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The synthesis, magnetic and mossbauer spectral properties of poly-[mu]-bis (di-n-octylphosphinato) iron(II)… Peers, James Richard Douglas 1989

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T H E S Y N T H E S I S , M A G N E T I C A N D M O S S B A U E R S P E C T R A L P R O P E R T I E S O F P O L Y - ^ - B I S ( D I - N - O C T Y L P H O S P H I N A T O ) I R O N ( I I ) A N D I T S Z I N C ( I I ) - D O P E D A N A L O G U E S by J A M E S R I C H A R D D O U G L A S P E E R S B . S c , The U n i v e r s i t y of B r i t i s h Columbia, 1986 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES Department of Chemistry We accept t h i s t h e s i s as conforming to the r e q u i r e d standard The U n i v e r s i t y of B r i t i s h Columbia October, 1989 © James Richard Douglas Peers, 1989 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of C U ^ i l S \C The University of British Columbia Vancouver, Canada Date 13 OcM&C ( W DE-6 (2/88) A B S T R A C T The inorganic coordination polymer, poly-u-bis(di-n-octylphosphinato)iron(II), (Fe[(n-C H ) PO ] } , 8 17 2 2 n was prepared and characterized. The physical properties of t h i s compound were analyzed using d i f f e r e n t i a l scanning calorimetry, v i b r a t i o n a l , e l e c t r o n i c and Mossbauer spectroscopy and temperature dependent magnetic s u s c e p t i b i l i t y studies. Evidence for polymorphism i n t h i s compound was found, leading to the postulation of the existence of two forms of t h i s material, l a b e l l e d I and I I . Evidence was seen suggesting that a Form I to Form II t r a n s i t i o n occurs upon the application of pressure. D i f f e r e n t i a l scanning calorimetry r e s u l t s suggested that t h i s t r a n s i t i o n was not thermally induced over the temperature range 35 to 300°C. Both forms were suggested to be four-coordinate and to possess a highly compressed tetrahedral metal-oxygen chromophore. Mossbauer spectral studies suggested that the iron(II) centres i n t h i s material were i n the rare t r i p l e t ground state, giving an intermediate spin S=l system. Mossbauer spectroscopy also showed a substantial p o s i t i v e contribution to the s p l i t t i n g of the S=l quadrupole doublet, possibly as a r e s u l t of a— donation properties of the ligands. The magnetic s u s c e p t i b i l i t y vs. temperature data, c o l l e c t e d i n the range of 2-80 K and analyzed according to a l i n e a r chain Heisenberg S=l model, showed the iron centres to be antiferromagnetically coupled and also to have unexpectedly large Lande s p l i t t i n g factor, g. The high g value was presumed to be the r e s u l t of large o r b i t a l angular momentum contributions. Based on these r e s u l t s , e l e c t r o n i c structure schemes were proposed for i i Forms I and I I . In a d d i t i o n , z i n c ( I I ) - d o p e d samples of t h i s compound, {Fe Zn [ (n-C H ) PO ] } , were prepared w i t h x=0.05, 0.1 and l -x x 8 11 2 2 2 n r e , 0.2. These compounds were analyzed by d i f f e r e n t i a l scanning c a l o r i m e t r y , v i b r a t i o n a l and Mossbauer sp e c t r o s c o p y and temperature dependent magnetic s u s c e p t i b i l i t y s t u d i e s and a l s o appeared t o occur i n the polymorphic forms I and I I . Mossbauer sp e c t r o s c o p y again suggested the presence of i r o n (II) S=l c e n t r e s , but a l s o showed the presence of S=2 i r o n ( I I ) . T h i s l e d t o the p r o p o s a l t h a t the e f f e c t of doping z i n c ( I I ) i n t o t h i s system i s t o d i s t o r t the geometries of the i r o n c e n t r e s adjacent t o the z i n c c e n t r e s t o a more t e t r a h e d r a l c o n f i g u r a t i o n . A l a r g e quadrupole s p l i t t i n g was observed f o r the S=2 l i n e s , a g a i n perhaps a r e s u l t of s u b s t a n t i a l cr-donation from the l i g a n d s . Magnetic s u s c e p t i b i l i t y vs. temperature data were a l s o c o l l e c t e d over the range 2-80 K f o r these samples; the d e t a i l s of these r e s u l t s are d i s c u s s e d i n a q u a l i t a t i v e manner. i i i Table of Contents Page A b s t r a c t i i Table of Contents i v L i s t of Tables v i L i s t of F i g u r e s v i i L i s t of A b b r e v i a t i o n s and Symbols i x Acknowledgements x CHAPTER I INTRODUCTION 1 I.A. Poly(metalphosphinates) 1 I.B. T r a n s i t i o n Metal D i - n - o c t y l p h o s p h i n a t e s 3 I. C. Aim of the Present Work and T h e s i s O u t l i n e 7 Chapter I References 9 CHAPTER II RESULTS AND DISCUSSION I: POLY-u-BIS(DI-N-OCTYLPHOSPHINATO)IRON(II) 12 I I . A. Syntheses 12 II.B. I n f r a r e d S p e c t r a 14 II.C. Thermal S t u d i e s 20 II.D. Mossbauer Spectroscopy 23 I I . E . E l e c t r o n i c Spectroscopy 33 I I . F. Magnetic S u s c e p t i b i l i t y Measurements 36 Chapter II References 53 CHAPTER I I I RESULTS AND DISCUSSION I I : ZINC DOPED POLY-u-BIS(DI-N-OCTYLPHOSPHINATO)IRON(II) 56 I I I . A. Syntheses 56 I I I . B . I n f r a r e d S p e c t r a 57 I I I . C . Thermal S t u d i e s 58 III.D. Mossbauer Spectroscopy 60 I I I . E . Magnetic S u c e p t i b i l i t y Measurements 65 Chapter I I I References 70 CHAPTER IV CONCLUSIONS AND SUGGESTIONS FOR FURTHER WORK 71 CHAPTER V EXPERIMENTAL 74 V.A. M a t e r i a l s and P r e p a r a t i v e Techniques 74 V.B. Elemental Analyses 74 V.C. I n f r a r e d Spectroscopy 74 V.D. E l e c t r o n i c Spectroscopy 74 V.E. Magnetic S u s c e p t i b i l i t y Measurements 74 V.F. Mossbauer Spectroscopy 76 i v V.G. Syntheses 76 Gl. Synthesis of Di-n-octylphosphinic Acid, ( C 8 H 1 7 ) 2 P 0 2 H 2 76 G2. Synthesis of Bis(di-n-octylphoshinato)iron(II), F e [ ( C 8 H 1 7 ) 2 P 0 2 ] 2 77 G2.1 F e [ ( C g H 1 7 ) 2 P 0 2 ] 2 ' s a m P l e 1 7 7 G2.2 F e [ ( C g H 1 7 ) 2 P 0 2 ] 2 , sample 2 78 G2.3 F e [ ( C g H 1 7 ) 2 P 0 2 ] 2 , sample 3 78 G2.4 F e [ ( C g H 1 7 ) 2 p 0 2 ] 2 ' s a m P l e 4 7 9 G3. Synthesis of Bis(di-n-octylphosphinato)zinc (II), Z n [ ( C g H 1 7 ) 2 P 0 2 ] 2 79 G4. Preparation of Mized-Metal Compounds, F e l - x Z n x [ ( C 8 H 1 7 > 2 P ( V 2 8 0 G4.1 F e 0 < 8 Z n 0 > 2 [ ( C 8 H 1 7 ) 2 P O 2 ] 2 , sample 5 80 G4.2 F e 0 > 9 Z n 0 ^ [ ( C g H 1 7 ) 2 P 0 2 ] 2 , sample 6 80 G4.3 F e 0 ; 9 5 Z n * # 0 5 [ ( C 8 H 1 7 ) 2 P O 2 ] 2 , sample 7 81 G4.4 F e 0 1 Z n 0 9 [ ( C g H 1 7 ) 2 P O 2 ] 2 81 V.H. Attempted Syntheses 82 HI. F e [ ( C g H 1 3 ) 2 P 0 2 ] 2 8 2 H2. F e 0 > 9 C d 0 1 t ( C 8 H 1 7 ) 2 P O 2 ] 2 82 Chapter V References 84 APPENDIX I Assignment of Infrared Data 85 APPENDIX II Magnetic S u s c e p t i b i l i t y Data 92 v L i s t of Tables Page 2.1 Frequencies of i>(P02) regions i n various various metal(phosphinate)polymers 16 2.2 P0 2 stretching frequencies, compounds 1-4 20 2.3 Mossbauer parameters for compound 2 2 9 2.4 Comparison of the Fisher, Lines and Weng S=l models for compound 2 44 2.5 Magnetic parameters for compounds 1-4, Fisher model 45 3.1 Infrared stretching frequencies of the v(P02) regions of doped samples Fe Zn [ (C H ) PO ] 57 ^ ^ l-X X 8 17' 2 2 J 2 3.2 Mossbauer spectral parameters for zinc-doped compounds 60 v i L i s t of F i g u r e s Page 1.1 S t r u c t u r e s of C u [ ( C H ) PO ] and 2 5 2 2 2 Mn [ (CH ) PO ] -2H 0 2 3 2 2 2 2 2.1 Comparison of P0 2 s t r e t c h i n g r e g i o n s of u n t r e a t e d and ground sample 1 19 2.2 Thermograms of u n t r e a t e d and ground samples of compounds 4 22 2.3 Decay scheme f o r 5 7Co 24 2.4 Mossbauer s p e c t r a of u n t r e a t e d and ground forms of compound 2 at 77 K 28 2.5 E l e c t r o n i c c o n f i g u r a t i o n s as a f u n c t i o n of symmetry f o r Fe ( I I ) complexes 30 2.6 E l e c t r o n i c spectrum i n the n e a r - i n f r a r e d r e g i o n of compound 1 34 2.7 M a g n e t i c a l l y c o n c e n t r a t e d systems 38 2.8 Magnetic s u s c e p t i b i l i t y vs. temperature p l o t of compound 1 , u n t r e a t e d 39 2.9 Magnetic s u s c e p t i b i l i t y vs. temperature p l o t of compound 2, u n t r e a t e d 39 2.10 Magnetic s u s c e p t i b i l i t y vs. temperature p l o t o f compound 2, untreated, Weng model 43 2.11 Magnetic s u s c e p t i b i l i t y vs. temperature p l o t of compound 2, u n t r e a t e d , L i n e s model 43 2.12 Magnetic s u s c e p t i b i l i t y vs. temperature p l o t o f compound 1-4, u n t r e a t e d 46 2.13 Comparison of magnetic s u s c e p t i b i l i t y vs. temperature of u n t r e a t e d and ground samples of compound 1 4 7 2.14 Magnetic s u s c e p t i b i l i t y vs. temperature of compound 1, ground 47 2.15 Magnetic s u s c e p t i b i l i t y vs. temperature f o r compound 3, u n t r e a t e d 4 9 2.16 Magnetic s u s c e p t i b i l i t y vs. temperature f o r compound 4, u n t r e a t e d 4 9 2.17 Comparison of the magnetic s u s c e p t i b i l i t y vs. temperature behaviours of u n t r e a t e d and ground samples of compound 3 50 v i i 2.18 Magnetic s u s c e p t i b i l i t y vs. temperature plot of compound 3, ground 50 2.19 Magnetic s u s c e p t i b i l i t y vs. temperature plots for compound 2, varying g and J 52 3.1 Thermograms of sample 6 (x=0.1) 59 3.2 Mossbauer spectrum of compound 5 (x=0.2) at 77 K 61 3.3 Mossbauer spectrum of compound 6 (x=0.1) at 77 K 61 3.4 Mossbauer spectrum of compound 7 (x=0.05) at 77 K 62 3.5 Magnetic s u s c e p t i b i l i t y vs. temperature plo t s of untreated and ground samples of compound 5 (x=0.2) 66 3.6 Magnetic s u s c e p t i b i l i t y vs. temperature plo t s of untreated and ground samples of compound 6 (x=0.1) 66 3.7 Magnetic s u s c e p t i b i l i t y vs. temperature p l o t of compound 7 (x=0.05), untreated 68 v i i i L i s t of A b b r e v i a t i o n s and Symbols NMR EPR v - l cm IR DSC Me OH asy sym s m w sh N k 8 AE Q EFG r g * M B.M. nuclear magnetic resonance e l e c t r o n paramagnetic resonance i n f r a r e d s t r e t c h i n g frequency r e c i p r o c a l centimeters i n f r a r e d d i f f e r e n t i a l scanning c a l o r i m e t r y methanol asymmetric symmetric strong medium weak shoulder Avogadro's number Boltzmann's constant isomer s h i f t quadrupole s p l i t t i n g e l e c t r i c f i e l d g r a d i e n t Mossbauer l i n e w i d t h Lande s p l i t t i n g f a c t o r molar magnetic s u s c e p t i b i l i t y e f f e c t i v e magnetic moment Bohr magneton i x A C K N O W L E D G E M E N T S I would f i r s t l i k e to express my s i n c e r e thanks t o my research s u p e r v i s o r s , Dr. R.C. Thompson and Dr. J.R. Sams, f o r t h e i r help and patience during the d u r a t i o n of my research i n t h e i r l a b s . My g r a t i t u d e and best wishes a l s o go t o the members of my l a b group f o r t h e i r t e c h n i c a l a s s i s t a n c e , companionship and good humour. S p e c i a l thanks a l s o t o M a r t i n E h l e r t , Tom Otieno and Mark Aston f o r t h e i r a s s i s t a n c e w i t h the p r o o f r e a d i n g of t h i s manuscript. I am a l s o indebted t o Mr. B i l l Lake, f o r generously a l l o w i n g me t o use the l a s e r p r i n t e r i n h i s o f f i c e , thus a v e r t i n g a major d i s a s t e r . I would a l s o l i k e t o extend fond regards t o my f r i e n d s and colleagues here i n the chemistry department at UBC, who made my time here very enjoyable, humourous and even s l i g h t l y t u n e f u l at times. Thanks are a l s o i n order t o the s t a f f of the mechanical, e l e c t r o n i c and glassblowing shops f o r t h e i r e x c e l l e n t work. Without the s k i l l of these people, the work de s c r i b e d i n t h i s t h e s i s would l i t e r a l l y be i m p o ssible. I would a l s o l i k e to thank Mr. Peter Borda f o r h i s m i c r o a n a l y t i c a l s e r v i c e s . F i n a l l y , I would l i k e t o express my s p e c i a l thanks to my parents f o r t h e i r support over these past two years. Most im p o r t a n t l y , I thank my mom f o r g e t t i n g b e t t e r . x I . I N T R O D U C T I O N A . P O L Y ( M E T A L P H O S P H I N A T E S ) Work on poly(metalphosphinate) compounds has been approached from a v a r i e t y of d i f f e r e n t angles over the years. A f t e r the polymeric nature of UO [ (n-C H ) PO ] was confirmed i n 1959 1, r l 2 1 4 9 2 2 J 2 ' research centred on the fo r m u l a t i o n of m a t e r i a l s w i t h p l a s t i c 2-10 . p r o p e r t i e s . At tha t time, some work was a l s o being conducted on changing the s u b s t i t u e n t s on phosphorus and u s i n g d i f f e r e n t m e t a l s 1 1 . Only r e c e n t l y , the employment of such techniques as 3 1P 12 13 • N.M.R. ' , e l e c t r o n paramagnetic resonance (EPR) spectroscopy, s p e c i f i c heat, and v a r i a b l e temperature magnetic s u s c e p t i b i l i t y 1 4 measurements has demonstrated the wealth of i n t e r e s t i n g m icroscopic p r o p e r t i e s of these compounds. One d i f f i c u l t y i n t h i s research has always been the i s o l a t i o n of s i n g l e c r y s t a l s f o r X-ray a n a l y s i s , although some success has been encountered f o r sh o r t e r chain a l k y l - and arylphosphinates. Two r e p r e s e n t a t i v e s t r u c t u r e s are shown f o r t h i s c l a s s of compound i n Fig u r e s I . l . a and I . l . b . I t can be seen from these diagrams t h a t the metal i n v o l v e d may be f o u r - or s i x - c o o r d i n a t e . F i v e - c o o r d i n a t e metal phosphinate systems have a l s o been observed 1 5. The geometry about the c e n t r a l metal atom plays a v i t a l r o l e i n determining the magnetic p r o p e r t i e s of t r a n s i t i o n metal complexes and the v a r i e t y of d i f f e r e n t geometries a v a i l a b l e i n poly(metalphosphinates) gives us i n t e r e s t i n g model systems f o r the study of magneto-structural c o r r e l a t i o n s . 3 1P NMR s t u d i e s of s e v e r a l poly(metalphosphinates) have shown 1 2 e l e c t r o n d e l o c a l i z a t i o n onto the phosphorus atom, causing magnetic superexchange between adjacent metal centres 1 Figure 1.1a. Section of the Figure 1.1b. Section of the C u [ ( C 2 H 5 ) 2 P 0 2 ] 2 chain (Ref. 16). Mn[(CH 3 )PO 2 ] 2 .2H 2 0 chain (Ref. 17). 2 through the b r i d g i n g phosphinate l i g a n d . This superexchange mechanism forms the b a s i s f o r many i n t e r e s t i n g s t u d i e s of the magnetic s u s c e p t i b i l i t y behaviour of these phosphinate bridged compounds, and has been seen before w i t h other types of b r i d g i n g i • J 1 8 , 1 9 l i g a n d s B . T R A N S I T I O N M E T A L D I - N - O C T Y L P H O S P H I N A T E S The research described i n t h i s t h e s i s concentrates on the di-n- o c t y l p h o s p h i n a t e of i r o n ( I I ) and i t s z i n c ( I I ) - d o p e d analogues. Some previous research which has been c a r r i e d out on di-n- o c t y l p h o s p h i n a t e polymers of d i v a l e n t metals w i l l now be reviewed. H.D. G i l l m a n 2 0 ' 2 1 synthesized the di-n-octylphosphinates of C r ( I I ) , Mn(II), F e ( I I ) , N i ( I I ) , Co (II) and Cu(II) and c h a r a c t e r i z e d them by i n f r a r e d and U V / v i s i b l e spectroscopy and d i f f e r e n t i a l scanning c a l o r i m e t r y . Room temperature magnetic s u s c e p t i b i l i t y measurements were a l s o conducted by Gillman i n t h i s study, although magnetic s t u d i e s on the Fe and Cr analogues were not i n c l u d e d due t o the a i r - s e n s i t i v e nature of these m a t e r i a l s . Later s t u d i e s by Banks 2 2, O l i v e r et a l . , 2 3 Haynes et al. 2 4 , 2 5 and Pe e r s 2 6 examined the N i , Co and Cu species f u r t h e r , i n c l u d i n g v a r i a b l e temperature magnetic s u s c e p t i b i l i t y measurements. The s y n t h e s i s of po l y ( d i - n - o c t y l p h o s p h i n a t e ) compounds u s u a l l y i n v o l v e s r e a c t i n g the metal c h l o r i d e , acetate or sulphate w i t h p a r t i a l l y n e u t r a l i z e d d i - n - o c t y l p h o s p h i n i c a c i d . In cases where the metal sulphate i s used as a s t a r t i n g reagent, i t has been found t h a t excess water should be added a f t e r a d d i t i o n of the metal sulphate t o prevent the formation of a sulphate copolymer 2 3. S o l u b i l i t y s t u d i e s i n a wide range of so l v e n t s of va r y i n g 3 d i e l e c t r i c constant have shown the metal di-n-octylphosphinate polymers to be insoluble or sparingly soluble i n a l l solvents tested except strong acids, which decompose the compounds 2 2 - 2 6. Unfortunately, there are as yet no known c r y s t a l structures for the di-n-octylphosphinate polymers. Characterization therefore i s incomplete, but good estimates of the structures of these compounds may be made by the use of such diagnostic tools as i n f r a r e d (IR) and UV/visible spectroscopy, Mossbauer spectroscopy, X-ray powder d i f f r a c t i o n , and EPR spectroscopy. The paramagnetic nature of the metal atom has lar g e l y precluded the s t r u c t u r a l characterization of these compounds by NMR. As mentioned e a r l i e r , some short chain a l k y l - and arylphosphinate species have provided single c r y s t a l s for X-ray analysis and the spectral data from those compounds with known structures can be compared to those for compounds where single c r y s t a l s have not been obtained, thus 2 3 2 6 providing i n d i r e c t s t r u c t u r a l information on the l a t t e r ' . The Co (II) and Cu(II) di-n-octylphosphinates have both been t » 2 1 2 2 shown to occur i n two polymorphic forms. The Co (II) polymer ' obtained from solution i s a l i g h t blue colour; on heating to about 80°C, i t undergoes an apparent t r a n s i t i o n to a navy blue material. UV/visible spectroscopy data indicate that the l i g h t blue form i s pseudooctahedral and the navy blue form i s pseudotetrahedral. Infrared studies reveal three P0 2 stretching bands at 1140, 1070 and 1015 cm-1 for the pseudooctahedral compound and only two bands at 1130 and 1050 cm-1 for the pseudotetrahedral form. The three bands seen for the pseudooctahedral form imply the presence of two d i f f e r e n t phosphinate groups, with two of the bands overlapping. A two-band v(PO ) region indicates the presence of only one type 4 of phosphinate ligand. Oliver found that Cu [ (CgH^) 2P0 2] 2 occurred i n two forms, a r b i t r a r i l y l a b e l l e d a and 0. The highly compressed tetrahedral a form, when melted at 135°C and then cooled, underwent an i r r e v e r s i b l e change to the less compressed p form. The 0 form had a melting point at around 98°C. In t h i s case, the IR data for the P0 2 stretching region were inconclusive, but UV/visible data suggest a relaxation from a more to a less compressed tetrahedral chromophore on going from the a to the 0 form. Variable temperature magnetic s u s c e p t i b i l i t y measurements have been performed on the Co, Cu and Ni complexes by the workers mentioned e a r l i e r , y i e l d i n g i n t e r e s t i n g r e s u l t s . The two forms of Co[(C H ) PO ] both display antiferromagnetic exchange; however, 8 17 2 2 2 the exchange i s stronger i n the case of the pseudooctahedral form (vide i n f r a ) . Magnetic s u s c e p t i b i l i t y data for the two forms of Cu [ (CgHi7) 2P0 2] 2, obtained by Haynes et al.2A show the a (highly compressed tetrahedral) form to exhibit antiferromagnetic magnetic exchange, while the 0 (less compressed tetrahedral) form i s weakly ferromagnetic. The Ni(II) di-n-octylphosphinate complex 2 6 shows quite unusual magnetic s u s c e p t i b i l i t y behaviour, but no evidence of polymorphism over the temperature range studied. Instead, the compound Ni[(CgH^) 2P0 2] 2 exhibits ferromagnetic exchange, with a t r a n s i t i o n to an antiferromagnetic state at around 6 K. The compound, moreover, shows field-dependent behaviour, also consistent with ferromagnetic exchange. The antiferromagnetic ordering at low temperatures i s quite possibly interchain coupling which may become important at low thermal energies. 5 A b r i e f d i s c u s s i o n of what i s known about the i n f l u e n c e of geometry on magnetic exchange i n these compounds should be u s e f u l here. There are two pathways f o r magnetic exchange, the <r and n 24 pathways. I t has been argued th a t cr-type o r b i t a l overlap provides the ferromagnetic exchange pathway, wh i l e i r-type o r b i t a l overlap i s the pathway conducive t o a n t i f e r r o m a g n e t i c exchange. I t has a l s o been seen th a t the magnitude of exchange i n ferromagnetic systems i s r e l a t i v e l y i n s e n s i t i v e t o small changes i n geometry, a consequence of o—type o r b i t a l overlap being b a s i c a l l y t h a t of two spheres. Conversely, i r-type o r b i t a l overlap i s q u i t e s e n s i t i v e t o small changes i n geometry; thus the magnitude of an t i f e r r o m a g n e t i c c o u p l i n g i s s e n s i t i v e t o s u b t l e changes i n geometry. Both pathways may be a v a i l a b l e , but the an t i f e r r o m a g n e t i c c o u p l i n g i s t y p i c a l l y of gr e a t e r magnitude than ferromagnetic c o u p l i n g . We now consider Cu(II) systems f o r the sake of s i m p l i c i t y , s ince there w i l l be only one unpaired e l e c t r o n i n t h i s system, thus g i v i n g one. magnetic o r b i t a l . I f the geometry about the copper atom i s p u r e l y t e t r a h e d r a l , there w i l l be only very weak jr overlap, so the <r pathway w i l l dominate, g i v i n g weak ferromagnetic exchange. Now, i f the symmetry about copper i s f l a t t e n e d t o give a squashed tetrahedron, there w i l l be b e t t e r overlap between the magnetic o r b i t a l of the metal and the n o r b i t a l cloud, which i n t u r n w i l l g ive r i s e t o measurable a n t i f e r r o m a g n e t i c exchange. However, i f the chromophore i s f l a t t e n e d f u r t h e r , u n t i l square planar symmetry i s achieved, the exchange w i l l once again be ferromagnetic because the net n overlap w i l l be zero, l e a v i n g only the <r pathway f o r exchange. Obviously, t h i s model w i l l be more complicated i n systems with 6 more than one unpaired e l e c t r o n , but the same geometrical c o n s i d e r a t i o n s may be used to p r e d i c t the type of magnetic exchange observed. This a n a l y s i s concurs w i t h observations of phosphinate systems made i n our group 2 3" 2 5. T h e o r e t i c a l treatments are a v a i l a b l e t o e x p l a i n the e f f e c t s of changing the l i g a n d f i e l d geometry about the metal atom using extended Huckel c a l c u l a t i o n s 2 7 - 2 9 as w e l l as a l i g a n d f i e l d theory approach 3 0, g i v i n g good agreement between the two separate treatments. Experimental r e s u l t s seem to confirm the conclusions of these t r e a t m e n t s 3 1 - 3 5 : the observations have been that ferromagnetic exchange i s seen i n square p l a n a r chromophores; t w i s t i n g towards t e t r a h e d r a l symmetry causes the exchange to become a n t i f e r r o m a g n e t i c , but greater d i s t o r t i o n towards tetrahedral.symmetry causes the exchange t o become ferromagnetic again. C . A I M O F T H E P R E S E N T W O R K A N D T H E S I S O U T L I N E The aim of the work described i n t h i s t h e s i s was t o examine the di - n - o c t y l p h o s p h i n a t e of i r o n (II) i n l i g h t of the i n f o r m a t i o n known about the other poly(metalphosphinates). Because of the ease of o x i d a t i o n of i r o n ( I I ) t o i r o n ( I I I ) the study of i r o n ( I I ) phosphinates presents a s y n t h e t i c challenge not present i n the study of the C o ( I I ) , N i ( I I ) and Cu(II) analoques. O f f s e t t i n g the s y n t h e t i c d i f f i c u l t i e s inherent i n studying i r o n ( I I ) compounds i s the f a c t t h a t i r o n i s a Mossbauer a c t i v e nucleus. I t was a n t i c i p a t e d t h a t 5 7Fe Mossbauer s t u d i e s would provide unique i n s i g h t s i n t o the s t r u c t u r e s and magnetic p r o p e r t i e s of p o l y (metalphosphinates) . To our knowledge, t h i s study represents 7 the f i r s t Mossbauer s p e c t r a l c h a r a c t e r i z a t i o n of a poly(metalphosphinate) system. The second aim of t h i s work was t o create a mixed metal system, i n which a non-magnetic i o n (zinc ( I I ) ) i s doped i n t o t h i s i r o n (II) system i n small q u a n t i t i e s . I t was a n t i c i p a t e d t h a t z i n c doping would i n f l u e n c e the p h y s i c a l p r o p e r t i e s of these m a t e r i a l s i n a i n t e r e s t i n g manner. In Chapter I I the r e s u l t s and d i s c u s s i o n f o r our s t u d i e s on F e [ ( C H ) PO ] are presented, while i n Chapter I I I the so c a l l e d 8 17 2 2 2 c doped systems, Fe Zn [ (C H ) PO ] , are discussed. A summary ^ J l-x x 8 17 2 2 2' 1 and suggestions f o r f u r t h e r work are provided i n Chapter IV. Experimental d e t a i l s can be found i n Chapter V. 8 C H A P T E R I R E F E R E N C E S 1. Healy, T.V.; Kennedy, J . J. Inorg. Nucl. Chem. 1959, 10, 128. 2. N a n n e l l i , P.; Block, B.P.; King, J.P.; Saraceno, A.J.; Sprout, O.S.; Peschko, N.D.; Dahl, G.J. J. Polym. Sci., Polym. Chem. Ed. 1973, 11, 2691. 3. N a n n e l l i , P.; Gillman, H.D.; Block, B.P. J. Polym. Sci., Polym. Chem. Ed. 1975, 13, 2849. 4. Block, B.P.; Rose, S.H.; Schaumann, C.W.; Roth, E.S.; Simkin, J . J. Am. Chem. Soc. 1962, 84, 3200. 5. C r e s c e n z i , V.; G i a n c o t t i , V.; Ripamonti, A. J. Am. Chem. Soc. 1965, 87, 391. 6. Rose, S.H.; Block, B.P. J. Am. Chem. Soc. 1965, 87, 2076. 7. Rose, S.H.; Block, B.P. J. Polym. Sci A-l 1966, 4, 573. 8. Rose, S.H.; Block, B.P., ibid, 583. 9. Delman, A.D.; K e l l y , J . ; Mironov, J . ; Simms, B.B. J. Polym. Sci. A-l 1966, 4, 1277. 10. P i t t s , J . J . ; Robinson, M.A.; T r o t z , S.I. J. Inorg. Nucl. Chem. 1968, 30, 1299. 11. P i t t s , J . J . ; Robinson, M.A.; T r o t z , S.I. J. Inorg. Nucl. Chem. 1969, 31, 3685. 12. Smith, L.S.; Newman, P.R.; Heeger, A . J .; G a r i t o , A.F.; Gill m a n , H.D. N a n n e l l i , P. J. Chem. Phys. 1977, 66, 5428. 13. Giordano, F.; Randaccio, L.; Ripamonti, A. J. Chem. Soc. Chem. Comm. 1967, 1239. 14. Stahlbush, R.E.; Bastuscheck, CM.; Raychaudhuri, A.K.; Sc o t t , J . C ; Grubb, D.; Gillman, H.D. Phys. Rev. B 1981, 23, 3393. 15. Betz, P.; Bino, A. Inorg. Chim. Acta 1988, 147, 109. 9 16. Oliver, K.W.; Rettig, S.J.; Thompson, R.C; Trotter, J. Can. J. Chem. 1982, 60, 2017. 17. Cicha, W.V.; Haynes, J.S.; Oliver, K.W.; Rettig, S.J.; Thompson, R.C; Trotter, J. Can. J. Chem. 1985, 63, 1055. 18. C a r l i n , R.L.; van Duyneveldt, A.J. Magnetic Properties of Transition Metal Compounds, Springer-Verlag, New York, 1977. 19. M i l l e r , J.S. ed. Extended Linear Chain Compounds, Vol. 3, Plenum Press, New York, 1983. 20. Gillman, H.D. Inorg. Chem. 1974, 13, 1921. 21. Gillman, H.D. Inorg. Chem. 1972, 11, 3124. 22. Banks, P.R., B.Sc. Thesis, University of B r i t i s h Columbia, 1986 . 23. Oliver, K.W., Ph.D. Thesis, University of B r i t i s h Columbia, 1984. 24. Haynes, J.S.; Oliver, K.W.; Thompson, R.C. Can. J. Chem. 1985, 63, 1111. 25. Haynes, J.S.; Oliver, K.W.; Rettig, S.J.; Thompson, R.C; Trotter, J. Can. J. Chem. 1984, 62, 891. 26. Peers, J.R.D., B.Sc. Thesis, University of B r i t i s h Columbia, 1987. 27. Hay, P.J.; Thibeault, J . C ; Hoffman, R. J. Am. Chem. Soc. 1975, 97, 4884. 28. Girerd, J . - J . ; Chariot, M.-F.; Kahn, 0. Mol. Phys. 1977, 34, 1063. 29. Albonico, C ; Bencini, A. Inorg. Chem. 1988, 27, 1934. 30. Bencini, A.; Gatteschi, D. Inorg. Chim. Acta 1978, 31, 11. 31. Estes, W.E.; Gavel, D.P.; Ha t f i e l d , W.E.; Hodgson, D.J. Inorg. Chem. 1978, 17, 1415. 10 32. Fletcher, R.; Hansen, J.J.; Livermore, J.; W i l l e t t , R.D. Inorg. Chem. 1983, 22, 330. 33. O'Connor, C.J.; Firmin, D.; Pant, A.K.; Babu, R.B.; Stevens, E.D. Inorg. Chem. 1986, 25, 2300. 34. Ajd, D.; Bencini, A.; Mani, F. Inorg. Chem. 1988, 27, 2437. 35. Snyder, B.S.; Patterson, G.S.; Abrahamson, A.J.; Holm, R.H. J. Am. Chem. Soc. 1989, 111, 5214. 11 I I . R E S U L T S A N D D I S C U S S I O N I : P O L Y - u - B I S ( D I - N - O C T Y L P H O S P H I N A T O ) I R O N ( I I ) A . S Y N T H E S E S As i s the case with almost a l l Fe(II) work, the preparation of poly-u-bis(di-n-octylphosphinato)iron(II) involved the use of standard vacuum l i n e and drybox techniques. Precautions were taken to remove gas from the solvents used by several freeze-pump-thaw cycles. Upon leaving glassware with small amounts of l e f t - o v e r product out i n the laboratory atmosphere, i t was found that the Fe(II) complexes made were not highly a i r - s e n s i t i v e , showing no signs of an obvious immediate reaction with the atmosphere, but over prolonged periods (several hours), they would turn dark brown. This i s l i k e l y due to oxidation. Thus, every precaution was taken to protect the compounds from the atmosphere as much as possible. I n i t i a l characterization of the products of synthetic reactions was achieved through the use of i n f r a r e d spectroscopy and, sometimes, d i f f e r e n t i a l scanning calorimetry, as a means of detecting hydrolysis or incomplete solvent (water and/or alcohol) removal. In both cases, an OH stretching v i b r a t i o n would show up i n the i n f r a r e d spectrum at around 3500 cm-1. I f such a v i b r a t i o n appeared, the products were then dried further and rechecked. Once no evidence of hydrolysis or excess solvent was present, the samples were submitted for microanalysis. The samples d i d appear to pick up water or other OH containing compounds slowly i n the glovebox, as evidenced by IR. This contaminant could be removed by heating at temperatures over 100° C for several hours. 12 D i f f e r e n t i a l scanning calorimetry was sometimes useful i n detecting excess water or solvent present, by giving a thermal event at or near the known b o i l i n g point of the solvent. The general procedure to synthesize these compounds was the slow addition of the metal chloride to the acid, neutralized with potassium carbonate, according to MeOH/H 0 FeCl -4H 0 + 2K(C H ) PO —> Fe[(C H ) PO ] + 2KC1 2 2 8 17 2 2 8 17 2 2 2 Care was taken to make the addition of the FeCl -4H 0 to the 2 2 neutralized acid solution as slow as possible, to ensure that chain lengths i n the product polymers would be maximized. However, the procedure was not standardized to a s p e c i f i c addition rate, so that some v a r i a b i l i t y of chain lengths may have resulted. This i s r e f l e c t e d i n the magnetic s u s c e p t i b i l i t y data, as w i l l be seen l a t e r . It was seen that reaction conditions and stoichiometry had a profound e f f e c t on the f i n a l state of the product, giving two d i f f e r e n t forms of Fe [ (C H ) PO ] , hereafter c a l l e d Forms I and 8 17 ' 2 2 2 ' I I . The physical d i s t i n c t i o n s between these two forms w i l l be described l a t e r i n t h i s section. The doped samples, Fe Zn [ (C H ) PO ] , were also seen to be subject to t h i s l - x x 8 1 7 ' 2 2 2 ' J phenomenon. The d e t a i l s of the syntheses of these compounds are given i n Chapter V. It was seen that keeping the stoichiometric r a t i o of (C H ) PO ~ to FeCl -4H 0 as close as possible to 2:1 8 17 2 2 2 2 r would give a Form I compound, whereas deviations from t h i s stoichiometry, p a r t i c u l a r l y towards an excess of FeCl 2-4H 20 or 13 potassium carbonate, seemed t o g i v e Form II compounds. The samples were a l s o p r e s s u r e s e n s i t i v e . Upon g r i n d i n g , the samples changed from a l i g h t t a n t o a dark brown c o l o u r . T h i s change a l s o suggests t h a t Fe [ (C gH i 7) 2P0 2] e x i s t s i n at l e a s t two polymorphic forms, and i n f a c t the ground form appears t o be Form I I , whereas the u n t r e a t e d samples appear t o be Form I. The b a s i c p h y s i c a l s t a t e of the m a t e r i a l s was of a q u i t e gummy nature, which made h a n d l i n g and p r e p a r a t i o n f o r the v a r i o u s c h a r a c t e r i z a t i o n s somewhat of a problem, and a c t u a l l y made Gouy balance magnetic measurements i m p o s s i b l e , due t o the importance of e f f i c i e n t sample packing i n t h a t t e c h n i q u e . D r y i n g at e l e v a t e d temperatures f o r s e v e r a l days d i d not remove t h i s p h y s i c a l c h a r a c t e r i s t i c . Four d i f f e r e n t samples of Fe [ (C gH i 7) 2P0 2] were prepared and c h a r a c t e r i z e d i n t h i s work. Samples 1 and 2, which were prepared under s i m i l a r r e a c t i o n c o n d i t i o n s , e x h i b i t s i m i l a r p r o p e r t i e s and are c o n s i d e r e d t o be Form I compounds, whereas samples 3 and 4 are c o n s i d e r e d t o be Form II compounds. The c o l o u r s of 1 and 2 were l i g h t t a n ; 3 and 4 were a l i t t l e d arker. B . I N F R A R E D S P E C T R A Complete l i s t i n g s o f i n f r a r e d data, along w i t h assignments of the bands observed, can be found i n Appendix I. The i>(P02) r e g i o n between ca. 1150-950 cm"1 i s the most d i s t i n c t i v e r e g i o n of the i n f r a r e d s p e c t r a of metal phosphinate compounds. In the past, t h i s has been the r e g i o n used t o assess the nature o f the M-O-P-O-M bonding network 1' 2, as w e l l as s t e r i c e f f e c t s of the hydrocarbon s i d e groups 3. R e s u l t s from X-ray 14 c r y s t a l l o g r a p h i c s t u d i e s show that the nature of the phosphinate l i g a n d has an e f f e c t on the geometry of the metal-oxygen chromophore. For one t h i n g , the presence of s m a l l e r groups around the c e n t r a l metal makes s i x coordinate species p o s s i b l e 4 . I t was a l s o seen t h a t l a r g e r a l k y l s i d e groups seem t o fo r c e f o u r - c o o r d i n a t e species from a t e t r a h e d r a l t o a f l a t t e n e d t e t r a h e d r a l or even square planar geometry. A l s o , i n f r a r e d s t u d i e s have shown tha t the separation of the symmetric and asymmetric v(P0 2) bands appears t o be g r e a t e r i n the case of unsymmetrical phosphinate b r i d g i n g groups, making IR spectroscopy a u s e f u l t o o l t o i n v e s t i g a t e the nature of phosphinate b r i d g i n g . A comparison of the v i b r a t i o n a l frequencies of the i>(P02) bands f o r compound 1 with those of s i m i l a r complexes i s i n f o r m a t i v e . These data, along with Lv (v -v ) f o r each asy sym compound, are presented i n Table 2.1. 15 Table 2 .1 . Frequencies (cm -1) of v(P0 2) Regions in Various Metal(phosphinate) Polymers Compound V asy V sym source Mn(Me 2 P0 2 ) 2 -2H 2 0 1123 1031 92 4 C u ( E t 2 P 0 2 ) 2 1110 1049 61 6 CU(BU 2 P0 2 ) 2 1116 1057 59 7 Cu(Hex 2 P0 2 ) 2 1113 1039 74 7 c u ( o c t 2 P o 2 ) 2 (a form) 1107 1043 1046 64 8 (0 form) 1112 66 8 C U ( * 2 P 0 2 ) 2 1132 1051 81 9 Mn(H«^P0 2) 2 1130 1018 112 10 C o ( O c t 2 P 0 2 ) 2 (Form I) 1125 1044 81 11 (Form II) 1142 1073 1018 N/A 11 Co(F 2 P0 2 ) 2 -2CH 3 CN 1280 1155 125 13 N i ( O c t 2 P 0 2 ) 2 1107 988 119 12 F e ( O c t 2 P 0 2 ) 2 (sample 1) 1140 1121 1107 1108 1074 1051 1022 N/A t h i s work (ground) 1050 58 t h i s work 16 The i n f r a r e d s p e c t r a l data show t h a t the i>(P02) r e g i o n i s very s e n s i t i v e t o the geometry of the l i g a n d s around the metal. The f i r s t f e a t u r e t h a t becomes apparent i s t h a t the c o o r d i n a t i o n number of the metal atom seems to i n f l u e n c e the Lv v a l u e s of the i>(P02) r e g i o n . Two compounds with c r y s t a l l o g r a p h i c a l l y v e r i f i e d p seudooctahedral geometry, Mn [ (CH3) 2P0 2] 2-2H 20 and C o ( F P O ) -2CH CN 1 3, show Lv v a l u e s on the order of 100 cm"1. In 2 2 2 3 ' a d d i t i o n , two compounds proposed t o be pseudooctahedral, N i [ ( C H ) PO ] 1 2 and Mn[(C H ) HPO ] \ show Lv v a l u e s of t h i s 8 17 2 2 2 6 5 2 2 ' same o r d e r . C o [ ( C H ) PO ] (Form I ) , which has a lower Lv of 81 8 17 2 2 2 cm"1, i s a l s o proposed to be o c t a h e d r a l , on the b a s i s of U V / v i s i b l e s p e c t r o s c o p i c data; however, t h i s c l a s s i f i c a t i o n may not be c o r r e c t . The compound i s a l i g h t b l u e c o l o u r , whereas o c t a h e d r a l Co (II) complexes are u s u a l l y p i n k . C r y s t a l s t r u c t u r e s 5 6 7 have been o b t a i n e d f o r the d i p h e n y l , d i e t h y l , d i - n - b u t y l and 7 d-n-hexylphosphinates of C u ( I I ) , showing these compounds t o be f o u r - c o o r d i n a t e about copper. The d i p h e n y l d e r i v a t i v e i s square p l a n a r about copper and the others have a f l a t t e n e d t e t r a h e d r a l CuO^ chromophore, with the d i e t h y l d e r i v a t i v e b e i n g the most n e a r l y p l a n a r of the t h r e e . The Lv v a l u e s f o r these s p e c i e s show no d e f i n i t i v e t r e n d as f a r as p r e d i c t i n g the degree of p l a n a r i t y i s concerned; they do however, show t h a t the f o u r - c o o r d i n a t e complexes have a s m a l l e r symmetric-asymmetric P0 2 s t r e t c h i n g frequency s e p a r a t i o n than the pseudooctahedral complexes d e s c r i b e d above. As i n d i c a t e d i n S e c t i o n I, the s o - c a l l e d a and /3 forms of C u [ ( C H ) PO ] were both proposed t o be f o u r - c o o r d i n a t e ; t h e i r 8 17 2 2 2 f f Lv v a l u e s seem t o be c o n s i s t e n t with t h i s argument. With the above c o r r e l a t i o n s i n hand, we see t h a t the IR 17 s p e c t r a l data f o r Fe [ (C H ) PO ] show the same c h a r a c t e r i s t i c s 8 1- i 2 2 2 as those of other f o u r - c o o r d i n a t e s p e c i e s , with a Lv v a l u e of ca. 60 cm - 1 f o r ground samples. I t i s here t h a t the p h y s i c a l d i s t i n c t i o n between Form I and Form II samples can be made. Table 2.2 summarizes the e f f e c t s of p r e s s u r e on the v(P0 2) r e g i o n of Form I and Form II compounds. T h i s e f f e c t i s shown i n F i g u r e 2.1. I t i s seen i n compounds 1 and 2 t h a t g r i n d i n g the sample causes the IR spectrum of the i>(P02) r e g i o n t o c o l l a p s e from a multi-band p a t t e r n t o a simple two-band p a t t e r n . Compounds 1 and 2 w i l l h e r e a f t e r be r e f e r r e d t o as Form I samples, and compounds 3 and 4 w i l l be r e f e r r e d to as Form II samples. In c o n t r a s t t o t h i s behaviour, g r i n d i n g compounds 3 and 4 seems t o have almost no e f f e c t on the v(P0 2) r e g i o n (In f a c t , some d i f f e r e n c e i s seen between the ground and unground samples of 4 ; s m a l l shoulders are seen on the two l a r g e r v(P0 2) bands, which dis a p p e a r upon g r i n d i n g . T h i s may suggest the presence of a s m a l l amount of Form I present i n the u n t r e a t e d compound 4 . ) . The complex v(P0 2) r e g i o n d i s p l a y e d i n the unground sample of compound 1 (Figure 2.1) i m p l i e s e i t h e r a more com p l i c a t e d l i g a n d bonding scheme, or perhaps some i n t e r c h a i n a s s o c i a t i o n which i s d e s t r o y e d upon g r i n d i n g . T h i s i n t e r c h a i n a s s o c i a t i o n c o u l d c o n c e i v a b l y g i v e c h e m i c a l l y d i f f e r e n t phosphinate l i g a n d s which c o u l d then manifest themselves i n the IR spectrum. 18 R g u r e 2., Comparison of PO, « * * * - H » of 1 Table 2.2. P0 2 Stretching Frequencies (cm - 1), Compounds 1-4: Fe[ (CHJ,PO ] *• 8 17' 2 2J 2 Sample Untreated V V asy sym Ground V V asy sym 1 1140 s 1074 s 1121 s sh 1051 s 1107 s 1022 s 1108 s 1050 s 2 1136 m sh 1070m sh 1101 s 1041 S 1022m sh 1103 S 1043 S 3 1104 S 1041 S 1105 S 1041 S 4 1105 S 1011 S 1138 sh 1055 sh 1101 S 1037 s 1068 Sh (s=strong / m=medium, sh=shoulder) Comparison of these re s u l t s with those of Gillman 1 4 shows disagreement between the two studies. Gillman found three bands i n the i>(P02) region at 1139, 1072 and 1020 cm-1. These bands are seen i n the Form I compounds of t h i s study, but along with other bands. This would make i t appear that the s o - c a l l e d Form I compounds are not r e a l l y purely Form I, but a mixture of two forms. It should also be noted that Gillman found no evidence for polymorphism i n his work on Fe[(C H ) PO ] . 8 1 / 2 2 2 C . T H E R M A L S T U D I E S Thermal studies were achieved through the use of d i f f e r e n t i a l scanning calorimetry (DSC). As mentioned before, the samples were 20 sometimes analyzed using DSC as a diagnostic technique to detect solvent impurities. Melting points may also be found by DSC; however, i n the case of the compounds studied here, thermal decomposition of the sample occurred before melting. It was mentioned previously that the samples seemed to be taking on OH-containing solvent slowly when l e f t i n the glovebox. This manifested i t s e l f quite c l e a r l y i n the form of an endothermic peak at 100° C. Once the sample had been cooled and then reheated, t h i s event d i d not occur. It was found that the DSC re s u l t s were not very useful i n d i s t i n g u i s h i n g between Forms I and I I . Figure 2.2 shows a representative heating curve of a Form I compound (sample 4) . Upon grinding and heating the sample through the same temperature ramp as before, no features appear which may indicate a t r a n s i t i o n from Form I to Form II nature. It appears, therefore, that DSC i s not as e f f e c t i v e as IR i n showing the difference between the two forms of Fe[(CH ) PO ] . What the re s u l t s do t e l l us i s that 8 17 2 2 2 the Form I to Form II t r a n s i t i o n i s not a thermal phenomenon (over the range tested), but rather one e n t i r e l y dependent upon pressure. The DSC re s u l t s Gillman obtained for Fe[ (C H ) PO ] are 8 17 2 2 2 s i m i l a r to those seen i n t h i s study. The assignment Gillman gave for his endothermic peak observed at 104° C may not be melting, as he termed i t , but rather the loss of water from his sample, as indicated e a r l i e r for the samples studied i n t h i s work. 21 Heat Flow (Exothermal) —> Heat Flow (Exothermal) —> W(T) = | f 4 e D . M O S S B A U E R S P E C T R O S C O P Y The Mossbauer e f f e c t p r o v i d e s a powerful t o o l f o r examining the chemical environment about the i r o n nucleus i n many d i f f e r e n t c l a s s e s of compounds. A b r i e f overview of t h i s technique may be u s e f u l . The experiment i s based on r e c o i l l e s s resonance y f l u o r e s c e n c e ; thus an a b s o r p t i o n w i l l be observed o n l y i f the sample r e c e i v e s the resonance energy without e x p e r i e n c i n g phonon e x c i t a t i o n . The p r o b a b i l i t y of such a t r a n s i t i o n o c c u r r i n g i s 1 7 £=e" 2 w ( T ) (2.1) where we use the Debye-Waller temperature f a c t o r 0/T , X dx (2.2) o e - 1 J Here R i s the r e c o i l energy, e i s the Debye temperature, used t o c h a r a c t e r i z e l a t t i c e v i b r a t i o n s , and x i s the time-dependent centre-of-mass c o o r d i n a t e of the n u c l e u s . I t can be shown t h a t £ approaches v a l u e s of u n i t y f o r low temperature (T«e) and Rs2ke. A l s o , % approaches zero f o r h i g h temperatures, so the experiment i s best c a r r i e d out at 77 K or lower. The r e c o i l energy i s r e l a t e d t o the y t r a n s i t i o n energy and the mass by the e x p r e s s i o n •p2 R = (2.3) 2mc thus we can see from equations 2.1, 2.2 and 2.3 t h a t E must be low and the atomic number of the nucleus must be h i g h . T h i s makes Mossbauer spectroscopy s p e c i f i c t o a s e l e c t few elements. The source of y - r a d i a t i o n used f o r i r o n Mossbauer sp e c t r o s c o p y i s 5 7Co, which f o l l o w s the decay scheme shown i n 23 F i g u r e 2.3. Here y i s the t r a n s i t i o n of i n t e r e s t , the 14.4 keV Ml "Mossbauer t r a n s i t i o n . " The n a t u r a l abundance of 5 7Fe i s approximately 2%, t h e r e f o r e c o l l e c t i o n time f o r a t y p i c a l -spectrum i s on the order of hours or days. Figure 2.3. Decay Scheme f o r 5 7Co (Ref. 18) 5 7 Co 270d / / E C / / 9 9 . B 4 * 13 6.4 1 4 . 4 M 1 Energy, keV The experiment c o n s i s t s of the 5 7Co source, moving back and f o r t h , the s t a t i o n a r y sample, and a dete c t o r behind the sample. I f the source and sample have the same resonance energy, E , an absorption w i l l be seen at AE=0. The v e l o c i t y of the source i s r e l a t e d t o energy by the Doppler e f f e c t : A E E + v c (2.4) Energies i n t h i s technique are t h e r e f o r e commonly expressed i n terms of v e l o c i t i e s . The two most important parameters t o be e x t r a c t e d by Mossbauer spectroscopy are the isomer s h i f t , 6, and the quadrupole s p l i t t i n g , AE . The isomer s h i f t i s the d i f f e r e n c e between the 24 sample and source resonance energies and i s r e l a t e d t o e l e c t r o n d e n s i t i e s at those r e s p e c t i v e nuclear s i t e s by 1 9 «=|«Ze2r2<5r/r) [|0S (0) ft | 2 -| ^ (0) a |2] (2.5) where Z i s the atomic number, e i s the charge of an e l e c t r o n , r i s the mean nuclear r a d i u s , 6r=r - r (the d i f f e r e n c e between e x c i t e d e g 2 2 and ground s t a t e nuclear r a d i i ) , and \\f> (0) a | and \\p (0) b| are the s - e l e c t r o n d e n s i t i e s at the n u c l e i of the source and sample r e s p e c t i v e l y . The d i f f e r e n c e i n 5 between i r o n (II) and i r o n (II I ) i s r e a d i l y seen; the e x t r a d - e l e c t r o n i n d 6 i r o n (II) complexes screens s - e l e c t r o n d e n s i t y so the isomer s h i f t w i l l i ncrease ( It i s important here t o note th a t 5 r / r < 0 f o r 5 7Fe) . Isomer s h i f t s of 0 . 2 - 0 . 6 mm s~l are t y p i c a l f o r i r o n ( I I I ) compounds, whereas i r o n (II) compounds have isomer s h i f t s i n the range 0 . 7 - 1 . 5 mm s - 1. The i n t e r a c t i o n of a nucleus having a quadrupole moment Q wit h an e l e c t r i c f i e l d gradient (efg) w i l l s p l i t a l e v e l having nuclear s p i n I> 1 / 2 i n t o d i s t i n c t s u b l e v e l s . The nuclear quadrupole c o u p l i n g Hamiltonian i s given by 1 9 H = e 2 q Q f 3 I 2 - I 2 + f * 1 ( I 2 + I 2) 1 (2.6) 41(21-1) L z I 2 > " J Here eq i s V , the z-component of the e f g tensor, and TJ i s the zz asymmetry parameter, d e f i n e d as T) = | (V -V ) | /V (2.7) 1 xx yy zz The e f g tensor i s w r i t t e n 25 efg V v ) xx xy xz V V V yx yy yz V V V v zx zy zz' (2.8) where V i s the e l e c t r i c a l p o t e n t i a l and a 2 v V . . = (2.9) 1 3 s i a j The efg tensor i s symmetric traceless, so that i t may be diagonalized by the correct choice of axis system. The quadrupole s p l i t t i n g for 1=3/2 i s then A E Q = V q Q ^ l + ^ 2 ] 1 / 2 (2.10) The efg may aris e from one or a combination of any of the following four sources 2 0: (i) an asymmetric d i s t r i b u t i o n of non-bonding electrons about the central atom; ( i i ) electrons i n bonds between the central atom and ligands ( i . e . d e l o c a l i z a t i o n ) ; ( i i i ) charges on the ligands; (iv) charges on surrounding ions and molecules i n the l a t t i c e . It can be seen therefore, that a nonspherically symmetric environment about the central iron atom w i l l give r i s e to an e l e c t r i c f i e l d gradient. Therefore, i n the case of low-spin octahedral Fe(II) complexes with a completely f i l l e d t s h e l l , one would expect no e l e c t r i c f i e l d gradient, 2g unless an asymmetric ligand environment ex i s t s about the central 26 Fe atom. Th e r e f o r e , the e l e c t r i c f i e l d g r a d i e n t w i l l be dependent onl y on the l i g a n d environment i n t h i s case, and a n a l y s i s of the quadrupole s p l i t t i n g seen should be r e l a t i v e l y simple. In the case of h i g h - s p i n S=2 F e ( I I ) , however, the s i t u a t i o n w i l l be more complex, but much i n f o r m a t i o n i s a v a i l a b l e . A n a l y s i s of the magnitude and s i g n of A E q can g i v e much i n f o r m a t i o n on the • 21 geometry of the l i g a n d s about the i r o n atom . There are many f a c t o r s which may i n f l u e n c e the e l e c t r i c f i e l d g r a d i e n t about an i r o n ( I I ) n u c leus; thus, one must be c a u t i o u s i n p o s t u l a t i n g the causes of e x p e r i m e n t a l l y observed quadupole s p l i t t i n g s . The Mossbauer s p e c t r a l s t u d i e s d e s c r i b e d i n t h i s t h e s i s were undertaken at l i q u i d n i t r o g e n temperatures o n l y . A more r i g o r o u s study, examining the temperature dependence of A E q and u s i n g a p p l i e d magnetic f i e l d p e r t u r b a t i o n techniques, can g i v e more i n s i g h t i n t o the nature of the e l e c t r i c f i e l d g r a d i e n t seen i n F e ( I I ) complexes 2 2" 2 4. The Mossbauer s p e c t r a of the ground and unground forms of Fe [ (C H ) PO ] (compound 2) , taken at 77 K, are shown i n F i g u r e s 8 17 2 2 2 2.4a and 2.4b. The r e s u l t i n g parameters from f i t s t o L o r e n t z i a n l i n e shapes are summarized i n Table 2.3. The f u l l l i n e widths at h a l f maximum f o r both l i n e s , r and T , are i n c l u d e d as w e l l . The 1 2 isomer s h i f t v a l u e s , c a l c u l a t e d from l e a s t - s q u a r e s f i t s t o L o r e n t z i a n l i n e s h a p e s , are too low t o be c o n s i s t e n t with S=2 i r o n ( I I ) : 5 i s on the order of 0.3 mm s - 1 here. I t i s of course assumed t h a t t h e r e i s a n e g l i g i b l e amount of i r o n ( I I I ) p r e s e n t i n the samples. Moreover, the A E v a l u e s are too s m a l l ( A E * 0 . 4 mm Q Q s - 1) to be a s s i g n e d t o t e t r a h e d r a l or o c t a h e d r a l h i g h s p i n i r o n (II) complexes. T h i s suggests the presence of a d i f f e r e n t 27 Figure 2.4. Mossbauer Spectra of (a) Untreated and (b) Ground forms of compound 2 at 77 K. Doppler Velocity (mm s 1 ) Doppler Velocity (mm s-1) Fe(II) spin state, S=l, caused by a highly tetragonally d i s t o r t e d ligand f i e l d geometry. Two el e c t r o n i c configurations giving r i s e to t h i s spin state are shown i n Figure 2.5. This i s not without precedent; i t has been well documented that square planar iron(II) 25 26 27 28 i s seen for several porphyrin ' , phthalocyanine ' as well as . • . 29 30 dumine ' complexes of iron (II). The tools used to a r r i v e at t h i s conclusion of S=l iron(II) i n the aforementioned studies were magnetic moment measurements and Mossbauer spectroscopy. Intermediate spin states have also been observed for a few porphyrinatoiron (III) complexes 3 1' 3 2, giving r i s e to an S= 3/2 system. Table 2.3 Mossbauer Parameters (mm s x) for Compound 2 s A EQ r i r2 Untreated 0.30 0.42 0.52 0.47 Ground 0.31 0.40 0.53 0.47 29 Figure 2.5. E l e c t r o n i c Configurations as a Function of Symmetry for Fe(II) Complexes xy J L J L J L d 2 z xy xz yz d 2 2 x -y d 2 z 1 t xy d 2 2 x -y d t d v z xz v z d 2 z l i _ L L i a. T (S=2) a b. (S=l) 2d C. D (S=l) 4n 30 Comparison of the isomer s h i f t s of the two forms of compound 2 w i t h the 6 values observed f o r the compounds of references 2 5 - 3 0 show tha t the S=l s t a t e of i r o n i s q u i t e p o s s i b l e i n Fe[(C H ) PO ] . Furthermore, the magnetic s u s c e p t i b i l i t y 8 17 2 2 2 r J r e s u l t s of the vari o u s samples of t h i s complex may only be analyzed s a t i s f a c t o r i l y by assuming an S=l s t a t e , and not by S=2 models. This proposed high degree of p l a n a r i t y can perhaps be accounted f o r a f t e r c o n s i d e r i n g the s t e r i c e f f e c t s the bulky a l k y l s i d e groups w i l l have on the complex. Another p o s s i b l e e x p l a n a t i o n f o r t h i s r are geometry i s the cooperative s t r e n g t h of the polymer chain, which could conceivably " p u l l " the FeO^ moiety i n t o a h i g h l y compressed conformation. I t i s i n t e r e s t i n g t o note t h a t g r i n d i n g the undoped sample of di - n - o c t y l p h o s p h i n a t o i r o n ( I I ) has a n e g l i g i b l e e f f e c t on the Mossbauer spectrum ( 5 = 0 . 3 1 mm s"1, A E Q = 0 . 4 0 mm s - 1) . Thus, d i s t i n c t i o n s between Forms I and I I can not be made by Mossbauer spectroscopy, the s t r u c t u r a l d i f f e r e n c e s being too su b t l e to a f f e c t the isomer s h i f t and e f g values. I t w i l l be shown that there i s i n f a c t evidence of a s t r u c t u r a l change, a l b e i t a small one, manifested markedly i n the magnetic s u s c e p t i b i l i t y data. The quadrupole s p l i t t i n g , A E q , of t h i s sample i s worthy of comment. Quadrupole s p l i t t i n g s may be estimated e a s i l y by c a l c u l a t i n g the c o n t r i b u t i o n of the metal o r b i t a l s t o V from 2 0 zz V = eq = -e< 3 cos 2 e - l><r" 3>(l-R) ( 2 . 1 1 ) zz where r and e are the p o l a r coordinates of the o r b i t a l s and R i s the Sternheimer f a c t o r , which accounts f o r s h i e l d i n g e f f e c t s due 31 t o the p o l a r i z a t i o n of the inner s h e l l e l e c t r o n s . The angular brackets denote the expectation value of the given f u n c t i o n . The f o l l o w i n g c o n t r i b u t i o n s are then c a l c u l a t e d f o r the d - o r b i t a l s : d 2 2=d =1<r"3>, d =d =--<r~3>, and d 2=-1<r"3>. The x - y x y 7 x z y z 7 z 7 Sternheimer f a c t o r i s i m p l i c i t i n these r e s u l t s and the greater r a d i a l extent of the 4p o r b i t a l s reduces t h e i r c o n t r i b u t i o n s u b s t a n t i a l l y (although not always completely). Thus, f o r the e l e c t r o n c o n f i g u r a t i o n (d ,d ) 4 (d 2 ) 1 (d J 1 , we obtai n xz yz z xy q=--<r~3>. S i m i l a r l y f o r the c o n f i g u r a t i o n (d 2 ) 2 (d ,d ) 3 7 z xz yz (d ) x , we c a l c u l a t e q=-i^<r"3>. In these two cases the quadupole s p l i t t i n g i s expected t o be la r g e and negative.This simple c a l c u l a t i o n does not take i n t o account c o n t r i b u t i o n s a r i s i n g from the cr-donor and/or n-acceptor p r o p e r t i e s of the l i g a n d s . I t i s u s e f u l t o compare t h i s system wi t h other known S=l i r o n ( I I ) complexes, namely p h t h a l o c y a n a t o i r o n ( I I ) and s e v e r a l p o r p h y r i n a t o i r o n ( I I ) complexes 2 0. These compounds have been shown to have s u b s t a n t i a l p o s i t i v e quadrupole s p l i t t i n g s , w i t h the phthalocyanine complex being the l a r g e s t , at 2.7 mm s"1. We see tha t V has been g r e a t l y a f f e c t e d by 0— donation i n t o the empty zz metal d 2 2 o r b i t a l , g i v i n g a p o s i t i v e c o n t r i b u t i o n . This x -y suggests t h a t the same e f f e c t i s happening i n Fe [ (CfiHi7) 2P0 2] 2, but t o a l e s s e r extent. Another p o s s i b i l i t y e x i s t s which w i l l add a p o s i t i v e c o n t r i b u t i o n t o V i f the h y b r i d bonding o r b i t a l s are zz considered. The c o n t r i b u t i o n s t o the e l e c t r i c f i e l d g radient from 20 2 3 4 3 p o r b i t a l s are as f o l l o w s : p =p =-<r~ > and p =—<r" >. Thus, x y 5 z 5 f o r dsp 2 h y b r i d bonding o r b i t a l s , cr-donation i n t o the 4p and 4p x y o r b i t a l s , w i t h 4p vacant, would a l s o make a p o s i t i v e c o n t r i b u t i o n z t o the e l e c t r i c f i e l d g r a d i e n t . The si g n of AE i s not known 32 here, but temperature dependent Mossbauer studies would be useful i n t h i s determination. At any rate, i t appears that the quadrupole coupling of t h i s compound has been made more p o s i t i v e by substantial <r-donation from the phosphinate ligands. E . E L E C T R O N I C S P E C T R O S C O P Y We have now seen, based on Mossbauer data that the e l e c t r o n i c structure of Fe[ (C H ) PO ] must be such that an S=l spin state 8 17 2 2 2 ^ i s exhibited. This w i l l mean that the compound w i l l have a t r i p l e t ground state. Iron(II) complexes with t r i p l e t ground states are not unknown. Perhaps the best known example i s the iron (II) phthalocyanine complex, which shows i n t e r e s t i n g magnetic 3 3and Mossbauer 2 8 properties. To observe a t r i p l e t ground state i n iron (II) complexes, i t i s required that the d 2 2 x -y o r b i t a l i s s u f f i c i e n t l y far separated i n energy from the lower o r b i t a l s , such that i t w i l l not be appreciably populated. The magnetic properties of S=l iron (II) complexes w i l l also be s i g n i f i c a n t l y affected by spin-orbit coupling, a r i s i n g from the t r i p l e t ground state, as would be the case for a quintet ground state. This can make the analysis of the magnetic properties of iron (II) complexes less than straightforward. The e l e c t r o n i c spectrum of Fe [ (CgHi7) 2P0 2] displays a broad peak at 1300 nm (7700 cm"1) (see Figure 2.6). In comparison, 14 r e s u l t s obtained by Gillman showed a single absorption at 8400 cm"1. This r e s u l t led Gillman to conclude that Fe[ (C H ) PO ] 8 17 2 2 2 had an octahedral coordination scheme. The r e s u l t s presented i n t h i s thesis seem to oppose t h i s assignment, on the basis of the Mossbauer and e l e c t r o n i c spectral r e s u l t s and the temperature 33 Figure 2.6. Electronic spectrum in the near-infrared region of compound 1. WAVELENGTH (NM) dependent magnetic s u s c e p t i b i l i t y studies (vide i n f r a ) . Assignment of t h i s spectrum i s d i f f i c u l t because of the d i f f e r e n t p o s s i b i l i t i e s available for the e l e c t r o n i c configuration of a ground state t r i p l e t d 6 system. Two p o s s i b i l i t i e s are shown in Figure 2.5. 35 F . M A G N E T I C S U S C E P T I B I L I T Y M E A S U R E M E N T S The study of the magnetic p r o p e r t i e s of i n o r g a n i c compounds has been of much importance over the years and continues t o be a dynamic f i e l d of research. Aside from r o u t i n e room-temperature magnetic moment measurements, v a r i a b l e temperature measurements to below 4 K can i l l u s t r a t e some very i n t e r e s t i n g p r o p e r t i e s i n these m a t e r i a l s . The two b a s i c types of magnetic behaviour are paramagnetism and diamagnetism. A l l m a t e r i a l s possess the property of diamagnetism, which gives r i s e t o a small negative molar s u s c e p t i b i l i t y . This i s the r e s u l t of the i n t e r a c t i o n of e l e c t r o n p a i r s w i t h the magnetic f i e l d . This i n t e r a c t i o n can be thought of i n terms of a system of current l o o p s 3 4 3 , which, as a consequence of Lenz's law, w i l l be r e p e l l e d from the f i e l d . When measuring the magnetic s u s c e p t i b i l i t i e s of m a t e r i a l s , the diamagnetism of the sample i s c o r r e c t e d f o r u s i n g Pascal's 34a constants . Each atom has i t s own diamagnetism and, based on the a d d i t i v i t y of atomic s u s c e p t i b i l i t i e s , the net diamagnetism of the molecule i s accounted f o r . Paramagnetism, on the other hand, i s not g e n e r a l l y a property of a l l m a t e r i a l s . Instead, i t i s the consequence of the i n t e r a c t i o n of an a p p l i e d magnetic f i e l d w i t h o r b i t a l - and spin-angular momenta. Paramagnetic s u s c e p t i b i l i t i e s are, compared to diamagnetic s u s c e p t i b i l i t i e s , l a r g e and p o s i t i v e . S u s c e p t i b i l i t y may be c a l c u l a t e d using Van Vleck's equation of magnetic s u s c e p t i b i l i t y 36 N I [w'1' / kT - 2W<2)j exp |-W° / kTJ Z exp |-W° /kTJ y = i (2.12) A Here xA i s magnetic s u s c e p t i b i l i t y per gram atom, N i s the number of atoms being considered, W° i s the energy of l e v e l i i n the absence of magnetic f i e l d . The terms W(1) and W(2) are then the f i r s t and second order Zeeman e f f e c t c o e f f i c i e n t s when the magnetic f i e l d i s applied on the sample. Exact expressions for magnetic s u s c e p t i b i l i t y may be calculated for f i n i t e systems, while polymeric systems require simplifying approximations to equation 2.12. The e f f e c t i v e magnetic moment i s often considered i n magnetic measurements; i t i s related to the s u s c e p t i b i l i t y by u - 2.828 (> T ) 1 / 2 (2.13) e f f V A ' Paramagnetic behaviour, i n the absence of any cooperative phenomena, may be described by the Curie Law: Xs = C/T (2.14) A where C i s a constant. Good descriptions of how non-Curie law magnetic behaviour may aris e are given i n references 30a and 30b. If we combine equations 2.13 and 2.14, we see that Curie law paramagnetism gives a temperature independent magnetic moment. More exotic behaviours are sometimes displayed. Simple schematic diagrams of such systems are shown i n Figure 2.7. Antiferromagnetism (Figure 2.7a) arises when the alignment of 37 adjacent s p i n v e c t o r s i n the l a t t i c e i s a n t i p a r a l l e l ; t h i s w i l l g i ve r i s e , upon complete o r d e r i n g , t o a magnetic moment of zero. The magnetic s u s c e p t i b i l i t y w i l l d i s p l a y a maximum i n i t s x vs. T M curve. The temperature at which t h i s maximum occurs i s r e f e r r e d to as the Neel p o i n t . Ferromagnetism (Figure 2.7b) i s observed when adjacent centres have t h e i r s p i n v e c t o r s a l i g n e d i n a p a r a l l e l manner; t h i s w i l l give r i s e t o an anomalously l a r g e magnetic moment. The x vs. T behaviour w i l l a l s o be d i s t i n c t i v e . M As temperature decreases, the s u s c e p t i b i l i t y w i l l t y p i c a l l y obey Curie or Curie-Weiss law u n t i l a temperature, termed the Curie temperature, at which the s u s c e p t i b i l i t y w i l l grow much f a s t e r w i t h decreasing temperature. Ferrimagnetism (Figure 2.7c) i s somewhat of a combination of the above two behaviours. I t i s the r e s u l t of the ant i f e r r o m a g n e t i c c o u p l i n g of two i n t e r p e n e t r a t i n g s u b l a t t i c e s of unequal s p i n magnitudes. Examples of f e r r i m a g n e t i c i n t e r a c t i o n s are seen i n systems i n v o l v i n g two metals of d i f f e r i n g s p i n s , ordered a n t i f e r r o m a g n e t i c a l l y and a l s o i n systems of i d e n t i c a l spins but o r i e n t e d d i f f e r e n t l y along a c h a i n 3 5 ' 3 6 . These systems are the so c a l l e d " magnetically concentrated" systems, as opposed t o "magnetically d i l u t e . " F igure 2.7. M a g n e t i c a l l y Concentrated Systems /K >ts sf. 1 1 >K >N yK a. antiferromagnetism b. ferromagnetism X X >L c. ferrimagnetism 38 TEMPERATURE (K) Figure 2.8. Magnetic susceptibility vs. temperature plot of compound 1. untreated. Solid line is generated by the Fisher S - l model. J—2.54 K, g-3.21, P=0.0. TEMPERATURE (K) Figure 2.9. Magnetic susceptibility vs. temperature plot of compound 2. untreated. Solid line is generated by the Fisher S=l model. J=-3.00 K. g=3.29, P=0.5. Systems l i k e the ones above are of sp e c i a l i n t e r e s t i n low dimensional compounds and clusters, where ordering i s more pronounced due to the proximity of the metal centres. The complete x vs. T data for the materials studied here are M reported i n Appendix I I . The data are plotted, along with t h e o r e t i c a l curves where applicable, i n Figures 2.8-2.18. The polymorphism described e a r l i e r i n Fe [ (CgHi7) 2P0 2] i s c l e a r l y manifested i n the x vs. T curves for the d i f f e r e n t samples. Let us f i r s t examine the untreated samples 1 and 2 and attempt to model them with t h e o r e t i c a l expressions. The x vs. T behaviour of unground samples of M Fe [ (CgHi7) 2P0 2] , compounds 1 and 2 , show t y p i c a l antiferromagnetic behaviour (see Figures 2.8 and 2.9), with Neel temperatures at approximately 6 K. Attempts to model these systems by S=2 models proved f r u i t l e s s , giving unsatisfactory r e s u l t s for the f i t t i n g parameter F, which w i l l be explained l a t e r . On the other hand, S=l models yielded better r e s u l t s . The model for an S=l magnetically coupled Heisenberg l i n e a r 37 chain system, from work by Fisher , i s based on the spin-exchange Hamiltonian H = -2J X S -S (2.15) L. 1 j and the s u s c e p t i b i l i t y has the following form: Ng2u 2S(S+1) ' B x = 3kT 1 + u 1 - u (2.16) where u=cosh[2JS(S+l)/kT] - kT/2JS(S+l). Here J i s the exchange 40 i n t e g r a l and w i l l be p o s i t i v e for ferromagnetic coupling and A A negative for antiferromagnetic coupling. S, and S_. are the spin vectors of atoms i and j , N i s Avogadro's number, g i s the Lande s p l i t t i n g factor, u i s the Bohr magneton, S i s the i n t e g r a l spin value and k i s Boltzmann's constant. A numerical approximation of these r e s u l t s was worked out by Weng38 i n his extension of the work by F i s h e r 3 9 and Bonner and 4 0 Fisher , y i e l d i n g the following r e s u l t s for an S=l system: 2 2 Ng u X = kT f 0.6667 + 2.5823 x' 1 + 3.6035 x + 39.558 x-(2.17) where x = |J|/kT. The expression for a two-dimensional quadratic layer . . 4 1 a n t i f erromagnet comes from work by Lines , based on the spin-exchange Hamiltonian and i s written A A H = y J s -s L i j (2.18) »j 2 2 " C N G U B = 3e + y — — xJ~ A e""1 (2.19) where e = kT/JS(S+l). It was found that taking the c o e f f i c i e n t s to n=6 provided suitable convergence of the solu t i o n . The c o e f f i c i e n t s for S=l are: C = 4, C= 1.834, C= 0.445, C= 0.224, 1 2 3 4 C = 0.132 and C = 0.019. 5 6 A least-squares f i t t i n g procedure was c a r r i e d out using the above models and minimizing the f i t t i n g parameter F, defined by 41 F = n I i i calc "^obs obs 1/2 (2.20) where n i s the number of data points, y i s the magnetic calc s u s c e p t i b i l i t y calculated from the model and x i s the obs experimentally observed s u s c e p t i b i l i t y . A l l models used were augmented to include a paramagnetic component, assumed to follow Curie law, which goes as > = N g V s(S+l) (2.21) 3kT This paramagnetic component was then coupled to the regular polymeric component using the weighting parameter P to give the observed s u s c e p t i b i l i t y : X. = P*+ (l-P)z . (2.22) obs P poly Comparison of the three models for the case of the untreated form of compound 2, as seen i n Figures 2.9, 2.10 and 2.11, shows the Fisher S=l model to be the most suitable i n t h i s case. The parameters from each of these models for the case of compound 2 are given i n Table 2.4. 42 Figure 2.10. Magnetic susceptibility vs. temperature plot of compound 2. untreated. Solid line is generated by the Weng S=l model. J=-2.65 K, g=3.26. P=2.2. < O oH 1 1 r 0.0 40.0 TEMPERATURE (K) Figure 2.11. Magnetic susceptibility vs . temperature plot of compound 2, untreated. Solid line is generated by the Lines S=l model. 1—1.89 K. g=3.31. P=9.5. 80.0 0.0 40.0 TEMPERATURE (K) Table 2.4. Comparison of the Fisher, Lines, and Weng S=l Models for Compound 2 Model J (K) g P F Fisher -3.00 3.29 0.4 0.003 Weng -2.65 3.26 2.2 0.015 Lines -1.89 3.31 9.4 0.017 The Lines and Weng models do not reproduce the s u s c e p t i b i l i t y maximum at the Neel point as well as the Fisher model. It i s seen also that the f i t t i n g parameter F i s lowest for the Fisher model, i n d i c a t i v e of a better f i t . Perhaps most remarkable of the parameters obtained for Fe[(CH ) PO ] i s the Lande s p l i t t i n g c 8 17 2 2 2 c 3 factor g, which has extremely large values of greater than 3 i n the case of the Form I samples; normal g values for Fe(II) complexes are i n the neighbourhood of 2.2. This g value may be the r e s u l t of o r b i t a l angular momentum which arises from a p a r t i a l l y f i l l e d 3e l e v e l , as i s seen i n Figure 2.5c. It was shown long ago by Bleaney and Bowers 4 2 that g values can be increased by the introduction of an o r b i t a l contribution by c r y s t a l f i e l d and spin-orbit coupling. Another observation which may indicate the presence of a large o r b i t a l contribution i s the magnitude of the magnetic moment at high temperatures. Due to the troublesome physical nature of the compound, samples could not be ground f i n e l y enough for Gouy tube magnetic moment measurements. This made the obtainment of a room temperature magnetic moment impossible with our equipment, but the low temperature data suggest that the moment w i l l not exceed a value of 4.4 B.M. for 44 Fe[ (C H ) PO ] . This value i s much higher than the spin-only 8 17 2 2 2 value of 2.83 B.M. for S=l (and s u b s t a n t i a l l y lower than the spin-only value of 4.90 B.M. for S=2 complexes). It appears that the magnetic moment r e f l e c t s a very large o r b i t a l contribution i n t h i s case. Another noteworthy feature of the magnetic s u s c e p t i b i l i t y r e s u l t s for these compounds i s the difference between the Forms I and II of Fe[(CH ) PO ] . Table 2.4 shows the values of the 8 17 2 2 2 exchange i n t e g r a l J i n Kelvin, the Lande s p l i t t i n g factor g and percent paramagnetic component P, along with the f i t t i n g parameter F, obtained by f i t s to the Fisher l i n e a r chain S=l model. Table 2.5. Magnetic Parameters for Compounds 1-4, Fisher Model Compound J (K) g P F 1 -2.54 3.21 0.0 0.015 1, ground -2 . 92 2.79 4.7 0.032 2 -3.00 3.29 0.4 0.003 3 -2.86 2.89 2.4 0.017 3 , ground -3.40 3.00 1.9 0.021 4 -2.82 2. 92 1.1 0.030 The difference between the two forms i s c l e a r l y seen i n Figure 2.12. Form I compounds (1 and 2) have a higher o v e r a l l s u s c e p t i b i l i t y than the Form II analogues. It i s also seen that grinding compound 1 (see Figures 2.15 and 2.16) causes i t s magnetic s u s c e p t i b i l i t y vs. temperature behaviour to become much O S U o 1—1 d .a U P CO U z o < 140-1 1 2 0 -100 8 0 H 6 0 H 4 0 H 20 Figure 2.12. Magneric Susceptibility vs. Temperature of compounds 1-4, untreated. O A A 10 20 + O 3 0 4 0 5 0 60 TEMPERATURE (K) 70 I 8 0 Legend O S A M P L E 1 • S A M P L E 2 A S A M P L E 3 + S A M P L E 4 c s u * o Figure 2.13 Comparison of magnetic susceptibility vs. temperature of untreated and ground sample 1. CO 8 CO CO U < 2 140-, 120-100-8 0 60 4 0 20 \ % Legend e SiM^U 1 _ , , , , 1 , — 10 20 30 40 SO 60 T E M P E R A T U R E ( K ) —r-70 — i 80 o 0.0 40.0 80.0 T E M P E R A T U R E ( K ) 47 the same as the Form II compounds. I t i s seen i n g e n e r a l t h a t the Form I compounds have h i g h e r g va l u e s than Form I I . T h i s may be the r e s u l t of a diminishment of o r b i t a l angular momentum c o n t r i b u t i o n s t o the g v a l u e . T h i s can be e n v i s i o n e d by comparing F i g u r e s 2.5b and 2.5c. We see t h a t as the geometry of the iron-oxygen chromophore becomes d i s t o r t e d towards a more t e t r a h e d r a l geometry, the (d ,d ) and d 2 2 l e v e l s c r o s s , thus xz yz x - y e l i m i n a t i n g the o r b i t a l angular momentum c o n t r i b u t i o n s by l e a v i n g the degenerate l e v e l h a l f - f i l l e d . Since the g v a l u e s are s t i l l q u i t e high, i t would appear t h a t the case here i s r e a l l y a mixture of these two d i f f e r e n t s c e n a r i o s . I t would appear t h a t Form I compounds thus seem t o have h i g h e r o r b i t a l angular momentum c o n t r i b u t i o n s t o the g value s than Form II compounds. The r e f o r e , i t would be expected t h a t ground Form I samples sh o u l d have lower g v a l u e s than t h e i r u n t r e a t e d c o u n t e r p a r t s . T h i s i s seen i n the r e s u l t s d e p i c t e d i n Table 2.5; upon g r i n d i n g , the Form I compounds w i l l go t o From II and the. g val u e decreases a c c o r d i n g l y . G r i n d i n g sample 3, a Form II compound, should have l i t t l e i f no e f f e c t on the g value (see F i g u r e s 2.17 and 2.18). I t i s seen, i n f a c t t h a t the g value r i s e s s l i g h t l y , although t h i s s l i g h t r i s e may be i n s i g n i f i c a n t , as w i l l be demonstrated soon. In a d d i t i o n t o t h i s r e d u c t i o n of o r b i t a l c o n t r i b u t i o n s , the observed paramagnetic component has i n c r e a s e d ; t h i s seems a l o g i c a l consequence of g r i n d i n g the extended polymer c h a i n and thus b r e a k i n g i t i n t o f i n i t e s e c t i o n s . The appearance o f the "paramagnetic t a i l " at low temperatures i s the most v i s i b l e m a n i f e s t i a t i o n of paramagnetic component i n a poly m e r i c a n t i f e r r o m a g n e t i c compound. The paramagnetic component i s 48 TEMPERATURE flO TEMPERATURE (K) Figure 2.17. Comparison of the magnetic susceptibility vs. temperature behaviours of untreated and ground compound 3. j O s C I u 6 C ioo H d CD 120 H 80 U g 60 U i C < ^ 20 4 0 •o Legend • SAM»L( J . G»0U*D -1 10 — I — 20 30 — i — 40 —I— 50 — i — 60 — l — 70 i 60 TEMPERATURE (K) Figure 2.18. Magnetic susceptibility vs. temperature of compound 3, ground, line is generated from the Fisher S - l model, J—3.40. g-3.00. P=1.98. Solid 0.0 40 .0 T E M P E R A T U R E ( K ) 80.0 5 0 a c t u a l l y seen to decrease m a r g i n a l l y f o r 3 upon g r i n d i n g . This i s not expected, but the value of F i n d i c a t e s t h a t t h i s f i t may have a l a r g e r amount of u n c e r t a i n t y a s s o c i a t e d w i t h i t than f o r the untreated sample. Note t h a t the x vs. T curves f o r unground samples of 1 and 2 M are almost i d e n t i c a l (Figures 2.8 and 2.9). This n e c e s s i t a t e s a d i s c u s s i o n of the p r e c i s i o n of the output parameters of the t h e o r e t i c a l f i t s . Figures 2.19 and 2.20 show F i s h e r S=l t h e o r e t i c a l f i t s t o the x vs. T data of the unground sample of 2. M In Figure 2.19, J i s f i x e d at -3.00 and g i s given the values 3.36, 3.29 and 3.22, r e p r e s e n t i n g a 2% v a r i a t i o n . In Figure 2.20, g i s f i x e d at 3.29 and J i s given the values -3.15, -3.00 and -2.85, r e p r e s e n t i n g a 5% v a r i a t i o n i n t h i s parameter. I f e r r o r bars c o n s t i t u t i n g +2% i n the value of the magnetic s u s c e p t i b i l i t y are drawn i n (see Chapter V) , we see t h a t these v a r i a t i o n s i n g and J are w i t h i n experimental e r r o r . Thus, we can say t h a t J i s accurate t o +5% and g i s accurate t o +2% as quoted. 51 cr *-~> 5 :-»» 3 II N i be to — T J o <»" c 3 j o n — 1-2 2 <w ^ 3 — i O I 3 c/> — c o r> T1TJ II 2 II < o IS S- 3 - n II 3 a c o o s i o § cr CX 3 c c 3 - 3 a O - w c II 2. cn > H C m ^ =f 2; "-jr* c n m > H C c n CD a MAGNETIC SUSCEPTIBILITY ( lO 3 C M 3 M O L 1 ) 0-0 60.0 120.0 o o MAGNETIC SUSCEPTIBILITY ( lO 3 C M 3 M O L 1 ) 0 . 0 60.0 1 2 0 . 0 a a C H A P T E R I I R E F E R E N C E S 1. Du, J.-L.; O l i v e r , K.W.; Thompson, R.C. Can. J. Chem. 1989, 67, 1239. 2. Haynes, J.S.; O l i v e r , K.W.; Thompson, R.C. Can. J. Chem. 1985, 63, 1111. 3. Gillman, H.D.; E i c h e l b e r g e r , J.L. Inorg. Chem. 1976, 15, 840 . 4. Cich a , W.V.; Haynes, J.S.; O l i v e r , K.W.; R e t t i g , S.J.; Thompson, R.C; T r o t t e r , J . Can. J. Chem. 1985, 63, 1055. 5. Bino, A.; Sissman, L. Inorg. Chim. Acta 1987, 128, L21. 6. O l i v e r , K.W.; R e t t i g , S.J.; Thompson, R .C; T r o t t e r , J . Can. J. Chem.1982, 60, 2017. 7. Haynes, J.S.; O l i v e r , K.W.; R e t t i g , S.J.; Thompson, R.C; T r o t t e r , J . Can. J. Chem. 1984, 62, 891. 8. O l i v e r , K.W., Ph.D. Th e s i s , U n i v e r s i t y of B r i t i s h Columbia, 1984 . 9. Du, J.-L.; O l i v e r , K.W.; Thompson, R.C Inorg. Chim. Acta 1988, 141, 19. 10. Du, J.-L., M.Sc. Th e s i s , U n i v e r s i t y of B r i t i s h Columbia, 1987. 11. Banks, P.R., B.Sc. T h e s i s , U n i v e r s i t y of B r i t i s h Columbia, 1986. 12. Peers, J.R.D., B.Sc. T h e s i s , U n i v e r s i t y of B r i t i s h Columbia, 1987. 13. Begley, M.J.; Dove, M.F.A.; Hi b b e r t , R . C ; Logan, N.; Nunn, M.; Sowerby, D.B. J. Chem. Soc. Dalton Trans. 1985, 2433. 14. Gillman, H.D. Inorg. Chem. 1972, 22, 3124. 53 15. Mackey, D.J.; McMeeking, R.F. Hitchman, M.A. J. Chem. Soc. Dalton Trans. 1979, 300. 16. Burns, R.G.; C l a r k , M.G.; Stone, A . J . Inorg. Chem. 1966, 5, 1268. 17. G o l ' d a n s k i i , V . I . The Mossbauer Effect and Its Applications in Chemistry, C o n s u l t a n t s Bureau, New York, 1964. 18. Muir, A.H., j r . ; Ando, K.J.; Coogan, H.M. Mossjbauer Effect Data Index 1958-1965, I n t e r s c i e n c e , New. York, 1966. 19. Haynes, J.S., Ph.D. Th e s i s , U n i v e r s i t y o f B r i t i s h Columbia, 1985. 20. Sams, J.R. MTP Int. Rev. Sci. 1972, 4, 183. 21. Haynes J.S.; K o s t i k a s , A.; Sams., J.R.; Simopoulos, A.; Thompson, R.C. Inorg. Chem. 1987, 26, 2630. 22. Sams, J.R.; T s i n , T.B Inorg. Chem. 1975, 14, 1573. 23. Sams, J.R.; T s i n , T.B. Chem. Phys. 1976, 15, 209. 24. Haynes, J.S.; Hume, A.R.; Sams, J.R.; Thompson, R.C. Chem. Phys. 1983, 78, 127. 25. Collman, J.P.; Hoard, J.L.; Kim, N.; Lang, G. Reed, C.A.; J. Am. Chem. Soc. 1975, 97, 2676. 26. Dolphin, D.; Sams, J.R.; T s i n , T.B.; Wong, K.L. J. Am. Chem. Soc. 1976, 98, 6970. 27. E p s t e i n , L.M. J. Chem. Phys. 1962, 36, 2731. 28. Dale, B.W.; W i l l i a m s , R.J.P.; Edwards, P.R.; Johnson, C.E. J. Chem. Phys. 1968, 49, 3445. 29. Konig, E.; Kannellakopulos, B. Chem. Phys. Lett. 1972, 12, 485. 30. Konig, E.; Madeja, K. Inorg. Chem. 1968, 7, 1848. 31. D o l p h i n . D.; Sams, J.R.; T s i n , T.B. Inorg. Chem. 1977, 16, 54 711. 32. Sams, J.R.; Tsin, T.B., i n The Porphyrins, Dolphin, D. ed. . Academic Press, New York, 1979. 33. Barraclough, C.G.; Martin, R.L.; Mitra, S.; Sherwood, R.C. J. Chem. Phys. 1970, 53, 1643. 34. a) Mabbs, F.E.; Machin, D.J. Magnetism and Transition Metal Complexes, Chapman and H a l l , London, 1973. b) Fi g g i s , B.N. Introduction to Ligand Fields, Interscience Publishers, New York, 1967. 35. Caneschi, A.; Gatteschi, D.; Rey, P.; Ses s o l i , R. Inorg. Chem. 1988, 27, 1756. 36. D r i l l o n , M.; Coronado, E.; Beltran, D.; Georges, R. Chem. Phys. 1983, 79, 449. 37. Fisher, M.E. Am. J. Phys. 1964, 32, 343. 38. Weng, C.H., Ph.D. Thesis, Carnegie-Mellon University, Pittsburgh, 1968. 39. Fisher, M.E. J. Math. Phys. 1963, 4, 124. 40. Bonner, J . C ; Fisher, M.E. Phys. Rev. Sect. A 1964, 135, 640. 41. Lines, M.E. J. Phys. Chem. Solids 1970, 31, 101. 42. Bleaney, K.; Bowers, K.D. Proc. Roy. Soc. London 1952, A214, 451. 55 I I I . R E S U L T S A N D D I S C U S S I O N I I : Z I N C D O P E D P O L Y - u - B I S ( D I - N - O C T Y L P H O S P H I N A T O ) I R O N ( I I ) We now t u r n to a d i s c u s s i o n of the p r e p a r a t i o n s , thermal, magnetic and i n f r a r e d and Mossbauer s p e c t r a l p r o p e r t i e s of the doped analogues of the type Fe Zn [ (C H ) PO ] , where x takes c ^ J C l - x x 8 17 2 2 2' the values 0.05, 0.1 and 0.2 (a sample was prepared w i t h x=0.9, but not analyzed i n d e t a i l ) . I t w i l l be seen t h a t not only do these samples f o l l o w the same polymorphic behaviour as the undoped analogues, but a l s o d i s p l a y evidence of having two d i f f e r e n t s p i n s t a t e s present at the same time. A . S Y N T H E S E S As discussed i n Section I I , the r e a c t i o n c o n d i t i o n s and s t o i c h i o m e t r i e s of the preparations of these species have a s i g n i f i c a n t e f f e c t on the p r o p e r t i e s of the sample. Thus, f o r the same reasons, Form I and Form I I doped samples have been obtained. The c l a s s i f i c a t i o n s are as f o l l o w s : samples w i t h x=0.2 and 0.05 were prepared according t o procedures which y i e l d Form I m a t e r i a l s ; the sample with x=0.1 was prepared according t o Form I I s y n t h e t i c techniques. In t h i s case the i s o l a t i o n of pure Form I and I I m a t e r i a l s was not as good as wi t h the undoped samples, but nonetheless evidence of the presence of the two forms i s observed. The y i e l d of the x=0.2 sample was too low t o do an in-depth a n a l y s i s of the thermal p r o p e r t i e s of the sample, and only the ground form of t h i s compound was analyzed by IR. However, there was enough sample f o r a n a l y s i s of the magnetic and Mossbauer 56 s p e c t r a l p r o p e r t i e s of the compound. B . I N F R A R E D S P E C T R A I n f r a r e d s p e c t r a l data f o r the zinc-doped samples are shown i n Table 3.1. Complete assignment of bands can be found i n Appendix I. I f we compare these data, we see the same d i s t i n c t i v e i>(P02) r e g i o n f o r the polymorphic Forms I and I I , w i t h the same e f f e c t d i s p l a y e d upon the e x e r t i o n o f p r e s s u r e on the sample: the complex multiband i>(PO ) r e g i o n s i m p l i f i e s t o a two band r e g i o n . T a b l e . 3.1. I n f r a r e d S t r e t c h i n g F r e q u e n c i e s (cm - 1) of i>(P02) Regions of Doped Samples Fe Zn [ (C H ) PO 1 3 r c 1-X X 8 17' 2 2 J 2 Untreated Ground Sample X V asy V sym V asy V sym 5 0.2 1110 s 1045 s 1137 m sh 1060 sh 6 0.1 1098 s 1040 s 1110 s 1046 s 1135 m sh 1070 m s h 1138 sh 1071 sh 1103 s 1021 s 1102 s 1019 sh 7 0.05 1119 sh 1050 s 1136 s h 1042 s 1138 s 1072 S 1070 sh (sh=shoulder; s=strong; m=medium) These r e s u l t s show the same type of behaviour as the undoped 57 samples, w i t h g r i n d i n g having the expected e f f e c t . We a l s o see, as i n compound 4, t h a t 6 l i k e l y contains some Form I contamination which i s removed upon g r i n d i n g . I t seems th a t g r i n d i n g 7 gave an incomplete conversion t o Form I I i n t h i s case, w i t h j u s t a red u c t i o n i n the i n t e n s i t y of the si d e bands as a r e s u l t . C . T H E R M A L S T U D I E S DSC s t u d i e s f o r these compounds showed the appearance of an endothermic event at 65° C (see Figure 3.1), which seems t o be a r e s u l t of z i n c doping. As with the pure samples, no evidence of me l t i n g before thermal decomposition i s seen. The data f o r 6, the sample wi t h x=0.1, show an endothermic event at 100°C, which disappears a f t e r one run. The second run on the same sample d i s p l a y s a s m a l l , broad endothermic event at 65° C. This same endothermic event i s seen i n 7, the x=0.05 sample, and becomes l a r g e r upon successive runs. There appears t o be no s i g n i f i c a n t d i f f e r e n c e i n the thermal p r o p e r t i e s of 6 and 7, proposed t o be Forms I and I I r e s p e c t i v e l y , except t h a t the 65° C event i s more pronounced i n the case of 7. This could be a d i s t i n g u i s h i n g f e a t u r e of the Form I doped samples and may then r e f l e c t some Form I i m p u r i t y i n 6. As before w i t h the undoped samples, the DSC r e s u l t s seem t o i n d i c a t e t h a t the Form I » Form I I t r a n s i t i o n i s one tha t i s induced by pressure only, and not heat. 58 Heat Flow (Exothermal) —> Heat Flow (Exothermal) —> D . M O S S B A U E R S P E C T R O S C O P Y The Mossbauer spectra of the doped samples show the doublet ascribed to S=l Fe(II) as seen i n the pure samples, but also contain a doublet i n the higher v e l o c i t y region. This second doublet has parameters t y p i c a l of S=2 iron (II) complexes, with a large quadrupole s p l i t t i n g and an isomer s h i f t i n the region of 1.1 mm s"1. The actual spectra are shown i n Figures 3.2-3.4. The parameters for samples 5-7 are shown i n Table 3.2. Another parameter, the r e l a t i v e area of the S=2 doublet to the S=l doublet y, i s included here. Table 3.2. Mossbauer Spectral Parameters for Zinc-doped Compounds Sample 6 (mm s S A E Q (mm s "*") y 5 0.28 1.12 0.31 3.17 0.14 6 0.31 1.10 0.45 3.18 0.16 7 0.36 0.45 N/A It should be noted here that the spectrum for 7 was d i f f i c u l t to f i t to Lorentzians for two doublets, owing to the small magnitude of the S=2 doublet. However, an examination of the spectrum shows clea r evidence of t h i s doublet. The presence of the two spin states of iron (II) i n these compounds raises some in t e r e s t i n g points. It i s apparent from these spectra and from arguments already made about the influence 60 Figure 3.2. Mossbauer spectrum of compound 5 (x=0.2) at 77 K. • $ T 1 — i 1 r - 3 - 2 - 1 0 1 2 Doppler Velocity (mm s-1) Figure 3.3. Mossbauer spectrum of compound 6 (x=0.1) at 77 K. - 3 - 2 - 1 0 1 2 Doppler Velocity (mm s*1) Figure 3.4. Mossbauer spectrum of compound 7 (x=0.05) at Doppler Velocity (mm s-1) 62 of geometry on the s p i n s t a t e of Fe(II) complexes t h a t the e f f e c t of doping z i n c atoms i n t o the poly m e r i c i r o n backbone causes a change i n the geometry about the i r o n n u c l e u s . I t can be surmised t h a t s i n c e z i n c i s o f t e n found i n a t e t r a h e d r a l l i g a n d environment t h i s i s indeed the case here and t h a t these z i n c atoms have i n f a c t puckered the i n o r g a n i c M-0-P-O-M backbone i n such a way t h a t the i r o n atoms adjacent t o the z i n c atoms have adopted a more t e t r a h e d r a l l i g a n d environment. F i g u r e 2.5 shows the consequences of such a change. T h i s would g i v e r i s e t o a g r e a t e r number of S=2 i r o n c e n t r e s and thus the h i g h v e l o c i t y doublet seen i n the Mossbauer s p e c t r a . The r e l a t i v e areas of the d o u b l e t s should be p r o p o r t i o n a l t o the amount of t e t r a h e d r a l i r o n c e n t r e s i n the c h a i n . I f t h i s i s the case, i t would seem t h a t the x=0.2 sample (compound 5) does not r e a l l y have an x=0.2 doping l e v e l , but r a t h e r a l e v e l more l i k e t h a t of the x=0.1 sample (compound 6) . However, i t may a l s o be t h a t as the doping l e v e l becomes higher, the l i k e l i h o o d of two z i n c c e n t r e s b e i n g adjacent t o each other i n c r e a s e s , thus the number of i r o n c e n t r e s a f f e c t e d by the p r o x i m i t y of the z i n c c e n t r e s w i l l seem s m a l l e r than expected. The Mossbauer r e s u l t s f o r the compounds a l s o a l l o w us t o make arguments about t h e i r s t r u c t u r a l d i m e n s i o n a l i t y . I f these compounds are indeed f o u r - c o o r d i n a t e as proposed, a t h r e e - d i m e n s i o n a l p o l y m e r i c system i s u n f e a s i b l e . I f we c o n s i d e r two- and one-dimensional systems, we can imagine the e f f e c t of doping z i n c i n t o such systems. A two-dimensional system would be more g r e a t l y a f f e c t e d by doping than a one-dimensional system, because each z i n c atom would " i n f l u e n c e " as many as f o u r i r o n 63 a t o m s a r o u n d i t , w h e r e a s a maximum o f j u s t two i r o n a t o m s w o u l d b e i n f l u e n c e d p e r z i n c a t o m i n a o n e - d i m e n s i o n a l p o l y m e r i c s y s t e m . T h i s i n t u r n w o u l d c a u s e a much h i g h e r amount o f S=2 i r o n t o b e s e e n i n t h e M o s s b a u e r s p e c t r a (y s h o u l d a p p r o a c h u n i t y f o r x = 0 . 1 ) . I n s t e a d , we c a n p r o p o s e t h e p o l y m e r i c c h a i n t o b e o f a o n e - d i m e n s i o n a l n a t u r e , d u e t o t h e l o w v a l u e s o f y s e e n i n t h e s p e c t r a l p a r a m e t e r s . T h i s a l s o s u p p o r t s t h e u s e o f a o n e - d i m e n s i o n a l l i n e a r c h a i n m o d e l i n m o d e l l i n g m a g n e t i c s u s c e p t i b i l i t y r e s u l t s f o r t h e s e c o m p o u n d s . A s i n t h e c a s e o f F e [ ( C g H i 7 ) 2 P 0 2 ] , t h e q u a d r u p o l e s p l i t t i n g s o f t h e d o p e d c o m p o u n d s w a r r a n t c o m m e n t . T h e s p l i t t i n g o f t h e S= l d o u b l e t i s a p p r o x i m a t e l y t h a t s e e n i n t h e u n d o p e d s a m p l e s . T h e s p l i t t i n g o f t h e S=2 d o u b l e t , h o w e v e r , i s much l a r g e r i n m a g n i t u d e t h a n w o u l d b e e x p e c t e d i n t h e c a s e o f a n o r m a l f o u r - c o o r d i n a t e S=2 c o m p l e x . I f we l o o k a g a i n a t F i g u r e 2 . 6 a n d c o n s i d e r t h a t t h e d 2 2 l e v e l w i l l r e d u c e i n e n e r g y a s t h e m e t a l - o x y g e n c h r o m o p h o r e x - y b e c o m e s m o r e t e t r a h e d r a l , t h i s u p p e r s t a t e w i l l t h e n become t h e r m a l l y a c c e s s i b l e . We w i l l t h e n h a v e a (d 2) 2 (d , d ) 2 z xz yz (d ) 1 (d 2 2) 1 c o n f i g u r a t i o n , g i v i n g S=2 a n d q=-^<r~ 3 > ( see xy x - y 7 E q u a t i o n 2 . 1 1 ) . I f t h e g e o m e t r y moves f u r t h e r t o w a r d s a t e t r a h e d r a l c o n f o r m a t i o n , t h e d 2 2 a n d d l e v e l s w i l l c r o s s , x - y x y • 4 -3 b u t t h e v a l u e o f q w i l l s t i l l b e ~~<r >• T h e d i f f e r e n c e i n t h e q v a l u e s o f t h e S = l a n d S=2 s p e c i e s c o r r e s p o n d s t o a d i f f e r e n c e i n t h e q u a d r u p o l e s p l i t t i n g s o f t h e two s p i n s t a t e s o f 2 - 3 mm s " 1 , w h i c h a c c o u n t s f o r t h e l a r g e q u a d r u p o l e s p l i t t i n g s e e n i n t h e S=2 d o u b l e t s o f t h e d o p e d c o m p o u n d s . T h e q u a d r u p o l e s p l i t t i n g i s p r o p o s e d t o b e p o s i t i v e , a l t h o u g h a s b e f o r e , t h i s c a n o n l y b e 64 v e r i f i e d through temperature dependent Mossbauer studies. E . M A G N E T I C S U S C E P T I B I L I T Y M E A S U R E M E N T S Again, as i s the case for pure samples of Fe [ (CgHi7) 2P0 2] 2, the two d i f f e r e n t forms of these compounds showed d i f f e r i n g magnetic s u s c e p t i b i l i t y behaviour. The difference between the two forms w i l l be argued i n an analogous manner to that used i n discussing the undoped samples. However, the x vs. T data could not be analyzed using the models described previously, owing to the two d i f f e r e n t spin states present i n these compounds. Systems of two d i f f e r e n t spins, such as mixed metal systems, have been . 1 2 studied ' , but the models used i n these cases are only applicable i n cases of c l a s s i c a l l y alternating spins. In t h i s case, we have a random system of two d i f f e r e n t spins, thus rendering the e x i s t i n g models for mixed metal systems inappropriate. These systems w i l l therefore be discussed only q u a l i t a t i v e l y , but some noteworthy conclusions ari s e from these discussions. We f i r s t discuss compound 5, where x=0.2. This compound i s proposed to be a Form I material, but the o v e r a l l s u s c e p t i b i l i t y i s higher than for the untreated forms of samples 1 and 2 (cf. Figures 2.9 and 2.10). This i s most c e r t a i n l y due to the i n c l u s i o n of S=2 components i n the sample, causing the o v e r a l l s u s c e p t i b i l i t y to increase. When the sample i s ground, l i t t l e e f f e c t i s seen, as displayed i n Figure 3.5. There appears to be some s l i g h t lowering of the o v e r a l l magnetic s u s c e p t i b i l i t y of the sample, which i s probably due to the d i s t o r t i o n from almost planar symmetry, as seen i n the pure samples. The paramagnetic component 65 3 COMPARISON OF GROUND/UNGROUND 5 x=0.2 O u ri CO w u m D t/3 u E Z o < K»0 SO • o e • e • o 10 — I — 20 i 30 i 4 0 I SO I *0 I 7 0 » 0 T E M P E R A T U R E (K) Figure 3.5. Magnetic susceptibility vs. temperature plots of untreated and ground samples of compound 5 (x=0.2). £ COMPARISON OF GROUND/UNGROUND 6 x=0.1 © 200 ri *° CQ KM e Xfi D to U to 9 «1 1 1 r . . . . < 0 tt SO M 40 SO SO ?0 2 TEMPERATURE (K) t • Figure 3.6. Magnetic susceptibility vs temperature plots of untreated and ground samples of compound 6 (x=0.1). 66 of the sample a l s o seems q u i t e high, making s u b t l e a l t e r a t i o n s i n the magnetic behaviour d i f f i c u l t t o spot. T h i s h i g h paramagnetic component i s expected here, s i n c e the doping l e v e l of x=0.2 w i l l cause more and more f i n i t e c hains of contiguous i r o n atoms to appear, d r i v i n g the o v e r a l l magnetic s u s c e p t i b i l i t y up. Next we t u r n t o compound 6, with x=0.1. The IR r e s u l t s f o r t h i s sample, as d i s c u s s e d e a r l i e r i n t h i s s e c t i o n , d i s p l a y the p r o p e r t i e s a t t r i b u t e d t o a mixture of mostly Form I I compound and som Form I compound. The vs. T data f o r the unground form show the same s o r t of behaviour (Figure 3.6), e s p e c i a l l y when compared to the u n t r e a t e d form of compound 4 (Figure 2.12). An unusual f e a t u r e , however, of t h i s compound i s i t s behaviour upon g r i n d i n g . I t i s expected t h a t g r i n d i n g a Form II compound w i l l cause no a p p r e c i a b l e e f f e c t on the geometry of the s p e c i e s . Thus, we expect the only v i s i b l e e f f e c t here t o be the i n t r o d u c t i o n of paramagnetic component t o the x data as a r e s u l t of the b r e a k i n g M of q u a s i - i n f i n i t e chains i n t o s m a l l e r , f i n i t e components. F i g u r e 3.6 shows t h a t the i n c r e a s e i n the o v e r a l l s u c e p t i b i l i t y of t h i s sample i s much h i g h e r than expected. T h i s may w e l l be the i n c l u s i o n of a l a r g e amount of paramagnetic component, but without the a p p l i c a t i o n of a s u i t a b l e q u a n t i t a t i v e model, t h i s can only be c o n j e c t u r e d . F i n a l l y , we look at the unground form of 7 (x=0.05). T h i s compound, as seen i n F i g u r e 3.7, shows very smooth x vs. T M behaviour, w i t h a w e l l - d e f i n e d maximum i n the magnetic s u s c e p t i b i l i t y at around 8 K and o n l y a s m a l l amount of paramagnetic component as evidenced i n the low temperature t a i l . 67 Figure 3.7. Magnetic susceptibility vs. temperature (x=0.05), untreated. 2 0 0 O u «? o d CD S U E O < 1 5 0 A 1 0 0 5 0 H 10 - 1 — 20 —I— 30 - 1 — 40 —I— 50 TEMPERATURE (K) 68 This compound i s proposed t o be Form I, but has a higher o v e r a l l magnetic s u s c e p t i b i l i t y than the pure Form I compounds, 1 and 2. This i s most l i k e l y due t o the i n c l u s i o n of S=2 character i n t h i s case, which w i l l increase the o v e r a l l s u s c e p t i b i l i t y and w i l l probably have some i n f l u e n c e on the magnitude of the exchange i n t e g r a l . Presumably, s i n c e the maximum i n ^  vs. T occurs at a higher temperature here, the an t i f e r r o m a g n e t i c exchange i s stronger. 69 C H A P T E R I I I R E F E R E N C E S 1. D r i l l o n , M.; Coronado, E.; Beltran, D.; Georges, R. Chemp. Phys. 1983, 79, 449. 2. Coronado, E.; D r i l l o n , M.; Nugteren P.R.; de Jongh, L.J.; Beltran, D.; Georges, R. J. Am. Chem. Soc. 1989, 111, 3874. 70 I V . C O N C L U S I O N S A N D S U G G E S T I O N S F O R F U R T H E R W O R K The compounds prepared i n t h i s study y i e l d e d some very i n t e r e s t i n g and unusual r e s u l t s . F i r s t l y , i t appears that p o l y - / x - b i s (di-n-octylphosphinato) i r o n (II) occurs i n two polymorphic forms. I t i s proposed t h a t Form I i s a quasi-square p l a n a r i r o n (II) complex. The geometry of t h i s complex and the high s e p a r a t i o n of the uppermost energy l e v e l , d 2 2, d i c t a t e s x *-y t h a t t h i s compound w i l l have the r a r e S=l s p i n s t a t e of i r o n ( I I ) . This t r i p l e t ground s t a t e i s most s t r o n g l y i n evidence i n the Mossbauer spectrum of the compound, g i v i n g isomer s h i f t s c h a r a c t e r i s t i c of S=l i r o n (II) compounds. A n a l y s i s of the quadrupole s p l i t t i n g s of these compounds i s not s t r a i g h t f o r w a r d , due t o the wealth of d i f f e r e n t p o s s i b l e c o n t r i b u t i o n s t o the e l e c t r i c f i e l d g radient of the complex. The magnetic p r o p e r t i e s are c o n s i s t e n t w i t h the S=l assignment; the high temperature magnetic moments of the samples are too low t o be c h a r a c t e r i s t i c of a r e g u l a r S=2 i r o n ( I I ) complex, and too high t o be d i s p l a y e d by a low-spin S=0 complex. A n a l y s i s of the magnetic s u s c e p t i b i l i t y vs. temperature, data of these compounds, through the use of a one-dimensional Heisenberg exchange model, shows them to be a n t i f e r r o m a g n e t i c a l l y coupled, w i t h an exchange i n t e g r a l of approximately J=-3 K and an extremely high Lande s p l i t t i n g f a c t o r , g being on the order of 3 f o r the Form I complexes. The Form I I complexes are i s o l a t e d from r e a c t i o n s having a s t o i c h i o m e t r y d i f f e r e n t from those producing Form I m a t e r i a l s . I t appears t h a t an excess of FeCl i s conducive t o the formation of Form I I 71 m a t e r i a l s . In a d d i t i o n t o t h i s , the Form I I m a t e r i a l s appear t o be more s t a b l e t o pressure than the Form I compounds, wi t h an apparent I >II t r a n s i t i o n o c c u r r i n g upon g r i n d i n g the Form I samples. The Form I I compounds, while having exchange i n t e g r a l s s i m i l a r i n magnitude t o the Form I compounds, have s u b s t a n t i a l l y s m a l l e r g values, i n d i c a t i n g p o s s i b l y s m a l l e r o r b i t a l angular momentum c o n t r i b u t i o n s i n the case of the Form I I compounds. The d i f f e r e n c e i n s t r u c t u r e and o r b i t a l angular momentum c o n t r i b u t i o n s i s not manifested i n the Mossbauer s p e c t r a l r e s u l t s , i n d i c a t i n g t h a t Form I I compounds are a l s o ground s t a t e t r i p l e t s . The magnetic s u s c e p t i b l i t y vs. temperature r e s u l t s show tha t while the exchange i n t e g r a l i s roughly the same i n Form I and Form I I compounds, the Lande s p l i t t i n g f a c t o r i s s u b s t a n t i a l l y lower i n the case of Form I I compounds. This i s i n d i c a t i v e of the red u c t i o n of o r b i t a l angular momentum c o n t r i b u t i o n s , although the mechanism f o r t h i s e f f e c t i s not c l e a r . Doping s t u d i e s i n which small amounts of z i n c ( I I ) were added to p o l y - j i - b i s (di-n-octylphosphinato) i r o n (II) a l s o showed the c h a r a c t e r i s t i c features of Form I and Form I I compounds, although i s o l a t i o n of pure Form I I samples from the r e a c t i o n s was more d i f f i c u l t . Mossbauer s t u d i e s on these compounds i n d i c a t e d the presence of two d i f f e r e n t s p i n s t a t e s of i r o n ( I I ) , w i t h a h i g h - v e l o c i t y doublet appearing, i n d i c a t i n g the occurrence of S=2 i r o n ( I I ) along w i t h the S=l sp e c i e s . This suggests t h a t when the z i n c atoms are inc o r p o r a t e d i n t o the r e g u l a r Fe-O-P-O-Fe backbone, the i r o n atoms adjacent t o the z i n c atoms are i n f l u e n c e d towards a more t e t r a h e d r a l environment, perhaps due i n p a r t t o the f a c t that 72 f o u r - c o o r d i n a t e z i n c i s normally t e t r a h e d r a l . The magnetic p r o p e r t i e s d i s p l a y e d a complicated mixture of the t r a i t s seen i n the undoped compounds, along w i t h the appearance of other e f f e c t s due t o some of the i r o n atoms having a pentet ground s t a t e . The randomly d i l u t e d magnetic systems d e s c r i b e d i n t h i s t h e s i s c ould not be modelled using the conventional equations. I t would appear here t h a t a s i t e d i l u t i o n approach i s necessary i n an a l y z i n g the magnetic p r o p e r t i e s of such systems. This may be a formidable computational challenge, but would be u s e f u l i n understanding the magnetic p r o p e r t i e s of t h i s type of compound. S y n t h e t i c a l l y , many other p o s s i b i l i t i e s e x i s t along t h i s l i n e . Other organic side groups may be used on the phosphinate l i g a n d . Studies i n v o l v i n g v a r y i n g these groups and examining the e f f e c t s on the magnetic and s p e c t r a l p r o p e r t i e s of these species could be e n l i g h t e n i n g . In a d d i t i o n , f u r t h e r Mossbauer s t u d i e s are necessary to determine the s i g n of A E q , i n order t o get a good estimate of the nature of the <r- and re-bonding of the compounds s t u d i e d . This would r e q u i r e temperature dependent s t u d i e s down t o l i q u i d helium temperatures. Mossbauer s t u d i e s i n the low temperature region would a l s o provide d i r e c t evidence of the onset of ant i f e r r o m a g n e t i c o r d e r i n g i n these compounds, by showing magnetic h y p e r f i n e c o u p l i n g beginning at the Neel temperature. 73 V . E X P E R I M E N T A L A . M A T E R I A L S A N D P R E P A R A T I V E T E C H N I Q U E S A l l m a t e r i a l s used were of reagent grade q u a l i t y and used without f u r t h e r p u r i f i c a t i o n . For syntheses d i r e c t e d towards Fe ( I I ) complexes, standard vacuum l i n e and drybox techniques were employed. Solvents used i n these pr e p a r a t i o n s were degassed by three or more freeze-pump-thaw c y c l e s and used immediately t h e r e a f t e r . A i r - s e n s i t i v e compounds were s t o r e d i n a n i t r o g e n atmosphere drybox and prepared f o r c h a r a c t e r i z a t i o n t h e r e . B . E L E M E N T A L A N A L Y S E S A n a l y s i s f o r carbon and hydrogen was performed by Mr. Peter Borda, M i c r o a n a l y s i s Lab, Chemistry Department, U n i v e r s i t y of B r i t i s h Columbia. C . I N F R A R E D S P E C T R O S C O P Y I n f r a r e d spectra were obtained using a Perkin-Elmer Model 598 spectrophotometer. The samples were mulled i n N u j o l and smeared between two KRS-5 p l a t e s (Harshaw Chemical Co.). D . E L E C T R O N I C S P E C T R O S C O P Y E l e c t r o n i c spectroscopy was performed on samples mulled i n N u j o l . A Cary 14 Spectrometer was used. E . M A G N E T I C S U S C E P T I B I L I T Y M E A S U R E M E N T S Magnetic s u s c e p t i b i l i t y data were obtained u s i n g a P r i n c e t o n 74 Applied Research Model 155 Vibrating Sample Magnetometer operating over the temperature range 2-80 K. The sample area was cooled through the use of l i q u i d helium. Temperature equilibrium was achieved using a Janis Research Company Model 153 Cryostat. The temperature was cont r o l l e d using a Princeton Applied Research Model 152 Cryogenic Temperature Controller with a GaAs diode temperature sensor. The thermocouple used was a chromel versus Au-0.02% Fe thermocouple located i n the sample holder immediately above the sample. The thermocouple was c a l i b r a t e d using the known s u s c e p t i b i l i t y , versus temperature behaviour of tetramethylenediammonium tetrachlorocuprate(II) 1 and checked with mercury (II) tetrathiocyanatocobaltate (II) . From the scatter seen in several separate c a l i b r a t i o n s , the temperature data are estimated to be accurate to ±1% over the temperature range studied. The pot e n t i a l across the thermocouple was measured on a Fluke 8200 A D i g i t a l Voltmeter. An applied magnetic f i e l d of 7501 G was attained through the use of a Walker-Magnion Model L75BF Electromagnet with a Model HS 1050 Power Supply. Accurately weighed samples of approximately lOOmg, contained i n Kel-F capsules, were attached to a Kel-F holder with an epoxy r e s i n . Corrections were made for the diamagnetic background of the sample holder. The accuracy of magnetic s u s c e p t i b i l i t y measurements using t h i s technique i s estimated to be ±2%. Corrections to measured magnetic s u s c e p t i b i l i t i e s were made using Pascal's constants 2 and calculated as follows. Diamagnetic s u s c e p t i b i l i t i e s (xlO - 6 cm3 mol" 1): H, -2.93; C, -6.00; P, -26.3; 0, -4.61; Zn 2 +, -10; Fe 2 +, -13. Thus, for a l l compounds studied, 75 the diamagnetic correction i s equal to -475x10 6 cm3 mol 1. F . M O S S B A U E R S P E C T R O S C O P Y The Mossbauer spectrometer consisted of a 5 7Co source, anchored i n a Rh matrix, and attached to a Technical Measurement Corporation Model 306 drive and l i n e a r motor. Detection was achieved using a Xe-C02 proportional counter.The signal was analyzed using a Tracor Northern TN-1706 Analyzer. To avoid problems of oxidation, the samples were encased i n a Mylar holder which was held together with epoxy. The Doppler v e l o c i t y scale was c a l i b r a t e d using iron f o i l and the isomer s h i f t s are quoted r e l a t i v e to the centroid of the iron f o i l spectrum. The spectra at 77 K were f i t t e d to Lorentzian l i n e shapes by a least-squares procedure. Errors i n isomer s h i f t s and quadrupole s p l i t t i n g s are estimated to be no greater than +0.01 mm s"1 for the S=l l i n e s and +_0.03 mm s - 1 for the smaller S=2 l i n e s . 6. S Y N T H E S E S Gl. Synthesis of Di-n-octylphosphinic Acid, ( C 8 H 1 7) 2 P 0 2 H -This synthesis was c a r r i e d out according to the method of Peppard et al.2. In a round-bottom flask, 315 ml (2.01 mol) 1-pctene, 90 ml 50% aqueous H2P02H (0.96 mol H2PO.H) , 14.5191 g (59.94 mmol) benzoyl peroxide, 350 ml ethanol and 65 ml water were combined and refluxed for 24 hr. The solution was then cooled and 500 ml 1.0 M HC1 and 800 ml benzene were added. The mixture was 76 agitated and the aqueous layer discarded. The organic layer was scrubbed with two 200 ml portions of 1.0 M HC1, y i e l d i n g a f r a c t i o n with undissolved product present. The product was dissolved upon addition of 400 ml 1.0 M HC1 and 600 ml petroleum ether. The mixture was shaken and the aqueous layer discarded. The organic layer was evaporated to dryness and r e c r y s t a l l i z e d from acetone to y i e l d the f i n a l product. Analysis for C H PO : J c 16 35 2 c a l c . C 66.17, H 12.15; found C 66.49, H 12.30. G2. Synthesis of Bis(di-n-octylphosphinato)iron(II), Fe[(C H ) PO ] . 8 17 2 2 2 As displayed i n Section II, reaction conditions are c r u c i a l i n determining which of the polymorphic forms of Fe [ (C H ) PO ] 3 IT j IT 8 17 2 2 2 i s obtained. It appears that Form I compounds form when the stoichiometric r a t i o of (C H ) PO to FeCl i s quite close 8 17 2 2 2 ^ to 2:1 and when no pressure i s exerted upon the sample. On the other hand, Form II compounds appear to form when there i s an excess of FeCl or (C H ) PO and when pressure i s applied to 2 8 17 2 2 r c c the sample. The synthesis of each i n d i v i d u a l sample of Fe[(CH ) PO ] w i l l be described to i l l u s t r a t e t h i s point. 8 17 2 2 2 ^ G2.1 Fe[(C H ) PO ] , sample 1 . 8 17 2 2 2 r A methanolic solution of 0.9792 g (3.372 mmol) (C H ) PO H was neutralized with an aqueous solution of 0.2512 g 8 17 7 2 2 ^ 3 (1.818 mmol) K 2C0 3. To t h i s s t i r r e d solution an aqueous solution of 0.2988 g (1.503 mmol) FeCl 2»4H 20 was added dropwise, whereupon a white p r e c i p i t a t e formed immediately. The solution was s t i r r e d overnight, f i l t e r e d and washed with water, then dried at 60° C for 77 about 4 hr. The product, a f t e r drying, had a l i g h t tan colour. Analysis for FeC H PO : c a l c . C 60.56, H 10.80; found C 60.44, J 32 68 2 4 H 10.88. G2.2 Fe[ (C 8H i 7) 2P0 2] 2, sample 2 A methanolic solution of 0.9914 g (3.414 mmol) (CH ) POH 8 17 2 2 was neutralized with an aqueous solution of 0.1885 g (1.364 mmol) K2C03- To t h i s s t i r r i n g solution an aqueous solution of 0.2851 g (1.434 mmol) FeCl 2-4H 20 was added dropwise. A white p r e c i p i t a t e formed immediately. The product was f i l t e r e d o f f immediately, then dried under vacuum at room temperature for 2 hr, then an 50° C for a t o t a l of 10.5 hr. As with 1, the product was a l i g h t tan af t e r drying. I n i t i a l microanalytical r e s u l t s indicated the possible excess of unreacted acid, so the compound was s t i r r e d i n ethanol for 4 days to remove t h i s excess. Analysis for FeC H PO : calc C 60.56, H 10.80; found C 60.90, H 32 68 2 4 10.82 .Analysis for FeC H P 0 : calc C 60.56, H 10.80; found C J 32 68 2 4 60.33, H 11.00. G2.3 Fe[(C H ) PO ] , sample 3. 8 17 2 2 2 A methanolic solution of 3.271 mmol (C H ) PO H was 8 17 2 2 p a r t i a l l y neutralized with an aqueous solution of 1.153 mmol K CO . To t h i s , an aqueous solution of 1.576 mmol of FeCl -4HO 2 3 2 2 was added dropwise, giving a white p r e c i p i t a t e immediately. The product was s t i r r e d for 36 hrs, then washed with methanol then water and dried under vacuum for a t o t a l of 10 hr at 75° C. The dried product was a darker tan than 1 or 2. Analysis for 78 FeC H P 0 : c a l c . C 60.56, H 10.80; found C 60.33, H 11.00. 32 68 2 4 G2.4 Fe[(CH ) PO] , sample 4 8 17 2 2 J 2' ^ A methanolic solution of 3.425 mmol (CH ) PO H was 8 17 2 2 neutralized with an aqueous solution of 2.312 mmol K 2C0 3. To t h i s , an aqueous solution of 1.138 mmol FeCl 2-4H 20 was added dropwise, giving a white p r e c i p i t a t e immediately. The product was f i l t e r e d o f f immediately af t e r addition was complete and washed with methanol, then l e f t overnight under a stream of nitrogen. The sample was then dried at room temperature under vacuum for 6 hr. The product was approximately the same shade of tan ( f a i r l y dark) as 3. Analysis for FeC H P 0 : c a l c . C 60.56, H 10.80; J 32 68 2 4 ' found C 60.29, H 11.00. G3. Synthesis of bis(di-n-octylphosphinato)zinc(II), Zn [ (C H ) PO ] . 8 17 2 2 2 The procedure used here was analogous to that described above for the preparation of bis(di-n-octylphosphinato)iron(II). A s t i r r e d methanolic solution of 0.5013 g (1.726 mmol) (C H ) PO H was p a r t i a l l y neutralized with 0.0915 g (0. 662 mmol) 8 1 7 2 2 r J 3 K 2C0 3 dissolved i n water. An aqueous solution of 0.2316 g (1.699 mmol) ZnCl 2 was added dropwise, forming a white s o l i d immediately, and the mixture was s t i r r e d for 4 hr. The white s o l i d was f i l t e r e d o f f and washed with methanol, then water, then methanol again. The product was dried under vacuum at 60°C for 8 hr. Analysis for ZnC H PO : c a l c . C 59.66, H 10.64; found C 59.57, J 32 68 2 4 79 H 10.73. G4. Preparation of Mixed-Metal Compounds, Fe Zn [(C H ) PO ] ^ ^ ' x 1-x 8 11 2 2 2 G4.a. Fe Zn [(C H ) PO ] , sample 5 0.8 0.2 8 17 2 2 2 ^ A s t i r r e d solution of 0.7182 g (2.473 mmol) (C H ) PO H was ^ 8 17 2 2 p a r t i a l l y neutralized with 0.1989 g (1.439 mmol) K 2C0 3 i n water. A mixture of 0.030 g (0.22 mmol) ZnCl 2 and 0.1715 g (0.8626 mmol) FeCl -4H 0 was dissolved i n water and added dropwise to the 2 2 s t i r r e d neutralized acid solution. A white p r e c i p i t a t e formed immediately aft e r the i n i t i a l few drops were added and the mixture was l e f t s t i r r i n g overnight. The product was f i l t e r e d o f f and dried at room temperature under vacuum for 1 hr. The product was a l i g h t tan colour at t h i s stage. Upon drying under vacuum at 80°C for 4 hr the product became a darker brown colour. Analysis for Fe Zn C H P 0 : ca l c . C 60.38, H 10.77; found C 60.22, 0.8 0.2 32 68 2 4 ' H 11.00. G4.b. Fe Zn [ (C H ) PO ] , sample 6 0.9 0.1 8 17 2 2 2 c A s t i r r e d solution of 1.0542 g (3.630 mmol) (C H ) PO H was 8 17 2 2 p a r t i a l l y neutralized with 0.2322 g (1.680 mmol) K 2C0 3 dissolved i n water. A combination of 0.0284 g (0.208 mmol) ZnCl 2 and 0.2961 g (1.489 mmol) FeCl -4H 0 was dissolved i n water and added 3 2 2 dropwise to the s t i r r e d neutralized acid solution. A white s o l i d formed immediately and was f i l t e r e d o f f immediately a f t e r addition 80 and then washed with methanol. The product was dried at room temperature under vacuum for 7 hr. Microanalysis showed the product to be high i n carbon and hydrogen content, implying that an excess of unreacted (CgHi7) 2P02H was present. The product was s t i r r e d i n methanol for one week to remove t h i s unreacted s t a r t i n g reagent, then f i l t e r e d o f f and dried at 85°C. Analysis for Fe Zn C H PO : c a l c . C 60.47, H 10.78; found C 60.68, H 0.9 0.1 32 68 2 4 10.86. G4.c. Fe Zn [ (C H ) PO ] , sample 7 0.95 0.05 8 17 2 2 2 c A s t i r r e d solution of 1.0 g (3.5 mmol) (C H ) PO H i n ^ 8 1 7 ' 2 2 methanol was p a r t i a l l y neutralized with 0.20 g (1.5 mmol) K 2C0 3 i n water. An aqueous solution of 0.011 g (8.1 pimol) ZnCl 2 and 0.30 g (1.5 mmol) FeCl 2-4H 20 was added dropwise to the neutralized acid solution and s t i r r e d about 20 min. A white s o l i d was f i l t e r e d o ff and washed with methanol. After drying for about 7 hr at 60° C the compound analyzed low i n carbon and hydrogen, i n d i c a t i n g the need for more drying. The compound was dried at 12 0° C under vacuum for 3 hr, whereupon the compound turned to an intense brown colour. The s o l i d also seemed b r i t t l e upon grinding, unlike the normally gummy texture of these compounds. Anal. for Fe Zn C H PO : c a l c . C 60.51, H 10.79; found C 60.80, H 0.95 0.05 32 68 2 4 ' ' 10.90. G4.d. Fe Zn [ (C H ) PO ] 0.1 0.9 8 17 2 2 2 81 A s t i r r e d solution of 1.0406 g (3.583 mmol) (C H ) PO H was 8 17 2 2 p a r t i a l l y neutralized with 0.2282 g (1.651 mmol) K 2C0 3 dissolved i n water. To t h i s s t i r r i n g solution was added an aqueous solution of 0.1961 g (1.440 mmol) ZnCl 2 and 0.0339 g (0.171 mmol) FeCl 2-4H 20. The white s o l i d , which formed immediately aft e r addition of the f i r s t few drops, was f i l t e r e d o f f and washed with methanol, then dried at 100°C under vacuum. Analysis for Fe Zn C H PO : ca l c . C 59.75, H 10.65, Zn 9.15; found C 0.1 0.9 32 68 2 4 60.16, H 10.85, Zn 8.88. H . A T T E M P T E D S Y N T H E S E S HI. Fe[(C H ) PO ] 6 13 2 2 2 A synthesis of di-n-hexylphosphinatoiron(II) was attempted using a route analogous to that for the preparation of the di- n - o c t y l d e r i v a t i v e . Di-n-hexylphosphinic acid, (C H ) PO H (1.0045 g, 6 13 2 2 4.287 mmol), was dissolved i n ethanol and p a r t i a l l y neutralized with 0.2854 g (2.065 mmol) K 2C0 3 i n water. A solution of 0.3994 g (2.009 mmol) FeCl 2-4H 20 was added dropwise, whereupon a white s o l i d p r e c i p i t a t e d out of solution. The product was washed with ethanol and dried under vacuum at 60° C for 8.5 hr. Analysis was, however, unsatisfactory: calc C 55.17, H 10.03; found C 54.13, H 9.60. Further drying at 75° C for 15 hr f a i l e d to improve the microanalysis. H2. Fe Cd [ (C H ) PO ] 0.9 0.1 8 17 2 2 2 82 It was thought that perhaps cadmium would make a good dopant for these types of compounds. To t h i s end an attempt at the synthesis of a cadmium(II) doped system was undertaken. Di-n-octylphosphinic acid (1.00 g, 3.45 mmol) was dissolved i n methanol and neutralized with 0.254 g (1.84 mmol) K CO i n water. ^ 2 3 To t h i s s t i r r i n g solution, an aqueous solution of 0.298 g (1.50 mmol) FeCl -4H 0 and 0.0418 g (0.180 mmol) CdCl -2.5HO were added 2 2 ^ 2 2 dropwise, bringing the immediate formation of a white p r e c i p i t a t e . This solution was s t i r r e d overnight, then f i l t e r e d and washed with methanol and water. The product was dried at room temperature under vacuum for 6 hr. Analysis: calc C 60.02, H 10.70; found C 60.76, H 10.71. 83 C H A P T E R V R E F E R E N C E S Brown, D.B.; Crawford, V.H.; H a l l , J.W.; Ha t f i e l d , W.E. J. Phys. Chem. 1977,82, 1303. Konig, E. Landolt-Bbrnstein Numerical Data and Functional Relationships in Science and Technology. Neue Serie 11/2. Hellwege, K.H.; Hellwege, A.M. eds.. Springer-Verlag, B e r l i n , 1966. Peppard, D.F.; Mason, G.W.; Lewey, S. J. Inorg. Nucl. Chem. 1965, 27, 2065. 84 

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