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The synthesis and spectral and magnetic properties of some iron sulfonate compounds Haynes, John Stephen 1980

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THE SYNTHESIS AND SPECTRAL AND MAGNETIC PROPERTIES OF SOME IRON SULFONATE COMPOUNDS  by  JOHN STEPHEN HAYNES Graduate  o f t h e Royal  Institute  of Chemistry,  1976  A T H E S I S SUBMITTED IN P A R T I A L FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE  in THE FACULTY OF GRADUATE STUDIES (Chemistry)  We a c c e p t t h i s  thesis  as c o n f o r m i n g  to the required standard  THE UNIVERSITY OF B R I T I S H COLUMBIA A u g u s t 1980 0  John Stephen Haynes,  1980  In  presenting  an  advanced  the I  Library  further  for  this  thesis  degree shall  agree  scholarly  at the U n i v e r s i t y make  that  purposes  his representatives.  of  this  written  may  be g r a n t e d  gain  Columbia  2075 W e s b r o o k P l a c e V a n c o u v e r , Canada V6T 1W5  Date  W.  i  by  mO  shall  Columbia,  f o r reference copying  t h e Head  I t i s understood  for financial  of British  of B r i t i s h  for extensive  of  University  f u l f i l m e n t o f the requirements f o r  available  permission.  Department The  i t freely  permission  by  thesis  in partial  that  not  be  I agree and  of this  o f my  study. thesis  Department  copying  or  allowed  without  that  or  publication my  i i  ABSTRACT  The w o r k d e s c r i b e d i n t h i s t h e s i s i n v o l v e d and c h a r a c t e r i s a t i o n o f Fe(XS03)n,  where  a number o f  X is CF3,  CH3 and p - C H 3 C g H 4 ,  The w o r k i s an a t t e m p t t o a n i o n and e x t e n d s divalent  metal The  general  studies  p h y s i c a l methods  These of  the  structure  FeOg o c t a h e d r a ;  of  techniques iron(II)  proposed  in this  involves  and m a g n e t i c  on  XS03  other  infrared,  susceptibility  t o be e n v i s a g e d .  terdentate  different  metal  from p e r f e c t  methanesulfonate forms,  and t h e  was f o u n d  bridging  of  The anions,  centres r e s u l t i n g octahedral  e-isomer containing  Fe(CF3S03)2  or FeCp-CHgCgH^SO.^ but  for  structural  isomerism in other a-  to e x i s t  the a-isomer c o n t a i n i n g  No e v i d e n c e  Both  laboratory  the  have e n a b l e d a d e t a i l e d p i c t u r e  octahedra.  and Z n .  3.  in  geometry  analysed.  related structural  structural  and n i s 2 o r  characterisation included  sulfonates  the d i s t o r t i o n s  Iron(II)  FeOg o c t a h e d r a  compounds,  coordinating a b i l i t y of  spectroscopy  each anion b r i d g i n g to t h r e e  have a l s o been  synthesis  sulfonates.  measurements. structure  probe the  previous  e l e c t r o n i c and M o s s b a u e r  the  iron sulfonate  the  i n two  trigonally  trigonally  FeOg  for  spectroscopy  ( M ( C H 3 S 0 3 ) 2 compounds,  a n d e - F e ( C H 3 S 0 3 ) 2 showed u n u s u a l  compressed  elongated  i s o m e r i s m was f o u n d  vibrational  closely  revealed  where M i s  magnetic  Co  properties  II  and M o s s b a u e r t o be o b s e r v e d  s p e c t r o s c o p y e n a b l e d an a n t i f e r r o m a g n e t i c i n the case o f  the  B-isomer.  Preliminary  phase  transition  results  for  iii  the  iron(III)  sulfonates,  Fe(p-CH3CgH^S0 ) 3  compounds.  3  Fe(CF S0 ) , 3  3  3  Fe(CH S0 ) 3  3  3  and  i n d i a t e a n t i f e r r o m a g n e t i c exchange i n  these  i v  TABLE OF  CONTENTS PAGE  ABSTRACT  i i  TABLE OF CONTENTS  iv  L I S T OF TABLES  ix  L I S T OF FIGURES  xi  ACKNOWLEDGEMENT  xiv  INTRODUCTION-  1  1.1  P r e v i o u s Work-  1  1.2  P u r p o s e and O u t l i n e  CHAPTER 1  CHAPTER 2  o f t h e P r e s e n t Work-  3  EXPERIMENTAL METHODS.  7  2.1  Introduction.  7  2.2  Materials.  8  2.3  The D r y B o x .  9  2.4  S y n t h e s i s o f Compounds.  9  2.4.1  Iron(II) Trifluoromethanesulfonate, Fe(CF S0 ) .  9  Iron(II) Paratoluenesulfonate, Fe(p-CH3CgH4S03)2.  10  2.4.3  Iron(II) Methanesulfonate,  Fe(CH3S03)2-  10  2.4.4  Preparation of other Methanesulfonates, M ( C H , S 0 o ) w h e r e M i s C o , N i , C u , Zn and J C a T ^  12  Iron(III) Trifluoromethanesulfonate, Fe(CF3S03)3.  12  Iron(III) Paratoluenesulfonate, Fe(p-CH3CgH4S03)3.  12  3  2.4.2  3  2  9  2.4.5  2.4.6  V  PAGE  2.4.7  Iron(III) Methanesulfonate, Fe(CH3S03)3.  2.5  Analytical  2.6  Physical  CHAPTER 3  13  Data.  13  Experimental  Techniques.  13  2.6.1  Infrared  Spectroscopy.  13  2.6.2  Electronic  2.6.3  Magnetic S u s c e p t i b i l i t y Measurements.  15  2.6.4  Mossbauer S p e c t r o s c o p y .  16  2.6.5  A n a l y s i s o f Mossbauer S p e c t r a .  21  Spectroscopy.  15  VIBRATIONAL SPECTROSCOPY.  23  3.1  Introduction.  23  3.2  Theory of V i b r a t i o n a l  3.3  Infrared  Spectrum of  3.4  Infrared  Spectrum o f F e ( p - C H 3 C g H 4 S 0 3 ) 2 .  33  3.5  Infrared  Spectra of  35  3.5.1  3.5.2  3.5.3  3.5.4  S p e c t r a and S t r u c t u r e . Fe(CF3S03)2.  a-Iron(II)  I n f r a r e d Spectrum of Methanesulfonate.  3-Iron(Il)  35  39  I n f r a r e d Spectrum o f a Mixture a - and 3 - F e ( C H 3 S 0 3 ) 2 . Infrared  31  Fe(CH3S03)2.  I n f r a r e d Spectrum o f Methanesulfonate.  Spectrum o f  of 41  Fe(CH3S03)2.CH3S03H.  3.6  Structural  I s o m e r i s m i n FeOg O c t a h e d r a .  3.7  The S e a r c h f o r S t r u c t u r a l I s o m e r i s m i n F e ( C F 3 S 0 3 ) 2 and F e ( p - C H 3 C 6 H 4 S 0 3 ) 2 u s i n g Spectroscopy.  24  41  43  Infrared 44  vi  PAGE 3.8  The S e a r c h f o r in M(CH3S03)2  S t r u c t u r a l Isomerism Compounds u s i n g I n f r a r e d  Spectroscopy.  3.9  CHAPTER 4  45  3.8.1  Infrared  Spectrum of  Co(CH3S03).2.  4 5  3.8.2  Infrared  Spectrum of  Ni(CH3S03)2.  47  3.8.3  Infrared  Spectrum of  Cu(CH3S03)2.  47  3.8.4  Infrared  Spectrum of Z n ( C H 3 S 0 3 ) 2 .  47  3.8.5  Infrared  Spectrum of  50  Summary o f  Ca(CH3S03)2.  R e s u l t s and C o n c l u s i o n s .  ELECTRONIC SPECTRA OF  Fe(XS03)2  51  COMPOUNDS.  54  4.1.  Introduction.  54  4.2  R e s u l t s and D i s c u s s i o n .  54  CHAPTER 5  MAGNETIC S U S C E P T I B I L I T I E S OF  Fe(XS03)2  COMPOUNDS.63  5.1  Introduction.  63  5.2  Origins  64  5.3  Diamagnetism.  64  5.4  Paramagnetism.  65  5.5  T h e o r y o f P a r a m a g n e t i c S u s c e p t i b i l i t y , t h e Van V l e c k E q u a t i o n and i t s A p p l i c a t i o n t o H i g h - S p i n I r o n ( I I ) Systems.  66  5.6  The  71  5.7  R e s u l t s and D i s c u s s i o n . 5.7.1  of  Figgis  the Magnetic E f f e c t s .  and Lewis  Model.  M a g n e t i c Moment D a t a f o r  73 Fe(CF3S03)2  Fe(p-CH3C6H4S03)2. 5.7.2  M a g n e t i c Moment D a t a f o r 3- F e ( C H 3 S 0 3 ) 2 .  and 79  a-  and  . 84  vii  PAGE 5.8  CHAPTER 6 6.1  Summary o f R e s u l t s a n d C o n c l u s i o n s ,  89  MuSSBAUER SPECTROSCOPY.  90  Introduction.  90  II  6.2  Theory o f Mossbauer S p e c t r o s c o p y . 6.2.1  E l e c t r i c Monopole  91  Interaction,  the  Isomer S h i f t .  6.3.  6.2.2  Second-Order  6.2.3  E l e c t r i c Quadrupole  7.2  93  Interaction,  Isomer S h i f t  6.3.2  Quadrupole  Crystal-Field,  Values.  103  S p l i t t i n g Values.  Spin-Orbit  Parameters  94  103  109  and S p i n - S p i n  for Iron(II) Sulfonates.  MAGNETICALLY-PERTURBED 7.1  Effect.  Sulfonates.  6.3.1  Splitting CHAPTER 7  Doppler  The Q u a d r u p o l e S p l i t t i n g . Isomer S h i f t and Quadrupole S p l i t t i n g s f o r Iron(II)  6.4  91  114 120  MOSSBAUER SPECTRA.  120  Introduction. M a g n e t i c a l l y - P e r t u r b e d Mossbauer S p e c t r a Fe(p-CH3C6H4S03)2.  of  2 o f t h e S i g n o f e qQ.  7.2.1  Determination  7.2.2  The S p i n H a m i l t o n i a n  121 124 125  Model.  7.3  M a g n e t i c a l l y - P e r t u r b e d Mossbauer S p e c t r a Fe(CF3S03)2.  7.4  M a g n e t i c a l l y - P e r t u r b e d Mossbauer S p e c t r a a-Fe(CH3S03)2.  7.5  Mossbauer S p e c t r a o f e-Fe(CH3S03)2  of  134  it  of  Below 25K.  141 146  vi i i  PAGE CHAPTER 8  STUDIES ON I R O N ( I I I )  SULFONATES.  151  8.1  Introduction.  151  8.2  Infrared  151  8.3  Magnetic S u s c e p t i b i l i t i e s of Sulfonates.  Spectra of Iron(II) Sulfonates. Iron(III)  153  II  8.4  Mossbauer Spectroscopy  of  Iron(III)  Sulfonates.  8.5  "159  8.4.1  Isomer  Shift  8.4.2  Quadrupole  Values.  S p l i t t i n g Values.  "161 "163  Conclusions.  164  CONCLUSIONS-AND.SUGGESTIONS, FOR FURTHER'STUDY.  165  9.1  Conclusions.  165  9.2  Suggestions  CHAPTER 9  f o r Further Study.  167  REFERENCES.  171  APPENDIX-  177  ix  L I S T OF TABLES TABLE  PAGE  2.1  Analytical  3.1  C o r r e l a t i o n T a b l e f o r C 3 v and C g P o i n t G r o u p s .  3.2  Data.  14  Infrared Spectral  Data  (cm~^)  for  25  Fe(XS03)2  Compounds. 3.3  3.4  3.5  29  Infrared Spectral Compounds.  Data  Infrared Spectral Compounds.  Data  Infrared Spectral  Data  (cm~^)  for  M(CF3S03)2 32  (cm-1)  for M(p-CH,CfiH,SOJ9 6  (cm-1)  b  4  for Fe(CH3S03)2  J  in  t h e CH^ S t r e t c h i n g a n d B e n d i n g R e g i o n s . 3.6  Infrared Spectral  Data  (cm-1)  for  34  40  Fe(CH3S03)2.  Ch^SO^H a n d a C o m p a r i s o n w i t h a - F e ( C H 3 S 0 3 ) 2 a n d  3.7  3.8  CH3S03H.  42  I n f r a r e d S p e c t r a l Data ( c m - 1 ) f o r C o ( C H 3 S 0 3 ) 2 B e f o r e and A f t e r T r e a t m e n t w i t h 2 , 2 - D i m e t h o x y p r o p a n e .  46  Infrared Spectral  Data  (cm~^)for  Zn(CH3S03)2  B e f o r e and A f t e r T r e a t m e n t w i t h 2 , 2 - D i m e t h o x y p r o p a n e •  48  3.9  Infrared Spectral  52  3.10  Summary o f R e s u l t s M(CH3S03)2  Data  (cm-1)  f o r Ca(.CH3S03)2.  Concerning Isomerism i n  Compounds.  53  4.1  E l e c t r o n i c Spectra of Fe(XS03)2  4.2  Dq V a l u e s ( c m - 1 )  5.1  Magnetic S u s c e p t i b i l i t y  Data f o r F e ( C F 3 S 0 3 ) 2 .  75  5.2  Magnetic S u s c e p t i b i l i t y  Data f o r a - F e ( C H 3 S 0 3 ) 2 .  76  5.3  Magnetic S u s c e p t i b i l i t y  Data f o r 6 - F e ( C H 3 S 0 3 ) 2 .  77  5.4  Magnetic S u s c e p t i b i l i t y  Data f o r F e ( p - C H 3 C g H 4 S 0 3 ) 2 .  78  for M(XS03)2  Compounds.  Compounds.  56 61  X  L I S T OF  TABLES  TABLE 5.5  PAGE C r y s t a l - F i e l d S p l i t t i n g Parameters Sulfonate  Iron(II)  Compounds.  82  6.1  Values of qVA|_ for  6.2  Mossbauer E f f e c t  6.3  Isomer  6.4  C r y s t a l - F i e l d S p l i t t i n g Parameters Quadrupole S p l i t t i n g Data.  7.1  for  II  Shift  t h e 3dd O r b i t a l s .  Data f o r  Values of  Iron(II)  Fe(XS03)2  99  Sulfonates.  Compounds Derived  a t 80K.  104 108  from 118  M a g n e t i c a l l y - P e r t u r b e d Mossbauer S p e c t r a l for Fe(p-CH3C6H4S03)2.  Parameters 128  II  7.2  8.1  M a g n e t i c a l l y - P e r t u r b e d Mossbauer S p e c t r a l for a-Fe(CH3S03)2 and F e ( H 2 0 ) g S i F g . Infrared Spectral Compounds.  Data  (cnf^)  for  Parameters  Iron(III)  145 Sulfonate 152  8.2  Magnetic S u s c e p t i b i l i t y Data f o r  Fe(CF3S03)3.  154  8.3  M a g n e t i c S u s c e p t i b i l i t y Data f o r  Fe(CH3S03)3.  155  8.4  Magnetic S u s c e p t i b i l i t y Data f o r  Fe(p-CH3CgH4S03)3.  156  8.5  Mossbauer E f f e c t  Data f o r  Iron(III)  Sulfonates.  160  xi  L I S T OF FIGURES  FIGURE  PAGE  1.1  Proposed S t r u c t u r e of F e ( X S 0 3 ) 2  2.1  Schematic Diagram o f a Mossbauer Spectrometer.  2.2  Schematic Diagram o f Apparatus used f o r O b t a i n i n g V a r i a b l e Temperature M o s s b a u e r - S p e c t r a .  19  Schematic Diagram o f Apparatus used f o r O b t a i n i n g M a g n e t i c a l l y - P e r t u r b e d Mossbauer S p e c t r a .  20  3.1  Normal  25  3.2  B o n d i n g a n d Symmetry  3.3  Infrared  2.3  Compounds.  2 I7  Modes o f V i b r a t i o n o f t h e X S 0 3 ~ A n i o n .  Spectra  P r o p e r t i e s o f t h e XS03~ A n i o n .  (1500-250cm_1)  o f Fe(CFoS0,)  ?  and F e ( p - C H 3 C g H 4 S 0 3 ) 2 . Spectra  27  30  3.4  Infrared  (1500-250cm_1)  of Fe(CH3S03.)2.  3.5  The Cadmium I o d i d e L a y e r  3.6 4.1  3 3 2' Infrared Spectra (1500-250cm_1) of Zn(CH,,S0,)9. S p l i t t i n g o f the Free-Ion D G r o u n d Term i nn a n  49  Octahedral  55  Structure •  38 J U  Crystal  36  ;  Field.  4.2  E l e c t r o n i c Spectrum o f F e ( C F 3 S 0 3 ) 2 >  57  4.3  S p l i t t i n g Diagram f o r H i g h - S p i n I r o n ( I I ) i n C r y s t a l F i e l d s o f 0 n , D^ h a n d D 3 d S y m m e t r y .  59  The E f f e c t o f S p i n - O r b i t Ground Term.  5.2  T e m p e r a t u r e D e p e n d e n c e o f t h e M a g n e t i c Moment f o r F e ( X S 0 3 ) 2 Compounds.  5.3  5.4  C o u p l i n g on t h e  5  5.1  T?  ^  Plots of Reciprocal S u s c e p t i b i l i t y Against Temperature f o r F e ( C F 3 S 0 3 ) 2 and F e ( p - C H 3 C g H 4 S 0 3 ) 2 . Plots of Reciprocal S u s c e p t i b i l i t y Against T e m p e r a t u r e f o r a- a n d Fe(CH3S03)2.  69  74  8 0  85  XI L I S T OF  1  FIGURES  FIGURE 5.5  6.1  6.2  6.3  PAGE Temperature  Dependence  of the Magnetic  for  a- a n d 3 - F e ( C H 3 S 0 3 ) 2 .  (i)  Source and A b s o r b e r  (ii)  Resultant  (i)  Energy Level  (ii)  Hyperfine Resultant  Moment 87  Nuclear  Energy L e v e l s .  Mossbauer Spectrum. Scheme  Including  92 Quadrupole  Interaction. Mossbauer Spectrum.  3d O r b i t a l S p l i t t i n g s Rhombic F i e l d s .  in Octahedral,  92  96 96 Axial  and 98  6.4  C4 Quantisation  Axis  and d O r b i t a l s .  101  6.5  C3 Quantisation  Axis  and d O r b i t a l s .  102  6.6  Temperature for  6.7  6.8  Dependence  Fe(XS03)2  o f the Quadrupole  Splitting  Compounds.  110  11  Mossbauer S p e c t r a o f F e ( p - C h L C g H 4 S 0 3 ) 2 a t Temperatures. Mossbauer S p e c t r a o f F e ( C H 3 S 0 3 ) 2  Various Ill  a t 78K.  112  11  7.1  M a g n e t i c a l l y - P e r t u r b e d Mossbauer S p e c t r a Fe(p-CH3CgH4S03)2 at 2.4K.  of 122  11  7.2  7.3  M a g n e t i c a l l y - P e r t u r b e d Mossbauer S p e c t r a Fe(p-CH3C6H4S03)2 at 4.2K.  F i e l d of 5.63T.  129  C o m p a r i s o n o f Computed a n d E x p e r i m e n t a l S p e c t r a f o r F e ( p - C H 3 C g H 4 S 0 3 ) 2 a t 2 . 4 a n d 4 . 2 K i n an A p p l i e d Magnetic  7.5  123  C o m p a r i s o n o f Computed a n d E x p e r i m e n t a l S p e c t r a f o r F e ( p - C H 3 C g H 4 S 0 3 ) 2 a t 2 . 4 and 4 . 2 K i n an A p p l i e d Magnetic  7.4  of  Field  of 4.50T.  130  C o m p a r i s o n o f Computed a n d E x p e r i m e n t a l Spectra f o r F e ( p - C H 3 C g H 4 S 0 3 ) 2 a t 4 . 2 K i n an A p p l i e d Magnetic  Field  of 3.38T.  131  xiii  L I S T OF  FIGURES  FIGURE 7.6  PAGE C o m p a r i s o n o f Computed and E x p e r i m e n t a l Spectra f o r F e ( p - C H 3 C g H 4 S 0 3 ) 2 a t 4 . 2 K i n an A p p l i e d Magnetic  Field  of  1.13T.  133 II  7.7  7.8  Magnetically-Perturbed Fe(CF 3S03)2 at 4.2K.  7.10  7.11  135 ?  Fields  of  1.13  and 5 . 6 3 T .  I40  C o m p a r i s o n o f Computed a n d E x p e r i m e n t a l Spectra f o r a - F e ( C H 3 S 0 3 ) 2 . Recorded at. 4 . 5 0 J V -  142  Mossbauer S p e c t r a of a-Fe(CH-S0o)o a t 4.2K A p p l i e d M a g n e t i c F i e l d s o f 4 : 5 0 and 5 . 6 3 T .  in I43  Mossbauer S p e c t r a o f B - F e ( C H 3 S 0 3 ) 2 i n the of the Phase T r a n s i t i o n Temperature..  Proximity  7.12  Mossbauer S p e c t r a of  8.1  T e m p e r a t u r e Dependence F e ( X S 0 3 ) 3 Compounds.  of  Mossbauer  F e ( C H 3 S 0 3 ) 3 a t 80K.  8.2  of  Comparison o f Mossbauer S p e c t r a o f Fe(CF^S0o) J L and F e ( ' p - C H 3 C 6 H 4 S 0 3 ) 2 at 4.2K i n Applied Magnetic  7.9  Mossbauer S p e c t r a  147  e - F e ( C H 3 S 0 3 ) 2 below 2 1 . 1 5 K .  Spectrum of  t h e M a g n e t i c Moment  149  for 157 162  xi v  ACKNOWLEDGEMENTS  I would l i k e supervisors,  Drs. J.R.  guidance throughout  The  t o e x p r e s s my g r a t i t u d e Sams a n d R . C .  this  informal  Thompson,  t o my two r e s e a r c h for their  help and  work.  discussions with  l a b o r a t o r y and the department  colleagues in this  were s t i m u l a t i n g and very  much  appreciated.  Most s i n c e r e thanks p r o c e s s i n g t h e Mossbauer d a t a ; programmes this  a r e due t o M r s . L i a S a l l o s f o r Dr. A . R .  Hulme f o r u s e o f  he d e v e l o p e d a n d t o M r s . C e l i n e Gunawardene  thesis.  computer  for  typing  1  CHAPTER I  INTRODUCTION  1.1.  PREVIOUS WORK Previous  basic anions  has  work  on t h e  coordinating  i n c l u d e d s t u d i e s on p e r c h l o r a t e s  tetrafluoroborates  (BF4~),  perrhenates  ( P F g ~ ) and h e x a f l u o r o a r s e n a t e s (XS03", often  where  X i s F,  CF3,  anions,  where  u s e d as c o u n t e r i o n s Transition  relevant  to  the  w h i c h X i s F,  - metal  where  by  cobalt(II)  layer  and t e r d e n t a t e metal  of  laboratory  anions  the  been  and c o p p e r ( I I ) .  The  bridging anions,  ions through  studies  and  widely  species.  type  and a r e studied  M(XS03)2  '  i a v e  particularly i n c l u d e those  a n a l o g u e s were and  in  and  The  general  i s shown  in Fig.  from r e g u l a r  1.1.  investigated  magnetic  indicated that  all  the  s i x - c o o r d i n a t e metal  each a n i o n b r i d g i n g to  oxygen.  t h e M0 f i c h r o m o p h o r e s  are  (15).  l a t t i c e structures with  M ( X S 0 3 ) 2 compounds of  The  C H 3 and p - C H 3 C g H 4 a n d M i s Co and Cu ( 1 4 ) ;  s u s c e p t i b i l i t y measurements. have  sulfonates  (1-13).  i n f r a r e d and e l e c t r o n i c s p e c t r a l t e c h n i q u e s  salts  as  cationic  Sulfonates  X i s F and M i s Fe  The  (C104~),  i n p a r t i c u l a r have  sulfonates  in this  weakly  very weakly c o o r d i n a t i n g  i s o l a t i o n of  present work.  CF3,  or  of  hexafluorophophates  as w e l l  p-CH3CgH4),  E i s P or As,  been s t u d i e d p r e v i o u s l y  that  CH3,  i n the  (Re04~),  (AsFg~),  r e g a r d e d as n o n - c o o r d i n a t i n g  theEFg"  properties  structure  proposed  Significant  octahedral  three  ions different  for  distortions  geometry  were  2  FIG.  1.1.  PROPOSED STRUCTURE 0 F F e ( X S 0 ' 3 ) 2 COMPOUNDS  3  indicated  for  all  the  c o b a l t and c o p p e r compounds  e x c e p t i o n s o f C o ( F S 0 3 ) 2 and Iron(II) spectrum reported  distorted state  showed  the  by a t r i g o n a l  i s an o r b i t a l  polymeric bridging  in  Fig.  In  very d i s t o r t e d species  c o n s i s t of  (17,18). terdentate  metal  centre  calcium.  silver(l)  trigonal  The  c o n s i s t o f monomeric  This general  The  study  Mossbauer measurements.  octahedra ground  bridging  resulting  structure  bipyramidal  units  and  OUTLINE OF  2H20  work c o n c e r n s  are  h a v e been  anions,  in  i s s i m i l a r to the  reported  is a  highly  each  anion  octahedral  silver  environment.  infinite  THE  compounds  calcium salt  methanesulfonate  4 H 2 0 and C d ( C H 3 S 0 3 ) 2 .  PURPOSE AND  FeOg  X-ray studies  c o p p e r a n d cadmium s a l t s c o n t a i n mono-  1.2.  infrared  susceptibility  h a v e a l s o b e e n s t u d i e d by C h a r b o n n i e r  Cu(CH3S03)2.  its  included  s t u d i e s on s u l f o n a t e  and A g ( C H 3 S 0 3 )  around  1.1.  (15)  and  and t h a t t h e e l e c t r o n i c  single crystal  a different  coordination  to  elongation  l a t t i c e containing to  possible  doublet.  l i m i t e d but  on C a ( C H 3 S 0 3 ) 2  and m a g n e t i c  compound  Crystallographic somewhat  was p r e p a r e d  Further studies  and e l e c t r o n i c s p e c t r o s c o p y These s t u d i e s  the  Co(p-CH3CgH4S03)2.  fluorosulfonate (16).  with  that  ion i s in a  Various  et a l .  (19,20)..  and b i d e n t a t e  hydrated  and  The.  proposed  include  hydrated, CH3S03~ anions  p a r a l l e l chains  respectively.  PRESENT WORK  iron(II)  sulfonates polymers  of  inorganic  coordination  t r a n s i t i o n metal  complexes  having  structures  and i s p a r t -  and  of  a  specifically  i n which metal  ions  are  4  bridged  i n c h a i n s , p l a n e s and t h r e e  d i m e n s i o n s by p o l y a t o m i c  anionic  ligands. The  r e s e a r c h d e s c r i b e d here  c h a r a c t e r i s a t i o n of and r e p r e s e n t s  Fe(CF3S03)2,  an e x t e n s i o n  related cobalt(II),  of  objectives  i n mind  (i)  previous  modes o f  and i r o n ( I I )  techniques  coordination  To  understand  of  coordination of  To e x a m i n e  To o b t a i n magnetic  the  and  these  The  sulfonate of  on  several  identifying  molecular structure  t h e mode and  the  determi-  structural  h a s on p o l y m e r  and t o  isomerism why  study  it  occurs  properties.  these,  exchange  strong to help  in  phenomena  centres.  used i n the  p r e s e n t work t o  be d i s c u s s e d  techniques  compounds  strength  ligands.  understanding  of magnetic  paramagnetic  polymers w i l l  of  it  interactions  experimental  characterisation  for  c o o r d i n a t i o n p o l y m e r s w h i c h show  techniques  sulfonate  for  determining  phenomenon  understanding  between  The  laboratory  compounds.  factors  and w h a t e f f e c t s  our  in this  compounds.  and c r i t e r i a  in coordination polymers,  (iv)  and  Fe(p-CH3CgH4S03)2  p r e p a r e d and s t u d i e d w i t h  nation in s u l f o n a t e  (iii)  studies  synthesis  :  To d e v e l o p  (ii)  the  F e ( C H 3 S 0 3 ) 2 and  copper(II)  The m a t e r i a l s w e r e  involves  characterise  briefly.  used i n the  studied w i l l  synthesis  be p r e s e n t e d  and in  5  Chapter  2. Vibrational  the  spectroscopy  a n i o n and p r o v i d e s  ( C h a p t e r 3) p r o b e s  insight into  anion-anion  the nature  as w e l l  as  of  anion-cation  interactions. Electronic to  spectroscopy  be o b s e r v e d a n d p r o v i d e s a m e a s u r e . o f  and e x c i t e d e l e c t r o n i c s t a t e s . field in  effects  Chapter  provided  the  u.v.)enables  d-d  separation of  T h e s e may be r e l a t e d t o  by t h e s u l f o n a t e  transitions  ground  the  ligand-.-:  a n i o n s and a r e d i s c u s s e d  4. Further information  electronic  state  from magnetic of  (visible -  Chapter  i n these  regarding  iron(II)  the nature  sulfonate  s u s c e p t i b i l i t y measurements  of  polymers  the  ground  may be  and t h e s e a r e  the  obtained topic  5.  57 The  presence of  the  Fe n u c l e u s i n t h e  compounds  prepared  II  has e n a b l e d t h e p o w e r f u l used to probe c a t i o n . This  tool  of  Mossbauer s p e c t r o s c o p y  the e l e c t r o n i c and s t r u c t u r a l technique  environment  i s discussed i n Chapter  to  be  of  the  iron  6.  •I  Magnetically-perturbed sample i s p e r t u r b e d detailed  possibility ions  by a n a p p l i e d m a g n e t i c  information In  through  and t h i s  view o f the exists  Mossbauer s p e c t r a i n which  for  i s the  topic of  polymeric nature  magnetic exchange  bridging anions.  field,  Previous  of  provide  Chapter these  between  the  even  7.  compounds  neighbouring  w o r k on t h e  more  "parent"  the iron  6  compound 23K  FeSO^ i n d i c a t e s t h a t  (21).  i t becomes m a g n e t i c a l l y o r d e r e d  I n t h e p r e s e n t work  exchange  in F e ^ H ^ S O ^  there  i s evidence  from both magnetic  for  below  magnetic  susceptibility  II  measurements  and Mossbauer  In F e ( F S 0 3 ) 3 , it  was o b s e r v e d  that  spectroscopy.  previously  s t u d i e d by Goubeau  t h e m a g n e t i c moment  and  Milnei(22),  i s significantly less  than  5 5.92  B.M. expected  for a high-spin d  temperature  and f i e l d  both  and a n t i f e r r o m a g n e t i c  in  ferro-  this  dependent.  Goubeau exchange  and M i l n e proposed mechanisms a r e  and i s that  operating  material. The p o s s i b i l i t y t h a t  in  electron configuration  the other  Fe(CF3S03)3, describes  iron(III)  sulfonates  comparison w i t h  temperatures  s t u d i e s on . t h e s e  FeSO^ t h e p a r e n t  Fe^SO^,  (23).  Chapter  compounds.  compound o f t h e s e  spontaneously  below 28.7K  may be p r e s e n t  l e d to the preparations  F e ( C H 3 S 0 3 ) 3 and F e ( p - C H 3 C g H 4 S 0 3 ) 3 .  the preliminary  sulfonates,  such magnetic exchange  of 8  Again  iron(III)  orders magnetically  at  in  7  CHAPTER 2  EXPERIMENTAL METHODS  2.1.  INTRODUCTION Experimental  d e t a i l s o f t h e work  are o u t l i n e d i n t h i s c h a p t e r ; s y n t h e s i s o f t h e compounds physical  techniques of  F,  CF3, CH3, p-CH3C6H4). (i)  of preparation  regarding the  have been u t i l i s e d  compounds o f t h e t y p e t r a n s i t i o n metal  M(XS03)2,  c a t i o n and X i s  These a r e :  A r e a c t i o n between acid  study  investigation.  for sulfonate  (where M i s a f i r s t - r o w  in this  included are sources of m a t e r i a l s ,  s t u d i e d and i n f o r m a t i o n  Two g e n e r a l m e t h o d s previously  involved  t h e anhydrous  metal  c h l o r i d e and t h e  (14,16). MC12  + 2XS03H — •  M ( X S 0 3 ) 2 + 2HC1 +  (2.1)  Where X i s F o r C F 3 > (ii)  A s t o i c h i o m e t r i c r e a c t i o n between aqueous silver  s a l t o f t h e a c i d and t h e h y d r a t e d  MC12.  xH20 + 2Ag(XS03)  solutions of the metal  • M(XS03)2.  chloride  aq + 2AgCl + ( 2 . 2 )  Where X i s C H 3 o r p - C H j C g h ^ . Dehydration  of the hydrated  species M(XS03)2.  a q . was  a c h i e v e d e i t h e r b y h e a t i n g u n d e r vacuum o r b y u s i n g t h e ether solvent  2,2-dimethoxypropane  t o be a good d e h y d r a t i n g  agent  (D.M.P.) w h i c h  (24).  (14).  proved  8  CH3C(0CH3)2 Boiling  CH3  •  2CH30H + ( C H 3 ) 2  under r e f l u x w i t h D . M . P .  structural  modifications for  Both methods o f study;  susceptible either of  to  iron(III)  of  all  freeze-pump-thaw Both methods o f  this  t o be  very  To p r e v e n t  s o l v e n t s were degassed p r i o r to  use  cycles.  p r e p a r a t i o n gave  data for  "nearly"  quantitative  t h e compounds p r e p a r e d a r e g i v e n  in  MATERIALS c h e m i c a l s and s o l v e n t s w e r e R e a g e n t  g r a d e and were used w i t h o u t  further  or A n a l y t i c a l  p u r i f i c a t i o n unless otherwise  stated.  The c o m m e r c i a l s o u r c e s o f  the m a t e r i a l s used were:  CF3S03H,  3M Company;  Ag(p-CH3CgH4S03)  CH3S03H,  Eastman  Ag(CH3S03),  Kodak Company  4H20 A n a l a r ,  6H90 A n a l a r ,  Ltd.  Mallinckrodt Inc.  A l d r i c h , C h e m i c a l Company CoCl9.  oxidation  2.1.  All  FeCl2.  handled  product. Analytical  2.2.  compounds w e r e f o u n d  i n an i n e r t a t m o s p h e r e o r u n d e r v a c u u m .  by s e v e r a l  Table  been used i n  and  isolated.  t o a t m o s p h e r i c m o i s t u r e and when i s o l a t e d w e r e  iron(II)  yields  methanesulfonate  t h i s compound t o be  preparation.have  the r e s u l t i n g anhydrous  (2.3)  l e d t o some i n t e r e s t i n g  iron(ll)  e n a b l e d two d i s t i n c t i s o m e r s o f  CO  NiCl9.  Inc.  ; ZnCl? ;  ; FeCl3,  6H90 A n a l a r ,  Analar  FeCl2  CuCl9.  and  and  Matheson,  and  2,2-dimethoxypropane, C o l e m a n and B e l l  2H90  Analar  and  Ltd.;  9  CaCl2.  2H20 A n a l a r ,  Scientific  Company  2.3.  DRY  THE  B r i t i s h Drug Houses  Ltd.  ;  FeClg.  (Model  BOX  Dri-Lab  HE-93).  (Model  Purified  was c i r c u l a t e d t h r o u g h An o v e n  2.4.  K-grade  t h e box  nitrogen  v i a Linde  (12  Iron (II)  a pressure of mmol).  method  (Canadian  Liquid Air  The  Ltd.)  4A M o l e c u l a r S i e v e s . be  atmosphere.  Trifluoromethanesulfonate,  20 mm Hg a t iron(II)  acid  7 0 ° C onto  Fe(CF3S03)2  (20 m l ) was f r e s h l y  distilled  anhydrous  chloride  iron(II)  c h l o r i d e was p r e p a r e d by a  literature  (25). Indicative  of  i t s polymeric nature  be i n s o l u b l e i n t h e a c i d . by t h e e v o l u t i o n o f product  Dry-train  COMPOUNDS  Trifluoromethanesulfonic at  equipped with a  p e r i o d i c a l l y to maintain a dry  SYNTHESIS OF  2.4.1.  HE-43),  Herring  i n c o r p o r a t e d i n t o the system enabled the s i e v e s to  regenerated  Fisher  Ltd.  I n e r t atmospheres were o b t a i n e d w i t h a D.L. Corporation  6H20,  During  hydrogen  t h e p r o d u c t was f o u n d  the course of  chloride gas,  developed around the r e a c t a n t  the r e a c t i o n ,  noted  an i n s o l u b l e l a y e r  inhibiting further  to  of  reaction.  To e n s u r e c o m p l e t e r e a c t i o n t h e m i x t u r e was s t i r r e d and b o i l e d  under  reflux  and  for  washed w i t h  approximately  40h.  freshly distilled  The  p r o d u c t was vacuum f i l t e r e d  trifluoromethanesulfonic acid.  Traces  10  o f e x c e s s a c i d were removed from t h e w h i t e vacuum a t  2.4.2  Iron(II)  silver(I)  iron(II)  Paratoluenesulfonate,  paratoluenesulfonate  chloride tetrahydrate  precipitated of  Fe(p-CH3C6H4S03)2  s a l t was p r e p a r e d by t h e r e a c t i o n o f a q u e o u s  r e s u l t i n g mixture  solution  (17  mmol  ( 8 . 5 mmol  i n 50 mL H 2 0 )  i n 10 mL H 2 0 ) .  The  was s t i r r e d u n d e r a f l o w o f n i t r o g e n g a s a n d  silver(I) iron(II)  c h l o r i d e was r e m o v e d by f i l t r a t i o n .  p a r a t o l u e n e s u l f o n a t e was e v a p o r a t e d  u n d e r vacuum a t 1 2 0 ° C .  Iron(II)  The a n h y d r o u s  Methanesulfonate,  Fe(p-CH3CgH4S03)2,  to  tetrahydrate chloride removal  i n 30 mL H 2 0 )  i n 10 mL H 2 0 )  and an a q u e o u s s o l u t i o n o f of s i l v e r ( I )  evaporated at  ( 4 . 6 mmol  heating solid.  used t o  prepare  and i r o n ( I I )  silver(I) chloride  resulted in a mixture the d e s i r e d product.  of  silver(I)  After  c h l o r i d e by f i l t r a t i o n t h e s o l u t i o n was  t o d r y n e s s under vacuum,  1 3 0 ° C f o r 12h g a v e t h e a n h y d r o u s Initially  dryness  Fe(CH3S03)2.  t h e s t o i c h i o m e t r i c r e a c t i o n between  ( 9 . 2 mmol  The  compound i s a p a l e g r e e n  In a m o d i f i c a t i o n o f t h e m e t h o d  methanesulfonate  solutions  with  u n d e r vacuum a n d c o m p l e t e d e h y d r a t i o n was a c c o m p l i s h e d b y  2.4.3.  under  50°C.  This of  p r o d u c t by h e a t i n g  and f u r t h e r product,  d e h y d r a t i o n by b o i l i n g  h e a t i n g under  vacuum  a-Fe(CH3S03)2. under r e f l u x  in  D.M.P. II  had r e s u l t e d i n a p r o d u c t w h i c h gave complex i n f r a r e d and Mossbauer spectra.  However,  prolonged r e f l u x i n g ,  t h r e e d a y s u n d e r an  inert  11  atmosphere,  gave  To  a s t r u c t u a l l y modified  check the  isomeric purity  s p e c t r o s c o p y c o u l d be u s e d b e c a u s e o f quadrupole Anything into  s p l i t t i n g values  less  the 3-form  was e s t i m a t e d  10%  all  temperatures.  98% c o n v e r s i o n o f  the  a-isomer  that  Mossbauer a b s o r p t i o n s .  t o be a l e s s infrared  ' methanesulfonate,  under anhydrous  8 . 5 mm Hg o n t o  anhydrous  acid  ( 2 0 mL)  iron(II)  reaction mixture  several  drying  portions  of  u n d e r vacuum f o r  less  than  regard. of  approximately  data, Solvate  when c o b a l t ( I I )  modifications  was  made t o  was d i s t i l l e d  c h l o r i d e (15  by t h e e v o l u t i o n was h e a t e d a t  freshly 48 h a t  see T a b l e s formation  3.6 of  of  at  mmol).A hydrogen  approximately  The w h i t e  distilled  shown  prepare  the  and 2 . 1 this  a pressure  acid.  chloride 100°C  However,  infrared  of  vigourous  p r o d u c t was  150° C methanesulfonic  r e m a i n e d a s a s o l v a t e a s e v i d e n c e d by t h e analytical  in this  conditions.  o c c u r r e d as noted  The  at  structural  an a t t e m p t  8 h and then f i l t e r e d u n d e r v a c u u m . with  sensitive test  more Infrared  s p e c t r o s c o p y was i n c a p a b l e  the d i f f e r e n t  Methanesulfonic  gas.  in  mixture.  by i r o n ( I I )  reaction  large differences isomers at  quadrupole-split  Because of  compound  each s p e c i e s Mossbauer  t h e a - i s o m e r when i t was p r e s e n t  i n the  3- Fe^H^SOg^.  c o u l d be e a s i l y d e t e c t e d by t h e p r e s e n c e o f  s p e c t r o s c o p y was f o u n d  detecting  of  t h e two  than approximately  t h a n one p a i r o f  It  for  isomer,  for  washed even  acid  spectrum  after  still and  respectively.  t y p e was o b s e r v e d  previously  c h l o r i d e was r e a c t e d w i t h m e t h a n e s u l f o n i c  acid  (26).  12  2.4.4.  Preparation of other Methanesulfonates, where M i s C o , The c o b a l t ( I I )  as d e s c r i b e d i n Ref. stoichiometric  14;  Ni,  Cu,  Zn and  MCCH^SO^;  Ca.  and c o p p e r ( I I )  a n a l o g u e s were  t h e r e m a i n i n g compounds w e r e p r e p a r e d  r e a c t i o n s between aqueous s o l u t i o n s o f  and A g C C H g S O g ) .  prepared  Silver(I)  MC^.xh^O.  c h l o r i d e was r e m o v e d by f i l t r a t i o n and  t h e p r o d u c t d r i e d by h e a t i n g u n d e r vacuum a t a p p r o x i m a t e l y The a n h y d r o u s  p r o d u c t s were then t r e a t e d w i t h D . M . P .  whether  any s t r u c t u r a l m o d i f i c a t i o n s t o o k  2.4.5.  Iron(III)  approximately  was f r e s h l y  20 mm Hg o n t o a n h y d r o u s i r o n ( I I I )  40h.  a c i d a n d d r i e d u n d e r vacuum a t  2.4.6.  Iron(III)  Paratoluenesulfonate, paratoluenesulfonate  was r e a c t e d w i t h an a q u e o u s s o l u t i o n o f  silver(I)  (3.6  mmol  i n 15 mL h ^ O ) .  Fe(p-CH3C6H4S03)3 (11.2  mmol  iron(III)  After  i n 20 mL  h^O)  chloride  removal  of  precipitated  c h l o r i d e t h e a q u e o u s s o l u t i o n was r e d u c e d i n v o l u m e  product.  reflux  150°C.  d e h y d r a t i o n was a c h i e v e d by h e a t i n g u n d e r vacuum a t the orange  under  mmol).  The w h i t e p r o d u c t was f i l t e r e d , w a s h e d w i t h  distilled  hexahydrate  distilled  c h l o r i d e (10  the mixture  freshly  Silver(I)  observe  FeCCF^SO^)^.  ( 2 0 mL)  C o m p l e t e r e a c t i o n was o b t a i n e d by b o i l i n g for  to  100°C.  place.  Trifluoromethanesulfonate,  Trifluoromethanesulfonic acid at a pressure of  by  and  70°C to y i e l d  13  2.4.7.  Iron ( I I I ) This  Methanesulfonate,  Fe(CH3S03)3  s a l t was p r e p a r e d by t h e r e a c t i o n o f s t o i c h i o m e t r i c  quantities  of s i l v e r (I)  methanesulfonate  iron (III)  c h l o r i d e hexahydrate  ( 5 . 8 mmol  (17.0mmol  i n 20 mL h^O) a n d  i n 15 mL H g O ) .  The p a l e  y e l l o w p r o d u c t was o b t a i n e d by t h e u s u a l t e c h n i q u e o f e v a p o r a t i o n excess  s o l v e n t a n d h e a t i n g u n d e r vacuum a t  2.5.  A N A L Y T I C A L DATA Elemental  a n a l y s e s were p e r f o r m e d  l a b o r a t o r y o f t h i s department by a Redox  All  2.6.1.  Borda.  110°C.  i n the m i c r o a n a l y t i c a l Iron  a n a l y s e s were  done  t i t r a t i o n w i t h potassium dichromate u s i n g sodium  diphenylamine  2.6.  by P.  of  sulfonate  as i n d i c a t o r  a n a l y t i c a l data are given i n Table  PHYSICAL EXPERIMENTAL Infrared  M u l l i n g agents  TECHNIQUES  s p e c t r a were r e c o r d e d over  the frequency  u s i n g a P e r k i n E l m e r 457 g r a t i n g used were N u j o l  and h e x a c h l o r o - 1 ,  M u l l s were p l a c e d between  KRS-5  from t h e Harshaw C h e m i c a l  Company.  All  2.1.  spectroscopy  Infrared 4,000-250cm~^  (27).  plates  (58% T i l l ,  range  spectrophotometer. 3-butadi.erie. 42% T I B r ) ,  supplied  m u l l s were p r e p a r e d i n t h e d r y box and t h e windows  sealed w i t h adhesive tape  to prevent  hydration of samples. A l l  s p e c t r a w e r e c a l i b r a t e d a t 1601 a n d 907cm~^  using a polystyrene  14  TABLE 2 . 1  ANALYTICAL  THEORY  COMPOUND  Fe  C  Fe(CF3S03)2  15.8  6.78  a-Fe(CH3S03)2  22.7  B-Fe(CH3S03)2 Fe(p-CH3C6H4S03)2  DATA  %  FOUND %  . H  Fe  C  H  0.00  15.9  6.75  0.00  9.76  2.46  22.5  9.93  2.48  22.7  9.76  2.46  22.5  9.59  2.60  14.0  42.22  3.55  13.9  42.50  3.60  10.53  2.95  10.37  2.86  Co(CH3S03)2  9.63  2.43  9.51  2.39  Ni(CH3S03)2  9.65  2.43  9.49  2.41  Cu(CH3S03)2  9.46  2.38  9.30  2.48  Zn(CH3S03)2  9.40  2.37  9.75  2.64  Ca(CH3S03)2  10.43  2.63  10.52  2.71  Fe(CH3S03)2.  CH3S03H  Fe(CF3S03)3  11.1  7.16  0.00  11.3  7.04  0.00  Fe(CH3S03)3  16.4  10.56  2.66  16.1  10.50  2.80  9.8  44.29  3.72  9.7  44.16  3.85  Fe(p-CH3C6H4S03)3  15  film,  and t a b u l a t e d  ± 5cm~^ f o r  2.6.2.  infrared  frequencies are considered accurate  b r o a d b a n d s and ± 2cm~^ f o r  Electronic  14  recording spectrophotometer  record e l e c t r o n i c spectra over state  the  filters  2.6.3.  Magnetic  i n the  temperature  the  reference  susceptibility  Magnetic  described  range 80-320K  (28).  A magnetic  c a l i b r a t e d to  for  as a s t a n d a r d  due t o  repacking of  susceptibility  Light neutral  measurements were r e c o r d e d  f i e l d strength  previously  o f 0 . 4 5 T was e m p l o y e d  i n a P y r e x t u b e w h i c h had  compensate  for  over  i t s diamagnetism.  and  been All  and c a l i b r a t i o n  of  tetrathiocyanatocobaltate(II)  (29).  m i n i m i s e d by p e r f o r m i n g  All  30,000 cm~^.  beam.  was a c h i e v e d u s i n g m e r c u r y ( I I )  Errors  involving  to  hexachlorobuta-  by p l a c i n g  m e a s u r e m e n t s w e r e made i n a n i t r o g e n a t m o s p h e r e the apparatus  or  g l a s s windows.  u s i n g a Gouy b a l a n c e  packed  was u s e d  range 4 , 0 0 0 -  s u s c e p t i b i l i t y measurements  s a m p l e was u n i f o r m l y  previously  silica  f r o m t h e s a m p l e was c o m p e n s a t e d  density  the  frequency  s p e c t r a w e r e r e c o r d e d on N u j o l  1 , 3 - d i e n e m u l l s c o n t a i n e d between scattering  bands.  spectroscopy  A C a r y Model  Solid  sharp  to  inhomogeneous at  packing of  l e a s t three  t h e Gouy  separate  the sample were determinations,  each  tube.  samples were t e s t e d f o r  f i e l d dependence o f  using a Faraday magnetic  the  magnetic  b a l a n c e , d e s c r i b e d now.  An  16  Alpha  Model  9500 6 " w a t e r - c o o l e d  d e s i g n was u s e d t o The  provide  electromagnet w i t h Heyding  constant  s a m p l e was p l a c e d i n a q u a r t z  electrobalance  and m e a s u r e m e n t s  Minimal room t e m p e r a t u r e correct  the  calculated  packing errors are  from the  where T i s the corrected for  E F F  involved  i n the  atmosphere.  F a r a d a y method  i n t h i s way w e r e u s e d  measurements  m a g n e t i c moment o f  to  f r o m t h e Gouy b a l a n c e .  the metal  . l) h  = 2.828 (xa temperature  i o n was  diamagnetism of  (2.4)  and  the molar  t h e atoms and  susceptibility  ions present.  The  2+ diamagnetic Fe3+ =10,  c o r r e c t i o n s used i n the p r e s e n t CF3S03"  are given  i n 10"  = 46, c.g.s.  from P a s c a l ' s c o n s t a n t s  CH3S03" = 35, units  (10  s t u d y w e r e Fe  p-CH3C6H4S03"  cm  mol  =13,  =89.  )and were  All  obtained  (30-32).  II  2.6.4.  Mossbauer Fig.  spectrometer.  spectroscopy  2.1  shows a s c h e m a t i c d i a g r a m o f  The  v e l o c i t y modulation  achieved using a Technical unit  p o w e r e d by a K 3 - K  r a d i a t i o n was d e t e c t e d counter,containing  of  Measurements  l i n e a r motor.  C02  Mossbauer  t h e gamma r a d i a t i o n Model  transmitted  using a Reuter-Stokes  Xe w i t h  a typical  Corporation  The  T2cm_1.  Rg  relationship  Kelvin the  253,526,869  s u s p e n d e d f r o m a Cahn  s u s c e p t i b i l i t i e s obtained  effective  u  bucket  of  w e r e made i n a n i t r o g e n  v a r i a b l e temperature  The  f i e l d gradients  pole  RSG-61  at a pressure of  is  306  drive  gamma  proportional  two a t m o s p h e r e s  and  and  17  FIG .  2.1  SCHEMATIC DIAGRAM OF A M5SSBAUER SPECTROMETER  3d 1—1  o o 00  OC  LU  00  C Qc < 1  o i— oc «c LU  i—i i—  LU CD  ME  o OO o _ l o _J  h-  OC LU ZD  ZD  ca  LU  <c  >"  OO  00  OC  30 s:  i—l Q  a: CQ  LU C_) Qi ZO Qi LU O  ZD  oo <z: a;c Q  a: OO o CO  oc  OO o  O  _ l D-  I—  0 0 2 :  LU  — I LU  <  Z < LU  OC  CD  CD  18  a Nuclear in  -  C h i c a g o Model  t h e m u l t i s c a l a r mode.  were a Model  40-9B  preamplifier, Model  23-4  24-2  400-word  Also  included (Nuclear  high-voltage  a Model  33-15  power  supply,  amplifier -  analog-to-digital  multichannel  converter,  -  analyser  Chicago  a Model  modules)  238105  s i n g l e channel and a Model  operating  analyser,  021308  a  time-base  generator. Shown i n F i g . used t o o b t a i n in  2.2  v a r i a b l e temperature  the absence of  The  cell  Mossbauer  field.  e x p e r i e n c e d w i t h more  c o n t a i n i n g the  t h e s a m p l e and t h e c o o l a n t , gas.  finely  t o w i t h i n ±. 0 . 0 2 ° C w i t h  temperature  a Cryogenic  All  c a l i b r a t e d Ge and P t  alleviate  s a m p l e was  DT-6  between cryostat  maintained  TC-101  Temperatures  resistance  s p e c t r a were r e c o r d e d  Model  R e s e a r c h Model  holders  contact  was s e t a n d  c o n t r o l l e r w h i l s t a s p e c t r u m was r e c o r d e d . measured w i t h  spectra  conventional  powdered  which i n the J a n i s  The  apparatus  Nylon sample  mounted on a c o p p e r a n n u l us t o e n s u r e good t h e r m a l  was h e l i u m e x c h a n g e  the  epoxy r e s i n were d e s i g n e d to  sample h y d r a t i o n  copper c e l l s .  (8-300K)  an a p p l i e d m a g n e t i c  w h i c h c o u l d be s e a l e d w i t h problems of  i s a schematic diagram of  temperature were  thermometers.  in a transmission  geometry,  57 the at  radiation  source (  room t e m p e r a t u r e .  a metallic iron foil to  the c e n t r o i d of The  perturbed  Co i n a Cu o r Rh m a t r i x ) The  Doppler  velocity  being  maintained  s c a l e was c a l i b r a t e d  a b s o r b e r and i s o m e r s h i f t s a r e quoted  the  cryostat  iron foil  relative  spectrum.  used i n t h i s work to  Mossbauer s p e c t r a  using  record  (magbauer s p e c t r a )  magnetically-  i s shown i n F i g .  2.3.  19  FIG.  2.2  SCHEMATIC DIAGRAM OF APPARATUS USED FOR OBTAINING V A R I A B L E TEMPERATURE M5SSBAUER SPECTRA  HELIUM  INLET  HELIUM VENT  ft*  TO VACUUM L I N E ^ - HELIUM F I L L  SAFETY VALVE-  EVACUATION VALVE  COMMON VACUUM SPACE L I Q U I D NITROGEN RESERVOIR  HELIUM EXCHANGE GAS  LIQUID HELIUM RESERVOIR  SOURCE RADIATION  DETECTOR  ALUMINIUM FOIL  COPPER ABSORBER CHAMBER  MYLAR WINDOW  SHIELD  20 FIG.  2.3  SCHEMATIC DIAGRAM OF APPARATUS USED FOR MAGNETICALLY-PERTURBED  TO DRIVE  UNIT  OBTAINING  MOSSBAUER SPECTRA  TRANSDUCER COMPARTMENT  TRANSDUCER HELIUM VENT  TO VACUUM LINE HELIUM F I L L h  TO VACUUM LINE  HOLLOW STEEL DRIVE ROD  SAFETY  VALVE  LIQUID HELIUM RESERVOIR  SOURCE  INNER VACUUM SPACE  COMMON VACUUM SPACE SUPERCONDUCTING SOLENOID  ABSORBER  MYLAR WINDOWS  • DETECTOR  21  A t r a n s m i s s i o n geometry and d e t e c t o r the  The  arrangement  a Westinghouse  magnetic  f i e l d s of  and i s d r i v e n ,  shaft,  by an A u s t i n The  used f o r  thermocouple;  a germanium d i o d e .  pumping s p e e d , v i a  generating  the  2 . 3 K and room  a  c a n be o p e r a t e d  2 . 3 and 4 . 2 K  gas  copper-  liquid  with  between pressure  by c o n t r o l l i n g  and hence the  helium  the  helium enable reservoir.  spectra  i n the absence of  Lorentzian curves  the data p o i n t s .  perturbed  b e l o w 80K w e r e m e a s u r e d  vapour space above the  to  drive  temperature.  was m e a s u r e d w i t h  arrangement,  Mossbauer  magnetic  motor.  A h i g h - c a p a c i t y vacuum pump was u s e d t o  the  the y-ray The  the m a g n e t i c a l l y  apparatus  to  fitted  stainless steel  linear  between  temperature  and between  Spectra obtained  l i n e widths  here i s  by c o n t r o l l i n g t h e e x c h a n g e  a valve  A n a l y s i s of  of  cryostat  i n f l u e n c e of  obtaining  The m a g b a u e r  and t h e h e a t e r c u r r e n t ,  f i e l d were f i t t e d  the  temperatures  and room t e m p e r a t u r e  treatment  absorber  the a p p l i e d f i e l d .  S c i e n c e A s s o c i a t e s K-3  a b o v e 80K t h e  t h e pumping o f  The  a long t h i n - w a l l e d  s p e c t r a c o u l d be o p e r a t e d  vapour p r e s s u r e .  2.2.  the centre of  via  cryostat  For magbauers  2.6.5.  in Fig.  source i s outside  field  4.2K  source,  up t o 5 . 6 3 T p a r a l l e l t o t h e d i r e c t i o n o f  v e r t i c a l l y mounted  constantan  the  superconducting solenoid capable of  sample i s l o c a t e d a t  Mossbauer  however,  are a l i g n e d v e r t i c a l l y i n t h i s c r y o s t a t as opposed  horizontal  with  was e m p l o y e d ;  The  an a p p l i e d  magnetic  by a l e a s t s q u a r e s  programme  treated  and i n t e n s i t i e s a s u n c o n s t r a i n e d f i t t i n g  fitting  the p o s i t i o n s , parameters.  .  beam.  22  Magnetically with Dr.  theoretical A.  Hulme a n d  phenomenological procedures programme will  -  p e r t u r b e d Mossbauer s p e c t r a were  spectra generated  by programmes w r i t t e n  b a s e d on one by Lang model  (33)  f i r s t u s e d by V a r r e t  compared by  o r one d e r i v e d f r o m a (34).  Details  f o r m a g n e t i c a l l y - p e r t u r b e d M o s s b a u e r s p e c t r a and used f o r  be g i v e n  d e r i v i n g the c r y s t a l - f i e l d s p l i t t i n g  i n the appropriate  sections.  of  fitti  the  parameters  23  CHAPTER 3  VIBRATIONAL SPECTROSCOPY  3.1.  INTRODUCTION  Vibrational tool  for inorganic  spectroscopy  the  coordination  h a v e been  p a r t i c u l a r l y where studies  spectroscopy  found  being confirmed In structure  chemists.  previous  species hydrated  CH3S03~ anions parallel  chains  polymeric with a layer  appear  (17)  a c t i n g as t e r d e n t a t e  l a t t i c e type s t r u c t u r e ,  possible in a suitable silver(I)  methanesulfonate  methods.  T h e s e c o n t a i n mono-  (36).  little  and  (e.g. Cu(CH3S03)2.  In c o n t r a s t  before  study  very  anhydrous  units  spectroscopy  compounds  by X - r a y d i f f r a c t i o n  (20)).  respectively.  these  t o be t h e o n l y  and c o n s i s t o f monomeric  anions  diffraction  (35),  has been  methanesulfonate  s p e c i e s h a v e been s t u d i e d 2H20,  elucidation,  X-ray  X-ray d i f f r a c t i o n  by X - r a y d i f f r a c t i o n  t o h a v e been s t u d i e d  and C d ( C H 3 S 0 3 ) 2 -  in structure  s t u d i e s o f M ( X S 0 3 ) 2 compounds  Calcium(II) (18)  a n d Raman  was p r o p o s e d  because o f t h e d i f f i c u l t i e s o f o b t a i n i n g  methanesulfonate  invaluable  On t h e b a s i s o f v i b r a t i o n a l  by a s i n g l e c r y s t a l  form.  Infrared  t o be u s e f u l  of (CH3)2Sn(FS03)2  determination  crystalline  t o be a n  the r e s u l t of s i n g l e c r y s t a l  are not a v a i l a b l e .  basic structure  has proven  Various  4H20,  (19)  and b i d e n t a t e  and i n f i n i t e  Ca(CH3S03)2 bridging  is  highly  ligands  s i m i l a r t o t h a t shown  forming  in Fig.  1.1.  24  Structure  determination  was p a r t i c u l a r l y i m p o r t a n t not  using v i b r a t i o n a l  i n t h e p r e s e n t work  The information caution,  could  methods.  frequency  a n d number o f v i b r a t i o n a l  on t h e a n i o n s y m m e t r y ,  t o deduce t h e geometry  probed  the nature This  work  the r e l a t i v e  protonic acids  3.,2.  of  uncoordinated  represents  coordination  local  symmetry  XSO^" a n i o n s  modes o f v i b r a t i o n ;  doubly  degenerate  the anion  an e x t e n s i o n o f p r e v i o u s  strengths  with  as  has-also  studies  of anions derived  from  strong  SPECTRA AND STRUCTURE a r o u n d t h e s u l f u r atom i n  three  i n both  Group t h e o r y  o f symmetry  o f symmetry  predicts s i x  E.  All six  i n f r a r e d a n d Raman a n d may be  d e s c r i b e d a s shown i n F i g . 3 . 1 .  If  i s lowered from C^v to C$ the doubly giving rise  free  s p e c i e s A-j a n d t h r e e  species  modes w i l l  split,  Again  a r e a l l i n f r a r e d a n d Raman a c t i v e  they  As w e l l  i h t e r a c t i o n s t h i s study  i s C^.  vibrations  are active  qualitatively  w h i c h i n t u r n may be u s e d ,  (14).  normal  vibrations  provide  anion-anion.interactions.  THEORY OF VIBRATIONAL The  bands  around the c a t i o n .  i n v e s t i g a t i n g these anion-cation  of  a s t h e compounds  be i s o l a t e d a s s i n g l e c r y s t a l s a n d h e n c e c o u l d n o t be s t u d i e d by  X-ray d i f f r a c t i o n  of  spectroscopy  t o n i n e normal  the  symmetry  degenerate  modes o f (see Table  E  vibration. 3.1).  25  FIG.  NORMAL MODES OF VIBRATION OF THE XS0 " ANION  3.1.  3  o  o v(S-C)  8S<S03)  «as(S03)  er(S03)  v (E) A  TABLE 3.1  Point  Group  CORRELATION  TABLE  Vg  v-|  v  C,  A]  A-,  A-,  E  E  E'  Cs  A1  A]  A1  A'+A"  A'+A"  A'+A"  '3v  2  v  FOR C 3 v AND C $ POINT GROUPS  3  26  through  Reduction  in point  site-symmetry  effects  effect  arises  anion  symmetry  example,  anion  effects  symmetry  (see F i g .  (37)).  to Cs-  affecting  The l a t t e r  on t h e o t h e r  o x y g e n atoms ; t h e n  i s usually less the magnitude  for FetXSO^  with  centre. This  structure  If  in FefFSO^  may be p r o p o s e d ,  (Fig.  anion  one o r two  hand,  the anion  This  t h e XSO^"  by e q u i v a l e n t  bonding  symmetry  is  (16),  site-symmetry  t h a n when a n i o n  coordination  of the s p l i t t i n g i s  usually  possibilities.  d i s c u s s i o n of the type  compounds  of  and t h e s t r u c t u r e  t h e XSO^" a n i o n  retains  terdentate  i n FeOg o c t a h e d r a  a type of s t r u c t u r e  its C3v  XSO^" b r i d g i n g  each oxygen c o o r d i n a t i n g  results  1.1),  of  anion coordination.  coordination  now t o a g e n e r a l  these m a t e r i a l s .  as o b s e r v e d  local  (for  effect  through  c r i t e r i o n f o r d i s t i n g u i s h i n g t h e s e two  spectra observed  the  3.2).  Thus,  We t u r n  former  splittings  coordinates  If,  The  s p l i t t i n g o f t h e E modes o b s e r v e d when  the cause.  metal  to small  or bidentate  in terdentate  are involved  the only  for  i.e.uni-  each o f t h e t h r e e  The  coordination.  rise  a r i s e s when t h e X S 0 3 ~  i s involved  again C 3 v  is  and u s u a l l y g i v e s  the anion  through  f r o m C g y t o C s may o c c u r  from t h e c r y s t a l l i n e environment  t h e oxygen atoms,  lowers  symmetry  o r anion  4-18 cm"1 in-Na(CH3S03)  coordination, of  group  to a  proposed symmetry,  anions  different  i n a polymeric  proposed  layer  f o r a l l of the II  F e ( X S 0 3 ) 2 compounds. spectra o f these distortion  However,  compounds,  as w i l l  be s e e n f r o m t h e  t o be p r e s e n t e d  o f t h e FeO f i o c t a h e d r o n  must  i n Chapter  be p r o p o s e d  Mossbauer  6, a  to e x p l a i n  the  27  FIG.  3.2.  BONDING AND SYMMETRY PROPERTIES OF THE X S 0 3 "  1  POINT GROUP  °s  ANION  MODE OF COORDINATION  O ^3v  F r e e  uncoordinated anion  ^  Uni d e n t a t e  Cg  Bi dentate  O  V ° •  •O.  3^..  -or  Sx  C  3  V  Terdentate  28  observed  quadrupole Two  proposed.  simple d i s t o r t i o n s  Firstly,  octahedron remaining  two a x i a l lower  observable  i n the  the  along the C3 surrounding retain In investigate  of  the anion  the  manner  structure  i n metal  proposed  of  should  of  the  the the  this  be  degeneracy  Here,  is a trigonal the  distortion  s i x oxygen and t h e  atoms  anion  shows t h e  infrared  Fe(CF3S03)2  infrared  spectra of  t h e a- and  following  s p e c t r a and a s s i g n m e n t s  for  (where M i s Co,  s p e c t r o s c o p y may be u s e d  sulfonate  spectra of  compounds  and t h i s  of  from  distortion  remain e q u i v a l e n t  vibrational  infrared  The  axis  symmetry.  studied  3.4.  Cs,  FeOg o c t a h e d r o n .  sulfonates  Fig.  to  distortion  iron(II)  in  A tetragonal  be  modes.  C3v  Table 3.2  may  along the  s p e c t r u m as a removal  i r o n c a t i o n would  this  FeOg o c t a h e d r o n  distortion  symmetry  infrared  axis of  its  the  t h e o x y g e n atoms w o u l d d i f f e r  second type o f  the  of  oxygen atoms.  E vibrational The  would  a tetragonal  i n Which f o u r  type would  of  splitting.  compounds.  frequencies  i n t h i s work and F i g .  for a l l  the  3 . 3 shows  and F e ( p - C H 3 C g H 4 S 0 3 ) 2 . 6-forms o f  Fe(CH3S03)2  Ni,  iron(II)  Cu,  Zn a n d  sulfonates Ca).  the  The a r e  s n o w n  s e c t i o n s d e s c r i b e i n some d e t a i l the  to  and  the  M(CH3S03)2  29  TABLE 3 . 2  C3y For  v4  INFRARED SPECTRAL DATA ( c m - 1 )  FOR F e ( X S 0 3 ) 2 COMPOUNDS  Assignment XS03"  (E)  ANION  S03 as. str.  (A.| ) S 0 3 s y m . s t r .  CF,  a-CH3  1239v.s.  1220 1175  1062 m  B-CH3  s s  p-CH3C6H4  1175s  1195  1066 m  1072 m  1145 m  s  \>2  (A-j) S - C s t r .  770 w  790 w  800 m  691  v5  (E)  647 m  587 m 531 m  551 m  580 m  v3  (A-j) S 0 3 s y m . d e f .  523m  513 m  507 m  493 w  v6  (E)  S03 as. def.  S-C d e f . and  internal vibrations of C F 3 , CH3 and p - C H 3 C g H 4  1300 1201 965 592 360  w.sh m w w m  3030 2940 1430 1400 1330 970 383 355  w m m m m v . w. m w  3040 3030 2950 1425 1415 1405 1330 1260 975 360 330  w w w m m m m m v.w. w w  m  3000-3100 v . w . 1270 v . w . 1112 v . w . 1070 m 1040 w 822 m 712 w 400 w 370 w 340 w  30  FIG.  3.3.  INFRARED SPECTRA  ( 1 5 0 0 - 2 5 0 c m " 1 ) OF F e ( C F 3 S 0 3 ) 2 Fe(p-CH3C6H4S03)2  AND  31  3.3.  INFRARED SPECTRUM OF  Several regarding  the  papers  of  (38-44)  vibrational  a n i o n and a s s i g n m e n t s  Fe(CF3S03)2  have  spectrum of  have  and T a b l e anion in  infrared  spectrum of  3 . 3 compares the  in various  the  b e e n made f o r  t h e a n i o n f r o m i n f r a r e d a n d Raman The  provided  information  trifluoromethanesulfonate both  the  CF3  and S 0 3  parts  spectra.  Fe(CF3S03)2  fundamental  first-row  considerable  i s shown i n F i g .  vibrations  t r a n s i t i o n metal  of  the  3.3  CF3S03  compounds w i t h  those,  Fe(CF3S03)2. Previously  the S 0 3 asymmetric  trifluoromethanesulfonate frequency  than  the S 0 3  r e s u l t was b a s e d upon is  followed  of  the  that  the  p o l a r i s e d Raman  used,  its C3v  The  has n o t  salts  absorption A weak  \>2 v i b r a t i o n ,  at  assigned to  symmetry  775  cm~^ i n t h e  this  higher This  (v-|).  This the  assignment  resolution  the doubly  and t h a t  degenerate  SO  suggests  no s i g n i f i c a n t  sulfur-carbon i n any o f  stretching  these :  a s s i g n e d t o a weak  cobalt(II)  cm" ^ i n t h e  vibration.  At  result  certainty  has b e e n t e n t a t i v e l y  770  This  d e s c r i b e d as t h e  been a s s i g n e d w i t h  at  3.3.  (v^) i n  Fe(CF3S03)2-  but  absorption  (39).  no s p l i t t i n g o f  s t r e t c h i n g mode i s o b s e r v e d .  anion d i s t o r t i o n occurs i n  CF3S03"  studies  h e r e and i s r e f l e c t e d i n T a b l e  anion r e t a i n s  frequency  h a s been a s s i g n e d a  symmetric s t r e t c h i n g frequency  spectrophotometer  asymmetric  compounds  stretching vibration  and c o p p e r ( I I )  iron(II)  Other assignments  compounds (38)  have  compounds(14). may  be  placed  32  TABLE 3 . 3  INFRARED  C3v  Assignment  f 0 r  C F  3  v  S 0  3  _  4  (cm-1)  FOR.M(CF3S03)2  COMPOUNDS  M 7e  Co*  Ni  Cu*  7 ?  1239 s  1235 s  1230 s  1280 s 1225 s  1235 s  X  v  n  1062 m  1042 s  1050 s  1058 s  1050 s  v  5  647 m  630 s  630 s  640 s  640 s  523 m  525 m  525 m  530 m  525 m  v-„  *  SPECTRAL DATA  Results  x R.C.  from  Thompson,  reference  14.  unpublished  results.  33  the s u l f u r - c a r b o n a s s i g n e d the  band a t  deformation. be s t r o n g l y  It  approximately  was n o t e d ,  the  similar  structure  infrared  structures  involved  centres,  3.4.  for  of  have  the  symmetric  these  two  vibrations  the  Fe,  first-row  CF3  similar.  Co,  Ni  This  a n d Zn  anion r e t a i n i n g C 3 v  in equivalent  coordination  to  may  of  the anion v i b r a t i o n s  3 . 3 and T a b l e with  t r a n s i t i o n metal  The  fundamental  assigned i n Table t h e number These The  of  3.2.  may be  internal important  3.4  symmetry  metal  indicative The  by  from a  acting  given  different  (Fig.  metal  1.1).  paratoluenesulfonate  compares the  infrared  previously  frequencies  studied  paratoluenesulfonates.  modes o f g  vibration  vibration  vibrations  vibrations  modes  of  of  remains the  t h e a n i o n have unassigned  been  due  p-CH3CgH4 part of  a l s o remain  observations  s t r e t c h i n g and d e f o r m a t i o n  copper(II)  compounds.  three  iron(II)  those of other  The v  internal  the  Fe(p-CH3CgH4S03)2  i n f r a r e d spectrum of  shown i n F i g .  of  transition  b r i d g i n g l i g a n d , w i t h each oxygen  is  first-row  and  to  the exception the  are very  INFRARED SPECTRUM OF  anion.  350 cm  resulting in a highly polymeric l a t t i c e  The  to  cm-''  that  with  spectra  p r o p o s e d has t h e  as a t e r d e n t a t e anion  770  however  3 . 3 shows t h a t ,  trifluoromethanesulfonates of  around  coupled.  Table compound.,  s t r e t c h i n g frequency  the  unassigned.  again are that  remain u n s p l i t ,  the S 0 3  asymmetric  i n d i c a t i n g C~  anion  34  TABLE 3 . 4  INFRARED SPECTRAL DATA ( c m - 1 )  FOR  M(p-CH3C6H4S03)2  COMPOUNDS  C3v for  Assignment  M  p-CH3C6H4S03"  Fe  Co*  Ni'  Cu*  Zn'  s  1200 s  1190 s  1275 1266 1240 1160  s sh sh s  1200  1145 m  1143 m  1140 s  1130 1110  s s  1142  m  673 m  683 s  6 80 s 680  687  580 m  570 m  574 m  588 m 575 m 560 m  575  1195  691  490 w  *  Results  from r e f e r e n c e  x R . C . Thompson,  14  unpublished  results.  490  35  symmetry.  From T a b l e  3 . 4 i t c a n be a s c e r t a i n e d t h a t ,  exception of the copper(II) M^-Ch^CgH^SO^  compound,  independent o f the c a t i o n .  compounds  i s one w i t h  ligands tri  3.  of  C o , Ni and Z n , a r e  The s t r u c t u r e p r o p o s e d  t h e a n i o n s a c t i n g as t e r d e n t a t e  for^these  bridging  r e s u l t i n g i n a p o l y m e r i c l a t t i c e as p r o p o s e d f o r t h e  f1uoromethanesulfonates.  5.  INFRARED SPECTRA OF  Fe(CH3S03)2  Two f o r m s o f t h i s c o m p o u n d ,  a and & , have been i s o l a t e d ,  a n d h a v e been c h a r a c t e r i s e d by i n f r a r e d s p e c t r o s c o p y . f r e q u e n c i e s o f both  forms a r e l i s t e d  s p e c t r a o f t h e a and & Both M i l e s e t a l . (38) concluded that  3.5.1.  dehydration  group and  Methanesulfonate  t h e m o d i f i c a t i o n p r o d u c e d by t h e r m a l  under vacuum,  exhibits  E modes h a v e b e e n s p l i t  4 5 a n d 56 c m - 1 f o r t h e \ ^ and  indicates  have  3 . 2 a r e b a s e d upon t h i s c o n c l u s i o n .  S 0 3 b e n d i n g and s t r e t c h i n g r e g i o n s degenerate  (45)  anion belongs to the C 3 v point  Spectrum o f a-Irori(II)  The a - i s o m e r ,  3 . 2 and the i n f r a r e d  and G i l l e s p i e and Robinson  the CH3S03~  Infrared  i n Table  The v i b r a t i o n a l  f o r m s a n d o f a m i x t u r e are shown i n F i g . 3 . 4 .  a s s i g n m e n t s made i n T a b l e  is  the  the i n f r a r e d s p e c t r a  compounds, where M i s F e ,  virtually  with  three a b s o r p t i o n s i n both (see Table  3.2).  Both  the  doubly  and t h e magnitude o f t h e s p l i t t i n g vibrations  a d i s t o r t i o n of the anion with  respectively.  a concomitant  This  lowering  36  FIG.  3.4  INFRARED SPECTRA ( 1 5 0 0 - 2 5 0 c m " 1 )  OF  Fe(CH3S03)2  • Nujol Wave number  (cm ) 1  — I — i — i — i — i — r ~ n — i — i — i — I — *  1500  1300  1100  900  700  500  300  37  of  anion  symmetry  site-symmetry ^.20  below C 3 y  effects  to  usually  cm-1  and t h e  splittings  explained  by t h i s  mechanism  The identical  to  cobalt(II) symmetry of  infrared that of  to  a CH3S03~ anion the t h i r d  along  the  distorted  give  s p l i t t i n g s of  a magnitude  here appear  spectrum of  Co(CH3S03)2  cobalt  are  of  species.  the This  to  having If  cation,  less  than  the  lead to a and a  3.5,  as w e l l by t h e  between  by t h e  for  6 and 7,  in  as t h e  the  solid  anion  bonding from  distortion  infrared of  indicate by a  to  be  that  in  trigonal  to e x p l a i n  the  a-Fe(CH3S03)^. layer structure  black l i n e s ,  layers,i.e.  the methyl  For  strongly  in light  interactions  black l i n e s .  in a displacement of  (14).  Mossbauer r e s u l t s ,  proposed  adjacent  broken  virtually  tetragonally  are d i s t o r t e d  symmetry  one l o o k s a t t h e  Fig.  to  be  o x y g e n atoms  unlikely  The  i n Chapters  C3y  to  nonequivalent  A n o t h e r m e c h a n i s m must be p r o p o s e d  an i n t e r a c t i o n  result  would  FeOg o c t a h e c t r a  represented  represented  two o f  may a l s o a c c o u n t  i n more d e t a i l  compression.  up  proposed t h a t the  through  CoOg o c t a h e d r o n  discussed  compounds,  Cs  i.e.  This  spectroscopic studies.  the  great  previously  et a l .  a - F e ( C H 3 S 0 3 ) 2 but appears  a-Fe(CH3S03)2  be t o o  c o b a l t i o n s more o r l e s s  Mossbauer  anion  reported  to  ions,  bonded  to  a-Fe(CH3S03)2 is  Arduini  oxygen atom.  axis  spectrum of  previously  reduced below C 3 v  oxygen atoms  than  As m e n t i o n e d  alone.  methanesulfonate  was  Cg.  for  between  there  anion  must a l s o  anion-anion  from the  and be  interactions,  Such i n t e r a c t i o n s groups  these  C3  could axis  of  38  FIG.  3.5  THE CADMIUM IODIDE LAYER STRUCTURE  39  the anion  methyl 1400 in  r e s u l t i n g i n Cg  anion  Table  t h e i n f r a r e d bands o b s e r v e d i n  3.5  s t r e t c h i n g and b e n d i n g r e g i o n s - a p p r o x i m a t e l y  cm~^ r e s p e c t i v e l y .  the subsequent  3.5.2.  Infrared  The with  lists  symmetry.  The d a t a i n t h i s  spectrum of  Msomer,  B — IronClI)  shows o n l y  (see  Fig.  3.4  to  i s observed.  The  infrared  the anion are given  for  the  i n Table 3 . 2 ,  XSO^"  for  both  part of  previous  Assignments  t h e CH^ v i b r a t i o n s  for  reported data As i n t h e SO^  the  SO3  3.2).  an  infrared  no s p l i t t i n g o f  the v  4  the  the  XSO^"  part  and T a b l e 3 . 5  lists  the  the a - and  infrared spectral studies  for  of  (38).  s t r e t c h i n g and b e n d i n g  a n d ^ - i s o m e r s show d i s t i n c t d i f f e r e n c e s  by  (39,45).  a r e made on t h e b a s i s  Ba^H^SOg^  methyl  g-isomers.  a n i o n may be made  regions,  i n t h e CH^  and  have a s i m i l a r  trifluoromethanesulfonate  f r e q u e n c i e s a s s i g n e d to  comparison with  a-  and T a b l e  the  analogues.  s t r e t c h i n g a n d b e n d i n g modes  previously  i n both  e - i s o m e r may be p r o p o s e d t o  t h e one d e s c r i b e d f o r  The  Assignments  a-FeCCH^SO^  to a-Fe^CH^SOg^ the g-isomer e x h i b i t s  and p a r a t o l u e n e s u l f o n a t e  of  of  two a b s o r p t i o n s  s p e c t r u m w h i c h i n d i c a t e s C-jv a n i o n symmetry;  structure  be d i s c u s s e d  methanesul fonate  p r e p a r e d by t r e a t m e n t  s t r e t c h i n g and b e n d i n g r e g i o n s  vg v i b r a t i o n s  3000 a n d  section.  boiling D.M.P.,  In c o n t r a s t  table w i l l  the  the  stretching  40  TABLE 3 . 5  INFRARED SPECTRAL DATA ( c m - 1 )  FOR  IN THE C H 3 STRETCHING AND BENDING  ASSIGNMENT  CH3 a s . s t r .  CH3  s y m . s t r . (A-j)  CH3 a s . d e f .  CH 3  *  (E)  (E)  sym. def.(A-|)  Infrared  a-Fe(CH3S03)2  Fe(CH3S03) REGIONS*  6-Fe(CH3S03)2  3030 w  3040 w 3030 w  2940 m  2950 m  1430 s 1400 m  1425 m 1415 m 1405 m  1330 s  1330 s  s p e c t r a were r e c o r d e d i n  hexachlorobuta-1,3-diene.  41  and b e n d i n g  r e g i o n s and t h i s may p o s s i b l y be due t o  i n the anion-anion g-isomer in C3v  i n t e r a c t i o n s i n t h e two s p e c i e s .  the methyl  with  It  i s not  understood  the a-isomer.  differences in anion-anion  3.5.3.  Infrared  Again  for  spectrum of  only  a few h o u r s  spectra of  the  a converts  d i r e c t l y to  isomers,  3.5.4.  Infrared The  solvate  i n d i v i d u a l a-and  detectable  methanesulfonic  spectrum of  i n Table  spectrum of in the  infrared  s i m i l a r to that of  The  the  complex  the  the  p-Fe(CH3S03)2  spectrum i n F i g . refluxing  g- f o r m s . appear  This  3.4,  the  spectroscopy,  indicates  present  the  a-isomer  t o be no o t h e r  the  that structural  i n the  system.  Fe(CH3S03)2.CH3S03H. iron(II)  methanesulfonate  and i s c o m p a r e d w i t h  The m a j o r  a-iron(II)  bands a p p e a r i n g  2CH3S03H  infrared acid,  i n the  the major  methanesulfonate  i n f r a r e d spectrum of  Co(CH3S03)2.  the  and t h e p a r e n t  c a n be c o r r e l a t e d w i t h  spectrum of acid.  3.6  o f a- a n d  after  methanesulfonate  (46).  the s o l v a t e  methanesulfonic is  acid  shows a more  i s simply a superposition of  g and t h e r e  by i n f r a r e d  spectrum of a - i r o n ( I I )  t h e moment why  i t may be due t o  a mixture  i n f r a r e d spectrum of  is listed  resulting  interactions.  s p e c t r u m w h i c h one o b t a i n s  in D.M.P.  the  cm~^ r e g i o n s o f  As c a n be s e e n f r o m t h e l o w e r infrared  at  a more r e g u l a r a n i o n s y m m e t r y ,  i n f r a r e d s p e c t r u m i n t h e 3000 and 1400 spectrum than  In  g r o u p may be s i t u a t e d on t h e C 3 a x i s  a n i o n symmetry.  3-isomer,  differences  infrared  bands and  Fe(CH3S03)2-CH3S03H (26).  42  TABLE 3 . 6  INFRARED SPECTRAL DATA ( c m " 1 )  FOR  Fe(CH3S03)2.GH^SQgH-r  AND A COMPARISON WITH a - F e ( C H 3 S 0 3 ) 2 AND  C3v  ASSIGNMENT  FOR  ANION  a-Fe(CH3S03)2  F e ( C H 3 S 0 3 ) 2 . CHgSO-^H  1323 m S03 as.  str.  1220 s 1175 s  S-C s t r .  1066 m  790 m  1066  def.  S 0 3 sym.  *  Results  def.  1338 m  S02 as.  1122 m  S02  str  sym.str  990 s  980 s  C H 3 wag  920 s  891  S-(0)H  787  s  str  m  587 m 531 m  566 s 556 m  513 m  542 m  from r e f e r e n c e 46.  ASSIGNMENT FOR CH3S03H  s  767 m S03 as.  CH3S03H*  1190 m . s h . 1150 s 1120 m  S 0 3 sym. s t r .  CH3S03H  760 s  S-C s t r .  506 s  502 m  S02  484 w  473 w  S - 0 wag  rock  43  3.6.  STRUCTURAL  Fe(H20)6  ISOMERISM IN FeOg OCTAHEDRA  ( C 1 0 4 ) 2 e x h i b i t s a t h e r m a l l y i n d u c e d phase II  t r a n s i t i o n w h i c h h a s b e e n m o n i t o r e d by M o s s b a u e r s p e c t r o s c o p y (47,48).  The i r o n c a t i o n i s s u r r o u n d e d by a n o c t a h e d r o n o f  molecules. 250K)  In t h e h i g h t e m p e r a t u r e  form (temperatures  the octahedron i s elongated along the t r i g o n a l  the low temperature  form  (temperatures  less  than  water  greater  than  a x i s and i n  220K) t h e  octahedron i s compressed a l o n g the t r i g o n a l a x i s .  The two f o r m s  a r e i n t e r c o n v e r t i b l e by c h a n g i n g t h e t e m p e r a t u r e .  In t h e p r e s e n t  case both forms o f between 4 . 2 results  just  in Chapters similar  F e t C H g S O ^ a p p e a r t o be t h e r m a l l y  300K a n d no p h a s e t r a n s i t i o n o c c u r s .  stable  The i n f r a r e d  p r e s e n t e d a n d t h e M o s s b a u e r r e s u l t s t o be d i s c u s s e d 6 a n d 7 s u g g e s t t h e FeOg o c t a h e d r o n i n t h e a - i s o m e r i s  to that  i n the low-temperature  and t h e FeOg c h r o m o p h o r e i n t h e high-temperature  form o f Fe(H20)g  B-isomer i s s i m i l a r  (C104)2  to that  form.  The n e x t s e c t i o n s ( 3 . 7 a n d 3 . 8 ) d e s c r i b e a t t e m p t s to i s o l a t e o t h e r similar  i n the  i s o m e r i c forms o f d i v a l e n t metal  to the m o d i f i c a t i o n s found to e x i s t  sulfonates  i n Fe(CHoS0o)9.  made  44  3.7.  THE  SEARCH FOR  STRUCTURAL ISOMERISM IN . F e ( C F 3 S 0 3 ) 2  AND  Fe(p-CH3C6H4S03)2  USING INFRARED SPECTROSCOPY  F u r t h e r s t u d i e s were c a r r i e d o u t whether is  or not  i n o r d e r to a s c e r t a i n  the isomerism observed i n i r o n ( I I )  methanesulfonate  p e c u l i a r t o t h i s p a r t i c u l a r compound. As n o t e d p r e v i o u s l y ,  was p r e p a r e d u n d e r a n h y d r o u s anion retained C 3 v  symmetry.  s e c t i o n 3 . 3 , when  Fe(CF3S03)2  c o n d i t i o n s from the parent a c i d However,  t h i s compound may a l s o be  p r e p a r e d by an a q u e o u s m e t h o d i n v o l v i n g p r e c i p i t a t i o n o f c h l o r i d e f r o m a r e a c t i o n between FeCl2<  4 H 2 0 and A g ( C F 3 S 0 3 ) .  thermal  dehydration of the  an i d e n t i c a l  When b o t h refluxed spectra.  in  aqueous s o l u t i o n o f  t h e one r e p o r t e d i n T a b l e  „ D . M . P . no c h a n g e s w e r e o b s e r v e d i n t h e i r  in  Fe(XS03)2  a n i o n i s t h e o n l y one t o  compounds, where  gave 3.2.  were infrared  symmetry.  From t h e o b s e r v a t i o n s made h e r e i t methanesulfonate  of  the  Fe(CF3S03)2  F e ( C F 3 S 0 3 ) 2 and F e ( p - C H 3 C 6 H 4 S 0 3 ) 2  Both anions r e t a i n  silver(I)  stoichiometric proportions  The compound r e s u l t i n g f r o m  i n f r a r e d spectrum to  the  X i s CF3,  appears that  the  show s t r u c t u r a l i s o m e r i s m  C H 3 and  p-CH3CgH4.  45  3.8.  THE  SEARCH FOR  STRUCTURAL ISOMERISM IN  M(CH3S03)2  COMPOUNDS USING INFRARED SPECTROSCOPY A number is  Co,  Ni,  Cu,  Zn  spectroscopy with not  structural  of  M(CH3S03)2  and Ca.  They were  Infrared  very  reported  i s b o i l e d under  shows s e v e r a l 3.7.  changes.  The  spectrum of  more c o m p l e x t h a n than  that  seen i n is of this anion  of  The  that  reflux  cobalt(II)  in D.M.P.  in that  s p e c i e s A^ a n d o n l y  d o u b l i n g o f A-| sites.  This  reference more  the  reversal  d i d not  infrared are  spectrum  given  a n d i s more  that  these  initial  e-  is  vibration Previously nonequivalent  here.  infrared spectral  c h a n g e s c o u l d be  compound u n d e r vacuum a t  i n f r a r e d s p e c t r u m was o b s e r v e d .  occur i n  complex  t h a n one a b s o r p t i o n This  in  is  modes h a s b e e n e x p l a i n e d by p r o p o s i n g  r e v e r s e d by h e a t i n g t h e c o b a l t ( I I ) whereupon  When  treatment  14  3.5.1.  one b a n d i s e x p e c t e d .  may a l s o be t h e c a s e  We f o u n d  Section  the  t h e compound a f t e r  2  results  methanesulfonate  t h e s e compounds.  the S 0 3 symmetric s t r e t c h i n g r e g i o n .  symmetry  (14).  i n f r a r e d s p e c t r a l data  reported 3  for  a-Fe(CH3S03)2  B- Fe(CH3S0 ) i:in  The  Co(CH3S03)2  i n f r a r e d data  those of  compounds.  or  3.8.5.  the proposed s t r u c t u r e s of  Co(CH3S03)2  Table  spectrum of  s i m i l a r to  discussed  to  infrared  i n a s c e r t a i n i n g whether  isomerism occurs i n these  The are  i n v e s t i g a t e d by  particular interest  are discussed i n s e c t i o n s 3.8.1  3.8.1.  compounds w e r e p r e p a r e d w h e r e M  Fe(CH3S03)2.  This  150°C, type  of  46  TABLE  -1 INFRARED SPECTRAL DATA (cm ) FOR  3.7  BEFORE AND AFTER TREATMENT WITH  C3v  Assignment  Before  for  CH3S03"  with  Treatment  D.M.P.*  1233 1170  s s  Co(CH3S03)2  2,2-DIMETHOXYPROPANE  After with  Treatment D.M.P.  1180 s . b r  1070 s  1070 s 1035 m  787 s  800 m 780 w  590 m 530 m  563 m 550 m  512  m  500 w  INTERNAL VIBRATIONS  '1330 970 385 373 350  w w w w w  *  14  v  6  A N D  C H  Results  3  from r e f e r e n c e  1330 1250 420 390  w w.sh w w  47  3.8.2.  Infrared  spectrum of  Nickel(II) in  this  laboratory  different study  gave  ^(Ch^SO.^  methanesulfonate  and the p r o d u c t s  infrared spectra.  has b e e n p r e v i o u s l y  from d i f f e r e n t  F u r t h e r work  prepared  preparations  as a p a r t  of the  gave  current  i n c o n s i s t e n t r e s u l t s and i n f r a r e d s p e c t r a w h i c h  exhibited  extremely  b r o a d a b s o r p t i o n b a n d s i n t h e SOg b e n d i n g a n d s t r e t c h i n g  regions.  Treatment w i t h  spectrum.  No i n t e r p r e t a t i o n  c o u l d be made f o r  3.8.3.  Infrared  The is  D.M.P.  this  as t o  the nature of  i n f r a r e d spectrum of  l a t t i c e was p r o p o s e d t o a c c o u n t f o r  in  anion  symmetry  CutCH^SOg^  c o m p l e x and t h e p r e s e n c e o f more t h a n  observed i n the  the  infrared  compound.  spectrum of  reported  p r o d u c e s no c h a n g e s i n t h e  this  copper(II)  one t y p e (14).  methanesulfonate  of anion i n  No c h a n g e s  i n f r a r e d s p e c t r u m when t h i s compound was  the  were  refluxed  D.M.P.  3.8.4.  Infrared spectrum of Zinc(II)  this  laboratory  The p r e p a r a t i o n  but  was p r e p a r e d p r e v i o u s l y  the i n f r a r e d s p e c t r a l d a t a were not  given  dehydration  lower part of  methanesulfonate  has been r e p e a t e d as a p a r t o f  i n f r a r e d data are thermal  Zn^HgSOg^  i n Table  3.8.  of a solution of  Fig.3.6.  The  The  this  spectrum i s of  reported.  study  and  spectrum obtained  ZntCHgSOg^  in  i s shown i n  a complex n a t u r e ,  the by the ,:<-.••  48  TABLE 3 . 8  INFRARED SPECTRAL DATA ( c m - 1 )  FOR Z n ( C H 3 S 0 3 ) 2  BEFORE AND AFTER TREATMENT WITH  C 3 v Assignment for  CH3S03"  Before Treatment with D.M.P.  (1288 1263 1230 1200 1170 J134  m s s sh sh s  2,2-DIMETHOXYPROPANE  A f t e r Treatment with D.M.P.  1170  s  v  l  1070 m 1040 m  1063 s  v  2  808 m 780 m  800 s  m m m m  560 s 550 s  503 w  502 m  '580 561 545 524  v  6  AND C H  3  INTERNAL VIBRATIONS  1420 1334 . 1288 370 350  w.br. w w w w  1429 1419 1406 1331 1259 360  w w w m m w  49  50  consisting  of  a broad a b s o r p t i o n  in  r e g i o n a n d more t h a n one a b s o r p t i o n stretching is  of  symmetry  observed sites  region.  As m e n t i o n e d p r e v i o u s l y  of  upper  as a r e s u l t o f  the  s p e c i e s . m u s t be spectrum of  Fig.  3.7  r e f l u x i n g a sample o f  p r o d u c e d i n t h i s way  with  symmetry.  a n i o n may h a v e i t s  The  C^y a s s e e n by t h e  sample  small  absorption. that  (prior  heated under  nonequivalent  the  vacuum a t  in D.M.P.).  For  s l i g h t l y lowered  below  mode a n d this  p r e s e n t i n the When  this  retaining  c m _ 1 ) o f the  i s not  because  3 - Fe^H^SOg^-  From t h e i n f r a r e d s p e c t r u m o f  to r e f l u x i n g  anion  The  3-isomer  the anion  symmetry  s p l i t t i n g (10  this modification  vibrations  shows t h e s i m p l i f i c a t i o n  is called  s i t e may be p r o p o s e d w i t h  appears  t h e v-| v i b r a t i o n  ZnCCH^SOg^ i n D . M . P .  f o r m one a n i o n  it  SO^  proposed.  infrared spectral similarities  broad  symmetric  spectrum a s i n g l e species with  or a mixture The  of  i n the  s p e c i e s A-| a n d t o e x p l a i n t h e d o u b l i n g o f  in this  modification  t h e a s y m m e t r i c SO3 s t r e t c h i n g  the  3-form original  3 - Z n ( C H g S 0 g ) 2 was  1 5 0 ° C no c h a n g e was o b s e r v e d  i n the  infrared  spectrum.  3.8.5.  Infrared  spectrum of  CatCHgSOg^  As n o t e d p r e v i o u s l y a c r y s t a l for  calcium(II)  preparative an a n a l o g o u s  methanesulfonate  method w e r e route  methanesulfonates  to  given.  (17). The  t h a t used f o r  (see Chapter  2).  structure  has b e e n  No i n f r a r e d d a t a  reported  or  compound was p r e p a r e d h e r e the f i r s t - r o w The  transition  by  metal  i n f r a r e d spectrum i s given  in  51  Table  3.9.  The d o u b l i n g o f t h e  modes  t h a n one t y p e o f a n i o n e n v i r o n m e n t The  crystal  anion  structure  sites,  although  prepared  by C h a r b o n n i e r  D.M.P.  t y p e o f compound,  study.  When  c o m  bridging  l i g a n d s and t h e metal  Pounc's  o x y g e n atoms  A general m  structural  a y be p r o p o s e d  model  in  spectrum.  whether  i t i s octahedral  investigate  appropriate a c t as  ions are octahedrally  from s i x d i f f e r e n t  anions.  Infrared  to a l l terdentate  c o o r d i n a t e d by  spectroscopy  or t r i g o n a l l y  one r e q u i r e s  namely Mossbauer s p e c t r o s c o p y which w i l l  study  o f t h e MOg c h r o m o p h o r e ,  or tetragonally  t h e MOg e n v i r o n m e n t  in this  isomers i n  i n which anions  incapable of probing the d e t a i l e d nature  i.e.  t h e compound  C a t C H ^ S O ^ was r e f l u x e d  showing the presence o r absence o f s t r u c t u r a l  M(XS0g)2  and  modifications  s p e c t r o s c o p y h a s been i n v a l u a b l e  systems.  To  nonequivalent  i t i s possible that  in i t s infrared  MUSOg^  is  compound.  SUMMARY OF RESULTS AND CONCLUSIONS Infrared  in  more  e t a l . i s n o t s t r u c t u r a l l y t h e same a s t h e  no c h a n g e was o b s e r v e d  3.9.  in this  because of the s t r u c t u r a l  in this  in this  must e x i s t  a l s o shows t h e p r e s e n c e o f  observed  one p r e p a r e d  indicate again that  another  distorted.  technique,  be d i s c u s s e d i n C h a p t e r s 6  7. Table 3 . 1 0 summarises t h e r e s u l t s c o n c e r n i n g i s o m e r i s m  in  MCCHgSOg^  compounds.  52  TABLE 3 . 9  INFRARED S P E C I A L . D A T A  C3v for  (cm-1)  FOR  Ca(CH3S03)2  Assignment CH3S03"  1200 s .  br  1085 m. s h . 1070 s 800 s 790 s 557 s 542 s 530 w. s h . 520 m Vg  AND  CH3  INTERNAL VIBRATIONS  1421 1330 1260 970 345  m m m w m  53  TABLE  3.10  SUMMARY OF RESULTS CONCERNING M(CH S0 ) 3  3  2  PRODUCT OBTAINED BY DEHYDRATION BETWEEN 100-150OC  ISOMERISM IN  COMPOUNDS  PRODUCT OBTAINED UPON REFLUXING IN D.M.P.  Fe  COMPLEX I . R . Co  SPECTRUM  8  a  4L Ni  INCONCLUSIVE  RESULTS  Cu  COMPLEX  I.R.  SPECTRUM  Zn  COMPLEX  I.R.  SPECTRUM  COMPLEX I . R .  SPECTRUM  NO CHANGE  r  Ca  NO CHANGE  54  CHAPTER 4  ELECTRONIC SPECTRA OF  4.1.  Fe(XS03)2  COMPOUNDS  INTRODUCTION For  relatively 5  term i s  a regular octahedral  complex o f  s i m p l e to a s s i g n a v a l u e  to  D which r e p r e s e n t s a ground  lODq.  state  d  iron(II) The  6  it  is  free-ion  electron  ground  configuration. 5  An o c t a h e d r a l  crystal  a s shown i n F i g .  field lifts  4.1,  into  the  degeneracy 5  a low energy  T^g  of  the  and a h i g h  D  state  energy  5 Eg  state,  the energy The  difference  compounds  being  lODq.  s t u d i e d i n t h i s work  are a l l  high  spin  II  a s e v i d e n c e d by M o s s b a u e r s p e c t r o s c o p y and m a g n e t i c s u s c e p t i b i l i t y 5 measurements. Hence t h e g r o u n d s t a t e i n t h e s e compounds i s T2g and t h e y from the  4.2.  should a l l  show o n l y one s p i n - a l l o w e d d - d a b s o r p t i o n  5  5  T2g  •  RESULTS AND  Eg  transition.  DISCUSSION  The e l e c t r o n i c s p e c t r a o f s t u d i e d here are a l l in Table  4.1.  The  a r o u n d 9000 c m - 1 typical  spectrum,  arising  very  the anhydrous  s i m i l a r and t h e  spectra consist of  with that  a less of  Here one can c l e a r l y o b s e r v e  the  species  band p o s i t i o n s a r e  a broad absorption  intense shoulder at  FeCCF^SO^),,,  sulfonate  maximum  lower energy.  i s reproduced i n F i g .  s p l i t t i n g of  the  listed  band i n t o  A 4.2.  two  55  FIG.  4.1.  S P L I T T I N G OF THE F R E E - I O N  5  D GROUND TERM  IN AN OCTAHEDRAL CRYSTAL F I E L D  lODq  FREE  ION  (  \  '2g OCTAHEDRAL CRYSTAL FIELD  56  TABLE 4 . 1 .  ELECTRONIC SPECTRA OF  Fe(XS03)2  POSITIONS ( c m - 1 )  COMPOUNDS  X  BAND  lODq  CF3  8600  7600  8100  a-CH3  9000  7400  8200  B-CH3  9000  7300  8150  p-CH3CgH4  8700  7300  8000  57  58  components.  As m e n t i o n e d  in section 4.1,  in regular  symmetry  o n l y one b a n d i s e x p e c t e d i n t h i s r e g i o n o f  however,  there  are several  octahedral the  spectrum;  m e c h a n i s m s by w h i c h a d o u b l e p e a k may be  observed.  (i)  As c a n be s e e n f r o m F i g . l o w e r e d from 0^ t o  4.3  if  the  symmetry  the degeneracy of  of  the octahedron  both the  ^Eg  is  and  5 l\>g s t a t e s  is lifted.  Two a b s o r p t i o n s w o u l d be e x p e c t e d 5  to  t r a n s i t i o n s from the ground s t a t e  excited  states.  The  of the order of spectra of  s p l i t t i n g of  300 c m - 1 ,  to  to the 5  the  be o b s e r v e d  t h e s e compounds.  due  5 A^g  state  and i s too  small,  i n the e l e c t r o n i c  A tetragonal  d i s t o r t i o n of  the  2+ Fe(rL,0)g 6^0,  octahedron occurs in Tutton's  salt,  (NH^  FetSO^.  w h e r e two a b s o r p t i o n s , a r e o b s e r v e d due t o a s p l i t t i n g  the e x c i t e d s t a t e  by 2400 c m - 1  (49,50).  In  t h e compounds  of  studied  11  here both t h e Mossbauer and i n f r a r e d d a t a around the c a t i o n i s not  tetragonal  i n d i c a t e that the  b u t t r i g o n a l , D^.  symmetry  As c a n be  5 seen from F i g . environment this  the  Spin-orbit  E„ excited state 9  and a l t h o u g h  s p l i t t i n g i s too  spectra. (ii)  4.3  the  small  An a l t e r n a t i v e coupling l i f t s  remains  ground s t a t e to  unsplit in  degeneracy i s  be o b s e r v e d  m e c h a n i s m m u s t be the degeneracy o f  i n the  this  removed  electronic  proposed. b o t h t h e ^Eg  and  5 T^g is too  l e v e l s , but  approximately small  for  iron(II)  100 c m - 1  to account f o r  the  (51) the  spin-orbit coupling  and i s an o r d e r o f  constant  magnitude'  observed s p l i t t i n g s of  greater  than  59 FIG.  4.3.  S P L I T T I N G DIAGRAM FOR H I G H - S P I N I R O N ( I I ) F I E L D S OF O h ,  IN CRYSTAL  D 4 h AND D 3 d SYMMETRY  lODq  TETRAGONAL D  4h  OCTAHEDRAL  TRIGONAL D  3d  60  1000 (iii)  cm  The m e c h a n i s m w h i c h i s m o s t p l a u s i b l e and has been p r o p o s e d account for  the  band s p l i t t i n g i n F e ^ S O g ^  Fe(SiFg)2.  6H20  (49)  degeneracy  by a d y n a m i c J a h n - T e l l e r  dynamic J a h n - T e l l e r  effect  species  eg.  to another,  elongation,  both  that  undistorted  of  the  time-averaged  If  effect,  may be e s t i m a t e d  Table  This  tetragonal  effect  the  value  us t o  4 . 2 , and a r e seen to  (52).  The  lODq f o r  t h e two f o r m s  the  c a l c u l a t e values of to  and  the  the  octahedron.  this  compounds  centre of  be c o m p a r a b l e  than  Under such c o n d i t i o n s  band s p l i t t i n g i s due t o of  one  tetragonal  having a lower energy  f o r m may be c l o s e t o an  the  state  compression to  between  from the approximate  enables  the e x c i t e d  octahedron.  oscillate  one a s s u m e s t h a t  Jahn-Teller  of  and  i s an i n t e r c o n v e r s i o n f r o m  configurations  m o l e c u l e may w e l l  band.  i s a removal  (15)  to  the  dynamic  studied  split  here  absorption  Dq w h i c h a r e p r e s e n t e d  the values  given  in  previously  (14,15). A c o r r e l a t i o n between anion,  XSOg" , a n d Dq m i g h t  If:one  compares the  given  in Table  800 e m " 1 .  It  4.2,  appears  the  be e x p e c t e d .  values of the v a l u e s that  base s t r e n g t h s  Dq f o r  This,  are a l l  very  the e s t i m a t i o n of  detect  small  differences  that  exist  the  particular  however,  compounds o f  from e l e c t r o n i c spectroscopy i s simply not to  of  the  similar,  type  sufficiently the  observed.  NKXSO^^  approximately  ligand f i e l d  between  i s not  strength sensitive  various  61  TABLE 4 . 2  Dq VALUES ( c m " ' )  F 0 R . M ( X S 0 3 ) 2 COMPOUNDS  M  X F  CF3  a-CH3  p-CH3C6H4  Co  765  780  765  780  Fe  800  810  820  800  Dq v a l u e f o r F e ( F S 0 3 ) 2 f r o m r e f e r e n c e 15 Dq v a l u e f o r C o ( X S 0 . J 9  compounds f r o m r e f e r e n c e 14  62  XSQ3  anions. The m a g n i t u d e o f  lODq o b s e r v e d i n t h e s e compounds i s  not  2+ u n r e a s o n a b l e when c o m p a r e d , f o r e x a m p l e , w i t h t h a t o f w h e r e lODq i s a p p r o x i m a t e l y a greater ligand f i e l d  10,000..cm" ^ ( 4 9 ) ,  Fe^O)^  ,  and i s c o n s i s t e n t w i t h  s t r e n g t h f o r w a t e r as compared w i t h t h e  XSO^-  anions. Comparison of  the  the c o r r e s p o n d i n g c o b a l t ( I I ) The  Dq v a l u e s f o r  Dq v a l u e s o f  F e ( X S 0 3 ) 2 compounds w i t h t h o s e  analogues i s a l s o i n f o r m a t i v e ,  the i r o n s a l t s  of the corresponding c o b a l t ( I I )  are approximately species  Table  5% g r e a t e r t h a n  4.2. those  as i s g e n e r a l l y e x p e c t e d 1 ( 5 3 ) .  of  63  CHAPTER 5  MAGNETIC S U S C E P T I B I L I T I E S OF F e ( X S 0 3 ) 2 COMPOUNDS  5.1.  INTRODUCTION  Inorganic properties oxidation  coordination  c h e m i s t s have l o n g u s e d  magnetic  o f d - t r a n s i t i o n metal  c o m p l e x e s a s a means o f  determining  states  measurements routinely  between  performed  low t e m p e r a t u r e 4.2K,  and s t e r e o c h e m i s t r i e s . M a g n e t i c l i q u i d nitrogen in this  cryostats  Studies  a n d room t e m p e r a t u r e  laboratory;and  have e x t e n d e d  enabling the chemist to e x t r a c t  susceptibility  i n other  establishments  the temperature  e v e n more  range  i n v o l v 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 measurements  (54), investigation  magnetic exchange  This effects of  o f s p i n c r o s s - o v e r phenomena  single (55) and  interactions (56).  chapter d i s c u s s e s the o r i g i n s of the magnetic  observed  paramagnetism  application  below  information.  include the i n v e s t i g a t i o n o f magnetic a n i s o t r o p i c s using crystals  are  and i n c l u d e s a b r i e f as d e r i v e d  of this  theory  d e s c r i p t i o n of the  by Van V l e c k .  theory  In p a r t i c u l a r t h e  to the case o f h i g h - s p i n i r o n ( I I )  will  be c o n s i d e r e d . The m a g n e t i c will  s u s c e p t i b i l i t y measurements  be d i s c u s s e d a n d a n a l y s e d u s i n g a model  and L e w i s  (57).  made i n t h i s  developed  by  Figgis  study  64  5.2.  ORIGINS OF THE MAGNETIC  The  e l e c t r o n h a s a m a g n e t i c moment  as l a r g e a s t h a t effects  EFFECTS  of the proton  and hence t h e v a r i o u s  c o n s i d e r e d here a r i s e only  these nuclear paramagnetic  approximately  effects  types  from the e l e c t r o n s . have g r e a t  1000 t i m e s of  magnetic  However,  s i g n i f i c a n c e f o r the  II  Mossbauer and n . m . r .  spectroscopist.  When t h e e l e c t r o n s a r e i n c l o s e d s h e l l s effect to  i s known a s d i a m a g n e t i s m a n d u n p a i r e d e l e c t r o n s g i v e  the magnetic behaviour  the paramagnetism  The m a g n e t i c  arrangements behaviour  by m e a s u r i n g t h e m a g n e t i c a p p l i e d magnetic experimental  field.  techniques,  a vibrating  compound  The n a t u r e  i s determined  of the unpaired  o f a compound  rise  is  of by  electrons.  investigated  p o l a r i s a t i o n o f t h e s u b s t a n c e by an  This  c a n be a c h i e v e d by a v a r i e t y  i n c l u d i n g f o r c e methods  Gouy o r F a r a d a y t e c h n i q u e example,  known a s p a r a m a g n e t i s m .  e x h i b i t e d by a g i v e n  t h e number a n d o r b i t a l  5.3.  the magnetic  ( f o r example,  ( 5 8 , 5 9 ) ) and i n d u c t i o n methods  sample magnetometer  of the  (using,  for  (60)).  DIAMAGNETISM  This  i s a property  o f a l l forms  of matter  and a r i s e s  f i e l d - i n d u c e d e l e c t r o n c i r c u l a t i o n which generates  a field  to  the lines' of  the a p p l i e d magnetic  field.  In c l a s s i c a l  i n s i d e a d i a m a g n e t i c sample a r e l e s s such a m a t e r i a l  terms  from  opposed force  c o n c e n t r a t e d than o u t s i d e and s o  when p l a c e d i n a h e t e r o g e n e o u s  magnetic  field will  move  65  to  r e g i o n s o f minimum f i e l d s t r e n g t h .  diamagnetism The is  is that  i n d u c e d moment o n l y not  temperature  5.4.  and/or  does not v a r y w i t h  temperature.  upon t h e e l e c t r o n c o n f i g u r a t i o n  a r i s e s as a consequence o f  s p i n a n g u l a r momentum o f  a p p l i e d magnetic  paramagnetic  field. lines  the  s a m p l e moves  paramagnetic  to  regions of  which  centres are  any c o o p e r a t i v e  cases of  magnetic  Paramagnetic temperature  two o p p o s i n g f o r c e s ;  tends  to  of  i s the  r e l a t i v e l y high f i e l d  the  effects.  with  reverse  in  far  removed  (Ferrothe  magnetic  from each o t h e r  these aligned  moments.  in  spins of of  one  adjacent  to  thermal  are  paramagnetic  ions,  respectively.  dependent  as a r i s i n g  f i e l d tends  the  where  and a n t i f e r r o m a g n e t i s m  d e p e n d e n c e may be t h o u g h t o f  i o n s and t h e  field  strength.  s u s c e p t i b i l i t i e s r a r e temperature  the a p p l i e d magnetic  of  the  Such s y s t e m s a r e t h o s e  opposed t o . t h o s e  paramagnetic  randomise  too  c o n c e n t r a t i o n where  i o n <are a l i g n e d . w i t h . o r  orbital  s u s c e p t i b i l i t i e s are f i e l d independent  transmit  moments  terms i t  force are concentrated  case of m a g n e t i c a l l y d i l u t e systems.  and t h i s  i n t e r a c t i o n of  unpaired e l e c t r o n density  In c l a s s i c a l of  the  s a m p l e a n d when p l a c e d i n a h e t e r o g e n e o u s  Paramagnetic  the  of  dependent.  diamagnetism; magnetic  the  depends  feature  PARAMAGNETISM  This  the  i t s magnitude  An i m p o r t a n t  to  energy  from  align of  the  the sample  66  magnitude with  Paramagnetic  s u s c e p t i b i l i t i e s are usually several  greater  diamagnetic  than  susceptibilities.  unpaired e l e c t r o n s p i n d e n s i t i e s almost always  paramagnetic  susceptibility.  By d e t e r m i n i n g  and e s t i m a t i n g t h e d i a m a g n e t i c the d e s i r e d paramagnetic  X  A  =  X  M "  X  f  DIA  c o n t r i b u t i o n s may be o b t a i n e d  (30,31,32),  which allow the diamagnetic  by summing t h e c o n t r i b u t i o n s bonds,  5  o n e  obtain  the r e l a t i o n s h i p ,  J  )  from P a s c a l ' s  contributions  from a l l the atoms,  c a n  constants  t o be c a l c u l a t e d  i , x^-j  and a l l the  j , xBj  X  5.5.  materials  have a n e t  XQJ^  r o m  (  Diamagnetic  of  t h e measured s u s c e p t i b i l i t y ,  contributions,  susceptibility,  Hence,  orders  DIA=  F*Ai  +  |  x  B j  (5-2>  THEORY OF PARAMAGNETIC S U S C E P T I B I L I T Y ,  THE VAN VLECK  EQUATION AND ITS A P P L I C A T I O N TO H I G H - S P I N I R O N ( I I )  Magnetic  s u s c e p t i b i l i t y may be d e f i n e d  B = H + 4nl where B i s the magnetic magnetic  The  i n the f o l l o w i n g way:  (5.3)  induction or f l u x ,  f i e l d and I i s t h e i n t e n s i t y  SYSTEMS  of  r a t i o B/H i s t h e m a g n e t i c  H -is the applied magnetisation.  permeability  of the substance  67  and i s g i v e n b y :  B/H  where x v  = 1 + 4nI/H  (5.4)  = 1 + 4nx..  (5.5)  i s the magnetic s u s c e p t i b i l i t y per u n i t  The m o l a r s u s c e p t i b i l i t y may t h e n b e d e f i n e d  X  =  M  x v (M.W./P)  volume.  thus:  (5.6)  w h e r e M.W. i s t h e m o l e c u l a r w e i g h t a n d p t h e d e n s i t y of  the material  under  investigation.  The p a r a m a g n e t i c s u s c e p t i b i l i t y  may t h e n be c o r r e c t e d f o r t h e d i a m a g n e t i c e f f e c t s o f t h e atoms a n d ions  p r e s e n t and  may be e v a l u a t e d  e f f e c t i v e m a g n e t i c moment,  J  where  Eff  =  y  k i s the Boltzman  familiar  y  5.1.  The  may t h e n be c a l c u l a t e d :  £ f f  3k x A T (5.7)  constant,  and 8 i s t h e Bohr Magneton. the  from e q u a t i o n  N i s Avagadro's  Evaluation  number  of these constants  gives  equation:  E f f  = 2.828(X l) h  (5.8)  A  P a r a m a g n e t i s m may be c o n s i d e r e d t o a r i s e f r o m c h a n g e s i n the t h e r m a l l y a c c e s s i b l e energy  l e v e l s o f an atom when i t i s  subjected to a magnetic  Studies  e n a b l e the magnetochemist  field.  o f p a r a m a g n e t i s m i n atoms  t o probe t h e ground s t a t e and t h e r m a l l y  68  accessible excited states.  Van V l e c k  (61)  e v a l u a t i n g the  l e v e l s of  the  ions the of  new e n e r g y  i n t h e m a g n e t i c f i e l d and t h e n , s u s c e p t i b i l i t y per mole o f  equation of  second  NE. ( W . ( 1 ) 2 / k T — —  =  £j  The W.(°), W ^ 1 ) level w^-  (2) '  states.  -  2W.(2))  exp(-Wi  i n the absence of  ( o )  c o n f i g u r a t i o n and a the previous  l e d t o Van  in standard  Vleck's  texts  (62,63)  (5.9)  /kT)  d e p e n d s upon t h e e v a l u a t i o n i s the energy of  an a p p l i e d f i e l d and  a r e t h e f i r s t and s e c o n d o r d e r case of  distribution  ]  w h e r e W.^  2  deriving  exp(-W.(o)/kT)  ]  and W^ \  and  statistics,  thermal  This  of  order:  c a l c u l a t i o n of  The  in  from the  paramagnetism which i s d e r i v e d  and i s g i v e n h e r e t o  xA  i n d i v i d u a l atoms  using Boltzman  atoms  a t o m s among t h e a v a i l a b l e e n e r g y  solved the problem  of  the  and  Zeeman c o e f f i c i e n t s r e s p e c t i v e l y .  i n t e r e s t here i s i r o n ( I I )  D high-spin free-ion  a d  electron  ground term.  c h a p t e r and i l l u s t r a t e d i n F i g .  4.1  As  mentioned  an o c t a h e d r a l  5 crystal  field ilifts  the degeneracy of  this  D term.  The  low  energy  5 T2g The  term i s f u r t h e r  split  resulting J-states  thus w i l l  be t h e r m a l l y  approximately  a r e s e p a r a t e d by a few h u n d r e d w a v e n u m b e r s populated;  200 c n f ^ ) .  the degeneracy of  by s p i n - o r b i t c o u p l i n g as shown i n F i g .  The  each J - s t a t e  (kT  at  room t e m p e r a t u r e  is  a p p l i e d magnetic f i e l d f u r t h e r into a multipletof  2J+1  lifts  levels.  5.1. and  69  FIG.  5.1  THE EFFECT OF S P I N - O R B I T COUPLING ON THE 5  T~  GROUND TERM  J=l  I  I  I I  I I I I I  I  5  /  x  T  1  /  J=2  2g  \ \  CUBIC F I E L D TERM  X  \ \ \  \ \ \  SPIN-ORBIT  J=3 COUPLING  70  The  magnitude  from a knowledge spin-orbit  of  of  t h e m a g n e t i c moment  the f r e e - i o n  coupling i s given  ground  high-spin iron(II)  momentum q u a n t u m and t h e  numbers,  values  and a v a l u e  than  and y  s.o.  =  is 4.89  s  ^(S+l))*  for  by t h e  crystal  p i c t u r e of for  to  t h e moment  3  momentum a b o u t  a specified axis  that  convert  orbital in dvw  the  to  that  into  ion,  the d  0  a 45° r o t a t i o n n  orbital.A  the  to  the  expression:  (5.11)  of  This  mathematical  the  the  has b e e n  complex.  a n g u l a r momentum  A  orbital  "quenched"  qualitative proposes  to possess o r b i t a l  i n t o an i d e n t i c a l  that  angular  the  z-axis  similar rotation  will  about  about  degenerate  electron concerned.  about  two,  this  i t m u s t be p o s s i b l e , by r o t a t i o n  orbital  w h i c h has a v a c a n c y f o r free  contribution  i n the f r e e - i o n  orbital  to  determined  p h y s i c a l l y by a s s u m i n g t h a t  f i e l d upon f o r m a t i o n  t h i s quenching of  equal  y c a l c u l a t e d from  B.M.  present  angular  B.M.  "spin-only"  an e l e c t r o n i n a p a r t i c u l a r o r b i t a l  axis,  are both  high-spin iron(II).  e x p r e s s i o n may be r e p r e s e n t e d contribution  i s 5.48  y a s s u m i n g no o r b i t a l  B.M.  s p i n and o r b i t a l  the e x p e r i m e n t a l l y  moment may be c a l c u l a t e d f r o m t h e  p  total  the values of  greater  of  no  (5.10)  S and L r e s p e c t i v e l y ,  i s found t h a t  expression are often  t e r m and a s s u m i n g  B.M.  the  c a l c u l a t e d m a g n e t i c moment It  estimated  by:  u = (L(L+1) + 4S(S+1))^  For  c a n be  Therefore,  convert the z - a x i s  the will  71  interchange arise  the d  x z  and d ^  z  o r b i t a l s , and o r b i t a l  from e l e c t r o n s occupying these o r b i t a l s .  octahedral  (or tetrahedral)  crystal  c o n t r i b u t i o n s may  However,  f i e l d the t „  and e  2g no l o n g e r d e g e n e r a t e z-axis  and hence t h e o r b i t a l  a r i s i n g from t h e  and  d  x  2_y2  The e ^ o r b i t a l s now p r o d u c e no o r b i t a l moment.  For a h i g h - s p i n d  some c o n t r i b u t i o n The model  of Figgis  g  contribution  a i r  o  f  o r b i t a l s are  about the  orbitals  contribution  vanishes.  to the magnetic  e l e c t r o n c o n f i g u r a t i o n we may s t i l l  from t h e t g  set  next s e c t i o n w i l l and Lewis  expect  of o r b i t a l s .  now d i s c u s s  the  (57) used t o a n a l y s e  d e t e r m i n e d m a g n e t i c moment  5.6.  P  i n an  three-parameter  the experimentally  data.  THE F I G G I S AND LEWIS MODEL  A theoretical  treatment of the magnetic  properties  of the  6 d  high-spin  model  i o n h a s been g i v e n b y F i g g i s  has s u c c e s s f u l l y p a r a m e t e r i s e d  t e r m s o f A, K a n d x. of  the magnetic  The model  properties  and Lewis  several  (57).  iron(II)  This  compounds  in  has a l s o been used i n t h e t r e a t m e n t  of other  first-row  transition  metal  complexes ( 6 4 ) . The model (tetragonal  simultaneously considers the e f f e c t s  or trigonal)  crystal  f i e l d and a s p i n - o r b i t  o f an a x i a l  coupling  5 perturbation any  on t h e  interactions with  1^  c u b i c f i e l d ground  higher excited  terms.  term and does n o t c o n s i d e r  72  A i s d e f i n e d as the  5  the  J^g t e r m i n t o a d o u b l e t  s p l i t t i n g of  the o r b i t a l  a n d a s i n g l e t by t h e  degeneracy  asymmetric  l i g a n d f i e l d c o m p o n e n t and i s t a k e n t o be p o s i t i v e when t h e singlet  i s lower i n energy  r e l a t i v e to  K i s the o r b i t a l the  doublet.  r e d u c t i o n f a c t o r and t a k e s  c o v a l e n t bond c h a r a c t e r .  moment  the  It  appears  orbital  into  i n the e f f e c t i v e  account  magnetic  operator:  y =•  ( K L + 2S)  y.  (5.12)  P  K can take  values  up t o a maximum o f  1 w h i c h i n d i c a t e s no e l e c t r o n  delocalisation.  Electron  d e l o c a l i s a t i o n i s a l s o taken  into  account  a l l o w i n g the s p i n - o r b i t c o u p l i n g constant to vary from free-ion  value,  \Q  (for  The o p e r a t o r wavefunctions,  iron(II),  \Q  ^AXIAL*  '"^  | M ^ , M<- > ,  by t h e  low symmetry  c o u p l i n g are a l s o perturbed first-order  level  its  (51).  on t h e  or tetragonal  fifteen symmetry.  crystal  r e s u l t i n g from f i e l d and  by t h e e f f e c t s o f  Zeeman c o e f f i c i e n t s a r e f o u n d  by c o n s t r u c t i n g t h e a p p r o p r i a t e  the  spin-orbit  the magnetic for  field.  each i n d i v i d u a l  secular determinant.  The  s e c o n d - o r d e r Zeeman c o e f f i c i e n t s a r e t h e n f o u n d by e v a l u a t i n g matrix  elements of  This  w h i c h i s s o l v e d n u m e r i c a l l y on a  The e n e r g i e s a n d w a v e f u n c t i o n s  perturbation  The  operates  in trigonal  r e s u l t s it) a s e c u l a r d e t e r m i n a n t computer.  *  = -103cm~^)  by  t h e m a g n e t i c moment o p e r a t o r  between  levels  the  of  73  which were not d e g e n e r a t e w i t h each o t h e r applied f i e l d .  i n the absence of  an  The m a g n e t i c s u s c e p t i b i l i t i e s may t h e n be c a l c u l a t e d  by s u b s t i t u t i n g t h e s e c o e f f i c i e n t s i n t o Van V l e c k ' s e q u a t i o n ,  5.7.  RESULTS AND  (5.9).  DISCUSSION  M a g n e t i c s u s c e p t i b i l i t i e s have been measured between a n d 31 OK f o r a-CHg,  t h e compounds  studied, Fe^SO-^*  3-CH3 a n d p - C h ^ C g h ^ .  moments  5.2  (15).  shows t h e t e m p e r a t u r e  and i n c l u d e s t h e d a t a f o r  comparison.  Tables  5.1  CFg,  Where X i s F t h e m a g n e t i c s u s c e p t i b i l i t y  d a t a were p r e v i o u s l y r e p o r t e d Fig.  where X i s  to 5.4  the  dependence o f  Fe^SOg^  the  compound  magnetic  for  show t h e m a g n e t i c s u s c e p t i b i l i t i e s  a n d e f f e c t i v e m a g n e t i c moments  for  t h e compounds  studied.  Tabulated  a r e r e s u l t s o b t a i n e d f r o m t h e Gouy b a l a n c e o v e r a r a n g e o f and r e s u l t s o b t a i n e d . f r o m strengths  at  room  It  B.M.  5.49 B.M.  Section  Faraday balance i n three magnetic  5.7.1  t h e e f f e c t i v e m a g n e t i c moments  for  for  e-Fe(CH3S03)2 at  Fe^SO.^-  range  low temperature  d i s c u s s e s t h e m a g n e t i c moment d a t a f o r the a n a l y s i s of  u s i n g the F i g g i s a n d L e w i s m o d e l , a n d a c o m p a r i s o n o f t h e s e  moment d a t a f o r  field  (80K),  FetCF^SO^.  and F e ( p - C H 3 C g H 4 S 0 3 ) 2 c o m p o u n d s ,  compounds w i t h  temperatures  temperature.  f r o m a minimum o f 4 . 7 1  Fe(CF3S03)2  the  c a n be s e e n t h a t  t o a maximum o f  80  Section 5.7.2  t h e a- and 8 - i s o m e r s o f  d i s c u s s e s the iron(II)  the  the  two  magnetic  methanesulfonate.  data  74  FIG.  5.2  TEMPERATURE  DEPENDENCE  OF THE MAGNETIC MOMENT FOR  F e ( X S 0 3 ) 2 COMPOUNDS.  •  '-I  •  CO  •  •  o CM  fJ  CO  ro  O 0 0  io  ^  i  1 0  O  o  i t  CM  i  Q.  o m  (VJ  ro  8 X  CVJ  ro  o  co  MP  cj> ro  o o  X  CO O uI Q. £ £ iff  (O  in  -r  -  •ri  - T CO  ~r— CM If)  -  in  " W a !N3rN0lr\ Dll3N0VlrM  LU  75  TABLE 5 . 1  MAGNETIC S U S C E P T I B I L I T Y DATA FOR  TEMP(K)  106  xA(cm3 mol"1)  Fe(CF3S03)  uEFF(B.M.)  300  1.2290  5.43  275  13450  5.44  250  14850  5.45  225  16570  5.46  200  18770  5.48  175  21530  5.49  150.  25120  5.49  125  30150  5.49  100  37270  5.46  80  45240  5.38  FARADAY RESULTS AT 29.5K  (T2  cm"1)  106  xA  (cm3 m o l " 1 )  yEFF(B.M.)  253  12600  5.45  526  12570  5.44  869  12630  5.45  Diamagnetic c o r r e c t i o n s  - 1 0 5 x 10  cm  mol  76  TABLE 5 . 2  MAGNETIC S U S C E P T I B I L I T Y DATA FOR  TEMP(K)  1 0 6 x A ( c m 3 TnOl" ) 1  a-Fe'(CH3S03)2  PEFjr(B.M.)  300  11620  5.28  275  12670  5.28  250  13890  5.27  225  15370  5.26  200  17230  5.25  175  19540  5.23  150  22630  5.21  125  26840  5.18  100  32910  5.13  80  40330  5.08  FARADAY RESULTS AT 295K  HdH ( T 2  cm"1)  IO6  xA(cm3 mol"1)  yEFF(B.M.)  dx  253  11840  5.28  526  11850  5.28  869  11870  5.29  Diamagnetic  corrections  -83x10"6  c m 3 mol  77  TABLE 5 . 3  MAGNETIC S U S C E P T I B I L I T Y DATA FOR  TEMP(K)  106 xA(cm3 m o l - 1 )  8-Fe(CH3S03)2  ^ ( B . M . )  300  11270  5.20  275  12250  5.19  250  13470  5.19  225  14910  5.18  200  16650  5.16  175  18800  5.13  150  21930  5.09  125  25310  5.03  100  30140  4.91  80  34670  4.71  FARADAY RESULTS AT 2 9 5 K  HdH(T2 c m - 1 )  106 x A ( c m 3 mol"1)  V £ f ?  dx 253  11650  5.24  526  11680  5.25  869  11750  5.26  Diamagnetic c o r r e c t i o n s  -6 -83x10"  3 -1 cm m o l "  (B.M.)  78  TABLE 5 . 4  MAGNETIC S U S C E P T I B I L I T Y DATA FOR  TEMP(K)  1 0 6 x (cm  3  A  mol" )  Fe(p-CH3CgH4S03)  P^pp  1  300  11970  5.36  275  13210  5.39  250  14640  5.41  225  16380  5.43  200  18570  5.45  175.  21220  5.45  150  24670  5.44  125  29380  5.42  100  36190  5.38  80  44400  5.33  (B.M.)  FARADAY RESULTS AT 2 9 4 K  HdH  (T  2  cm" ) 1  IO  6  x  A  (cm"  3  mol" ) 1  u  EFF  (B.M.)  dx  253  12390  5.40  526  12350  5.39  869  12340  5.39  Diamagnetic corrections - 1 9 1  x 10~  cm  mol"  79  5.7.1.  M a g n e t i c moment  data  The m a g n e t i c moments and p a r a t o l u e n e s u l f o n a t e with  5.2  temperature  t h i s behaviour  Plots  of  5.3)  Curie  Law b e h a v i o u r ,  d e c r e a s e s to 80K.  field Tables  strengths 5.1  field.  are not  the  hence a s m a l l  at  temperature  deviation  room t e m p e r a t u r e ,  i o n i n an  the magnetic  Fe(CF3S03)2  to analyse the experimental in section  is  magnetic in moments  indicating that the  from  lines.  in three d i f f e r e n t  r e s u l t s show t h a t  impurity  from  fluorosulfonate  for a high-spin d6  Measurements  These  and  (15).  f e r r o m a g n e t i c a l l y o r d e r e d and t h a t  any f e r r o m a g n e t i c  discussed  of  using a Faraday magnetic balance are given  and 5 . 4 .  For  a maximum  r e p r e s e n t e d by t h e s t r a i g h t b r o k e n  are f i e l d independent materials  an i n c r e a s e  As c a n be s e e n  s i m i l a r to that  r e s u l t s are t y p i c a l  crystal  exhibit  They pass t h r o u g h  i s very  Felp-Cf^CgH^SO^  trifluoromethanesulfonate  initially  show a s l i g h t c u r v a t u r e ,  These  the  and  reciprocal s u s c e p t i b i l i t y against  (Fig.  octahedral  Fe(CF3S03)2  both  compounds  compound p r e v i o u s l y d i s c u s s e d  of  of  decrease in temperature.  d e c r e a s e as t h e Fig.  for  the  presence  unlikely.  and F e ( p - C H 3 C g H 4 S 0 3 ) 2 data u s i n g the  three  it  is possible  parameter  model  5.6.  The e x p e r i m e n t a l  d a t a w e r e a n a l y s e d by p l o t t i n g values of  magnetic  moment a g a i n s t kT/A  ; various  A w e r e c h o s e n , 100 > - A >  A s u i t a b l e value of  k. was d e t e r m i n e d f r o m t h e a b s o l u t e m a g n i t u d e  of  70.  80  FIG.  5.3  PLOTS OF RECIPROCAL S U S C E P T I B I L I T Y TEMPERATURE FOR F e ( C F 3 S 0 3 ) 2  AND  AGAINST  Fe(p-CH3CgH4S03)2  -1 X  A  100-  80-  60Fe(CF3S03)2  .-o  40-  20-  100  200  300  Temp / K  x -l A  100-  8 OH 60-  4 OH Fe(p-CH3CgH4S03)2  20H  100  200  Temp / K  300  81  t h e m a g n e t i c moment a n d t h e n t h e t e m p e r a t u r e d e p e n d e n c e was by a d j u s t i n g t h e v a l u e o f  Values of lines  in Fig.  visual  5.2  v, w h e r e v = A / A .  the three parameters  are given  comparison of  i n Table  experimental  used to generate  K given  i n Table  magnitude o f  the  solid  and t h e o r e t i c a l p l o t s ;  a b s o l u t e m a g n i t u d e o f the m a g n e t i c moment. p a t any g i v e n t e m p e r a t u r e  the  5 . 5 a n d w e r e o b t a i n e d by a  The v a l u e o f K i s d e t e r m i n e d t o a l a r g e e x t e n t  of  fitted  The  by  the  l a r g e r the value  l a r g e r i s the magnitude of  K .  of  The  5 . 5 a r e p r o b a b l y a c c u r a t e t o ± 0 . 0 5 u n i t s as  t h e m a g n e t i c moment i s d e t e r m i n e d t o a n a c c u r a c y  values  the  of  1-2%. It FSO^-  the values of K decrease i n the  c a n be s e e n t h a t  > CF^SOg" > p-CH-jCgH^SOg".  T h i s may be a t t r i b u t e d  t o an i n c r e a s e i n t h e c o v a l e n c y o f anions  from the s t r o n g e r a c i d s ,  i n more i o n i c  Fe-0  bonds t h a n  the iron-oxygen bond,  order,  qualitatively that  n a m e l y FSO3H and C F ^ S O ^ H , a r e  is,  the  involved  i s the a n i o n from p a r a t o l u e n e s u l f o n i c  acid. The v a r i a t i o n o f temperature In f a c t  c a l c u l a t e d m a g n e t i c moment  i s determined to a large extent  the s i g n of  s t a t e and a n e g a t i v e  with  by t h e v a l u e s o f A and A .  A (a p o s i t i v e v a l u e i n d i c a t e s a s i n g l e t  ground  v a l u e i n d i c a t e s an o r b i t a l d o u b l e t g r o u n d  may be d e t e r m i n e d f r o m m a g n e t i c moment m e a s u r e m e n t s .  However,  compounds s t u d i e d h e r e t h e v a r i a t i o n s o f m a g n e t i c moment w i t h are too small  t o d e t e r m i n e t h e s i g n o f A w i t h any d e g r e e o f  state) in  the  temperature  certainty.  82  TABLE 5 . 5  C R Y S T A L - F I E L D S P L I T T I N G PARAMETERS FOR  IRON(II)  SULFONATE COMPOUNDS  COMPOUND  K  A(cm-1)  A(cnf1)  Fe(FS03)2*  0.95  290  -90  Fe(CF3S03)2  0.80  180  -90  a-Fe(CH3S03)2  0.70  500  -100  B-Fe(CH3S03)2  0.50  160  -80  0.75  270  -90  Fe(p-CH3C6H4S03)2  *  Results  from r e f e r e n c e  15  83  Equally  good f i t s  of  A.  Hence  ,  of  the ground  may be o b t a i n e d w i t h  it  i s d i f f i c u l t to  state  p o s i t i v e or negative  identify with certainty  f r o m m a g n e t i c moment  data  alone.  values  the  nature  However, as  will  II  be s e e n i n C h a p t e r quadrupole of  6 the  temperature  splittings is definitive  as t o  ground  state  ground  states  have been i d e n t i f i e d as o r b i t a l  fits  for  negative  of  model  i s the  values of  same as t h e  the Mossbauer s p e c t r a l  The m a g n i t u d e A, i s o f  the  same o r d e r  approximately  300cm"1,  t h e s e compounds. the  three  ion in t h i s  parameter,  of for  properties  doublets.  A are given  parameter  3D$  of  the  Hence A < o  i n Table  the A v a l u e  the a x i a l  5.5.  the  Figgis  used i n the  distortion,  F e C p - C H ^ C g H ^ S O . ^ and  reflecting similar axial value  of  A for  analysis  as w i l l  as measured  distorted  f i e l d strengths lowest  environment  the  same  in of  around  T h e r e i s some u n c e r t a i n t y be s e e n l a t e r ,  by  FeCFSOg^,  FeCCF-^SOg^ i s the  a less  compound.  however,  Mossbauer  data.  r e f l e c t i n g perhaps,  the metal this  The  the  F e C C F g S O g ^ and F e ^ - C h g C g H ^ O g ^  N o t e m u s t be made h e r e t h a t and Lewis  of  the o r b i t a l  the  and o n l y  and f o r  dependence  regarding parameter  II  derived  from Mossbauer data  approximately apparent  equal  from the  values  shows a l l of A.  interpretation  simply r e f l e c t the  relative  This of  three  compounds  difference  to  have  in A values,  t h e m a g n e t i c moment  data,  i n s e n s i t i v i t y o f m a g n e t i c moments,  may when  II  compared w i t h Mossbauer s p e c t r a l d a t a , strengths.  This  to variations  in axial  may be e s p e c i a l l y t r u e when t h e m a g n e t i c  field  moments  84  show o n l y a v e r y s m a l l  temperature  dependence as i n the p r e s e n t  A reduction i n the value of the s p i n - o r b i t coupling  case.  constant  below the f r e e - i o n value o f -103 c m - 1 i s i n d i c a t e d f o r a l l these This  i s i n d i c a t i v e o f t h e p r e s e n c e o f some m e t a l - a n i o n  associated with  5.7.2.  Fe(CF3S03)2  and  M a g n e t i c moment d a t a f o r a- a n d g - F e ( C H 3 S 0 3 ) 2  in Tables  compounds and t h e i r o n ( I I ) previous section. moments  f o r t h e s e two i s o m e r s a r e g i v e n  5 . 2 and 5 . 3 and i l l u s t r a t e d i n F i g .  t h a t t h e r e a r e d i f f e r e n c e s between  methanesulfonate  no maximum i s o b s e r v e d  5.4.  are s i g n i f i c a n t l y smaller  or Fe(p-CH3CgH4S03)2.  i s o m e r s show a d i f f e r e n c e  Secondly, in  that  temperature  decrease monotonically with decreasing  P l o t s of reciprocal  a r e shown i n F i g .  i n the  of the magnetic  i n t h e m a g n e t i c moment a g a i n s t  i n s t e a d t h e moments  temperature.  methanesulfonate  the a b s o l u t e magnitudes  Fe(CF3S03)2  I t may be o b s e r v e d  compounds d i s c u s s e d  methanesulfonates  those of F e ( F S 0 3 ) 2 ,  5.2.  the i r o n ( I I )  sulfonate  Firstly,  of the i r o n ( I I )  t h e two i r o n ( I I )  plot;  covalency  Fe(p-CH3CgH4S03)2.  The m a g n e t i c moment d a t a  than  compounds.  Both  s u s c e p t i b i l i t y against  show d e v i a t i o n s  r e p r e s e n t e d by t h e b r o k e n l i n e s .  This  able f o r the g-isomer at temperatures  f r o m C u r i e Law  deviation below  temperature behaviour,  is particularly notice-  150K.  85  FIG.  5.4  PLOTS OF RECIPROCAL S U S C E P T I B I L I T Y AGAINST TEMPERATURE FOR a-AND 3 - F e ( C H 3 S 0 3 ) 2  x "I A  1000*  80-  60a-Fe(CH3S03)2  4 0-  20-  I 100  C)  x -  Temp/K  1  1  200  300  1  A  100-  80603-Fe(CH3S03)2  4020**  0  **  I 200  1  100  Temp / K  1  300  86  Tables  5.2  and 5 . 3  show t h e r e s u l t s o b t a i n e d  d i f f e r e n t magnetic f i e l d strengths moment found  i s independent for  are not  Fe(CF3S03)2  both  of magnetic f i e l d at  forms of  successful magnitude  methanesulfonate  Fe(CF3S03)2  Fe(CH3S03)2  o b t a i n e d between about  dependence o f  B u t due t o  t h e m a g n e t i c moment  Satisfactory  200K a n d room t e m p e r a t u r e ,  t h e d e c r e a s e i n m a g n e t i c moment,  i s a p p r e c i a b l y more t h a n  data  for  u s i n g t h e model w h i c h was  and F e ( p - C H 3 C g H 4 S 0 3 ) 2 .  no r e a s o n a b l e f i t s c o u l d be o b t a i n e d .  B-.isomer,  a- and 6-  as  ordered.  and t e m p e r a t u r e  temperatures  magnetic  w e r e made t o a n a l y s e t h e m a g n e t i c moment  iron(II)  for  the  three  room t e m p e r a t u r e ,  and F e ( p - C H 3 C g H 4 S 0 3 ) 2 .  ferromagnetical ly  Attempts  and i n d i c a t e t h a t  in  that  fits  the  data  could only  whilst at  lower  especially for  p r e d i c t e d from the  be  the  theoretical  model. The are given  parameters  i n Table  a b s o l u t e magnitude < values of 0.7 These  K values,  degree of  5.5. of  used t o g e n e r a t e It  the  and 0 . 5  c a n be s e e n t h a t  room t e m p e r a t u r e  for  the s o l i d  latter,  in Fig.  to a l l o w f o r  the  moment one h a s t o  t h e a- a n d B - i s o m e r s  e s p e c i a l l y the  lines  employ  respectively.  i n d i c a t e an a n o m a l o u s l y  e l e c t r o n d e l o c a l i s a t i o n i n t h e s e two c o m p o u n d s .  high  This  •t  seems u n r e a s o n a b l e i n l i g h t o f shifts  (see Table  sulfonates covalency.  6.3)  for  the  fact  that  t h e s e compounds  the Mossbauer  and o t h e r  isomer  iron(II)  are s i m i l a r , which would i n d i c a t e a s i m i l a r degree  of  5.5  87  TEMPERATURE DEPENDENCE OF THE MAGNETIC MOMENT FOR a- AND 3- F e ( C H S 0 ) 3  3  2  a-Fe(CH S0 ) 3  100  150  200  3  250  TEMP / K  3-Fe(CH S0 ) 3  —,  100  1  1  150  200  TEMP/ K  3  i 250  2  88  A n o t h e r m e c h a n i s m by w h i c h s u c h l o w m a g n e t i c may a r i s e i s by a n t i f e r r o m a g n e t i c iron  centres,  rather  delocalisation especially later  effects.  c o u p l i n g between  as a consequence o f abnormal  This  f o r the B-isomer,  proposal  seems more  state At  exchange  in this  t i m e no model  methanesulfonate  iron centres  FeCCF^SOg^  it  of  compounds  antiferromagnatic  Due t o t h e  a complex  data  polymeric  to  three  situation.  f o r magnetic exchange  in  and m a g n e t i c exchange  i s somewhat  o f t h e number o f b r i d g i n g atoms t o be t r a n s m i t t e d  compounds.  i s obviously  or Fetp-CH^CgH^SO.^  methanesulfonate  Fe^SO-^,  i n the  s u r p r i s i n g not o n l y  because  t h r o u g h w h i c h an e x c h a n g e w o u l d  but a l s o because o f the h i g h l y  a s i n d i c a t e d by t h e h i g h  isomer s h i f t  m a g n e t i c e x c h a n g e was p r o p o s e d t o o c c u r t h r o u g h  i o n i c nature  have  of  the  values.  Nevertheless  t h e FSO^"  anion  in  (22). Magnetic  RCG^-,  antiferromagnetically  i n which each anion b r i d g e s  T h e r e i s no e v i d e n c e  Fe(FS03)3  reasonable,  c o u p l i n g h a s been u s e d t o a n a l y s e t h e m a g n e t i c moment  o f t h e s e compounds  compounds  electron  compound.  the present  of the i r o n ( I I )  different  adjacent  a s Mossbauer r e s u l t s t o be d i s c u s s e d  i n d i c a t e a m a g n e t i c p h a s e t r a n s i t i o n t o an  ordered  nature  than  exchange  moments  exchange  has been p r o p o s e d  through  previously  more b a s i c t h a n  the methanesulfonate  a r e more h i g h l y  covalent.  bridging carboxylate (65).  Carboxylates  anions,  are,  a n i o n a n d f o r m compounds  however, which  89  5.8.  SUMMARY OF RESULTS AND CONCLUSIONS  From t h e m a g n e t i c moment d a t a t h e F e l X S O ^ appear to f a l l (i)  into  two c a t e g o r i e s :  Where X i s F , analysis Figgis  compounds  CF^ o r p - C H ^ C g H ^ .  In t h e s e c a s e s a r e a s o n a b l e  o f t h e m a g n e t i c moment d a t a  i s possible using the  and L e w i s m o d e l , and v a l u e s o f t h e p a r a m e t e r s  K , A and  X  and a x i a l  f i e l d strengths  g i v e an i n d i c a t i o n o f t h e e l e c t r o n d e l o c a l i s a t i o n i n t h e s e compounds.  No m a g n e t i c  e x c h a n g e seems l i k e l y .  (ii)  Where X i s a - C H g data  or  using the Figgis  parameters  g-CH^.  and Lewis  d e r i v e d from  Magnetic exchange  The a n a l y s i s o f m a g n e t i c  a p p r o a c h i s poor and t h e  i t may have  between  moment  little significance.  i r o n c e n t r e s i s proposed here but  no d e t a i l e d a n a l y s i s h a s y e t b e e n  undertaken.  90  CHAPTER 6 MOSSBAUER SPECTROSCOPY  6.1.  INTRODUCTION  In  1957 R . L .  Mossbauer observed  recoilless  nuclear  r e s o n a n c e w h i c h h a s become known a s t h e M o s s b a u e r e f f e c t  gamma  (66).  The  57 effect the  i n the  technique  applications physics  (67),  mineralogical centres  'Fe  has been w i d e l y using various  until  1959 b u t s i n c e 1961  a p p l i e d i n c h e m i s t r y and o t h e r  isotopes  electronic structure  ( e . g . n u c l e a r and s o l i d of impurity  and g e o l o g i c a l a p p l i c a t i o n s  i n iron porphyrins  57 the  Fe n u c l e u s was not o b s e r v e d  (70)).  atoms  diverse state  in alloys  ( 6 9 ) , and t h e n a t u r e  The m a j o r i t y  (68), of  active  o f work has i n v o l v e d  119 and  Sn n u c l e i ;  however,  over  50 o t h e r  i s o t o p e s show t h e  effect. A brief the  treatment  for  the observed  d i s c u s s i o n o f t h e Mossbauer e f f e c t  f o c u s s e s on  the nature  t o be d e r i v e d  are discussed i n sections 6.2.1 interactions treatments this  and 6 . 2 . 3 .  are d i s c u s s e d i n Chapter  the reader  is referred  discussion of the theory,  obtained  in this  of the i n t e r a c t i o n s  s p e c t r a . The i s o m e r s h i f t  and t h e c h e m i c a l i n f o r m a t i o n  study.  will  7.  responsible  and q u a d r u p o l e from these Magnetic  texts  splitting,  parameters, hyperfine  For d e t a i l e d  to standard  f o l l o w and  (71,  theoretical 72).  s e c t i o n s 6 . 3 and 6 . 4 p r e s e n t  After  the r e s u l t s  91  6.2.  THEORY OF MOSSBAUER  6.2.1.  Electric The  because  nucleus  size  has a f i n i t e  probability  to change,  thereby  energy.  n u c l e a r energy  which,  in general,  will  volume  o f being found i t i s usual  slightly altering  This levels  the isomer  shift  and t h e isomer  o f t h e n u c l e a r volume  a nuclear y - t r a n s i t i o n  interaction of  interaction,  of the penetration  have a f i n i t e During  monopole  SPECTROSCOPY  interaction but r e s u l t s  be d i f f e r e n t  shift  arises  by e l e c t r o n s  i n the region  which  of the nucleus.  f o r the e f f e c t i v e  nuclear  the nucleus-electron  does n o t l e a d t o a s p l i t t i n g in a shift  o f energy  i n source(B)  levels  and a b s o r b e r ( A ) as  shown i n F i g . 6 . 1 . If energy  nucleus B i s chosen as a r e f e r e n c e  o f n u c l e u s A i s measured w i t h  difference shift,  i n y-ray  6, w h e r e  e n e r g i e s may be e x p r e s s e d  6 i s given  z i s the atomic  elementary r  "  -  r  9  ,  charge, r  number,  states.  "2 ks(0)A|  nuclear  volume  *  s  (0)  AI  to B, then the as the chemical  isomer  *s  ( 0 )  (6.1)  B  e i s the positive  i s t h e mean n u c l e a r  the difference  relative  by:  6 = 4 / 5 nzeMdr/r> where  respect  and the  i n nuclear  radii  radius,  d r i s equal  of the excited  to  and ground  2 and |if>s(0)B|  are the s-electron  f o r A and B r e s p e c t i v e l y .  densities  i n the  92  FIG.  6.1  (i)  SOURCE AND ABSORBER NUCLEAR  FREE SPACE  (i i )  SINGLE L I N E SOURCE  RESULTANT  FREE SPACE  MOSSBAUER SPECTRUM  ABSORPTION  -ve  ENERGY  0 VELOCITY  LEVELS  SINGLE L I N E ABSORBER  93  The and hence t h e  term 4/5 n z e ^ r 2 isomer s h i f t  (^r/r)  i s a constant  i s l a r g e l y dependent  for  a given  upon t h e  nucleus  s-electron  57 density. the  In  particular for  isomer s h i f t .  also,  Fe t h e 4 s e l e c t r o n s p r i m a r i l y  O t h e r e l e c t r o n s h a v e some e f f e c t  since s-electron density  d-electron density  on i s o m e r  i s s e n s i t i v e to changes  as a r e s u l t o f  screening  determine  i n p-  shifts and  effects.  57 For state to Hence,  the  n u c l e u s expands  the ground n u c l e a r s t a t e w i t h  dr/r  s-electron shift.  Fe  i s negative density  (73).  at the  In o t h e r w o r d s ,  For  of  iron  i n some o f  negativities  6.2.2.  of  i t s complexes,  some l i g a n d s  to  temperature  i s experimentally dependent.  Mossbauer atoms, vibrational  i.e.  modes.  and i s n o t  This  value of  as t h e  be d e t e r m i n e d  isomer shift  fact  relative  has  configurations electro-  (74).  effect observed  t h a t the  a r i s e s from the  effect  This  ray.  in  the isomer  s t a t e s and e l e c t r o n  as w e l l  a temperature  This  a gamma  in a decrease in  investigation.  oxidation  Second-order Doppler It  shift  of  the  under  excited  i s o t o p e an i n c r e a s e  nucleus r e s u l t s  t h e more i o n i c i s t h e m a t e r i a l  goes from the  the emission of  this  the higher  enabled the determination  as i t  thermal  dependence  i s small  chemically significant.  isomer s h i f t  of  motion  the  of  is the  lattice  compared t o t h e  isomer  94  6.2.3.  E l e c t r i c quadrupole  interaction,  The e l e c t r i c q u a d r u p o l e with  the chemical environment  quantum  number  bution,  the magnitude  the  I greater  or negative,  flattened  along the spin  = -V vE r e p r e s e n t s  charge d i s t r i b u t i o n elongated  that  may b e e x p r e s s e d b y t h e f o l l o w i n g  6  e QvE  V  xx  Hamiltonian:  (6.2)  a t the nucleus i s a tensor second d e r i v a t i v e s  E.F.G.  quantity  at the whose  of the e l e c t r o s t a t i c  V  to express  values of V . . .  Following  |V__|*|V zz  distribution  axis.  convention  |<i|v*  yy  J  xx  + V + V =0. yy zz  .  vE i n a C a r t e s i a n a x i s  A principal axis  such t h a t a l l v . . terms w i t h matrix.  distri-  along the  c o r r e s p o n d i n g t o an o b l a t e charge  are the negative  In o r d e r are nine  a spin  The s i g n o f Q may be p o s i t i v e ,  the e l e c t r i c f i e l d gradient,  The E . F . G .  potential,  Nuclei with  i n t e r a c t i o n o f t h e n u c l e a r q u a d r u p o l e moment w i t h t h e  e l e c t r o n i c environment  elements  around t h e n u c l e u s .  moment.  spin axis,  nucleus.  moment o f t h e n u c l e u s c a n i n t e r a c t  t h a n % have a n o n - s p h e r i c a l c h a r g e  corresponding to a prolate  where  splitting  o f t h e c h a r g e d i s t o r t i o n b e i n g m e a s u r e d by Q,  nuclear quadrupole  The  the quadrupole  i f j  there  s y s t e m may be d e f i n e d  are zero,  r e s u l t i n g i n a diagonal  t h e p r i n c i p a l axes  Also the tensor  system  a r e chosen such  is traceless, i . e .  95  In o r d e r only  two p a r a m e t e r s  to specify the e l e c t r i c  are necessary i n the p r i n c i p a l axis  They a r e n t h e asymmetry of  the E.F.G.  f i e l d gradient  tensor.  parameter,  and V z z  tensor  system.  the p r i n c i p a l  component  Where n a n d v " z Z may be d e f i n e d a s f o l l o w s :  (Vxx-Vyy)  n =  (6.4)  — r ,  zz  Vzz=  The following  (6.5)  asymmetry  limits, The  of  eq  nuclear quadrupole  3I_2 z  Iz  may t a k e  v a l u e s between  the  0 s n s 1.  s p i n I c a n be w r i t t e n  where  parameter  -  coupling Hamiltonian  f o r a nucleus  as:  1(1+1) +  n  2  ( i .  + i  2  +  i s the nuclear spin operator,  2  "  and I + ,  (6.6)  )  I_ a r e s h i f t o p e r a t o r s  (75),  57 Fe h a s a g r o u n d a first latter n = 0.  state with  excited state with is split  into  I = h and hence z e r o q u a d r u p o l e moment, and  I = 3/2.  In t h e p r e s e n c e o f an E . F . G .  two s u b s t a t e s w i t h  Iz  The s e p a r a t i o n o f t h e s e s u b s t a t e s  A E Q and i s g i v e n AEQ  = ± 3/2 and ± 1 / 2 , f o r i s the quadrupole  splitting  by:  = h e 2 q Q (1  Both  the  + n /3) 2  h  (6.7)  p o s s i b l e t r a n s i t i o n s a r e a l l o w e d a s shown i n F i g .  and a two l i n e s p e c t r u m i s o b s e r v e d .  A E Q i s t a k e n as b e i n g  6.2  positive  96  6.2  (i)  ENERGY LEVEL SCHEME INCLUDING QUADRUPOLE HYPERFINE INTERACTION  3/2  +  AE  0  f  +1/2  + 1/2  1/2  (ii)  RESULTANT MOSSBAUER SPECTRUM  ABSORPTION  < •ve  •  0 VELOCITY  +ve  ,  97  when t h e ±h s t a t e  i s lower  i n energy  symmetric  two l i n e s p e c t r a o n l y  splitting  may be e v a l u a t e d ,  than  the ±3/2 s t a t e .  From s u c h  the isomer s h i f t and quadrupole  neither  the sign of V  z z  nor t h e magnitude  o f n may be d e t e r m i n e d . The detail  case o f h i g h - s p i n i r o n ( I I )  a s much i n f o r m a t i o n  occupations  about  c a n be o b t a i n e d  will  now be d i s c u s s e d i n more  the orbital  u s i n g Mossbauer  ground s t a t e  and o r b i t a l  spectroscopy.  c The arises  D free-ion  from a d  crystal  spectroscopic state  electron configuration.  f i e l d the d o r b i t a l s  degeneracy populates  In a p e r f e c t l y  t 2 g o r b i t a l s a n d h e n c e no f i n i t e  of  gives  the contributions  the d orbitals  (71)  VAL  to the E.F.G.  to the E.F.G.  o f t h e p and d o r b i t a l s .  -o  4',.  q  is  splitting is  '5 f K  ' 7  r  >  approximation  p  d  (73,76).  Table  from a s i n g l e e l e c t r o n i n each  and t h e T o w n e s - D a i l e y  the valence c o n t r i b u t i o n population  E.F.G.  equally  The same c o n c l u s i o n may be a r r i v e d a t b y c o n s u l t i n g  T a b l e 6.1 and u s i n g t h e T o w n e s - D a i l e y 6.1  octahedral  the s i x t h e l e c t r o n  e x p e r i e n c e d b y t h e i r o n n u c l e u s a n d no q u a d r u p o l e observed.  iron(II)  s p l i t a s shown i n F i g . 6 . 3 a n d t h e  o f the t ^ g l e v e l s i s not removed, the three  for high-spin  approximation  discusses  i n terms o f t h e e f f e c t i v e  Thus  98  FIG.  6.3  3d ORBITAL S P L I T T I N G S I N OCTAHEDRAL, AND RHOMBIC  AXIAL  FIELDS  10 Dq 3d FREE  ION  3D. OCTAHEDRAL CRYSTAL F I E L D AXIAL  FIELD  \ RHOMBIC  12 D FIELD  99  TABLE 6 . 1  VALUES OF q  y A L  FOR THE 3d ORBITALS  3d ORBITAL  d o .2  q  r>  +4  2  +  / 7  /7  <r  V A L  -3 J >  ~y 2  -  4  /7  <r"3>  d  xy  +  4  /7  <r"3>  d  xz  -  2  /7  <r"3>  -  2  /7  <r"3>  d  z  d  y z  100  w h e r e Npn-  and  are the e f f e c t i v e  populations of  the  appropriate  _3 4p and 3d i r o n o r b i t a l s , r e s p e c t i v e l y , 1 value of  Jahn-Teller  taken over  iron(II)  occupies  the d  6 . 3 and the  to  if  the  the e q u a t o r i a l  orbital  i n h e r e n t l y s u b j e c t to  ligands are  the the  compressed  ligands the e l e c t r o n  a n d g e n e r a t e s an E . F . G .  a  preferentially  in proportion  to  <r"3>.  splits  the  this  t2g  orbitals into  s p l i t t i n g i s of  between  t h e s e two  degeneracy of  If  the  levels. t  the f o u r f o l d  axis  quantisation,  (Cg) then,  a s shown i n F i g .  6.5  of  (77).  and i n the t r i g o n a l  the  remaining  6.4.  However,  i s a s s u m e d t o be t h e a x i s  t h e r e a l d o r b i t a l s , one has  In t h e case i t  (Fig.6.3).  i s t a k e n as t h e q u a n t i s a t i o n  the octahedron  i n terms o f  remove  tetragonal i s the  |z  case the  > orbital.  3DS.  distribution  s p l i t t i n g t h e d o u b l e t by 1 2 D p  (C^)  D.^)  splitting will  d e p e n d e n c e c a u s e d by a B o l t z m a n A rhombic f i e l d w i l l  or  s e p a r a t e d by  the quadrupole  t h e d o r b i t a l s t r a n s f o r m a s t h o s e shown i n F i g . threefold axis  field (D^  a s i n g l e t and a d o u b l e t  orbitals,  2 g  6 . 3 the a x i a l  the o r d e r of kT  show a l a r g e t e m p e r a t u r e  |xy>  function.  sixth electron occupies  axial  As c a n be s e e n f r o m F i g .  If  expectation  4p o r 3d r a d i a l  compounds a r e  For example,  relative  /7  the a p p r o p r i a t e  a s shown i n F i g .  slightly  4  the  d i s t o r t i o n w h i c h removes t h e d e g e n e r a c y o f  lowest l e v e l .  +  >  3 /r  However,  orbitals  and <r  axis,  if  the of  those  singlet  is  101  |xy>  | xz> |yz>  102  FiL  6.5  C 3 QUANTISATION A X I S AND d ORBITALS  (2/3)%  |x2-y2>  (Z/3)  |xy> + ( 1 / 3 ) * *  h  -  (V3)  h  |xz>  |yz>  103  6.3  ISOMER S H I F T S AND QUADRUPOLE S P L I T T I N G S FOR I R O N ( I I )  SULFONATES  II  Mossbauer sulfonates  s t u d i e d f r o m 4 . 2 K t o room t e m p e r a t u r e .  parameters, widths  isomer s h i f t  (r) a r e g i v e n  6.3.1.  Isomer The  spin  s p e c t r a h a v e been r e c o r d e d f o r a l l t h e i r o n ( I I )  iron(II)  (<5), q u a d r u p o l e  i n Table 6 . 2  shift  splitting  values  isomer s h i f t compounds  values  normally  are of the order  relatively  high  indicative  o f a h i g h degree  isomer s h i f t s ,  i n t h e s e compounds.  comparable w i t h some i r o n ( I I )  those  observed  1.1  fluorides  a n d 1 . 4 5 mm s  - 1  1.4 -  -  studied  "highly  values  ionic"  (78),CsFeF2  a t 78K, r e s p e c t i v e l y .  Using  electron configuration  cation  compounds  may be d e r i v e d  well  differences  isomer s h i f t  i n isomer s h i f t  and as t h e y a r e a f u n c t i o n  as the s - e l e c t r o n d e n s i t y  isomer s h i f t s  are in  fact These  include  v a l u e s - . o f 1 . 4 8 mm s " 1 a t 7 8 K , 1 . 4 9 mm s " 1 a t  a derived  small  is  (79) and Rb2FeF^ (80)  configurations,  are only  a t 80K ( 7 1 ) .  h e r e a l l have  compounds.  (81) which r e l a t e s  The  high-  i n the m e t a l - l i g a n d  J a c c a r i n o model  i n these  - 1  1 . 5 mm s " 1 a t 8 0 K . T h i s  The i s o m e r s h i f t  FeF2  f o r octahedral  1 . 3 mm s  of ionic character  o f known  w h i c h have i s o m e r s h i f t 4.2K  (AEQ) a n d l i n e  (i-iv).  As c a n be s e e n f r o m T a b l e 6 . 3 t h e compounds  bonds  The M o s s b a u e r  as  the values  Walker-Wertheimto electron  f o r the  iron(II)  3d^"^4s^"^.  values  shown  i n Table 6 . 3  o f l a t t i c e dynamics as  any a t t e m p t a t a c o r r e l a t i o n  and t h e base s t r e n g t h s  o f the anions  is  between  tenuous.  104  TABLE 6 . 2  MOSSBAUER EFFECT DATA FOR I R O N ( I I )  Note u n i t s (i)  of  SULFONATES  * 6 , A E Q and r are a l l given  i n mm s  -1  Fe(CF3S03)2  TEMP(K)  6  AEQ:  r  l  r  2  6.5  1.46  2.01  0.49  0.52  17.7  1.46  1.98  0.52  0.54  38.8  1.45  1.95  0.55  0.55  64.4  1.45  1.91  0.51  0.49  78.8  1.39  1.82  0.28  0.31  80.0  1.45  1.84  0.47  0.44  104  1.46  1.88  0.50  0.50  115  1.43  1.81  0.33  0.33  131  1.42  1.78  0.55  0.54  183  1.40  1.68  0.41  0.39  233  1.37  1.59  0.46  0.44  272  1.35  1.51  0.45  0.41  293  1.32  1.44  0.28  0.26  *  A l l isomer s h i f t values are quoted r e l a t i v e o f an i r o n f o i l s p e c t r u m .  to the c e n t r o i d  105  TABLE 6 . 2  (ii)  Continued  a-Fe(CH3S03)2  6  AEQ  r  4.2  1.35  3.31  0.52  0.54  10.5  1.21  3.39  0.40  0.40  35.2  1.44  3.34  0.55  0.51  60.0  1.42  3.35  0.56  0.54  84.7  1.45  3.37  0.41  0.37  110  1.44  3.36  0.41  0.38  140  1.42  3.30  0.47  0.44  170  1.41  3.29  0.39  0.36  200  1;40  3.24  0.40  0.38  235  1.37  3.19  0.40  0.37  264  1.36  3.12  0.44  0.41  293  1.34  2.95  0.41  0.39  TEMP(K)  ]  r  2  106  TABLE  6.2  (iii)  Continued  B-Fe(CH3S03)2  6  AEQ  r1  r  25.3  1.37  1.54  0.41  0.39  30.0  1.49  1.55  0.39  0.37  80.0  1.48  1.41  0.45  0.44  109  1.46  1.38  0.35  0.34  139  1.46  1.33  0.35  0.33  169  1.43  1.28  0.34  0.33  209  1.43  1.20  0.33  0.33  239  1.41  1.14  0.34  0.32  260  1.40  TV TO  0.33  0.32  293  1.31  0.94  0.28  0.33  TEMP(K)  2  107 TABLE  (iv)  TEMP(K)  6.2  continued  Fe(p-CH3C6H S0 ) 4  3  2  6  AE  3.9  1.30  1.99  0.32  0.34  9.0  1.45  2.03  0.41  0.42  33.5  1.44  1.92  0.32  0.30  55.7  1.43  1.91  0.31  0.30  78.6  1.42  1.91  0.36  0.35  96.0  1.42  1.88  0.34  0.33  no  1.41  1.84  0.35  0.34  115  1.42  1.83  0.33  0.32  135  1.40  1.79  0.33  0.31  165  1.39  1.72  0.32  0.31  195  1.37  1.66  0.32  0.31  225  1.36  1.58  0.31  0.31  260  1.34  1.51  0.30  0.30  291  1.32  1.39  0.30  0.28  Q  r1  r2  108  TABLE 6 . 3  ISOMER SHIFT VALUES FOR F e ( X S 0 3 ) 2  X  6 (mm s " " 1 )  F  *  C F  1.49  1.45  3  a-CH-j  1.45  B-CH3  1.48  p-CH3C6H4  1.42  *  Reference  15  COMPOUNDS AT 8 0 K  109  The  temperature  dependence o f  the  isomer s h i f t  values  i n t h e s e compounds may be a s s i g n e d t o a s e c o n d - o r d e r D o p p l e r T h i s may be c o n f i r m e d i n F e C p - C h ^ C g H ^ S O ^ as t h e a t 3 . 9 K was m e a s u r e d w i t h t h e and i s o f  6.3.2.  Quadrupole s p l i t t i n g  s t r u c t u r e below 8K;  hyperfine  spectrum below ^25K.  shown i n F i g .  the temperature  291K.  show a  range s t u d i e d . and  The  magnetic  a l s o p - F e l C H ^ S O . ^ e x h i b i t s a complex These o b s e r v a t i o n s w i l l  modifications  dependence o f  6 . 6 and t y p i c a l  Fe^-CHgCgr^SO.^ of  at various  be d i s c u s s e d  the quadrupole  spectra are i l l u s t r a t e d temperatures  Fe^HoSO^  s p e c t r o s c o p y and s p e c t r a o f  were f i r s t the a-,  F e C C H g S O . ^ a r e shown i n F i g .  t h a n 2 mm s " 1  t o g i v e an E . F . G .  The  two  Mossbauer of  6.8.  in proportion  w i t h a s i n g l e t ground s t a t e .  for  B - f o r m s and a m i x t u r e  splitting  and s i n c e a s i n g l e t g r o u n d  s p l i t t i n g values  splittings  in Fig.6.7.  i d e n t i f i e d by  a - F e C C H ^ S O . ^ has a q u a d r u p o l e  quadrupole  temperature  7. The t e m p e r a t u r e  greater  studied a l l  a r e F e C C F - j S O g ^ w h i c h shows some a s y m m e t r y  hyperfine  i n Chapter  same  isomer s h i f t measured a t  t h e compounds  symmetric spectrum over  exceptions  value  values  Mossbauer s p e c t r a of two-line  isomer s h i f t  s o u r c e and a b s o r b e r a t t h e  a comparable value to the  effect.  for  to  substantially  state  (see Table  the a-isomer are only  In t r i g o n a l  is  symmetry  expected  6.1)  the  consistent  this  orbital  is  110  FIG.  TEMPERATURE DEPENDENCE  6.6  FOR  OF THE QUADRUPOLE  SPLITTING  F e ( X S 0 ) COMPOUNDS  (Solid  3  lines  2  are generated using  parameters  listed  T a b l e 6.4)  • a-Fe(CH3S03)2 o Fe(Cf^S0 ) * F (p-CH C H S0 ) - Fe(FS0 ) 3 2  e  3  6  4  3  2  3 2  3.5  0  100  TEMR/K  200  300  in  in G.  6.7.  MOSSBAUER SPECTRA OF  Fe(p-CH3CgH4S03)2  AT VARIOUS TEMPERATURES  •  v..^—, .  ^ .  v  * . .• /  \ - :  =  3  3  4  8  K  T=78.58K  s  '  T  "*/  T=135.00K  T=225.00K  f *  **\ 5% ABSORPTION  ~i 3.0  i -2.0  \  1  -1.0 VELOCITY  - J*'  - / ^ v *  1  0.0  "  1  1  1  1.0  2.0  3.0  (mm.s ) - 1  *.  T=291.00K  r 4.0  112  FIG.  6.8  MOSSBAUER SPECTRA OF F e ( C H 3 S 0 3 ) 2 AT 78K  "\ r\  f  /  MIXTURE  5% ABSORPTION  "I  6.0  1 -4.0  1 -2.0  1  1  1  I  0.0  2.0  4.0  6.0  VELOCITY  (mm s " 1 )  113  singlet |xy>  ground  orbital  presented thought  s t a t e w o u l d be  ground  state.  i n Chapter  that  3,  and i n t e t r a g o n a l  \z > L  For  a-Fe^HgSC^^  i n d i c a t e s Cg  anion  the a - s p e c i e s contained  the  symmetry  infrared  symmetry  tetragonally  the  data,  and we i n i t i a l l y  distorted  FeOg  II  octahedra. magnetic  However,  field  combination a  |z  (Chapter  of  7)  a negative  > and n o t  we h a v e  Mossbauer s p e c t r a l measurements  an  |xy>  show V z z E.F.G.  orbital  ground  t h e i r quadrupole Fe(FS03)2  B - i s o m e r the  value.than of  for  A E g i s 1.41  and 1 . 9 1 This field  indicate  threefold  - 1  for  for  1  B-Fe(CH3S03)2  Fe(CF3S03)2  than  i n the  latter  to  2.1  be t h a t  for  smaller  80K t h e AEQ=  value  1.84  respectively.  i n terms  of  the  crystal-  6.4.  mm s " 1  an o r b i t a l  case the  compared w i t h  has been a n a l y s e d  state  At  and F e ( p - C H 3 C g H 4 S 0 3 ) 2  B-Fe(CH3S03)2  s i n g l e t ground  previously  appears  and F e ( p - C H 3 C g H 4 S 0 3 ) 2 -  i n A E Q values  less  difference  the  dependencies  s p l i t t i n g has a c o n s i d e r a b l y  discussed in section  of  B-FetCHgSO.^  s i m i l a r temperature  The m a j o r  quadrupole  indicates either  an o r b i t a l  exhibit  Fe(CF3S03)2  difference model  (15).  m s "  mm s  A E Q values  300K;  state  a-FetCH^SO.^  6.6, FelCF^SOg^j  s p l i t t i n g s , comparable with  Fe(CF3S03)2,  This  and i n  the  axis.  and F e t p - C H g C g H ^ S O g ^ a l l  the  state,  applied  Thus  and a s i n g l e t g r o u n d  As c a n be s e e n f r o m F i g .  studied  be n e g a t i v e .  FeOg o c t a h e d r a w h i c h a r e c o m p r e s s e d a l o n g t h e  trigonal  of  to  i n an  if  and F e ( p - C H 3 C g H 4 S 0 3 ) 2  over  all  doublet 3Ds/k  thermal  temperatures  ground  state  or  all  studied. possibly  i s n o t much g r e a t e r  population  of  have  than  the doublet  would  114  be s i g n i f i c a n t a n d A E Q w o u l d b e e x p e c t e d t o show a p r o n o u n c e d  increase  as t h e t e m p e r a t u r e  in  the s i n g l e t .  was l o w e r e d a n d t h e e l e c t r o n was l o c a l i s e d  F o r t h e compounds  s t u d i e d here t h i s  and a d e t a i l e d a n a l y s i s o f t h e q u a d r u p o l e compounds  t o have o r b i t a l  FetFSO-^  compound.  doublet  The i n f r a r e d d a t a  consistent with a trigonal perturbed  ground  s p l i t t i n g s show states  Hence  d i s t o r t i o n and r e s u l t s from  t h e ground  state  6.4.  CRYSTAL-FIELD,  The  temperature  The  theoretical  effect of  the perturbation  V  SULFONATES  formulated  by I n g a l l s  T  V  of the c r y s t a l  +  V  R  +  V  s . o .  f i e l d term  + V  s p l i t t i n g has  (82) and G i b b ( 8 3 ) .  by I n g a l l s  f i e l d i s treated  s . s .  (tetragonal  the s p i n - o r b i t  i n terms  <6-9) or t r i g o n a l ) ,  c o u p l i n g parameter  i n t r a i o n i c s p i n - s p i n coupling parameter.  omitted  SPLITTING  Hamiltonian:  where V j i s t h e a x i a l  the  and t h e  a p p r o a c h i s b a s e d upon t h e c r y s t a l - f i e l d m o d e l ; t h e  of the non-cubic part  rhombic t e r m ,  magnetically-  doublet  dependence o f t h e quadrupole  b e e n a n a l y s e d u s i n g a model  are only  elongation.  S P I N - O R B I T AND S P I N - S P I N  PARAMETERS FOR I R O N ( I I )  f o r the  t o have a p o s i t i v e  i s the o r b i t a l  FeOg o c t a h e d r a a r e d i s t o r t e d b y a t r i g o n a l  these  a s was f o u n d  f o r t h e s e compounds  M o s s b a u e r s p e c t r a show t h e s e compounds  value of V 2 Z -  i s not the c a s e ,  and Gibb i n t h e i r  the  and V  T h e l a s t t e r m was  treatments  b u t was i n c l u d e d  115  in  t h e m o d e l o f Sams a n d T s i n  behaviour  of the quadrupole  (84) i n o r d e r  to account f o r the  s p l i t t i n g s b e l o w 80K.  If  Vg  is  o m i t t e d t h e computed v a l u e s o f AEQ d e c r e a s e w i t h d e c r e a s i n g b e l o w 80K a n d t h i s b e h a v i o u r experimentally  (Lz2  t o what i s o b s e r v e d  ( s e e F i g . 6.6).  In o p e r a t o r  = Ds  i s contrary  notation  e q u a t i o n 6.9 c a n be w r i t t e n :  - 2) + D r ( L + 2 + L_ 2 )  - A(LZSZ  -D a Here t h e s m a l l L.j a n d S^  and  fourth-order  are the o r b i t a l  respectively, A and D  axial  + h (L+S_ + L_S+))  (S 2 - 2)  (6.10)  z  and rhombic terms a r e i g n o r e d ;  a n d s p i n a n g u l a r momentum o p e r a t o r s  Dg and D r a r e t h e a x i a l q  temperature  and rhombic f i e l d  parameters  a r e t h e s p i n - o r b i t and s p i n - s p i n c o u p l i n g  parameters  respectively.  Optical show t h a t  f o r the sulfonates  approximately time  s p e c t r a o f t h e s e compounds,  9000  orbitals.  i n Chapter  s t u d i e d h e r e lODq h a s a v a l u e  4,  of  c m - 1 and so i n o r d e r t o m i n i m i s e t h e c o m p u t a t i o n  i t i s assumed t h a t t h e r e  and e  presented  i s no a p p r e c i a b l e m i x i n g o f t h e  Hence a 25 x 25 m a t r i x  may be t r u n c a t e d  to a  9 15 x 15 m a t r i x .  This  t r u n c a t i o n h a d no a d v e r s e e f f e c t s on t h e r e s u l t s  o b t a i n e d by Sams a n d T s i n (84). For  the t r i g o n a l l y d i s t o r t e d complexes the b a s i s s e t o f  15 t 0 _ w a v e f u n c t i o n s  used was:  116  |M S >  |2,0> { /3) 2  where  i n the |L,  total  orbital  the  h  \2,±2>  + (1/3)^  > |M g > n o t a t i o n ,  a n g u l a r momentum,  L,  \2,+ 1> |M > S  i s t h e z-component o f the and M s i s the z-component o f  s p i n a n g u l a r momentum w h i c h c a n t a k e  The q u a n t i t i e s  v a l u e s o f 0, ± 1 , ± 2.  D /A, D /A a n d D^/A w e r e t r e a t e d a s i n d e p e n d e n t s  r  parameters w h i c h were read i n t o t h e computer. diagonalised to obtain the eigenvalues, eigenvectors,  The  m a t r i x was  e^/A a n d c o r r e s p o n d i n g  | i > , w h i c h were then used t o c a l c u l a t e t h e q u a d r u p o l e  splittings. The  contributions  t o t h e n i n e components  t e n s o r were c a l c u l a t e d f o r each e i g e n v e c t o r averages  formed:  Z"1  15 z < i i=l  |V../e|i>  | i > , and t h e ensemble  exp (-e./kT)  (6.11)  1 J  where Z = E exp (e^/kT) i s t h e p a r t i t i o n  function.  was d i a g o n a l i s e d t o o b t a i n t h e t e n s o r e l e m e n t s system.  AEQ  The q u a d r u p o l e  =  h  e Q 2  V . . of the E.F.G.  (1-R)  = h e2Q (1-R)  The E . F . G .  i n the principal  s p l i t t i n g may b e w r i t t e n a s :  q2 (4/7  matrix  +• 1/3 ( n q ) 2 < r " 3 >) ( F q 2 + 1 / 3 F n q 2 ) %  (6.12) (6.13)  axis  117  where  (1-R)  i s the Sternheimer  Fq a n d F E.F.G.  are given  tensor  correction for  i n terms of  the  from r e f e r e n c e 82.  h a s been e s t i m a t e d t o h a v e  c o r e p o l a r i s a t i o n and  p r i n c i p a l components  The  quantity  a numerical  4 /  value of  7  e  of  the  Q(l-R)<r~ >  4 . 5 mm s " 1  (85),  whence: A Eg = 4 . 5  Various used to  generate  parameters given  plots to  Table  6.4  field,  However,  Fetp-CHoCgH^SOg^*  of  only  160  compressed  several  electrons  and A were  temperature.  lines  in Fig.  here.  cm-1.  The  Firstly,  i s very  axial  a-Fe(CH3S03)2  parameters  The  6.6  are  similar for  cm"1), towards  s h o u l d be  viewed  r e s u l t s shown of  the  Fe^F^SO.^  r e s p e c t i v e l y and i s  i n the  in axial and  comparable  8-Fe(CH3S03)2,  a  value  trigonally  i n the a - i s o m e r . A , the  80-90% of  the  spin-orbit free-ion  coupling value  suggesting a s l i g h t d e l o c a l i s a t i o n of the  employed  s p e c i e s i s c o n s i d e r a b l y l a r g e r and may  values of  are approximately  has been  the magnitude  f i e l d produced  l i g a n d geometry the  that  comments on t h e  320 and 300 c m - 1  Secondly,  = -103  solid  (6.14)  Dg , D^,  but c o n s i d e r a b l y s m a l l e r f o r  be a f u n c t i o n o f  constant,  the  the derived  a s m e a s u r e d by 3 D g ,  Fe(FS03)2  parameters  c r y s t a l - f i e l d treatment  are relevant  to  mm s " 1  A E Q as a f u n c t i o n o f  generate  i s only approximate,  accordingly.  (x  of  the  F^2)^  6.4.  Since the here  + 1/3  values of  obtained  i n Table  (Fq2  ligands.  the  3d  118  TABLE 6 . 4  C R Y S T A L - F I E L D S P L I T T I N G PARAMETERS DERIVED FROM QUADRUPOLE S P L I T T I N G DATA  3Dc(cm_1)  COMPOUND  A (cm"1)  D (cm"1)  Dfcm"1)  Fe(FS03)2  288  -90  22  0  Fe(CF3S03)2  320  -80  20  0  a-Fe(CH3S0,)2  510  :100  25  0  3-Fe(CH3S03)2  160  -80  16  0  300  ^80  24  0  Fe(p-CH3CgH4S03)2  *Reference  15  119  As s t a t e d p r e v i o u s l y t h e in  the  spin  low t e m p e r a t u r e  temperature  r e g i o n c a n o n l y be r e p r o d u c e d when t h e  c o u p l i n g parameter  is included.  The  values of  here are s i m i l a r to those obtained f o r other frome.s.r. At  measurements  t h e p r e s e n t moment i t  (86)  i s not  D  q  for  noted here t h a t the data  i s the  d e r i v e d from the  dependence of Figgis  contained i n Tables Figgis  t h e two m e t h o d s , w i t h  the  rather  and L e w i s  and L e w i s m o d e l ,  Fe^F^SOg^-  for  Although  the A E Q a g a i n s t  this  lack of  i t must  the be  temperature  obtained  s p l i t t i n g s with  The  3Dg,  relevant  parameters  which i s equal  the a x i a l this  dependence o f  any s u c h d a t a b e l o w  80K.  distortion  are  to A i n  in  i s p r o b a b l y due  the  from  those  and x a r e q u i t e s i m i l a r a s d e r i v e d  i n s e c t i o n 5.7.1  temperature  the  compound.  model. Both  (84).  i r o n c e n t r e s , has  studied.  the e x c e p t i o n of  As n o t e d  small  d a t a and the  between  the quadrupole  5 . 5 and 6 . 4 .  complexes  u s e o f t h i s model  i s i n t e r e s t i n g t o compare t h e p a r a m e t e r s  the temperature  the  fit  least satisfactory for  It  obtained  u n d e r s t o o d why g - F e t C H ^ S O g ^ ,  t h e compounds  theoretical  spin-  t r a n s i t i o n metal  and from p r e v i o u s  compound w h i c h shows m a g n e t i c e x c h a n g e lowest value of  dependence o f A E Q  to  m a g n e t i c moment  from  120  CHAPTER 7  MAGNETICALLY-PERTURBED MOSSBAUER SPECTRA  7.1  INTRODUCTION  M o s s b a u e r s p e c t r a have been in  l o n g i t u d i n a l l y a p p l i e d magnetic  spectra  obtained  f o r these  deal  of information  environment usually  The  Fe^SOg^  g-CHg a n d p-CH^CgH^ h a v e diversity magnetic  of behaviour  been  This  successful  complexes a r e has e n a b l e d a  the e l e c t r o n i c  type o f i n f o r m a t i o n  is  measurements.  , where  X i s CFy  a-CHg,  s t u d i e d and they e x h i b i t  a t low temperatures  7.2 w i l l  a surprising  and i n a p p l i e d  d i s c u s s FeCp-CH^CgH^O.^ and the  a n a l y s i s o f the observed  Hamiltonian  model.  The e x p e r i m e n t a l  spectra generated  spectra using a spin s p e c t r a were  by a programme  w h i c h was b a s e d upon o n e by L a n g i ( 3 4 ) . was p e r f o r m e d model  The  fields.  Section  computed  t o be d e d u c e d a b o u t  from e . s . r .  compounds  iron(II)  a n a l y s i s of the data  of the iron nucleus.  not a v a i l a b l e  f i e l d s o f up t o 5 . 6 T .  paramagnetic  complicated but a t h e o r e t i c a l great  r e c o r d e d a t 2 . 4 and 4 . 2 K  by J . R .  Sams.  has y e t t o p r o v i d e  observations  may be made  written  compared by A . R .  The c o m p u t e r  (section  7.3).  Sections  Hulme  analysis  In t h e case o f F e C C F ^ S O . ^  a c o m p l e t e a n a l y s i s b u t some  with  this  general  7 . 4 and 7 . 5 a r e  121  concerned with discusses to  treat  t h e a- a n d B - f o r m s  t h e a - i s o m e r a n d t h e model the observed s p e c t r a .  antiferromagnetic topic of section  7.2.  of F e ^ H ^ S O ^ .  The  Section  p r o p o s e d by V a r r e t e-isomer  7.4  (34) i s used  undergoes  an  phase t r a n s i t i o n a t ^23K and t h i s w i l l  be t h e  7.5.  MAGNETICALLY-PERTURBED  MOSSBAUER SPECTRA OF F e ( p - C H 3 C 6 H 4 S 0 3 ) 2  II  Mossbauer s p e c t r a have been r e c o r d e d i n a p p l i e d fields  o f up t o 5 . 6 T a t t e m p e r a t u r e s  illustrated in  in Figs.  7.1  and 7 . 2  remain, with  within experimental  no e v i d e n c e  for line  o f 2 . 4 and 4 . 2 K and a r e  respectively.  t h e a b s e n c e o f an a p p l i e d m a g n e t i c error,  magnetic  At these  temperatures  f i e l d the Mossbauer  symmetric quadrupole  spectra  doublets  broadening. II  The  general  a p p l i e d magnetic as f o l l o w s . the  o f t h e Mossbauer s p e c t r a as t h e  f i e l d i s i n c r e a s e d may be q u a l i t a t i v e l y  In F i g . 7.1  spectrum obtained  small  features  a comparison o f the 1.13T  high v e l o c i t y positive  value  line s p l i t s into for Vzz  spectrum  i n z e r o f i e l d shows t h a t t h e e f f e c t  a p p l i e d f i e l d i s to broaden  the low v e l o c i t y  a doublet.  and t h a t  the z - a x i s  This  described  line,  with  of  this  w h i l s t the  i s i n d i c a t i v e of a  o f the E.F.G.  and t h e  II  internal at  magnetic  higher magnetic  substantial magnetic  f i e l d a r e p a r a l l e l . The M o s s b a u e r s p e c t r a f i e l d strengths  magnetic s p l i t t i n g s .  obtained  a r e more c o m p l e x a n d show The s p e c t r a i n t h e s e  larger  f i e l d s may b e s t be d e s c r i b e d a s c o n s i s t i n g o f a s i x - l i n e  122  FIG.  7-1  MAGNETICALLY-PERTURBED MOSSBAUER Fe(p-CH3C6H4S03)2AT 2.4K  SPECTRA OF  .  v ^ ^ - v . - - > ^ > >.-/'-,  ''•s-.vx*»*vvtw: , 1  ^ao  ^AO  x  •  wvv.v-v~.Zero  . .r>::->A S  ^ . / r r ^  field  1.13T  4.50T  oo So ao iZo  Velocity (mm/sec)  123  FIG.  7.2  MAGNETICALLY-PERTURBED MOSSBAUER SPECTRA OF Fe(p-CH3C6H4S03)2 AT 4 . 2 K  1.13T  •* •  •  ••  ...  •  >• 3.38T  •• V  •  4.50T  s  *  a •  a 5.63T • *  • a %  HBU)  ^40  QO  *I  \ * a •  40  BO  Velocity (mm/sec)  12^0  124  pattern  with  the  four  i n n e r l i n e s s h i f t e d to  a p o s i t i v e quadrupole  At overall of  4.2K  magnetic  i n a p p l i e d magnetic s p l i t t i n g appears  Determination  For there for  the  of  change o n l y  these  e  the e f f e c t i v e  where  magnetic  may be v e r y d i f f e r e n t may be r e l a t e d  H  EFF  where  <s>  is  H°  i s the  For  technique  the usual  hyperfine  technique  complexes  a  (87,  88).  t h e m a g n e t i c s u s c e p t i b i l i t y becomes e x p e r i e n c e d by t h e  f r o m t h e a p p l i e d f i e l d H^pp.  iron  H^pp  large  nucleus  and  H^pp  thus:  =  H  APP  saturation  specimen at e l e v a t e d  situation  magnetic  FeCp-CHgCgH^SOg^  diamagnetic  +  <  W  value value  S  H  of of  INT  ^7-  the the  total  temperature  internal  so t h a t  1 )  electronic spin  T h e s e d i f f i c u l t i e s may be o v e r c o m e  This  function  has been used p r e v i o u s l y  f i e l d H^pp,  the average  p r o d u c e d by t h e  as a  the  qQ  complex such as  Vzz-  t h a n ^3T  conditions.  the sign of  sign of  low temperatures  T N T  to  are c e r t a i n d i f f i c u l t i e s associated with  determining  INT  under  a paramagnetic  magnetic-perturbation At  f i e l d s greater  i n d i c a t i n g t h a t the i n t e r n a l  has b e e n s a t u r a t e d  7.2.1  by  interaction.  the a p p l i e d f i e l d ,  field  lower energy  hyperfine  that  field  by m a i n t a i n i n g  the magnetisation  a p p l i e d f i e l d i s n e g l i g i b l e a n d H^pp ^ i s then s i m i l a r to  for  and  a diamagnetic  the <s>  H^pp. complex  (88)  125  where  the  l i n e of  the quadrupole  \±h> -+ | ± % > p t r a n s i t i o n s p l i t s  i n t o an a p p a r e n t  a  from the  l+^g-*- | ± 3 / ' 2 > e  A spectrum o f  splits  positive  relative  in this  7.2.2  The  perturbed This  In field  to  the d o u b l e t ,  t r i p l e t was  model  s e c t i o n d i s c u s s e s the a n a l y s i s of  the  magnetically-  a s p i n H a m i l t o n i a n model  the eigenvalue spectrum, o b t a i n a b l e the o r b i t a l  appreciable mixing of  doublet  from the c r y s t a l -  ground s t a t e  i s well  s t a t e s and a t 4 . 2 K t h e r e w i l l  h i g h e r terms i n t o  or a s i n g l e hole.  The  latter  view i s advantageous  t h e s y s t e m as a p s e u d o - K r a m e r s  h o l e an e f f e c t i v e  spin  isolated be no  the ground d o u b l e t .  d o u b l e t may t h e n be t r e a t e d a s c o n t a i n i n g t h r e e  doublet  This  electrons  s i n c e one can  by a s s i g n i n g t h e  S=%.  A s p i n H a m i l t o n i a n may be u s e d t o d e s c r i b e t h e interactions  (89).  be d i s c u s s e d h e r e .  from h i g h e r s p i n - o r b i t s p l i t  now t r e a t  at  complex.  parameters,  orbital  that  and h e n c e t h a t e 2 q Q i s •  Mossbauer s p e c t r a i n terms o f  model w i l l  and  doublet.  2 . 8 2 T showed t h a t t h e  spin Hamiltonian  This  into a  triplet,  the  F e ( p - C H 3 C 6 H 4 S 0 3 ) 2 o b t a i n e d a t 298K i n an  a p p l i e d magnetic f i e l d of lower energy  doublet which a r i s e s from  i n the presence of  an a p p l i e d m a g n e t i c f i e l d  hyperfine (62).  126  =  p. H .  g . S + i . A. 1-  3IZ  gn3nI.H + eqVzz  -  (7.2)  1(1+1)  41(21-1) where  g  i s the nuclear g - f a c t o r ,  n  n u c l e a r magneton. (i)  The f o u r  terms  i n 7.2 describe  t h e e l e c t r o n i c Zeeman i n t e r a c t i o n b e t w e e n  and t h e e l e c t r o n i c s p i n , of  p t h e Bohr magneton  S v i a the g-tensor,  the e l e c t r o n s p i n and t h e n u c l e a r s p i n ,  hyperfine and  tensor,  A,  and ^  respectively:  the applied f i e l d ,  H  ( i i ) the coupling  I v i a the magnetic  ( i i i ) t h e d i r e c t n u c l e a r Zeeman  interaction  ( i v ) t h e i n t e r a c t i o n o f t h e n u c l e a r q u a d r u p o l e moment w i t h t h e  E.F.G.  a t the i r o n nucleus.  a zero value o f  To  This  t h e asymmetry  quadrupole  parameters: constant  interaction  use the Hamiltonian  given  ( i ) the s i g n and magnitude  and t h e Mossbauer l i n e w i d t h  above  to calculate  of the following  of the quadrupole (these  values  result described i n section 7.2.1),  and d i r e c t i o n o f t h e a p p l i e d m a g n e t i c components  o f the g-tensor,  (v) the temperature.  about  field,  ( i v ) the three  a fast  or slow s p i n - r e l a x a t i o n  around  iron  magnetic  ( i i ) t h e magnitude  ( i i i ) the three  components  Also the isomer s h i f t  the spin-relaxation rate  coupling  c a n be o b t a i n e d  from t h e zero f i e l d spectrum and the high temperature perturbation  assumes  parameter, n .  Mossbauer s p e c t r a r e q u i r e s t h e knowledge  and  the  of the A-tensor  a n d an a s s u m p t i o n  ( s p e c t r a may b e c a l c u l a t e d i n e i t h e r limit).  In view o f the high  i n t h i s complex i t i s assumed t h a t  symmetry  t h e g , A and E . F . G .  127  tensors w i l l  have t h e  gx  x  A  same p r i n c i p a l a x i s  s y s t e m a n d we may  -  -  9y -  =  A  y  9X  ;  V  =  gz  '  A  Mossbauer s p e c t r a r e c o r d e d a t magnetic  f i e l d s of  3.38,  4.50  a n a l y s e d u s i n g one s e t o f listed  i n T a b l e 7.1  (solid  l i n e s ) are  parameter  experimental  a p p l i e d magnetic f i e l d s .  A  doublet  that  doublet  i s as  the e f f e c t i v e  is parallel  spin density  This  to  the  rate,  the to  parameters  7.5.  are  spectra  All  theoretical limit,  spectra  r a t e was a l s o i n zero  as were  employed  by G r i f f i t h the  with  indicated  field.  g-values  f i e l d of  large  responsible for  the spectrum.  applied  (62)  are  and  ground  only  a very  small  direction.  the  of  in  e s p e c i a l l y in small  the  z-axis  sensitive  width  -  observed  hyperfine  i n the p e r p e n d i c u l a r  largely  The  and t h e o r e t i c a l  spectra are extremely parameter  and 4 . 2 K  spin-relaxation  predicted  trigonal  As a c o n s e q u e n c e o f  »  and c o m p u t e d  7.3  As c a n be s e e n f r o m T a b l e 7.1  indicates  2.4.  fast relaxation  symmetric quadrupole  highly anisotropic.  A  values.  illustrated in Figs.  obtained assuming a slow r e l a x a t i o n  by t h e  =  and t h e e x p e r i m e n t a l  between  g„  a n d 5 . 6 3 T have b e e n s u c c e s s f u l l y  s p e c t r a were computed a s s u m i n g a f a s t poor agreement  z  write:  the  A value of -1.79  gn  value  value of  the A„  determining mm s  _ 1  for  theoretical .  This  is  the  overall  A.  gives  128  TABLE 7.1  MAGNETICALLY-PERTURBED MOSSBAUER SPECTRAL PARAMETERS FOR Fe(p^CH C H S0 ) 3  H  APP  TEMP  9  4  9  i  3  2  A  H  (T)  (K)  5.63  2.4  0.35  1  9  2.05  -1.79  5.63  4.2  Q. 30  1  9  2.05  -1.79  4.50  2.4  0.35  1  9  2.05  -1.79  4.50  4.2  0.25  1  9  2.05  -1.79  3.38  4.2  0.25  1  9  2r05  -1.79  1.13  4.2  0.30  1  9  2.05  -1.18  For  a l l spectra  9X  ~  (mm  6  axial  9y  A =A = x  AEQ=  y  (mm  symmetry  g  A  s"1)  ;  ±  x  1 . 9 8 mm s  gz  ;  1  A  ;  z  was a s s u m e d ,  = g  = A  n  n  6 = 1 . 35 mm s " 1  n~:0  s"1)  (mm  s-1)  129  FIG.  7.3  COMPARISON OF COMPUTED AND EXPERIMENTAL SPECTRA FOR F e ( p - C H 3 C 6 H 4 S 0 3 ) 2 AT 2 . 4 AND 4 . 2 K IN AN A P P L I E D . M A G N E T I C F I E L D OF  -1 -8.0  1  5.63T  1 -4.0  1  1  1  0.0 VELOCITY  I +4.0  (mms-1)  I  1  +8.0  130  n -8.0  1  r-4.0  1  1 0.0  VELOCITY(mms-1)  1  1 +4.0  »  i +8.0  131  FIG.  7.5  COMPARISON OF COMPUTED AND EXPERIMENTAL SPECTRA FOR F e ( p - C H 3 C 6 H 4 S 0 3 ) 2 AT 4 . 2 K IN AN A P P L I E D MAGNETIC  _________  -8.0  -4.0  0.0 VELOCITY  +4.0 (mms"1)  +8.0  132  reasonable f i t s ;  this  is equivalent  to a f i e l d of  13.OT.  computed s p e c t r a a r e l e s s  s e n s i t i v e to the value of  value  the  of  2 . 0 5 mm s  Attempts at a temperature  fits  - 1  to  fit  of 4.2K  a r e shown i n F i g .  7.6.  the spectrum o f  The  lower spectrum employs the  spectrum.  saturation  under  Hence, it  i s important  value of  H/T)  saturated.  the  internal  unique s e t of  hyperfine  f i e l d has n o t  parameters  the  (89)  ( C 1 0 4 ) 2 are very s i m i l a r to  analysis of  Fe^-CHgCgH^SOg^.  the environment  consist of  (8.6T). reached  from such s p e c t r a  internal  fields  (or are  f i e l d s are saturated a  v a l u e s may be d e f i n e d t o d e s c r i b e t h e  Fe(C5H5N0)fi  of  may be  conditions.  hyperfine  This  As  reproduction  the a p p l i e d magnetic f i e l d  The p r e v i o u s l y r e p o r t e d  basis  4 . 5 0 and 5 . 6 0 T ) .  to - l . 1 8 . m m . s ~ 1  i s l a r g e enough so t h a t internal  parameters  o f A^  to o b t a i n meaningful to ensure t h a t  1.13T  However, an e x c e l l e n t f i t  these experimental  When t h e  (3.38,  g i v e an u n s a t i s f a c t o r y  a c h i e v e d by r e d u c i n g t h e m a g n i t u d e indicates that  Fetp-CHgCgH^SOg^  i n an a p p l i e d m a g n e t i c f i e l d o f  c a n be s e e n t h e s e p a r a m e t e r s  This  and a  ±  spectra s a t i s f a c t o r i l y .  used to a n a l y s e the h i g h f i e l d s p e c t r a  of the experimental  A  The  g - and A t e n s o r s .  g - and A p a r a m e t e r s  of  those obtained i n  this  may be r a t i o n a l i s e d on  around the i r o n n u c l e u s .  Both  compounds  t r i g o n a l l y e l o n g a t e d FeOg o c t a h e d r a w i t h o r b i t a l  g r o u n d s t a t e s and s i m i l a r / c r y s t a l - f i e l d  the  doublet  s p l i t t i n g parameters.  133  FIG.  7.6  COMPARISON OF COMPUTED AND EXPERIMENTAL SPECTRA FOR F e ( p - C H 3 C 6 H 4 S 0 3 ) 2 . A T 4 . 2 K IN AN A P P L I E D MAGNETIC F I E L D OF  T7T3T  9|  =  9.0  =  1.0  \  = -1.79  Ax  =  1 •8.0  ~  ~  V  2.05  1  1 -4.0  1  1  1  0.0 , VELOCITY ( m m s - 1 )  I +4.0  I +8.0  134  However,  Fe(C5HgN0)g  relaxation  rate  differences to  the  which i s  of  Fe(CgHgN0)g  whose  anions  compound  4.2K  is  probably  single crystal  (90).  The  more  the  present  defined  resolved  hyperfine  extensive  study  and c o m p a r i s o n s  7.3.  absorptions  F e ^ S O ^  may be  for  the  probably  the  lattice  by l a y e r s  of to  X-ray structure  i n which  the  were o b s e r v e d for  layers  cobalt(II)  has b e e n  determined  noncoordinated  lattice in  has o n l y  5.0T  of  anions;  spin-lattice relaxation  f i e l d of  related  structure  c a t i o n s and  FetFSOg^  These  solid-state  proposed  isomorphous  spectra observed  of  are  r i g i d polymeric  time  i n an a p p l i e d m a g n e t i c  poorly  rates  d i s c r e t e CoOg o c t a h e d r a l  spin-lattice  Fe.Cp-CH-jCgH^SO-^.  a polymeric  are sandwiched  s h o u l d i n c r e a s e the  At  have a s l o w  case f o r  Whereas  c o n s i s t s of  (CI0^)2  as c o n t a i n i n g ClO^"  the  compounds.  iron(II), cations  analogue,  not  to  w h i c h may b e e n v i s a g e d  these  FeOp-^CgH^Og^ of  was shown  in spin-lattice relaxation  differences  structure  (CI0^)2  the  former  rate.  been examined  (15).  O n l y two  broad  rather  than  well  the  Fetp-CH^CgH^SOg^-  i s necessary before  any  A  at  more  conclusions  made.  MAGNETICALLY-PERTURBED MOSSBAUER SPECTRA OF Fe ( C F S 0 ) 3  3  2  11  Mossbauer fields in  Fig.  of  up t o  7.7.  s p e c t r a have been r e c o r d e d i n a p p l i e d  5.6T  In  Fetp-CHgCgH^SO^  at  a temperature  comparison the  to  the  Fe^F^SO..,^  of  4.2K  and a r e  illustrated  zero f i e l d spectrum compound,  exhibits  magnetic  of  asymmetric  135  FIG.  7.7  MAGNETICALLY-PERTURBED MOSSBAUER SPECTRA OF F e ( C F 3 S 0 3 ) 2 AT 4 . 2 K  Zero field • • •  0.22T  •  •.  •  w  1.13T • • •  •• • • •  *  1.69T  ^-v'.'-\^V>/v;.\~V"'.><W...  ....  •  •  ••  ^ao 5o oo So  izo 1 —  RO  Velocity (mm/sec)  136  FIG.  7.7  -  Contd.  MAGNETICALLY-PERTURBED MOSSBAUER SPECTRA OF F e ( C F 3 S 0 3 ) 2 AT 4 . 2 K 2.81  r  T  \  .wr**-"  ^ ^ ^ w : . . . / ^ .  3 . 38  T  4.50 T  5.63 T  Si  -8.0  -4.0  0.0  4.0  80  Velocity (mm/sec)  12.0  137  line  broadening at  hyperfine  structure  5 mm s ~ \ be m a d e , appears  and t h e r e  to  splitting  a t 0.22T the  broaden, into  low v e l o c i t y  has b e e n p r o p o s e d  and  somewhat  at  (ii)  rates  in this  the  remainder  spin-relaxation  in  to  Fe^FgSOg^  saturated  at  be a f u n c t i o n the  the  one o f  at  all  of  temperatures  be  at  high  the  two  phenomenon  Fe(C5H5N0)fi  (C104)2  (89).  spin  spectrum r e s u l t s  width  f i e l d becomes field  from a  This  the  This the  spectrum  field.  (i)  spectrum  preferential  m e c h a n i s m may be use and  effect  case f o r  Thus  fully  zero f i e l d  ground p r i o r to  same a s y m m e t r y .  high  strength.  i n the  s e v e r a l mechanisms:  which i s not  of  the a p p l i e d magnetic  hyperfine  samples were t h o r o u g h l y  This  f i e l d i s i n c r e a s e d the  c r y s t a l l i t e s (91).  s a m p l e s showed t h e  r ••• r .  rate.  l i n e broadening observed  may a r i s e t h r o u g h  as t h e  of  v e r y low a p p l i e d magnetic  The  ordering of  internal  of  may  intensity.  coming from a slow  l i n e i n t e n s i f i e s and t h e o v e r a l l  only appears  split.,lihe  compound.  behaviour  As t h e a p p l i e d m a g n e t i c velocity  around  t h e weak l i n e o b s e r v e d  high v e l o c i t y  rate w h i l e the  faster  magnetic  may i n d i c a t e t h e p o s s i b i l i t y o f  to e x p l a i n  The weak a b s o r p t i o n  some  l i n e seems t o  z e r o f i e l d s p e c t r u m has g a i n e d i n  spin-relaxation  relaxation  quadrupole  the high v e l o c i t y  These o b s e r v a t i o n s different  for  f i e l d i s i n c r e a s e d two o b s e r v a t i o n s  whereas  a doublet,  i n the  i s evidence  as i l l u s t r a t e d by t h e weak a b s o r p t i o n  As t h e m a g n e t i c (i)  velocity  4.2K  eliminated  different  s h o u l d be  Fe(CFoS0o)o-  present  138  (ii) (92,  Slow s p i n - s p i n r e l a x a t i o n 93,  94).  Kramers'  However,  i o n and t h e o b s e r v e d asymmetry  of  the  Karyagin  effect  (iv)  iron(II)  dependence o p p o s i t e  of  l i n e broadening  (93,  dependent  and d e c r e a s e s w i t h  that  it  97).  phenomenon  to t h a t observed  consistent with  This  hyperfine  BaFeSi^O-jQ ( 9 8 ,  Fe(C8H6N2)(C104)2  a tetrakis  present  temperature temperature is  thought  asymmetry field.  the  observed  gillespite,  (1,8-napthyridine)  complex,  successful for  being unable  the experimental  f i e l d s using the s p i n Fe(p-CHgCgH4S0g)2.  t i m e no d e t a i l e d p a r a m e t e r  t h e model  spectra  (100).  in a p p l i e d magnetic  model w h i c h p r o v e d  is It  to e x p l a i n  the mineral  A t t e m p t s were: made t o a n a l y s e obtained  rate  s p l i t t i n g observed i n zero  (89),  anisotropy  has a  as the  the observed  mechanism has been p r o p o s e d  99),and  the  here.  decreasing temperature.  i n Fe(CgHgNO)g ( C 1 0 4 ) 2  is  the observed  spin-lattice relaxation  i s t h i s mechanism which l e a d s to  and t h e o n s e t o f  spectra  The  a  96) w h i c h a r i s e s from t h e  a decrease i n the s p i n - l a t t i c e r e l a x a t i o n rate  decreases  i s not  should increase with  but again t h i s  The o n l y e x p l a n a t i o n  doublets  p o s s i b i l i t y c a n be e l i m i n a t e d .  (95,  recoil-free fraction  temperature  is  This  Another p o s s i b l e explanation  Gol'danskii  Kramers'  unlike iron(III),  increasing temperature.  (iii)  between  to reproduce  spectra  Hamiltonian At  the  v a l u e s a r e a v a i l a b l e due some o f  the  features  in  to  139  the experimental of  Fe(CF3S03)?  spectra.  is  less  Fig.  in relative  the  are poorest  nature case of  However,  intense i n the  7.3  of  fits  of  in this  there  case of  the  i n a magnetic  The  Fe(CF3S03)2  spectra for  the  tensors  g - and A-  5-.63T  differences  l i n e a t ^ 2 mm s  and as c a n be s e e n  - 1  from  may be made a b o u t  the  compound.  observed  spectra..  the o v e r a l l  i s ^15%  than  i n the  be r e f l e c t e d i n a h i g h e r  Secondly, magnetic  case of  value  (C104)2,  reproduce the  that  general  Firstly, the  .  looking at  splitting in  One  as i n  the  g-tensor  features  Fe(p-CH3CgH4S03)2.  f o r A|(  qualitative  Fig.  of 7.8  the it  Fe(CF3S03)2 This  can a l s o say  will  that  A ^ > 0.  At  the  cannot  t h e model  f i e l d of  spectra  compound  in this  may be o b s e r v e d  spectra  the  Fe(p-CH3CgH4S03)2  F e ( p - C H 3 C g H 4 S 0 3 ) 2 and F e ( C 5 H 5 N 0 ) g  < 0 and  that  region.  observations  greater  appears  a r e some s u b t l e  A few g e n e r a l  experimentally  may n o t  it  line intensities.  must be h i g h l y a n i s o t r o p i c t o  A|(  7,8  and F e ( p - C H 3 C g H 4 S 0 3 ) 2  are very s i m i l a r . especially  From F i g .  present  time  it  i s not  be a n a l y s e d u s i n g t h e  case  here.  u n d e r s t o o d why  spin Hamiltonian  i m p l i c i t l y a s s u m e s no o r b i t a l  be t h e  fully  model.  a n g u l a r momentum and  these However, this  140  FIG.  7.8  COMPARISON OF MOSSBAUER SPECTRA OF F e ( C F 3 S 0 3 ) 2 AND Fe(p-CH3C6H4S02)2 OF 1 . 1 3  A T . 4 . 2 K IN A P P L I E D  MAGNETIC  FIELDS  AND 5 . 6 3 T 1.13T  v ' % r . — • • { A A A * - V'-f^-*v.. Fe(CF3S03)2  \ •  •• .^•.•v.-.v-*v'-1.1 3T Fe(p-CH3CgH4S03)2  \ . - /»'••. • • .* •» •. . . *. . ••  .—-•>-••"• 5 . 6 3 T Fe(CF3S03)2 •  • •  • •  •  5.63T Fe(p-CH3C6H4S03)2-i  • •  •  • •  *. •  T  -8.0  1  -4.0  1  0.0  1  4.0  1  8.0  Velocity (mm/sec)  r  12.0  141  7.4  MAGNETICALLY-PERTURBED MOSSBAUER SPECTRA OF  <x-Fe(CH3S03)2  II  Mossbauer fields  of  up t o  absence of  5.6T  This  a c t i n g as a f a s t previously  serves only  4.2K to  the  paramagnet  f i e l d s of  produced  (Fig.  doublet,  the  4.50  7.10).  tensor,  of  for  (101).  of  spectral  and i s comparable  lines.  triplet  i s negative.  the  This  a polycrystalline  i s at  to  1.1T applied  pattern  of  Thus t h e  determining  ground  state  is  relative  p r i n c i p l e component  method  doublet  7.2).  in  higher energy  the  the  f i e l d of  However,  in  iron(II)  of  the  sample has been d i s c u s s e d  and i n s e c t i o n 7 . 2 . 1 .  4.2K  (section  a magnetic  magnetic  quadrupole  and 5 . 6 3 T a d o u b l e t - t r i p l e t The  At  high-spin  Fe(p-CH3CgH4S03)2  indicating that Vzz,  E.F.G.  4.2K  is typical  a p p l i c a t i o n of  broaden  of  in applied  f i e l d a symmetric  observation  relaxing  magnetic  (102,103)  a temperature  discussed case of At  Vzz  at  have been r e c o r d e d  an a p p l i e d m a g n e t i c  is observed.  the  spectra  to  the sign  previously in  this  2 isomer  i s the  symmetry  |z  > orbital  corresponds  These r e s u l t s Fe(H20)g Si Fg,  are  to  and t h e  a compression along  s i m i l a r to  where  the  compressed octahedron  distortion  those  iron  of water  Attempts were.made  to  the  observed  cation  from  octahedral  trigonal  FeOg  axis.  i n the  case  of  i s surrounded  by a  trigonally  molecules analyse  (104). the  observed  spectra 5  assuming i s o t r o p i c magnetic  interactions.  free-ion  term  iron(II)  magnetic  properties  for  high-spin (105)  However,  results  the  in highly  a n d a s c a n be s e e n f r o m  Fig.  D anisotropic 7.9  fits  142  143  FIG.  7.10  MOSSBAUER OF a - F e ( C H 3 S . 0 3 ) 2 F I E L D S ' O F 4 . 5 0 AND Computed  1 -8.0  1  AT 4 . 2 K IN A P P L I E D MAGNETIC  5.63TT  S p e c t r a g e n e r a t e d by t h e p a r a m e t e r s T a b l e 7.1  1 -4.0  1  1 0.0  VELOCITY  (mms-1)  I  I  +4.0  given i n  I  '  +8.0  144  of  c o m p u t e d and e x p e r i m e n t a l  the  top  spectrum i n F i g .  splitting spectra of  the  is less  than  s p e c t r a are poor  7.9  that  it  using t h i s model.  may be s e e n t h a t  a s s u m i n g H^pp  i n d i c a t e t h a t .the e f f e c t i v e  the  = HApp.  magnetic  The  two  of  the doublet  lower  f i e l d i s a n i s o t r o p i c ; the  t r i p l e t may be r e p r o d u c e d a s s u m i n g an e f f e c t i v e  3 . 5 0 T and t h a t  a s s u m i n g an e f f e c t i v e  From  width  field  field  of  of  2.80T. A more s u c c e s s f u l t r e a t m e n t model  of  f i e l d t o be p a r a m e t e r i s e d i n t h e  hyperfine  Varret  (34)  the data  phenomenological the  of  of  has u s e d  which enables the  the  anisotropy  case of  weak  magnetisation.  The of  parameters  a-FetCHgSOg^  given  i n Table  d e r i v e d from the  i n a p p l i e d magnetic  7.2.  a r e shown i n F i g .  Experimental  f i e l d s of  Reasonable  and c o m p u t e d s p e c t r a  fits  of  the  parameters  experimental  and computed  parameter,  and H I Y ,  This which  n and i d e n t i c a l v a l u e s o f  f i e l d s i n the  value  HIX  X and Y d i r e c t i o n s .  may be o b t a i n e d u s i n g a f i n i t e ofn  are lines)  the  7.2  are  spectra  asymmetry the  However,  internal a  v a l u e o f n^O-3  better and HIX? 4  HIY.  suggests a rhombic d i s t o r t i o n i n the a - s p e c i e s  i s consistent with  was shown t o  (solid  i n Table  for  agreement  spectra  4 . 5 0 and 5 . 6 3 T  may be o b t a i n e d by a s s u m i n g a z e r o v a l u e  magnetic  the  7.10.  A f e w comments a b o u t relevant.  analysis of  have C g  the  i n f r a r e d s p e c t r a l d a t a where  symmetry.  the  anion  TABLE  PARAMETERS OBTAINED FROM THE  7.2  FOR a - F e ( C H 3 S 0 3 ) ?  COMPOUND  TEMP  HApp  AND  VARRET MODEL  Fe(H20)g  r  SiFg  AEQ  (mms" )  n  (mms' )  HIX  HIY  HIZ  (T)  (T)  (T)  (K)  (T)  a-Fe(CH3S03)2  4.2  4.50  0.40  -3.31  0.30  -1.00  -0.60  -2.00  a-;Fe(CH3Sp3)2  4.2  5.63  0.40  -3.31  0.35  -1.00  -0.60  -2.50  -0.60  -0.60  3.30  1  1  Fe(H20)6  SiFg  3.00  7.5  0.46  -3.35  0.00  Fe(H20)g  SiFg  4.2  2.0  0.25  -3.52  0.35 -10.7  -12.3  -7.00  146  Varret's the  temperature  anisotropy This  the  internal  the magnetic  From t h i s  magnetic  the l a r g e  temperature  are presented  F e ( H 2 0 ) g S i Fg  i n Table it  7.2  i s observed  in  the  Fe(H20)g SiFg  the case of a - F e ( C H 3 S 0 3 ) 2 at  susceptibility in  of  At  this  is expected,  to  field  4.2K  as  the  reversed.  susceptibility  highly  anisotropic  nature  Some p a r a m e t e r s  o b t a i n e d by  Varret  along with  Fe(H20)g S i f g .  susceptibility  hyperfine  i s d e c r e a s e d and t h e  interactions.  table  for  indicate that  increase i n magnetic  that  c o r r e s p o n d a l o t more c l o s e l y t o obtained  (34)  was d e c r e a s e d f r o m room t e m p e r a t u r e  may be due t o  as the of  of  results for  the  those;;for  the  values  a-Fe(CH3S03)2. for  a-Fe(CH3S03)2  high temperature  high temperatures is relatively  of  magnetic  low and even  low t e m p e r a t u r e s  a proposal  the  values  a high  though  magnetic  antiferromagnetism  compound w o u l d s e r v e as an e f f e c t i v e  mechanism f o r  decreasing  susceptibility.  7.5.  MOSSBAUER SPECTRA OF  B- Fe(CH3S03)2  BELOW 25K  II  Unlike  the  remains a quadrupole a complex  temperature  magnetic  hyperfine  magnetic  ordering of  of  the a - i s o m e r  d o u b l e t down t o  the  4.2K,  s p e c t r u m on c o o l i n g b e l o w ^ 2 5 K  range o f  the  Mossbauer spectrum of  transition  t h e two  pattern the  (101).  Fig.  7.11).  are  and m a g n e t i c  the r e s u l t of interactions.  shows  Over a very  This  s a m p l e and t h e o b s e r v e d  temperature  both quadrupole  8 - isomer  l i n e spectrum s p l i t s  (see  which  the  into  a  narrow  complex  indicates spectra combined  below effects  A few t e n t h s  of  a  147 FIG.7.11  MOSSBAUER SPECTRA OF  B-Fe(CHgS03)2  OF THE PHASE TRANSITION  IN THE  PROXIMITY  TEMPERATURE  23.12K ..•v.  22.92K •  r  • • • • • •  «^ •  .  ..»  . • •  •  • •  . <»  22.70K  22.30K  21.63K  -i -4.0  r — — i -2.0  0.0 VELOCITY  1  1  +2.0  +4.0  (mms-1)  r~ +6.0  148  K e l v i n degree above t h e phase t r a n s i t i o n spectrum i s a sharp quadrupole is  lowered  (e.g.  to 22.70K)  splitting  into  a doublet  (see F i g .  triplet  an a p p a r e n t  application  d o u b l e t and as t h e  t r i p l e t and the h i g h energy This  H j ^ - i s small  pattern  the sign of  this  lower  decreasing temperature,  on t h e m a g n e t i c  This  3 - Fe^HgSOg^  quadrupole  V__.  increases  (see F i g .  at 4.2K only serves  showing t h a t the observed  t o an a n t i f e r r o m a g n e t i c  phase  t o a random d i s t r i b u t i o n o f i n t e r n a l  directions  i n an a n i s o t r o p i c  to  transition (102,103).  c o n d i t i o n r e s u l t s because the a p p l i e d f i e l d s i m p l y  vectorally  adds  hyperfine  field  powder.  The t r a n s i t i o n i s a c c o m p a n i e d by a s l i g h t h y s t e r e s i s ; upon w a r m i n g t h e s a m p l e t h r o u g h  the t r a n s i t i o n r e g i o n ,  At  f i e l d has  value of ^14.0T at 4.2K  o f a magnetic f i e l d o f 1.1T  from a paramagnetic  this  interaction.  a n d by 1 8 . 2 K t h e i n t e r n a l  saturation  broaden the s p e c t r a l l i n e s , is  V__.  s i t u a t i o n i s r e v e r s e d and t h e  The i n t e r n a l m a g n e t i c f i e l d i n  Application  the  temperatures  22.70K the t r i p l e t a t low v e l o c i t y i n d i c a t e s a p o s i t i v e  reached ^90% o f . i t s  into a  i s observed because a t  i n t e r a c t i o n . At  i n t e r a c t i o n a c t s as a p e r t u r b a t i o n  with  into  so t h e magnetic i n t e r a c t i o n appears as  of the quadrupole  w h e r e ti^j i s l a r g e r ,  line  s p l i t t i n g o f t h e two l i n e s  of a magnetic f i e l d to determine  a perturbation  line  i s v e r y s i m i l a r t o t h a t o b s e r v e d upon  At 22.70K t h i s t r i p l e t - d o u b l e t temperature  the  temperature  one o b s e r v e s t h e l o w e n e r g y  7.11).  and a d o u b l e t  ( e . g . a t 22.92K)  final  7.12).  149  FIG.  7.12  MOSSBAUER SPECTRA OF  g - F e ( C H 3 S 0 3 ) 2 BELOW  21.15K  3^21.15 K  .-/-:. 20.68 K  •"...  ^-18.18 K  :•>•• 5.97 K 4.30 K  -4.0  -2.0  0.0  2.0  4.0  Velocity (mm/sec)  6.0  150  collapse of below  where  the  hyperfine  s p l i t spectrum to a doublet  the  From t h e  i l l u s t r a t e d spectrum at 22.70K  internal  f i e l d is small,  on l o w e r i n g t h e  major  the  axis of  z-axis  of the  internal  the E . F . G . ,  hyperfine  is  easy plane o f m a g n e t i s a t i o n  place within  FeOg c h r o m o p h o r e .  this  plane.  This  this  the  indicates that  case i s a l s o the  suggests  7.11),  triplet  f i e l d is perpendicular  which i n t h i s  of  (see F i g .  the s p l i t t i n g of  temperature;  z-axis the  observed  24.4K.  appears f i r s t  the  i s not  t h a t the  the  to  trigonal xy  plane  and t h a t m a g n e t i c o r d e r i n g  takes  151  CHAPTER 8  STUDIES ON I R O N ( I I I )  8.1.  SULFONATES  INTRODUCTION  An e a r l i e r r e p o r t exchange This  i n the i r o n ( I I I )  observation,  in  both  forms  of  several  iron(III)  Fe(p-CH3CgH4S03)3-  spectroscopy.  sulfonate  along with  of iron(II)  as a p a r t o f t h i s  suggested the presence o f magnetic  the evidence  study  Magnetic  three  prompted  Fe(CF3S03)3, compounds  Fe(FS03)3 (22).  f o r magnetic  methanesulfonate,  sulfonates, These  compound,  exchange  an i n v e s t i g a t i o n  F e ( C H 3 S 0 3 ) 3 and  h a v e been  synthesised  and have been i n v e s t i g a t e d by i n f r a r e d s u s c e p t i b i l i t y measurements  have  been  r e c o r d e d b e t w e e n 8 0 a n d 31 OK u s i n g a Gouy b a l a n c e a n d t h e f i e l d dependence o f t h e magnetic  s u s c e p t i b i l i t y was m e a s u r e d a t  different  magnetic  balance.  M o s s b a u e r s p e c t r a have  only  (80 and 2 9 3 K ) .  8.2.  These  using a Faraday  a r e b a s e d upon formally  doubly  reduction  expected  temperatures  p r e l i m i n a r y r e s u l t s a r e now d i s c u s s e d .  SULFONATES  s p e c t r a l data a r e given  C 3 v a n i o n symmetry. degenerate,^  i n Table  8.1;  assignments  S i g n i f i c a n t s p l i t t i n g o f the  and v  i n a n i o n symmetry  f o r the i r o n ( I I I )  magnetic  b e e n r e c o r d e d a t two  INFRARED SPECTRA OF I R O N ( I I I ) Infrared  with  f i e l d strengths  three  g  modes  below C 3 y .  sulfonates  i s observed, This  consistent  i s of course  since the stoichiometry  of  152  TABLE 8 . 1  INFRARED SPECTRAL DATA ( c m " 1 ) FOR  IRON(III)  SULFONATE COMPOUNDS  C3v  ASSIGNMENT  Fe(CF3S03)3  Fe(CH3S03)3  Fe(p-CH3CgH4S03)3  FOR ANION  v^(E)  1230 s 1078 s  S03 as. str  1014 s  v-j (A-j) S 0 3 s y m . s t r .  v5(E)  v3(A-|)  S03 as.def.  S 0 3 sym. d e f .  1279 s 1050 s . b r 980 s h  S-C d e f .  and i n t e r n a l v i b r a t i o n s o f C F 3 > CH3 and «  p-CH3C6H4  1000 s  780 m 760 w  675 m  635 m 600 w  565 m. s h 530 m  553 s 540 s h  515 w 505 m  498 m  481 w  f v6(E)  1280 s 1030 s  1370 1150 780 570 428 355 328  m v.w. w w m w w  1340 w. s h 4 1 0 m. b r . 355 m  1375 1112 810 700 420  w. s h m. s h s w m. b r  153  Fe(XS03)g requires iron(III) atoms  that  f o r an o c t a h e d r a l  c a t i o n each s u l f o n a t e  to coordinate  essentially  to i r o n ,  environment  l i g a n d must u t i l i s e  around the  only  t h e t h i r d oxygen r e m a i n i n g  two o x y g e n non-bonding,  as S=0,which accounts f o r the high frequency  o f the  vibration. A doubling of the v F e ( C H g S O g ) g compound a n d t h i s sites.  (A-j) v i b r a t i o n  2  A d o u b l i n g o f t h e Vg (A-|) v i b r a t i o n  fact  be s t r u c t u r a l  possibility  In g e n e r a l compounds  contain  compared t o t h o s e  8.3  of  less  highly  8.2 -  iron(III)  compounds.  SULFONATES  s u s c e p t i b i l i t y results are reported  8 . 4 and F i g . 8 . 1  t h e m a g n e t i c moments  i l l u s t r a t e s the temperature  f o r these  The m a g n i t u d e that a l l three  but t h i s  r e s o l v e d a b s o r p t i o n s as  in-the?corresponding iron(II)  The m a g n e t i c  in dependence  compounds.  o f t h e m a g n e t i c moment v a l u e s  compounds  for  explored.  the i n f r a r e d spectra o f these  broader,  anion  T h e r e may  i n t h e s e compounds  MAGNETIC S U S C E P T I B I L I T I E S OF I R O N ( I I I )  Tables  i s a l s o observed  by a s i m i l a r p r o p o s a l .  isomers present  has n o t y e t been  f o r the  may be c a u s e d b y n o n - e q u i v a l e n t  F e ( C F g S O g ) g a n d may be e x p l a i n e d in  i s observed  a r e h i g h - s p i n and t h u s  indicates  have a s p h e r i c a l l y  5 symmetric to a  half-filled d  A-jg g r o u n d  electron configuration.  term f o r which there  moment b e l o w t h e s p i n - o n l y v a l u e ligand  f i e l d terms.  This  corresponds  s h o u l d be no r e d u c t i o n o f t h e  by s p i n - o r b i t  For high-spin i r o n ( I I I )  coupling with  compounds  higher  one e x p e c t s  154  TABLE 8 . 2  MAGNETIC S U S C E P T I B I L I T Y DATA FOR  TEMP(K)  106xfl  (cm  3  mol-1)  Fe(CF3S03)  y  F F F  (B.M.)  306  13830  5.82  279  14740  5.73  253  16340  5.75  228  17860  5.71  203  19840  5.67  179  22310  5.65  154  25360  5.59  130  29720  5.56  105  35140  5.43  80  42580  5.22  FARADAY RESULTS AT  294K  HdH(T2cm_1)  IO6  X / v  (cm3  mol"1)  p  E F p  (B.M.)  253  14210  5.78  526  14190  5.77  869  14220  5.78 D  Diamagnetic c o r r e c t i o n s  -148  x 10"  3 cm , mol  155  TABLE 8 . 3  MAGNETIC S U S C E P T I B I L I T Y DATA FOR  Fe(CH3S03)3  TEMP(K)  106 x A ( c m 3 mol"1);  303  12530  5.51  280  13670  5.53  255  14950  5.52  232  16400  5.52  208  18190  5.50  182  20400  5.45  149  24450  5.39  124  28470  5.31  101  34010  5.24  84  38570  5.09  FARADAY R E S U L T S ' A T  HdH dx  (T2  p_FF(B.M.)  294K  cm-1)  106  x  n(cm3 mol"1) A  y - ^ B . M . ) t  n  253  12940  5.52  526  12950  5.52  869  13030  5". 5 3  Diamagnetic c o r r e c t i o n s  -115  -6 x 10~  3 -1-" cm mol  156  TABLE 8 . 4  MAGNETIC S U S C E P T I B I L I T Y DATA FOR  TEMP(K)  106 x  A  (cm3 moJ"1)  Fe(p-CH3CgH4S03)  yEFF(B.M.)  304  11740  5.34  279  12550  5.29  254  13830  5.30  230  15190  5.29  207  16870  5.28  182  18860  5.23  156  21390  -5.16  130  24810  5.08  106  29420  4.99  85  34930  4.87  FARADAY RESULTS AT 294K  HdH dx  (T2  cm-1)  106 x A  (cm3 m o l " 1 j ,  u  E F F  (B.M.)  253  12320  5.30  526  12370  5.31  869  12410  5.32  Diamagnetic  corrections  -  377  x 10"  cm  mol"  157  FIG 8.1  TEMPERATURE DEPENDENCE Fe(XS03)3  OF MAGNETIC MOMENT  FOR  COMPOUNDS  o  r-O CO  o -m  ""To  CM  o  o  CO  CJ X CJ  o  o •o  CM  I CL  _  o  _ o • in  JO  6  "ro  o  L_° x O CJ LL_  •  LL_  o  -ro  —t—  CO  IrMa  .o  if)  O  if)  If)  lN3lrN0lrN  0ll3N9VlrN  158  a "spin-only" independent  of  experimental temperature  m a g n e t i c moment o f temperature.  data  B.M.  However,  presented  here,  t h e m a g n e t i c moments  are reduced below the of  5.92  "spin-only"  i s not  the three  value.  t h e m a g n e t i c moment d e c r e a s e s i n t h e  The  the  studied.  order  of  This  absolute  monotonically  temperature as the  At  room  sulfonates magnitude  order over  the  temperature  d e c r e a s e i n m a g n e t i c moment may r e f l e c t  increasing metal-anion  a pronounced  the  case.  iron(III)  Fe(CF3S03)3 > Fe(CH3S03)3 > Fe(p-CH3CgH4S03)3 range  be  as c a n be s e e n f r o m  this of  which should  covalency.  dependence;  temperature  There are several  Also  t h e moments  the  t h e moments  show  decreasing  decreases.  m e c h a n i s m s by w h i c h t h e m a g n e t i c moment  may be r e d u c e d b e l o w t h e " s p i n - o n l y "  v a l u e a n d show s u c h a  temperature  dependence. 3 (i) electron if  A spin crossover s i t u a t i o n , configuration  i n which a h i g h - s p i n 5  goes t o a l o w - s p i n  (t2g  ) electron  t h e l i g a n d f i e l d and e l e c t r o n p a i r i n g e n e r g i e s a r e  (t2g  2 eg  )  configuration  approximately  equal. (ii) iron(III)  An a n t i f e r r o m a g n e t i c centres The  a d  5  through  presence of  as o p p o s e d t o a d  6  for  exchange  i n t e r a c t i o n between  bridging sulfonate greater  to  unpaired electron spin density  compared to  take  adjacent  anions.  electron configuration,  n u c l e a r charge i n i r o n ( I I I ) plausible  exchange  and g r e a t e r  iron(II),  p l a c e between  make i t  iron(III)  in  effective more  rather  than  159  iron(II)  centres. Hence c a s e ( i i ) a p p e a r s t h e more l i k e l y c a u s e o f t h e l o w  magnetic  moments. All  three  compounds  s t u d i e d h e r e h a v e m a g n e t i c moments  which  i are independent of magnetic for  f i e l d strength.  F e ^ S O g J g where a f i e l d dependence  was p r o p o s e d  This  was n o t t h e c a s e  i s o b s e r v e d and f e r r o m a g n e t i s m  (22).  At the present time a d e t a i l e d a n a l y s i s o f the magnetic moment d a t a f o r t h e s e compounds h a s n o t b e e n p e r f o r m e d . studies proved  u s i n g a model unsuccessful.  p r o p o s e d by E a r n s h a w , This  model  evaluates  f u n c t i o n o f k T / J , where J i s t h e exchange c h a i n o f i n t e r a c t i n g s p i n s o f S = ^lz. of  iron(III)  lattice  arrangement,  iron(III)  the polymer;  integral, for a linear  bridging anions,  MOSSBAUER SPECTROSCOPY  OF  structure each  cations i n a polymeric p l a c e i n more  a more s o p h i s t i c a t e d model  may h a v e t o be a p p l i e d t o a n a l y s e t h e m a g n e t i c moment 8.4.  (106)  t h e m a g n e t i c moment a s a  a n d m a g n e t i c e x c h a n g e may t a k e  t h a n one d i r e c t i o n t h r o u g h  and Lewis  However t h e p o s s i b l e  sulfonates contains bidentate  a n i o n b r i d g i n g t o two d i f f e r e n t  Figgis  Preliminary  IRON(III)  data.  SULFONATES  II  Limited sulfonate Table  8.5.  Mossbauer data  compounds  have been o b t a i n e d f o r t h e  s t u d i e d and the r e s u l t s a r e p r e s e n t e d  iron(III) in  160  •TABLE 8 . 5  MOSSBAUER EFFECT DATA FOR  COMPOUND  TEMP (K)  Fe(CF,SCO~ J  J  J  Fe(CH.S0?). J  J  J  Fe(p-CH-CfiH.SO.,)v J D 6 J -  Isomer s h i f t foil  values  spectrum.  6 -1 (mm s ~ )  IRON(III)  AEn  SULFONATES  r, -1  (mm s  )  T  9  -1 (mm s ~ )  -1 (mm s " )  293 80  0.55 0.60  0.25 0.33  0.78 0.52  0.22 0.42  293 80  0.48 0.59  0.34 0.36  0.49 0.50  0.41 0.46  293 80  0.49 0.60  0.37 0.39  0.57 0.59  0.44 0.49  quoted  relative  t o t h e c e n t r o i d o f an i r o n  161  All respect  to  spectrum,  three  isomer s h i f t that of  8.4.1.  compounds  and q u a d r u p o l e  Fe^HgSOg)^ at  Isomer s h i f t The  usual  range  i s 0 . 1 - 0 . 6 mm s  iron(III)  sulfonates  The  of - 1  highly  compounds  compounds  and as w i t h  c a n be d r a w n  between  isomer s h i f t  values  with  its  on t h e  varying  d  6  considerably  The dependence. is  not  to  a d  all  tend  typical  8.2.  high-spin  to the of  for  the  these  the  and a n i o n  values  values  i n the  power,  iron  no  basicity.  a change  in  of  these  correlation The  similar  sulfonate  has l i t t l e  group,  effect  nucleus.  isomer s h i f t  shows t h e  values.  electron  sulfonates  this  sulfonate  show c o m p a r a b l e  iron(II)  the  high side of  similar s-electron density  sulfonates  i s due t o  for  obtained  ionic character  comparison of  isomer s h i f t This  at  larger 5  with  A  in Fig.  values  values  electron withdrawing  and i r o n ( I I I )  as opposed  The  indicate that  As e x p e c t e d ,  exhibit  (71)  isomer s h i f t  s-electron density  iron(II)  i s shown  studied a l l  isomer s h i f t which i n d i c a t e s three  s p l i t t i n g values.  isomer s h i f t  (Table 8.5)  i n d i c a t i n g the  compounds.  80K,  spectra  values  iron(III)  range  show s i m i l a r M o s s b a u e r  This  values  iron(II)  of  the  compounds  i s as e x p e c t e d  for  to  a  configuration. all  show a s m a l l  a second-order  c h e m i c a l l y s i g n i f i c a n t and w i l l  not  temperature  Doppler e f f e c t be c o n s i d e r e d  which further.  162  163  8.4.2.  Quadrupole  splitting  No q u a d r u p o l e in  s p l i t t i n g i s expected  cubic l i g a n d f i e l d environments  all in  values  three  compounds  the range  ( i . e . unequal  E.F.G.  non-bonding o r b i t a l s ) 3  mm s " 1 .  a small quadrupole  electron distributions in either  8.5  splitting  Any v a l e n c e c o n t r i b u t i o n  to the  bonding  or  i s d i f f i c u l t to imagine i n the case o f a  2  t2  eg  this  small s p l i t t i n g i s a l a t t i c e c o n t r i b u t i o n  electron configuration.  distribution  A more p l a u s i b l e e x p l a n a t i o n  o f l a t t i c e charges around  The  quadrupole  the i r o n ( I I I )  s p l i t t i n g shows o n l y  of  from a n o n - c u b i c cation.  a small  temperature  d e p e n d e n c e p r e s u m a b l y b e c a u s e no l o w - l y i n g t h e r m a l l y are  iron(III)  b u t a s c a n be s e e n f r o m T a b l e  studied exhibit  0.25-0.39  for high-spin  accessible  levels  present. I t was m e n t i o n e d  spin  c r o s s o v e r phenomenon  in section 8.3 that was u n l i k e l y .  This  the p o s s i b i l i t y of a i s b e c a u s e o n l y one  II  pair of lines  i s observed  i n the Mossbauer spectrum.  In a s p i n  c r o s s o v e r s i t u a t i o n two p a i r s o f l i n e s w o u l d be e x p e c t e d relaxation  rate  between  t h e two s p i n s t a t e s  o n l y one p a i r o f l i n e s w o u l d be o b s e r v e d ; a c c o m p a n i e d by l i n e b r o a d e n i n g  i s very  but t h i s  unless the  rapid, is  then  often  and a s t r o n g t e m p e r a t u r e  dependence  Of AEQ. The is  always  broadening  l i n e width  greater (107).  values  than r . 2  The v a l u e s  given  i n Table  T h i s may i n d i c a t e f o r Fe(CF^SO^)^  8 . 5 a r e l a r g e and magnetic  exchange  a t 293K a r e p o s s i b l y  164  s p u r i o u s a n d c a u s e d by t h e s m a l l this  quadrupole  compound.  The M o s s b a u e r p a r a m e t e r s similar  investigation, fields  o b t a i n e d f o r t h e s e compounds a r e  t o t h o s e o f some i r o n ( I I I )  antiferromagnetic  carboxylate  c o u p l i n g was p r e s e n t  (108).  e s p e c i a l l y a t low temperature  compounds More  i n these  i n which  detailed  and i n a p p l i e d m a g n e t i c  s h o u l d h e l p i n e x a m i n i n g t h e phenomenon o f  exchange  8.5.  i n t e r a c t i o n seen i n  magnetic  compounds.  CONCLUSIONS  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 c l e a r l y show t h a t exchange the metal in  in iron sulfonate  i s i n t h e +3 o x i d a t i o n  s p i t e of the f a c t  exchange  i s p o s s i b l e , p a r t i c u l a r l y where  state.  This  exchange  takes  place  t h a t t h e F e - 0 bonds a r e h i g h l y i o n i c a n d  takes place over  The compounds bidentate  polymers  magnetic  three  contain octahedral  bridging sulfonate  atoms  i n the bridging  high spin i r o n ( I I I )  anions.  ligand. centres  with  165  CHAPTER 9  CONCLUSIONS AND  SUGGESTIONS FOR  The w o r k d e s c r i b e d i n t h i s experimental polymers.  techniques  This  FURTHER STUDY  t h e s i s has u s e d s e v e r a l  to c h a r a c t e r i s e various  iron  c h a p t e r d i s c u s s e s some c o n c l u s i o n s t o be made  f r o m t h i s w o r k and t h e d i r e c t i o n s i n w h i c h f u r t h e r  9.1.  for  iron(II)  by p l a n e s o f  i n d i c a t e the  sulfonates.  sulfonate  ion i s surrounded  (?ee F i g .  1.1.)  The  three  following  Planes of  anions.  l i g a n d s each b r i d g i n g to metal  s t u d y may  general are  sandwiched  The a n i o n s a r e a c t i n g a s  terdentate  different  by o x y g e n atoms  FeOg c h r o m o p h o r e s  i r o n atoms  structural  metal  centres,  and each  from s i x d i f f e r e n t  are not p e r f e c t l y  anions,  octahedral  t h e d i s t o r t i o n w h i c h i s p r e s e n t may be d e f i n e d as f o l l o w s . compression of O-S-0  the  XS03~ a n i o n a l o n g i t s C3 a x i s w i l l  bond a n g l e and w i l l  FeOg o c t a h e d r a iron  take.  CONCLUSIONS These s t u d i e s  model  sulfonate  atoms.  This  B-Fe(CH3S03)2 reported  i s the  increase  elongation  of  C3 axis  p e r p e n d i c u l a r to  the plane  form of  d i s t o r t i o n found  in  and F e ( p - C H 3 C g H 4 S 0 3 ) 2 a n d t h e  the  the of  Fe(CF3S03)2,  previously  Fe(FS03)2. The  situation  along the  result in a trigonal  A  a-form o f  in which,  F e ( C H 3 S 0 3 ) 2 on t h e o t h e r  relative  to  g-Fe(CH3S03)2,  hand,  has a  the CH3S03"  anions  and  166  are elongated along t h e i r of  C 3 axes  resulting in a trigonal  FeCv o c t a h e d r a . 6 There i s a l a c k of evidence  in  Fe(FS03)2,  any  a-forms o f  Fe(FS03)2  X i n c r e a s e s the e x t e n t  increase,  favouring  of  effects.  fluorosulfonates  FeOg o c t a h e d r a ,  i.e.  such m o d i f i c a t i o n s o f other  for  the c o b a l t ( I I )  and C o ( I I ) w h e r e the  For  this  metal  i n the  a-form.  i t may be p o s s i b l e t o  obtain  c o n t a i n i n g X groups  However,  a trigonal  m a g n e t i c moment  and c o p p e r ( I I )  the anion i s  t h i s was  FS03~,  analogues.  CF3S03~  symmetry.  It  i n the c o b a l t ( I I )  not  factors.  In  both  and is possible the  evidence  analogues only  data recorded over a l i m i t e d temperature  Co(CH3S03)2  of  iron(II)  have s i m i l a r s t r u c t u r e s a l t h o u g h  distortion  reason  F e ( C H 3 S 0 3 ) 2 and p o s s i b l y  to CH3-  anions r e t a i n C 3 y  t h e s e compounds  (80-300K).  therefore  i s i n t e r e s t i n g t o c o m p a r e t h e w o r k on  p-CH3CgH4S03~, that  should  X i s p - C H 3 C g H 4 a n d t h i s may be due t o s t e r i c  sulfonates with  of  electronegativity  isolate divalent  M ( X S 0 3 ) 2 compounds  s i m i l a r or lower e l e c t r o n e g a t i v i t y  It  isomerism  absence  the 8-form.  and t r i f l ; u o r o m e t h a n e s u l f o n a t e s  and Z n ( C H 3 S 0 3 ) 2 s u g g e s t s  the c a s e where  As t h e  bond a n g l e s a n d  The e x i s t e n c e o f a - f o r m s o f Co(CH3S03)2  The  S-0 double bonding i n XS03~  may be d i f f i c u l t o r i m p o s s i b l e t o  Fe(II)  any s t r u c t u r a l  a n d F e ( C F 3 S 0 3 ) 2 may be r a t i o n a l i s e d on  l a r g e r O-S-0  t r i g o n a l l y elongated it  for  F e ( C F 3 S 0 3 ) 2 and F e ( p - C H 3 C g H 4 S 0 3 ) 2 .  the b a s i s o f e l e c t r o n e g a t i v i t y of  compression  has an a l m o s t i d e n t i c a l i n f r a r e d  comes  range spectrum  from  167  to  a-FeCCHoSO^-  Hence,  the a n i o n s a r e d i s t o r t e d  a n d i t was s u g g e s t e d t h a t t h i s the  C0O5 c h r o m o p h o r e .  this  need n o t  be t h e  arose from a t e t r a g o n a l  As c a n be s e e n f r o m t h e case and i n d e e d i t  Co(CH3S03)2 contains a t r i g o n a l l y  Copper(II) because of  the  from C 3 y  sulfonates  high d i s t o r t i o n  distortion  p r e s e n t w o r k on  appears as l i k e l y  d i s t o r t e d CoOg  of  Fe(CH3S03)  that  chromophore.  have been s t u d i e d  present  symmetry  before(14)  i n t h e s e compounds  but  arising  Q from a d is  electron configuration  difficult.  It  any c o m p a r i s o n w i t h  was p r e v i o u s l y  contained tetragonally  proposed  that copper(II)  d i s t o r t e d CuOg o c t a h e d r a .  p r e s e n t w o r k t h e d i s t o r t i o n may be a t r i g o n a l o r b o t h w h i c h may a c c o u n t f o r  the  iron(II)  In  sulfonates  sulfonates  view of  the  compression or  complex nature  of  their  elongation  infrared  spectra.  9.2.  SUGGESTIONS FOR  FURTHER WORK  The m e c h a n i s m f o r understood iron(II) only  magnetic exchange  and the a n t i f e r r o m a g n e t i s m  methanesulfonate  because o f  t h e number  exchange w o u l d have t o i o n i c nature  of  i s somewhat  t h e s e compounds.  magnetometer  The  by p e r f o r m i n g  in this  department  is  following  of  not  through which  of: a v i b r a t i n g  will  This  understanding the  fully  forms  but a l s o because of  A fuller  imminent a r r i v a l  i n both  surprising.  b r i d g i n g atoms  be t r a n s m i t t e d  m e c h a n i s m c o u l d be o b t a i n e d  (i)  of  observed  i s not y e t  an the  of  highly the  experiments:  sample  enable magnetic s u s c e p t i b i l i t i e s  168  to  be m e a s u r e d down t o a t e m p e r a t u r e  to observe vicinity Low  the  of  temperature  dependence o f  4.2K.  It  will  sulfonates  s u s c e p t i b i l i t y measurements  would enable b e t t e r  (ii)  Preparation  of  B-FexZn-|_x(CH3S03)2 w i l l  be p e r f o r m e d .  The  effect  of  in  interest the  3-Fe(CH3S03)2.  on t h e o t h e r  crystal-field fits  a range o f  be o f  t h e m a g n e t i c moment i n  t h e m a g n e t i c phase t r a n s i t i o n o b s e r v e d  temperature  formula  of  to  be  iron(II) obtained.  m i x e d compounds o f  general  allow spin d i l u t i o n experiments  t h i s d i l u t i o n may be m o n i t o r e d  by  Mossbauer s p e c t r o s c o p y and l o w - t e m p e r a t u r e  magnetic s u s c e p t i b i l i t y  measurements.  temperature  The  r e s u l t i n g e f f e c t on t h e  p h a s e t r a n s i t i o n may t h e n  (iii) suggest value of future,  that the  at  the  magnetic  the  presented  hyperfine  case of  became  magnetic  a-Fe(CH3S03)2 5.63T the  been a t t a i n e d .  a r e a n t i c i p a t e d by  extensive  Under t h e s e c o n d i t i o n s  a-Fe(CH3S03)2  may become  f i e l d s between the  1.13  region  and 3.38T a t  saturation  In  the  saturated.  F e ( p - C H 3 C g H 4 S 0 3 ) 2 a more d e t a i l e d  w o u l d e n a b l e one t o d e f i n e field  7 for  f i e l d has n o t  helium bath.  f i e l d of  a p p l i e d magnetic  i n Chapter  as l o w as  liquid  the  be a n a l y s e d .  i n an a p p l i e d m a g n e t i c f i e l d o f  internal  In in  4.2K  temperatures  pumping o f internal  Results  of  to  2.4  and  i n which the magnetic  investigation 4.2K hyperfine  saturated.  A-re-examination unsatisfactory  nature  of  of  the  Fe(FS03)2 fit  of  i s d e s i r a b l e i n view of  computed  to experimental  the  spectra  (15).  169  R e s u l t s w e r e o n l y o b t a i n e d i n one m a g n e t i c be e x t e n d e d  field,  and t h i s work  s o d e t a i l e d c o m p a r i s o n s may be made b e t w e e n  the  should  FeCXSOg^  compounds.  For is  still  to  the  be o b t a i n e d ,  susceptibility at  iron(III)  (i) (ii)  low-temperature  information  (<80K)  more i n f o r m a t i o n  M o s s b a u e r s p e c t r a t o be  to  These measurements would a g a i n  be d e d u c e d a b o u t t h e  i n t e r a c t i o n s i n these  nature of  the temperature  Unlike  X i s CF3,  F e ( X S 0 3 ) 3 where  compound e x h i b i t s  be  an  enable  compounds.  spectrum recorded over  range 4.2K  to  CH 3 and p - C H 3 C g H 4 ,  Mossbauer room  the  temperature.  Fe(FS03)3  a f i e l d dependent magnetic s u s c e p t i b i l i t y i n d i c a t i v e  f e r r o m a g n e t i c exchange  field  recorded  magnetic  F e ( F S 0 3 ) 3 s h o u l d a l s o be r e - e x a m i n e d a n d i t s  of  magnetic  l o w e r t h a n 80K i n t h e p r e s e n c e a n d a b s e n c e o f  a p p l i e d magnetic f i e l d .  exchange  e.g.  measurements.,  temperatures  s u l f o n a t e s more d e t a i l e d  (22).  dependence where X i s C F 3 ,  In  view of  CH3,  the absence of  and p - C H 3 C g H 4 t h i s  any  study  should  repeated. The  not y e t  p o s s i b i l i t y of  isomerism i n i r o n ( I I I )  b e e n p u r s u e d a n d t h e s e compounds  and t h e e f f e c t s  s h o u l d be t r e a t e d w i t h  i s o m e r i s m and m a g n e t i c exchange  investigation anions,  ( 109,110)  R9P09",  has D.M.P.  examined.  Other i r o n c o o r d i n a t i o n polymers structural  sulfonates  where  s h o u l d be e x a m i n e d b o t h interactions.  Much  i s t a k i n g place using the weakly b a s i c  R i s an a l k y o r a r y l  group.  These  for  anions  phosphinate  170  exhibit  v a r i o u s modes o f  c h a r a c t e r i s a t i o n of  coordination,  a s e r i e s of  and p r e p a r a t i o n  and  Fe(R2P02)2 compounds may p r o v e  interesting.  (111,112), c o o r d i n a t i n g a b i l i t i e s o f w e a k l y  Previously basic anions, A", tetrakis-  have been examined by t h e c h a r a c t e r i s a t i o n  and b i s p y r i d i n e metal ( I I )  compounds  M ( p y ) 4 A 2 a n d M(py)2A » r e s p e c t i v e l y .  The  2  the  preparation  Fe(py) (XS0 ) 4  3  and c h a r a c t e r i s a t i o n o f and F e C p y ^ X S O . ^ .  2  t h e a n i o n s may be s t u d i e d by t h e thesis  The  techniques  diffraction  measurements  exists for  of  substituted  briding  e s p e c i a l l y i n the  Again  bispyridine  The  b a s e p y r a z i n e may a l s o r e s u l t i n e x t e n d e d  lattices ligand) of  (bridging  o c c u r r i n g through  c o m p l e x e s may a l s o be  p y r a z i n e as w e l l  e x h i b i t i n g s t r o n g magnetic exchange  very weakly  coordinating anions,  e.g.  PFg  variety  base s t r e n g t h s  of  the  magnetic  complexes  the p r o p e r t i e s use o f  sulfonate  varying  X-ray  Using a  3  of  of  this  single crystal  XS0 ~ a n i o n s may be p r e s e n t .  these i r o n  for  compounds,  described in  these m a t e r i a l s .  p y r i d i n e s the e f f e c t s  formula  coordinating a b i l i t y  the p o s s i b i l i t y of  where b i d e n t a t e  general  two s e r i e s o f  in addition,  may be o b s e r v e d ,  the  possibility exists  and,  exchange  of  of  between  on  studied.  polymeric  as the  sulfonate  iron centres.  and A s F g  , may  Use  enable  2+ the  Fe(py)6  c a t i o n t o be i s o l a t e d a n d t h e  t o be c o m p a r e d t o t h e  FeO f i o c t a h e d r a  studied  r e s u l t i n g FeNg here.  octahedra  171  REFERENCES  1.  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