.M. (CCl^ solution) (66); Cu[(t-C^Hg) 2P0 2] 2, 1.8 B.M. (67); Cu[(n-C l t H 9 ) 2 P 0 2 ] 2 , 1.89 B.M. (67), and Cu[(C 6H 5NHCH 2) 2P0 2] 2 , 1.8 B.M. (68). A l a t e r measurement of the magnetic s u s c e p t i b i l i t y of the n-butyl d e r i v a t i v e (89) over the temperature range 77 to 300K, found C u r i e - l i k e behavior with a Curie constant of 0.485 (u =1.97 B.M.). The excep-e r r . tions to moments of these magnitudes are the s o l i d i f i e d melt of the n-octyl derivative (66), which has a moment (1.75 B.M.) only s l i g h t l y - 33 -above the spin-only value of 1.73 B.M., and the methylphenyl compound, with a reported room temperature moment of 1.56 B.M. (18,87). No studies over a range of temperatures have been done on these compounds. The variable temperature magnetic s u s c e p t i b i l i t y studies reported i n the present work then represent the f i r s t such study of a series of copper(II) phosphinates containing c l o s e l y related l i g a n d s . 1 The unexpected discovery of both antiferromagnetic and f e r r o -magnetic exchange i n some of these compounds, and the c o r r e l a t i o n of th i s behavior to the thermal properties, spectra ( v i b r a t i o n a l and e l e c t r o n i c ) , and the structures of the polymers, are discussed i n Chapter 2. 1.2.5 X-Ray Crystallography. The i n d i r e c t methods of characterization discussed i n the preceding sections, while able to provide, i n some cases, s t r u c t u r a l information, cannot, of course, y i e l d precise d e t a i l s on molecular geometries or intermolecular packing. These features can only be obtained from single c r y s t a l X-ray c r y s t a l l o g r a p h i c studies. I t can be d i f f i c u l t to obtain single c r y s t a l s of monomeric, dimeric, and c l u s t e r compounds containing t r a n s i t i o n metals; with polymeric materials the generally amorphous or s e m i - c r y s t a l l i n e nature of the systems, while advantageous as polymer properties, can preclude the i s o l a t i o n of Scott et_ a l . reported studying a series of f i r s t row t r a n s i t i o n metal phosphinates over the range 4 - 300K but did not specify which copper(II) compounds were examined (84). They found no evidence of spin interactions i n these polymers. - 34 -c r y s t a l s suitable for X-ray a n a l y s i s . This has been the case i n the study of metal phosphinates, where very few s t r u c t u r a l determinations have been accomplished. The f i r s t c r y s t a l l o g r a p h i c proof that a phosphinate ligand can act as a bridge between two metals came with the so l u t i o n , i n 1963, of the structure of the l i n e a r chain compound, Mn[Cl 2P0 2] 2[CH 3C00C 2H 5] 2 (263), containing octahedral manganese and eight-membered Mn£0-P-0} 2Mn ri n g s . The f i r s t structure solved containing phosphinate ligands with organic substituents on the phosphorus was that of the chromium dimer, C r 2 [ ( C 6 H 5 ) 2P0 2] 2 [ a c a c ^ (264), involving bridging phosphinates and chelating acetylacetonates. S t r u c t u r a l studies on the polymeric phosphinates have primarily involved the i n t e r -pretation of X-ray d i f f r a c t i o n photographs on oriented f i b e r s and/or on powders (45-49,53-55,72,75,76), due to the lack of single c r y s t a l s . There was disagreement as to the nature of the backbone structure i n the l i n e a r divalent metal phosphinates; some researchers attributed t h e i r f l e x i b i l i t y to a double bridged structure (46,48,49,71) while others (45,54,55,75) att r i b u t e d i t to an al t e r n a t i n g s i n g l e - t r i p l e bridging system. The single c r y s t a l s t r u c t u r a l determination of two zinc polymers (72,73) f i r s t confirmed the presence of the l a t t e r backbone type i n these compounds. The zinc di-n-butylphosphinate (72) was found to involve repeating units containing two metal atoms, the i d e n t i t y period being 9.90 A (3.55 A for the t r i p l e cage, 6.35 A for the si n g l e bridge; r e f e r to Figure 1.2.5.1.b)). The top t r i p l e t of oxygen - 35 -Figure 1.2.5.1. Structures of Some Metal(II) Phosphinates. O -O' O o O c a) Zn((C%H5)(n-C4H9)PC^)2. L b)Zn((n-C4H g)2P02)2. From Ref. 73. a) b) c) Chain packing in orthorhombic ZnttCgHgMn-C^HgJPC^ From Ref. 74. d) Linear chain structure of PbftCgHg^PC^ • From Ref. 100. - 36 -atoms 1 i s rotated with respect to the bottom t r i p l e t so that two i s o -energetic enantiomorphic t r i p l e bridged units are possible (72). These are randomly d i s t r i b u t e d r e s u l t i n g i n disorder i n the s t r u c t u r e . The c r y s t a l s were of poor q u a l i t y and the a l k y l groups could not be located. S i m i l a r l y , disorder introduced by the random s i t e occupation of the n-butyl and the phenyl groups i n the monoclinic Zn[(C 6H 5)(n-C l tH g)P0 2] 2 (73) , precluded the l o c a t i o n of the carbon atoms, other than those d i r e c t l y attached to phosphorus, i n t h i s compound. The replacement of an n-butyl group with the bulkier phenyl group i n the polymer r e s u l t s i n a d i f f e r e n t conformation i n the t r i p l e bridged cage. The r o t a t i o n of one t r i p l e t of oxygens with respect to the other, seen i n the n-butyl d e r i v a t i v e , does not occur In the n-butylphenyl compound (Figure 1.2.5.1.a)) as a r e s u l t of increased in t e r c h a i n interactions (73). The presence of only one type of t r i p l e bridged unit means the backbone structure of the n-butylphenyl polymer i s more ordered than that of the di-n-butyl despite the random occurrence of the organic groups. In addition, the d i f f e r e n t conformation r e s u l t s i n an increase i n the i d e n t i t y period from 9.90 A to 10.16 A due to the increased r i g i d i t y of the t r i p l e bridged u n i t . A l a t e r i n v e s t i g a t i o n of t h i s n-butylphenyl d e r i v a t i v e (monoclinic) and of an orthorhombic form of the same compound (74) , showed the two isomers to have the same backbone structure and s i m i l a r chain packing (Figure 1.2.5.1.c)), where pairs of A " t r i p l e t of oxygen atoms" refe r s to the three oxygen atoms, one from each phosphinate of the t r i p l e bridged unit, bonded to one metal. "Top" and "bottom" are a r b i t r a r y and refer to the two t r i p l e t s i n each t r i p l e bridged cage. - 37 -chains are aligned such that the t r i p l e bridged unit of one chain i s adjacent to the single bridged unit of the other. (Again, the l o c a t i o n of the organic side groups was d i f f i c u l t ; out of four butyl and four phenyl groups per asymmetric unit, only one n-butyl and two phenyls, each with an occupancy factor of 0.5, could be located.) A s i m i l a r chain packing was found for the copolymer, Zn[(n-C 1 |H 9) 2P0 2] [(n-CgH 1 3) 2 -P0 2] (53), which, l i k e the n-butyl homopolymer (72), has an i d e n t i t y period of 9.90 A and a random d i s t r i b u t i o n of the enantiomorphic t r i p l e bridged u n i t s . On the basis of d i f f r a c t i o n photographs, the cobalt and zinc phosphinates Involving s t r a i g h t chain a l k y l groups, (methyl, n-butyl, n-hexyl, n-decyl) or phenyl groups, as well as the mixed ( i . e . , M[R 1R 2P0 2] 2) polymers and the various copolymers ( i . e . , M[R 1R 2P0 2]2-2x~ [R 3R l*P0 2]2 x)» are a l l proposed to have the same s i n g l e - t r i p l e bridged backbone (45,47,53,55,72,73). S i m i l a r l y , the beryllium polymers (45, 54,73-75) are thought to have the same basic structure and chain packing as the cobalt and zinc analogues. The previously mentioned double bridged structure has been proposed for the zinc d i - i s o p e n t y l d e r i v a t i v e , Zn[(CT 3CH 2CT 2CH 2(CH 3)) 2~ P 0 2 ] 2 (76), on the basis of X-ray d i f f r a c t i o n photographs of oriented f i b e r s . The change to t h i s type of backbone from the s i n g l e - t r i p l e kind found i n the other zinc compounds was a t t r i b u t e d to " d r a s t i c " (76) s t e r i c i n t e r a c t i o n s between the branched a l k y l groups which placed r e s t r i c t i o n s on the formation of the t r i p l e bridged cage. The i d e n t i t y period between the repeating units was found to be considerably shortened compared to the zinc s i n g l e - t r i p l e structures, from at least 9.90 A to 9.16 A (76). This may be due to the d i f f e r e n t bridge-bridge - 38 -int e r a c t i o n s i n the two structures; these interactions would not e x i s t i n the single bridge which i s extended (6.35 A (72)) but would be strong i n the t r i p l e bridged cage where the s t e r i c repulsion between the three phosphinates brings the metal atoms f a i r l y close together (3.55 A (72)). The double bridged structure would f a l l i n between these two extremes with, assuming reasonably equivalent eight-membered rings, z i n c - z i n c separations of approximately one-half the i d e n t i t y period (|x 9.16 A = 4.58 A). Single c r y s t a l studies on P b [ ( C 6 H 5 ) 2 P 0 2 ] 2 ( l o n ) (see Figure 1.2.5.1.d)), and Cu^n-C^Hg) 2P0 2] 2 (89) confirmed the occurrence of this type of bridging polymer and the copper-copper separation i n the l a t t e r compound1 i s 4.938 A (89). In the course of the present work, cr y s t a l s of the copper(II) ethyl and n-hexyl d e r i v a t i v e s , suitable for X-ray analysis, were obtained; the d e t a i l s of these structures, both involving the double bridged structure, are discussed i n Section 2.1.2. Apart from the two s t r u c t u r a l types discussed above, none of the other proposed structures for these polymers, for example, crosslinked tetrahedral, or octahedral (involving only phosphinate ligands, c f . Figure 1.2.2.1) have been confirmed by X-ray a n a l y s i s . Recently, however, the c r y s t a l structure of the manganese(II) dimethylphosphinate dihydrate, Mn[(CH 3) 2P0 2] 2»2H 20, was determined (265). This unique structure involves l i n e a r double bridged M n [ ( C H 3 ) 2 P 0 2 ] 2 chains, the eight-membered rings of which are extremely puckered due to hydrogen-bonding involving the water molecules which f i l l the f i f t h and s i x t h See Section 2.1.2 for further discussion on this structure. - 39 -coordination s i t e s of the manganese. One proton per water molecule hydrogen-bonds to two phosphinate oxygen atoms bonded to a d i f f e r e n t manganese atom, the two water molecules on one metal each hydrogen-bonding to two d i f f e r e n t manganese atoms, r e s u l t i n g i n an extended cage structure (265). The other water proton i s involved i n strong i n t e r -chain hydrogen-bonding to one phosphinate oxygen of an adjacent chain, which are arranged so that the cage of one f a l l s midway between two cages of the other. The o v e r a l l r e s u l t i s a very e f f i c i e n t , dense chain packing. 1.2.6 Proposed Structures of Some Divalent F i r s t Row T r a n s i t i o n Metal  Phosphinates. This section summarizes the proposed structures that a p a r t i c u l a r metal might be expected to form with a phosphinate ligand, depending on the substituents on phosphorus. The structures proposed are based on information obtained by the methods of cha r a c t e r i z a t i o n discussed i n the e a r l i e r sections of t h i s Chapter. For z i n c ( I I ) and c o b a l t ( I I ) , the coordination number and geometry of the metals do not appear to be affected by R; they form t e t r a h e d r a l 1 complexes involving symmetric phosphinate bridges. With l i n e a r a l k y l chains they seem to adopt the al t e r n a t i n g s i n g l e - t r i p l e bridged structure, regardless of the length of R. With branched a l k y l groups they are proposed to have the double bridged structure or the crosslinked structure depending on the amount However, a form of Co[(n-C 8H 1 7)2P0 2]2 proposed to be octahedral, has been i s o l a t e d (65). - 4 0 -of branching, so that the isopentyl derivatives have the former s t r u c -ture, and the t-butyl compounds the l a t t e r . I n t e r e s t i n g l y , the zinc and cobalt polymers containing phenyl groups seem to have the s i n g l e - t r i p l e bridged structure, where one might have expected a double bridged system due to the bulkiness of the l i g a n d . Manganese(II) phosphinates may exhibit tetrahedral or octahedral coordination, depending on the nature of R, and have symmetric phosphi-nate bridging. With straight chain a l k y l groups, six-coordinate Mn 2 + i s proposed (on the basis of the i n f r a r e d spectrum and the isomorphism of the n-octyl d e r i v a t i v e with the Fe(II) and Co(II) analogues), whereas tetrahedral manganese i s thought to occur when R i s branched. In t h i s case, the polymer may be double bridged or crosslinked depending on the extent of branching, l i k e the cobalt and zinc compounds. In n i c k e l ( I I ) complexes the r e l a t i o n s h i p between the substituents on phosphorus and the mode of phosphinate bridging, and the coordination number and geometry of the metal i s more vague. When R i s a s t r a i g h t chain a l k y l group, the n i c k e l i s proposed to be octahedrally coordinated, with unsymmetrlc phosphinate bridging. However, melting these forms converts them to four-coordinate complexes with symmetric phosphinate bridging and the crosslinked structure (67). This same structure i s obtained when R i s a highly branched group ( t - b u t y l ) . Comparatively few n i c k e l compounds have been prepared, so the existence of l i n e a r chains containing s i n g l e - t r i p l e or double bridged units i s uncertain. Chromium(II) and i r o n ( I I ) phosphinates have also been sparsely investigated; however, the n-octyl derivatives are proposed to have octahedral metal centers and symmetric phosphinate bridging. I t - 41 -should be emphasized that these are proposed structures only; confirma-t i o n of the structures and of the e f f e c t of R, for the various metals, w i l l require the study of a wider range of compounds, and the determina-t i o n of more representative c r y s t a l structures. As mentioned e a r l i e r , copper(II) phosphinates have been poorly characterized and, with the exception of the c r y s t a l structure of the n-butyl compound (89) and the c h a r a c t e r i z a t i o n of the t-butyl as being four-coordinate and crosslinked, s t r u c t u r a l assignments have not been made. On the basis of the present study, i t could be suggested that copper w i l l form l i n e a r polymers, with "tetrahedral" metal centers and double phosphinate bridges, c e r t a i n l y when the ligand contains two a l k y l groups, and probably when the phosphinate contains branched R groups, although c r o s s l i n k i n g may increase with increased branching. With the diphenyl- and the monosubstituted phosphinates, the copper(II) complexes appear to be crosslinked; however, four-coordinate copper(II) Is proposed for a l l d e r i v a t i v e s . - 42 -CHAPTER 2 RESULTS AND DISCUSSION 2.1 Diorganophosphinate Derivatives, [Cu(R 2P0 2) 2I X» Containing Straight Chain A l k y l Groups. 2.1.1 Introduction. The major portion of this work involved the synthesis and characterization of a series of copper phosphinate polymers containing progressively longer, unbranched, a l k y l group substituents on the phosphorus atom of the lig a n d . It was found that these compounds were i s o l a b l e i n one or two forms, l a b e l l e d the a- and B-isomers, depending on the length of the a l k y l groups and that, i n some cases, i t was possible to convert, i r r e v e r s i b l y , one form to the other. The remainder of Section 2.1 explores the d i f f e r e n t s t r u c t u r a l , physical, spectral and magnetic properties of the two polymer forms. 2.1.2 C r y s t a l and Molecular Structures of C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 and C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 . The c r y s t a l structures of copper(II) d i e t h y l and di-n-hexylphos-phinate consist of well-separated i n f i n i t e chains of centrosymmetric spiro-fused eight-membered rings, each of which i s made up of two copper atoms bridged by two phosphinate groups. In each compound, the confor-mations of the two c r y s t a l l o g r a p h i c a l l y independent rings are s i m i l a r and can be described as di s t o r t e d c h a i r s . These polymeric structures are i l l u s t r a t e d i n Figure 2.1.2.1 and are very si m i l a r to those found - 43 -Figure 2.1.2.1 Polymeric Structures of C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 and C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 . (a) {Cu[(C 2H 5) 2P0 2] 2} . (b) {Cu[(n-C 6H 1 3) 2P0 2] 2} . - 44 -for copper(II) di-n-butylphosphinate (89), for lead(II) diphenylphosphi-nate (100) and suggested for z i n c ( I I ) di-l-methylbutylphosphinate (76) (see Section 1.2.5). Crystallographic data for the two compounds are given i n Table 2.1.2.1. The atom numbering scheme and the coordination around the copper atoms, for each compound, are i l l u s t r a t e d i n Figure 2.1.2.2. The f l a t -tened tetrahedral coordination geometry of the copper atoms r e s u l t s i n approximately symmetry i n the CuO^ chromophore, as observed previously for the n-butyl derivative (89). In this respect, there are s l i g h t differences between the compounds, the ethyl d e r i v a t i v e showing a s l i g h t l y greater f l a t t e n i n g of the CuO^ tetrahedron than either the n-butyl or the n-hexyl d e r i v a t i v e s . The d i s t o r t i o n (from regular T, d symmetry)'angle, a, as defined by Gerloch and Slade (161) i s one half of the largest O-Cu-0 angle. The average values of a are 74.27°, 73.25° and 73.04° for the e t h y l , n - b u t y l 1 and n-hexyl d e r i v a t i v e s , r e s p e c t i v e l y 2 . As can be seen from Tables 2.1.2.2 (selected bond lengths and 2.1.2.3 (selected bond a n g l e s ) 3 , there are few other d i f f e r -ences i n the average bond lengths and angles between the ethyl and the n-hexyl d e r i v a t i v e s , and the values are comparable to those found i n the the n-butyl de r i v a t i v e (89). The average Cu-0 bond lengths are not s i g n i f i c a n t l y d i f f e r e n t (1.9183 A for the e t h y l compound versus 1.909 A Data from Reference 89. This diff e r e n c e i n the coordination geometry i s s i g n i f i c a n t with respect to the e l e c t r o n i c and magnetic properties of these compounds, discussed i n l a t e r sections of t h i s chapter. Complete cr y s t a l l o g r a p h i c data are given i n Appendix 1. - 45 -Table 2.1.2.1 Crystallographic Data for Copper(II) D i e t h y l - and Di-n-hexylphosphinate. C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 C r y s t a l system t r i c l i n i c t r i c l i n i c a 7.700(1) A 9.800(3) A b 9.807(1) A 12.336(6) A c 10.101(1) A 13.352(8) A a 90.48(1)° 88.53(3)° 8 104.77(1)° 112.21(1)° 74.02(4)° 82.33(3)° Y Z 2 2 space group P I P I V 678.2(2) A3 1538(1) A3 Pc 1.497 g cm"3 1.145 g cm"3 - 46 -Figure 2.1.2.2 Atom numbering and coordination around copper for C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 and C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 . (b) C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 . - 47 -Table 2.1.2.2 Selected Bond Lengths 1. Cu[(( : 2 H 5 ) 2 P O 2 ] 2 Cu[(n-C 6H 1 3 ) 2 P O 2 ] 2 Bond Length (A) Bond Length (A) Cu-O(l) 1.9158(11) Cu-0(4)" 1.896(3) Cu-0(3) 1.9171(11) Cu-0(2)' 1.902(3) Cu-0(2)' 1.9224(10) Cu-0(3) 1.932(2) Cu-0(4)" 1.9177(11) Cu-0(1) 1.907(3) av. = 1.9183 av. = 1.909 P d ) - O ( l ) 1.5233(10) P(2)-0(4) 1.515(2) P (D-0(2) 1.5164(11) P(2)-0(3) 1.513(3) P(2)-0(3) 1.5191(10) P(l)-0(2) 1.514(3) P(2)-0(4) 1.5125(11) P(l)-0(1) 1.521(3) av. = 1.5178 av. = 1.516 P (D-C(1) 1.795(2) P(2)-C(19) 1.789(5) P(l)-C(2) 1.800(2) P(2)-C(13) 1.798(4) P(2)-C(3) 1.790(2) P ( l ) - C ( l ) 1.779(5) P(2)-C(4) 1.802(2) P(l)-C(7) 1.807(5) av. = 1.797 av. = 1.793 Cu Cu* 4.9555(8) Cu Cu" 4.9310(8) Cu Cu" 5.0245(8) Cu Cu' 4.9277(8) av. = 4.9900 av. = 4.929 Standard deviations are i n parentheses, av. = average. - 48 -Table 2.1.2.3 Selected Bond Angles 1. C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 Bonds 0(l)-Cu-0(3) 0(l)-Cu-0(2)' 0(l)-Cu-0(4)" 0(3)-Cu-0(2)' 0(3)-Cu-0(4)" 0(2)'-Cu-0(4)" 0 ( l ) - P ( l ) - 0 ( 2 ) 0(1)-P(1)-C(1) 0(1)-P(1)-C(2) 0 ( 2 ) - P ( l ) - C ( l ) 0(2)-P(l)-C(2) C ( l ) - P ( l ) - C ( 2 ) 0(3)-P(2)-0(4) 0(3)-P(2)-C(3) 0(3)-P(2)-C(4) 0(4)-P(2)-C(3) 0(4)-P(2)-C(4) C(3)-P(2)-C(4) Cu-0(1)-P(l) P(l)-0(2)-Cu' Cu-0(3)-P(2) P(2)-0(4)-Cu" P( l ) - C ( l ) - C ( 5 ) P(l)-C(2)-C(6) P(2)-C(3)-C(7) P(2)-C(4)-C(8) Angle (deg) 149.85(6) 94.88(5) 93.20(5) 92.74(5) 96.00(5) 147.24(6) 114.99(6) 109.72(8) 106.37(8) 109.51(7) 108.26(8) 107.69(10) 115.31(7) 110.00(9) 105.11(7) 109.76(8) 108.30(8) 108.03(10) 130.08(7) 132.30(7) 133.70(7) 135.45(8) 115.3(2) 113.6(2) 114.4(2) 114.84(15) Bonds 0(4)"-Cu-0(2)' 0(4)"-Cu-0(3) 0(4)"-Cu-0(l) 0(2)'-Cu-0(3) 0(2)'-Cu-0(l) 0(3)-Cu-0(l) 0(4)-P(2)-0(3) 0(4)-P(2)-C(19) 0(4)-P(2)-C(13) 0(3)-P(2)-C(19) 0(3)-P(2)-C(13) C(19)-P(2)-C(13) 0 ( 2 ) - P ( l ) - 0 ( l ) 0 ( 2 ) - P ( l ) - C ( l ) 0(2)-P(l)-C(7) 0(1)-P(1)-C(1) 0(1)-P(1)-C(7) C ( 7 ) - P ( l ) - C ( l ) Cu"-0(4)-P(2) P(2)-0(3)-Cu Cu'-0(2)-P(l) P(l)-0(1)-Cu P(2)-C(19)-C(20) P(2)-C(13)-C(14) P(l)-C(7)-C(8) P ( l ) - C ( l ) - C ( 2 ) Angle (deg) 146.71(14) 95.39(10) 94.04(12) 94.14(12) 95.96(11) 145.43(14) 115.0(2) 110.0(2) 105.4(2) 109.6(2) 108.2(2) 108.2(2) 116.0(2) 108.7(2) 105.7(2) 110.5(2) 107.1(2) 108.5(3) 130.5(2) 134.5(2) 132.4(2) 138.2(2) 115.7(3) 113.4(4) 114.3(4) 115.2(4) Standard deviations are i n parentheses. - 49 -for the n-hexyl and 1.920 f o r the n-butyl (89)); however, there i s , i n the n-hexyl d e r i v a t i v e , one Cu-0 bond that i s s i g n i f i c a n t l y longer (by up to 0.036 A) than the other three Cu-0 bonds for the Cu0 4 chromophore. This i s f i v e times the difference between the longest and the shortest Cu-0 bonds i n the ethyl compound. The long Cu-0 bond i n the n-hexyl der i v a t i v e may be a consequence of the conformations of the two c r y s t a l l o g r a p h i c a l l y independent rings, both of which are considerably puckered (Table 2.1.2.4 l i s t s the interannular torsion angles for the two complexes). The ethyl compound has one ring that i s s i m i l a r to, though s l i g h t l y more puckered, those of the n-hexyl d e r i v a t i v e , while the second ring i s considerably more puckered. A measure of a ring's deviation from p l a n a r i t y i s given by the average of the absolute values of the interannular to r s i o n angles (or the complements of those angles greater than 90°). These values are 48.2° and 46.6° for the n-hexyl der i v a t i v e while for the ethyl compound they are 49.4° and, for the much more puckered r i n g , 55.1°. In the n-hexyl compound, the s t e r i c s t r a i n of j o i n i n g the two f l a t t e r rings at the common copper atom may cause the elongation of one of the Cu-0 bonds, a phenomenon not observed i n j o i n i n g the two more puckered rings of the ethyl d e r i v a t i v e . There i s less v a r i a t i o n i n the values of the O-Cu-O angles i n the n-hexyl com-pound than i s found for the e t h y l (Table 2.1.2.3), perhaps as a r e s u l t of t h i s bond elongation. For example, among the four approximately ninety degree O-Cu-O angles, the maximum difference i n value i s only 1.92° for the hexyl while for the ethyl i t i s 3.26°. The 0-P-O angles are e s s e n t i a l l y equal i n a l l rings, while the Cu-O-P angles are somewhat larger i n the more puckered ri n g of the ethyl d e r i v a t i v e . Both the - 50 -Table 2.1.2.4 Interannular Torsion Angles. C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 Bonds 0(2)'-Cu-0(l)-P(l) 0(2)-P(l)-0(l)-Cu 0 ( l ) - P ( l ) - 0 ( 2 ) - C V 0(l)-Cu-0(2)'-P(l)' 0(4)"-Cu-0(3)-P(2) 0(4)-P(2)-0(3)-Cu 0(3)-P(2)-0(4)-Cu" 0(3)-Cu-0(4)"-P(2)" Angle (deg) -2.39 (12) 57.64(13) -129.07(9) -93.26(9) -13.30(13) 67.94(14) -120.60(10) -79.73(11) C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 Angle (deg) -2.0(3) 54.1(3) -128.2(3) -95.1(2) -0.1(3) 47.3(3) -124.3(3) -96.7(3) Bonds 0(3)-Cu-0(4)"-P(2)" 0(3)-P(2)-0(4)-Cu" 0(4)-P(2)-0(3)-Cu 0(4)"-Cu-0(3)-P(2) 0(l)-Cu-0(2)'-P(l)' 0(l)-P(l)-0(2)-Cu» 0(2)-P( l ) - 0 ( l ) - C u 0(2)'-Cu-0(l)-P(l) - 51 -rings of the ethyl compound have, i n general, somewhat smaller Cu-O-P angles, as well as smaller differences between the values of the Cu-O-P angles within each r i n g , than does the n-hexyl d e r i v a t i v e . These differences between the two compounds are as expected considering the differences i n the p l a n a r i t y of the r i n g s . Other bond lengths and angles are almost i d e n t i c a l i n the two compounds; however, the through space separations of the copper atoms are not. In the hexyl compound these separations, for the two s i m i l a r rings, are 4.9310 A and 4.9277 A, while, i n the ethyl d e r i v a t i v e , they are 4.9555 A and 5.0245 A. The longer Cu Cu separations found In the l a t t e r compound ari s e as a r e s u l t , again, of the greater ring puckering observed i n t h i s s tructure. As expected, the ring i n the ethyl compound that i s only s l i g h t l y more puckered than the rings of the hexyl has only a s l i g h t l y longer copper-copper separation (an increase of 0.0262 A over the average of the two hexyl values). On the other hand, the much more puckered ri n g shows increases of 0.0952 A over the hexyl average and of 0.0690 A over the other ethyl r i n g . Apart from the differences i n bond lengths and angles between the ethyl and the n-hexyl derivatives discussed above, the most important difference between the two structures i s i n the orientations of the a l k y l side chains. In the hexyl compound, each phosphorus has one a l k y l chain i n which the hydrogens on the a-carbon atom are staggered with respect to a P-0 bond and one i n which the hydrogens are staggered with respect to a P-C bond. This has the e f f e c t of orienting both a l k y l groups i n a x i a l configurations with respect to the eight-membered r i n g s . The butyl d e r i v a t i v e (89) has equivalent a l k y l group o r i e n t a t i o n s . The - 52 -ethyl d e r i v a t i v e , on the other hand, has one ring with a l k y l group orientations the same as those found i n the hexyl compound, while i n the other ring (the more puckered one discussed above) both a l k y l groups on each phosphorus are oriented such that the hydrogens on the o-carbons are staggered with respect to the P-0 bonds. This orients one a l k y l group a x i a l to t h i s r i n g , as i n the hexyl d e r i v a t i v e , but the second a l k y l group i s now oriented e q u a t o r i a l l y to the eight-membered r i n g . The d i f f e r e n t o r i e n t a t i o n of t h i s a l k y l group r e s u l t s i n modifications i n the interchain packing of these polymers. Figures 2.1.2.3 and 2.1.2.4 i l l u s t r a t e the chain packing of the ethyl and the n-hexyl compounds, res p e c t i v e l y . The a l k y l chains with a x i a l orientations l i e approximately perpendicular to the backbone chain, while the unique a l k y l group i n the ethyl d e r i v a t i v e projects outwards from the "plane" of the backbone. For the n-hexyl d e r i v a t i v e 1 , with a l l the a l k y l groups i n equivalent ( a x i a l ) o r i e n t a t i o n s , the polymer chains pack e f f i c i e n t l y , such that the a l k y l groups on one backbone f a l l midway between the a l k y l groups on the adjacent polymer, rather l i k e a zipper (Figure 2.1.2.4.(a)). The layers then are stacked so that again the a l k y l groups of one f i t i n between those of the other, Figure 2.1.2.4.(b). Similar packing i s seen for the a x i a l l y oriented a l k y l groups i n the ethyl compound. The a l k y l groups having equatorial orientations are not involved i n that z i p p e r - l i k e packing, being almost perpendicular to the "plane" of the meshed a l k y l chains (Figure 2.1.2.3.(a)). These groups would a f f e c t the packing between the layers The n-butyl de r i v a t i v e i s equivalent to the n-hexyl. - 53 -Figure 2.1.2.3 Chain Packing i n Cu[(C 2H 5) 2P0 2] (a) chain packing (b) layer packing These designations are a r b i t r a r y and could be Figure 2.1.2.4 Chain Packing i n C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 . These designations are a r b i t r a r y and could be reversed. - 55 -of aligned polymer chains (Figure 2.1.2.3.(b)), possibly forcing a greater separation between them than i s found for the n-hexyl d e r i v a t i v e due to s t e r i c i n t e r a c t i o n . This e f f e c t would be p a r t i c u l a r l y pronounced i n compounds having the ethyl structure but longer a l k y l chains. Although s t r u c t u r a l data are available only for copper(II) d i e t h y l - , d i - n - b u t y l - and di-n-hexylphosphinate, the other d i - n - a l k y l compounds prepared i n t h i s study are proposed to have s i m i l a r structures. On the basis of t h e i r physical properties, i n f r a r e d spectra and e l e c t r o n i c and magnetic properties, the compounds are c l a s s i f i e d as a-Isomers, having the same structure as the d i e t h y l complex, or as 8-isomers, having the same structure as the di-n-butyl and di-n-hexyl d e r i v a t i v e s . The discussion of these properties and the differences found between the two isomers follows. 2.1.3. Synthesis, S o l u b i l i t i e s and Thermal Properties. Complete descriptions of the experimental procedures involved i n the synthesis of the phosphinic acids and of the copper(II) d i - n - a l k y l -phosphinates are given i n Chapter 4. I t was, i n general, not possible to apply one synthetic method to the preparation of the e n t i r e class of compounds. Given the s i m i l a r i t y of the ligands, i t was somewhat s u r p r i -sing to f i n d that, i n some cases, subtle changes i n reaction conditions were required i n order to obtain pure products. Hence, for example, while the synthetic methods used to prepare the s i x , eight, ten and twelve carbon chain copper(II) phosphinate derivatives were s i m i l a r , i t was found that the precautions s u f f i c i e n t to prevent the formation of - 56 -the sulfate copolymer i n the hexyl and o c t y l compounds, did not prevent i t s formation i n the synthesis of the decyl and dodecyl d e r i v a t i v e s , and appropriate changes had to be made i n the procedure. These and other d i f f i c u l t i e s encountered i n the preparation of the copper(II) d i - n - a l k y l -phosphinates are discussed i n d e t a i l i n Chapter 4. It was also i n t e r e s t i n g to note the e f f e c t of reaction condi-tion s , s p e c i f i c a l l y the solvent, on the structure and properties of the product. (As w i l l be discussed more f u l l y i n l a t e r sections of th i s chapter, the compounds under i n v e s t i g a t i o n were found to ex i s t i n two isomeric forms; the a-form and the B-form.) In a l l cases, except for the n-octyl, n-decyl and n-dodecyl d e r i v a t i v e s , the compounds are i s o l a -ted as either the a-isomer or the B-isomer, regardless of reaction conditions. The eight, ten and twelve carbon chain d e r i v a t i v e s , on the other hand, p r e c i p i t a t e p r e f e r e n t i a l l y from aqueous alcohol i n the a-form but may be is o l a t e d i n the p-form i f the reaction i s ca r r i e d out in an organic solvent such as chloroform or carbon t e t r a c h l o r i d e 1 . Attempts to prepare, for example, the a-form of copper(II) di-n-hexyl-phosphinate by following exactly the procedure that y i e l d s the a-form of the n-octyl compound proved f u t i l e ; the hexyl compound i s i s o l a b l e only The 6-forms of the long (eight, ten or twelve carbon) chain compounds may also be obtained from the melts of the a-forms. See Section 4.3.8 and the l a t e r discussion on D.S.C. - 57 -i n the 8-form. S i m i l a r l y , the ethyl d e r i v a t i v e i s i s o l a t e d i n the a-form, i r r e s p e c t i v e of the solvent used 1. Hence, except for the Cg, C 1 Q and C 1 2 d e r i v a t i v e s mentioned above, none of the other compounds were found to e x i s t i n both forms. The p a r t i c u l a r form i s o l a t e d was also found to be independent of the copper(II) s t a r t i n g m a t e r i a l . This i s i n contrast to, for example, the d i - n - o c t y l d e r i v a t i v e of c o b a l t ( I I ) (65), where d i f f e r e n t c o b a l t ( I I ) s t a r t i n g materials r e s u l t i n isomers with d i f f e r e n t stereochemistries (tetrahedral and octahedral). The octahedral isomer i s converted i r r e v e r s i b l y to the tetrahedral isomer by melting or d i s s o l v i n g i n an organic solvent (65), conversion methods equivalent to those found i n t h i s work 2. The q u a l i t a t i v e s o l u b i l i t i e s and thermal properties of these coordination compounds were investigated i n order to examine the e f f e c t that the nature of the organic substituents on phosphorus has on the physical properties of the polymers (Section 1.2.1). The r e s u l t s of the s o l u b i l i t y t e s t s , for a number of common solvents, are given i n Table 2.1.3.1. Several generalizations may be made from these data. F i r s t l y , the compounds are more soluble i n r e l a t i v e l y non-polar, organic solvents (e.g., CHC13) than i n polar solvents (e.g., MeOH). Secondly, the This i s s i m i l a r to the behavior of Co[(n-C t tH 9) 2P0 2] 2 (45): the compound i s o l a t e d from benzene or carbon te t r a c h l o r i d e i s i d e n t i c a l to that i s o l a t e d from water. The a •* 8 conversion seen here does not, however, involve changes i n coordination number. The differences between the isomers are discussed i n the subsequent sections of this chapter. - 58 -Table 2.1.3.1 S o l u b i l i t i e s of Copper(II) Di-n-alkylphosphinates 1. Compound Solvent H 20 MeOH EtOH acetone CH 2 C I 2 C H C 1 3 CCl^ benzene 60°-90° pet.ether a - C u [ ( C H 3 ) 2 P 0 2 ] 2 s s ss ss s s s ss i a - C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 s s ss ss s s s ss i B - C u K n - C t ^ a ^ P O ^ s ss ss i ss s ss ss i 8 - C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 i ss ss i s s ss ss s a - C u [ ( n - C 8 H 1 7 ) 2 P 0 2 ] 2 i i i i vss ss ss i i P - C u [ ( n - C 8 H 1 7 ) 2 P 0 2 ] 2 i i i i ss s vss vss i a - C u [ ( n - C 1 Q H 2 1 ) 2 P 0 2 ] 2 i i i i ss ss vss 1 i p - C u [ ( n - C 1 0 H 2 1 ) 2 P 0 2 ] 2 i i i i I s vss 1 i a - C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 i i i i vss ss i i i p - C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 i i i i vss ss i i i s, soluble, > .1 g/100 mL; ss, s l i g h t l y soluble, ca. .01 g/100 mL; vss, very s l i g h t l y soluble, < .01 g/100 mL; i , i n s o l u b l e . - 59 -s o l u b i l i t y i n a l l solvents decreases with increasing a l k y l chain length, with a few exceptions. T h i r d l y , there appears to be no recognizable trends i n the s o l u b i l i t i e s of the a-isomers as compared to the 8-isomers. The f i r s t two observations on the s o l u b i l i t i e s of phosphinate polymers have been noted before (22,46,48,49,55) and have been att r i b u t e d to the r e l a t i v e a b i l i t i e s of the a l k y l chains of d i f f e r e n t lengths to sh i e l d the inorganic polymer backbone. The process of d i s s o l u t i o n can be viewed as in v o l v i n g , primarily, the breakdown of the three-dimensional structure a r i s i n g through interchain a s s o c i a t i o n s . These associations a r i s e from a combination of dipole-dipole interactions Involving the inorganic polymer backbone, expected to be maximized when the a l k y l group i s small (and hence unable to sh i e l d the backbone) and of induced dipole-induced dipole interactions involving interleaved a l k y l groups, expected to be maximized when the a l k y l group i s large (and the inorganic backbone dipole-dipole i n t e r a c t i o n s are minimized due to the shiel d i n g of the backbone by the long organic groups). In polar solvents such as water, methanol, ethanol and acetone, therefore, s i g n i f i c a n t s o l u b i l i t y Is expected only i n those cases where the polar inorganic backbone i s accessible, that i s , where the a l k y l group i s small. Hence, for these solvents the one, two, four and six carbon chain derivatives were found, generally, to be soluble or s l i g h t l y soluble (with the s o l u b i l i t y decreasing with increasing chain length), while the eight, ten and twelve carbon chain compounds (both oc-and 8-isomers) were found to be Insoluble i n these solvents. (These - 60 -l a t t e r polymers were not even wetted by water but remained as dry powders on the surface of the solvent.) In non-polar (petroleum ether, carbon te t r a c h l o r i d e and benzene) or s l i g h t l y polar (dichloromethane and chloroform) solvents, an explanation of the s o l u b i l i t i e s i s more d i f f i -c u l t . Compounds with shorter a l k y l groups have stronger dipole-dipole associations and might be expected to be insoluble i n non-polar or s l i g h t l y polar solvents; however, the a c c e s s i b i l i t y to the inorganic backbone may enhance t h e i r s o l u b i l i t y i n polarizable chlorinated solvents, a dipole-induced dipole i n t e r a c t i o n . The methyl and ethyl derivatives are, then, soluble i n chlorinated solvents, while, for those compounds with longer than two carbon chains, a pattern of s o l u b i l i t y i n these solvents i s less c l e a r . There i s , however, a general decrease i n the s o l u b i l i t y with increasing chain length, due to the decreasing a c c e s s i b i l i t y of the polar polymer backbone and to increasing i n t e r c h a i n a l k y l group-alkyl group i n t e r a c t i o n s . In the non-polarizable solvents, benzene and petroleum ether, the s o l u b i l i t i e s of a l l compounds i s low, ranging from s l i g h t l y soluble to i n s o l u b l e, with the n-hexyl de r i v a t i v e being a notable (and inexplicable) exception. These solvents are generally unable to break up the dipole-dipole interchain interactions dominant i n the short a l k y l chain compounds, or the induced d i p o l e -induced dipole interactions that predominate as the size of the R group increases, hence a l l s o l u b i l i t i e s are low. As mentioned e a r l i e r , there are no s i g n i f i c a n t differences or trends i n the s o l u b i l i t i e s of the oc-isomers as compared to that of the 8-isomers. This i s probably not too surprising as the s t r u c t u r a l d i f f e -rences between the isomers a r i s e from changes i n the orientations of the - 61 -a l k y l groups on phosphorus and the e f f e c t , i f any, of th i s on s o l u b i l i t y appears to be outweighed by the o v e r a l l reduction i n s o l u b i l i t y that comes from increasing the length of the carbon chain. There are ins t a n -ces where isomers have quite varied s o l u b i l i t i e s , for example, z i n c ( I I ) and cobalt(II) methylphenylphosphinate (48,49) both e x i s t i n two c r y s t a l l i n e forms and an amorphous form; the c r y s t a l l i n e isomers tend to be rather insoluble while the amorphous forms are soluble or s l i g h t l y soluble i n water and common organic solvents such as benzene and chloro-form. Assuming t h i s dependence of the s o l u b i l i t y on the c r y s t a l l i n i t y extends to the copper(II) di-n-alkylphosphinates, i t can be concluded that the a- and 8-isdmers under discussion here have s i m i l a r degrees of c r y s t a l l i n i t y and again the main factor determining s o l u b i l i t y i s the length of the a l k y l chain. The r e s u l t s of the D.S.C. ( D i f f e r e n t i a l Scanning Calorimetry) analyses are given i n Table 2.1.3.2. As with the s o l u b i l i t i e s , i t i s possible to draw some general conclusions about the thermal properties of these polymers with respect to the length of the a l k y l group on the phosphorus atom. The melting points tend to decrease with increasing chain length, the largest decrease (85°C) occurring between the ethyl and the butyl d e r i v a t i v e s . At the same time the heat required to melt the sample (AH^°) tends to increase with increasing chain length, as does the fusion entropy, AS^°. The melting process, i n these polymers, may be considered as involving the breaking apart of the intermeshed R groups and the disruption of the dipole-dipole i n t e r a c t i o n s between the polymer backbones, i n analogy to the process of d i s s o l u t i o n . As R gets longer, AH ° would increase due to increased meshing of the a l k y l Table 2.1.3.2 D.S.C. Studies on Copper(II) Di-n-alkylphosphinates. a-Isomers R Group T(°C) AHf ° kJ mol -1 AS f° Jmol" 1 deg - 1 Comments1 B-Isomers R Group T(°C) AHf ° kJ mol"1 AS f° Jmol" 1 deg"1 Comments1 CH, C 2H 5 251.0 106.4 128.1 240.0 n-C 8H 1 7 n-C 1 0H 2 1 n-C 1 2H 2 5 123.8 122.7 97.1 125.3 21 3 7 13 63 93 19 86 40 10 20 30 160 180 50 220 begins to decompose high T sh. reversible broad, irreversible broad, irreversible sharp broad, irreversible n—C^Hg n " ° 6 H 1 3 n-C 8H 1 7 n-C 1 0H 2 1 n-C 1 2H 2 5 130.5 155.2 108.8 89.4 92.0 94.5 96.8 6 28 40 53 71 94 10 70 100 150 190 250 high T sh. reversible reversible sharp, low T sh., reversible sharp, low T sh., reversible sharp doublet, reversible 1 Sharp, broad and doublet refer to the shape of the D.S.C. curve; sh, shoulder; T, temperature. - 63 -groups, which would require greater energy to disrupt and to set the longer a l k y l chains into thermal motion. AS f° would also increase due to the freeing up of the more meshed chains and because the number of possible configurations of the a l k y l chains, i n the melt, w i l l increase as the number of carbon atoms increases, hence causing greater disorder and a larger entropy difference between the s o l i d and the l i q u i d (102). The melting temperature decreases with increasing chain length, then, because the r e l a t i v e increase i n AS^° i s greater than that i n AH^0 AH f° C# " A G a (266)). This i s not unexpected since the increase i n AH,°, x Iso £ r with increasing a l k y l chain length, i s o f f s e t by a concomitant decrease i n AH^° caused by the reduced dipole-dipole interpolymer i n t e r a c t i o n s involving the inorganic backbone. In e f f e c t , the polymers with the longer a l k y l chains are inherently more f l e x i b l e (46,53,55) as a r e s u l t of the a b i l i t y of the a l k y l groups to act as " i n t e r n a l p l a s t i c i z e r s " (19,22) by reducing polar i n t e r a c t i o n s , thereby allowing increased ease of movement of the polymer m o l e c u l e s O n the other hand, the increase i n AS^° i s determined s o l e l y by the length of R, hence AS^° increases more ra p i d l y , with a l k y l chain length, than AH^° and T^ are decreased. Another e f f e c t of increasing the length of the a l k y l chain i s to decrease the thermal s t a b i l i t y of the compounds. For the d i - n - a l k y l -The r e l a t i v e l y high AH f° (21 kJ m ol - 1) for the methyl d e r i v a t i v e appears to r e s u l t from a combination of the fact that methyl groups are the l e a s t e f f e c t i v e at shielding dipole-dipole i n t e r a c t i o n s (48,49,72,101) with the fact that the "melting point" a c t u a l l y represents the beginning of the decomposition of the polymer (see l a t e r d i s c u s s i o n ) . - 64 -phosphinate polymers, thermal decomposition begins at the following temperatures: C u [ ( C H 3 ) 2 P 0 2 ] 2 , 285°C; Cu[ (C 2H 5) 2P0.J z , 280°C; Cu[(n-C l t H 9 ) 2 P 0 2 ] 2 , 280°C; Cu[(n-C 6H 1 3) 2P0 2] 2, 260°C; Cu[(n-C 8H 1 7) 2P0 2] 2, 265°C; C u [ ( n - C 1 0 H 2 1 ) 2 P O 2 ] 2 , 250°C; and C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 , 235°C. These values indicate a small but r e a l decrease i n thermal s t a b i l i t y with the increasing number of carbon atoms i n the a l k y l c h a i n 1 . This e f f e c t has been attributed to the ease of oxidation of the a l k y l side groups (22,46), which presumably increases with increasing chain length. The mode of decomposition of the metal phosphinates has not been well studied (20); however, analysis of the v o l a t i l e decomposition products of some zinc and beryllium phosphinates (20,49) indicates that the a l k y l (or a r y l ) groups on phosphorus are l o s t f i r s t , probably as r a d i c a l s which then attack other a l k y l groups. One advantage the use of a D.S.C. instrument has over that of a conventional melting point apparatus i s that thermal behavior not r e a d i l y v i s i b l e to the eye i s detected and recorded. As can be seen from Table 2.1.3.2, the e t h y l , butyl and a-dodecyl derivatives show "two- or three-event" melting curves. The endothermic peaks at temperatures lower than the true melting points are, by v i r t u e of t h e i r small AH° values (66), phase t r a n s i t i o n s . This may involve a t r a n s i t i o n to a p a r a c r y s t a l l i n e form from a c r y s t a l l i n e form, as found for Due to the very complex decomposition patterns for these compounds, i t was not possible to determine AH values. However, the decomposi-tions are extremely exothermic with t o t a l AH values for the main peaks ranging from 760 to 4,500 kJ m o l - 1 . - 65 -n i c k e l ( I I ) di-n-octylphosphinate (66). For zi n c ( I I ) di-n-butyl-, di-n-hexyl- and di-n-decylphosphinates (53), the observed phase t r a n s i t i o n s are believed to be associated with the onset of disorder along the polymer as a r e s u l t of the loosening of the contacts between the a l k y l side groups on d i f f e r e n t polymer molecules. The exact nature of the t r a n s i t i o n s observed here i s not known; except for the n-dodecyl d e r i v a t i v e (see l a t e r discussion), the t r a n s i t i o n s are completely re v e r s i b l e ; cooling and reheating the samples generates D.S.C. curves i d e n t i c a l to the o r i g i n a l patterns. Heating both the ethyl and the butyl compounds, to above the t r a n s i t i o n temperature (approx. 135°C), then cooling to room temperature produced no changes i n the in f r a r e d spectra of these polymers nor could any changes ( i n color or texture, for example) be detected by c a r e f u l observation of powdered samples being heated i n a Gallenkamp melting point apparatus. However, examination of c r y s t a l s of copper(II) diethylphosphlnate showed that from ca. 122°C to 130°C 1, the color of the c r y s t a l s darkened and they became opaque. The color lightened with cooling and i n fact appeared l i g h t e r than unheated c r y s t a l s . The c r y s t a l s were fractured and no longer transparent when viewed under a microscope. Equivalent observations were noted for c r y s t a l s of copper(II) d i - n - b u t y l -phosphinate. Again no differences were observed i n the in f r a r e d spectra of the heated and unheated c r y s t a l s , Indicating the r e v e r s i b i l i t y of the phase changes. I t i s l i k e l y that the f r a c t u r i n g observed i n the 1 No changes were observed around 105°C, the f i r s t t r a n s i t i o n temperature. - 66 -c r y s t a l s i s a r e s u l t of the thermal motion of the a l k y l groups that disturbs the interchain packing. There are s i g n i f i c a n t differences i n the thermal behavior of the a-isomers as compared to the 8-isomers. I t i s only possible to discuss the compounds which ex i s t i n both forms i n this respect since, as with the s o l u b i l i t i e s , the differences between the methyl and the ethyl (a-isomers) and the butyl and the hexyl (8-isomers) a r i s e from th e i r d i f f e r e n t a l k y l chain lengths as well as from the fact that they e x i s t i n d i f f e r e n t forms. I t i s not possible, i n these cases, to separate the two e f f e c t s or determine which predominates, although i t i s most l i k e l y chain length. (These compounds w i l l be discussed shortly.) For those derivatives that do e x i s t i n both forms, some i n t e r e s t i n g trends a r i s e . The actual melting "points" of the a-isomers appear as broad curves, spanning up to t h i r t y degrees, while those of the p-isomers are very sharp, with low temperature shoulders present for the n-octyl and n-decyl d e r i v a t i v e s 1 . (The dodecyl de r i v a t i v e i s a s p e c i a l case as the a-isomer shows an i r r e v e r s i b l e phase t r a n s i t i o n at 97.1°C and the p-isomer y i e l d s a D.S.C. curve with two minima (a "doublet"). The thermal behavior of t h i s compound w i l l be discussed i n d e t a i l l a t e r i n t h i s section.) This i s i l l u s t r a t e d i n Figure 2.1.3.1 2. The melting These shoulders may be associated with minor a l k y l chain rearrange-gements occurring before melting. This figure i s meant only as an i l l u s t r a t i o n ; temperature and energy scales for the d i f f e r e n t thermograms are not necessarily the same. Refer to Table 2.1.3.2 for accurate values. ure 2.1.3.1 Thermograms of the a- and 8-isomers. A heat flow (exothermic) c=» TCC) - 68 -behavior of the 8-isomers i s completely r e v e r s i b l e , while for the a-isomers i t i s not; they are, upon melting, converted i r r e v e r s i b l y to the 8-isomers. Also of note i s the fact that the temperature and energy required to melt the samples i s higher for the a-isomers than for the 8-isomers. I f the assumption 1 i s made that the a-isomers have s t r u c -tures equivalent to that of the ethyl d e r i v a t i v e while the B-isomers have the structure of the butyl and hexyl de r i v a t i v e s , then the s t r u c t u -r a l differences between the isomers are related primarily to changes i n the o r i e n t a t i o n of one of the a l k y l side groups on each phosphorus atom of one of the eight-membered rings of the a-isomers. As discussed i n Section 2.1.2, th i s unique a l k y l group occurs on a ri n g that i s s u b s t a n t i a l l y more puckered than the other ri n g i n the a-isomer or ei t h e r rings of the 8-isomers. This may introduce a s l i g h t increase i n r i g i d i t y into the backbone and hence increase the melting points by increasing AH^0. However, the greatest s i g n i f i c a n c e of the d i f f e r e n t a l k y l group orientations i s the e f f e c t on the interchain packing. In the 8-isomers, the packing of the a l k y l chains between adjacent polymer molecules and between layers of these molecules i s very symmetrical and e f f i c i e n t but noninteracting. The a l k y l chains of one polymer l i e i n planes i n between the planes formed by the a l k y l groups of the next polymer (Figure 2.1.2.4 (a)) and there i s no d i r e c t contact between them. In the a-isomers, on the other hand, the conformation of the unique a l k y l groups on one ring changes the o r i e n t a t i o n of those Support for t h i s assumption i s presented i n the remaining sections of t h i s chapter. - 69 -groups with respect to the polymer backbone; they now l i e i n the "plane" of the backbone instead of approximately perpendicular to i t (Figure 2.1.2.3). The interpolymer packing, as a r e s u l t , i s less regular and now there i s "entangling" of these unique a l k y l groups with the a l k y l groups on adjacent polymers. In e f f e c t these groups now project through the planes formed by the a l k y l groups on adjacent l a y e r s 1 . This increase i n interpolymer i n t e r a c t i o n through the increased contact between the a l k y l groups would then increase the melting point by increasing the amount of heat (AH") required to melt the a-isomers compared to the 8-isomers 2. The presence, i n the a-isomers, of the two d i f f e r e n t rings with t h e i r d i f f e r e n t a l k y l groups, and perhaps s l i g h t l y d i f f e r e n t energy thresholds, may account for the broadness of the i n i t i a l melting curves. (The broadness of these curves may also be associated with the presence, i n the sample, of a d i s t r i b u t i o n of molecular weights ( i . e . , polymer chain lengths), the lowest of which w i l l melt f i r s t (102).) There are instances (55) where the o r i g i n a l isomer may be recovered from a melted sample by simply s e t t i n g aside at room temperature; for example, the amorphous form of z i n c ( I I ) n-butylphenylphosphinate (55) converts back This e f f e c t i s most e a s i l y v i s u a l i z e d by rotating appropriate a l k y l groups i n Figure 2.1.2.4.(b), so that the hydrogens on the a-carbon are staggered with respect to a P-0 rather than a P-C bond. It i s i n t e r e s t i n g to note that the melting temperature differences between the a- and (3-isomers are nearly equal (~ 30°C) for these derivatives as are, to a lesser extent, the differences i n AH?: (~10-20 kJ m o l - 1 ) , hence there i s very l i t t l e difference i n the entropy change from one isomer to the other, as might be expected. - 70 -to the c r y s t a l l i n e a-form on standing. With the compounds i n t h i s study there i s no tendency for the 8-isomers to convert back to the a-isomers, making the melting points of the l a t t e r i r r e v e r s i b l e , while those of the former are r e v e r s i b l e . The i r r e v e r s i b i l i t y of the melting points of the a-isomers, and hence, of the conversion to the 8-forms, may indicate that the polymer structure and packing of the 8-isomers are the more en e r g e t i c a l l y stable. The D.S.C. curves for the methyl, e t h y l , n-butyl and n-hexyl derivatives are given i n Figure 2.1.3.21. As mentioned e a r l i e r , the melting point of CuKCHg^PC^l 2 i s a c t u a l l y the beginning of the decom-pos i t i o n of t h i s compound. If the sample i s heated to j u s t above the melting point (to 275°C), then cooled and reheated, a d i f f e r e n t D.S.C. curve i s obtained. A new peak involving both endothermic and exothermic energy changes appears at approximately 130°C and the "melting point" i s lowered by 2°C 2. This i s shown i n curves (a) and (b), Figure 2.1.3.2. In a melting point apparatus, the sample i s seen to undergo an i r r e -v e r s i b l e blue to green color change with the i n i t i a l melting. The green l i q u i d cools to a b r i t t l e green glass, the i n f r a r e d spectrum of which shows the presence of water and a loss of res o l u t i o n i n the bands a r i s i n g from stretching of the P-0 and P-C bonds, as well as i n the bands a r i s i n g from the bending of the C 2P0 2 moiety (see Section 2.1.4 on in f r a r e d spectroscopy). With reheating, the sample bubbles and then ~ * A g a i n , t h i s figure i s meant only as an I l l u s t r a t i o n ; t e m p e r a t u r e and energy scales for the d i f f e r e n t curves may not be the same. 2 This value i s outside the range of temperature r e p r o d u c i b i l i t y found. See Experimental, Chapter 4. - 71 -Figure 2.1.3.2 Thermal Behavior of the Methyl, E t h y l , n-Butyl, and n-Hexyl Derivatives. ( c ) a - C u ( ( C 2 H 5 ) 2 P 0 2 ) 2 . < d ) 0 - C u « n - C 4 H g ) 2 P O 2 ) 2 . ( e J / S - C u W n - C g H ^ P O g ^ . - 72 -becomes opaque at approximately 130°C, followed by melting at ca. 250°C. Further heating r e s u l t s i n complete decomposition at ~ 280°C. The melting properties of C u [ ( C 2 H 5 ) 2 P 0 2 ]2 a n d Cu^n-C^Hg) 2P0 2] 2, as powders and as c r y s t a l s , were discussed e a r l i e r i n this section. The D.S.C. curves have been included i n Figure 2.1.3.2, curves (c) and (d), for completeness. The presence of high temperature shoulders, v i s i b l e on the peaks associated with phase t r a n s i t i o n s i n these compounds, at 128.1°C and 130.5°C for the ethyl and butyl d e r i v a t i v e s , r e s p e c t i v e l y , should be noted. These probably ar i s e from minor rearrangements accom-panying the phase t r a n s i t i o n s . The D.S.C. curve of the n-hexyl derivative (curve (e), Figure 2.1.3.2) i s somewhat misleading i n that i t appears to represent a simple melting point at 108.8°C. No other t r a n s i t i o n s appear on the thermogram above or below t h i s temperature u n t i l the compound begins to decompose at about 260°C. In a melting point apparatus, however, i t can be seen that the n-hexyl d e r i v a t i v e does not melt to a clear l i q u i d , as do a l l the other phosphinates studied here. Rather, t h i s polymer appears to "soften" (49,55) at 108.8°C and becomes a wetted, opaque plug; no further change i s observed u n t i l the compound decomposes. Even with repeated cooling and reheating, the sample does not melt i n the conven-t i o n a l sense, that i s , to a l i q u i d . I t could be that the amount of heat absorbed at the "melting" point i s s u f f i c i e n t to melt portions of the polymer, hence the wetted appearance, but i s not s u f f i c i e n t to break down the interchain i n t e r a c t i o n s of (perhaps) the more c r y s t a l l i n e portions of the polymer. The cause of this behavior i s , however, not c e r t a i n . - 73 -As mentioned e a r l i e r , the n-dodecyl compound i s unique. I t displays an i r r e v e r s i b l e phase t r a n s i t i o n i n the D.S.C. thermogram of the a-Isomer 1, unlike the re v e r s i b l e t r a n s i t i o n s seen i n the ethyl and n-butyl d e r i v a t i v e s . The thermal properties of this compound were investigated and the re s u l t s are i l l u s t r a t e d i n Figure 2.1.3.3 1. Curves (a) and (b) are the simple melting of the a- and p-forms 2, resp e c t i v e l y ( c f . Figure 2.1.3.1). If a new sample of the a-lsomer i s heated to 103°C, i . e . , to just above the t r a n s i t i o n at 97.1°C, cooled and reheated to 103°C, curve (c) r e s u l t s . The single phase t r a n s i t i o n at 97.1°C (AH° = 19 kJ m o l - 1 ) becomes a doublet, with minima at 93.2°C and 96.0°C ( t o t a l AH° = 15 kJ m o l - 1 ) . These l a t t e r t r a n s i t i o n s are re v e r s i b l e ; cooling and reheating to 103°C several times generates i d e n t i c a l doublets. Heating t h i s sample to 150°C produces curve (d), with the same doublet phase t r a n s i t i o n and the broad "true" melting of the a-isomer at 125.0°C (AH f° = 81 kJ m o l - 1 ) . Cooling and reheating this sample, which i s now the p-isomer, gives curve (e), i d e n t i c a l to (b), except for a s l i g h t asymmetry i n the doublet. The f i n a l curve, ( f ) , of the Figure, represents the heating of a sample of the p-isomer, a f t e r i t has been cooled to l i q u i d nitrogen temperature. (This modifi-cation was discovered by accident. The p-isomer was found to have These la b e l s are used here for consistency with the e a r l i e r discus-sion, but, as w i l l be discussed shortly, are not s t r i c t l y c orrect. Temperature and energy scales are not necessarily the same for the d i f f e r e n t curves. - 74 -Figure 2.1.3.3 Thermal Behavior of C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 . (exothermic) TCC) See text for explanation of Figure. - 75 -undergone a blue to mauve color change af t e r the measurement of the magnetic s u s c e p t i b i l i t y to 80K (Gouy method).) A sample of the mauve compound, when heated, y i e l d s a small endotherm at 45.4°C (AH° = 5 kJ mol" 1), followed by a peak at 96.9°C (AH f° = 94 kJ mol - 1) with a low temperature shoulder, which i s s i m i l a r to the shoulders on the melting curves of the n-octyl and n-decyl 8-isomers. The former peak repre-sents the t r a n s i t i o n from the mauve form to a blue form 1, while the l a t t e r , more endothermic peak i s the melting point of this blue form. Cooling to room temperature and reheating r e s u l t s i n a D.S.C. curve l i k e curve (e) of Figure 2.1.3.3; however, the asymmetry of the doublet i s more pronounced. The mauve form may be regenerated by recooling to l i q u i d nitrogen temperature. The complex thermal behavior of t h i s compound may be explained with the aid of Figure 2.1.3.4. The form i s o l a t e d from the preparative mixture, c a l l e d , to t h i s point, the a-n-dodecyl d e r i v a t i v e , i s composed of two isomers 2, a and (3 of the Figure. Heating the sample to above 97.1°C melts 8, which, with cooling to room temperature, i s converted, i r r e v e r s i b l y , to a mixture of 8 and y. The small doublet at 93.2°C and 96.0°C (Figure 2.1.3.3 ( c ) ) , then, i s the r e v e r s i b l e melting of the y-and p-forms, r e s p e c t i v e l y . Melting oc+ p(melt), at 125.3°C, or a + p(melt) + Y( m elt)» a t 125.0°C, followed by cooling to room temperature, This was determined by heating a sample to ca. 60°C, then opening the sample pan. This point w i l l be returned to s h o r t l y . - 76 -2.1.3.4 Polymorphism i n Cu[(n-C 1 2H 25)2 p n2^ 7(melt) /3(melt) a+/3(melt)+ 7(melt) - 77 -i r r e v e r s i b l y converts the a-form i n the o r i g i n a l sample to a mixture of P and y. The presence of these two forms, i n the frozen melt, was f i r s t observed when large samples of the a + B form were melted, then cooled to room temperature. The s o l i d i f i e d sample was composed of two d i s t i n c t l y colored sections; l i g h t blue around the edges (the p-form) and l i g h t mauve towards the middle (the y-form). Cooling p + y to l i q u i d nitrogen temperature converts both to 9, a completely mauve s o l i d which, when heated to 45.4°C converts t o t a l l y to p, giving a completely blue sample. This purely p-form then melts at 96.9°C to give, with cooling, the p + y mixture again. The "doublet" observed on remelting P + Y i s then the r e v e r s i b l e melting of Y ~ f o r m » a t 95.5°C, followed by that of the p-form, at 96.8°C. The asymmetry observed i n this doublet upon melting the cooled and reheated a + P(melt) + y ( m e l t ) mixture (curve (e), Figure 2.1.3.3) or upon remelting the melted blue p-isomer, arises from the d i f f e r e n t thermal treatment of the samples p r i o r to melting. This r e s u l t s i n varying amounts of the B- and Y - i s o m e r s i n the melt which, i n turn, e f f e c t s the shape of the "doublet". The observed asymmetries are preserved with repeated meltings of the samples. The small differences i n the melting points observed for the Y ~ f o r m (93.2°C and 95.5°C) and the p-form (97.1°C, 96.0°C, 96.8°C, and 96.9°C) also a r i s e from the varying amounts of these isomers present i n the p a r t i c u l a r sample under i n v e s t i g a t i o n . I t has been suggested (vide supra) that the "a-isomer" of the n-dodecyl d e r i v a t i v e was, i n f a c t , a mixture of two isomers, a and p, the l a t t e r of which melts at 97.1°C. Support for the presence of two isomers i n t h i s case comes from the fact that a sample of t h i s compound - 78 -from a d i f f e r e n t preparation does not show the peak at 97.1°C, when heated to 105°C. Hence, cooling and reheating t h i s sample does not produce the r e v e r s i b l e t r a n s i t i o n s at 93.2°C and 96.0°C (curve ( c ) , Figure 2.1.3.3). This compound melts at a s l i g h t l y higher temperature (129.1°C) than the a + p mixture (125.3°C) and requires a somewhat greater heat of fusion, 96 kJ mol" 1 compared to 86 kJ mol" 1. This i s a consequence of the increased " p u r i t y " , due to the presence of only one isomer, the a-isomer, and i s consistent with the e a r l i e r discussion on the values of AH°^ and T^ of the a-isomers as compared to the p-isomers. Reheating the cooled melt of this pure a-form y i e l d s the previously observed "doublet" at 94.4°C and 96.4°C, for the melting of the y- and p-forms, res p e c t i v e l y ( t o t a l AH°^, 87 kJ m o l - 1 ) , with the peak due to the y-isomer being larger and broader than that of the p-isomer. Once completely melted and cooled, the y + p form from the pure a-isomer i s i d e n t i c a l i n a l l respects to that from the a + p form. In subsequent discussions on these two modifications of the n-dodecyl compound, the pure a-isomer w i l l be referred to as the a-isomer, while the a + p mixture w i l l be referred to as the a'-Isomer 1. The y + p cooled melt w i l l continue to be c a l l e d the p-isomer, for s i m p l i c i t y . That the a'-isomer contains a mixture of the a-form and the p-form, as opposed to some other low melting modification, i s supported by Infrared spectroscopy, to be discussed i n the next section of t h i s chapter. The spectra of the a- and the a'-isomers are i d e n t i c a l , with the exception of the presence, i n the spectrum of the a'-isomer, of an This d i s t i n c t i o n i s relevant p r i m a r i l y to the discussion on the magnetic properties of these compounds, Section 2.1.6. - 79 -absorption at 807 cm" , that w i l l be shown to be c h a r a c t e r i s t i c of the 8-isomers. I t i s also supported by the magnetic s u s c e p t i b i l i t y studies, to be discussed i n Section 2.1.6. 2.1.4 Infrared Spectra. The in f r a r e d data for the s t r a i g h t a l k y l chain phosphinate derivatives are given i n Tables 2.1.4.1 to 2.1.4.5. There are s t r i k i n g s i m i l a r i t i e s between the spectra of the compounds, as expected from the r e l a t i v e l y small differences between the ligands. As with the s t r u c t u -r a l and physical properties discussed e a r l i e r , the a-isomers may be, distinguished from the 8-isomers on the basis of th e i r i n f r a r e d spectra. The in f r a r e d data i n Tables 2.1.4.1 to 2.1.4.4 are arranged to f a c i l i -tate a comparison between the two forms. The absorptions appearing i n the 1200 cm - 1 - 1000 cm - 1 region are r e a d i l y assigned as the asymmetric and symmetric P0 2 stretches of coordinated phosphinate groups and show the s h i f t s from the "free ion" values, to lower and higher frequencies, r e s p e c t i v e l y , expected upon coordination to a metal (23,30-32,34,103,126,128,136-138,140,142). The frequencies, assignments and A values (A = v - v (23,66,67, asy. sym. 136)), for the copper(II) compounds and for the non-coordinated li g a n d , are given i n Table 2.1.4.1. There i s very l i t t l e d ifference i n the positions of the asymmetric and of the symmetric P0 2 s t r e t c h e s 1 , at approximately 1110 cm - 1 and 1045 cm - 1, res p e c t i v e l y , from one n - a l k y l We are ignoring, for the moment, the 1160 cm - i peak i n the spectrum of the methyl d e r i v a t i v e . See l a t e r discussion. Table 2.1.4.1 Infrared Bands Associated with P-0 Stretching1. oc~Isoner8 B-Isasers Free Anion Ganpound v an-1 asy. v . { a n _ 1 ) A(CB_l) v (ca"1) asy.v ' v . ( c - " l ) tfcm"1) v (an-1) asy.v ' tfar1) Counter-cation References *U60 v.s. 1123 s.sh. *11U sh. *1051 v.8. 1039 s.sh. 109 60 1169 1155 s. 1065 985 s.br. 104 170 *h+ H*" 128 this work. 1110 v.s. 1049 v.s. 61 - 1097 v.8. 1014 s. 83 Ag + this work Oa[(n^H9)2P02J2 1116 v.s. 1057 s. 59 1140 1151 8. 1067 973 s.br. 73 178 fc+ H*" 34 this work. Qi[(iK^H 13) 2F0 2J 2 1111 v.s. .1061 s.sh. k!l04O s. 61 1150 s.br. 951 s.br. 199 B+ this work O4[(n-CaH17)2P02J2 1170 m.sh. *1107 v.s. *1043 v.8. 64 1119 s.sh. •1112 V.8. 1065 m.sh. *1046 s. 66 U44 1047 965 a. 97 m+ 66 this work 1097 s.sh. 1029 s.sh. 1153 s.br. 958 s.br. 195 H*" this work2 1171 m.sh. *1109 v.s. 1072 m.sh. 1058 s.sh. 66 * l l l l v.s. 1090 m.sh. 1064 m.sh. 1057 m.sh. 69 1131 V.8. il053 a. '1039 a. 85 l b + this work 1100 s.sh. *1043 v.8. 1048 flush. *1042 8. 969 s. H*" this work Cu[(tt-C12H25)2P02]2 1171 m.sh. * i l l i v.s. 1100 s.sh. *1046 v.s. 65 d.115 v.s.ah 1111 v.8. 1099 s.sh. 1068 m.sh. 1054 m.sh. *1044 s. 1025 m.sh. 69 1141 s.br. 959 v.s. 182 this work * Asterisks nark die strangest FOj stretching frequencies, from which the A values were calculated, unless there was a shoulder of equal Intensity present, in which case the frequencies were averaged. (This was found for the B-C& and B-C12 derivatives). 1 v.s., very strong; s., strong; m., mediun; sh., shoulder; br., broad. 2 Solution spectrum in chloroform. - 81 -derivative to another or from one isomer to another. The A values are of approximately equal magnitude (ca. 65 cm - 1) and f a l l into the range expected for equivalent P-0 bonds and double bridging phosphinate groups (32,65,66). The s i m i l a r i t y i s not unexpected since a l l compounds are proposed to have common s t r u c t u r a l features, that i s , d i s t o r t e d tetrahedral metal centers joined by two bridging phosphinate anions. The lack of s i g n i f i c a n t changes i n the frequencies of the strongest P0 2 stretching absorptions (marked with aster i s k s i n Table 2.1.4.1) i n going from the a-isomers to the 8-isomers supports the contention that i n a l l cases the s t r u c t u r a l differences between the two groups are related p r i m a r i l y to rearrangements i n the conformations of the a l k y l groups (55,66), as opposed to major rearrangements of the polymer backbone (65,67,100), from, for example, double bridging to al t e r n a t i n g s i n g l e - t r i p l e bridging . However, i t should be pointed out that the medium i n t e n s i t y peak at ca. 1170 cm - 1 i n the a-isomers 1 of the n - o c t y l , n-decyl and n-dodecyl d e r i v a t i v e s , which could a r i s e from the presence of a small percentage of the phosphinate groups being involved i n unsymmetric bonding of the type V or VI (Figure 1.2.2.1), completely disappears upon conversion to the 8-forms, i n d i c a t i n g , perhaps, a rearrangement to a symmetric bonding mode. Bonding of type V could r e s u l t from polymer chain terminating, i . e . , monodentate, phosphinate groups (21,56), i n which case, i t s absence i n the 8-isomers may indicate a greater degree of polymerization i n t h i s form than i n the o-isomer, The methyl compound has a s i m i l a r , though stronger, band at 1160 cm - 1 • - 82 -hence, fewer terminal groups 1. Also of i n t e r e s t i s the consistent i n t e n s i t y difference i n the P0 2 stretching absorptions between the a-isomers (v and v of equal i n t e n s i t y ) and the B-isomers (v v asy. sym. H 3 r asy. more intense than v ). This difference i s , unfortunately, not sym. r e a d i l y explainable. In compounds with greater than four carbon atoms per a l k y l chain, there tends to be numerous shoulders, of lesser i n t e n s i t y , on the strong P0 2 stretching absorptions. This has been observed i n the i n f r a r e d spectra of a number of t r a n s i t i o n metal phosphinates (67,68) and the shoulders have been described (67) as "very weak and may be either overtones, combination bands or P0 2 stretching frequencies caused by phosphinate structures not predominant i n the bulk polymer". This may be the explanation for the appearance of shoulders i n the present case; however, the bands seen are of medium to strong i n t e n s i t y and perhaps a better explanation i s that they a r i s e from v i b r a t i o n a l coupling between adjacent rings (23) and/or from such e f f e c t s as factor group s p l i t t i n g (103), giving r i s e to f a i r l y intense absorptions. It i s i n t e r e s t i n g to note that the differences between the c r y s t a l l o g r a p h l c a l l y d i s t i n c t eight-membered rings i n C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 (Section 2.1.2) are not manifested i n the P0 2 stretching absorptions of the i n f r a r e d spectrum, as only two strong bands are present i n t h i s region. In contrast, the n-hexyl derivative shows two absorptions of The magnetic studies on these compounds (Section 2.1.6) support t h i s view. - 83 -almost equal i n t e n s i t y i n the symmetric P0 2 stretching r e g i o n 1 . This i s i l l u s t r a t e d i n Figure 2.1.4.1. The reasons for t h i s d u p l i c i t y are not clear as both compounds have s i m i l a r P-0 bond lengths and O-P-0 angles. The hexyl compound i s also composed of two c r y s t a l l o g r a p h i c a l l y d i s t i n c t rings; however, unlike the ethyl compound, there are some obvious s t r u c t u r a l differences between the two rings i n t h i s d e r i v a t i v e . One ring has Cu-0-P-O-Cu moieties that involve one long (1.932 A) and one short (1.896 A) Cu-0 bond ( c f . VI, Figure 1.2.2.1), while i n the other, the two Cu-0 bonds are both r e l a t i v e l y short (1.902 A and 1.907 A, c f . I I , Figures 1.2.2.1) 2. This d i f f e r e n c e i n the bonding symmetry may give r i s e to the two symmetric P0 2 stretches seen i n the i n f r a r e d spectrum. The ethyl compound, on the other hand, has four nearly equivalent (1.9158 A to 1.9224 A) Cu-0 bonds per copper atom and only one symmetric P0 2 s t r e t c h . The butyl d e r i v a t i v e (89) also has four nearly equal Cu-0 bonds, ranging from 1.916 A to 1.926 A, and only one symmetric P0 2 s t r e t c h 3 . This has been observed previously i n some hypophosphite s a l t s (126). This means that each copper forms one long (1.932 A) and three shorter (average 1.902 A) bonds to oxygen. Gillman and Eichelberger (67) report the presence of weak shoulders at 1085 and 1032 cm - 1. We observed weak shoulders at 1096, 1043 and 1035 cm - 1; however, as these were present i n the parent acid and well separated from the strong P0 2 stretches, at 1151 and 973 cm - 1, i t was f e l t that they were not associated with these modes. - 85 -The methyl derivative i s unique i n t h i s group of n-alkyl s u b s t i -tuted phosphinates, and indeed i n a l l the compounds prepared i n t h i s study, i n that i t i s the only complex that exhibits three strong or very strong well separated P0 2 stretches, accompanied by strong shoulders on the two lower frequency absorptions (Figure 2.1.4.2). This m u l t i p l i c i t y has been reported i n dimethylphosphinate s a l t s of l e a d ( I I ) , manga-nese(II) (69), and c o b a l t ( I l ) (69,71), and, for Pb(II) and Mn(II), was proposed to a r i s e from unsymmetric phosphinate bonding ( c f . VI, Figure 1.2.2.1), i . e . , r e s u l t i n g i n unequal M-0 bonds, as discussed above. This type of bonding, however, would not be expected to give r i s e to asymmetric P0 2 stretching absorptions with frequencies so close to the free ion value of 1169 cm - 1 (128) (for the sodium s a l t ) , as found i n the lead (at 1165 cm - 1 (69)), and copper (at 1160 cm - 1) compounds. Nor i s i t easy to envisage why dimethylphosphinate, with probably the l e a s t s t e r i c hindrance of a l l the ligands studied, would adopt such a bonding mode. The cobalt compound (69,71) i s proposed to have symmetric phosphinate bonding and yet has a very high frequency P0 2 s t r e t c h at ca. 1190 cm - 1 (1191 cm"1 (69); 1196 cm"1 (71)). On the other hand, the manganese compound lacks such a high frequency peak and the reported (69) absorptions, at 1127, 1108, 1053, 1029 and 1014 cm"1, correspond well to those found for the p-forms of the eight, ten, and twelve carbon chain derivatives discussed e a r l i e r , for which unsymmetric bonding was not suggested. It may be that the appearance of the high frequency band i n lead, cobalt and copper dimethylphosphinates i s related to the presence of some monodentate phosphinate groups ( i . e . , chain terminating - 86 -Figure 2.1.4.2 Infrared Spectrum of a-Cu[(CH 3) 2P0 2] 1200 1000 800 W a v e n u m b e r ( c m - 1 ) T - 87 -groups), In analogy to the a-C 8, -C^Q and - C 1 2 d e r i v a t i v e s , discussed e a r l i e r , but i n greater proportions than found i n those compounds, to account for the i n t e n s i t y . That more than one type of phosphinate group i s present i n C u [ ( C H 3 ) 2 P 0 2 ] 2 i s manifested not only i n the P0 2 stretching region, but also i n the in f r a r e d areas associated with the methyl group v i b r a t i o n s , P-C stretching and C 2P0 2 bending modes, as w i l l be discussed presently. Gillman (66) proposed unsymmetric bonding of type VII (Figure 1.2.2.1) and di s t o r t e d octahedral metal centers to account for the P0 2 stretching absorptions, appearing at 1160 and 1040 cm - 1 (A = 120 cm - 1), of C u [ ( C 8 H 1 7 ) 2 P 0 2 ] 2 dissolved i n carbon t e t r a c h l o r i d e . The structure i n sol u t i o n i s c l e a r l y d i f f e r e n t from that i n the s o l i d state, for which the P0 2 stretching frequencies are almost the same as those reported here (Table 2.1.4.1). However, from the above discussion, i t would seem more l i k e l y that these frequencies a r i s e from monodentate anions, r e s u l t i n g from extensive polymer d i s s o c i a t i o n i n s o l u t i o n . The determined molecular weight, corresponding roughly to a trimer (66), would then appear to be a consequence of the averaging of the molecular weights of a number of oligomers (100). As discussed i n Section 1.2.2, the s h i f t s In the phosphinate P0 2 stretching frequencies from the free anion values and the frequency of the metal-oxygen stre t c h can be rel a t e d , not only to the mode of coor-dination and hence polymer structure, but also to the type ( i o n i c or covalent) and the strength of the i n t e r a c t i o n . As can be seen from the data i n Table 2.1.4.1, s h i f t s i n both P0 2 stretching frequencies occur upon coordination and comparison to the frequencies observed for the - 88 -sodium s a l t s , which are i o n i c , indicate that the i n t e r a c t i o n i s covalent i n nature (32). The largest s h i f t , to a lower frequency, occurs for the asymmetric s t r e t c h , while the symmetric stretch remains approximate-l y the same or decreases s l i g h t l y (ca. 10 cm - 1) i n frequency 1. The greatest decrease (58 cm - 1) i n the frequency of the asymmetric s t r e t c h occurs i n the dimethyl d e r i v a t i v e , while the longer a l k y l chain com-pounds show s h i f t s from 20 to 32 cm - 1. This would seem to i n d i c a t e that, for the bridging phosphinate groups i n the dimethyl compound (see previous discussion on C u [ ( C H 3 ) 2 P 0 2 ] 2 ) , t n e nietal-ligand Interaction i s stronger than for the other d e r i v a t i v e s . That postulation may be borne out by the p o s i t i o n of the peak assigned to the Cu-0 s t r e t c h i n t h i s complex (Table 2 . 1.4 . 2 ) , where the weak to medium i n t e n s i t y band at 406 cm - 1 i s the highest frequency assigned to a Cu-0 s t r e t c h i n any of the compounds. The c o r r e l a t i o n between a higher frequency M-0 s t r e t c h and a stronger metal-ligand i n t e r a c t i o n has been noted i n studies of compounds of this type (12,16,17,86), as well as of those involving phosphine oxides (R3PO) as ligands (7,8 , 1 1 ) . There appears to be no r e a d i l y recognizable trend i n the values of the s h i f t s i n the P 0 2 stretching frequencies from the free ion v a l u e 2 , where one may have anticipated a larger s h i f t for the phosphinates containing the more electron-releasing groups, i . e . , the longer a l k y l chains. However, the frequencies of the The constancy of the frequency of the symmetric stre t c h has been noted previously (136). The comparison between the copper compounds and the sodium s a l t s i s complicated by the lack of in f r a r e d data for some of the l a t t e r . - 89 -Table 2.1.4.2 Infrared Bands Associated with Cu-0 S t r e t c h i n g 1 . Freqi lencies (cm - 1) Compound a-Isomers B-Isomers C u [ ( C H 3 ) 2 P 0 2 ] 2 C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 C u [ ( n - C 4 H 9 ) 2 P 0 2 ] 2 C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 C u [ ( n - C 8 H 1 7 ) 2 P 0 2 ] 2 C u [ ( n - C 1 0 H 2 1 ) 2 P O 2 ] 2 C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 406 w.-m. 335 m. 383 m.s. 382 m. 383 m. 362 m. 361 w.-m. 373 w.-m. 359 w.-m., b r . 2 399 w., 387 w., 360 w., 341 w.3 1 w., weak; m., medium; m.s., moderately strong; br., broad. 2 Weak shoulders at 395, 384, 372, 352, 343, and 337 cm - 1. 3 Assignment uncertain. See text. - 90 -bands assigned to Cu-0 stretches do tend to increase with increasing chain length, with the exception of the methyl d e r i v a t i v e , to a maximum of ca. 380 cm - 1 i n the o-forms of the n-octyl, n-decyl and n-dodecyl compounds. Upon conversion to the p-forms, the Cu-0 stretching frequencies decrease while there i s a very s l i g h t increase i n the asymmetric P0 2 stretching frequency, perhaps i n d i c a t i n g a somewhat lessened i n t e r a c t i o n . There i s also a marked difference i n the i n t e n s i t i e s of the Cu-0 absorptions between the a-forms (medium to moderately strong) and the p-forms (weak to weak-to-medium). The assignment of the Cu-0 str e t c h i n p-Cu[ (n-C, 2H 2 5) 2P0 2] 2 * s u n c e r t a i n due to the appearance, upon conversion from the a-form, of four bands of equal i n t e n s i t y (weak) i n the 340 - 400 cm - 1 region, i n contrast to the a-isomer which shows one medium absorption at 383 cm - 1 (See Figure 2.1.4.3). The reasons for t h i s m u l t i p l i c i t y and for the i n t e n s i t y difference are unclear. The r e l a t i v e l y low frequency (335 cm - 1) of the absorption assigned to the Cu-0 stretch i n the ethyl compound i s puzzling since this compound has approximately the same average Cu-0 bond lengths (1.9182 A) as the n-butyl (1.920 A (89)) and the n-hexyl (1.909 A) compounds, for which Cu-0 stretches are assigned to 362 and 361 cm - 1, r e s p e c t i v e l y . I t may be that the weak band at 375 cm - 1 i n the ethyl compound should be assigned as the metal-oxygen stretch; the 335 cm - 1 band may a r i s e from deformation modes of the ligand (128). There i s a roughly corresponding weak, broad absorption at 335 cm - 1 i n the i n f r a r e d spectrum of s i l v e r diethylphosphinate. While there were i n s i g n i f i c a n t differences between the frequen-c i e s assigned to the PO stretches i n the a-isomers as compared to the - 91 -p-isomers, the absorptions assigned to the PC 2 asymmetric and symmetric stretches (31,32,69,128,134,144) provide a means of dis t i n g u i s h i n g one form from the other on the basis of the i r infrared spectra. Table 2.1.4.3 l i s t s the relevant frequencies for the two groups, and the a-and p-isomers of C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ^ 2 a r e i l l u s t r a t e d i n Figure 2.1.4.3. The a-isomers show a broad, medium i n t e n s i t y asymmetric stre t c h i n the 750-775 cm - 1 region, while i n the B-isomers, this band has s h i f t e d to the 800 - 810 cm - 1 region and become a sharp, medium to moderately strong absorption. The symmetric stretching frequency i s v i r t u a l l y the same, ca. 725 cm - 1, i n both isomers but the r e l a t i v e i n t e n s i t i e s are not. In the a-isomers this band i s somewhat more intense than the asym-metric stre t c h while i n the p-forms i t i s , generally, less intense (see, for example, Figure 2.1.4.1.b)). In both cases, the frequencies of the symmetric stre t c h are around 30 cm - 1 lower than found i n the parent a c i d s 1 , while the asymmetric stretching absorptions are approximately 20 cm - 1 higher, i n the p-isomers, and approximately 10 cm - 1 lower, i n the a-isomers, than the corresponding absorptions i n the acid spectra. These differences between the isomers allow for ready i d e n t i f i c a t i o n of the form present i n a copper(II) di-n-alkylphosphinate sample and allow a pred i c t i o n of the magnetic and e l e c t r o n i c properties, to be discussed i n the following sections of th i s chapter. For example, the presence of an absorption at 807 cm - 1 ( v a s v p C 2 ) i n o n e preparation of the a-n-dodecyl d e r i v a t i v e (see e a r l i e r discussion on D.S.C.) indicated the presence of v PC, ca. asy. /- 780 cm -1. sym. PCn ca. 750 cm- 1. Table 2.1.4.3 Infrared Bands Associated with P-C S t r e t c h i n g 1 . a-Isomers Compound Frequency (cm - 1) C u [ ( C H 3 ) 2 P 0 2 ] 2 C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 C u t ( n - C 1 + H 9 ) 2 P 0 2 l 2 C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 C u [ ( n - C 8 H 1 7 ) 2 P 0 2 ] 2 C u t ( n - C 1 0 H 2 1 ) 2 P O 2 ] 2 C u l ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 753 m.sh. 748 m. 739 m. 718 w.sh. 707 w.sh. 757 m.sh. 728 m. 772 m.br. 721 m.s. 773 m.br. 723 m.s. 775 m.br. 724 m.s. Assignment a s y . P C 2 V o , r m P C 3 sym. VSVm. P C2 vsym. P C2 vsym. P C2 vsym. P C2 B-Isomers Frequency (cm - 1) 806 m. 8 . 725 m. 803 m. s. 722 m. 804 m. 8 . 722 m. 805 m. 8 . 723 m. 806 m. 723 m. Assignment vsym. P C2 sym* 2 v a 8 v . P C 2 vsym.PC2 vsym. P C2 V a « y - ^ 2 vsym. P C2 w., weak; m., medium; m.s., moderately strong; sh., shoulder; br., broad. - 93 -Figure 2.1.4.3 Infrared Spectra of the oc- and B-forms of C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 . - 94 -some 8-isomer, a fact confirmed by magnetic s u s c e p t i b i l i t y measurements (Section 2.1.6) where the impurity resulted i n some ferromagnetism (8-isomer) appearing i n the l a r g e l y antiferromagnetic sample (a-isomer). The observed frequency differences a r i s e as a r e s u l t of the s t r u c t u r a l differences between the two isomers; the d i f f e r e n t o r i e n t a -tions of the a l k y l groups i n the two forms re s u l t i n changes i n the o v e r a l l geometry of the P - a l k y l 2 moieties, perhaps r e s u l t i n g i n d i f f e r -ing i n t r a - and interchain a l k y l group interactions and d i f f e r e n t frequencies for the v i b r a t i o n s . The m u l t i p l i c i t y observed i n t h i s region of the spectrum of the methyl derivative i s a consequence of the presence of phosphinate groups i n d i f f e r e n t coordination modes, as discussed e a r l i e r . The in f r a r e d spectra of the two isomers also d i f f e r i n the region associated with the angle bending modes of the C 2P0 2 grouping (32,50,69,71,126,128,145). The absorptions appearing i n this 600 to 400 cm - 1 region are l i s t e d i n Table 2.1.4.4. Assignments to the asymmetric and symmetric C 2P0 2 bending modes have not been made due to the complexity, i n most cases, of the spectra i n this region, a r i s i n g from the number of bands present, some of which are, no doubt, due to i n t e r n a l a l k y l group v i b r a t i o n s . However, the asymmetric modes are reported (128) to appear at lower frequencies than the symmetric. There are small increases (of up to ca. 15 cm - 1) i n the frequencies of the more intense bands, within an isomer group, with increasing a l k y l chain - 95 -Table 2.1.4.4 Infrared Bands i n the 600 cm"1 - 400 cm"1 Region 1. a-Isomers B-Isomers Compound Frequency (cm - 1) Frequency (cm" 1) C u [ ( C H 3 ) 2 P 0 2 ] 2 513 m.s.sh. 504 m.s. 483 m.s. 468 m.sh. C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 508 m.sh. 487 m. 422 m. Cu[(n-C l tH 9) 2P0 2] 2 545 m.s. 517 m. 448 v.w. C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 551 m.s. 514 m. 480 w.sh. C u [ ( n - C 8 H 1 7 ) 2 P 0 2 ] 2 586 m.s. 556 m. 564 v.w.sh. 515 m. 550 m. 493 w.sh. 518 w. 478 w. 479 v.w. C u [ ( n - C 1 0 H 2 1 ) 2 P 0 2 ] 2 586 m.s. 559 m. 562 w.sh. 523 m. 552 m. 516 m.sh. 521 w. 502 w.sh. 503 w. 475 w. 481 v.w.sh. 474 w. C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 590 m. 561 m. 558 m. 530 w.-m.sh. 523 w. 521 w.-m. 506 w. 505 w. 495 w.sh. 492 w.sh. 1 v.w., very weak; w., weak; w.-m., weak-to-medium; m., medium; m.s., moderately strong; sh., shoulder. - 96 -length, the largest increases (60 - 80 cm"1) occurring between the et h y l and n-octyl a-forms 1. This trend has been noted previously (267). The a-isomers reveal, generally, a pattern of numerous absorptions, the i n t e n s i t y of which decrease with decreasing frequency; the B-isomers tend to have fewer bands with lower frequencies than found i n the a-isomers (see Figure 2.1.4.3). The a-isomers of the C 8, and C 1 2 show medium to moderately strong bands at approximately 585 and 550 cm - 1, with several weaker bands and shoulders present 2, while i n a l l 8-isomers, the most intense bands appear at ca. 555 and 520 cm - 1, with d i f f e r i n g numbers of weaker bands present, depending on R. In the p-isomers, the most intense bands are closer i n frequency than the corresponding absorptions i n the parent acid, the higher frequency band having decreased by ca. 10 cm - 1, and the lower frequency peak having increased by ca. 30 cm - 1. The highest frequency absorption i n the a-isomers i s ca. 20 - 30 cm""1 higher than the corresponding band i n the a c i d . The s h i f t s i n the frequencies, from the acid spectra, are not unexpected since, upon coordination, v i b r a t i o n a l modes involving the oxygens and phosphorus are going to be affected the most by changes i n ligand geometry and electron density. The appearance, i n the spectra of the a-isomers, of higher frequency absorptions than found i n the There are also increased numbers of bands with the larger R groups. The strongest absorptions for the methyl and ethyl occur, as men-tioned, at s i g n i f i c a n t l y lower frequencies. - 97 -6-isomers, probably r e s u l t s from a combination of the e f f e c t s of the uniquely oriented a l k y l groups and of the greater puckering of the eight-membered rings which could r e s u l t i n greater ring s t r a i n and, hence, higher frequencies for the C 2P0 2 bending modes. The remaining i n f r a r e d bands for these compounds are l i s t e d i n Appendix 2.a). These are, primarily, absorptions associated with the a l k y l group vibrations and no attempt has been made to assign these. The extremely weak bands i n the 8-C8 and a-C 1 2 d e r i v a t i v e s , at 1728 and 1729 cm - 1, r e s p e c t i v e l y , are due to a POO combination mode (141); these absorptions are, apparently, too weak to be seen i n the other d e r i v a t i -ves. Torsion and deformation C 2P0 2 modes appear below approximately 400 cm - 1 (128). 2.1.5 E l e c t r o n i c Spectra. Absorptions observed i n the v i s i b l e and near in f r a r e d region (350 nm to 2200 nm; 28,600 cm - 1 to 4550 cm - 1) are l i s t e d i n Table 2.1.5.1, which i s arranged for f a c i l e comparison of the a- and 8-isomers 1. The spectra of the s t r a i g h t chain a l k y l derivatives are characterized by the presence of a peak at 810 nm to 880 nm (12,350 cm - 1 to 11,400 cm - 1), with a high energy shoulder at 695 nm to 760 nm (14,400 cm - 1 to 13,200 cm - 1). Ty p i c a l spectra are shown i n Figure 2.1.5.1. The exception to t h i s two band spectrum i s the methyl d e r i v a t i v e , which shows a broad, unresolved absorption centered at 830 nm (12,000 cm - 1). Diffuse reflectance spectra (350 nm to 740 nm; 28,600 cm - 1 to 13,500 cm - 1) are not included here, as only the high energy shoulder i s observable and t h i s precludes wavenumber assignment. Table 2.1.5.1 E l e c t r o n i c Spectra of Copper(II) Di-n-alkylphosphinates 1. 0t-l8< >mers B-ISOB iers Compound X(nm) v(cm" X(nm) v(cm~ 1) C u [ ( C H 3 ) 2 P 0 2 ] 2 830 br. 12,000 br. C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 835 700 sh. 12,000 14,300 br. C u K n - C ^ g ^ P O ^ 870 760 sh. 11,500 13,200 sh. C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 860 750 sh. 11,600 13,300 sh. C u [ ( n - C 8 H 1 7 ) 2 P 0 2 ] 2 815 700 sh. 12,300 14,300 sh. 880 760 sh. 11,400 13,200 sh. C u [ ( n - C 1 0 H 2 1 ) 2 P O 2 ] 2 810 700 sh. 12,300 14,300 sh. 875 760 sh. 11,400 13,200 sh. C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 810 695 sh. 12,300 14,400 sh. 865 760 sh. 11,600 13,200 sh. br., broad; sh., shoulder. - 99 -Figure 2.1.5.1 E l e c t r o n i c Spectra of C u [ ( n - C 1 0 H 2 1 ) 2 P O 2 ] 2 . « — 1 1 l i ' ' Wavelengt h ( nm ) - 100 -While the shape of the band envelope i s s i m i l a r for a l l these compounds, the positions of the absorption maxima are not. The a-isomers exhibit maxima at ca. 815 nm and 700 nm (12,300 cm"1 and 14,300 cm"1, r e s p e c t i v e l y ) , while the maxima In the p-isomers are s h i f t e d to higher wavelengths (lower energy) by an average of 60 nm, to ca. 870 nm and 760 nm (11,500 cm"1 and 13,200 cm"1, r e s p e c t i v e l y ) , as i l l u s t r a t e d i n Figure 2.1.5.1 for the a- and p-forms of the n-decyl d e r i v a t i v e . The s i m i l a r i t y of the spectra, within each isomer group, supports the contention that the a-forms have structures equivalent to that of the d i e t h y l d e r i v a t i v e and the p-forms have the structure of the n-butyl and n-hexyl d e r i v a t i v e s . Both groups of compounds have di s t o r t e d (flattened) tetrahedral CuO^ chromophores of approximately symmetry and the t r a n s i t i o n energy s h i f t s seen i n the e l e c t r o n i c spectra then a r i s e from subtle differences i n the degree of d i s t o r t i o n from regular tetrahedral geometry. The spectra have been assigned u t i l i z i n g the c r y s t a l f i e l d model of Gerloch and Slade (161). This involves point charge c a l c u l a t i o n s of the energy l e v e l s r e s u l t i n g from a x i a l , i n t h i s case, tetragonal, d i s t o r t i o n s from regular cubic symmetry. The model assumes that the a x i a l d i s t o r t i o n i s related to changes i n bond angles, rather than bond lengths (161), an assumption completely compatible with the case at hand, where X-ray crystallography (Section 2.1.2) has shown that there are i n s i g n i f i c a n t differences i n the average Cu-0 bond lengths of the two forms; 1.9182 A for C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 (a-isomer) and 1.920 A and 1.909 A for the n-butyl (89) and n-hexyl derivatives (p-isomers), r e s p e c t i v e l y . The e f f e c t of the J)^ p o t e n t i a l ( V Q ) on 2d - 101 -the d- o r b i t a l s i s calculated from matrix elements of the type <m^jVp |m t^>, which are parameterized i n terms of Dq and Cp; the 2d fourth- and second-order r a d i a l parameters 1, respectively, and a, the angular d i s t o r t i o n from regular T, symmetry. The d i s t o r t i o n angle, a, d i s i l l u s t r a t e d i n Figure 2.1.5.2, and, for the compounds under discus-sion here, i s taken as one-half of the average of the two largest O-Cu-O bond angles. The matrix elements are (161): <0JV |0> = -y Dq(X) + 2Cp(Y), [2.1] 2d <±1|V |±1> =" 4 °q(X) + Cp(Y), [2.2] 2d <±2|V |±2> = j Dq(X) - 2Cp(Y), [2.3] 2d <±2JV |+2> = -5Dq(Z), [2.4] 2d where X =• 35 cosV-SOcos 2a+3, Y = 3 c o s 2 a - l , and Z = s i n ^ a . Solution of the secular determinant gives the energies of the A,(d 2 ) , E (d ,d ), z xz B 1(d x2_ y2) a n t * B 2 ^ x y ^ t e r m s * ^he ground state i s then 2 B 2 , with 2 E , 2B^ and 2A^ excited states. The 2 B 2 *• 2B± t r a n s i t i o n i s formally symmetry forbidden (268), so that only two t r a n s i t i o n s , 2 B 2 • 2Aj^ and 1 r 4 2 r 2 Dq = — z e 2 (—r—); Cp = — z e 2 (—5—), where ze i s a point charge at 6 a 7 a J a distance a from the metal, and r represents the r a d i a l polar coor-dinate of a general point less than a away from the metal (161). - 102 -Figure 2.1.5.2 The D i s t o r t i o n Angle a. z A - 103 -Z B 2 — • E, are expected i n symmetry. I n i t i a l l y , before s t r u c t u r a l d e t a i l s of the ethyl d e r i v a t i v e were known, the approach to f i t t i n g the spectra involved generating a serie s of energy l e v e l diagrams, energy versus d i s t o r t i o n angle a, for set values of Dq and Cp. Values of Dq 1 ranged from 700 cm - 1 to 1700 cm - 1 and Cp was chosen such that the r a t i o Cp/Dq varied from less than one to t h r e e 2 . The observed t r a n s i -t i o n energies were compared to the calculated energies i n order to obtain possible values of Dq, Cp and a. This was rather a tedious process and resulted i n several possible f i t s , none of which could be unambiguously deemed c o r r e c t . The determination of the precise s t r u c -ture of the ethyl d e r i v a t i v e , hence the value of a (74.27°), s i m p l i f i e d the assignment, as the values of X, Y and Z i n equations [2.1] to [2.4] were then known. The mathematical expressions for the predicted ener-gies of the t r a n s i t i o n s from 2 B 2 to 2 E , 2A^ and for a = 74.27°, are given i n Table 2.1.5.2, as are some possible values of the parameters Dq and Cp. These were calculated by assigning the two t r a n s i t i o n s observed for the d i e t h y l compound, 12,000 and 14,300 cm - 1, to combinations of the three possible t r a n s i t i o n s , and solving the set of equations generated by su b s t i t u t i n g E ( 2 E ) , E ( 2 A L ) or E ( 2 B 1 ) with 12,000 cm"1 or 14,300 cm"1, as appropriate. T r a n s i t i o n energies for the missing peak(s) were then calculated by sub s t i t u t i n g Dq and Cp back into the o r i g i n a l Note that Dq i s as defined by Gerloch (161), i . e . , 10 Dq = % A t e t . The values of Cp/Dq found for compounds assigned using t h i s model f a l l into the range of 2 to 14; however, Cp/Dq values for copper compounds are below two (161). See l a t e r discussion. Table 2.1.5.2 Possible Assignments for the Ele c t r o n i c Spectrum of Cu[(C 2H 5) 2P0 2] and Calculation of the Crystal F i e l d Parameters. Equations for t r a n s i t i o n energies with a » 74.27°: E ( 2 E ) - 2 B 2 - 2E - 4.9949 Dq + 2.3385 Cp E ( 2 A X ) - 2 B 2 - 2 A j - 3.5891 Dq + 3.1180 Cp E ^ B j ) - 2 B 2 - 2 B 1 - 8.5840 Dq Tr a n s i t i o n Energies (cm - 1) Assignment Number Assigned Calculated DqCcm"1) Cp(cm - 1) Cp/Dq 1) B2 — • 2 E : „ 2 A . • A l -14,300 12,000 „ 2 R . 19,750 2300 1200 0.52 2) 2 B 2  2B2 — • 2ES 14,300 12,000 2 B 2 • 2 B . 4,750 550 3950 7.18 3 > 2 B 2 > 2» . • B x. 12,000 2 B 2 B 2 — 2 E : • 2 A . 14,100 14,500 1400 3050 2.18 4) 2 B 2 „ 2 R . • B l - 14,300 2 B 2  2B — * 2 E . r 2 A . 12,500 11,600 1665 1800 1.08 Crystal F i e l d Parameters - 105 -equations. In assignments 3) and 4), (see Table 2.1.5.2), Cp was calculated by assigning the t r a n s i t i o n at 14,300 cm - 1 or 12,000 cm"1, respectively, as the arithmetic average of E( 2E) and E ( 2 A ^ ) , that i s , | ( E ( 2 E ) + E ( 2 A 1 ) ) = 14,300 cm"1 or 12,000 cm"1. Of the possible f i t s l i s t e d i n Table 2.1.5.2, the f i r s t two were rejected for several reasons. The value of Dq i n the f i r s t case i s anomalously high, r e s u l t i n g i n a value for A of 10,200 cm - 1. This tet value i s reminiscent of octahedrally coordinated copper(II), f o r example, & Q C t for copper i n the host l a t t i c e ZnSiF 6»6H 20, i . e . , "regular" octahedral C u ( H 2 0 ) 6 2 + , was found to be 10,000 cm"1 (164). Values of 10 Dq are expected to be less for four-coordinate compounds than for six-coordinate compounds (161,173). In addition, the value of Cp calculated from t h i s assignment (1200 cm"1) r e s u l t s i n a Cp/Dq r a t i o of only 0.52, well below the range of 2 to 14 mentioned e a r l i e r and much lower than found previously for copper compounds (161). The second assignment has d i f f i c u l t i e s the opposite to those of the f i r s t . Here the calculated Dq value of 550 cm"1 y i e l d s a A of only 2400 cm"1. Cp i s then 3950 cm"1, giving a very high Cp/Dq r a t i o of 7.18. Previously (161), the e l e c t r o n i c spectra of Cs 2CuBr l + (187) and C s ^ u C l ^ (188) for which the d i s t o r t i o n angles are known, have been assigned using this model. The Dq values that gave the best f i t s were 1100 cm,"1 (A = tet 4900 cm" 1), for the bromide, and 1150 cm"1 (A =5100 cm" 1), for the tet ' chloride, with Cp values of 1660 cm"1 and 2025 cm"1, r e s p e c t i v e l y . Oxygen bonding ligands are expected to be higher i n the Spectrochemical Series than chloride which i s , i n turn, higher than bromide (160,161) - 106 -( c f . , DqCCuCli^ 2 -) = 1150 cm - 1>Dq(CuBr 4 2 -) = 1100 cm - 1), and hence the phosphinate ligands considered here should cause a greater s p l i t t i n g of the d o r b i t a l s than either the chloride or the bromide. The fact that the Dq value for t h i s second f i t i s only approximately half that of these l a t t e r ligands i s probably s u f f i c i e n t to disregard i t as a reasonable p o s s i b i l i t y . Further support for i t s u n s u i t a b i l i t y comes from an examination of the Cp/Dq r a t i o of 7.18. As mentioned e a r l i e r , the Cp/Dq r a t i o s for copper compounds have been found to be below two, outside the range of 2 to 14 found for other metal complexes (161). Gerloch and Slade have suggested that this r e s u l t s from increased covalency i n compounds of the more electronegative copper ion, compared to compounds of other metals. In examining the e f f e c t s of such factors as coordination number, bond lengths and charge d i s t r i b u t i o n on Dq, Cp and Cp/Dq, i t was pointed out the Dq and Cp increase with decreasing bond length but not at the same rate ( r e f e r to e a r l i e r d e f i n i t i o n s of Dq and Cp), so that Cp/Dq decrea-ses with decreasing bond length. Ligand to metal charge trans f e r i s expected to increase the r a d i a l parameters by decreasing the e f f e c t i v e charge on the metal (Zg£f)» hence causing expansion of the d- o r b i t a l s and greater repulsive i n t e r a c t i o n with the "point charges" (161). Dq w i l l increase fa s t e r than Cp so that Cp/Dq i s again decreased with increasing charge t r a n s f e r . (This e f f e c t i s countered by the loss of charge on the ligand, reducing ze, by which both r a d i a l parameters are m u l t i p l i e d , hence reducing Dq and Cp but by the same amount, so that Cp/Dq remains unchanged.) In addition, for tetrahedral ions there i s a s l i g h t l y greater Nephelauxetic e f f e c t than i n octahedral ions, r e s u l t i n g from the greater amount of s - o r b i t a l character i n the hybrid bonding - 107 -o r b i t a l s (161); s p 3 for the tetrahedron versus d 2 s p 3 for the octahedron. Electron density transferred v i a these o r b i t a l s then has greater s character and i s able to sh i e l d the d- o r b i t a l s more e f f e c t i v e l y , allowing greater "cloud-expansion" by reducing Z e ^ . This w i l l increase Dq and reduce Cp/Dq, although the e f f e c t i s small. It i s , then, a combination of the above e f f e c t s , that increase Dq and Cp but reduce Cp/Dq, that have been used to explain the low Cp/Dq values i n tetrahe-d r a l copper(II) complexes. Greater covalency, involving ligand to metal charge transfer, r e s u l t s i n r e l a t i v e l y short bonds and i n reduced e f f e c -t i v e nuclear charge, leading to smaller values of Cp/Dq than might otherwise be expected. It was on t h i s basis that the value of 7.18 for Cp/Dq i n the second f i t was considered unreasonable. It was more d i f f i c u l t to decide which of the two remaining f i t s was more reasonable; however, on the basis of the above discussion, i t was f e l t that the Cp/Dq r a t i o of 2.18, found for assignment 3), was too high. In addition, i t seemed u n l i k e l y that the formally forbidden 2 B 2 *• 2B^ t r a n s i t i o n would give r i s e to the major peak i n the spec-trum, with the 2 B 2 • 2E and 2 B 2 • 2Aj^ allowed t r a n s i t i o n s giving r i s e to a high energy shoulder. This i s p a r t i c u l a r l y incongruous i n the case of the methyl d e r i v a t i v e , where the observed absorption at 12,000 cm - 1 would then be assigned as the 2 B 2 *• 2 B X (forbidden) t r a n s i t i o n , with the allowed t r a n s i t i o n s not being observed. Hence, the preferred f i t (4), (Table 2.1.5.2) involved assigning the shoulder at 14,300 cm - 1 to the 2 B 2 • 2Bj^ t r a n s i t i o n and the absorption at 12,000 cm"1 to the unresolved 2 B 2 • 2Aj_, 2E t r a n s i t i o n . This assignment r e s u l t s i n calculated Dq and Cp values of 1665 cm - 1 and 1800 cm - 1, respectively, - 108 -with Cp/Dq equal to 1.08. A i s then 7400 cm - 1, some 30% higher than A t e t for CuCl 1 + 2~ (5100 cm - 1), as expected for an oxygen bonding l i g a n d . The energies calculated for the 2 B 2 • 2E (12,500 cm - 1) and 2 B 2 • 2Aj^ (11,600 cm - 1) t r a n s i t i o n s using these parameters then agree well with the observed energy of 12,000 cm - 1, supporting the assignment of the l a t t e r to the unresolved 2 B 2 • 2 E , 2k-^ t r a n s i t i o n . The spectra of the other a-isomers (Table 2.1.5.1) are assigned as above, on the basis of the s i m i l a r i t y of the observed t r a n s i t i o n energies to those of copper(II) diethylphosphinate. (The absorption observed for the methyl d e r i v a t i v e , at 12,000 cm - 1, i s then more reasonably assigned as the unresolved 2 B 2 • 2E, 2A^ t r a n s i t i o n , with the formally forbidden 2 B 2 *• 2 B 1 t r a n s i t i o n not appearing as a high energy shoulder.) These compounds would be predicted to have a d i s t o r t i o n angle a of around 74.3°, comparable to the ethyl d e r i v a t i v e . The energy l e v e l diagram, energy versus a, for Dq = 1665 cm - 1 and Cp = 1800 cm - 1, i s shown i n Figure 2.1.5.3 and i l l u s t r a t e s the predicted t r a n s i t i o n s at a = 74.3°. The 8-forms of the di-n-alkylphosphinates may also be assigned using the parameters of Figure 2.1.5.3. D i s t o r t i o n angles for two of these compounds are known from X-ray crystallography; for the n-butyl (89) and the n-hexyl (Section 2.1.2) derivatives the values of a are 73.25° and 73.04°, r e s p e c t i v e l y . Values of Dq = 1665 cm - 1 and Cp = 1800 cm - 1 then give calculated t r a n s i t i o n energies that agree reasonably well with those observed, assuming again that the high energy shoulder i s due to the 2 B 2 *• 2B^ t r a n s i t i o n and the lower energy band arises from the unresolved 2 B 2 • 2E, 2A^ t r a n s i t i o n . The calculated and observed energies are given i n Table 2.1.5.3. The agreement between the c a l c u l a -- 109 -Figure 2.1.5.3 Energy Level Diagram for Dq = 1665 cm"1 and Cp = 1800 cm - 1. Table 2.1.5.3 Calculated and Observed Tran s i t i o n Energies for 6-Cu[(n-C 4Hcj) 2P0 2] and B - C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 : Dq - 1665 cm"1 and Cp - 1800 cm"*. Trans i t i o n Enei rgies (cm - 1) Compound Tra n s i t i o n Calculated Observed 8-Cu[(n-C l tH 9) 2P0 2] 2 p - C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 2n », 2a , b2 * , A1 2B, • 2E 2p/ • 2 B B 2 • B t 2 B , 2 A 5 2 9 1 2B, • 2 E 2** . 2 B B 2 • B x 11,500 11,900 14,000 11,500 11,800 13,900 | 11,500 13,200 | 11,600 13,300 - I l l -ted and the observed energies for the ^B 2 • t r a n s i t i o n i s not as good as seen for the d i e t h y l d e r i v a t i v e and the other a-isomers. This arises from the r e l a t i v e invariance of the energy of the l e v e l , for d i f f e r i n g a values and fixed Dq and Cp, as compared to the 2E, 2A^ and 2 B 2 l e v e l s (refer to Figure 2.1.5.3). In addition, the positions of the high energy shoulders are less c e r t a i n than those of the primary absorp-ti o n , due to the nature of the spectra. Hence, while the lower energy peaks are considered accurate to ca. ± 1.5% (± approximately 200 cm - 1), the shoulders are only considered to be accurate to within ca. 3% (± approximately 400 cm" 1). There w i l l also be error i n Dq and Cp, a r i s i n g from the basic assumption of the model i t s e l f , that the ligands may be treated as point charges (202). Overall uncertainty i n Dq and Cp i s estimated to be ca. ± 5%, on the basis of c a l c u l a t i o n s , equivalent to those carried out for the d i e t h y l compound (Table 2.1.5.2, assignment 4)), carried out for the n-butyl and n-hexyl d e r i v a t i v e s . These cal c u l a t i o n s yielded average values of Dq and Cp that were within 5% of those found for the the d i e t h y l compound. Given the above mentioned unce r t a i n t i e s , the discrepancy between the calculated and observed t r a n s i t i o n energies, for the B-isomers, i s within experimental error and does not in v a l i d a t e the proposed f i t . The p-forms of the n - o c t y l , n-decyl and n-dodecyl phosphinates can then be assigned by analogy to the n-butyl and n-hexyl compounds, the observed t r a n s i t i o n energies for a l l the p-forms being nearly i d e n t i c a l . The former compounds are predicted to have CuO^ chromophores involving s l i g h t l y less compression than i s found in the a-isomers, with d i s t o r t i o n angles of around 73.1°. The fact that the spectra of both a-- 112 -and 8-forms of these compounds can be assigned with the same values of the c r y s t a l f i e l d parameters, Dq and Cp, i s not unexpected. The c r y s t a l f i e l d strength of the ligands would not vary s i g n i f i c a n t l y on the basis of the r e l a t i v e l y small, and i n the case of the two forms of the C Q, C 1 0 and C^2 d e r i v a t i v e s , non-existent, differences In the substituents on the ligands. The observed differences In the e l e c t r o n i c t r a n s i t i o n energies are then a d i r e c t consequence of the s t r u c t u r a l d i f f e r e n c e s , between the two groups of compounds, which re s u l t i n d i f f e r i n g degrees of d i s t o r t i o n from regular tetrahedral geometry. F i n a l l y , the calculated value of Cp/Dq, 1.08, i s s u b s t a n t i a l l y lower than that found for CuBr 4 2~ (Cp/Dq = 1.51) or for C u C l ^ 2 " (Cp/Dq = 1.76) (161), i n d i c a t i n g greater covalency i n the copper(II) d i - n - a l k y l -phosphinates than i s found i n the copper(II) halides, on the basis of the e a r l i e r discussion on Cp/Dq r a t i o s . 2.1.6 Magnetic Properties. One of the most i n t e r e s t i n g discoveries of these studies was that these phosphinate bridged polymers exhibit s i g n i f i c a n t magnetic exchange. In addition, the sign of the exchange i n t e g r a l , J , i n the two forms i s opposite; the oc-forms show antiferromagnetism (J<0), while the 8-forms are ferromagnetic (J>0). This section discusses the treatment and f i t t i n g of the magnetic data to t h e o r e t i c a l models, the r e s u l t s of t h i s analysis and a discussion of possible mechanisms for the magnetic exchange. Tables of molar s u s c e p t i b i l i t y and e f f e c t i v e magnetic moment data - 113 -over the temperature range 4.2K to 300K, for the compounds under discus-sion, are given i n Appendix 3. The high temperature (80K to 300K) data used i n the analysis are, i n most cases, the averages of measurements obtained using the Gouy equipment and more than one packing of the Gouy tube. This averaging was done to avoid excess weighting of these data during the computer f i t t i n g to the t h e o r e t i c a l models (see l a t e r d i s cus-s i o n ) . S i m i l a r l y , magnetometer data (4.2K to 125K) were averaged where appropriate. The uncertainty i n the calculated moments i s ca. ± 2% by the Gouy method (203) and ca. ± 1% i n the v i b r a t i n g sample magnetometer (V.S.M.) moments1. The temperature measured by the l a t t e r equipment i s considered to be accurate to ± 1% and was c a l i b r a t e d using both a cobalt(II) (HgCo(SCN)l+) and a copper(II) ((CH 3) 2NHCH 2CH 2NH(CH 3) 2CuCl^) standard (269) over the e n t i r e range (4.2K to 125K), as well as at three fixed points (the b o i l i n g points of helium, nitrogen, and oxygen), as described previously (270). The same cobalt(II) standard, HgCo(SCN)^, was used as a c a l i b r a n t for the Gouy method; however, the Weiss con-stant (9) employed i n t h i s case was -10K (271) as opposed to the value of -1.86K recommended by H a t f i e l d et a l . (269) for the c a l i b r a t i o n of the temperature range of the magnetometer. The Weiss constant of -10K i s good for the higher temperature region (100K to 300K) covered by the Gouy method, but r e s u l t s i n an uncertainty of ca. 5% i n the temperatures below ca. 100K. The lack of consistent d i s c o n t i n u i t y i n the e f f e c t i v e moment (u f f ) i n the overlap region of the two techniques This uncertainty i s represented as error bars on some of the data points i n Figures 2.1.6.3-.9. - 114 -indicates that t h i s i s not a serious problem; the approximately 2% error i n l ^ f f produced by th i s discrepancy i s probably accounted for i n the general uncertainty of the Gouy method. Poor o v e r a l l agreement between the two sets of data does occur for those compounds containing a l k y l chains of greater than s i x carbons and this appears to be due to the packing error inherent i n the Gouy method (203). It was not possible to use the v i b r a t i n g sample magnetometer data (for which there i s no packing e r r o r ) , i n the region of overlap, to determine a packing correction to the Gouy d a t a 1 . This i s due to there being maximum uncer-t a i n t y i n both measurements i n t h i s region: the values of the su s c e p t i -b i l i t y determined with the magnetometer at these temperatures are small and the diamagnetlc correction of the sample holder constitutes up to ca. 10% of the observed reading, p a r t i c u l a r l y for antiferromagnetic compounds. The Gouy data are affected by the uncertainty i n the temperature mentioned above and by experimental d i f f i c u l t i e s i n s u s c e p t i b i l i t y measurements at the lowest temperatures. Hence, no attempt was made to correct the Gouy data and, i n the cases where the data c o r r e l a t i o n i s poor, only the low temperature (T<100K) data were used for the computer f i t s (see l a t e r d i s c u s s i o n ) . The exception to thi s use of only T<100K data was the a-n-dodecyl d e r i v a t i v e . There was considerable scatter i n the V.S.M. data, for this compound, a r i s i n g from the very small s u s c e p t i b i l i t i e s measured over the enti r e temperature range (see Figures 2.1.6.6.b) and 2.1.6.12). (This 1 Due to the small s u s c e p t i b i l i t y of these copper(II) polymers at room temperature, i t was not possible to determine a packing correction using the Faraday method. - 115 -problem was avoided somewhat with the other compounds, p a r t i c u l a r l y the antiferromagnetic forms, by using more sample i n a larger sample container. See Experimental, Section 4.1.5.) Emphasis on the V.S.M. data was avoided by including a l l s u s c e p t i b i l i t y data for the oc-n-dodecyl isomer i n the computer f i t . The magnetic parameters (Table 2.1.6.1) are then less well-determined than for the other compounds l i s t e d . In accordance with the polymeric structures of these compounds; known for the e t h y l , n-butyl (89), and n-hexyl derivatives and proposed for the others, the magnetic data were analyzed according to the i s o t r o p i c Heisenberg models (85,203) for exchange coupled l i n e a r chains with spin (S) equal to one-half. The antiferromagnetic a-isomers were f i t to the polynomial expression for the molar s u s c e p t i b i l i t y , from the Bonner and Fisher (257) model, developed by H a l l (242,272) v i z . : 0.250 + 0.14995X"1 + 0.30094X - 2 [2.5] 1 + 1.9862X - 1 + 0.68854X"2 + 6.0626X - 3 where X = k T / | j | . The 8-isomers were f i t to the polynomial expression of Baker et a l . (242,258) for ferromagnetically coupled S = 1/2 chains, equation [2.6], where K = J/2kT. Ng 28 2 - 116 -2Q2 m^ — 4kT 1 + 5.7979916K + 16.902653K2 + 29.376885K3 + 29.832959K1* 1 + 2.7979916K + 7.0086780K2 + 8.6538644K3 + 4.5743114K1* + 14.036918K5 2/3 [2.6] In both cases, computer f i t s were made to the s u s c e p t i b i l i t y data with g and percent monomer1 ( i . e . , paramagnetic impurity) as the f i t t i n g parameters. In addition, the computer program used 2 allowed f i t t i n g to "mixed" models, that i s , antiferromagnetic with ferromagnetic "impurity" and antiferromagnetic with both ferromagnetic and paramagnetic impurities (see l a t e r discussion on the a'-n-dodecyl d e r i v a t i v e ) . For a l l the models, the best f i t was considered to be that set of f i t t i n g parameters which gave the minimum value of the r.m.s. deviation, that i s , that minimized . NT — E NT i c a l c . obs. obs. 1/2 where NT i s the number of data points, and x^  * and x^  a r >e the experimental and t h e o r e t i c a l s u s c e p t i b i l i t i e s , r e s p e c t i v e l y . The r e s u l t s of these analyses are given i n Table 2.1.6.1. The values of J and g reported are considered to be accurate to within at The paramagnetic impurity i s assumed to follow Curie Law, so that the monomer s u s c e p t i b i l i t y i s given by x ™ ^—^—S(S+1) . g ^ g a s s u m e ( i mon. 3kT to have the same value as the polymer. Then X o D S < = Xm^. + Xc^ain* This program was written by D.H. Jones of this Department and I am extremely g r a t e f u l to him for allowing me to use i t . - 117 -Table 2.1.6.1 Magnetic Parameters, a) ct-Isomera Compound J(cm _ 1) g t »n • 8 • X Monomer a-Cu[(CH 3) 2P0 2] 2 - 8.5 2.19 .008 21.7 a-Cu[(C 2H 5) 2P0 2] 2 - 1.3 2.19 .012 -ct-Cu[(n-C eH 1 7) 2P0 2J 2 - 25 2.23 .0221 5.2 a-Cu[(n-C 1 0H 2 1) 2PO 2] 2 - 29 2.19 .0171 1.4 o-Cu[(n-C 1 2H 2 5) 2P0 2] 2 - 28 2.21 .045 3.9 a ,-Cu[(n-C 1 2H 2 5) 2P0 2] 2 - 24 + 2.3 2.24 .0271 2.3Z monomer and 18Z ferromagnet b) B-Isomers Compound J(cm _ 1) g r.m.s. B-CuKn-C^H^^jJj + 2.2 2.16 .018 B-Cu[(n-C 6H 1 3) 2P0 2] 2 + 2.6 2.16 .013 B-Cu[(n-C 8H 1 7) 2P0 2] 2 + 1.8 2.24 .0171 B-Cu[(n-C 1 0H 2 1) 2PO 2] 2 + 2.1 2.13 .0121 B-Cu[(n-C 1 2H 2 5) 2P0 2] 2 + 2.3 2.11 .0181 1 r.m.s. values for f i t to K100K data only. - 118 -l e a s t ± 10% and ± 2%, r e s p e c t i v e l y . Figure 2.1.6.1 shows the agreement between theory and experiment for a 10% v a r i a t i o n i n J , while Figure 2.1.6.2 shows the agreement for a 2% v a r i a t i o n i n g. The parameters and low temperature s u s c e p t i b i l i t y data employed i n th i s analysis are for a-Cu[(C 2H 5) 2P0 2]2* Plots of the data as magnetic moments versus temperature are given i n Figures 2.1.6.3 to 2.1.6.9; the s o l i d l i n e s 1 are calculated from the theory using the best f i t values of J and g (and percent monomer and/or percent ferromagnet where a p p l i c a b l e ) . I t may be appropriate at th i s point to make some comments on the f i t t i n g proce-dure. The parameters given for the a-isomers were arrived at by using a least squares f i t t i n g program (273), incorporated into the main program as a subroutine. The antiferromagnetic model included, as mentioned e a r l i e r , a parameter to account for paramagnetic impurity and describes the magnetic properties of the a-isomers well, as indicated by the r.m.s. values (see Table 2.1.6.1). I t was not possible to f i t these compounds s a t i s f a c t o r i l y assuming a ferromagnetic, rather than a paramagnetic, impurity. The exception to this procedure was the modifi-cation of the a-n-dodecyl compound that contains more than one isomer, l a b e l l e d the a*-n-dodecyl de r i v a t i v e i n the e a r l i e r discussion on D.S.C, Section 2.1.3. In th i s case, the antiferromagnetic model i n c l u -ding both ferromagnetic and paramagnetic impurities was needed to The poor agreement between the t h e o r e t i c a l curve and the high tempera-ture data (T>100K), for the eight, ten and twelve carbon chain com-pounds, i s the r e s u l t of the poor c o r r e l a t i o n between the Gouy and the V.S.M. data, discussed e a r l i e r . F i t s i n these cases are to T<100K data only. - 119 -Figure 2.1.6.1 I l l u s t r a t i o n of the Estimated Accuracy of J (± 10Z). o C D o E 00 E o o CO 'o o _ *— _ J CD r— Q_ 111 o o o _ CO CO o o 0.0 1 1 1— 20 .0 40.0 T E M P E R A T U R E (K) top line = J=~114 cm -1 middle line = J = ~1.27 cm" 1 . bottom Iine : J = ~1.39 cm" 1 . - 120 -top line* g= 2.23 . middle line= g= 2.19 bottom line=g=2.15 - 121 -Figure 2.1.6.3 Magnetic Moments Versus Temperature for n-1 a) a-Cu[(CH 3) 2P0 2] 2: J - -8.5 cm - 1, g - 2.19, 21. b) 0 f-Cu[(C 2H 5) 2PO 2] 2: J - -1.3 cm"1, g - 2.19. 7% monomer. 100.0 TEMPERATURE (K) 333 .0 CD Z 111 5 o in 'NJ 0.0 .0 | c o o 100.0 200.0 TEMPERATURE (K) 300.0 - 122 -Figure 2.1.6.4 Magnetic Moments Versus Temperature for a - C u [ ( n - C 8 H 1 7 ) 2 P 0 2 ] 2 : J = ~ 2 5 cm - 1, g • 2.23, 5.2% monomer. in CNJ T E M P E R A T U R E (K) - 123 -Figure 2.1.6.5 Magnetic Moments Versus Temperature for a - C u [ ( n - C 1 0 H 2 1 ) 2 P O 2 ] 2 : J = -29 cm"1, g - 2.19, 1.4% monomer. - 124 -Figure 2.1.6.6 Magnetic Moments Versus Temperature for a) a ' - C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 : J = -24 cm"1, J f m - + 2.3 cm"1, g = 2.24, 2.3% monomer and 18% ferromagnet. b) o - C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 : J - -28 cm - 1, g = 2.21, 3.9% monomer. d~i i 1 1 1 1 1— 0 0 100.0 200.0 • 3D0 0 TEMPERATURE (K) - 125 -Figure 2.1.6.7 Magnetic Moments Versus Temperature for a) 6-Cu[(n-C l tH 9) 2P0 2] 2: J = +2.2 cm - 1, g - 2.16. b) B - C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 : J - +2.6 cm - 1, g - 2.16. - 126 -.8 Magnetic Moments Versus Temperature for a) B - C u [ ( n - C 8 H 1 7 ) 2 P 0 2 ] 2 : J = +1.8 cm"1, g b) 8 - C u [ ( n - C 1 0 H 2 1 ) 2 P 0 2 ] 2 : J - +2.1 cm - 1, g 2.24. 2.13. ~ i r 100 .0 -1 r 200.0 0.0 3C0 .0 T E M P E R A T U R E (K) ~i r 100.0 i r 200.0 o.o 300.0 T E M P E R A T U R E (K) - 127 -Figure 2.1.6.9 Magnetic Moments Versus Temperature for 6 - C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 : J = +2.3 cm - 1, g = 2.11. T E M P E R A T U R E (K) - 128 -account for the magnetic properties of this compound (see Figure 2.1.6.6.a)). As t h i s model then has f i v e f i t t i n g parameters (percent paramagnet, percent ferromagnet, g, antiferromagnetic J (J ) and ferromagnetic J (Jf m))» attempts to use the f i t t i n g routine resulted i n unreasonable values of some of the parameters, for example, negative values of the ferromagnetic exchange parameter. Hence the values of g, J and J . were fixed and the percent impurities were varied u n t i l the am fm the best f i t was obtained. The f i t l i s t e d i n Table 2.1.6.1 i s , then, not unique but was judged the most reasonable for this compound (see l a t e r d i s c u s s i o n ) . The program used to f i t the p-isomers (ferromagnets) also i n c l u -ded percent monomer as a parameter; however, i n these cases, no reason-able f i t s could be obtained for nonzero values of the paramagnetic impurity. In addition, the f i t t i n g program did not converge when attempts were made to f i t a l l three parameters; Jc , g and percent tm monomer, supporting the setting of the l a t t e r parameter to zero. The presence of paramagnetic impurity i n the a-isomers, but not i n the p-isomers, i s supported by the in f r a r e d spectra of these com-pounds. As discussed i n Section 2.1.4, the a-isomers exhibit an absorp-ti o n at 1160 - 1170 cm - 1 that was t e n t a t i v e l y assigned as an e s s e n t i a l l y non-coordinated P-0 stretch, a r i s i n g from the presence of short polymer chains, or monomers. (This d i s t r i b u t i o n of chain lengths was also pro-posed to give r i s e to the broad i n i t i a l melting curves of the a-isomers containing long (greater than six carbon atoms) a l k y l chains (Section 2.1.3).) This band i s not present i n the spectra of compounds i s o l a t e d as p-isomers from the preparative reaction mixture ( i . e . , the butyl and - 129 -hexyl d e r i v a t i v e s ) , and disappears from the spectra of the eight, ten and twelve carbon chain complexes upon conversion to the 8-forms from the a-forms. Consistent with t h i s , the infrared spectrum of the ethyl d e r i v a t i v e does not show the 1160 - 1170 cm - 1 peak, and the magnetic data can be f i t very well without the i n c l u s i o n of paramagnetic impurity as a f i t t i n g parameter. I n t e r e s t i n g l y , the methyl compound, proposed to contain the highest percent monomer (ca. 22%), has the most intense absorption at 1160 cm - 1, while the inf r a r e d spectra of the n - o c t y l , n-decyl, and n-dodecyl compounds show weak to medium peaks at th i s wave-number, and contain much less paramagnetic impurity. The presence of t h i s paramagnetic impurity can be seen i n the s u s c e p t i b i l i t y data, for those d e r i v a t i v e s which have a Neel point (T.T) i n the temperature range studied, as an increase i n ^  at temperatures below T N (234,244). This i s i l l u s t r a t e d i n Figures 2.1.6.10 to 2.1.6.12 for the n- o c t y l , n-decyl, and n-dodecyl d e r i v a t i v e s . The s o l i d l i n e s are the t h e o r e t i c a l curves for the parameters l i s t e d i n Table 2.1.6.1 for these compounds. As mentioned e a r l i e r , the f i t t i n g of the magnetic data of one modification of the a-n-dodecyl d e r i v a t i v e , the so-called o'-n-dodecyl compound, required the i n c l u s i o n of ferromagnetic impurity, as well as paramagnetic impurity, as parameters, i n order to obtain a s a t i s f a c t o r y f i t . The data can be f i t with just ferromagnetic impurity but the appearance i n the in f r a r e d spectrum of a medium i n t e n s i t y band at 1161 cm - 1 implies, on the basis of the above discussion, the presence of paramagnetic impurity. On the other hand, attempts to f i t t h i s compound with only paramagnetic, and not ferromagnetic, impurity resulted i n t h e o r e t i c a l curves that could not account for the increase i n u - 130 -Figure 2.1.6.10 Magnetic S u s c e p t i b i l i t y Versus Temperature for a - C u [ ( n - C 8 H 1 7 ) 2 P 0 2 ] 2 . T E M P E R A T U R E (K) - 131 -ure 2.1.6.11 Magnetic S u s c e p t i b i l i t y Versus Temperature for o - C u [ ( n - C 1 0 H 2 1 ) 2 P O 2 ] 2 . - 132 -Figure 2.1.6.12 Magnetic S u s c e p t i b i l i t y Versus Temperature for a - C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 . ' O >-CQ Q_ LU O CO CO 0.0 100.0 200.0 T E M P E R A T U R E (K) 300.0 - 133 -at temperatures below 11.5K (refer to Figure 2.1.6.6.a)). Support for the i n c l u s i o n of ferromagnetic impurity again comes from the in f r a r e d spectrum and from the D.S.C. studies on this compound. The inf r a r e d spectrum reveals an absorption at 807 cm"1 that has previously (Section 2.1.4) been shown to be c h a r a c t e r i s t i c of the 8-isomers, which are ferromagnetic. This i s the only a-isomer that exhibits t h i s absorption and, indeed, as discussed e a r l i e r i n Section 2.1.3 (D.S.C. st u d i e s ) , only one preparation of th i s compound shows th i s peak. In a l l other respects, the inf r a r e d spectrum of the a' der i v a t i v e i s i d e n t i c a l to that of the "pure" antiferromagnetic a-isomer. Hence, for t h i s prepara-t i o n , the product i s o l a t e d i s a mixture of the a- and the B-isomers, a phenomenon r e f l e c t e d i n the in f r a r e d spectrum, the D.S.C. studies, and i n the magnetic properties. On th i s basis, then, the magnetic data were f i t by setting the values of J and J , close to those found for the am fm "pure" a- and "pure" 8-forms of the n-dodecyl d e r i v a t i v e , r e s p e c t i v e l y . The values of the exchange parameters found for these copper(II) di-n-alkylphosphinate polymers reveal some i n t e r e s t i n g features, not the le a s t of which i s the reversal i n the sign of the exchange i n going from one group of isomers to the other. Secondly, and perhaps not unex-pectedly (203,228,246), the magnitude of | j | for the ferromagnetically coupled systems i s , i n general, much smaller than that of the a n t i f e r r o -magnetically coupled compounds. In addition, the size of | j | increases, roughly, with the length of the a l k y l chain for the a-isomers, while f o r the 8-isomers this value i s approximately constant. I t Is also of note that, within the a-form group, those compounds which contain some para-- 134 -magnetic impurity have larger | j | values than the a-isomer that does not (the ethyl compound). The exchange i n the l a t t e r compound i s of the same magnitude as that found i n the p-isomers, though the sign i s oppo-s i t e . Correlations between s t r u c t u r a l features and the sign and magni-tude of J are well established i n other copper(II) systems (91,92,246, 259,274). For example, the exchange i n copper(II) dimers with single atom bridges such as oxygen (from a u-hydroxo group) (93,240,246,248, 274) i s known to vary from ferromagnetic to antiferromagnetic depending on the Cu-O-Cu bridging angle, d>. These l a t t e r compounds contain predominantly four-coordinate copper atoms; i n five-coordinate complexes with chloride or s u l f u r bridges (236,251,274) the exchange i s found to depend on the r a t i o <t>/RQ > where R q i s the long out-of-plane copper-ligand distance. To try to explain the differences observed i n the compounds under discussion here, i t i s necessary to examine the t h e o r e t i c a l basis for exchange coupling and to try and reconcile t h i s with the s t r u c t u r a l differences observed between the a- and p-isomers. The focus w i l l be directed to the o r b i t a l overlap model of Anderson (203), as described by Ginsberg (228). While t h i s model refe r s to dimers and c l u s t e r s , the symmetry arguments can be seen to extend to l i n e a r chains. In the simplest terms the o r b i t a l overlap approach re l a t e s the sign of the exchange to the symmetry properties of the o r b i t a l s i n which the unpaired spins are located (228). These d- o r b i t a l s overlap with f i l l e d d and p o r b i t a l s or hybrid o r b i t a l s of the bridging atom(s); the o r b i t a l s containing the unpaired spins, then, are no longer l o c a l i z e d - 135 -metal d - o r b i t a l s but are now antibonding o r b i t a l s , encompassing both the metal atom and the intermediate atom(s). The spins from two d i f f e r e n t metal atoms (or by extension, a larger number of metal atoms) can then i n t e r a c t , through these delocalized "magnetic" o r b i t a l s , to give r i s e to two categories of exchange. K i n e t i c exchange a r i s e s when nonorthogonal overlap of the magnetic o r b i t a l s occurs, and spin information i s d i r e c t -l y communicated from one atom to i t s neighbor, r e s u l t i n g i n a n t i p a r a l l e l spin coupling between the metal atoms. This i s referred to as " i n c i -pient bond formation" (203,228). P o t e n t i a l exchange arises when there i s orthogonality i n the overlap i n t e g r a l ; a d i s c o n t i n u i t y i n the exchange pathway that blocks the o r b i t a l overlap transmission of antiferromagnetic spin information. P o t e n t i a l exchange i s weaker than k i n e t i c and r e s u l t s i n a p a r a l l e l coupling of the spins on neighboring metal atoms, a r e s u l t of the adherence to Hund's rules (202,275). The o v e r a l l exchange observed i n a given compound i s then the sum of a l l the contributions of these types of exchange; however, because k i n e t i c exchange i s much stronger than p o t e n t i a l , i f there i s any pathway of nonorthogonal o r b i t a l overlap, the o v e r a l l i n t e r a c t i o n w i l l usually be antiferromagnetic (203). Conversely, i f a l l pathways contain at l e a s t one orthogonal overlap the i n t e r a c t i o n w i l l always be ferromagnetic. C l e a r l y then, the symmetry of the magnetic o r b i t a l s w i l l determine the magnitude and sign of the exchange. This symmetry, i n turn, w i l l depend on the stereochemistry of the metal atoms, which determines the d - o r b i t a l l i k e l y to contain the unpaired spin, and on the geometry of the bridging ligand, which w i l l determine the orientations of the o r b i t a l s with which the d - o r b i t a l s overlap. For highly symmetric - 136 -systems involving single atom or l i n e a r polyatomic bridges forming 90° or 180° linkages between metal atoms with regular coordination geometry, such as square planar, t h i s approach can rather elegantly account for the observed magnetic exchange, as i l l u s t r a t e d very n i c e l y i n Ginsberg's review a r t i c l e (228). For compounds such as those under consideration here, t h i s approach i s less s a t i s f a c t o r y , due to the lack of symmetry i n the eight-membered ring units of the polymers. In addition, the r e l a t i v e l y small s t r u c t u r a l differences that e x i s t between the two isomers do not lend themselves to ready i n t e r p r e t a t i o n of the magnetic properties observed. A s t r u c t u r a l l y related copper(II) phosphate dimer (220,276), expected to be ferromagnetically spin coupled on the basis of the orthogonality of the tetrahedral PO^ 3 - bridging sp 3 hybrid o r b i t a l s , was, i n f a c t , found to be antiferromagnetically coupled (J = -5.4 cm - 1). This apparent anomaly was explained as perhaps being due to the deviation of the bridging O-P-O angles from the tetrahedral value of 109.47° and/or the "admixture of other o r b i t a l s (phosphorus d - o r b i t a l s ? ) that lead to net antiferromagnetic exchange" (220). The eight-membered Cu-(0-P-0)2~Cu ring i n t h i s compound i s very s i m i l a r to those found i n the dialkylphosphinate polymers, although the copper atoms have a di s t o r t e d square pyramidal geometry i n the former case (276). The O-P-O angle would, then, not appear to be an important factor i n determining the sign of the exchange, as i t i s e s s e n t i a l l y the same i n a l l rings; i . e . , those of the a- and p-phosphinate derivatives and the phosphate dimer, while the exchange i s not. For the phosphinates, more relevant s t r u c t u r a l features may be the o v e r a l l symmetry within the ring and the d i s t o r t i o n i n the CuO chromophore; the s t r u c t u r a l differences between - 137 -the two Isomers l i e i n these areas. Hence, while the O-P-0 angles are the same for a l l rings ( r e c a l l that the ethyl compound contains one ring that i s s i g n i f i c a n t l y more puckered than any of the others, Section 2.1.2), the Cu-O-P angles are not. Those of the ethyl d e r i v a t i v e (an a-isomer) are smaller and on the average, more "equivalent" than those of the hexyl (and butyl) d e r i v a t i v e s , there being a difference of ca. 2° between these angles i n the same ring for the ethyl while the hexyl shows a difference of 4° i n one ring and of nearly 6° i n the other (see Table 2.1.2.3). Further asymmetry i s present i n the rings of the hexyl compound that arises from i n e q u a l i t y i n the lengths of the Cu-0 bonds; one i s 0.030 A longer than the average of the other three, while the ethyl compound shows a maximum difference of only 0.0066 A i n i t s Cu-0 bond lengths (the phosphate dimer also has nearly equivalent Cu-0 bond lengths). A consequence (or cause?) of these differences i s that, for the ethyl compound, the 0-Cu-O angles are larger and show a greater v a r i a t i o n i n value than i n the hexyl d e r i v a t i v e . In terms of the CuOit chromophore present this means that the copper(II) i n the ethyl compound Is i n an environment that i s closer to square planar than i s the metal In the hexyl d e r i v a t i v e . I t has been shown experimentally (93,231,234, 246,247) that the i n t e r a c t i o n between copper(II) atoms, i n binuclear compounds, becomes incr e a s i n g l y antiferromagnetic with an increasing pl a n a r i t y of the metal chromophore. This i s found to be true for the polymer systems under discussion here, where the more planar a-isomers are antiferromagnetic while the less planar 8-isomers are ferromagnetic. The difference between the two forms then must ar i s e from differences i n the overlap of the metal o r b i t a l s with the o r b i t a l s of the phosphinate - 138 -li g a n d . On the basis of the e a r l i e r discussion, the metal-metal i n t e r -action i n the 8-isomers occurs primarily through orthogonal ligand o r b i t a l s , and, while t h i s ferromagnetic pathway undoubtedly e x i s t s i n the a-isomers as w e l l , there i s at least one nonorthogonal overlap pathway, leading to antiferromagnetism, that dominates i n these l a t t e r compounds (228). An orthogonal pathway would r e s u l t from overlap of the metal o r b i t a l containing the unpaired spin, the d o r b i t a l ( i f we xy r e t a i n the coordinate system of Section 2.1.5, Figure 2.1.5.2), with oxygen o r b i t a l s involved i n bonding to phosphorus i n a a manner. Metal-metal i n t e r a c t i o n would then take place v i a the tetrahedral s p 3 hybrid o r b i t a l s on phosphorus which are, of course, orthogonal. Nonorthogonal overlap would r e s u l t from Interaction of the metal o r b i t a l with the it system of the O-P-O portion of the phosphinate bridge. The u t i l i z a t i o n of the empty d 2 2 a n < i d 2 o r b i t a l s on phosphorus i n forming it-bonds x ™ y z with the lone pairs of ligands such as oxygen and f l u o r i d e i s well known (3,23,137,138,277,278) and e f f e c t i v e metal o r b i t a l overlap with t h i s it system should r e s u l t i n antiferromagnetism. I t would then appear that i n the a-isomers (and the previously mentioned phosphate dimer (220)) the overlap with the it-system i s s u f f i c i e n t to r e s u l t i n net antiferromagnetism, while i n the p-isomers i t i s not; the o v e r a l l exchange i s ferromagnetic. S t r u c t u r a l features preventing e f f e c t i v e overlap of the metal o r b i t a l s with the it-system of the ligand have been suggested to account for the weak ferromagnetism (J = +1.22 cm - 1) found i n sodium biscarbonatocuprate(II) trihydrate (237), and i n the s t r u c t u r a l l y related anhydrous sodium (279,280) and potassium (281) biscarbonate copper(II) extended l a t t i c e compounds (J = +4.1 and +1.19 - 139 -cm - , r e s p e c t i v e l y ) . On the other hand, where overlap with the u-system of the bridging carbonate i s more e f f i c i e n t the exchange i s antiferromagnetic, as i s the case i n Cu(NH 3) 2C03 (282,283), where J = -5.2 cm - 1. In the dimer, [Cu(L2)] ^ O g ^ l O ^ ) 2 , where 12 i s 2,4,4,9-tetramethyl-l,5,9-triazacyclododec-l-ene (243), the carbonate acts as a symmetrical bidentate ligand to both metals and spin coupling i s so strong that the complex i s completely diamagnetic i n the temperature range studied (100 - 300K); The above discussion presents a rather s i m p l i f i e d explanation of the d i f f e r e n t magnetic properties of the o- and p-isomers of the copper(II) di-n-alkylphosphinate polymers. There can be no doubt, however, that the small s t r u c t u r a l v a r i a t i o n s between the forms r e s u l t i n the predominance of one superexchange pathway over another. The r e l a t i v e magnitudes of the exchange parameter, J , and the approximate increase i n | j | with increasing a l k y l chain length i n the a-isomers, but not i n the p-isomers, i s more d i f f i c u l t to reconcile with s t r u c t u r a l d i f f e r e n c e s . I t may be that the presence of the long a l k y l chains causes, i n the a-isomers, even greater puckering of the eight-membered rings than i s found i n the ethyl d e r i v a t i v e , r e s u l t i n g i n increased overlap with the n-system of the ligand, while maintaining the same Cu01+ chromophore geometry. The answer to this question w i l l require more detailed knowledge of the structures of the long chain derivatives than i s currently a v a i l a b l e . I t has been shown (93,246,274) that the e l e c t r o n e g a t i v i t y of the substituents on the bridging atom(s) a f f e c t s the magnitude of by causing changes i n the electron density present i n the bridge. Hence, less electronegative substituents mean more - 140 -electron density i n the bridge and a larger While the e l e c t r o -n e g a t i v i t i e s of the a l k y l groups on phosphorus, i n the compounds under discussion here, decrease roughly with increasing length, i t i s d i f f i c u l t to invoke t h i s e f f e c t for the a-isomers but not the 8-isomers. It may be that the very small e l e c t r o n e g a t i v i t y differences between the ligands do not manifest themselves i n the very weak ferromagnetism of the 8-isomers. - 141 -2.2 Diorganophosphinate Derivatives, [ C u ( R 2 P 0 2 ) 2 ] x > Containing Branched Chain A l k y l or Phenyl Groups. 2.2.1 Introduction. The primary focus of this work was the preparation and inv e s t i g a t i o n of the di-n-alkylphosphinates discussed i n the preceding sections of Chapter 2; however, several branched chain a l k y l , diphenyl, and monosubstituted compounds (Section 2.3) were also synthesized. I t was of in t e r e s t to examine the e f f e c t the presence of these quite d i f f e r e n t R groups on phosphorus has on the phys i c a l , spectral and magnetic properties of the copper(II) polymers containing these ligands. 2.2.2 Synthesis, S o l u b i l i t i e s and Thermal Analysis. The preparations, and any d i f f i c u l t i e s encountered i n the synthe-ses, of the d i - i - p r o p y l , d i - t - b u t y l and diphenyl copper phosphinates are described i n Chapter 4, Sections 4.3.9 - 4.3.11. The s o l u b i l i t i e s of the compounds i n a number of solvents are l i s t e d i n Table 2.2.2.1. The i-propyl and t-butyl derivatives show e s s e n t i a l l y the same, l i m i t e d s o l u b i l i t y , except for a reduced s o l u b i l i t y i n water for the l a t t e r compound. The diphenyl complex Is insoluble i n a l l solvents tested. The s o l u b i l i t y of the branched a l k y l chain compounds i s i n t e r e s t i n g , p a r t i c u l a r l y that of the t-butylphosphinate. As mentioned e a r l i e r , t h i s compound has been prepared by Gillman (67) who found i t to be insol u b l e i n common organic solvents and assigned i t a crosslinked polymeric structure involving four-coordinate copper. In contrast, we observe Table 2.2.2.1 S o l u b i l i t i e s of Copper(II) D i - i - p r o p y l - , D i - t - b u t y l - , and Diphenylphosphinates 1. Compound Solvent H 20 MeOH EtOH acetone CH 2 C 1 2 CHCI3 CCl^ benzene 60°-90° pet. ether C u [ ( i - C 3 H 7 ) 2 P 0 2 ] 2 s. s.s. v.s.s i . v.s.s. s.s. v.s.s i . i . C u [ ( t - C l t H 9 ) 2 P 0 2 ] 2 s.s. s.s. v.s.s. i . v.s.s. s.s. v.s.s. i . i . C u [ ( C 6 H 5 ) 2 P 0 2 ] 2 i . i . i . i . i . i . 1. i . i . s., soluble, >.lg/100mL; s.s., s l i g h t l y soluble, ca. .01g/100mL; v.s.s., very s l i g h t l y soluble, <.01g/100mL; i . , i n s o l u b l e . - 143 -some s o l u b i l i t y i n polar and polarizable solvents. I t could be that the d i f f e r e n t synthetic methods we employed to prepare t h i s compound (Sec-t i o n 4.3.10) resulted i n a somewhat d i f f e r e n t polymer structure, our polymer being e s s e n t i a l l y l i n e a r , and t h e i r s e s s e n t i a l l y c r o s s l i n k e d . The reason for this discrepancy i s not c l e a r ; however, on the basis of the e a r l i e r discussions on s o l u b i l i t y versus polymer structure, i t seems reasonable to formulate both the i - p r o p y l - and the t-butylphosphinates as b a s i c a l l y l i n e a r polymers, with the backbone structure found pre-vi o u s l y for the d i - n - a l k y l d e r i v a t i v e s 1 . For the i - p r o p y l and t-butyl derivatives i t i s useful to compare t h e i r s o l u b i l i t i e s to those of the methyl and the e t h y l compounds (Table 2.1.3.1). The number of methyl groups attached to the carbon atoms bonded to phosphorus increases, sequentially, from zero i n the methyl to three i n the t-butylphosphinate; however, the addition of the f i r s t -CH3 group ( i n the ethyl compound) does not greatly a f f e c t the s o l u b i l i -ty, nor does the addition of the t h i r d -CH 3 group change the s o l u b i l i t y s i g n i f i c a n t l y from that of the disubstituted i-propyl d e r i v a t i v e . With reference to the e a r l i e r discussion on the s o l u b i l i t i e s of the n - a l k y l d e r i v a t i v e s , i t may be concluded that the s o l u b i l i t y of the i-propyl and t-butyl compounds ar i s e s from e f f e c t s equivalent to those that impart s o l u b i l i t y to the methyl and ethyl derivatives when compared to the longer a l k y l chain compounds. In polar solvents (H 20, MeOH, EtOH) t h i s 1 See l a t e r discussions on the i n f r a r e d and e l e c t r o n i c spectra. - 144 -arises from the a c c e s s i b i l i t y of the polar inorganic backbones 1; the presence of the increasingly branched a l k y l groups reduces but does not eliminate t h i s a c c e s s i b i l i t y . The greatest reduction i n s o l u b i l i t y , i n a l l solvents, then occurs between the ethyl (unbranched) and the i-propyl (one branch) compounds, a r e s u l t of the increased shielding of the backbones i n the l a t t e r case. This shielding appears to be only s l i g h t l y enhanced with the a d d i t i o n a l branching found i n the t-butyl d e r i v a t i v e . The s o l u b i l i t y of the branched chain a l k y l phosphinates i n non-polar (60° - 90° pet.ether, benzene, CCl^) and, p a r t i c u l a r l y , i n s l i g h t l y polar (CH 2Cl2, CHC1 3) solvents i s s i g n i f i c a n t l y reduced from that of the unbranched methyl and ethyl d e r i v a t i v e s . While the s o l u b i -l i t y of a l l the polymers prepared i n t h i s study i s small or non-existent i n non-polar solvents, the reduction i n the s o l u b i l i t y i n p o l a r i z a b l e solvents, noted above, can again be a t t r i b u t e d to the increased s h i e l -ding of the polymer backbone, since the i n t e r c h a i n i n t e r a c t i o n s (induced dipole-induced dipole) Involving the a l k y l groups would be expected to increase more with a l k y l chain length than with a l k y l chain branching. The I n s o l u b i l i t y of the copper(II) diphenylphosphinate i n a l l solvents i s both not unexpected ( v i r t u a l l y a l l polymeric metal diphenyl-phosphinates are insoluble (22,48,49,56,71) with the exception of P b [ ( C 6 H 5 ) 2 P 0 2 ] 2 (10°)) and not r e a d i l y explainable. Phenyl groups, along with methyl groups, are thought (22,46,53,55,72,101) to be the least e f f e c t i v e i n preventing dipole-dipole interactions between the The induced dipole-induced dipole interchain Interactions, discussed e a r l i e r , are minimized i n these compounds due to the short chain lengths. - 145 -inorganic backbones. Hence, while these interactions are strong i n the methyl compound ( r e c a l l the high melting point of 251.6°C), the polymer backbone i s s t i l l a ccessible, as evidenced by i t s s o l u b i l i t y i n most polar and pol a r i z a b l e solvents. In the diphenyl d e r i v a t i v e , these interactions could be so strong that the energy required to disrupt them i s not compensated for by the solvent-backbone interactions or the entropy e f f e c t s . On the basis of the thermal s t a b i l i t y of this com-pound, which i s e s s e n t i a l l y equivalent to that of the t-butyl deriva-t i v e 1 (which has some s o l u b i l i t y i n polar and polarizable solvents), t h i s explanation seems u n l i k e l y , or at l e a s t , not the only factor contributing to the I n s o l u b i l i t y . There may be a contribution from induced dipole-induced dipole interchain interactions i f the phenyl groups, as a r e s u l t of polymer chain packing, come i n close contact ( t h i s close packing has been shown, for example, i n Zn[(C 6H 5)(n - C i +H 9)-P0 2]2 (74)). The e f f e c t of both of these types of Interchain i n t e r -actions would be to reduce polymer backbone a c c e s s i b i l i t y to solvents and hence i n h i b i t s o l u b i l i t y . However, the most probable explanation of the i n s o l u b i l i t y of Cu[(CgH 5) 2P0 2] 2 * s that i t i s a crosslinked polymer (96). This structure could a r i s e as a r e s u l t of s t e r i c repulsions between the phosphinate bridges containing the bulky phenyl groups. The fact that lead diphenylphosphinate i s soluble i n a vari e t y of organic solvents including benzene, chloroform, and dichloromethane, and i s known, from single c r y s t a l X-ray studies (100), to have a l i n e a r , double bridged structure may support the formulation of the copper See l a t e r discussion. - 146 -derivative as cro s s l i n k e d . This polymer structure r e s u l t s i n unique spectra ( v i b r a t i o n a l and e l e c t r o n i c ) for the diphenyl compound as compared to the other derivatives (see l a t e r d i s c u s s i o n ) . Thermal analysis indicates that none of the three compounds under discussion here melt before decomposition. Copper(II) d i - i - p r o p y l -phosphinate undergoes an i r r e v e r s i b l e phase t r a n s i t i o n at 171.5°C (AH = 20 kJ m o l - 1 ) , followed almost immediately by an endothermic-exothermic p a r t i a l decomposition at 212° and 216°C. This i s i l l u s t r a t e d i n Figure 2.2.2.1. V i s u a l observation of the "melting" behavior indicates that the lowest temperature t r a n s i t i o n r e s u l t s i n a color change, from l i g h t blue to a very d u l l blue, and that, with continued heating, the color becomes a khaki green before complete decomposition begins at 275°C, re s u l t i n g i n a dark brown l i q u i d . The D.S.C. curves of the t-butyl and phenyl derivatives show no melting or phase t r a n s i t i o n s before extremely exothermic decomposition begins at 301.7°C and 320.4°C, r e s p e c t i v e l y . This i s shown i n Figure 2.2.2.2 (note the heat flow scales are d i f f e r e n t for the two curves). Like the i-propyl compound, the t-butyl d e r i v a t i v e decomposes to a brown l i q u i d ; the phenyl compound, on the other hand, melts to a blue-green l i q u i d at 327.0°C (AH i s ca. 55 kJ m o l - 1 ) , a f t e r the beginning of decom-po s i t i o n at 320.4°C. This i s seen i n the D.S.C. curve as the sharp endothermic peak immediately following the i n i t i a l exothermic r i s e . The subsequent decomposition then occurs over a much larger temperature range than for the i-propyl or t-butyl d e r i v a t i v e s , and, i n f a c t , does not appear to be complete at the upper temperature l i m i t of the i n s t r u -ment (600°C); t h i s may be a r e s u l t of the proposed c r o s s l i n k i n g . - 147 -- 148 -Figure 2.2.2.2 D.S.C. Curves of a) Cu [ ( C 6 H 5 ) 2 P 0 2 ] 2 and b) Cu[(t-C,,H 9) 2P0 2 1 2 . T C f f P C R A Y U R C » C - 149 -The thermal properties of these compounds i l l u s t r a t e a number of points; i ) the increased thermal s t a b i l i t y as a re s u l t of the branched a l k y l chain and phenyl groups on phosphorus as opposed to straight chain a l k y l groups, i i ) the increased r i g i d i t y and i n f l e x i b i l i t y imparted to the polymer backbone as a r e s u l t of these groups means decomposition occurs before melting, I i i ) the higher decomposition temperature and very broad curve of the diphenyl compound, compared to the i-propyl and t-butyl d e r i v a t i v e s , may be i n d i c a t i v e of somewhat greater thermal s t a b i l i t y as a r e s u l t of c r o s s l i n k i n g , and, f i n a l l y , i v ) the phenomenon of polymorphism, observed i n the di-n-alkylphosphinates, does not ex i s t i n these compounds. This l a t t e r observation may be as a r e s u l t of the limi t e d number of d i f f e r e n t orientations that the branched a l k y l chain and phenyl groups can adopt, due to s t e r i c requirements. 2.2.3 Infrared Spectra. The infrared absorptions observed for the copper(II) d i - i -propyl-, d i - t - b u t y l - , and diphenylphosphinates are l i s t e d i n Tables 2.2.3.1 to 2.2.3.4. These compounds are characterized by reasonably simple spectra, as i l l u s t r a t e d for the i-propyl and diphenyl d e r i v a t i v e s i n Figure 2.2.3.1. The P0 2 asymmetric and symmetric stretching v i b r a -tions are r e a d i l y assigned by comparison to free anion spectra, as described e a r l i e r (Sections 1.2.2 and 2.1.4). The free anion values of v P0 o. v P0 0 and A are very s i m i l a r to those found for the n-a l k y l asy. 1 sym. L anions, as expected from the small differences i n the organic group e l e c t r o n e g a t i v i t i e s . The exception i s the phenyl derivative which has a higher (by ca. 40 cm - 1) free anion asymmetric P0 2 s t r e t c h , and, hence, a Table 2.2.3.1 Infrared Bands Associated with P-0 Stretching1. Copper Compound Frequencies Free Anion Frequencies Compound Vasy.** 0*- 1) v_, P00(cm-1) sym. ^ x ' ACcm"1) Counter-cation vasy. P°2( a n' 1) V . P ° 2 ( c m " 1 ) tfcm-1) Reference Cu[(i-C 3H 7) 2P0 2] 2 1133 v.s. 1059 s. 74 Ag+ 2 (1118 s. '1089 s. 1009 v.s. 95 This work H+- 1159 s.br. 954 s.br. 205 This w>rk Cuj(t-q iH 9) 2ro 2] 2 1137 v.s. (1060 sh.) 1044 s. 93 H+ 1151 s. 943 v.s. 208 This work Cu[(C 6H 5) 2P0 2] 2 1132 v.s. br. 1051 s. 81 Na+ H+ 1189 1181 s. 1058 956 v.s. 131 225 34 This work v.s., very strong; s., strong; sh., shoulder; br., broad. These frequencies have been averaged for the calculation of A. - 151 -Figure 2.2.3.1 Infrared Spectra of a) C u [ ( i - C 3 H 7 ) 2 P 0 2 ] 2 and b) C u [ ( C 6 H 5 ) 2 P 0 2 ] 2 . I-Q_ DC O CO CD < 1200 ~800 ~600~ 1000 W a v e n u m b e r (cm-1) Too " o \— o CO CO < 1200 "c300~ ~60o" 1000 W a v e n u m b e r (cm - 1 ) T o o " - 152 -larger free anion A, as observed previously (23,34,137,138,140,143) upon replacing the a l k y l substituents on phosphorus with phenyl groups. In the i-propyl and t-butyl copper compounds the s h i f t s i n both frequen-c i e s , from the free anion values, are not as great as i n the n-a l k y l d e r i v a t i v e s . In p a r t i c u l a r , ^ a S y P0 2, i n the spectra of the branched a l k y l chain compounds, i s approximately 20 cm - 1 higher than the corres-ponding frequency i n the n-alkyl d e r i v a t i v e s , r e s u l t i n g i n higher A values i n the former case. The s i g n i f i c a n c e of this i s not c l e a r ; on the basis of the e a r l i e r discussion on the s h i f t s In vP0 2 t h i s seems to imply less M-L i n t e r a c t i o n i n these compounds; however, the frequencies assigned to Cu-0 stretching are as high, i f not s l i g h t l y higher, than i n the n- a l k y l derivatives (refer to Table 2.2.3.2), Implying an equivalent Table 2.2.3.2 Infrared Bands Associated with Cu-0 S t r e t c h i n g 1 . Compound Frequency (cm - 1) C u [ ( i - C 3 H 7 ) 2 P 0 2 ] 2 Cu[(t-Ci tH 9) 2P0 2] 2 C u [ ( C 6 H 5 ) 2 P 0 2 ] 2 397 m., 384 w.sh. 393 w.sh., 384 w., 376 v.w.sh. 386 m., 377 w.sh. m., medium; w., weak; v.w., very weak; sh., shoulder. i n t e r a c t i o n i n a l l compounds. (This contention i s supported by the el e c t r o n i c spectra of the branched chain a l k y l compounds, see Section 2.2.4.) This implies that vCu-0 may be a more sens i t i v e i n d i c a t o r of the strength of the metal-ligand i n t e r a c t i o n , for the branched chain a l k y l compounds, than i s the p o s i t i o n of v P0 2 with respect to the - 153 -free ion value. It may be that, for these compounds, the s t e r i c h i n -drance and increased r i g i d i t y i n the polymer backbone, as a r e s u l t of the presence of the bulkier side groups, causes an increase i n the asym-metric P0 2 stretching frequencies that i s not related to the strength of the metal-ligand i n t e r a c t i o n . In t h i s case then, the c o r r e l a t i o n between vM-0 and the s h i f t i n v P0 0, seen to some extent i n the d i - n -asy. ^ alkylphosphinates, does not apply, and other factors such as the e l e c -tronic spectra must be considered i n discussing the M-L i n t e r a c t i o n . The asymmetric P0 2 stretching frequency of the diphenyl compound l i e s i n the same region (ca. 1130 cm - 1) as those of the i-propyl and t-butyl d e r i v a t i v e s , and represents a decrease from the free ion (Na s a l t ) value of 57 cm - 1. This i s the largest decrease i n v a g ^ P0 2, upon coordination, seen i n any of the phosphinates prepared i n t h i s study (with the exception of the methyl compound, which shows a decrease i n vasy °^ c m _ 1 » see discussion of Section 2.1.4), and implies a greater metal-ligand i n t e r a c t i o n i n this compound than i n the others. The value of the Cu-0 stretching frequency, 386 cm - 1, does not seem to confirm t h i s , occurring i n the same range as the other compounds. As with the branched chain a l k y l d e r i v a t i v e s , v P0 o and vM-0 do not ' asy. ^ appear to c o r r e l a t e . The diphenyl compound i s proposed to have a cross-linked polymeric structure, as opposed to the l i n e a r structure of the n-alkyl and branched a l k y l compounds, and, as a r e s u l t , t h i s d e r i v a t i v e i s unique (see l a t e r discussion on the e l e c t r o n i c spectrum). The cross-linked structure proposed for the diphenyl compound appears to cause s h i f t s i n the v i b r a t i o n a l frequencies ( v a s y P0 2 a n d / o r vM-0) that may not be e n t i r e l y related to the strength of the metal-ligand i n t e r -- 154 -a c t i o n . The i n f r a r e d absorptions a r i s i n g from the asymmetric and symmetric P-C stretching vibrations are l i s t e d i n Table 2.2.3.3. These were assigned by comparison to the free anion spectra and with reference Table 2.2.3.3 Infrared Bands Associated with P-C S t r e t c h i n g 1 . Compound Frequency (cm - 1) v a s y . P C 2 vsym. P C2 C u [ ( i - C 3 H 7 ) 2 P 0 2 ] 2 717 s. 674 v.w.sh., 670 w.-m. C u [ ( t - C l t H 9 ) 2 P 0 2 ] 2 680 s.sh. 674 s. 605 w. C u [ ( C 6 H 5 ) 2 P 0 2 ] 2 730 s. 705 s.sh. 1 s., strong; w.-m., weak-to-medium; w., weak; v.w., very weak; sh. shoulder. to the relevant l i t e r a t u r e (56,71,87,132-134,284,285). The assignments i n the copper(II) diphenylphosphlnate compound are considered very tentative as a r e s u l t of the presence i n t h i s region of a number of absorptions a r i s i n g from the phenyl group (144,145) (the same s i t u a t i o n holds for the bending modes of the C 2P0 2 portion of the molecule, see l a t e r d i s c u s s i o n ) . In a l l three compounds, very l i t t l e difference i s observed i n the positions of these absorptions, when compared to the corresponding bands i n the free anion spectra. This may be due to a lack of change i n the orientations of the organic groups, compared to the straight chain a l k y l groups, upon incorporation of the ligand into a - 155 -metal complex; that i s , they are r e l a t i v e l y r e s t r i c t e d even i n the free anion due to the i r bulkiness. The largest change occurs i n the i-propyl d e r i v a t i v e where v PC 0 increases by 7 cm - 1 (from 710 cm - 1 i n the asy. 1 J v acid) and v PC, increases by 19 cm - 1 (from 651 cm - 1), consistent with sym. z t h i s a l k y l group having the most conformational freedom while uncom-plexed, hence the "largest" changes i n the PC 2 stretching frequencies upon coordination. The other two compounds show v i r t u a l l y no change i n these absorptions. Somewhat greater frequency s h i f t s are observed i n the absorptions due to the bending modes of the C 2P0 2 moiety, as expected due to the changes i n the P-0 bonds upon coordination. These absorptions are l i s t e d i n Table 2.2.3.4. The three bands l i s t e d for the diphenyl Table 2.2.3.4 Infrared Bands Associated with C 2P0 2 Bending 1. Compound Frequency (cm - 1) C u [ ( i - C 3 H 7 ) 2 P 0 2 ] 2 C u [ ( t - C 4 H 9 ) 2 P 0 2 ] 2 C u [ ( C 6 H 5 ) 2 P 0 2 ] 2 590 v.w.sh., 587 m., 463 m., 452 w.sh. 540 w.sh., 508 m.sh., 494 m., 471 w.sh. 571 s., 547 m.sh., 525 m.sh. 1 s., strong; m., medium; w., weak; v.w., very weak; sh., shoulder. der i v a t i v e probably include phenyl vibrations (monosubstituted benzene modes se n s i t i v e to the mass of the substituent (145)) and no attempt has - 156 -been made to d i s t i n g u i s h these bands from those a r i s i n g from C 2P0 2 bending v i b r a t i o n s . The greatest frequency s h i f t s again occur for the i-p r o p y l d e r i v a t i v e , an increase of 43 cm - 1 i n the higher frequency absorption, and a decrease of ca. 10 cm - 1 i n the 463 cm - 1 band. The medium i n t e n s i t y absorptions i n the t-butyl d e r i v a t i v e move some 8 cm - 1 c l o s e r together, and there are v i r t u a l l y no s h i f t s seen i n the spectrum of the copper(II) diphenylphosphinate. Table 2.2.3.5 Infrared Bands Associated with the Internal Vibrations of the i- P r o p y l , t-Butyl, and Phenyl Groups 1. Compound Frequency (cm - 1) Assignment Reference C u [ ( i - C 3 H 7 ) 2 P 0 2 ] 2 1168 m. 926 w. 891 m. v C-C-C x asy. \ 6CH3 of J P-i-C 3H 7 133,286 C u [ ( t - C l t H 9 ) 2 P 0 2 ] 2 824 m. 6CH3 of P-t-C.Hg 285 C u [ ( C 6 H 5 ) 2 P 0 2 ] 2 3045 w. 1592 w. 1027 m. 755 m. 695 m. vC-H vC-C ( i n plane) PC-H yC-H <bC-C-284,286 1440 s. 1002 m. 1 P - C 6 H 5 j (see text) 132 s., strong; m., medium; w., weak; p, in-plane deformation; y, out-of-plane deformation; out-of-plane ring deformation. - 157 -The remaining absorptions i n the inf r a r e d spectra of these compounds a r i s e p r i m a r i l y from the i n t e r n a l v ibrations of the organic groups, and many are of very weak i n t e n s i t y . No attempt has been made, i n the present work, to i d e n t i f y a l l of these bands; they are l i s t e d i n Appendix 2.b) for completeness. Table 2.2.3.5, however, gives the frequencies and assignments of some absorptions considered to be diagnostic of the p a r t i c u l a r organic group present. This i s e s p e c i a l l y true for the phenyl v i b r a t i o n s , where i t was found (132) that the C 6H 5-P group exhibits the aromatic absorptions c h a r a c t e r i s t i c of the C 6H 5~C group. The f i r s t f i v e absorptions l i s t e d for C u [ ( C 6 H 5 ) 2 P 0 2 ] 2 i n the Table are then vibrations associated p r i n c i p a l l y with the phenyl r i n g . In addition, the l a s t two frequencies, 1440 and 1002 cm - 1, are cons i -dered to be c h a r a c t e r i s t i c of the P-C 6H 5 group (132), although they may be ring v i b r a t i o n s . 2.2.4 E l e c t r o n i c Spectra. The absorptions observed i n the v i s i b l e and near in f r a r e d region are l i s t e d i n Table 2.2.4.1. Copper(II) di-i-propylphosphinate y i e l d s a spectrum almost i d e n t i c a l to those of the oc-forms of the stra i g h t chain a l k y l d e r i v a t i v e s (Section 2.1.5), with the c h a r a c t e r i s t i c peak at 835 nm (12,000 cm - 1), and a high energy shoulder at 715 nm (14,000 cm - 1). The spectrum of the t-butyl d e r i v a t i v e i s reminiscent of that of copper dimethylphosphinate, co n s i s t i n g of a broad absorption centered at 800 nm (12,500 c m - 1). On t h i s basis and consistent with the e a r l i e r discussion on the structure of these two compounds, the assignments l i s t e d i n the - 158 -Table 2.2.4.1 E l e c t r o n i c Spectra of Copper(II) D i - i - p r o p y l , D i - t - b u t y l , and Diphenylphosphinate 1. Compound \(nm) v( cm"1) Assignment C u [ ( i - C 3 H 7 ) 2 P 0 2 ] 2 835 715 sh. 12,000 14,000 sh. 2 B 2 _ > 2 A i f 2 E B 2 • B L C u [ ( t - C 1 + H 9 ) 2 P 0 2 ] 2 800 br. 12,500 br. 2 B 2 • 2&lt2E C u [ ( C 6 H 5 ) 2 P 0 2 ] 2 870 670 610 sh. 11,500 14,900 16,400 sh. Refer to text 1 sh., shoulder; br., broad. Table appear reasonable, with the 2 B 2 — • 2B± t r a n s i t i o n not being resolved i n the t-butyl d e r i v a t i v e . These compounds would then be predicted to have d i s t o r t i o n angles of ca. 74° and contain d i s t o r t e d tetrahedral CuO^ chromophores, as found previously for the n-alkyl d e r i -v a t i v e s . That the i-propyl and t-butyl derivatives can be assigned „ using the same values of the parameters Dq (1665 cm"1) and Cp (1800 cm" 1), determined from the straight chain compounds, indicates the r e l a -t i v e invariance of the ligand f i e l d s p l i t t i n g a b i l i t y of these ligands to the d i f f e r e n t substituents on phosphorus, when R i s a l k y l . The e l e c t r o n i c spectrum of copper(II) diphenylphosphinate i s unique among the spectra of a l l other compounds prepared i n t h i s study. It consists of three absorptions; the p r i n c i p a l peak appears centered at 670 nm (14,900 cm" 1), with a d i s t i n c t high-energy shoulder at 610 nm (16,400 cm" 1), and a f a i r l y well-separated lower energy shoulder at 870 nm (11,500 cm" 1). Figure 2.2.4.1 i l l u s t r a t e s the spectrum (Nujol mull) Figure 2.2.4.1 Ele c t r o n i c Spectrum of Cu[ ( C 6 H 5 ) 2 P 0 2 ] 400 500 600 700 800 900 1000 1100 1200 Wavelength (nm) - 160 -and i s reproduced exactly from the spectrometer-recorded chart (to show the lack of background absorptions and noise i n this spectrum). This spectrum cannot be f i t u t i l i z i n g the above parameters and the energy l e v e l diagram of Section 2.1.5 (Figure 2.1.5.3). The best assignment according to the l a t t e r i s for an a value of 77.5° and results i n the following t r a n s i t i o n s and energies: 2 B 2 — • 2 A 1 at 11,800 cm - 1, 2 B 2 • 2E at 14,300 cm - 1, and 2 B 2 • 2 B 1 at 15,700 cm - 1. The frequencies of the l a s t two t r a n s i t i o n s are 600 and 700 cm - 1 lower than the energies of the observed t r a n s i t i o n s . On the basis of the e a r l i e r discussion (Section 2.1.5) on the accuracies of Dq, Cp and the observed t r a n s i t i o n energies, these discrepancies are considered to be outside the range of experimental error, e s p e c i a l l y as the t r a n s i t i o n s of the diphenyl compound are not obscured by background absorption and the energies therefore are somewhat better determined than i n the other compounds. A more s a t i s f a c t o r y f i t i s obtained by increasing Dq and decreasing Cp (Cp/Dq reduced), so that each i s 1700 cm - 1. The calculated t r a n s i t i o n energies are then: 2 B 2 • 2 k l at 11,700 cm"1, 2 B 2 • 2E at 15,000 cm"1, 2 B 2 *• 2 B L at 16,000 cm - 1, with a d i s t o r t i o n angle, a, of 79°. This implies a greater f l a t t e n i n g - 161 -of the CuO^ chromophore towards square planar geometry In the diphenyl compound than i s found i n the d i - n - a l k y l or branched a l k y l d e r i v a t i v e s , which may be a r e s u l t of the s t e r i c requirements of the bulky phenyl groups, and the proposed crosslinked structure. The higher value of Dq (1700 cm - 1 compared to 1665 cm - 1) i s not unexpected i n view of the higher t r a n s i t i o n energies observed and i s consistent with there being a somewhat greater metal-ligand i n t e r a c t i o n i n this compound. The lower value of Cp (1700 cm"1 compared to 1800 cm - 1), and hence a Cp/Dq r a t i o of 1.0 (compared to 1.08), implies shorter Cu-0 bond lengths and increased covalency (161) i n the diphenyl d e r i v a t i v e . This assignment, while f i t t i n g the two lower energy t r a n s i t i o n s w e l l , results i n a 2 B 2 • 2B^ t r a n s i t i o n energy of 16,000 cm"1, some 400 cm"1 lower than i s a c t u a l l y observed. This i s not considered a serious d i s p a r i t y for several reasons; i ) while the nature of the spectrum i s such that the error i n the two lowest energies i s considered to be small (< ± 1%, ± ca. 100 cm"1) the highest energy t r a n s i t i o n appears as a shoulder, therefore, the frequency i s somewhat less accurate (± ca. 250 cm"1 (1.5%)), and i i ) the calculated energies involve computations involving three unknowns; a, Dq, and Cp, so the uncertainty i n each Is greater than for the case where a i s known. The suggested f i t then i s not unique but was judged superior to other p o s s i b i l i t i e s a f t e r a consideration of the c o r r e l a t i o n between calculated and observed t r a n s i t i o n energies, and of the values of Dq, Cp, Cp/Dq and a, which appeared chemically reasonable. For example, values of Dq = 1300 cm"1, Cp = 3900 cm"1 and a = 73° result i n calculated t r a n s i t i o n energies of 11,000 ( 2 B 2 • 2 B 1 ) , 14,800 ( 2 B 2 »• - 162 -2E) and 16,400 cm - 1 ( 2 B 2 *• 2A-i)i however, the large reduction i n Dq, to close to the value found for C u C l ^ 2 - (1150 cm - 1), seemed unreasonable, on the basis of the e a r l i e r discussion (Section 2.1.5), as did the large increase i n Cp, r e s u l t i n g i n a Cp/Dq r a t i o of 3, outside the range of 1-2 normally found for copper(II) compounds (161); hence t h i s f i t was considered unsuitable. A knowledge of the d i s t o r t i o n angle, a, would, of course, help i n the assignment of t h i s compound, but i t has not been possible, to t h i s point, to grow single c r y s t a l s suitable for X-ray an a l y s i s , although numerous attempts have been made. 2.2.5 Magnetic Properties. Molar s u s c e p t i b i l i t i e s and e f f e c t i v e magnetic moments, over the temperature range 300 - 80K, are l i s t e d i n Appendix 3; the magnetic moments at the two temperature extremes are given i n Table 2.2.5.1. These moments l i e i n the range expected for magnetically d i l u t e copper (II) compounds (157) and are independent of temperature, obeying the Curie Law to within experimental e r r o r . Clear evidence for or against magnetic exchange, as found i n the di-n-alkylphosphinates, w i l l have to come from measurements of the magnetic s u s c e p t i b i l i t y at temperatures below 80K. - 163 -Table 2.2.5.1 Magnetic Moments at ca. 300K and 80K. Compound T(K) u e f f #(B.M.) C u [ ( i - C 3 H 7 ) 2 P 0 2 ] 2 302.0 1.85 78.3 1.88 C u [ ( t - C i t H 9 ) 2 P 0 2 ] 2 302.4 1.86 82.8 1.87 C u [ ( C 6 R 5 ) 2 P 0 2 ] 2 303.2 1.89 83.7 1.93 2.3 Monoorganophosphinate Derivatives, [Cu(R(H)P0 2) 2] x, Containing Straight Chain A l k y l Groups or Phenyl Groups. 2.3.1 Introduction. The monosubstituted copper(II) phosphinates discussed i n th i s section are characterized by low thermal s t a b i l i t y , complex i n f r a r e d spectra, broad unresolved e l e c t r o n i c spectra, and magnetic moments of ca. 1.90 - 1.94 B.M. over the temperature range studied (300 to 80K). Comparisons with the corresponding disubstituted compounds indicate that the monoorgano derivatives have flattened tetrahedral CuO^ chromophores and symmetric phosphinate bridges, although they are probably crosslinked polymers. 2.3.2 Synthesis, S o l u b i l i t i e s and Thermal Properties. The procedures involved i n the preparation of these compounds are - 164 -detai l e d i n Chapter 4; there were, generally, few problems encountered i n the syntheses. The monosubstituted phosphinates are insoluble i n a l l solvents t e s t e d 1 with the exception of the monophenyl der i v a t i v e which i s s l i g h t l y soluble (ca. O.Olg i n 100 mL) i n water. Given the l i m i t e d s o l u b i l i t y of the corresponding d i a l k y l compounds, the i n s o l u b i l i t y of the monoalkyl derivatives may be i n d i c a t i v e of crosslinked structures. Why the presence of one organic group and one hydrogen substituent on phosphorus r e s u l t s i n a crosslinked, instead of a l i n e a r , polymer, i s not c l e a r . The monophenylphosphinate, i n analogy to the diphenyl compound, i s also proposed to have a crosslinked structure. The monosubstituted copper(II) phosphinates a l l decompose at temperatures s u b s t a n t i a l l y below 200°C, and are the least thermally stable of a l l the phosphinates prepared i n t h i s study. The monoalkyl derivatives exhibit sharp exothermic decomposition peaks as i l l u s t r a t e d i n Figure 2.3.2*1, while the monophenyl compound has a D.S.C. curve characterized by one sharp peak and two broader, less exothermic peaks as shown i n Figure 2.3.2.2. The temperature^ of the peak maxima and the decomposition energies are given i n Table 2.3.2.1. The monophenyl deri v a t i v e appears to be the least thermally stable, requiring l e s s energy and a lower temperature to cause decomposition. The monodecyl compound has a s l i g h t l y higher decomposition point than the monohexyl, 1 H 20, MeOH, EtOH, acetone, CH 2C1 2, CHC13, CCl^, benzene and 60°-90° petroleum ether. - 165 -Figure 2.3.2.1 Thermograms of the Copper(II) Monoalkylphosphinates. I 1 1 1 I 1 ' 1 | 1 1 1 | 1 • ' | ' | i I I | i I I | i i i | i I I | i i i ) i * « • t « I I I I I £ T E M P E R A T U R E * C I ' I ' ' 1 I ' 1 1 I ' ' ' | ' ' ' | • I I | I I I \ I I I | T E M P E R A T U t t C * C - 166 -Figure 2.3.2.2 Thermograms of Copper(II) Monophenylphosphinate. a)Cu((C6H5)(H)P02)2-I i i | i i i i | i i i i | i i i 1 1 i 1 1 q i i i i [ i i i i | i i 11 | n i 11 111 i | i i i i • i f i i i i s i i i T K M P C R A T U M C »C b ) , a) after cooling and reheating. - 167 -Table 2.3.2.1 D.S.C. Studies on Copper(II) Monosubstituted Phosphinates. Compound T(°C) AH(kJ mol" 1) C u [ ( n - C 6 H 1 3 ) ( H ) P 0 2 ] 2 143.7 250 C u [ ( n - C 1 0 H 2 1 ) ( H ) P O 2 ] 2 150.7 170 C u [ ( C 6 H 5 ) ( H ) P 0 2 ] 2 130.5 ) 137.4 > 140 145.7 ) but needs s i g n i f i c a n t l y less heat to e f f e c t the degradation. This l a t t e r observation i s consistent with the e a r l i e r discussion on the e f f e c t s of long a l k y l chains on the thermal s t a b i l i t y of phosphinate polymers (Section 2.1.3). The f a c i l e decomposition of the monophenyl deri v a t i v e i s somewhat s u r p r i s i n g , as one might have expected the a r y l substituted compound to be the most stable of the three, on the basis of the increased thermal s t a b i l i t y of the diphenylphosphinates when compa-red to the dialkylphosphinates. When observed i n a melting point appa-ratus, the three compounds exhibit almost i d e n t i c a l behavior; the s o l i d s f i r s t "melt" to a clear yellow or golden l i q u i d which turns a clear red or red-brown immediately. Continued heating re s u l t s i n increased darkening and loss of transparency. The monophenyl and mono-decyl compounds cool to red-brown and black residues, r e s p e c t i v e l y , while the monohexyl sample cools to a shiny golden s o l i d . This behavior i s s i m i l a r to that observed previously (26) for copper(II) hypophosphi-te, Cu[H 2P0 2] 2, which decomposes at room temperature, i n an exothermic reaction, to y i e l d m e t a l l i c copper. Copper(II) monophenylphosphinate - 168 -decomposes overnight i f warmed (ca. 50°C) under vacuum, and also decomposes i n coordinating solvents such as p y r i d i n e . The anhydrous hypophosphites of copper(II), n i c k e l ( I I ) and i r o n ( I I ) also undergo self-oxidation-reduction i n pyridine (26), i n d i c a t i n g the r e a c t i v i t y of the P-H bond. Cooling a decomposed sample and then reheating r e s u l t s i n D.S.C. curves l i k e that shown for C u [ ( C 6 H 5 ) ( H ) P 0 2 ] 2 i n Figure 2.3.2.2.b). These are characterized by a featureless, increasingly exothermic curve, the nature of which i s not understood. 2.3.3 Infrared Spectroscopy. The i n f r a r e d spectra of the monosubstituted phosphinates are distinguishable from those of the d i s u b s t l t u t e d derivatives by t h e i r complexity, r e s u l t i n g from the large number of bands present, p a r t i c u l a r l y i n the 1200 - 950 cm - 1 region. The spectrum of C u [ ( n - C 1 0 H 2 1 ) ( H ) P 0 2 ] 2 , shown i n Figure 2.3.3.1, i l l u s t r a t e s t h i s . Similar band m u l t i p l i c i t y , i n f i r s t row t r a n s i t i o n metal hypophosphites, has been at t r i b u t e d to the presence of more than one type of H 2P0 2~ anion, i . e . , bridging and chelating (27,146); however, i t appears u n l i k e l y that t h i s anion w i l l act as a chelating ligand, as a r e s u l t of the angle s t r a i n that would be present i n the four-membered ring (142). In a d d i t i o n , the values of the frequencies assigned as asymmetric P0 2 stretching v i b r a t i o n s are i n the range 1220-1160 cm - 1, and i t would seem more appropriate to assign them as non-coordinated P0 stretches (126) - 169 -Figure 2.3.3.1 Infrared Spectrum of Cu[(n-C 1 0H 2 1)(H)PO 2] 2« - 170 -r e s u l t i n g , perhaps, from chain terminating groups 1. In the spectra under discussion here, the large number of absorptions i n the spectral region associated with the P0 2 stretching vibrations may be related to the presence of terminal, as well as bridging, phosphinate ligands. There may also be absorptions due to bending modes ( s c i s s o r i n g and wagging) of the (C)(H)P0 2 portion of the molecule i n t h i s region; some-what s i m i l a r band m u l t i p l i c i t y i s observed i n this region i n the free anion spectra. V i b r a t i o n a l coupling and/or combinations and overtones of the fundamental frequencies may also contribute to the number of bands observed. No attempt has been made, i n this study, to assign a l l of the observed frequencies. Absorptions t e n t a t i v e l y assigned to P-0, P-H and P-C stretching and bending modes are l i s t e d i n Tables 2.3.3.1 to 2.3.3.5, and, analogous to the diphenyl d e r i v a t i v e (Section 2.2.3), Table 2.3.3.6 l i s t s absorptions a r i s i n g from the phenyl group In Cu[(C 6H 5)(H)P0 2]2 ' T ^ e remaining unassigned bands are l i s t e d , f o r completeness, i n Appendix 2.c). The absorptions a r i s i n g from the asymmetric and symmetric P0 2 stretching vibrations are l i s t e d i n Table 2.3.3.1. For the bridging phosphinates i n the monoalkyl d e r i v a t i v e s , the positions of the asym-metric (ca. 1115 cm - 1) and the symmetric (ca. 1050 cm - 1) P0 2 stretching v i b r a t i o n s , and hence the A values (ca. 65 cm - 1), are very s i m i l a r to those of the corresponding d i a l k y l compounds (Table 2.1.4.1), i n d i c a t i n g This i s s i m i l a r to the e a r l i e r discussion on the di-n-alkylphosphlnates (Section 2.1.4). Table 2.3.3.1 Infrared Bands Associated with P-0 Stretching1. Copper Compound Frequencies Free Anion Compound v„_- (cm-1) asy.v ' v__ (cm-1) sym. N Atari"1) v (cm-1) asy. v ' v „ (cm-1) sjin. v ' A(cm-1) Counter-cation Reference Cu[(n-C6H13)(H)P02]2 1166 s. 1116 v.s. 1052 s. 114 64 — — — — _ 2 Cu[(n-C10H21)(H)PO2]2 1162 s. 1115 v.s. 1050 s. 112 65 1161 v.s. 1054 s. 107 Na + This work Cu[(C6H5)(H)P02]2 1185 s. 1141 v.s. 1127 s.sh. 1047 s. 138 94 1170 1152 v.s. 1049 987 s.) 3 980 s. J 121 169 Na+ 34 This work 1 v.s., very strong; s., strong; sh., shoulder. 2 Not available. 3 These frequencies were averaged for the calculation of A. - 172 -s i m i l a r phosphinate bridging. This, and the fact that there i s an almost equivalent change i n the PO stretches from the free ion values, for the bridging ligands i n the monodecyl de r i v a t i v e , when compared to the di-n-decyl d e r i v a t i v e , may imply an equal metal-ligand i n t e r a c t i o n i n these compounds (and, probably, i n the hexyl compound as we l l , although no spectrum of the free anion i s available i n t h i s case. The monohexylphosphinic acid was obtained as one component of an o i l , from which i t could not be separated, (see Section 4.2.7).) The higher frequency (ca. 1160 cm"1) band i s then t e n t a t i v e l y assigned as the asymmetric P0 2 s t r e t c h of the terminal phosphinate, with the symmetric P0 2 s t r e t c h probably being a c c i d e n t a l l y degenerate with that of the bridging ligand at ca. 1050 cm - 1, analogous to the dimethyl d e r i v a t i v e . In the monophenyl d e r i v a t i v e , the asymmetric P0 2 stretching v i b r a t i o n of the bridging ligand appears at 1141 cm - 1 (with a shoulder at 1127 cm - 1), a higher frequency than i s found for the corresponding absorption i n the diphenyl derivative (1132 cm - 1). This r e s u l t s i n a larger A value for the monosubstituted compound (94 cm - 1 versus 81 cm - 1) The s h i f t s , for the bridging phosphinate, i n both the asymmetric and the symmetric P0 2 stretching frequencies from the respective free ion values are much less for the monophenyl der i v a t i v e than for the diphenylphos-phinate, perhaps implying, together with the higher v a g y p 0 2 frequency, a decreased metal-ligand i n t e r a c t i o n i n the monophenyl compound. The absorption at 1185 cm - 1 i s t e n t a t i v e l y assigned as the asymmetric P0 2 stretching v i b r a t i o n of the terminal phosphinate; the symmetric stretching frequency appearing at 1047 cm - 1. The nature of the spectra of these monosubstituted d e r i v a t i v e s - 173 -i s not well understood, and the above assignments are considered tenta-t i v e . Support for the presence of more than one type of phosphinate binding i n these compounds may be indicated by the m u l t i p l i c i t y observed i n the Cu-0 stretching region (Table 2.3.3.2) and p a r t i c u l a r l y , i n the s p e c t r a l regions associated with P-H stretching (Table 2.3.3.3), P-C stretching (Table 2.3.3.4), and (C)(H)P0 2 bending (Table 2.3.3.5), although some of the l a t t e r absorptions l i s t e d probably a r i s e from Internal vibrations of the organic groups. Hence, for example, two absorptions appear i n the 2300-2400 cm - 1 region, assigned to P-H stretching (27,30,126,132,142,145,146), where only one band i s expected. Comparison of these frequencies to the free ion values i s d i f f i c u l t ; as mentioned, no spectrum i s available for the monohexylphosphinic a c i d , and, for (C 6H 5)(H)P0 2H, bands i n t h i s region are obscured by strong absorptions due to the P-OH group (132,147). In the spectrum of sodium monodecylphosphinate there i s a medium i n t e n s i t y , broad absorption at 2297 cm - 1, with weak shoulders at 2347 cm - 1 and 2375 cm - 1, assigned as a r i s i n g from the P-H stretching v i b r a t i o n . The absorptions i n t h i s region, for the copper(II) monodecylphosphinate (Figure 2.3.3.1), are at higher frequencies than the p r i n c i p a l band i n the free anion spectrum. Similar increases i n vP-H have been observed i n the hypophosphite anion upon incorporation into t r a n s i t i o n metal complexes, and these s h i f t s are believed to occur as a r e s u l t of the phosphorus atom attempting to compensate for electron density l o s t through donation from oxygen to the metal, i . e . , the P-H bond i s somewhat strengthened. (This i s analogous to the increase i n vP-F seen upon the coordination of F 2P0 2~ to a metal (287).) The presence of two absorptions i n the P-H stretching region of - 174 -Table 2.3.3.2 Infrared Bands Associated with Cu-0 S t r e t c h i n g 1 . Compound Frequency (cm" 1) C u [ ( n - C 6 H 1 3 ) ( H ) P 0 2 ] 2 C u [ ( n - C 1 0 H 2 1 ) ( H ) P O 2 ] 2 C u [ ( C 6 H 5 ) ( H ) P 0 2 ] 2 375 w., 348 w.sh. 394 w., 383 v.w.sh., 358 w., 350 v.w.sh. 396 v.w., 387 v.w., 363 w. w., weak; v.w., very weak; sh., shoulder. Table 2.3.3.3 Infrared Bands Associated with P-H S t r e t c h i n g 1 . Compound Frequency (cm - 1) C u [ ( n - C 6 H 1 3 ) ( H ) P 0 2 ] 2 2398 m. 2362 m. C u [ ( n - C 1 0 H 2 1 ) ( H ) P O 2 ] 2 2403 m. 2364 m. C u [ ( C 6 H 5 ) ( H ) P 0 2 ] 2 2382 m. 2342 m. 1 m., medium. Table 2.3.3.4 Infrared Bands Associated with P-C S t r e t c h i n g 1 . Compound Frequency (cm - 1) C u [ ( n - C 6 H 1 3 ) ( H ) P 0 2 ] 2 792 m.s. 721 m.s. C u [ ( n - C 1 Q H 2 1 ) ( H ) P 0 2 ] 2 792 m.s. 724 m.s. 720 m.s. C u [ ( C 6 H 5 ) ( H ) P 0 2 ] 2 756 m.sh. 716 s. 8., strong; m.s., moderately strong; m., medium; sh., shoulder. - 175 -the spectra of the copper compounds may then imply the presence of phosphinate ligands i n d i f f e r e n t coordination modes. ( I n t e r e s t i n g l y , the absorptions for the two monoalkyl derivatives appear at almost i d e n t i c a l frequencies, while those of the monophenyl occur some 20 cm - 1 lower; the separation between the two bands i s ca. 40 cm - 1 i n a l l compounds.) S i m i l a r l y , multiple bands are observed In the sp e c t r a l region associated with P-C stretching vibrations (Table 2.3.3.4), where only one i s expected. The absorptions assigned to (C)(H)P0 2 bending modes (Table 2.3.3.5) show si m i l a r patterns for the two monoalkylphosphinates, consisting of three moderately strong bands between 500 and 600 cm - 1, and a number of weaker bands between 450 and 500 cm - 1. Comparison to the free ion spectra indicates increases i n the frequencies of these absorptions of up to 65 cm - 1, for the monodecyl and monophenyl derivatives and, presumably, for the monohexyl compound, as expected upon coordination through oxygen. F i n a l l y , Table 2.3.3.6 l i s t s i n f r a r e d bands c h a r a c t e r i s t i c of the phenyl group i n Cu[ ( C 6 H 5 ) ( H ) P 0 2 ] 2 , a n ^ t n e comments made i n the discussion of the equivalent absorptions i n C u [ ( C 6 H 5 ) 2 P 0 2 i 2 (Section 2.2.3) apply equally here. - 176 -Table 2.3.3.5 Infrared Bands Associated with (C)(H)P0 2 Bending 1. 1 Compound Frequency (cm - 1) Cu [ ( n - C 6 H 1 3 ) ( H ) P 0 2 ] 2 857 m. 574 m.s. 544 m.s. 508 m.s. 468 m. C u [ ( n - C 1 0 H 2 1 ) ( H ) P O 2 ] 2 833 w.-m. 583 m.s. 554 m.s. 515 m.s. 485 w.-m. 478 w.-m. 458 w.-m. Cu [ ( C 6 H 5 ) ( H ) P 0 2 ] 2 592 m.s. 572 m.s. 503 w.sh. 498 w.-m. 477 w. s., strong; m.s., moderately strong; m., medium; w.-m., weak-to-medium; w., weak; sh., shoulder. Table 2.3.3.6 Infrared Absorptions Associated with the Internal Vibrations of the Phenyl Group i n C u [ ( C 6 H 5 ) ( H ) P 0 2 ] 2 l • Frequency (cm - 1) Assignment Reference 1595 w. vC-C in-plane (132, 1026 m. 8C-H 284) 750 s. yC-H 698 s. <t>c-c 1440 s. | P - C 6 H 5 132 1004 w.sh. s., strong; m., medium; w., weak; sh., shoulder; 8, in-plane deforma-t i o n ; y» out-of-plane deformation; <J>, out-of-plane ring deformation. - 177 -2.3.4. E l e c t r o n i c Spectra. The e l e c t r o n i c spectra of the copper(II) monosubstituted phosphi-nates consist of single broad absorptions centered at approximately 11,000 cm - 1. The band maxima are given i n Table 2.3.4.1. The Table 2.3.4.1 E l e c t r o n i c Spectra of Copper(II) Monosubstituted Phosphinates. Compound \(nm) v(cm - 1) C u [ ( n - C 6 H 1 3 ) ( H ) P 0 2 ] 2 C u [ ( n - C 1 0 H 2 1 ) ( H ) P O 2 ] 2 C u [ ( C 6 H 5 ) ( H ) P 0 2 ] 2 860 br. 900 br. 885 br. 11,600 br. 11,100 br. 11,300 br. br., broad. unresolved nature of the spectra and the uncertainty i n the peak positi o n s , estimated to be approximately ± 200 cm - 1, preclude a d e f i n i t i v e assignment of the t r a n s i t i o n s . However, i f we assume that the values of Dq and Cp (1665 cm - 1 and 1800 cm" 1), used to f i t the spectra of the d i a l k y l - and the branched a l k y l phosphinates, are v a l i d for the monosubstituted compounds, the broad t r a n s i t i o n s may be assigned as the unresolved 2 B 2 »• 2A],, 2E t r a n s i t i o n , with the 2 B 2 »• 2 B X - 178 -t r a n s i t i o n not being observed. At a d i s t o r t i o n angle of 72.5°, the calculated t r a n s i t i o n energies are 11,400 cm - 1 and 13,700 cm - 1, while at a value of a somewhat closer to that found i n the p-copper(II) di-n-alkylphosphinates, ca. 73°, the energies would be 11,500, 11,800 (average: 11,600) and 13,900 cm - 1 for 2 B 2 *• 2A X, • 2E, and *• 2Bl t r a n s i t i o n s , r e s p e c t i v e l y . Both of these are i n reasonable agreement with the observed spectra and indicate the presence of CuO^ chromophores, i n the monosubstituted d e r i v a t i v e s , with s i m i l a r degrees of d i s t o r t i o n as found i n a l l other copper phosphinate compounds, with the probable exception of the diphenyl d e r i v a t i v e (Section 2.2.4). 2.3.5 Magnetic Properties. A complete l i s t i n g of molar s u s c e p t i b i l i t i e s and calculated magnetic moments for the temperature range 300K to 80K i s given In Appendix 3. Like the compounds with branched chain a l k y l and phenyl substituents on phosphorus (Section 2.2), the monosubstituted d e r i v a t i -ves exhibit magnetic moments, i n the temperature range studied, t y p i c a l of magnetically d i l u t e copper(II) complexes, although the moments tend to be somewhat higher than the i - p r o p y l , t - b u t y l , and phenyl compounds (ca. 1.92 B.M. versus ca. 1.86 B.M. on average). Values of u f 4. at room and l i q u i d nitrogen temperatures are given i n Table 2.3.5.1. - 179 -Table 2.3.5.1 Magnetic Moments at ca. 300K and 80K. Compound Temperature(K) H eff.< B' M') C u [ ( n - C 5 H 1 3 ) ( H ) P 0 2 ] 2 302.8 1.94 83.5 1.92 C u [ ( n - C 1 0 H 2 1 ) ( H ) P O 2 ] 2 303.0 1.93 Cu [ ( C 6 H 5 ) ( H ) P 0 2 ] 2 304.0 1.91 78.0 1.86 For the monoalkyl d e r i v a t i v e s , these moments are close to the values observed for the p-forms of the corresponding d i a l k y l compounds; however, whether or not there i s ferromagnetism present i n the mono-substituted phosphinates, cannot be determined from the data obtained over the 300 to 80K range. - 180 -CHAPTER 3 SUMMARY, CONCLUSIONS AND SUGGESTIONS FOR FURTHER WORK The series of copper(II) phosphinate polymers prepared and characterized i n t h i s study revealed many i n t e r e s t i n g and sometimes surp r i s i n g features. The phosphinates containing s t r a i g h t chain a l k y l groups were found to e x i s t i n two forms, each isomer having c h a r a c t e r i s -t i c thermal properties, i n f r a r e d spectra, and e l e c t r o n i c and magnetic properties. The so l u t i o n of the c r y s t a l structures of a representative of each form allowed discussion of co r r e l a t i o n s between s t r u c t u r a l para-meters and the above properties. The e f f e c t that the d i f f e r e n t organic substituents on phosphorus have on the bulk polymer properties such as the s o l u b i l i t i e s and the thermal behavior, as well as the s p e c t r a l and magnetic properties, were examined, both within the groups of compounds with the same type of R group, and between the d i f f e r e n t groups. The less well-characterized compounds containing branched a l k y l chains, phenyl groups and hydrogens on phosphorus warrant further study, p a r t i c u l a r l y i n l i g h t of the reported room temperature magnetic moment of 1.56 B.M. (18,87) for Cu[(CH 3)(C 6H 5)P0 2] 2» n o evidence for magnetic exchange was found over the 300 - 80K temperature range for either the diphenyl or the dimethyl de r i v a t i v e s . Low temperature studies may, however, reveal spin i n t e r -actions i n those compounds for which Gouy data only are a v a i l a b l e . The presence of magnetic exchange i n the dialkylphosphinates that i s ferromagnetic or antiferromagnetic depending on which isomer i s - 181 -present was one of the most i n t e r e s t i n g r e s u l t s of t h i s work. Given that | j | appears to increase with increasing chain length for the a n t i -ferromagnetic compounds, i t may be possible to magnify the exchange by incorporating even longer a l k y l groups into the phosphinate ligand than those studied here. In addition, i t would be i n t e r e s t i n g to examine phosphinate ligands that, due to s t e r i c requirements, might force the copper into a square planar or nearly square planar coordination geometry, r e s u l t i n g i n more e f f e c t i v e metal-oxygen o r b i t a l overlap and, hence, greater exchange. Ligands of t h i s type might include those that incorporate the phosphorus atom into a carbon r i n g , for example, penta-methyltrimethylenephosphinlc acid (288) and derivatives of biphenyl-phosphinic acid (289). Ligands of this type have not yet been studied. Another area of i n t e r e s t would be the i n v e s t i g a t i o n of the behavior of these polymers with coordinating neutral ligands, such as pyridine and substituted pyridines, with the aim of forming dimers analogous to the copper carboxylates. Compounds of this type would be predicted to show stronger exchange than l i n e a r chain compounds, and a study of the e f f e c t of the b a s i c i t y of the donor ligand on the exchange, for a given phosphinate compound, may reveal some i n t e r e s t i n g trends. I f dimer formation did not occur, the e f f e c t of the coordinated ligand on the exchange propagated through the inorganic polymer backbone, would also be of i n t e r e s t . I n i t i a l i n v e s t i g a t i o n s , by us, involving pyridine and 4-methylpyridine indicate that with pyridine and copper dimethyl-, d i e t h y l - , di-n-hexyl-, and di-n-octylphosphinate, stable adducts are not formed; the base appears to be merely adsorbed onto the s o l i d . The monosubstituted phosphinates decompose, as mentioned e a r l i e r , while the - 182 -diphenyl d e r i v a t i v e i s i s o l a t e d as a 2:1 pyridine:copper adduct 1 which loses the coordinated pyridine e a s i l y . Copper diethylphosphinate forms a 1:1 adduct with 4-methylpyridine, that i s somewhat more stable than C u [ ( C 6 H 5 ) 2 P 0 2 ] 2 p y 2 , n a s a temperature independent moment (down to 80K) of ca. 1.90 B.M., and a broad absorption centered at 13,100 cm"1 i n the el e c t r o n i c spectrum. Further i n v e s t i g a t i o n of this type of compound perhaps with more strongly coordinating donor ligands, i s worthwhile and would help explain why the diphenyl d e r i v a t i v e seems to form 2:1 adducts while the straight chain compounds appear to form 1:1 complexes. F i n a l l y , the synthesis and ch a r a c t e r i z a t i o n of series of compounds containing the same ligands employed i n th i s study (as well as other phosphinates), but d i f f e r e n t metals, for example, other f i r s t row t r a n s i t i o n metals such as n i c k e l ( I I ) , c o b a l t ( I I ) and manganese(II), would be of i n t e r e s t . Given that we now have the c a p a b i l i t y of measuring magnetic s u s c e p t i b i l i t i e s down to 4.2K and below, the exploration of magneto-structural c o r r e l a t i o n s i n these other systems may y i e l d rewarding r e s u l t s and help to c l a r i f y the e f f e c t of R on the structures of phosphinate polymers as discussed i n Section 1.2.6. Research of t h i s type, involving manganese(II) and n i c k e l ( I I ) i s already underway i n th i s laboratory (265). The best analyses for the st r a i g h t chain compounds indicated a 1:1 "adduct" formation; however, the inf r a r e d indicated the pyridine was not coordinated. - 183 -CHAPTER 4 EXPERIMENTAL 4.1 Methods of Characterization. 4.1.1 Elemental A n a l y s i s . A l l carbon and hydrogen analyses were performed by Mr. Peter Borda, Micro-analysis Laboratory, Department of Chemistry, Un i v e r s i t y of B r i t i s h Columbia. The copper content of the coordination polymers was determined by EDTA t i t r a t i o n (290,291). 4.1.2 Thermal Studies. Uncorrected melting points were obtained on powdered samples, contained i n c a p i l l a r y tubes, using a Gallenkamp Melting Point Apparatus. D i f f e r e n t i a l Scanning Calorimetry (D.S.C.) was performed u t i l i z i n g a Mettler TA3000 System, consisting of a Mettler DSC 20 Standard C e l l , a Mettler TC 10 TA Processor and a Print Swiss Matrix R0-80 p r i n t e r / p l o t t e r . Powdered samples (2-4 mg) were sealed i n standard aluminum pans (40 uL volume). Two small holes punched i n the l i d allowed for free access to the measuring c e l l atmosphere, i n t h i s case, a i r . The heating rate was 4°C per minute. The temperature was c a l i b r a t e d over the en t i r e temperature range, 25°C to 600°C, with a sample (provided with the instrument) containing exactly known quantities of indium, zinc and lead i n separate compartments. Heat flow c a l i b r a t i o n was achieved using the average of the heats of fusion of - 184 -several accurately weighed samples of indium. Both c a l i b r a t i o n s were checked p e r i o d i c a l l y , p a r t i c u l a r l y a f t e r periods of instrument disuse. 4.1.3 Infrared Spectroscopy. Infrared spectra, over the range 4000 cm - 1 to 200 cm - 1, were recorded on a Perkin-Elmer 598 Infrared Spectrophotometer. F i n e l y ground samples were mulled i n Nujol and contained between KRS-5 plates (42% thaHum bromide - 58% thalium iodide, Harshaw Chemical Co.). Wavelength was c a l i b r a t e d with the polystyrene peaks at 1601 cm - 1 and 907 cm - 1. 4.1.4 E l e c t r o n i c Spectroscopy. E l e c t r o n i c spectra, i n the near Infrared (2200 nm to 650 nm; 4545 cm - 1 to 15,400 cm"1) and v i s i b l e (650 nm to 350 nm; 15,400 cm"1 to 28,600 cm"1) regions, were recorded on a Cary Model 14 Recording Spectrophotometer. Thick Nujol mulls were contained between s i l i c a glass windows; l i g h t scattering was compensated for with a Nujol soaked tissue or f i l t e r paper i n the reference beam and the absorbance l e v e l was adjusted with neutral density f i l t e r s . D iffuse reflectance spectra, over the range 725 nm to 350 nm (13,800 cm"1 to 28,600 cm" 1), were recorded on a Bausch and Lomb Spectronic 600 Spectrophotometer equipped with a v i s i b l e reflectance attachment and a Sargent recorder Model SR. The samples were f i n e l y powdered s o l i d s . A block of magnesium carbonate was used as the reflectance standard. - 185 -4.1.5 Magnetic S u s c e p t i b i l i t y Measurements. S u s c e p t i b i l i t y measurements over the temperature range 300K to 80K were made on a Gouy balance (292) using a magnetic f i e l d of approxi-mately 8000 gauss. Mercury tetrathiocyanocobaltate, HgCo(SCN)lt (293), was used as the c a l i b r a n t . Molar s u s c e p t i b i l i t i e s were corrected for the diamagnetic contributions of the metal and the ligands (196,294-296). These corrections were ( i n 10~ 6 cm3 m o l - 1 ) : Copper, -11; (CH 3) 2P0 2-, -42; ( C 2 H 5 ) 2 P 0 2 ~ , -72; (n-C^Hc,) 2P0 2", -132; ( n - C 6 H 1 3 ) 2 P 0 2 " , -166; (n- C 8 H 1 7 ) 2 P 0 2 ~ , -210; ( n - C 1 Q H 2 1 ) 2 P 0 2 ~ , -257; ( n - C 1 2 H 2 5 ) 2 P 0 2 ~ , -300; ( i - C 3H 7) 2P0 2-, -98; (t-C^Hg) 2P0 2 _, -121; ( C 6 H 5 ) 2 P 0 2 _ , -127; (n-C 6H 1 3)(H)P0 2", -98; (n-C 1 0H 2 1)(H)PO 2-, -143; (C 6H 5)(H)P0 2~, -78. A value of 60 cm3 m o l - 1 was used to correct for the temperature indepen-dent paramagnetism (T.I.P.) of copper(II). Measurements were usually obtained on each compound at least twice, with d i f f e r e n t tube packings. (See Section 2.1.6 for data treatment.) S u s c e p t i b i l i t y measurements from 125K to 4.2K were obtained using a Princeton Applied Research Model 155 Vi b r a t i n g Sample Magnetometer, as previously described (270). Measurements were normally obtained with a f i e l d of 9735 gauss with checks for f i e l d dependence of the magnetic s u s c e p t i b i l i t i e s using several or a l l of the following values: 1280, 2549, 3850, 5251, 6200, 7501, 8520, 9225, and 9625 gauss. No evidence of f i e l d dependence was found i n any of the compounds studied. Magnetic s u s c e p t i b i l i t i e s were corrected for the diamagnetism of a l l atoms and the T.I.P. of copper(II) with the values l i s t e d above. Samples were contained i n g e l a t i n capsules attached to a Kel-F - 186 -holder and corrections were applied for the background diamagnetism of the sample holder. The optimum size for the g e l a t i n capsule i s 7 mm; thi s w i l l hold an approximately 80-100 mg sample. However, given the large molecular weights, sizeable diamagnetlc corrections for the ligands, and small s u s c e p t i b i l i t i e s of these copper polymers, p a r t i c u -l a r l y the antiferromagnetic a-isomers, i n some cases a longer tube (13 mm) was employed to contain the sample. These held ca. twice as much sample, 110-210 mg, and t h e i r use then produced larger moment readings, improving the accuracy of the measurements. The data gathered using the longer tubes were corrected for the extra length by applying a graphi-c a l l y determined c o r r e c t i o n factor to the molar s u s c e p t i b i l i t i e s . The inverse of the molar s u s c e p t i b i l i t y , l ^ - 1 * v a a plotted against tempera-ture, T, for data obtained from both a 7 mm sample and a 13 mm sample. Values of X ^ 1 (13 mm)/^ - 1 (7 mm) were determined over the enti r e temperature range, and these values were then plotted against tempera-ture y i e l d i n g a cor r e c t i o n c u r v e 1 . A l l compounds, except the a-n-dodecyl, the 8-n-butyl, and the 8-n-decyl, were measured i n 13 mm sample holders. The e t h y l , 8-n-hexyl and 8-n-octyl compounds were measured i n both sized holders and the data from these compounds were used to determine the cor r e c t i o n f a c t o r s . 4.1.6 X-Ray Crystallography. The c r y s t a l structures of copper(II) d i e t h y l - and di-n-hexyl-The corrections were ca. 5% ± 1% over the temperature range of the magnetometer, 4.2K to 125K. - 187 -phosphinate were determined by Dr. S.J. R e t t i g , Department of Chemistry, University of B r i t i s h Columbia. Suitable c r y s t a l s were obtained as described In Sections 4.3.4 (ethyl compound) and 4.3.6 (hexyl compound) of this chapter. Complete descriptions of the s t r u c t u r a l analyses are given elsewhere (270,297); s t r u c t u r a l parameters are given i n Section 2.1.2 and Appendix 1. 4.2 Synthesis of Phosphinic Acids. 4.2.1 Introduction. The dialkylphosphinic acids described i n this section have a l l been synthesized previously, many by a wide v a r i e t y of r o u t e s 1 . In some instances, p a r t i c u l a r l y with the methyl d e r i v a t i v e , considerable d i f f i -c u l t y was encountered i n obtaining pure acids i n reasonable y i e l d s . This was due p a r t l y to our own inexperience i n t h i s f i e l d at the begin-ning of the work and p a r t l y to the problems associated with dealing with the l i t e r a t u r e d e scriptions, many of which are old and rather sparsely d e t a i l e d . Moreover, scaling down the quantities of reactants used tended, i n some cases, to a f f e c t the outcome of the reaction, usually decreasing the y i e l d s s u b s t a n t i a l l y . I t was also found that procedures outlined for the treatment of one compound, for example, di-n-octylphos-phinic acid (Section 4.2.6) were not necessarily applicable to another c l o s e l y related compound, for example, di-n-hexylphosphinic acid (Section 4.2.7). For these reasons, a quite d e t a i l e d account of our 1 Reference 298 o f f e r s a comprehensive survey of the various synthetic methods. - 188 -synthetic work i s included here and comments are made, where appropria-te, on some of the approaches. We did not o r i g i n a l l y set out to synthesize the monosubstituted de r i v a t i v e s , R(H)P0 2H; however, where these occurred as by-products i n reasonable y i e l d s , they were i s o l a t e d and t h e i r complexes with copper were investigated. This i s the case for the hexyl and decyl compounds. F i n a l l y , we note that the d i e t h y l - and di-isopropylphosphinic acids were i s o l a t e d as the s i l v e r s a l t s , and not as the free acids. This was due to the fact that diethylphosphinic acid i s a low (19°C (298)) melting s o l i d and that the di-Isopropyl compound was obtained as an o i l which would not c r y s t a l l i z e . 4.2.2 Materials. A l l chemicals used were reagent grade and were used as received except d i - n - b u t y l - and diethylphosphite, phosphorus t r i c h l o r i d e and thiophosphoryl chloride which were d i s t i l l e d under vacuum j u s t p r i o r to th e i r use. The d i e t h y l ether used i n the Grignard reactions was dried by r e f l u x i n g over benzophenone-sodium for twenty-four hours. Other solvents were used as received, unless otherwise noted. The Grignard reactions described were performed i n a nitrogen atmosphere. The chemicals used, t h e i r p u r i t i e s and suppliers are given i n Table - 189 -Table 4.2.2.1 Reagents, P u r i t i e s and Suppliers. Compound Stated P u r i t y Suppliers Benzoyl peroxide Di-n-butylphosphite 1-Decene 1-Dodecene Phosphorus t r i c h l o r i d e 96% 96% 95% 98% A l d r i c h Chem. Co., Inc. fft rt • i •• Thiophosphoryl chloride 98% A l f a Products Ammonium chloride Hydrochloric acid Hydrogen peroxide N i t r i c acid Sodium hydroxide S u l f u r i c acid Magnesium turnings Potassium carbonate S i l v e r n i t r a t e Reagent, A.C.S. 37-38% 30% 70% Reagent Grade 95.5-96.5% 99% 99.9% Amachem (American S c i e n t i f i c and Chemical Co.) IS BDH Laboratory Reagants • t N-butyl bromide T-butyl chloride Ethyl bromide Hypophosphorus acid Methyl iodide 1-Octene Potassium chloride I-propyl chloride Diethylphosphite 1-Hexene Mercuric oxide Sulphuryl chloride 98% 98% 98% 50% 99.9% 97% Reagent Grade 97% P r a c t i c a l 99% Reagent, H.C.S. 99% Fisher S c i e n t i f i c Co. t i II t i •• i i •• MCB (Matheson, Coleman and B e l l Manufacturing Chemists) MCB t i Chlorine (gas) — Matheson of Canada Nitrogen (gas) — Union Carbide - 190 -4.2.3 Dimethylphosphinic Acid, (CH 3) 2P0 2H. (CH 3CH 2) 20 [4.1] 6CH3MgI + 2PSC1 3 > (CH 3) 2PP(CH 3) 2 + 6MgICl + CH 3CH 3 SS [0] + 2(CH 3) 2P0 2H + by-products [4.2] Tetramethyldiphosphine d i s u l f i d e was prepared following a scaled down version of Parshall's method (299). The Grignard reaction between 40.1251 g (1.65 mol) of magnesium i n 200 mL of dry ether and 93.45 mL (1.50 mol) of methyl iodide i n 100 mL of dry ether was i n i t i a t e d by the addition of a few grains of iodine. The methyl iodide was added over three hours at such a rate as to maintain a gentle r e f l u x and when addition was complete, the mixture was refluxed a further half-hour. The r e s u l t i n g clear grey so l u t i o n was cooled i n an ice bath and f r e s h l y d i s t i l l e d thiophosphoryl chloride (52.10 mL, 0.51 mol) i n 50 mL dry ether was added slowly. A vigorous reaction occurred r e s u l t i n g i n the formation of a thick white p r e c i p i t a t e . After the addition was comple-te, the reaction mixture was cooled and poured over 350 g of ice causing an exothermic reaction, a f t e r which 600 mL of 10% s u l f u r i c acid was added and the mixture was s t i r r e d overnight. The white p r e c i p i t a t e formed was f i l t e r e d o f f and r e c r y s t a l l i z e d from 5 to 1 (by volume) - 191 -benzene-ethanol, y i e l d i n g 30.7645 g (30%) of tetramethyldiphosphine d i s u l f i d e (m.p. 226-227.S^ 1). I s o l a t i o n of the d i s u l f i d e ; although i n a lower y i e l d than expected (30% versus l i t . 67-74%), proved to be the simplest aspect of the synthesis of dimethylphosphinic acid; poor y i e l d s , incomplete oxida-t i o n and impure products were obtained i n many of the attempted oxida-tions of the d i s u l f i d e . Oxidation with hydrogen peroxide, according to SS Nil ( C H 3) 2PP(CH 3) 2 + 3H 20 2 • 2(CH 3) 2P0 2H + 2S + 2H20 [4.3] was adapted ( i . e . scaled down) from the procedure outlined by Reinhardt et a l . (300). A t o t a l of 18.6 mL of 30% aqueous hydrogen peroxide was added dropwise to a r e f l u x i n g , s t i r r i n g suspension of 2.4633 g (13.23 mmol) of tetramethyldiphosphine d i s u l f i d e i n 75 mL of carbon t e t r a -c h l o r i d e . A yellow p r e c i p i t a t e formed a f t e r the addition of the i n i t i a l portions of the peroxide, and when addition was complete, the mixture was refluxed for an a d d i t i o n a l hour, then cooled and f i l t e r e d to remove the p r e c i p i t a t e d s u l f u r . The aqueous layer was separated from the f i l t r a t e and evaporated. During evaporation a white waxy f i l m formed on the surface of the aqueous solu t i o n . This s o l i d was removed by f i l t r a -t i o n and i t s i n f r a r e d spectrum (134) indicated that i t was unreacted 1 l i t . : 227°C(299). - 192 -d i s u l f i d e . Complete evaporation of the r e s u l t i n g f i l t r a t e produced a mixture of white and blue c r y s t a l l i n e s o l i d s . R e c r y s t a l l i z a t i o n from hot benzene f a i l e d to remove th i s blue material; however, a separation was effected by adding benzene to the dried mixture and heating on a hot plate. The blue-tinged c r y s t a l s melted forming a blue l i q u i d , immiscible with the hot benzene which was then pipetted into a separate . f l a s k . Evaporation of the benzene and a subsequent r e c r y s t a l l i z a t i o n from benzene yielded 0.50 g (20%) pure dimethylphosphinic a c i d , m.p. 86-88.5°C 1. Anal, calcd. for C 2H 7P0 2: C 25.54, H 7.50; found: C 25.20, H 7.30. S l i g h t l y better y i e l d s were obtained from the hydrolysis of dimethyltrichlorophosphorane, Me 2PCl 3, formed by the oxidation of the diphosphine with chlorine according t o 2 SS (CH3)2PP'(CH3)2 + 5C1 2 • 2(CH 3) 2PC1 3 + 2SC1 2 [4.4] Tetramethyldiphosphine d i s u l f i d e (2.1958 g, 11.79 mmol) and 150 mL of carbon te t r a c h l o r i d e were placed i n a 250.0 mL three-necked, round-bottomed f l a s k equipped with a r e f l u x condenser, a gas i n l e t tube and a drying tube. As the suspension was s t i r r e d , chlorine gas was bubbled through the carbon t e t r a c h l o r i d e u n t i l no more s t a r t i n g material was v i s i b l e on the surface of the sol u t i o n , then for a further half-hour to ensure complete c h l o r i n a t i o n . As the reaction proceeded the s o l u t i o n gradually became yellow and a flocculent white p r e c i p i t a t e formed; t h i s 1 l i t . : 87.5-88.5°C (298); 85-87°C (301). 2 This method was suggested to us by Dr. K. Gallicano, formerly of t h i s Department. See also reference (302). - 193 -s o l i d was i s o l a t e d by f i l t r a t i o n i n a i r and immediately dissolved i n wet a c e t o n i t r i l e causing a vigorous, exothermic reaction. Evaporation of t h i s s o l u t i o n produced 0.5417 g (24%) of the desired a c i d . P a r t i a l evaporation of the f i l t r a t e yielded more white s o l i d which, when hydro-lyzed and evaporated to dryness, resulted i n blue c r y s t a l s l i k e those formed i n the oxidation with hydrogen peroxide. These were discarded. A second attempt to oxidize (CH 3)^P 2S 2 with chlorine, following the same procedure, resulted i n the formation of a. viscous orange o i l which, when taken up i n acetone and allowed to evaporate slowly, gave (CH 3) 2P0 2H i n approximately 35% y i e l d . The quest for better y i e l d s led to an attempt at o x i d i z i n g the d i s u l f i d e with mercuric oxide (303): SS l l l l (CH 3) 2PP(CH 3) 2 + 3Hg0 + H 20 • 2(CH 3) 2P0 2H + 2HgS + Hg [4.5] A mixture of 5.1007 g (27.39 mmol) of ( C H ^ P ^ , 17.8049 g (82.21 mmol) of HgO, 200 mL of benzene and a few mL of water was refluxed for an hour, r e s u l t i n g i n a clear s o l u t i o n and a dark black p r e c i p i t a t e which was subsequently removed by f i l t r a t i o n and washed well with benzene. An i n f r a r e d spectrum of the residue remaining following evaporation of the benzene showed a P-H stre t c h at 2310 cm - 1 (304), due to the presence of (CH 3) 2P(0)H, i n d i c a t i n g incomplete oxidation. The s o l i d was redissolved i n benzene, an a d d i t i o n a l 4.0 g of HgO and 5 mL of water were added and the mixture was refluxed for a further f o r t y - f i v e minutes. A f t e r f i l t e r i n g and evaporating the benzene, the residue (a mixture of white and grey s o l i d s ) was taken up i n a minimum of benzene and f i l t e r e d to - 194 -remove the grey s o l i d . Evaporation of t h i s s o l u t i o n gave a white c r y s t a l l i n e material and a brown-yellow impurity which was separated by f i l t r a t i o n a f t e r d i s s o l v i n g the residue i n a c e t o n i t r i l e . Dimethyl-phosphinic acid (1.4215 g, 28%) was obtained, f i n a l l y , by sublimation (at 80°C under vacuum) from the yellow o i l remaining a f t e r the evapora-t i o n of the a c e t o n i t r i l e . (An u n i d e n t i f i e d hygroscopic white s o l i d sublimed under the same conditions as the acid but was e a s i l y removed by washing the sublimate with cold acetone.) A s a t i s f a c t o r y y i e l d of the acid was u l t i m a t e l y obtained by the oxidation of the d i s u l f i d e with sulphuryl c h l o r i d e . Maier (303) noted, in his discussion of the oxidation of asymmetric tetraalkyldiphosphine SS llll d i s u l f i d e s ( i . e . RR'PPRR') to dialkylthiophosphinic chlorides (RR'P(S)Cl), that an excess of S0 2C1 2 r e s u l t s i n the formation of the dialkylphosphinic chloride RR'P(0)C1 rather than the s u l f u r substituted compound, i n analogy to the oxidation with th i o n y l chloride (305,306). Hence the oxidation occurs according to SS llll (CH 3) 2PP(CH3) 2 + x s S 0 2 C l 2 • 2(CH 3) 2P(0)C1 + S + S0 2 + S 2 C 1 2 [4.6] and hydrolysis of the phosphinic chloride gives the a c i d . Sulphuryl chloride (40.0 mL, 0.49 mol) was added dropwise to a cooled, (0°C) s t i r r i n g benzene sol u t i o n of (CH 3)^P 2S 2 (18.5286 g, 99.50 mmol). (A large excess of S0 2C1 2 was used to ensure complete oxidation.) The s o l u t i o n immediately became a cloudy yellow. After addition was complete the mixture was refluxed for f o r t y - f i v e minutes, cooled, and - 195 -the solvent, any remaining sulphury1 chloride and v o l a t i l e reaction by-products were removed by pumping under vacuum. Crude (CH 3) 2P(0)C1 was i s o l a t e d from the dried reaction mixture by vacuum sublimation and was dissolved, with f i z z i n g and heat evolution, i n water. This s o l u t i o n was f i l t e r e d and hydrochloric a c i d , produced by the hy d r o l y s i s , was neutralized with aqueous sodium hydroxide. The residue from the evapo-ra t i o n of the aqueous sol u t i o n was taken up i n dry a c e t o n i t r i l e and f i l t e r e d to remove sodium c h l o r i d e . The desired dimethylphosphinic acid was obtained i n 89% y i e l d (16.6226 g) by evaporation of the a c e t o n i t r i l e s o l u t i o n , mp. 86-89°. Anal, calcd. for C 2H 7P0 2: C 25.54, H 7.50; found: C 25.50, H 7.63. 4.2.4 Diethylphosphinic Acid, (C 2H 5) 2P0 2H. 6CH3CH2MgBr + 2PSC1 3 (CH 3CH 2) 20 SS l l l l (CH 3CH 2) 2PP(CH 2CH 3) 2 + 6MgBrCl CH2CH2CH2CH2 [4.7] SS l l l l (CH 3CH 2) 2PP(CH 2CH 3) 2 + 3H 20 2 H 20 •»• 2(CH 3CH 2) 2P0 2H + 2S + 2H20 [4.8] H 20 + (CH 3CH 2) 2P0 2Ag [4.9] (CH 3CH 2) 2P0 2H + xsAg 20 The Grignard reaction between ethyl bromide (75 mL, 1.01 mol i n 75 mL dry ether) and magnesium (26.7223 g, 1.10 mol i n 300 mL dry - 196 -ether) was I n i t i a t e d with a few grains of iodine and the ethyl bromide was added such that a gentle r e f l u x was maintained (301). Upon completion of addition, the mixture was refluxed for f o r t y - f i v e minutes and, a f t e r cooling (0°C), f r e s h l y d i s t i l l e d thiophosphoryl chloride (34.7 mL, 0.33 mol i n 35 mL of dry ether) was added over one hour, causing a vigorous reaction and the formation of a white s o l i d i n the grey sol u t i o n . The mixture was refluxed for two hours, then poured over 500 g of i c e . A vigorous reaction occurred causing a separation into two layers. A f t e r a c i d i f i c a t i o n with 100.0 mL of concentrated s u l f u r i c acid i n 500 mL of water, the ether layer was separated and the aqueous layer was washed with a t o t a l of 500 mL of ether. The residue from the evaporation of the combined ether layers was taken up i n water and treated with an excess of 30% hydrogen peroxide. The su l f u r formed was separated by f i l t r a t i o n and the f i l t r a t e was boiled to decompose the excess peroxide. An excess of f r e s h l y prepared s i l v e r oxide (307) was added r e s u l t i n g i n vigorous f i z z i n g . This mixture was f i l t e r e d and crude (CH3CH2) 2P0 2Ag was p r e c i p i t a t e d from the f i l t r a t e by the addition of acetone 1. This s a l t was dissolved i n a minimum amount of water, f i l t e r e d to remove tan- colored impurities and re p r e c i p i t a t e d with acetone to y i e l d 35.0 g (46%) s i l v e r diethylphosphinate. Anal, calcd. for AgCi tH 1 0PO 2: C 20.98, H 4.40; found: C 20.95, H 4.20. Kosolapoff and Watson used 95% ethanol (301). - 197 -4.2.5 Di-n-butylphosphinic Acid, (n-C^Hg) 2P0 2H. I n i t i a l attempts to prepare di-n-butylphosphinic acid v i a the d i s u l f i d e route (134), i n analogy to the methyl and ethyl d e r i v a t i v e s , f a i l e d . Addition of thiophosphoryl chloride to the Grignard reagent n-butylmagnesium iodide did not appear to r e s u l t i n any reaction and the subsequent workup yielded no tetrabutyldiphosphine d i s u l f i d e . The synthesis was repeated, as i t was f e l t that perhaps the f i r s t Grignard reagent was no good; however, the re s u l t was the same. The desired acid was prepared by the reaction of diethylphosphite with n-butylmagnesium bromide (308) ( C 2 H 5 ) 2 0 n-C4HgMgBr + -| (C 2H 50) 2P0H • (n-C^Hg) 2P0H [4.10] N 2 [0] (n-C l tH 9) 2P0H • (n-CHEg) 2V02H [4.11] This reaction sequence was not immediately successful. Hydroly-s i s of the reaction mixture, followed by evaporation of the ether layer, f a i l e d to y i e l d the intermediate di-n-butylphosphine oxide, (n-C^Hg)^ POH, as an o i l y layer on the aqueous solution as decribed i n the l i t e r a -ture. Extraction of the aqueous layer with benzene and evaporation of the benzene gave, i n two separate syntheses, a viscous yellow o i l which could not be c r y s t a l l i z e d and which did not react with hydrogen pero-xide. I t was f e l t that perhaps the diethylphosphite s t a r t i n g material was impure or p a r t i a l l y decomposed and that t h i s was the source of the problem. Hence the synthesis was repeated using f r e s h l y d i s t i l l e d d i e -- 198 -thylphosphite, r e s u l t i n g i n a 21% y i e l d of di-n-butylphosphinic a c i d . N-butylbromide (196 mL, 1.83 mol i n 200 mL dry ether) was added to magnesium turnings (48.81 g, 2.01 mol i n 250 mL dry ether) over three and a half hours, at a rate such that a gentle r e f l u x was maintained, the reaction being i n i t i a t e d with a few c r y s t a l s of iodine. When the addition was complete, the reaction mixture was refluxed for another hour then cooled i n an i c e bath (0°C) while fres h l y d i s t i l l e d diethylphosphite (78.5 mL, 0.61 mol) was added dropwise with vigorous s t i r r i n g , over an hour. The reaction was vigorous and resulted i n the formation of clumps of white s o l i d . The mixture was refluxed for two hours a f t e r the phosphite had been added, then cooled and hydrolyzed by pouring over ice-water (1000 mL) that had been a c i d i f i e d with concentrated hydrochloric acid (40 mL). The mixture was l e f t standing overnight which resulted i n the evaporation of the ether. At t h i s stage, as expected (308), an o i l was v i s i b l e on top of the aqueous layer and this was extracted with three 200 mL portions of benzene. Evaporation of the benzene gave a l i g h t yellow o i l , ca. 100 mL, from which was taken a 5 mL portion to be oxidized to the acid with 30% hydrogen peroxide. This oxidation was delayed and extremely v i o l e n t and appeared to cause p a r t i a l decomposition as evidenced by the appearance of a dark, charred brown s o l i d . The oxidation was achieved under milder conditions with potassium permanganate. The o i l was suspended i n water ( a c i d i f i e d with a few mL cone. HC1) and aqueous potassium permanganate was added causing a gentle f i z z i n g . The addition was continued u n t i l no further reaction was observed and a f a i n t pink color persisted. The phosphinic acid was separated by extraction into benzene (300 mL) and - 199 -evaporation of the solvent yielded approximately 25 g of crude product. R e c r y s t a l l i z a t i o n from benzene, as outlined by Kosolapoff and Watson (308), gave a somewhat o i l y s o l i d , which was impure as evidenced by elemental a n a l y s i s . The s o l i d was dissolved i n benzene and re p r e c i p i t a t e d by the addition of acetone, followed by cooling i n an i c e bath. The product was separated by f i l t r a t i o n and washed with cold acetone. The r e s u l t i n g f i l t r a t e and washings were evaporated, taken up i n a minimum of benzene and further product was p r e c i p i t a t e d by the addition of acetone and c o o l i n g . After several cycles of f i l t r a t e evaporation, d i s s o l u t i o n i n benzene and p r e c i p i t a t i o n of the product with acetone, the evaporation of the benzene-acetone f i l t r a t e yielded ca. 15 mL clear yellow o i l from which no further phosphinic acid could be p r e c i p i t a t e d . From the i n f r a r e d spectrum, t h i s o i l appeared to be i d e n t i c a l to the o i l i s o l a t e d as the sole product of the f i r s t two attempts at t h i s synthesis and was discarded. Total y i e l d of d i - n -butylphosphinic acid; 22.7037 g (21% of theory), m.p. 68-69 0C. x Anal, c a l c d . for C 8H 1 9P0 2: C 53.92, H 10.75; found: C 53.97, H 10.66. 4.2.6 Di-n-octylphosphinic Acid, (n-C 8H 1 7) 2P0 2H. The di-n-hexyl-, - n - o c t y l - , -n-decyl- and -n-dodecylphosphinic acids were a l l prepared, usually along with the monosubstituted d e r i v a -t i v e s , by the peroxide catalyzed reaction between the appropriate 1-alkene and hypophosphorus acid (310), according to 1 L i t . : 71°C (308), 70.5°-71.0°C (309). - 200 -benzoyl peroxide 2 1-alkene + H 2P0 2H * a l k y l 2 P 0 2 H CH3CH2OH/H20 + alkyl(H)P0 2H [4.12] Di-n-octylphosphinic acid was prepared following the procedure of Peppard et a l . (311), deta i l e d here. Our experience showed that the steps outlined for the separation of the monosubstituted acid from the disubs t i t u t e d acid were not applicable to any syntheses other than that of the di-n-octylphosphinic acid.. The reasons for t h i s are unclear; however, i t should be noted that very l i t t l e , i f any, monooctylphos-phinic acid was formed (none could be i s o l a t e d ) , whereas for the hexyl, decyl and dodecyl d e r i v a t i v e s , the monosubstituted acid appeared to be the major product. 1-Octene (329.5 mL, 2.10 mol), 88.4 mL of 50% aqueous hypophos-phorous acid (0.95 mol H 2P0 2H), 14.523 g (59.95 mmol) of benzoyl pero-xide, 66 mL of water and 350 mL of ethanol were combined i n a round-bottomed f l a s k and refluxed for twenty-four hours. To the cooled, cloudy white so l u t i o n was added 500 mL of 1.0 M HC1 and 800 mL of benzene. The mixture was thoroughly agitated and the aqueous layer was discarded. The benzene layer was scrubbed with two 200 mL portions of 1.0 M HC1 and was then evaporated. The product was converted to i t s sodium s a l t by d i s s o l v i n g i n 600 mL of 2.0 M NaOH, and, a f t e r cooling, 800 mL of ether was added and the two phases were shaken i n a 2 L separatory funnel. The aqueous layer was separated and the ether layer was scrubbed with s i x 400 mL portions of 1.0 M NaOH. (The purpose of - 201 -t h i s step was to remove any (n-C 8H 1 7)(H)P0 2Na present by extraction into the aqueous base. However, r e a c i d i f i c a t i o n of the basic washings, and extraction with benzene, followed by evaporation of the benzene f a i l e d to y i e l d any monosubstituted acid, as mentioned e a r l i e r . ) Following r e a c i d i f i c a t i o n of the ether layer by contacting with 400 mL of 3.0 M HC1 and scrubbing with two 400 mL portions of 1.0M HC1, the ether was evaporated to give crude di-n-octylphosphinic a c i d , coated with a l i g h t yellow o i l . R e c r y s t a l l i z a t i o n from acetone gave 65.3 g (24% y i e l d ) of the pure acid, m.p. 82-83.5°C 1. Anal, calcd. for C 1 6 H 3 5 P 0 2 : C 66.17, H 12.15; found: C 66.34, H 12.09. 4.2.7 Di-n-hexylphosphinic Acid, (n-C 6H 1 3) 2P0 2H. 1-Hexene (125 mL, 1.00 mol), 45 mL of 50% aqueous hypophosphorus acid (0.48 mol H 2P0 2H), 5 mL of water, 155 mL of ethanol and 4.0 g (16.51 mmol) of benzoyl peroxide were combined i n a round-bottomed f l a s k and refluxed vigorously for two and a half hours. The mixture was cooled and a further 2.0 g (8.26 mmol) of peroxide was added. Aft e r r e f l u x i n g an add i t i o n a l two hours and cooling, the remaining 2.0 g of peroxide ( t o t a l 8.0 g, 33.03 mmol) was added. 2 The mixture was then refluxed overnight r e s u l t i n g i n a c l e a r , c o l o r l e s s s o l u t i o n , to which 500 mL of 1.0 M HC1 and 130 mL of benzene were added. Aft e r thorough 1 L i t . : 85°C (312). 2 The increase i n the mole r a t i o of peroxide to hypophosphorus acid and the addition of the peroxide i n portions was a vain attempt to decrease the amount of monosubstituted acid formed. - 202 -ag i t a t i o n , the aqueous phase was discarded and the organic layer was washed with two 120 mL portions of 1.0 M HC1. Evaporation of the benzene f r a c t i o n with an Infrared lamp produced a yellow o i l which was taken up i n 200 mL of acetone. 1 A white s o l i d p r e c i p i t a t e d from this s o l u t i o n a f t e r p a r t i a l evaporation and was separated by f i l t r a t i o n and washed sparingly with cold acetone, y i e l d i n g the desired di-n-hexyl-phosphinic a c i d . More acid was i s o l a t e d from the f i l t r a t e , a f t e r p a r t i a l evaporation, by cooling r a p i d l y i n l i q u i d nitrogen (which caused the acid to p r e c i p i t a t e ) , f i l t e r i n g and washing the s o l i d with cold acetone. This procedure was repeated several times to give a t o t a l y i e l d of 13.2381 g (12%) of the aci d , m.p. 74.5-76.5°C. 2 Anal, c a l c d . for C 1 2 H 3 7 P 0 2 : C 61.51, H 11.61; found: C 61.25, H 11.52. Evaporation of the f i l t r a t e , remaining a f t e r the i s o l a t i o n of the di-n-hexylphosphinic a c i d , yielded a yellow o i l (ca. 50 mL). The i n f r a -red spectrum of th i s o i l was very complicated and appeared to indicate the presence, i n the o i l , of a mixture of the monosubstituted phosphinic acid, reaction by-products such as benzoic a c i d , and/or unreacted benzoyl peroxide. Attempts to i s o l a t e the phosphinic acid (as the sodium s a l t ) from the other components of th i s mixture according to the 1 In an e a r l i e r attempt to make the di-n-hexylphosphinic a c i d , the conversion to the sodium s a l t , i n order to remove (n-C 6H 1 3)(H)P0 2Na, resulted i n a one phase inseparable s o l u t i o n . This was r e a c i d i f i e d and worked up as above. 2 l i t . : 78-79°C (313). - 203 -procedure outlined for the mono-n-decyl d e r i v a t i v e , Section 4.2.8, f a i l e d to y i e l d a pure product. The crude o i l was, however, used to prepare the copper(II) monohexylphosphinate compound, as described i n Section 4.3.6. 4.2.8. Dl-n-decylphosphinic Acid, ( n - C 1 Q H 2 1 ) 2 P 0 2 H . 1-Decene (94.1 mL, 0.50 mol), 22 mL of 50% aqueous hypophosphorus acid (0.24 mol H 2P0 2H), 32 mL of water, 170 mL of ethanol and a t o t a l of 6.7123 g (27.71 mmol) of benzoyl peroxide were refluxed for a t o t a l of twenty-six hours. As i n the n-hexyl case, the amount of peroxide, r e l a t i v e to H 2P0 2H, was increased and i t was added i n three portions of approximately one-third each, at three hour i n t e r v a l s , a f t e r the i n i t i a l t h i r d was added. When cooled the mixture separated into two layers with a white s o l i d i n the top (organic) layer. After s t i r r i n g with 500 mL of 1.0 M HC1, the solution was extracted with 300 mL of benzene, i n which the s o l i d dissolved. After scrubbing with two 125 mL portions of 1.0 M HC1, the benzene layer was i s o l a t e d , and with evaporation of the solvent, p r e c i p i t a t i o n of a white s o l i d occurred. When the benzene was completely evaporated, a mixture of s o l i d and o i l remained. The o i l was removed by washing with cold ethanol. The s o l i d was r e c r y s t a l l i z e d from benzene, y i e l d i n g 11.4 g (14%) of di-n-decylphosphinic a c i d , m.p. 85.6°C. 1 Anal, calcd. for C 2 0H l t 3PO 2: C 69.32, H 12.51; found: C 69.07, H 12.70. 1 l i t . : 87-88°C (88); 87.7-88.3°C (310). - 204 -The ethanol washings were evaporated to approximately 45 mL of yellow o i l , taken up i n 200 mL of petroleum ether (30°-60°) and scrubbed with three 100 mL portions of 1.0 M NaOH. The basic washings were concentrated to about 150 mL and (n-C 1 0H 2 1)(H)PO 2Na was pr e c i p i t a t e d by the addition of acetone, f i l t e r e d and washed with acetone. Y i e l d : 1.45 g. Anal, calcd. for NaC 1 0H 2 2PO 2: C 52.62, H 9.72; found: C 52.50, H 9.77. The combined f i l t r a t e and washings were evaporated to remove the acetone and, aft e r concentration of the r e s u l t i n g aqueous s o l u t i o n and p r e c i p i t a t i o n with acetone, a further 8.29 g of the sodium s a l t was i s o l a t e d . This s o l i d , however, was contaminated with 4.52% NaOH. Anal, calcd. for (NaC 1 0H 2 2PO 2). 9 5 t t 8(NaOH). Q 1 + 5 2 : C 50.24, H 9.39; found: C 50.24, H 9.22. The extraction of the monosubstituted acid into the aqueous sodium hydroxide was incomplete as evaporation of the petroleum ether f r a c t i o n gave a yellow o i l , the i n f r a r e d spectrum of which indicated the presence of (n-C 1 0H 2 1)(H)PO 2Na, as well as some (n-C 1 QH 2 1) 2P0 2Na. No attempt was made to separate this portion of the reaction mixture. 4.2.9 Di-n-dodecylphosphinic Acid, ( n - C 1 2 H 2 5 ) 2 P 0 2 H . This acid was prepared i n a manner analogous to the synthesis of the decyl d e r i v a t i v e . After r e f l u x i n g a mixture of 130 mL of 50% aqueous hypophosphorus acid (0.1398 mol H 2P0 2H), 62.5 mL of 1-dodecene (0.29 mol), a t o t a l of 3.912 g of benzoyl peroxide (16.15 mmol, added i n three portions of a t h i r d each), 10 mL of water and 45 mL of etha-- 205 -no l , for twenty-four hours, the two phase mixture was poured into 250.0 mL of 1.0 M HC1 and thoroughly s t i r r e d . A t o t a l of 300 mL of benzene was needed to dissolve a l l of the white s o l i d that was present i n the organic phase. This phase was i s o l a t e d , and the aqueous layer was ex-tracted with a further 150 mL of benzene. This was i s o l a t e d and added to the organic l a y e r . Evaporation of the combined benzene washings yielded a mixture of a white s o l i d and an o i l ; the l a t t e r was removed by washing with cold acetone. The crude acid was dissolved i n chloro-form and rep r e c i p i t a t e d by the addition of acetone to y i e l d 14.02 g (25%) of di-n-dodecylphosphinic a c i d , m.p. 93.5°C. 1 Anal, calcd. for C 2 t tH 5 1P0 2: C 71.59, H 12.77; found: C 71.54, H 12.75. The o i l , recovered by evaporation of the acetone f i l t r a t e , was treated with base and worked up i n a manner analogous to that described for the decyl d e r i v a t i v e (see preceeding section, 4.2.8). However, (n-C^ 2H 2 5)(H)P0 2Na could not be i s o l a t e d i n a pure form. 4.2.10 D i - i - propylphosphinic Acid, ( i - C 3 H 7 ) 2 P 0 2 H . ( C 2 H 5 ) 2 0 3i-C 3H 7MgCl + (n-C l tH 90) 2P0H • (i-C 3H 7) 2P0H [4.13] HC1 H 20 2 HC1 Ag 20 (i-C 3H 7) 2P0H • ( i - C 3 H 7 ) 2 P 0 2 N a • ( i - C 3 H 7 ) 2 P 0 2 H *• NaOH ( i - C 3 H 7 ) 2 P 0 2 A g [4.14] The Grignard reaction between 30.2443 g (1.24 mol) of magnesium l l i t . : 93.8-94.8°C (310). - 206 -turnings i n 300 mL of ether and 102.1 mL (1.12 mol) of isopropyl chloride i n 100 mL of ether was i n i t i a t e d with a few grains of iodine and isopropyl chloride was added so that a gentle r e f l u x was maintained (314). The mixture was refluxed a further t h i r t y minutes a f t e r addition was complete, then dibutylphosphite (73.0 mL, 0.37 mol, f r e s h l y d i s t i l -led i n 75 mL of ether) was added dropwise over three hours. The r e s u l t i n g milky brown solution was refluxed for two hours, then l e f t to stand overnight. The mixture was decomposed by pouring over 1000 g of ice a c i d i f i e d with 120.0 mL of concentrated hydrochloric a c i d , then evaporated to ca. 350 mL and extracted with benzene (350 mL) i n a c o n t i -nuous extraction apparatus for s i x t y hours. The benzene was d i s t i l l e d o ff the combined extracts and 50.0 mL of 30% hydrogen peroxide was added to the residue, causing heat evolution and the appearance of a yellow orange color i n the s o l u t i o n . Excess peroxide was decomposed by adding aqueous sodium hydroxide and b o i l i n g , a f t e r which excess HC1 and 100 mL p-xylene were added and the water was removed by azeotroping (Dean and Stark apparatus). S o l i d sodium chloride was removed by f i l t r a t i o n and washed with dry benzene; then the combined f i l t r a t e and washings were evaporated. The residue was taken up i n water, treated with charcoal (to d e c o l o r i z e ) , f i l t e r e d and evaporated to give a yellow o i l . When th i s o i l did not c r y s t a l l i z e with cooling, as i n Crofts and Kosolapoff's preparation (314), i t s i n f r a r e d spectrum was recorded and indicated the presence of unoxidized dl-isopropylphosphine oxide, ( i - C 3 H 7 ) 2 P ( 0 ) H , (vP-H at 2270 cm - 1, vP=0 at 1184 cm - 1 (304)). The treatment with hydrogen peroxide and sodium hydroxide was repeated. After r e a c i -d i f i c t i o n and cooling, a yellow o i l rose to the top of the aqueous s o l u -- 207 -t i o n and was pipetted o f f . Concentration of the aqueous solution produ-ced a d d i t i o n a l o i l which was also separated. The combined o i l s were pumped under vacuum to remove any r e s i d u a l water, taken up i n acetone and f i l t e r e d to remove traces of sodium ch l o r i d e . Evaporation of the acetone did not r e s u l t i n c r y s t a l l i z a t i o n of the a c i d , hence the o i l was dissolved i n a minimum amount of water and treated with an excess of f r e s h l y prepared s i l v e r oxide. A f t e r f i l t r a t i o n and concentration of the aqueous so l u t i o n , acetone was added, causing the p r e c i p i t a t i o n of a grey-white s o l i d . This was removed by f i l t r a t i o n and upon the addition of a large excess of acetone (ca. three times the volume of the aqueous solution) a pure white p r e c i p i t a t e formed. The product was i s o l a t e d by f i l t r a t i o n and washed well with acetone, y i e l d i n g 9.7643 g (10%) of s i l v e r di-isopropylphosphinate. Anal, calcd. for AgC 6H l l tP0 2: C 28.04, H 5.49; found: C 27.78, H 5.51. 4.2.11 Di-t-butylphosphinic Acid, (t-C^Hg) 2P0 2H. N 2 2t-C l +H 9MgCl + PC1 3 • ( t - C 4 H 9 ) 2 P C l [4.15] ( C 2 H 5 ) 2 0 NR\C1 H 20 2 (t-C^Hg^PCl — — > ( t - C ^ ^ P O H • ( t - C H H 9 ) 2 P 0 2 H [4.16] Di-t-butylchlorophosphine was prepared by the method described by F i l d et^ a l . (315). To the cooled (R.T.) Grignard reagent, formed from 18.2328 g (0.75 mol) of magnesium i n 635 mL of dry ether and 82 mL (0.75 mol) of t-butyl chloride i n 80 mL of ether, was added fresh l y - 2 0 8 -d i s t i l l e d phosphorous t r i c h l o r i d e (16.0 mL, 0.18 mol) i n 40 mL of ether. This resulted i n an exothermic reaction and the immediate formation of a thick white p r e c i p i t a t e . When addition was complete, the mixture was refluxed for two hours and, a f t e r cooling, the di-t-butylchlorophosphine was converted, i n s i t u , to di-t-butylphosphine oxide ((t-C^Hg) 2P0H) by the addition of 80 g (1.5 mol) of NH^Cl i n 450 mL of water (314). The ether layer was decanted off and f i l t e r e d into a round-bottomed f l a s k ; however, during t h i s process the solution i n the f i l t e r paper began to c r y s t a l l i z e . The c r y s t a l s i n the funnel, when the ether had evaporated, began rapidly to pick up water and would not redissolve i n ether. These were dissolved i n carbon t e t r a c h l o r i d e and kept separate from the f i l t e r e d ether layer, which was evaporated and treated with 25.0 mL of 30% hydrogen peroxide (314). The r e s u l t i n g milky solution was d i l u t e d with 200 mL of water and allowed to stand overnight. Aqueous sodium hydroxide (20 g i n 100 mL of water) was then added and the so l u t i o n was boiled to decompose the excess peroxide and to reduce the volume to ca. 150 mL. With cooling, a white p r e c i p i t a t e formed; t h i s was separated by f i l t r a t i o n and then dissolved i n a minimum amount of water (ca. 75 mL). The so l u t i o n was a c i d i f i e d with 1.0 M HC1 r e s u l t i n g i n the p r e c i p i t a t i o n of the desired di-t-butylphosphinic a c i d . The carbon t e t r a c h l o r i d e solution containing the hygroscopic c r y s t a l s was evaporated, y i e l d i n g a yellow o i l which was treated with peroxide and sodium hydroxide, as above. The o i l lay on top of the aqueous layer and s o l i d i f i e d with cooling. The s o l i d was i s o l a t e d by f i l t r a t i o n and an i n f r a r e d spectrum was recorded. The spectrum was - 209 -i d e n t i c a l to that of the o i l before the peroxide treatment, i n d i c a t i n g that no reaction had occurred. The i n f r a r e d spectrum indicated, when compared to the spectra of other compounds containing the P-t-C^Hg moiety (285), that the s o l i d i s o l a t e d was di-t-butylphosphinous chl o r i d e , (t-C^Hg) 2P(0)C1. This had been formed from the di-t-butylphosphine oxide according to (t-C l tH 9) 2P(0)H + CCl^ • ( t - C k H 9 ) 2 P ( 0 ) C l + CHCI3 [4.17] This exchange reaction has been observed previously for d i a r y l -phosphine oxides (316), which are then e a s i l y hydrolyzed, i n the presence of moisture, to the corresponding a c i d s . Straight chain a l k y l phosphinic halides are also r e a d i l y hydrolyzed (303,304,312,317). D i - t -butylphosphinic ch l o r i d e , however, was extremely r e s i s t a n t to hydrolysis and even prolonged (43 hours) r e f l u x i n g i n aqueous sodium hydroxide (100 mL of 1.0 M NaOH), followed by a c i d i f i c a t i o n (285), resulted i n incomplete h y d r o l y s i s . A mixture of the desired acid and the phosphinic chloride was i s o l a t e d from the a c i d i c s o l u t i o n by f i l t r a t i o n , and the chloride was separated by sublimation. The residue was dissolved i n acetone and f i l t e r e d to remove a grey-white insoluble s o l i d . Evapora-t i o n of the acetone yielded the desired di-t-butylphosphinic a c i d . The a c i d i c f i l t r a t e was concentrated, r e s u l t i n g i n the p r e c i p i t a t i o n of a gelatinous grey-white s o l i d (apparently a product of the decomposition of the chloride and/or the a c i d ) , which was removed by f i l t r a t i o n and - 210 -washed with chloroform. Evaporation of the chloroform gave a further 0.2333 g of acid; t o t a l y i e l d 4.4175 g (14%), m.p. 208.5°C. 1 Anal, calcd. for C 8H 1 9P0 2: C 53.92, H 10.75; found: C 53.90, H 11.04. 4.3 Synthesis of Copper(II) Phosphinate Polymers. 4.3.1 Introduction. There are many methods of metal phosphinate syntheses described in the l i t e r a t u r e , including some novel and exotic preparations. Block et a l . (42) used a Waring blender to make z i n c ( I I ) diphenylphosphinate through the i n t e r f a c i a l polymerization of an aqueous sol u t i o n of z i n c ( I I ) acetate with a benzene sol u t i o n of the phosphinic acid. Mikulski et a l . (18,86,87) prepared a l k a l i , d i - , t r i - , and tetravalent metal methylphenylphosphinates, i n near quantitative y i e l d s , through the high temperature reaction of the appropriate metal halide with an excess of methyl methylphenylphosphonate: MXn + n(CH 3)(C 6H 5)P(0)(0CH 3) — • M [ ( C H 3 ) ( C 6 H 5 ) P 0 2 ] n + nCH3X [4.18] However, the more conventional syntheses generally involve the reaction between a metal s a l t and either the acid or the s a l t of the a c i d , i n an appropriate solvent, e.g., 1 l i t . : 210-212°C (314). - 211 -M(II)SCvxHoO + 2R 2P0 2K »• M(R 2P0 2) 2 + K 2SO t t [4.19] Previously prepared copper(II) complexes (66,67,88) were made according to t h i s equation, and one aim of our synthetic work was to investigate the a p p l i c a b i l i t y of t h i s reaction to a range of copper phosphinate polymers, with the intent of developing one convenient route to a l l copper compounds, and by extension, to other metal phosphi-nates. This proved to be impossible, as many of the compounds prepared had d i f f e r e n t problems associated with t h e i r i s o l a t i o n , from d i f f i c u l -t i e s i n separating soluble polymers from the reaction solvent, to the persistent presence of impurities i n products, and the occurrence of copolymerization with the s u l f a t e and other anions of the copper(II) s t a r t i n g materials. On the other hand, some compounds were s u r p r i s i n g l y f a c i l e to i s o l a t e a n a l y t i c a l l y pure and i t was found that for phosphinic acids of a s i m i l a r nature, for example, di-n-hexyl-, d i - n - o c t y l - , d i - n -d e c y l - and di-n-dodecylphosphinic acids, the preparation of the copper compounds followed very s i m i l a r procedures. The y i e l d s i n these synthetic reactions varied from nearly quantitative to less than 50% of theory and, where appropriate, comments on t h i s are included with the i n d i v i d u a l syntheses. 4.3.2 M a t e r i a l s . Copper containing s t a r t i n g materials used i n these preparations were commercially available reagent grade and were used without further p u r i f i c a t i o n . The exception was copper(II) benzoate which was prepared - 212 -from copper s u l f a t e pentahydrate and sodium benzoate. Copper s u l f a t e pentahydrate and copper n i t r a t e trihydrate were supplied by Fisher S c i e n t i f i c Co.; copper chloride dihydrate was supplied by BDH Laboratory Reagents. Phosphinic acids or s a l t s used were synthesized as described i n Section 4.2, except the diphenyl- and monophenylphosphinic acids, which were obtained from A l d r i c h Chemical Co., i n 99% and 97% purity, r e s p e c t i v e l y . A l l other reagents and solvents were as described i n Section 4.2.2. 4.3.3 Copper(II) Dimethylphosphinate, C u [ ( C H 3 ) 2 P 0 2 ] 2 . The synthesis of C u [ ( C H 3 ) 2 P 0 2 ] 2 was i n i t i a l l y attempted following the general procedure outlined by Glllman and Eichelberger (67), i . e . H 20 CuSO^'SR^O + 2(CH 3) 2P0 2K • Cu[(CH 3) 2P0 2] 2 + K^O^ [4.20] This preparative method presented several problems. Complete n e u t r a l i z a t i o n of the phosphinic acid resulted i n the i s o l a t i o n of a copper compound which contained hydroxyl groups, as evidenced by bands i n the 3500 cm - 1 region of the in f r a r e d spectrum (103). The in f r a r e d spectrum also indicated that t h i s compound contained no phosphinate lig a n d . The synthesis was repeated with the pH of the aqueous acid s o l u t i o n adjusted to approx. 5.0 with aqueous KOH. The addition of the copper s u l f a t e s o l u t i o n to the p a r t i a l l y neutralized acid s o l u t i o n did not r e s u l t i n any observable r e a c t i o n . The reaction mixture was evapo-rated by b o i l i n g , y i e l d i n g a mixture of blue and white c r y s t a l s which - 213 -in f r a r e d spectroscopy showed to be unreacted copper s u l f a t e , dimethyl-phosphinic acid and potassium dimethylphosphinate. I t was f e l t that a change i n the counter-anion of the copper(II) s t a r t i n g material from sul f a t e to the less strongly coordinating n i t r a t e , would promote the formation of the desired compound. However, the reaction between aqueous solutions of copper(II) n i t r a t e trihydrate and of p a r t i a l l y neutralized dimethylphosphinic acid (pH 5.3) again yielded, a f t e r evapo-r a t i o n , a mixture of the unreacted s t a r t i n g materials. As i t appeared that the s o l u b i l i t y of copper dimethylphosphinate i n water was contributing to the d i f f i c u l t i e s encountered i n these aqueous reactions, a nonaqueous synthesis was attempted, according to the reaction: Cu(C 6H 5COO) 2 + 2(CH 3)2P0 2H a c e t o n e , C u [ ( C H 3 ) 2 P 0 2 ] 2 + benzoic acid [4.21] Dimethylphosphinic acid (1.0245 g, 10.89 mmol) i n 100 mL of acetone was added to a solution of copper(II) benzoate (1.7553 g, 5.74 mmol) i n acetone (100 mL), causing the immediate p r e c i p i t a t i o n of a l i g h t blue s o l i d . The mixture was s t i r r e d for approximately half an hour, then the s o l i d was separated by f i l t r a t i o n and washed with 200 mL of warm acetone. After drying under vacuum at 55°C for twenty-four hours, the elemental analysis of th i s product indicated the presence of a small amount of impurity, which could have been copper benzoate (ca. 3%), benzoic acid (ca. 2%), or dimethylphosphinic acid (ca. 6%), any of which would have resulted i n the high percentages of carbon and hydrogen - 214 -observed. In an e f f o r t to remove and i d e n t i f y the impurity, a sample of the compound was placed i n a vacuum sublimation apparatus and heated overnight at 125°C, r e s u l t i n g i n d i s c o l o r a t i o n , and probable p a r t i a l decomposition, of the s o l i d . The sublimation was repeated with a fresh sample at a lower temperature (85°C); however, while there was no v i s i b l e decomposition, neither was there any sublimate on the cold finger, and the i n f r a r e d spectrum was i d e n t i c a l to the spectrum of the bulk sample. We next t r i e d to dissolve and substitute the impurity with the desired l i g a n d . The s o l i d was refluxed overnight i n acetone (100 mL) which contained dimethylphosphinic acid, separated by f i l t r a t i o n , washed repeatedly with hot acetone, then dried under vacuum at 53°C for 12 hours. -The i n f r a r e d spectrum of this s o l i d showed no changes and the elemental analysis was again high i n carbon and hydrogen, i n d i c a t i n g that the impurity had not been removed. The synthesis was then repeated a number of times varying d i f f e -rent reaction conditions. A 70% excess of phosphinic acid and r e f l u x i n g overnight resulted i n d i s c o l o r a t i o n of the i n i t i a l p r e c i p i t a t e from bright blue to d u l l blue-green. Less vigorous overnight r e f l u x i n g with a 50% excess of the acid eliminated the d i s c o l o r a t i o n ; however, the s o l i d s i s o l a t e d i n each preparation had i d e n t i c a l Infrared spectra and nearly i d e n t i c a l elemental analyses, again both high i n carbon and hydrogen percentages. Feeling that the prolonged r e f l u x i n g may have been promoting hydrolysis, the synthesis was repeated with a 70% excess of the acid but with only 15 minutes of r e f l u x i n g . This gave the same r e s u l t as the previous synthesis i n acetone; however, the in f r a r e d - 215 -spectrum of a very concentrated Nujol mull of the product revealed two very weak peaks at 1600 and 1563 cm - 1, leading to the b e l i e f that the impurity was copper benzoate (a copolymerisation reaction) and/or i t s basic s a l t and not benzoic or phosphinic acid (as these would be expected to be removed with the repeated acetone washings). Hence, the synthetic route which f i n a l l y resulted i n the i s o l a t i o n of pure copper(II) dimethylphosphinate eliminated these two p o s s i b i l i t i e s . The very slow, dropwise addition of the copper benzoate so l u t i o n to the acid ( i n 50% excess) s o l u t i o n , kept the phosphinic acid i n large excess and hence prevented copolymerization. In addition, the reaction was c a r r i e d out under anhydrous conditions, to prevent formation of the basic s a l t . I t should be noted, however, that the y i e l d i n th i s reaction was low (ca. 50% of theory), due to the s o l u b i l i t y of the compound i n acetone and to the fact that not a l l the copper(II) benzoate so l u t i o n was added to the reaction mixture as a p r e c i p i t a t e , presumably the basic s a l t , began to form a f t e r approximately three-quarters of the solu t i o n had been added. Hence, dimethylphosphinic acid (4.6771 g, 49.73 mmol), dissolved i n acetone (150 mL, dried by r e f l u x i n g over K 2C0 3), was f i l t e r e d into a three-necked round-bottomed f l a s k equipped with a magnetic s t i r r e r . Copper(II) benzoate (5.1063 g, 16.70 mmol) was weighed into a nitrogen purged stoppered b o t t l e , dissolved i n dry acetone (120 mL) and then f i l t e r e d into an addition funnel through which a stream of nitrogen passed. In a s t a t i c nitrogen atmosphere the copper solution was added dropwise, over a period of three hours, to the s t i r r i n g acid s o l u t i o n . A f l o c c u l e n t l i g h t blue p r e c i p i t a t e appeared a f t e r the addition of the - 216 -f i r s t ten mL of the copper s o l u t i o n . After the addition was complete, the s o l i d was separated by f i l t r a t i o n and washed repeatedly with a t o t a l of 500 mL of dry acetone. The product was then dried i n vacuo at 25°C for four hours. Y i e l d : 2.0589 g, 50% of theory. Anal, c a l c d . for CuC l tH 1 2P 20 l t: Cu 25.45, C. 19.25, H 4.85; found: Cu 25.59, C 19.15, H 4.85. 4.3.4 Copper(II) Diethylphosphinate, C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 . The synthesis of t h i s compound involved the reaction between the s i l v e r s a l t of the acid and cupric chloride dihydrate, In aqueous sol u t i o n , according to CuCl 2«2H 20 + xs(C 2H 5) 2P0 2Ag »• Cu[(C 2H 5) 2P0 2] 2 + AgCl [4.22] As i n the case of the methyl d e r i v a t i v e , (Section 4.2.3) the water s o l u b i l i t y of copper diethylphosphinate resulted i n d i f f i c u l t y i n i s o l a t i n g the product i n a pure form. The conditions required to evaporate the solvent (heating to 85°C under vacuum) and force p r e c i p i t a t i o n of the product appeared to promote the formation of a compound containing both copper phosphinate and copper oxide moieties, i . e . , C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 _ x ( 0 ) x , where, for several d i f f e r e n t preparations, x was found to range from .14 to .55, on the basis of elemental a n a l y s i s . (The presence of Cu-OH moieties was ruled out since the impurity was found even when 100% excesses of the ligand were employed, the excess s i l v e r being removed by p r e c i p i t a t i o n with d i l u t e hydro-- 217 -c h l o r i c acid, r e s u l t i n g i n an a c i d i c reaction media.) The impurity was found to be insoluble i n methanol, hence r e c r y s t a l l i z a t i o n from methanol proved to be the successful route to t h i s compound. S i l v e r diethylphosphinate (16.2371 g, 71.07 mmol, a 30% excess) i n water (250 mL) was added slowly to an aqueous sol u t i o n (100 mL) of cupric chloride dihydrate (4.6066 g, 27.02 mmol), r e s u l t i n g i n the immediate p r e c i p i t a t i o n of s i l v e r c h l o r i d e . This was removed by f i l t r a -t i o n and approximately 0.5 M hydrochloric acid was added u n t i l no further s i l v e r chloride p r e c i p i t a t e d . The f i l t e r e d s o l u t i o n (450 mL) was concentrated under vacuum at 85°C to 150 mL, then aliquots were tested with s i l v e r diethylphosphinate or hydrochloric a c i d , for excesses of chloride ion or s i l v e r ion, r e s p e c t i v e l y . When none were found the sol u t i o n was evaporated to dryness, y i e l d i n g a gummy blue s o l i d . The excess phosphinic acid, an o i l at room temperature, was removed by washing the s o l i d thoroughly with acetone. (This' process also dissolved some of the copper s a l t and evaporation i n a i r of the acetone washings yielded a deep blue o i l In which blue c r y s t a l s developed, over approxi-mately a week. These c r y s t a l s , one of which was chosen for an X-ray cr y s t a l l o g r a p h i c study (see Section 2.1.2 for s t r u c t u r e ) , were separated from the o i l by washing with cold acetone ( y i e l d : 0.15 g).) The crude copper(II) diethylphosphinate was dissolved i n methanol (250 mL) and f i l t e r e d to remove 1.3285 g of insoluble blue m a t e r i a l . The f i l t r a t e was evaporated to dryness under vacuum, y i e l d i n g 3.1753 g ( t o t a l y i e l d : 40% of theory) of pure C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 , a l i g h t blue powder. Anal, c a l c d . for CuC 8H 2 0P0 2: Cu 20.78, C 31.43, H 6.59; found: Cu 20.92, C 31.19, H 6.61. - 218 -4.3.5 Copper(II) Di-n-butylphosphinate, Cu^n-C^Hg) 2P0 2] 2 . The previously prepared (67,88) copper di-n-butylphosphinate was synthesized by e s s e n t i a l l y the same method as used by H.D. Gillman and J.L. Eichelberger (67) ( c f . equation [4.20]), except that the di-n-butylphosphinic acid was neutralized with s l i g h t l y less than the stoichiometric amount of base and that sodium hydroxide was used for thi s n e u t r a l i z a t i o n rather than potassium carbonate. (This less than 100% n e u t r a l i z a t i o n of the phosphinic acid was employed rou t i n e l y to avoid problems with copper hydroxide formation. See, for example, section 4.3.6.) The preparative reaction, then, i s CuSCVSR^O + 2(n - C i tH 9) 2P0 2H N a 0 H > Cu[(n-C^Hg) 2P0 2] 2 + Na 2SC\ [4.23] Di-n-butylphosphinic acid (2.8441 g, 15.96 mmol, i n 200 mL water) was neutralized with aqueous sodium hydroxide (0.6370 g, 15.93 mmol i n 50 mL water); the so l u t i o n was then f i l t e r e d and cupric s u l f a t e pentahydrate (1.9927 g, 7.98 mmol i n 40 mL water) was added dropwise with s t i r r i n g . The reaction mixture clouds only a f t e r the addition of ca. half of the copper(II) s o l u t i o n . When a l l the copper(II) solution had been added, the resultant mixture was s t i r r e d for an hour and a h a l f , then the s o l i d was separated by f i l t r a t i o n , washed with cold water (ethanol washing caused a blue to green color change) and a i r dried overnight. This s o l i d represented a y i e l d of only 36% of pure Cu[(n-C 1 +H 9) 2P0 2] 2; - 219 -however, evaporation of the f i l t r a t e , under vacuum, to 150 mL (from ca. 400 mL) caused the p r e c i p i t a t i o n of a bright blue c r y s t a l l i n e s o l i d which was i s o l a t e d by f i l t r a t i o n and washed with water, then acetone, y i e l d i n g 0.7727 g of the desired product. A i r evaporation of the f i l t r a t e from t h i s process gave, over approximately four days, large rectangular blue c r y s t a l s , 1.0391 g a f t e r f i l t r a t i o n and drying, r e s u l t i n g i n a t o t a l y i e l d of 3.0259 g, or 91% of theory. Anal, c a l c d . for CuC 1 6H 3 6P 20 £ t: Cu 15.20, C 45.98, H 8.68; found Cu 15.23, C 45.80, H 8.60. 4.3.6 Copper(II) Di-n-hexylphosphinate, C u [ ( n - C f i H 1 3 ) 2 P 0 2 ] 2 . I n i t i a l attempts to prepare t h i s compound involved the reaction between copper(II) benzoate and di-n-hexylphosphinic a c i d , with acetone as the solvent due to the i n s o l u b i l i t y of the acid i n water. However, even when very d i l u t e solutions of the reagents and dropwise addition of the copper to the acid (to keep the acid In excess) were employed, the compound i s o l a t e d was, on the basis of i t s i n f r a r e d spectrum, a benzoate-phosphinate copolymer. The next approach was to use ethanol (95%) solutions of copper(II) perchlorate hexahydrate and of p a r t i a l l y n eutralized (pH ca. 6) phosphinic a c i d . The presence of such a concen-t r a t i o n of ethanol seemed to promote the formation of a blue-green s o l i d , from which a small amount of pure product could be i s o l a t e d by extraction into chloroform, i n which the green impurity was i n s o l u b l e . This problem was overcome by using an aqueous sol u t i o n of copper su l f a t e and an ethanol:water (75:25) s o l u t i o n of the a c i d , followed by the - 220 -addition to the reaction mixture of large volumes of water. This e l i m i -nated the e f f e c t of the ethanol on the product and stopped the formation of the sul f a t e copolymer which occurred i n more concentrated s o l u t i o n s . Di-n-hexylphosphinic acid (1.3371 g, 5.71 mmol) was dissolved i n aqueous ethanol (300 mL ethanol: 100 mL water) and neutralized with a s l i g h t l y l e s s than stoichiometric amount of sodium hydroxide (0.2255 g, 5.64 mmol i n 60 mL water). Copper(II) su l f a t e pentahydrate (0.7122 g, 2.85 mmol i n 75 mL water) was added dropwise with s t i r r i n g ; p r e c i p i t a -t i o n of a blue s o l i d began a f t e r the addition of ca. 5 drops. When the addition was complete, the volume of the reaction mixture was made up to 1000 mL with water and the so l u t i o n was s t i r r e d overnight. The s o l i d was removed by f i l t r a t i o n , washed with water and a i r dried, y i e l d i n g 1.1623 g. (77% of theory) of pure copper(II) di-n-hexylphosphinate. Anal, calcd. for CuC 2 4H 5 2P 20 l t: Cu 11.98, C 54.37, H 9.89; found: Cu 12.04, C 54.25, H 9.88. Crystals suitable for X-ray c r y s t a l l o g r a p h i c studies were obtained by the slow evaporation (over about three weeks) of a so l u t i o n of the product i n 60°-90° petroleum ether. (See Section 2.1.2 for structure.) 4.3.7 g-Forms of the n - o c t y l , n-decyl and n-dodecyl De r i v a t i v e s. As discussed i n Chapter 2, the eight-, ten- and twelve-carbon chain derivatives e x i s t i n two forms; the a-forms, i s o l a t e d from the preparative reaction mixture, and the 8-forms, obtained from the melt of the a-forms. This section describes the syntheses of the a-forms. - 221 -4.3.7.1 a-Copper(II) Di-n-octylphosphinate, <x-Cu[(n-C 8H 1 7) 2P0 2] 2* Copper dl-n-octylphosphinate was prepared In a manner analogous to that used by Gillman (66), except, as was the case with the butyl d e r i v a t i v e (Section 4.3.5), sodium hydroxide was employed for the p a r t i a l n e u t r a l i z a t i o n of the phosphinic a c i d . "Excess" water was added to the reaction mixture to prevent formation of the s u l f a t e copolymer, as was done with the hexyl d e r i v a t i v e (Section 4.3.6). A solution of di-n-octylphosphinic acid (6.2603 g, 21.56 mmol) in methanol 1 (500 mL) was taken to pH 6.0 with aqueous sodium hydroxide, then added dropwise to a s t i r r i n g s o l u t i o n of cupric s u l f a t e pentahy-drate (2.6615 g, 10.66 mmol) dissolved i n 60% methanol (185 mL). A bright blue s o l i d began to p r e c i p i t a t e immediately. After the addi-ti o n was complete, water (400 mL) was added and the so l u t i o n was s t i r r e d for two hours. The s o l i d was removed by f i l t r a t i o n , washed with metha-nol, water and, f i n a l l y , methanol and a i r dr i e d , y i e l d i n g 6.7202 g (98% of theory) of copper(II) di-n-octylphosphinate. Anal, calcd. for CuC 3 2-H68p2°i+: C u 9 ' 8 9 » c 59.83, H 10.67; found: Cu 9.87, C 60.04, H 10.73. 4.3.7.2 a-Copper(II) Di-n-decylphosphinate, oc-Cu[(n-C 1 0H 2 1) 2P0 2] 2 . Copper di-n-decylphosphinate, previously prepared by Drinkard and Kosolapoff (88), was synthesized by e s s e n t i a l l y the same method as was the n-hexyl d e r i v a t i v e . In this case, however, the addition of excess water to the reaction mixture was not s u f f i c i e n t to prevent the Gillman (66) used 50% methanol; however, we found that the water insoluble acid would not dissolve i n this mixture. - 222 -formation of the sul f a t e copolymer; hence, water was added to the acid s o l u t i o n before the addition of the copper su l f a t e s o l u t i o n was begun, as described below. Di-n-decylphosphinic acid (3.0211 g, 8.72 mmol), dissolved i n ethanol (500 mL), was p a r t i a l l y neutralized with aqueous sodium hydroxide (0.3374 g, 8.44 mmol i n 90 mL water). This s o l u t i o n was f i l t e r e d , and water was added u n t i l the so l u t i o n just clouded ( t h i s clouding was, presumably, water insoluble di-n-decylphosphinic a c i d , which was d i s p e l l e d by the addition of a few mL ethanol). The t o t a l volume was approximately 1000 mL. Dropwise addition of cupric s u l f a t e pentahydrate (1.0767 g, 4.31 mmol i n 60 mL water) to the s t i r r i n g a c i d s o l u t i o n resulted i n the immediate p r e c i p i t a t i o n of a bright blue s o l i d . After the addition of the copper was complete, the reaction mixture was s t i r r e d for an hour and a h a l f . The s o l i d was i s o l a t e d by f i l t r a t i o n and washed with ethanol, water and, f i n a l l y , ethanol and a i r dried. Y i e l d : 3.0381 g, 93% of theory. Anal, c a l c d . for C u C ^ H g ^ P C u 8.42, C 63.87, H 11.22; found: Cu 8.33, C 63.84, H 11.12. 4.3.7.3 a-Copper(II) Di-n-dodecylphosphinate, a-Cu[(n-C12H25^2P02]2* The twelve carbon a l k y l chain d e r i v a t i v e was synthesized e a s i l y by the same method as employed for copper di-n-decylphosphinate (Section 4.3.7.2). Di-n-dodecylphosphinic acid (3.2181 g, 7.99 mmol), dissolved In ethanol (850 mL), was p a r t i a l l y neutralized with aqueous sodium hydro-xide (0.3117 g, 7.79 mmol, i n 50 mL water). The solu t i o n was f i l t e r e d - 223 -and a further 300 mL of water was added, u n t i l clouding just began. To the s t i r r i n g acid s o l u t i o n was added, dropwise, cupric s u l f a t e penta-hydrate (0.9969 g, 3.99 mmol, i n 75 mL water). A bright blue s o l i d began p r e c i p i t a t i n g immediately. After the addition of copper(II) was complete, the reaction mixture was s t i r r e d for one and a half hours, and the s o l i d was removed by f i l t r a t i o n , washed well with ethanol and a i r dried, y i e l d i n g 3.4096 g (98% of theory) of pure copper di-n-dodecyl-phosphinate. Anal, c a l c d . for CuCltgH^g0P2Oit: Cu 7.33, C 66.51, H 11.63; found: Cu 7.37, C 66.51, H 11.70. 4.3.8 8-Forms of the n - o c t y l , n-decyl and n-dodecyl D e r i v a t i v e s . The 8-isomers were obtained from the melt of samples of the a n a l y t i c a l l y pure a-forms. The 8-isomers may also be obtained by d i s -solving the a-isomers i n an organic solvent, such as chloroform or carbon t e t r a c h l o r i d e and then evaporating the solvent. The l a t t e r method was not the conversion method of choice, however, due to the lim i t e d s o l u b i l i t y of these polymers (see Section 2.1.3). A l t e r n a t i v e -l y , the preparative reactions c a r r i e d out i n organic solvents also y i e l d the 8-isomers. Hence, i n a t y p i c a l conversion, ca. one gram of the compound was placed i n a 100 mL Kjeldahl f l a s k and melted i n an o i l bath at a tempe-rature just above the appropriate melting point (given below). When judged, v i s u a l l y , to be completely melted, the sample was removed from the o i l bath and allowed to freeze completely. I t was then remelted and recooled, the process being repeated at least three times to ensure complete conversion of the a-isomer to the 8. - 224 -4.3.8.1 B-Copper(II) Di-n-octylphosphinate, 8-Cu[(n-C 8H 1 7) 2P0 2] 2. O i l bath temperature: 135°C. Anal, calcd. for C u C j ^ g g P ^ : Cu 9.89, C 59.83, H 10.67; found: Cu 9.87, C 59.98, H 10.70. 4.3.8.2 p-Copper(II) Di-n-decylphosphinate, p - C u [ ( n - C 1 0 H 2 1 ) 2 P 0 2 ] 2 . O i l bath temperature: 130°C. Anal, calcd. for CuC^gHg^P^: Cu 8.42, C 63.87, H 11.22; found: Cu 8.36, C 63.63, H 11.10. 4.3.8.3 p-Copper(II) Di-n-dodecylphosphinate, 8 - C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 . O i l bath temperature: 130°C. Anal, calcd. for CuC^gR^QQP^: Cu 7.33, C 66.51, H 11.63; found: Cu 7.31, C 66.30, H 11.55. 4.3.9 Copper(II) Di-isopropylphosphinate, C u [ ( i - C 3 H 7 ) 2 P 0 2 ] 2 . This compound was prepared by the reaction of the s i l v e r s a l t of di-isopropylphosphinic acid with cupric chloride dihydrate, i n analogy to the synthesis of the d i e t h y l compound, except i n t h i s case i s o l a t i o n of the pure compound from the aqueous s o l u t i o n presented no problems. Copper(II) chloride dihydrate (1.4954 g, 8.77 mmol), dissolved i n water (50 mL) was added slowly to a s t i r r i n g s o l u t i o n of s i l v e r d i - i s o -propylphosphinate (4.1000 g, 17.55 mmol) i n water (75 mL). Af t e r remo-v a l of the i n i t i a l p r e c i p i t a t i o n of s i l v e r chloride by f i l t r a t i o n , the f i l t r a t e was corrected for the small excess of A g + by the dropwise addition of d i l u t e hydrochloric a c i d . A f t e r r e f i l t r a t i o n the s o l u t i o n - 225 -was transferred to a 250 mL round-bottomed f l a s k and the solvent was evaporated under vacuum at 50°C. (A test for the presence of excess Ag + or C l ~ was performed when the volume of the so l u t i o n had been reduced to ca. 50 mL from 175 mL; neither were found.) When the reaction mixture was dry, the s o l i d was ground to a f i n e powder, transferred to a clean f l a s k and heated at 55°C under vacuum for twelve hours to ensure com-plete dehydration. Y i e l d 2.9536 g, 93% of theory. Anal, c a l c d . for CuC 1 2H 2 gP 20 1 +: Cu 17.56, C 39.83, H 7.80; found: Cu 17.56, C 39.90, H 7.69. 4.3.10 Copper(II) Di-tert-butylphosphinate, C u t C t-C^Hg) 2P0 2] 2. Gillman and Eichelberger (67) prepared this compound according to equation [4.20]; however, the compound they i n i t i a l l y i s o l a t e d contained copper hydroxide moieties as evidenced by the in f r a r e d spectrum. This impurity was removed by sublimation at 235°C (67). We were interested i n a route which would afford us the pure compound d i r e c t l y , without the need to separate i m p u r i t i e s . Hence i n an e f f o r t to avoid the formation of copper hydroxide i n the reaction mixture, the amount of base (potas-sium carbonate) used i n the aqueous preparation was reduced such that the pH of the acid s o l u t i o n was approximately 5.5. The addition of t h i s s o l u t i o n to aqueous copper(II) s u l f a t e pentahydrate gave no Immediate reaction and evaporation of the solvent under vacuum resulted i n the i s o l a t i o n , a f t e r washing with cold water and acetone, of a dark blue s o l i d , the i n f r a r e d spectrum of which showed a sharp hydroxide band at 3635 cm - 1, and multiple bands i n the region associated with P0 2 - 226 -stretching, i n d i c a t i n g perhaps, the presence of unreacted acid or of a s u l f a t e copolymer. The problem of hydroxide contamination was solved by going to a synthesis using acetone as the solvent and involving no n e u t r a l i z a t i o n of the a c i d . Copper(II) benzoate (1.1349 g, 3.71 mmol), dissolved i n warm acetone (100 mL), was added slowly with s t i r r i n g to a so l u t i o n of di-t-butylphosphinic acid (1.3254 g, 7.44 mmol) dissolved i n warm ace-tone (300 mL). I n i t i a l l y the reaction mixture was cloudy and had the deep blue color of the copper benzoate solution; however, with c o n t i -nued s t i r r i n g and addition of the copper, the color lightened and a f i n e , very pale blue p r e c i p i t a t e was v i s i b l e . The mixture was l e f t s t i r r i n g overnight, then the acetone was removed under vacuum. - The semi-dry. s o l i d was washed well with warm acetone and a i r dried, y i e l d i n g 1.5146 g (98% of theory) of pure copper di-t-butylphosphinate. Anal, ca l c d . for C u C 1 6 H 3 6 P 2 0 4 : Cu 15.20, C 45.98, H 8.68; found: Cu 15.33, C 45.85, H 8.55. 4.3.11 Copper(II) Diphenylphosphinate, C u [ ( C 6 H 5 ) 2 P 0 2 ] 2 * We encountered some d i f f i c u l t y i n i s o l a t i n g copper diphenylphos-phinate (88) i n an a n a l y t i c a l l y pure form. Synthesis involving complete n e u t r a l i z a t i o n of the phosphinic acid i n 6:1 ethanol:water led to the p r e c i p i t a t i o n of a compound the elemental analysis of which Indicated the presence of copper hydroxide or copper oxide moieties. This may have been contributed to by the vigorous heating needed to i s o l a t e the - 227 -compound, which appeared to be soluble i n the ethanol-water mixture (once i s o l a t e d and dr i e d , however, the compound was insoluble i n a l l solvents tested, see Section 2.2.2). These problems were overcome by n e u t r a l i z i n g the acid s o l u t i o n to pH 5.3 only and by gentle warming of the reaction mixture to evaporate the ethanol and cause the p r e c i p i t a -t i o n of the desired product. Diphenylphosphinic acid (3.9525 g, 18.11 mmol) was dissolved i n 700 mL aqueous ethanol (6:1 ethanol:water) and f i l t e r e d a f t e r the pH was adjusted to 5.3 with aqueous sodium hydroxide. A f i l t e r e d s o l u t i o n of copper su l f a t e pentahydrate (2.2160 g, 8.88 mmol i n 135 mL water) was added dropwise, over an hour, to the s t i r r i n g , heated (to ca. 60°C 1) acid s o l u t i o n . A blue s o l i d began p r e c i p i t a t i n g a f t e r the addition of approximately ten drops. When the addition was complete, the reaction mixture was warmed to f a c i l i t a t e evaporation of the ethanol and then l e f t s t i r r i n g overnight, r e s u l t i n g i n a reduction of the volume from 800 mL to 200 mL. The s o l i d was separated by f i l t r a -t i o n and washed with hot water, followed by hot ethanol, then dried under vacuum at 85°C for twelve hours, y i e l d i n g 2.4462 g (55% of theory) of pure copper diphenylphosphinate. Concentration of the f i l t r a t e yielded a further 0.9618 g of material; however, this product was not a n a l y t i c a l l y pure. Anal, c a l c d . for C u C ^ H ^ P ^ : C u 1 2 * 7 6 » c 57.89, H 4.05; found: Cu 12.80, C 57.75, H 4.05. 4.3.12 Copper(II) Mono-n-hexylphosphinate, Cu[(n-C 6H 1 3)(H)P0 2] 2« Heating was necessary to keep the phosphinic acid i n s o l u t i o n . - 228 -The i s o l a t i o n of t h i s compound was an event that i s , i n science, commonly c a l l e d "serendipitous". In an attempt to i d e n t i f y the o i l formed as a by-product i n the synthesis of di-n-hexylphosphlnic acid (Section 4.2.7), a sample of the o i l , taken up i n acetone, was treated with a so l u t i o n of copper benzoate i n acetone. This resulted In the p r e c i p i t a t i o n of a fin e l i g h t blue powder which was i s o l a t e d by f i l t r a -t i o n and washed with acetone; however, even extensive washing resulted i n a gummy s o l i d . This s o l i d was refluxed overnight i n acetone, separa-ted by f i l t r a t i o n and washed with acetone, y i e l d i n g 7.6396 g of pure copper(II) mono-n-hexylphosphinate. Anal, c a l c d . for CuC^H^P-jO^: ^ u 17.56, C 39.83, H 7.80;^found: Cu 17.64, C 39.71, H 7.70. 4.3.13 Copper(II) Mono-n-decylphosphinate [Cu(n-C 1 0H 2 1)(H)PO 2] 2* The synthesis of this compound involved the use of the sodium s a l t of the phosphinic ac i d , described e a r l i e r (Section 4.2.8). This material was not i s o l a t e d a n a l y t i c a l l y pure but rather contained ca. 5% sodium hydroxide impurity, hence i t s use as a reagant required compensa-ti o n for t h i s impurity. In the f i r s t attempted preparation the pH of the aqueous s o l u t i o n of the s a l t was adjusted to s l i g h t l y a c i d i c (pH ca. 6) with d i l u t e s u l f u r i c a c i d . The addition of a stoichiometric amount of cupric s u l f a t e pentahydrate, however, resulted In the p r e c i p i t a t i o n of a s o l i d the elemental analysis of which indicated the presence of basic s a l t impurity (C and H low). This problem was overcome by lower-ing the pH of the s a l t s o l u t i o n to ca. 5. Sodium monodecylphosphinate (2.5108 g, 11.00 mmol pure sodium - 229 -s a l t ) dissolved i n a mixture of water (320 mL) and ethanol (50 mL), was taken to pH 5 by the dropwise addition of d i l u t e s u l f u r i c a c i d . This caused the p r e c i p i t a t i o n of a white s o l i d , presumably the phosphinic ac i d , which was redissolved by the addition of ethanol (500 mL). The so l u t i o n was f i l t e r e d , then cupric s u l f a t e pentahydrate (1.3722 g, 5.50 mmol, i n 50 mL water) was added dropwise with s t i r r i n g , causing the formation of a f i n e pale blue s o l i d . The reaction mixture was s t i r r e d for a half hour a f t e r the addition of copper was complete, then the s o l i d was separated by f i l t r a t i o n , washed with ethanol and a i r d r i e d . Y i e l d 1.8455 g, 71% of theory. Anal, c a l c d . for CuC 2 0H l t l tP 2O 1 +: Cu 13.40, C 50.67, H 9.36; found: Cu 13.46, C 50.87, H 9.45. 4.3.14 Copper(II) Monophenylphosphinate, C u [ ( C 6 H 5 ) ( H ) P 0 2 ] 2 . The preparation of t h i s compound presented few problems, with the exception that, curiously, the addition of aqueous cupric s u l f a t e to the p a r t i a l l y neutralized acid s o l u t i o n (pH 5.3) resulted i n the i s o l a t i o n of a compound with low carbon and hydrogen analyses, whereas the reverse order of addition, i . e . acid s o l u t i o n to copper, gave an a n a l y t i c a l l y pure product. Monophenylphosphinic acid (12.2245 g of 97% pure material, 83.45 mmol pure acid) was dissolved i n water (250 mL) and adjusted to pH 5.3 with aqueous sodium hydroxide. This s o l u t i o n was added slowly with s t i r r i n g to aqueous cupric s u l f a t e pentahydrate (10.4803 g, 41.98 mmol i n 100 mL water), causing the immediate p r e c i p i t a t i o n of a blue s o l i d . 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Downie, and K. Williamson. J . Chem. Soc. 1240 (1964). (317) H.B. S i l v e r . J . Chem. Soc. Sect. C, 1326 (1967). - 248 -Appendix 1. Complete Structural Parameters for a-Cu[(C 2H 5) 2P0 2] 2 and p-Cu[(n-C 6H 1 3) 2P0 2] 2. a) a-Cur(C 2H 5) 2P0 2] 2 Final positional (fractional: C x I0k, Cu, P and 0 x 105, H x 10 3) and isotropic thermal parameters (U x 10 3 A 2) with estimated standard deviations in parentheses. Atom X L V " i s o Cu 23567(2) 25977(2) 51902(2) 29 P(D 14361(5) -1713(4) 68056(4) 30 P(2) 35286(5) 49660(4) 31273(4) 29 0(1) 28359(17) 12912(12) 65019(12) 40 0(2) 3632(15) -13622(11) 55821(11) 33 0(3) 25850(18) 34068(12) 34918(11) 40 0(4) 57350(16) 56604(11) 36271(12) 36 C(l) -301(3) 153(2) 7521(2) 43 C(2) 2890(3) -844(2) 8108(2) 46 C(3) 2543(3) 6152(2) 3738(2) 48 C(4) 2810(3) 4792(2) 1270(2) 44 C(5) 573(5) 1378(3) 8724(3) 64 C(6) 4424(5) -1147(4) 7657(4) 77 C(7) 325(4) 5573(5) 3280(4) 80 C(8) 3480(5) 6247(3) 654(2) 69 H(la) -134(3) 45(2) 671(2) 57(6) H(lb) -109(4) -79(3) 781(3) 79(9) H(2a) 350(4) -24(3) 885(3) 65(7) H(2b) 190(4) -177(3) 842(3) 76(8) H(3a) 288(4) 613(3) 453(3) 59(7) H(3b) 299(4) 706(3) 338(3) 62(7) H(4a) 317(4) 410(3) 102(3) 69(8) H(4b) 159(4) 444(3) 97(3) 59(7) H(5a) 135(5) 125(4) 941(4) 92(11) H(5b) 144(3) 231(2) 836(2) 54(6) H(5c) -54(6) 154(4) 874(4) 127(14) H(6a) 503(5) -144(3) 837(3) 78(9) H(6b) 391(5) -182(4) 664(4) 106(12) H(6c) 515(5) -18(4) 720(3) 90(10) H(7a) -30(5) 609(4) 368(3) 86(9) H(7b) -5(9) 580(6) 199(6) 217(23) H(7c) -32(5) 474(3) 348(3) 91(11) H(8a) 470(4) 681(3) 100(3) 76(9) H(8b) 331(4) 599(3) -16(3) 77(9) H(8c) 290(6) 692(5) 81(4) 131(17) * U - 1/3 trace (U ). —eq —diag - 249 -b) a-Cu[(C 2H 5 ) 2 P0 2 ]2 Bond lengths (A) with estimated standard deviations i n parentheses.* Bond uncorr. corr. Bond uncorr. corr. Cu -0(1) 1.9158(11) 1.922 P(2)-0(3) 1.5191(10) 1.528 Cu -0(3) 1.9171(11) 1.923 P(2)-0(4) 1.5125(11) 1.521 Cu -0(2)' 1.9224(10) 1.928 P(2)-C(3) 1.790(2) 1.801 Cu -0(4)" 1.5177(10) 1.924 P(2)-C(4) 1.802(2) 1.812 P(D-0(1) 1.5233(10) 1.531 C(l)-C(5) 1.524(3) 1.529 P(D-0(2) 1.5164(11) 1.524 C(2)-C(6) 1.492(4) 1.499 P d ) - C ( l ) 1.795(2) 1.804 C(3)-C(7) 1.521(3) 1.527 P(D-C(2) 1.800(2) 1.809 C(4)-C(8) 1.521(3) 1.527 * Atoms denoted by ' and " are related to those in Table a) by the centres of symmetry at 0, 0, 1/2 and 1/2, 1/2, 1/2 respectively. c) a-Cu[(C 2H 5 ) 2 P 0 2 ] 2 Bond angles (deg) with estimated standard deviations i n parentheses. Bond Angle(deg) Bonds Angle(deg) 0(1' >-Cu -0(3) 149.85(6) 0(3)-P(2)-C(3) 110.00(9) 0(1 >-Cu -0(2)' 94.88(5) 0(3)-P(2)-C(4) 105.11(7) 0(1 )-Cu -0(4)" 93.20(5) 0(4)-P(2)-C(3) 109.76(8) 0(3' >-Cu -0(2)' 92.74(5) 0(4)-P(2)-C(4) 108.30(8) 0(3; >-Cu -0(4)" 96.00(5) C(3)-P(2)-C(4) 108.03(10) 0(2] )*-Cu -0(4)" 147.24(6) Cu -0(1)-P(1) 130.08(7) 0(1] )-P(l)-0(2) 114.99(6) P(l)-0(2)-Cu l 132.30(7) o( i ; >-P(l)-C(l) 109.72(8) Cu -0(3)-P(2) 133.70(7) o( i ; |-P(1)-C(2) 106.37(8) P(2)-0(4)-Cu" 135.45(8) 0(2] >-P(l)-C(l) 109.51(7) P(l)-C(l)-C(5) 115.3(2) 0(2; >-P(l)-C(2) 108.26(8) P(l)-C(2)-C(6) 113.6(2) c a : l-P(l)-C(2) 107.69(10) P(2)-C(3)-C(7) 114.4(2) o(3; >-P(2)-0(4) 115.31(7) P(2)-C(4)-C(8) 114.84(15) - 250 -d) o-Cu[(n-C 6H 1 3)2P0 2]2 F i n a l p o s i t i o n a l ( f r a c t i o n a l x 1 0 \ Cu and P x 10 5) and i s o t r o p i c thermal parameters (U x 10 3 A 2) with estimated standard deviations i n parentheses. ~~ * Atom X U £ 1 Cu 25661(5) 48080(4) 48964(4) 62 P ( D 3754(11) 55705(10) 35525(10) 67 P(2) 47367(10) 41029(9) 62447(10) 62 0(1) 1297(3) 4768(2) 4045(2) 70 0(2) -1194(3) 5415(3) 3819(2) 80 0(3) 4140(2) 4029(2) 5320(2) 65 0(4) 6325(2) 4192(2) 5973(2) 69 C ( l ) 532(5) 6936(4) 3863(4) 85 C(2) -361(6) 7827(4) 3400(5) 100 C(3) -182(7) 8966(5) 3650(6) 128 C(4) -1035(8) 9888(6) 3246(7) 159 C(5) -841(11) 11021(6) 3519(9) 197 C(6) -1726(13) 11886(8) 3312(9) 227 C(7) 1043(5) 5385(4) 2157(4) 84 C(8) 976(6) 4272(6) 1784(6) 116 C(9) 1534(8) 4035(9) 656(7) 159 C(10) 1387(21) 2922(19) 332(17) 323 C ( l l ) 1796(22) 2358(17) -192(23) 381 C(12) 1580(14) 1233(12) -416(11) 277 C(13) 4485(5) 2866(4) 6980(4) 79 C(14) 5263(6) 1849(4) 6367(5) 95 C(15) 5157(7) 810(4) 6975(5) 113 C(16) 5961(8) -205(5) 6396(6) 132 C(17) 5930(9) -1212(6) 6995(7) 161 C(18) 6681(10) -2194(6) 6427(7) 171 C(19) 3772(4) 5221(4) 7065(4) 79 C(20) 4298(5) 5428(4) 8024(5) 93 C(21) 3480(7) 6422(5) 8639(5) 116 C(22) 3951(9) 6710(7) 9557(6) 149 C(23) 3035(13) 7744(11) 10122(8) 233 C(24) 3328(16) 8108(16) 10869(13) 327 * U - 1/3 trace U eq diag. e) o-Cu[(n^C 6H 1 3) 2P0 2]2 B o n d lengths (A) with estimated standard deviations i n parentheses* Bond Length( A) Bond Length(A) Cu -0(1) 1.907(3) C(5)-C(6) 1.366(11) Cu -0(3) 1.932(2) C(7)-C(8) 1.488(8) Cu -0(2)' 1.902(3) C(8)-C(9) 1.479(9) Cu -0(4) M 1.896(3) C(9)-C(10) 1.48(2) P(D-0(1) 1.521(3) C(10)-C(ll) 0.97(2) P(D-0(2) 1.514(3) C ( l l ) - C ( l 2 ) 1.48(2) P(D-C(1) 1.779(5) C(13)-C(14) 1.521(7) P(D-C(7) 1.807(5) C(14)-C(15) 1.498(7) P(2)-0(3) 1.513(3) C(15)-C(16) 1.507(8) P(2)-0(4) 1.515(2) C(16)-C(17) 1.459(9) P(2)-C(13) 1.798(4) C(17)-C(18) 1.455(10) P(2)-C(19) 1.789(5) C(19)-C(20) 1.543(7) C(l)-C(2) 1.547(6) C(20)-C(21) 1.510(8) C(2)-C(3) 1.493(8) C(21)-C(22) 1.488(9) C(3)-C(4) 1.510(8) C(22)-C(23) 1.553(13) C(4)-C(5) 1.500(10) C(23)-C(24) 1.221(14) * Primed and double-primed atoms have coordinates related to those i n Table d) by the symmetry operations -x, l-y_, l-£ and 1-x, l-y_, l-£ res p e c t i v e l y . £) o-Cu[(n-C 6H 1 3)2 p 02l2 Bond angles (deg) with estimated standard deviations i n parentheses. Bonds Angle(deg) )-Cu -0(3) )-Cu -0(2)' >-Cu -0(4)" )-Cu -0(2)' )-Cu -0(4)" I'-CU -0(4)" )-P(l)-0(2) >-P(l)-C(l) )-P(l)-C(7) ) - P ( l ) - C ( l ) )-P(l)-C(7) )-P(l)-C(7) )-P(2)-0(4) )-P(2)-C(13) )-P(2)-C(19) )-P(2)-C(13) )-P(2)-C(19) C(13)-P(2)-C(19) Cu -0(1)-P(1) P(l)-0(2)-Cu' Cu -0(3)-P(2) 145.43(14) 95.96(11) 94.04(12) 94.14(12) 95.39(10) 146.71(14) 116.0(2) 110.5(2) 107.1(2) 108.7(2) 105.7(2) 108.5(3) 115.0(2) 108.2(2) 109.6(2) 105.4(2) 110.0(2) 108.2(2) 138.2(2) 132.4(2) 134.5(2) Bonds Angle(deg) P(2)-0(4)-Cu" P(l)-C ( l ) - C ( 2 ) C(l)-C(2)-C(3) C(2)-C(3)-C(4) C(3)-C(4)-C(5) C(4)-C(5)-C(6) P(l)-C(7)-C(8) C(7)-C(8)-C(9) C(8)-C(9)-C(10) C(9)-C(10)-C(ll) C(10)-C(ll)-C(12) P(2)-C(13)-C(14) C(13)-C(14)-C(15) C(14)-C(15)-C(16) C(15)-C(16)-C(17) C(16)-C(17)-C(18) P(2)-C(19)-C(20) C(19)-C(20)-C(21) C(20)-C(21)-C(22) C(21)-C(22)-C(23) C(22)-C(23)-C(24) 130.5(2) 115.2(4) 114.1(5) 117.7(6) 116.3(7) 119.4(9) 114.3(4) 118.2(7) 115.4(12) 144(3) 139(3) 113.4(4) 114.9(5) 116.0(6) 116.5(7) 116.4(8) 115.7(3) 112.2(5) 116.0(6) 111.2(8) 118.9(14) - 253 -Appendix 2. Unassigned Infrared Absorptions* a) Copper(II) Di-n-alkylphosphinates. 1 Compound Frequencies (cm - 1) a-Cu[(CH 3 ) 2 P0 2 h 1418 v., 1309 m.sh., 1292 s., 1283 m.sh., 935 v.w., 921 v.w., 878 8., 871 s., 858 m.sh., 374 v.w., 309 v.w., 288 v.w. a-Cu[(C 2H 5 ) 2 PO 2l 2 1413 m., 1279 m.sh., 1270 m., 1245 m., 1237 m.sh., 1188 m., 997 m.sh., 976 m.sh., 780 s., 771 s., 673 w., 667 w.sh., 400 v.w., 385 v.w.sh., 375 w., 302 v.w. (3-Cu[(n-CltH9)2 P O 2 ] 2 1409 w., 1304 m., 1276 w., 1223 m., 1215 m.sh., 1204 w.sh., 1096 w.sh., 1043 w.sh., 1035 w.sh., 904 m., 892 m.sh., 780 v.w., 772 w., 745 w., 428 w., 420 w.sh., 322 w. 6-Cu[(n-C 6H 1 3) 2 P O 2 ] 2 1407 w., 1317 w., 1289 w., 1259 w.-m., 1238 w., 1205 w.-m., 975 v.w., 963 v.w., 891 w., 880 v.w., 865 w., 856 w.sh., 777 v.w.sh., 751 v.v.w., 709 w.sh., 442 w., 401 w.-m., 380 v.w.sh., 339 m.sh. a-Cu[(n-C 8H 1 7) 2 P 0 2 ] 2 1407 w., 1322 v.w.sh., 1308 w., 1291 v.w.sh., 1278 v.w., 1259 w., 1235 w., 1219 w., 1192 w.sh., 1180 w.sh., 971 w., 890 v.w., 848 w., 742 v.w.sh., 707 v.w.sh., 412 w.sh., 347 v.w., 342 v.w.sh. B-Cu[(n-C 8H 1 7) 2 P O 2 ] 2 1728 v.v.w., 1405 w., 1320 v.w., 1294 v.w.br., 1278 v.w.sh., 1261 v.w., 1240 w., 1220 w.sh., 1202 w.sh., 1196 w., 979 v.v.w., 921 v.w., 899 v.w., 890 v.w.sh., 880 v.w., 851 w., 779 w., 756 v.w.sh., 740 w.sh., 711 m.sh., 425 w., 332 w., 321 v.v.w.sh. o-Cu[(n-C 1 0H 2 1 ) 2 P O 2 J 2 1408 w., 1308 w., 1291 w.sh., 1271 v.w., 1257 v.w., 1240 v.w., 1223 v.w., 1207 v.w., 1189 m.sh., 996 v.w.sh., 973 v.w., 897 v.w., 707 w.sh., 438 v.v.w.sh., 417 w.sh., 358 v.w.sh., 349 v.w.sh. (3-Cu[(n-C 1 0H 2 1 ) 2 P O 2 ] 2 1405 w., 1292 w., 1259 v.w., 1239 v.w., 1226 w.sh., 1222 w., 1210 w.sh., 1190 w., 1160 v.w.sh., 899 w.sh., 893 w., 855 w., 841 w., 780 w., 763 v.w., 741 w.sh., 714 w.sh., 438 v.w.sh., 413 w.-m. - 254 -Appendix 2.a) (contd) Compound Frequencies (cm"1) a-Cu[(n-C 1 2 H25)2 P 02l2 1729 v.v.w., 1408 v.w., 1300 v.w.br., 1271 v.w., 1253 v.w.sh., 1243 v.w.sh., 1227 v.w.sh., 1215 v., 1186 w.sh., 1082 m.sh., 971 w., 893 w., 834 v.w., 807 v.w., 740 w.sh., 710 w.sh., 420 v.w.sh., 407 v.w.sh., 398 v.w.sh., 360 v.w.sh. p-Cu[(n-C 1 2H 2 5) 2P0 2] 2 1408 w., 1323 v.w., 1302 v.w., 1290 v.w., 1273 w., 1254 v.w.sh., 1227 v.w.sh., 1215 w., 1207 v.w.sh., 1189 w., 1162 v.w.sh., 982 v.w., 945 v.v.w.sh., 934 v.w., 919 v.v.w.sh., 895 w., 881 v.w.sh., 834 w., 783 w., 765 v.w., 751 v.v.w.sh., 458 v.v.w., 443 v.v.w., 418 v.v.w., 335 v.w.sh. 1 v.v.w., very very weak; v.w., very weak; w., weak; w.-m., weak-to-medium; m., medium; a., strong; br., broad; sh., shoulder. b) Copper(II) Di-i-propyl-, Di-t-butyl-, and Diphenylphosphinate 1. Compound Frequency (cm - 1) Cu[(i-C 3H 7) 2P0 2] 2 1293 v.v.w., 1269 w.-m., 1261 v.w.sh., 1034 m., 974 v.w., 665 v.w.sh., 318 v.v.w.br. CuKt-C^ c j^POjljj 1210 v., 1024 v.w.sh., 1009 v.w.sh., 941 w., 403 v.w.sh., 350 v.v.w.sh., 343 v.v.w.sh., 333 w., 311 v.w., 297 v.w., 287 v.w. Cu[(C 6H 5) 2P0 2] 2 1315 v.w., 1071 m.sh., 471 w., 437 w., 342 w., 336 w.sh. v.v.w., very very weak; v.w., very weak; w., weak; w.-m., 1 weak-to-medium; t n . , medium; br., broad; sh., shoulder. - 255 -c) Copper(II) Di-monosubstituted phosphinates 1. Compound Frequency (cm - 1) C u [ ( n - C 6 H 1 3 ) ( H ) P 0 2 ] 2 1405 w., 1286 v.w., 1265 w., 1246 v.w., 1211 w., 1192 w.sh., 1024 m.sh., 999 w.sh., 965 w., 944 w., 897 v.w.sh., 448 v.w.sh., 434 v.w.sh., 318 v.w. Cu [ ( n - C 1 Q H 2 1 ) ( H ) P 0 2 ] 2 1403 w., 1291 w., 1274 v.w.sh., 1269 v.w.sh., 1259 v.w., 1241 v.w., 1226 w., 1209 w.sh., 1195 w.sh., 1178 w.sh., 1066 m.sh., 1059 m.sh., 1026 m., 1016 m.sh., 1002 w.sh., 994 w.sh., 984 w.sh., 960 w.sh.', 944 w.sh., 890 w.-m., 776 w.sh., 744 w.sh., 501 w.sh., 432 v.w.sh., 406 v.w.sh., 317 w.-m., 309 w.-m.sh. Cu[ ( C 6 H 5 ) ( H ) P 0 2 ] 2 1321 v.w.sh., 1314 v.w., 1196 m., 1064 m.sh., 1035 w.sh., 1020 m.sh., 995 m., 991 m.sh., 975 w.sh., 970 w.sh., 928 w., 868 v.w., 727 w., 624 w., 534 v.w., 521 v.w.sh., 419 w., 405 v.w.sh. v.w., very weak; w., weak; w.-m, weak-to-medium; m., medium; sh., shoulder. - 256 -Appendix 3. Magnetic Data. (T i n degrees K; i n 0 0 3 m o l - 1 and u^ f^ i n B.M.) a) a-Cu[(CH 3) 2P0 2] 2« T l 0 \ I ^eff 303 .1 1 .410 1 .85 300.9 1 .410 1 .84 27B.4 1 .540 1 .85 275.0 1 .540 1 84 253.7 1 .690 1 .65 250 4 1 .690 1 .84 22B 8 1 .870 1 .85 226.2 1 .880 1 .84 204 .6 2 .090 1 .85 200.7 2 .090 1 .83 178.7 2 .400 1 .85 177.0 2 .400 1 84 154 0 2 .750 1 .84 151 .7 2 .750 1 .83 130.6 3 220 1 .83 128 .4 3 .250 1 .83 109.8 3 .770 1 .82 96.0 4 . 1 10 1 .80 90.2 4 .450 1 .79 80.6 4 .900 1 .78 69.9 5 .590 1 .77 60.3 6 .300 1 .74 48.6 7 .490 1 .71 43.4 8 . 170 1 .68 40.2 8 .620 1 .66 33 4 9 .790 1 .62 30.8 10 .340 1 .60 27.8 11 .010 1 .56 24 .8 11 .790 1 .53 22 .4 12 .360 1 .49 20.75 12 .970 1 .47 18.75 13 690 1 43 16.6 14 . 410 1 .38 14 6 15. 310 1 .34 12.65 16 .260 1 .28 10.9 17 . 330 1 .23 9. 10 1B. 790 1 . 17 7.07 21 . 420 1 . 10 6.21 23. 070 1 .07 5.29 25. 590 1 .04 4 91 27 . 010 1 .03 4.20 29. 630 0 .998 b) a - C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 . T l0\ •*•££. 4.20 •2.43 1.45 4.55 60.96 1 .49 5.05 57.94 1.53 5.49 55.51 1.56 S.09 53.02 1.61 6.88 48.95 1.64 7.80 44.68 1.67 8.82 40.81 1.70 9.90 37.31 1 .72 10.85 34.40 1.73 11.8 31 .80 1 .73 13.1 29.85 1 .77 13.8 28. 18 1.76 14.6 26.66 1.76 16. 1 24.57 1 .77 16.8 23.35 1.76 17.0 22.25 1.78 18.7 21.29 1.78 19.4 20.52 1 .78 20.4 19.59 1.78 21 .35 18.80 1 .78 21 .9 18.29 1.78 25.2 16.34 1 .81 28.4 14.79 1.83 31 .0 13.57 1 .83 33.7 12.53 1 .84 36. 1 11.68 1 .84 39.4 10.78 1 .84 42 .6 8.98 1.84 48.0 8.91 1 .85 54 .4 7.86 1.86 €0.6 7.22 1 .87 70.3 6.25 1 .87 81.8 5.41 1 .88 91.8 4.81 1 .88 100.5 4.39 1 .88 110.7 3.97 1 .87 125. 1 3.51 1 .87 129.3 3.40 1 .87 154. 1 2.85 1 .88 179. 1 2.45 1.87 203.3 2. 18 1.88 230.0 1.91 1 .87 253.9 1 .72 1 .87 278.5 1 .87 1 .87 304. 1 1.43 1.86 - 257 -c) 6-Cu[(n-C i tH 9) 2P0 2] 2* T 1 0 \ " e f f . 4.20 177.6 2.44 4.65 159.34 2.43 4 88 147.79 2.40 5 58 124.59 2.36 5.90 113.63 2.32 6.90 92. 11 2.25 7.85 72.22 2.23 8.95 66 .80 2. 19 9.80 59.54 2. 16 10.95 51 .55 2. 12 11.8 47.04 2.11 12.6 43.26 2.09 13.65 39.40 2.07 14.8 35.96 2.06 16.65 30.97 2.03 18.7 26.98 2.01 20.4 24.44 2.00 22. 15 22.30 1.99 25.2 19.46 1.98 28.2 17.27 1 .97 31 . 1 15.51 1 .96 33.8 14 .09 1 95 36 . 1 13. 15 1.95 39.5 11 .90 1 .94 42 .8 10.96 1 .94 48.3 9.62 1 .93 54.6 8.42 1 .92 60.6 7.56 1 .92 70.4 6.57 1 .92 80.5 5.63 1 .90 82 . 1 5.54 1 .91 92.2 4.94 1.91 100.5 4.51 1 .90 110.3 4.08 1 .90 124.7 3.61 1 .90 128.8 3.54 1.91 152.3 2.96 1 .90 179. 1 2.56 1 .92 203.8 2.21 1 .90 228.5 1.95 1.89 254.6 1 .79 1.91 279.4 1 .62 1 .90 304. 1 1.51 1.92 d) 6 - C u [ ( n - C 6 H 1 3 ) 2 P 0 2 ] 2 . T 10\ " e r f . 4.25 185.34 a.51 4.73 1SB.63 2.45 5.07 144.03 2.42 6.06 113.OS 2.34 6.82 95.4 2.28 7.99 78.3 2.24 9. 15 66.36 2.20 10. 1 59.64 2. 19 11 .0 53.26 2. 16 11.7 48.51 2. 13 12.6 43.58 2.10 13.8 39.81 2. 10 16 . 15 33.09 2.07 18 .0 29.03 2.04 19.4 25.32 1.98 22.35 22.37 2.00 25.5 19.47 1 .99 28.2 17 .44 1.98 31 . 1 15.59 1 .97 33.8 14.25 1.96 36.2 13.21 1 .96 39.9 11 .93 1 .95 43.0 11 .01 1 .95 48.3 9.62 1 .93 54 .7 8.40 1.92 60.9 7.59 1.92 70.4 6.54 1 .92 82.0 5.67 1 .93 92. 1 5.04 1.93 100.0 4.58 1.91 110.5 4.11 1.91 123.9 3.59 1 .89 129.9 3.47 1 .90 145.6 3.08 1.89 179.4 2.49 1 .89 202.4 2. 19 1 .88 228.8 1.96 1.89 253.9 1.73 1.87 279.4 1.59 1.88 S04.7 1.45 1.88 0 - 258 e) a - C u [ ( n - C 8 H 1 7 ) 2 P 0 2 ] 2 . T 1 0\ " • f f . 304 .4 1.580 1 .96 302 . 3 1.570 1 95 279.3 1 .670 1 .93 277 .4 1 .660 1 .92 254 .C 1 .780 1 .90 252 . 1 1.760 1 89 230.5 1.910 1 .88 227.4 1 .880 1 .85 203 7 2. 120 1 .86 202 0 2.090 1 .84 180 1 2 .280 1 .81 177.9 2.280 1 .80 156 8 2.450 1 .75 153 3 2.490 1 .75 127.9 2 .800 1 .69 118 3 2.870 1 .65 99.3 3.230 1 .60 89 4 3.420 1 .56 80.2 3.610 1 .52 68 8 3.780 1 . 44 59.6 3.980 1 .38 47.7 4.070 1 .25 42 4 4. 160 1 . 19 39 2 4. 160 1 . 14 35 6 4 . 190 1.09 33. 1 .4.240 1 .06 30.4 4.270 1 .02 27.6 4.300 0.974 24.8 4.340 0.928 21.9 4 .400 0 878 20.2 4 .470 0.850 18.3 4.570 0 . 8 1 8 16.45 4.670 0.784 14.3 4.840 0.744 12 .4 5.040 0.707 10.5 5.310 0.667 8.50 5.840 0.630 6.65 6.330 0.580 6 05 6.780 0.573 5. 10 7.260 0.544 4 .45 7.670 0 522 4.20 8. 140 0.523 f ) B - C u [ ( o - C 8 H 1 7 ) 2 P 0 2 ] 2 . T l 0 \ ^ e f f . 303.4 1.730 2 05 302. 1 1 .750 2 05 277.2 1 .870 2 04 276.8 1.870 2 .03 251.5 2.060 2 .04 251 2 2.060 2 03 227 6 2.260 2 .03 227.5 2.240 2 .02 203.4 2.550 2 .04 202.5 2.530 2 .03 178.3 2.860 2 02 178.0 2.880 2 .02 153.5 3.290 2 01 152.9 3.290 2 00 128.4 3.890 2 00 127.9 3.890 2 00 106.7 4.660 1 .99 92.2 5.230 1 .96 91.S 5.410 1 .99 81 .8 6. 140 2 .00 81.4 6.060 1 .99 70.7 6.970 1 .99 70.6 6.680 1.97 61.7 8O90 2 • 00 61.4 8.020 1 .98 61.3 6.160 2 00 52.9 9.200 1 .97 51.7 9.610 1 .99 50.3 10.040 2 .01 45.6 11.180 2 02 44.6 11.200 2 00 40. 1 12.600 2 .01 39.7 12.700 2. 01 39.5 12.720 2 .00 34.4 14.860 2. 01 34.2 14.870 2. 02 308 16.500 2, 02 30.6 16.690 2 02 27.1 19.100 2. 03 26.7 19.130 2. 02 24 8 20.760 2. 03 23 3 22.500 2. 05 21.3 24.700 2. 05 19.7 27.000 2. 06 18 5 28.070 2. 04 16.3 32.000 2. 05 15.5 34.800 2. 08 14.7 37.100 2. 10 14.3 37.290 2. 06 13.2 41.800 2. 10 12.5 43.840 2. 09 12.2 45.700 2. 11 10.6 63.320 2. 13 10.2 86.700 2. 19 6.82 68 700 2. 18 6.80 67.410 2. 16 6.44 T2.70O 3. 21 7 89 77.600 2. 23 7.23 66.800 2. 24 7.02 91.690 2. 27 6.37 102.000 2. 28 6. 13 107.400 2. 29 6.02 112 700 2. 33 6.35 130.700 2. 36 4 75 144.500 2. 34 4 32 174.300 2. 45 4.20 179.900 2 46 - 259 -g) a - C u [ ( n - C 1 0 H 2 1 ) 2 P O 2 ] 2 . T 10 X " e r f . 304 .9 1.440 1 .87. 304 .8 1 . 350 1.81. 280.4 1 .400 1 .77. 279.8 1 .500 1 .83. 255 4 1 .490 1 .74. 254 .5 1 .580 1 .79. 230. 9 1 .590 1.71. 230 1 1 .660 1 .75. 204 .6 1 .750 1 .69. 203 5 1 .870 1 .74. 181 .7 1 .970 1 .69. 178.5 2 .080 1 .72. 154 .8 2. 150 1 .63. 150.8 2. 250 1 .65. 129.3 2.460 1 60. 129.2 2 460 1 .59. 123 5 2.520 1 .SB. 106.6 2 .640 1 . 50. 94.3 2 830 1 .46. 76.4 3.070 1 .37. 69.6 3. 140 1 .32. 64 .3 3. 190 1 .28. 59.3 3.200 1 .23. 54.9 3.220 1 . 19. 50.3 3.230 1.14. 46.8 3.230 1 . 10. 42 .4 3.210 1 .04. 39.5 3. 180 1 .00. 35.7 3. 140 .945. 33.0 3. 130 .909. 29.9 3.080 .858. 27.5 3.010 .814. 24 .6 2 .960 .763. 21.9 2.930 .716. 20.3 2.890 .685. 18 3 2 .880 .649. 16.3 2 .870 .612. 14 .2 2.880 .572. 11 .95 2.930 .529. 10.4 2.920 .493. 8 .60 2.960 .451. 6.50 3. 150 .405. 5.75 3.250 .387. 4 .95 3 530 .374. 4.20 3.910 .362. h) 6 - C u [ ( n - C 1 0 H 2 1 ) 2 P O 2 ] 2 . l 0 \ " e f f . 303 0 1 . •60 1 •5 279.3 1. •60 1 .03 253 9 1 . • 20 1 .92 229.6 2. 030 1 .93 202. 1 2. 290 1 .92 171.5 2. 710 1 .93 145. 1 3. 150 1 .91 120.8 3. 750 1 .90 97.9 4 .600 1. 90 79.3 5.720 1. 90 60.3 7.490 1 . 90 54.2 8.310 1. 90 52. 1 8.610 1 . 89 49.6 9. 130 1 . 90 46.6 9.650 1 . 90 43 8 10 200 1 . 89 40 • 11. . 100 1 . • 1 37 6 12 . 100 1. • 1 34 1 13 40O 1. • 1 90.6 15 .200 1. 93 26.8 17.600 1. •4 22.9 21 . 100 1 . 97 21 .6 22 .500 1. 97 19.8 24 .800 1. 98 18.9 26 . 300 1. •9 18.5 26 .700 1. 99 17.0 29 .700 2. 01 14.7 35 .200 2. 03 14.3 36 .000 2. 03 12.5 42 .400 2. 06 12.4 42 .400 2 . 05 11.2 47 .900 2 .07 10.6 51 .500 2 09 10.2 54 .200 2 . 10 9.43 59 .900 2. . 13 8.95 63 . 300 2 . 13 8.63 •6 .700 2 . 15 7.61 76 .•00 2 . 16 7.35 • 2 .400 2 .20 €.91 •7 .600 2 .20 5.64 113.300 2 .30 5.56 114.300 2 .25 5.00 134.OOO 2 .31 4.24 166.700 2 .38 4.20 166.600 2 .37 - 260 -i ) o-Cu[(n-C 1 2H25)2 p0 2] 2* T l 0 \ " e f f . •03.7 1 .310 1 .78 279.8 1 .390 1.76 254 .9 1 .470 1.73 230 4 1 .610 1.72 202.4 1 .840 1.72 179.3 2 1.040 1.71 153.3 2 .210 1 .65 129.3 2 .580 1 .63 1034 2 .810 1 .53 73.4 3. 430 1 .42 71.7 3. 410 1 .40 70.0 3. 400 1 .38 •8 3 3. 400 1 .36 •6.6 3. 360 1 .34 •0.7 3. 580 1 .32 •8.9 3. SCO 1.30 56 6 3. 550 1.27 53.6 3. 480 1 .22 51.2 3. 560 1.21 49. 1 3. 600 1 . 19 47. 1 3. 570 1 . 16 44.9 3. 470 1. 12 42.7 3. 450 1.09 41.3 3. 470 1 .07 38 7 3. 470 1 .04 36. 1 3. 3B0 0.988 34.7 3. 400 0.971 33.3 3. 400 0.952 30.7 3. 510 0.928 29.4 3. 520 0.910 28 .0 3. 630 0.901 26.5 3. COO 0.873 24.2 3. 710 0.848 22.2 3. 840 0.826 20. 1 3. 680 0.769 18. 1 3. 900 . 0.751 17. 1 3. 870 0.727 15.0 4. 010 0.693 12.6 4 . 120 0.645 11.6 4 . 110 0.618 10. 1 4. 290 0.588 8.70 4 . 990 0.589 7.86 5. 090 0.565 7.35 5. 060 0.546 6 91 5. 240 0.538 6.43 5. 180 0.516 5.77 S. 210 0.491 5. 16 5. 310 0.468 4.24 8. 610 0.436 j ) B - C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 . T 1 0\ " e f f . 304 .8 1 .530 1 .93 302 .9 1 .540 1 .93 302.7 1 .500 1 .90 279. 3 1 .680 1 .94 278 .6 1 .660 1 .92 278.3 1 .650 1.91 254 .2 1 .800 1.91 253.7 1 .800 1 .91 253.5 1 .800 1.91 229.6 1 .960 1 .90 229.3 1 .960 1 .90 228. 2 1 .950 1 . B9 204 .2 2. 180 1.69 203.3 2. 180 1 .88 202 .9 2 200 1 .89 179.7 2.500 1 .90 178.8 2 .550 1.91 177 . 3 2 .510 1 .89 155.3 2.850 1 .86 153.8 2 .900 1 .89 153.3 2.900 1 . 8 8 130.6 3.380 1 . 8 8 128.0 3.440 1 . 8 8 128.0 3.440 1 . 8 8 107 .4 4 . 100 1 . 8 8 107.3 4. 180 1 ,89 107 . 2 4 . 100 1 .87 82 .4 5.510 1 .91 80.0 5.650 1 .90 79.0 5.640 1 .69 69.0 6.450 1 .89 59.3 7.520 1 .69 42 .0 10.830 1 .91 36 .0 12.730 1.91 30.7 15.180 1 .93 27.9 16.830 1 .94 25 .0 18.930 1 .95 22 .5 21 .030 1 .95 22 1 21 .750 1 .96 19.95 23.940 1 .95 18.3 26.420 1 .97 16 25 30.160 1 .98 14.5 34.800 2 .01 12.5 41 .100 2.03 10.6 50.140 2 .06 8.73 63.890 2.11 6.98 86 030 2. 19 6. 15 103 6B0 2.26 5. 18 129.580 2.32 4 .80 145.250 2 . 36 4.30 169.360 2.41 - 261 -k) a ' - C u [ ( n - C 1 2 H 2 5 ) 2 P 0 2 ] 2 . T l0\ "eff. SOS.4 1.340 1.81 281 .2 1 .440 1 .80 255. 1 1 .680 1 .85 230.4 1.790 1 .82 202.3 1.960 1.78 175.5 2.290 1.79 154.0 2.480 1.75 129.2 2.810 1 .70 107.9 3.200 1 .66 95.2 3.490 1 .63 81 . 1 3.960 1 .60 C6.6 4.290 1 .51 BO.6 4.800 1 .39 36 1 5.670 1 .28 24 8 C.660 1 . 15 20.4 7.480 1 . 11 16.9 8.580 1 .08 16.0 8.940 1 .07 14 .7 9.640 1 .06 11.5 11 .610 1 .03 10.35 13.060 1 .04 6.62 15.970 1 .05 6.05 24.BB0 1 . 10 5.20 29.950 1 . 12 4.45 37.220 1 . 15 1) C u [ ( l - C 3 H 7 ) 2 P 0 2 ] 2 . T(K) lO^X-a (cm 3mol~ 1) u E F F # ( B . M . ) T(K) (cm •'mol"*) H e f f . ( B . M . ) T(K) I O 6 * . (an 3mol _ 1) "eff . ( B . M . ) 302.1 1,410 1.85 227.0 1,890 1.85 128.2 3,390 1.86 302.0 1,410 1.85 202.9 2,130 1.86 127.5 3,380 1.86 276.9 1,550 1.85 202.6 2,160 1.87 107.4 4,090 1.87 276.8 1,550 1.85 178.2 2,430 1.86 107.4 4,110 1.88 252.2 1,710 1.86 176.9 2,460 1.86 78.3 5,660 1.88 252.1 1,700 1.85 154.4 2,820 1.87 77.5 5,730 1.89 227.3 1,910 1.86 152.0 2,810 1.85 m) Cu[( t - C „ H 9 ) 2 P 0 2 ] 2 . T(K) (cm'mol - 1) H E F F # ( B . M . ) T(K) (cm 3mol~ A) r - e f f . ( B . M . ) T(K) l o 6Xm (cm 3mol~ l) " e f f . ( B . M . ) 305.1 1,480 1.90 227.1 1,890 1.85 131.0 3,280 1.85 302.4 1,430 1.86 205.5 2,150 1.88 128.4 3,240 1.82 279.6 1,590 1.88 200.7 2,130 1.85 111.0 3,950 1.87 276.6 1,540 1.85 179.8 2,450 1.88 107.1 4,000 1.85 254.6 1,750 1.89 178.7 2,390 1.85 82.8 5,280 1.87 251.3 1,680 1.84 155.3 2,810 1.87 77.5 5,470 1.84 229.4 1,920 1.87 153.5 2,730 1.83 - 263 -N> N> N> IO tO CO CO NUIUIMNIOO oo r o c o V I oo r o co • • • • • • • ON CO K> 4 > CO OO 4 > r o O 00 00 ON ON U l U l 00 U l v l 00 00 U l ON o o o o o o o v© NO NO NO VO NO NO c n c o 4> co c o 4> U I H H H H N N N U l U l M v l O O N W v i ON CO N U M • • • • • • • W M W O H U i b ) c o t o r o r o r o r o r o o NO ON ON c o r o o W ON ON H H 00 *> o o o o o o © NO VO NO ^9 vO NO c o c o J> co c o c o c o oo o o r o 4> co t o v j oo o • • • • • UN 00 v l 00 00 U l 4 > 4 > CO CO «• w w w « cn cn 4> c n r o 8 »— r - 00 00 o o o o NO NO NO \D NO r o c o u i t o t o H 0 s CO ON 8r H v^ U> ON if 00 EC H B O CO ON o r (0 CO o c 9 I f l ON SS t— to •0 o to to t o t o r o t o t o c o c o 4> U l v i v l 00 O O • • • • • • • 00 v i c o t o t o t o oo oo ON ON u i *- *~ ON O * - t-> U l U l 00 o o o o o o o CO vO 00 00 00 00 00 O O NO NO vO v i vO H H H H N N N U l ON v i NO O H M N v i u H H v i v i • • • • • • • v i O U l U l O O ON t o r o t o r o t o t o r " NO v i ON CO t o r-1 NO NO CO Q 00 ON O v l O O O O O O O NO NO NO NO NO NO 00 r-> r " » - • » - • r-1 NO 00 O O t o CO CO 4 > 00 v l SO • • • • • v l O t o O O U l 4> 4> CO CO « « w- w w c n ** * * ON c o ON oo co co t o o o o o o NO NO SO NO NO c o c o ON t o t o H n e 3 5 U l ON o ON a U l w to 3 to 0B H /~v 8 5 CO ON 8^ H 8 5 CO ON sr. i p) C u [ ( n - C 1 0 H 2 1 ) ( H ) P O 2 ] 2 . T(K) i o 6 x u (B.M.) T(K) 10 6X u (B.M.) T(K) i o 6 x u (B.M.) e f f . ( c m 3 m » l - 1 ) e f f . ( c n ^ m B l - 1 ) e f f . 303.0 1,570 1.95 227.5 2,030 1.92 130.6 3,570 1.93 302.1 1,560 1.94 205.4 2,290 1.94 129.3 3,600 1.93 279.6 1,670 1.93 204.6 2,300 1.94 110.0 4,280 1.94 279.4 1,680 1.94 181.7 2,560 1.93 106.7 4,320 1.92 255.4 1,840 1.94 177.3 2,600 1.92 82.4 5,600 1.92 255.1 1,820 1.93 153.3 3,040 1.93 80.3 5,680 1.91 229.3 2,030 1.93 145.L 3,210 1.93 q) Cu [(C 6H 5)(H)PC T(K) i o 6 x u (B.M.) T(K) i o 6 x u (B.M.) T(K) i o 6 x u (B.M.) e f f . ( c m ^ B l - 1 ) e f f . ( c m 3 m B l _ 1 ) e f f . 304.0 1,520 1.92 227.2. 2,030 1.92 141.4 3,140 1.88 304.0 1,500 1.91 204.0 2,230 1.91 128.8 3,490 1.90 279.2 1,630 1.91 201.3 2,270 1.91 109.3 4,160 1.91 277.4 1,660 1.92 179.8 2,560 1.92 104.3 4,170 1.86 254.5 1,780 1.91 179.6 2,520 1.90 86.8 4,940 1.85 252.6 1,810 1.91 158.0 2,820 1.89 79.3 5,400 1.85 229.2 1,980 1.91 154.0 2,960 1.91 78.0 5,530 1.86 

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