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High-valent fluorides and oxyfluorides. Beaton, Stephen Peter 1966

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\ HIGH-VALENT FLUORIDES AND 0XYFLU0RIDE& by STEPHEN PETER BEATON B.Sc. (Hons.) U n i v e r s i t y of B.C., Vancouver, 1963. A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n the Department of CHEMISTRY We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA September, 1966. In presenting this thesis in p a r t i a l fulfilment of the requirements for an advanced degree at the University of Bri t i s h Columbia, I agree that the Library shall make i t freely available for reference and studyo I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of B r i t i s h Columbia Vancouver 8, Canada The University of British Columbia FACULTY OF GRADUATE STUDIES PROGRAMME OF THE FINAL ORAL EXAMINATION FOR THE DEGREE OF DOCTOR OF PHILOSOPHY of STEPHEN PETER BEATON B.Sc. (Hons.), The University of British Columbia TUESDAY, SEPTEMBER 20, 1966 at 3:30 P.M. IN ROOM 26l, CHEMISTRY BUILDING COMMITTEE IN CHARGE External Examiner: R. S. Hyholm Department of Chemistry University College London Gover Street London, WC1, England 1963 Chairman: Gordon M. Tener N. Bartlctt B. A. Duncll L. D. Hayuard E. Teghtsoonian B. James' N. Paddock C. A. McDowell R. C. Thompson Research Supervisor: N. Bartlett HIGH-VALENT FLUORIDES A11D OXYFLUORIDES ABSTRACT A new compound of iodine (VII), IOF . was pre-pared pure i n bulk quantities by the reaction of IF with IUO or SiO„ followed by the removal of 7 2 2 IF from the resulting IF /IOF mixture with ShF . IOF was characterized by i t s infrared and F n.m.r. 5 spectra, both of which confirmed the expected symmetry for the molecule. Since our studies indi-cated that previous work on IF was carried out with samples containing IOF , IF was reinvestigated, 5 7 19 using F n.m.r. and infrared spectroscopy to estab-l i s h i t s stereochemistry. The infrared spectrum suggested a high symmetry, l i k e l y D,_, , for IF 19 5h 7 while the F n.m.r. spectrum showed that rapid intramolecular rearrangement occurred in the l i q u i d phase. Vapour pressure-temperature data were obtained for both UT and IOF ; these suggested that neither 7 5 IF nor IOF was associated i n the li q u i d or solid 7 5 states. Some comments have been made on the acid-base behaviour of IF„ and IOF . IOF shows no ten-7 5 5 dency to act as either a fluoride ion donor or acceptor, but IF i n addition to acting as a donor to AsF and SbF may show acceptor properties, 5 5, previously unrecorded. X The acid-base adduct IF .AsF was charac-7 5 terized by i t s structure, determined from X=ray powder data ; and infrared spectrum as the ionic salt, IFgAsF^, The results of magnetic measurements on XeF^ have been presented and have been suggested to be inconsistent with the hypothesis that XeFg is a molecule with a non-octahedral ground state and a low-lying t r i p l e t state. The reactions of ONF with the third tran-sition series hexafluorides, and with ReF^, ReOF,. and OsOF^ w e r e studied, along with the reactions of NO with ReF , ReOF and ReF.. I 5 o The results confirmed the trend of increasing oxidizing power across the series from tungsten to platinum, established previously i n these laboratories. The decreasing tendency to form higher coordinate anions and the variation in anion sizes across the series has been noted, and these have been shown to be consistent with the trend of oxidizing power. The reaction of ONF with IrF. and PtF^ has 6 o provided the f i r s t example of a fluorine e l i -mination reaction: ONF + MF,—»-N0MF 6 + F 2(+ ONF-,). The existence of fluorine as a reaction product was conclusively proven and comments on the mechanism of the reaction have been made. The OMT-PtFg reaction also provided the f i r s t synthetic route to the preparation of pure NO^PtF^. Infrared spectro-scopic, magnetic susceptibility, and X-ray powder data have been given for this salt. The experimental evidence i s consistent with the formulation of the compound as a derivative of platinum (v). The magnetic data for HOPtFg, along with the data for 02PtF£, has been used to derive magnetic moments for + + the dioxygenyl cation, 02- The volumes of the 0 2 + and HO cations have been compared. GRADUATE STUDIES Field of Study: Inorganic Chemistry Topics i n Physical Chemistry A. V. Bree J. A. R. Coope Seminar in Chemistry N.. Bartlett Topics in Inorganic Chemistry If. Bartlett R. C. Thompson Advanced Inorganic Chemistry H. C. Clark W. R. Cullen Crystal Structures S. A. Melzak J. Trotter Inorganic Reaction Mechanisms B. R. James G. B. Porter Topics i n Organic Chemistry J. P. Kutney D. E. McGreer PUBLICATIONS N. Bartlett, S.P. Beaton and N.K. Jha, "Oxidizing Trends in the Third-transition-series Hexafluorides", Chem. Comm., 1966, 168 IT. Bartlett and S.P. Beaton, "TTitrosyl Hexafluoroplatinate (v), ITO Preparation and Magnetic Susceptibility. Tiie Magnetic Susceptibility of 0*", Chem. Comm., 1966, 167. H. Bartlett, S. Beaton, L. U. Reeves, and E. J. Wells, N.M.R. Spectra of Heptavalent Fluorides and Oxide Pentafluorides", Can. J. Chem. k2, 2531 (1961+) STEPHEN PETER BEATON. HIGH-VALENT FLUORIDES AND OXYFLUORIDES. Supervisor: Dr. N. Bartlett. i ABSTRACT A new compound of i o d i n e ( V I I ) , IOF 5, was prepared pure i n bulk q u a n t i t i e s by the r e a c t i o n of IF- w i t h or SiOg f o l l o w e d by the removal of IF- from the r e s u l t i n g IF7/IOF5 mixture w i t h SbFg. was c h a r a c t e r i z e d by i t s i n f r a r e d and -^F n.m.r. s p e c t r a , both of which confirmed the expected C^ y symmetry f o r the molecule. Since our s t u d i e s i n d i c a t e d t h a t p r e v i o u s work on IF- was c a r r i e d out w i t h samples c o n t a i n i n g 19 IOF5, IF- was r e i n v e s t i g a t e d , u s i n g F n.m.r. and i n f r a r e d s pectroscopy to e s t a b l i s h i t s s t e r e o c h e m i s t r y . The i n f r a r e d spectrum suggested a h i g h symmetry, l i k e l y Dg h, f o r IF- w h i l e 19 the F n.m.r. spectrum showed that r a p i d i n t r a m o l e c u l a r r e -arrangement o c c u r r e d i n the l i q u i d phase. Vapour p r e s s u r e -temperature data and d e r i v e d thermodynamic data were obtained f o r both IF- and IOFgj these suggested that n e i t h e r IF- nor IOFg was a s s o c i a t e d i n the l i q u i d or s o l i d s t a t e s . Some comments have been made on the a c i d - b a s e behaviour of IF- and IOF^. 10*"^ shows no tendency to a c t as e i t h e r a f l u o r i d e i o n donor or accep'tor, but IF-, i n a d d i t i o n t o a c t i n g as a donor to AsF^ and SbFg, may show ac c e p t o r p r o p e r t i e s , p r e v i o u s l y unrecorded. The a c i d - b a s e adduct IFy'AsFg was c h a r a c t e r i z e d by i t s s t r u c t u r e , determined from X-ray powder data, and i n f r a r e d spec-*, trum as the i o n i c s a l t , IFg+AsFg". The r e s u l t s of magnetic measurements on XeFg have been presented and have been suggested to be i n c o n s i s t e n t w i t h the h y p o t h e s i s that XeFg i s a molecule w i t h a non-octahedral ground s t a t e and a l o w - l y i n g t r i p l e t s t a t e . i i The r e a c t i o n s of ONF w i t h the t h i r d t r a n s i t i o n s e r i e s h e x a f l u o r i d e s , and w i t h ReF_, ReOFg and OsOFg were s t u d i e d , a l o n g w i t h the r e a c t i o n s of NO w i t h ReYj, ReOF5 and ReFg. The r e s u l t s confirmed the t r e n d of i n c r e a s i n g o x i d i z i n g power a c r o s s the s e r i e s from tungsten to platinum, e s t a b l i s h e d p r e v i o u s l y i n t h e s e l a b o r a t o r i e s . The d e c r e a s i n g tendency to form higher c o o r d i n a t e anions and the v a r i a t i o n i n anion s i z e s a c r o s s the s e r i e s has been noted, and these have been shown to be c o n s i s t e n t w i t h the t r e n d of o x i d i z i n g power. The r e a c t i o n of ONF w i t h I r F g and P t F g has pr o v i d e d the f i r s t example of a f l u o r i n e e l i m i n a t i o n r e a c t i o n : ONF + MF g —+» NOMFg + Fg(+ ONF3). The e x i s t e n c e of f l u o r i n e as a r e a c t i o n product was c o n c l u s i v e l y proven and comments on the mechanism of the r e a c t i o n have been made. The ONF-PtF g r e a c t i o n a l s o p r o v i d e d the f i r s t s y n t h e t i c r o u t e to the p r e p a r a t i o n of pure N0 +PtF g~. I n f r a r e d s p e c t r o s c o p i c , magnetic s u s c e p t i b i l i t y , and X-ray powder data have been g i v e n f o r t h i s s a l t . The experimental evidence i s c o n s i s t e n t w i t h the f o r m u l a t i o n of the compound as a d e r i v a t i v e of p l a t i n u m ( V ) . The magnetic data f o r NOPtFg, along w i t h the data f o r 02PtFg, has been used to d e r i v e magnetic moments f o r the d i o x y g e n y l c a t i o n , Og"1". The volumes of the 02+ and N0+ c a t i o n s have been compared. ( i i i ) TABLE OF CONTENTS Page A b s t r a c t i Table of Contents i i i L i s t of• Tat»0iesw_ v i i L i s t of F i g u r e s i x Acknowledgements x i CHAPTER I GENERAL INTRODUCTION 1 II GENERAL EXPERIMENTAL TECHNIQUES 6 1. Vacuum Systems and P a r t s . Apparatus 6 1.1 General Comments 6 1.2 M a t e r i a l s of C o n s t r u c t i o n 7 1.3 Apparatus u s e d t o C o n s t r u c t Vacuum Systems 8 i 1.4 Valves 10 1.5 General Purpose Vacuum L i n e Fume Hoods 13 1.6 Vacuum L i n e f o r the F l u o r i n e Supply 15 2. P r e s s u r e Measurement 2.1 The M o d i f i e d Booth-Cromer Pressure i T r a n s m i t t e r 18 2.2 H e l i c o r d Gauge 21 2.3 Crosby High Pressure Gauge 21 2.4 Thermocouple and I o n i z a t i o n Gauges 21 3. Experimental Techniques 23 3.1 I n f r a r e d Spectroscopy 23 3.2 X-Ray Powder Photography 26 3.3 T e n s i m e t r i c T i t r a t i o n of Gases 27 3.4 Measurement of Magnetic S u s c e p t i b i l i t i e s 29 3.5 A n a l y t i c a l and P u r i f i c a t i o n Techniques 32 iv. l> CHAPTER Page I I I THE HEPTA- AND OXYPENTAFLUORIDES OF IODINE AND RHENIUM. MAGNETIC MEASUREMENTS ON XeF g I I n t r o d u c t i o n 34 1.1 Survey of the L i t e r a t u r e Work 34 1.2 A c i d s and Bases i n F l u o r i d e Systems 36 II Experimental 2.1 P r e p a r a t i v e Methods 40 2.2 I n f r a r e d S p e c t r o s c o p i c S t u d i e s 48 2.3 The U l t r a v i o l e t Spectra of IF- and IOF 5 53 19 2.4 F Nuclear Magnetic Resonance Spectroscopy 56 2.5 Vapour Pressure Measurements 62 2.6 The Acid-Base P r o p e r t i e s of IF- 67 2.7 The Acid-Base P r o p e r t i e s of I0F5 70 2 . 8 The Acid-Base P r o p e r t i e s of ReF 7 and ReOF5 71 2.9 The Re a c t i o n of ONF w i t h I F 5 71 2.10 Magnetic Measurements on XeFg 72 I I I D i s c u s s i o n 3.1 I n f r a r e d and U l t r a v i o l e t S p e c t r o s c o p i c S t u d i e s 74 19 3.2 F n.m.r. Spectra of Heptavalent F l u o r i d e s and OxypentafluoritlSs 85 3.3 The Shape of the IF- Molecule and Ligand I n t e r c o n v e r s i o n , 92 3.4 Vapour Pressure Data f o r IF- and IOFc. 93 A s s o c i a t i o n i n the Ligand and S o l i d States,. h 3.5 The Acid-Base P r o p e r t i e s of IFy and IOF5 96 3.6 The Rea c t i o n of ONF wit h I F 5 1 99 3.7 Magnetic R e s u l t s on XeFg. The Shape of 99 the XeFg Molecule V CHAPTER Page IV THE CHARACTERIZATION OF I F 6 + A s F g ~ . THE CRYSTAL STRUCTURE FROM POWDER DATA I I n t r o d u c t i o n 102 II Experimental 104 2.1 P r e p a r a t i o n of the Adduct 104 2.2 The I n f r a r e d Spectrum of I F g + A s F 6 ~ 105 2.3 X-Ray Powder Photographs of IFg +AsFg~ 107 * . I l l R e s u l t s 3.1 The Arrangement of the Iodine and A r s e n i c Atoms 110 3.2 The Use of I n t e n s i t y Data i n the L o c a t i o n of the F l u o r i n e Atoms 112 3.3 The Sj>ace Group of IFy.AsFc. Placement of F l u o r i n e Atoms i n Uni t C e l l 113 3.4 The Method of A t t a c k Using X-ray Powder Data 115 3.5 Application of the T r i a l - a n d - E r r o r Method to IFg AsFg". Values of F l u o r i n e C o o r d i n a t e s 117 IV D i s c u s s i o n 4.1 The I n f r a r e d Spectrum of IFg +AsFg~ 123 4.2 The S t r u c t u r e of IFg +AsFg~ 126 ' V THE REACTIONS OF THIRD TRANSITION SERIES HEXAFLTJO-: > RIDES AND OXYPENTAFLUORIDES, AND OF ReF ? WITH NO AND ONF I I n t r o d u c t i o n 129 1.1 The Chemical P r e p a r a t i o n of F l u o r i n e 129 1.2 Evidence f o r Seven and E i g h t C o o r d i n a t i o n i n T r a n s i t i o n Metals. 131 VI CHAPTER Page II Experimental 133 2.1 P r e p a r a t i o n of S t a r t i n g M a t e r i a l s 133 2.2 The Reactions of NO and ONF w i t h MO xF y 138 I I I D i s c u s s i o n 3.1 O x i d i z i n g P r o p e r t i e s of the H e x a f l u o r i d e s and R e l a t e d Species 164 3.2 The O x i d a t i o n of ONF by I r F and P t F g : A F l u o r i n e L i b e r a t i o n R e a c t i o n 170 3.3 The V a r i a t i o n i n Anion S i z e s of the N0 + S a l t s 174 3.4 A R a t i o n a l e of the V a r i a t i o n i n N0M0 xF y P r o p e r t i e s 182 3.5 V a r i a t i o n i n the C o o r d i n a t i o n Numbers of the Complex Ions 187 VI THE PREPARATION AND CHARACTERIZATION OF N0 +PtFg~. THE MAGNETIC SUSCEPTIBILITY OF 0 2 + I Experimental 193 1.1 P r e p a r a t i o n of the S a l t s . X-Ray Powder Photographs 193 1.2 The I n f r a r e d Spectrum of NOPtFg 195 1.3 Magnetic S u s c e p t i b i l i t y S t u d i e s on NOPtFg and 0 2 P t F g 198 II R e s u l t s - A n a l y s i s of the S u s c e p t i b i l i t y Data 198 I I I D i s c u s s i o n 3.1 The NOPtFg S t r u c t u r e . R e l a t i v e Volumes of N0+ and 0 2 + 203 3.2 The I n f r a r e d Spectrum of NOPtFg. \>3 Frequency of P t F g - 204 3.3 The Magnetic Moments of NOPtFg and 0 2 + 207 APPENDIX I 209 II 217 REFERENCES- 220 v i i LIST OF TABLES TABLE Page 1 1 9 F Chemical S h i f t s and Couplings 58 2 Vapour Pressure Data f o r IF- 65 3 Vapour P r e s s u r e Data f o r IOFg 66 4 I n f r a r e d Data and Assignments, IFy(g) 75 5 I n f r a r e d Data and Assignment, IOFg(g) 80 6 I n f r a r e d Data and Assignments, ReOFg(g) 84 7. Some P h y s i c a l Data f o r IF- and I0F_, and R e l a t e d Species 94 8 T e n s i m e t r i c R e s u l t s , IF- + AsFg R e a c t i o n 105 9 X-Ray Powder Data f o r IFg +AsFg~ 108 10 IFg +AsFg~ S t r u c t u r e D etermination. £ A as a F u n c t i o n of Bondlengths 118 11 C r y s t a l l o g r a p h i c Data f o r IFg+AsFg - 120 12 Observed and C a l c u l a t e d R e l a t i v e I n t e n s i t i e s f o r IFg+AsFg" 122 13 Table 13 I n f r a r e d Assignments f o r IFg+AsFg" 123 14 Comparison of Frequencies f o r Some CMFg] Species 125 15 M-F Bond D i s t a n c e s i n I s o e l e c t r o n i c MFg . Species (X) 127 16 Intense Fundamental A b s o r p t i o n s of ReFg, ReF-and ReOF5 136 17 T e n s i m e t r i c Data f o r NO and ONF Reactions 139 18 X-Ray Powder Data f o r NOWF- and NOOsF- 144 19 X-Ray Powder Data f o r (N0) 2WFg and (NO) 2ReF 8 145 20 X-Ray Powder Data f o r NOReOF. 148 6 21 G r a v i m e t r i c Data f o r the ONF + PtFg Reaction. 157 22 X-Ray Powddr Data f o r N0ReF c and NOPtFg 159 V I 1 1 TABLE Page 23 X-Ray Powder Data f o r NOOsOF 5 and NOReOFg 162 24 Estimated E l e c t r o n A f f i n i t i e s of the H e x a f l u o r -i d e s 169 25 R e s u l t s f o r the ONF + PtFg R e a c t i o n 172 26 B r a v a i S f L a t t i c e Parameters and E f f e c t i v e M o l e c u l a r Volumes, N0 + S a l t s 175 27 E f f e c t i v e M o l e c u l a r Volumes, ;NOMFx and MF g, A*3 180 28 Higher Coordinate Anions of the T h i r d T r a n s i t i o n S e r i e s Metaals 188 29 A n a l y t i c a l R e s u l t s f o r NOPtFg 194 30 S u s c e p t i b i l i t i e s f o r NOPtFg and 0 2 P t F g from 77°K t o 300°K 200 31 Molar S u s c e p t i b i l i t y Data f o r 0 Q P t F f i , NOPtF c, and 0 2 + 6 202 32 E f f e c t i v e M o l e c u l a r Volumes of NOPtFg and 02P.tE3 204 33 V 3 and \>± Frequencies of P t F g ~ x 205 i x LIST OF FIGURES FIGURE Page 1 K e l - F Trap and Adapter 11 2 General Purpose Vacuum L i n e 14 3 A Vacuum L i n e f o r a F l u o r i n e Supply 17 4 The Diaphragm Gauge 19 5 I n f r a r e d Gas C e l l 24 6 Flow Apparatus f o r the P r e p a r a t i o n of ReOFg 46 7 I n f r a r e d Spectrum of I F 7 ( g a s ) 50 8 I n f r a r e d Spectrum of I 0 F 5 ( g a s ) 51 9 I n f r a r e d Spectrum of ReOF 5(gas) 52 10 The U l t r a v i o l e t Spectrum of I F 7 54 11 The U l t r a v i o l e t Spectrum of I 0 F 5 55 1 Q 12-a F Spectra of I F ? at 40 Mc/s 59 12- b 1 9 F Spe c t r a of I 0 F 5 at 56.4 Mc/s 60 13- a I n f r a r e d Spectra of T e F g , IOF 5, and IFy 77 13-o I n f r a r e d Spectra of I 0 F 5 , ReOFg, and OsOF 5 82 19 14 Schematic Diagram of 56.4 Mc/s F Spectra 88 15 I n f r a r e d Spectrum of IFg+AsFg" 106 16 Schematic R e p r e s e n t a t i o n of the IF + A s F ~ X-Ray Powder Photograph 111 17 The U n i t C e l l of I F 6 + A s F 6 ~ 114 18 Comparison of Log X vs S i n 2 Q P l o t s 121 19 P o s s i b l e U n i t C e l l of N0MoF 5 178 20 P l o t s of E f f e c t i v e M o l e c u l a r Volume i s M- 180 21 Bonding i n a Metal H e x a f l u o r i d e 183 22 Schematic R e p r e s e n t a t i o n of t 9 O r b i t a l s 183 X FIGURE Page 23 I n f r a r e d Spectrum of NO +PtFg~ 196 24 1 / X M vs T P l o t s , N O +PtF 6~ and 0 2 + P t F 6 ~ 199 25 A e f f V S T f ° r N 0 + p t F 6 ~ 199 x i ACKNOWLEDGEMENTS I would l i k e to thank Dr. N. B a r t l e t t f o r h i s encouragement and guidance throughout the course of t h i s t h e s i s and f o r many s t i m u l a t i n g d i s c u s s i o n s . I would a l s o l i k e t o thank my c o l l e a g u e , Mr. J . Passmore, f o r p e r m i t t i n g me t o quote some of h i s r e s u l t s and my t y p i s t , Miss L y n e t t e L i u , f o r t y p i n g my manuscript i n a s h o r t p e r i o d of time. I am g r a t e f u l to Mr. ,Emil Matter, of the workshop of the chemistry department, not only f o r b u i l d i n g most of the metal apparatus d e s c r i b e d i n t h i s work, but a l s o f o r g i v i n g u s e f u l s u g g e s t i o n s to the d e s i g n of much of i t . F i n a l l y , I thank the N a t i o n a l Research C o u n c i l of Canada f o r the Award of a bursary (1963-64) and a s t u d e n t s h i p (1964-66). 1 CHAPTER I GENERAL INTRODUCTION The content of the g e n e r a l i n t r o d u c t i o n w i l l be l i m i t e d mainly to a d i s c u s s i o n of the p o i n t s which i n d i c a t e why the var-ious p r o j e c t s d e s c r i b e d i n t h i s t h e s i s were i n i t i a t e d . B r i e f reviews of the p e r t i n e n t l i t e r a t u r e and other background m a t e r i a l necessary to the development of the d i s c u s s i o n s i n the v a r i o u s chapters w i l l be presented i n the chapter i n t r o d u c t i o n s . The high r e a c t i v i t y of f l u o r i n e and i t s a b i l i t y to e x c i t e h i g h o x i d a t i o n s t a t e s i n the compounds i t forms are two of the " c h a r a c t e r i s t i c f e a t u r e s of i t s chemistry. It combines d i r e c t -l y or at e l e v a t e d temperatures w i t h a l l of the elements except He, Ne, Ar, Kr, N 2 and 0 2 , i n r e a c t i o n s which are o f t e n extremely 1 2 3 e x o t h e r m i c . ( F l u o r i d e s of Kr , N and 0 are known, but they have never been i s o l a t e d v i a the thermal r e a c t i o n of the elements;) The r e c e n t preparation'* of f l u o r i d e s of Xe, Kr and Rn i s perhaps the most s p e c t a c u l a r demonstration of f l u o r i n e ' s r e a c t i v i t y and o x i d i z i n g power; only oxygen can r i v a l f l u o r i n e i n a b i l i t y t o 5 e x c i t e high o x i d a t i o n s t a t e s . These p r o p e r t i e s are a well-known 6 7 consequence of the low bond d i s s o c i a t i o n energy ' , high e l e c t r o -5 8 ^ n e g a t i v i t y , s m a l l s i z e , and high bond formation energy of f l u o r i n e . T h i s t h e s i s i s concerned w i t h the p r e p a r a t i o n and chemical and p h y s i c a l p r o p e r t i e s of some of the compounds formed by f l u o r i n e , i n which an element i s e x c i t e d to the +6 or +7 o x i -d a t i o n s t a t e . Work which has been done on the h e x a f l u o r i d e s of 2 W, Re, Os, I r and Pt; the compounds ReOF^, OsOF 5 and ReFy; and the i o d i n e compounds IF7 and IOF5 w i l l be d i s c u s s e d . Some i n -v e s t i g a t i o n s were a l s o c a r r i e d out on XeFg and XeOF^, but s i n c e the experimental work i n t h i s area i s incomplete, few of the r e -s u l t s o btained w i l l be presented. 9,10 Jha and B a r t l e t t ' s s t u d i e s on OsOFg and t h e i r demonstration that t h i s molecule had the expected C^ y symmetry l e d t o an i n t e r e s t i n the p r e p a r a t i o n and c h a r a c t e r i z a t i o n of 11 12 other s p e c i e s of the type AOFg. As i d e from ReF- , I F 7 i s the only known MF- s p e c i e s , and B a r t l e t t reasoned that the prepara-t i o n of the IOFg from the h e p t a f l u o r i d e should be f e a s i b l e . 13 (ReOF5 was a known s p e c i e s . ) The a t t a c k of the h e p t a f l u o r i d e on g l a s s wool, or i t s r e a c t i o n w i t h water l e d to the f i r s t p re-14 p a r a t i o n of pure IOFg by B a r t l e t t and Levchuk. Independent r e p o r t s " ^ ' ^ on the e x i s t e n c e of lOF^ appeared n e a r l y s i m u l t a n -eously w i t h B a r t l e t t and Levchuk's announcement, the new compound 19 being i d e n t i f i e d i n samples of I F ? used i n F n.m.r. s t u d i e s . P r i o r to the d i s c o v e r y of IOF5 and OsOF^, the onl y 17 known oxide p e n t a f l u o r i d e was ReOF 5 . Aynsley, Peacock, and Robinson had prepared the compound by p a s s i n g f l u o r i n e over Re02 or KReO^. ReOF5 was c h a r a c t e r i z e d as a v o l a t i l e yellow s o l i d . (m.pt. 35°C, b.pt. 55°C) F u r t h e r c h a r a c t e r i z a t i o n of the com-18 pound was l i m i t e d to the vapour pr e s s u r e s t u d i e s of Cady and Hargreaves. An i n v e s t i g a t i o n of these two compounds, i n p a r t i c u l a r 19 of t h e i r F n.m.r. and i n f r a r e d s p e c t r a , forms p a r t of t h i s t h e s i s . The parent compound used to make IOF p., namely IFy, has i t s e l f not been e x t e n s i v e l y s t u d i e d . It was f i r s t prepared i n 12 1930 by Ruff and Keim , by the f l u o r i n a t i o n of IF^. Scnumb and 19 Lynch m o d i f i e d the o r i g i n a l p r e p a r a t i v e method and b r i e f l y i n -v e s t i g a t e d the f l u o r i n a t i n g p r o p e r t i e s of IFy on s e v e r a l c h l o r o -f l u o r o c a r b o n s . Samples of IFy s u p p l i e d by the l a t t e r workers 2 0 were used i n i n f r a r e d s t u d i e s by Lord et a l . , e l e c t r o n d i f f r a c -21 19 t i o n s t u d i e s by La V i l l a and Bauer, and F n.m.r. s p e c t r o s c o p i c 22 s t u d i e s by Gutowsky and Hoffman. The i n f r a r e d and e l e c t r o n d i f f r a c t i o n data were b e l i e v e d to be c o n s i s t e n t w i t h symmetry f o r IFyj the n.m.r. r e s u l t s were thought to i n d i c a t e s t r u c t u r a l l y nonequivalent f l u o r i n e l i g a n d s . However, our i n f r a r e d r e s u l t s on IOFg (and IFy) showed that IF^ samples used by Lord et a l . were very badly contaminated w i t h IOFg and that t h e i r assignments were i n e r r o r because of t h i s . (See chapter I I I , s e c t i o n 3.1.) The data of La V i l l a and Bauer and Gutowsky and Hoffman c e r t a i n l y r e q u i r e d c o n f i r m a t i o n i n view of the p o s s i b l e contamination of t h e i r I F ^ samples w i t h IOFg. IF^ has been the s u b j e c t of only 23 24 one s i n g l e - c r y s t a l X-ray i n v e s t i g a t i o n ' , and t h e r e has been . ... . . , 23-25 , ,26-28 much c o n t r o v e r s y over where t h i s data does or does not d i s p r o v e a symmetry f o r the molecule i n the s o l i d s t a t e . The d i s c o v e r y of the xenon f l u o r i d e s and, i n p a r t i c u l a r , the q u e s t i o n of whether or not the nonbonding e l e c t r o n p a i r of X e F g was s t e r i c l y a c t i v e l e d to renewed i n t e r e s t i n the shape of the IFy molecule. If XeFg has a s t e r i c l y a c t i v e lone p a i r , i t would be e f f e c t i v e l y h e p t a - c o o r d i n a t e , and some i n s i g h t i n t o i t s s t e r e o c h e m i s t r y might be gained from a study of IFy. E l u c i -d a t i o n of the shape of IF7 i s i n t e r e s t i n g i n i t s own r i g h t , of course; i t seems to be a c l e a r e x c e p t i o n t o the type of three 29 c e n t r e bonding scheme developed by Rundle and used, f o r example, 30 to e x p l a i n bonding i n the xenon f l u o r i d e s and i n t e r h a l o g e n 31 anions In view of the i n t e r e s t i n the s t r u c t u r e of IF-, and i n view of the u n c e r t a i n t y and co n t r o v e r s y surrounding much of the e a r l i e r work, an i n v e s t i g a t i o n of t h i s molecule was c a r r i e d out i n c o n j u n c t i o n w i t h our s t u d i e s on IOF_. 5 As p a r t of a c o n t i n u i n g program i n t h i s l a b o r a t o r y on the o x i d i z i n g p r o p e r t i e s of the h e x a f l u o r i d e s , the r e a c t i o n of ONF w i t h the h e x a f l u o r i d e s of W, Re, Os, Ir and Pt, and wi t h ReF^, ReOFg and OsOF^, was s t u d i e d . Our o r i g i n a l i n t e n t i o n was to prepare a s e r i e s of NOMF- s a l t s and compare the t r e n d i n MF_ - 9 32 volumes t o the trend s found f o r MFg ' i n the NOMFg s a l t s . However, the r e a c t i o n s proved to be more complicated and c o n s i d e r -a b l y more i n t e r e s t i n g than f i r s t a n t i c i p a t e d , and the study and d i s c u s s i o n of these r e a c t i o n s forms another p a r t of t h i s t h e s i s . The r e a c t i o n s between NO and ReFg, ReFy and ReOF 5 are a l s o i n c l u d -9 32 ed; these complete the i n i t i a l s t u d i e s ' on the r e a c t i o n of NO with MO xF v s p e c i e s . 33 34 The p r e p a r a t i o n ' of 0 2 P t F g by B a r t l e t t and Lohmann and i t s c h a r a c t e r i z a t i o n as the s a l t 0 2 + P t F g - had f i r s t demonstra-ted the powerful o x i d i z i n g p r o p e r t i e s of PtFg. The c h a r a c t e r i z a -t i o n had i n c l u d e d s u s c e p t i b i l i t y s t u d i e s and, assuming a s p i n only value of 1.73 B.M. f o r PtFg" ( t 2 g 5 ) i n 0 2 P t F g , B a r t l e t t p o i n t e d out that 0 g + appeared to show magnetic behaviour s i m i l a r 5 to i s o - e l e c t r o n i c NO(g). To o b t a i n experimental data f o r the 9 magnetic behaviour of PtF~ , Jha attempted , u n s u c c e s s f u l l y , to b prepare samples of pure NO +PtFg~ f o r s u s c e p t i b i l i t y s t u d i e s . T h i s s a l t i s isomorphous w i t h C>2+PtFg~ and c o n t a i n s a diamagnetic c a t i o n . Hence, i t can be used to o b t a i n a measure of the suscept-i b i l i t y of P t F g ~ i n 0 2 P t F g . A r e a c t i o n was d i s c o v e r e d i n t h i s work which l e d to the formation of pure NOPtFg i n bulk q u a n t i t i e s . The remeasured s u s c e p t i b i l i t y of OgPtFg and the c h a r a c t e r i z a t i o n of NOPtFg form another p a r t of t h i s t h e s i s . 6 CHAPTER II GENERAL EXPERIMENTAL TECHNIQUES 1 VACUUM SYSTEMS AND PARTS. APPARATUS. 1.1 GENERAL COMMENTS: Since most of the compounds used and prepared i n the course of t h i s work were moisture s e n s i t i v e , they c o u l d only be handled i n a vacuum system or, i f i n v o l a t i l e , i n the moisture-f r e e atmosphere of a drybox. 1.1.1 A t t a i n a b l e vacuum -3 For r o u t i n e work, a vacuum of 5x10 mm c o u l d be ob-t a i n e d i n a metal vacuum system of the type d e s c r i b e d i n s e c t i o n 1.4, without d i f f i c u l t y . A vacuum of t h i s magnitude was p e r f e c t l y s a t i s f a c t o r y f o r most work c a r r i e d out i n these l a b o r a t o r i e s . _4 For i s o l a t e d experiments, an u l t i m a t e vacuum of 5x10 mm co u l d be obtained i f extreme care and p a t i e n c e were used i n assembling the apparatus. A leak g r e a t e r than 5 mm i n an e i g h t hour p e r i o d i n any p a r t of the vacuum system was regarded as u n s a t i s f a c t o r y . Under r o u t i n e o p e r a t i n g c o n d i t i o n s , l e a k s of l e s s than 3-4 mm i n e i g h t hours were r o u t i n e . 1.1.2 Drybox The drybox used f o r almost a l l of the experiments d e s c r i b e d i n t h i s t h e s i s was a Vacuum Atmospheres C o r p o r a t i o n Model HE-43-2 Dri-Lab w i t h a Model HE93-B D r i - T r a i n . N i t r o g e n 7 was used as the i n e r t atmosphere, and the D r i - T r a i n p r o v i d e d f o r the removal of t r a c e s of oxygen as w e l l as mpisture from the n i t r o g e n , i f d e s i r e d . The D r i - T r a i n maintained the moisture content i n the Dri-Lab at <v 1 ppm. In a few experiments, s o l i d m a t e r i a l s were handled i n a Towers glove box, f l u s h e d w i t h n i t r o g e n d r i e d by ^2^5' 1.2 MATERIALS OF CONSTRUCTION To permit r o u t i n e h a n d l i n g of m a t e r i a l s at pr e s s u r e s g r e a t e r than two or three atmospheres, and to overcome the pro-blems a s s o c i a t e d w i t h the a t t a c k of r e a c t i v e f l u o r i d e s on the g l a s s and grease of a c o n v e n t i o n a l vacuum system, systems were c o n s t r u c t e d of metal, l a r g e l y monel. Monel, a n i c k e l - c o p p e r a l l o y , was p a s s i v a t e d to a t t a c k by f l u o r i n e and f l u o r i d e s by the formation of an impervious l a y e r of NiF„ on exposed metal s u r -f a c e s . The formation of CF^, a problem with s t a i n l e s s s t e e l , was avoided by u s i n g monel wherever p o s s i b l e . Copper t u b i n g ( J " O.D.) was used to make connections when f l e x i b i l i t y i n a l e n g t h of t u b i n g was r e q u i r e d . L i k e monel, copper i s p a s s i v a t e d by the form a t i o n of an i n e r t f l u o r i d e l a y e r . (CuF 2) Valves, and unions used to connect p i e c e s of metal t u b i n g were made of monel, s t a i n l e s s s t e e l , or b r a s s . 8 1.3 APPARATUS USED TO CONSTRUCT VACUUM SYSTEMS 1.3.1 Tubing Tubing connecting v a l v e s , p r e s s u r e measuring d e v i c e s , and c o n t a i n e r s on the vacuum system was O.D., 1/32" w a l l t h i c k n e s s monel t u b i n g , (except f o r the l i n e s i n the high pressure f l u o r i n e system - see s e c t i o n 1.6) Copper t u b i n g of the same s p e c i f i c a t i o n s was used to make f l e x i b l e c o n n ections. 1.3.2 Socket Weld F i t t i n g s and Compression F i t t i n g s P i e c e s of t u b i n g were connected together u s i n g e i t h e r socket weld f i t t i n g s or compression f i t t i n g s , both a v a i l a b l e form of s t r a i g h t unions, tees and c r o s s e s . (Swagelok and Cajon f i t t i n g s ) Tubing was s i l v e r - s o l d e r e d i n t o the seat of socket weld f i t t i n g s and such connectors were t h e r e f o r e u s e f u l where r e l i a b l y l e a k - t i g h t j o i n t s were needed, and where the d i f f i c u l t y of d i s a s s e m b l i n g s o l d e r e d j o i n t s was not a problem. Socket weld connectors were thus used on p a r t s of the vacuum system which were more or l e s s permanently mounted. Tubing was held i n the seat of compression f i t t i n g s by means of a cone-shaped t e f l o n f e r r u l e which was h e l d snugly a g a i n s t the outer w a l l of the t u b i n g and a g a i n s t the tapered i n n e r w a l l s of the compression f i t t i n g by a nut screwing onto the body of the compression f i t t i n g . A l e a k - t i g h t s e a l was e f f e c t e d by t i g h t e n i n g the nut f i n g e r - t i g h t . These f i t t i n g s were very u s e f u l i n p a r t s of the vacuum system wich r e q u i r e d frequent disassembly. Compression f i t t i n g s sometimes leaked s l i g h t l y , p a r t i c u l a r l y when s t r a i n was imposed on the j o i n t . 9 In f a c t , p e r i o d i c disassembly (~ every three months) of p a r t s of the system c o n t a i n i n g compression f i t t i n g s was r e q u i r e d t o maintain adequate vacuum c o n d i t i o n s . 1.3.3 G l a s s - M e t a l Connections The c o n n e c t i o n between g l a s s and metal p a r t s of the vacuum system was made by d r i l l i n g out the seat of a compression f i t t i n g s l i g h t l y , so that 7 mm g l a s s t u b i n g c o u l d be f i t t e d i n t o the s e a t , which was designed by the manufacturer t o r e c e i v e t u b i n g of |" O.D. c :"; . 1.3.4 Metal C o n t a i n e r s Monel metal c o n t a i n e r s f o r h a n d l i n g and s t o r i n g v o l a t i l e compounds were made from monel metal pipe and sheets, (both turned down to 1/32" t h i c k n e s s from 1/8") top and bottom p l a t e s b e i ng welded to a c y l i n d r i c a l l e n g t h of pi p e , w i t h a le n g t h of 1 , 1 monel t u b i n g welded i n t o a s u i t a b l e opening on the top p l a t e . C o n t a i n e r s capable of w i t h s t a n d i n g p r e s s u r e s of 400 p s i and l e a k - t i g h t i n d e f i n i t e l y c o u l d be obtained. C o n t a i n e r s were made i n two s i z e s , 16 cm x 10 cm ( r e f e r r e d t o as "1 l i t e r " or "1.25 l i t e r " c o n t a i n e r s ) and 7 cm x 5 cm ( r e f e r r e d to as "100 ml" c o n t a i n e r s ) . 1.3.5 ^Kel-F Traps K e l - F t r a p s were used as c o n t a i n e r s when a v i s u a l examination of a r e a c t i o n was d e s i r a b l e , i n experiments where s o l i d s were formed which were to be removed from the r e a c t i o n c o n t a i n e r , and as t r a p s on the vacuum system to stop v o l a t i l e m a t e r i a l s from p a s s i n g t o the pump. The Kel-F t r a p s , commercially 10 a v a i l a b l e from Argonne Business L a b o r a t o r i e s , had a 3/4" SAE f l a r e which was clamped a g a i n s t a tapered cone d r i l l e d from a monel b l o c k . A l e n g t h of |" t u b i n g on the bl o c k served as a connection to a v a l v e ( f i g u r e 1). Blocks f o r Ke l - F t r a p s to be used i n flow experiments had two lengths of t u b i n g , one s e r v -i n g as an o u t l e t , the other as an i n l e t f o r the gas stream. 1.3.6 Au t o c l a v e E n g i n e e r i n g P a r t s Vacuum apparatus r e q u i r e d to withstand p r e s s u r e s of f l u o r i n e exceeding 200 p s i was c o n s t r u c t e d of p a r t s a v a i l a b l e from A u t o c l a v e E n g i n e e r i n g Company. These p a r t s are d e s c r i b e d i n s e c t i o n s 1.4.3 and 1.6. 1.4 VALVES Three types of v a l v e s were i n common use. 1.4.1 Hoke Valves Hoke 431 v a l v e s were a br a s s - b o d i e d b e l l o w s - s e a l e d v a l v e w i t h a metal V-stem and seat. Hoke v a l v e s o f f e r e d the advantages of r e l a t i v e l y l i g h t weight (The weight of a monel c o n t a i n e r , of 100 ml. c a p a c i t y , f i t t e d w i t h a Hoke v a l v e , c o u l d e a s i l y be kept under 200 gm, the upper l i m i t f o r use with the a n a l y t i c a l balance^ and the a b i l i t y t o withstand the h i g h e s t f l u o r i n e p r e s s u r e s commonly used i n our experimental work. ( «\> 200 p s i . v a l v e s r a t e d by manufacturer to 400 p s i . ) Hoke v a l v e s w i t h helium l e a k - t e s t e d s e a t s were found to be very r e l i -a b l e f o r use on storage c o n t a i n e r s , a i r le a k s over a p e r i o d of 11 dimensions i n mm 63 r 27 i 21 8 f" I. T " 23 — 3 3 — — 2 7 — * t- 24 Y n monel t u b i n g -wedge cut from c i r c u l a r b l o c k to g i v e g r i p f o r wrench |" SAE f l a r e -Kel-F t r a p (15 cm length; 1 mm w a l l t h i c k n e s s ) •monel c o l l a r < hex nut F i g u r e 1 K e l - F Trap and Adapter 12 months being l e s s than 1 mm. The major disadvantage of Hoke v a l v e s was t h a t they c o u l d not be r e p a i r e d when they began to leak, e i t h e r through the stem or bellows. The v a l v e bodies were of b r a s s , which corroded more r a p i d l y and e x t e n s i v e l y than monel metal and consequently Hoke v a l v e s c o u l d not be cleaned and pressed i n t o s e r v i c e a g a i n . Hoke v a l v e s were connected to \" monel t u b i n g by s o l d e r tube f i t t i n g s , c o n s i s t i n g at one end of a tapered cone which was h e l d a g a i n s t a tapered seat of the v a l v e by a nut screwing onto the v a l v e , at the other, of a s h o r t narrow l e n g t h of t u b i n g which c o u l d be s i l v e r - s o l d e r e d i n t o the \" monel tub i n g . 1.4.2 . Whitey Valves Whitey v a l v e s were monel, w i t h a monel body and stem wit h a Kel-F t i p . U n l i k e the Hoke v a l v e s , the Whitey v a l v e s were a gasket-type ( t e f l o n gasket) v a l v e and c o u l d be disassembled f o r easy c l e a n i n g . Corroded l a y e r s on the monel seat and stem were e a s i l y washed away, r e s t o r i n g the s u r f a c e to i t s o r i g i n a l c o n d i t i o n and hence Whitey v a l v e s c o u l d be reused. Since the c o n n e c t i o n to monel t u b i n g was made w i t h a compression f i t t i n g , Whitey v a l v e s c o u l d be e a s i l y removed from the vacuum system. Whitey v a l v e s , although the gasket was g e n e r a l l y l e a k - t i g h t , tended to be somewhat u n r e l i a b l e w i t h r e s p e c t to leakage through the s e a t . Hence Whitey v a l v e s were g e n e r a l l y avoided f o r use as t e r m i n a l v a l v e s i n s i t u a t i o n s where no leak-through over a p e r i o d of time was needed.(e.g., v a l v e on storage c o n t a i n e r ) 13 1.4.3 A u t o c l a v e E n g i n e e r i n g Valves Autoclave E n g i n e e r i n g Valves were made of monel, wi t h a t e f l o n gasket s e a l . These v a l v e s are intended f o r use under high p r e s s u r e s (up to 30,000 p s i . ) and were the v a l v e used i n c o n s t r u c t i o n of the f l u o r i n e system, these v a l v e s , when i n good c o n d i t i o n , would hol d a good vacuum over long p e r i o d s of time. T h e i r major disadvantages were t h e i r l a r g e s i z e , great expense and tendency to leak through the seat i f t r e a t e d improperly.(by o v e r t i g h t e n i n g s l i g h t l y when c l o s i n g ) On the other hand, they c o u l d be disassembled and r e s e r v i c e d e a s i l y . 1.5 GENERAL PURPOSE VACUUM LINE.FUME HOODS A schematic diagram of a metal vacuum system s u i t a b l e f o r r o u t i n e o p e r a t i o n s i s shown i n f i g u r e 2. T h i s i s the b a s i c d e s i g n of the apparatus which was used f o r most of the work des-c r i b e d i n t h i s t h e s i s . Valves G, H, I, and J i n the diagram were Whitey v a l v e s . Thus, the s e c t i o n of the apparatus contained by these v a l v e s , which was the p a r t of the system most o f t e n exposed to vapours d u r i n g r o u t i n e t r a n s f e r o p e r a t i o n s , c o u l d e a s i l y be dismounted, e i t h e r or c l e a n i n g , or i f a m o d i f i e d d e s i g n below G was needed f o r some s p e c i f i c experiment. The arrangement shown was s a t i s f a c t o r y f o r most purposes, p e r m i t t i n g the t r a n s f e r of gases from one c o n t a i n e r to another, or to an i n f r a r e d c e l l or other apparatus, and a l l o w i n g f o r easy measurement of gas p r e s s u r e s . The apparatus was b u i l t on a frame housed i n a walk-i n fume hood which gave access to both s i d e s of the frame. T h i s To good pump (shared) glass manifold To roughing pump (shared) Whitey or Hoke valve glass-metal compression fitting monel tubing To fluorine supply A C C D — K Cu D -T-Inlet TIE -HG M Booth-Cromer Pressure Transmitter f\l -rHT Inlet Inlet •4 copper tubing socket weld tee socket weld cross Figure 2. General Purpose Vacuum Line. hood had a metal s u r f a c e d work bench, about 5^' long by 4' wide, wi t h the vacuum frame i n the middle, thus g i v i n g a work space of about 5' x 2' i n f r o n t of each vacuum system. The work bench was about 2' from the f l o o r and the v e r t i c a l l y moving window frame of the hood, when f u l l y r a i s e d , was about 4' above the f l o o r of the work bench, a l l o w i n g the experimenter to c a r r y out m a n i p u l a t i o n s without uncomfortable bending or r e a c h i n g . The vacuum pumps were i n the space under the work bench, there b e i ng a h o l e i n the c e n t r e of the hood f o r the m a n i f o l d l i n e s of the two pumping systems. As i n d i c a t e d i n the f i g u r e , the vacuum m a n i f o l d was designed so as to permit s h a r i n g of two pumps between the users of the two separate systems i n the fume hood. The advantage was that one pump, a Welch duo-seal Mechanical Pump, c o u l d be used f o r i n i t i a l pumping down o p e r a t i o n s , and f o r pumping o f f c o r r o s i v e vapours i n the systems, w h i l e the second pump, a Welch Duo-Seal Mechanical Pump wit h an o i l diffusion-pump, c o u l d be r e t a i n e d f o r o b t a i n i n g h i g h vacuum c o n d i t i o n s on e i t h e r system. Care was taken to a v o i d u s i n g the good pump f o r i n i t i a l e v a c u a t i o n s . The ma n i f o l d s were i n t e r c o n n e c t e d so that one system c o u l d be evacu-ated on the roughing pump, w h i l e the other was being evacuated on the good pump, and were designed so that vapours from one s y s -tem never passed t o the other m a n i f o l d . 1.6 VACUUM SYSTEM FOR THE FLUORINE SUPPLY The system which was used f o r s u p p l y i n g f l u o r i n e i s 16 shown i n f i g u r e 3. I t was designed so as to have at l e a s t two high p r e s s u r e A u t o c l a v e E n g i n e e r i n g v a l v e s between the f l u o r i n e c y l i n d e r and the low p r e s s u r e p a r t of the vacuum s y s t e m . ( i . e . } p a r t s of the vacuum apparatus not c o n s t r u c t e d of A u t o c l a v e E n g i n e e r i n g p a r t s ) . The high p r e s s u r e p a r t of the system, which was the only s e c t i o n of the vacuum l i n e which was ever exposed to the f u l l 400 p s i , p r e s s u r e of the f l u o r i n e from the c y l i n d e r was c o n s t r u c t e d e n t i r e l y of A u t o c l a v e t u b i n g v a l v e s and connec-t i n g b l o c k s i n the form of c r o s s e s and t e e s , a l l p i e c e s being r a t e d t o w i t h s t a n d at l e a s t 30,000 p s i . Systems c o n s t r u c t e d of A u t o c l a v e p a r t s were found to be r e l i a b l y l e a k - t i g h t , and stood moderate s t r a i n reasonably w e l l without d e v e l o p i n g l e a k s . Blocks i n which conn e c t i o n s had been made s e v e r a l times needed to be r e s e r v i c e d , s i n c e the t u b i n g tended to b i t e i n t o and deform the seat of the b l o c k . The most s e r i o u s problem w i t h A u t o c l a v e p a r t s was a tendency f o r the v a l v e s to develop leak-through, because of deformation of the seat and/or stem through s l i g h t o v e r t i g h t e n i n g of the v a l v e . As the f i g u r e i n d i c a t e s , the f l u o r i n e supply was de-signed w i t h one high p r e s s u r e o u t l e t f o r both u s e r s , and w i t h two low p r e s s u r e l i n e s , one l e a d i n g to each of the two g e n e r a l purpose vacuum l i n e s i n the hood. The f l u o r i n e supply system, l i k e the g e n e r a l purpose systems, was e n t i r e l y w i t h i n the w a l k - i n fume hood;. As a r o u t i n e s a f e t y p r e c a u t i o n , the fume hood fan was always turned on when the f l u o r i n e c y l i n d e r was opened to take f l u o r i n e . The v a l v e on the f l u o r i n e c y l i n d e r was always l e f t c l o s e d except when tak-i n g f l u o r i n e . F l u o r i n e was obtained from the Matheson Company. To roughing pump v i a Ca(OH) 2/NaOH trap"** D i r e c t l y to roughing pump Cros b y high pressure gauge EH = Au t o c l a v e Engineering v a l v e , low pressure F T o ?2 supply* ( c y l i n d e r at 400 psi) |^  | = A u t o c l a v e Engineering tee or c r o s s = 3/8" O.D. , 1/8" I.D. Aut o c l a v e M o n e l tubing. = 1/4" M o n e l or C u t u b i n g . n *high pressure . ^ o u t l e t (monel) 23m threaded cap Figure 3. A Vacuum Line for a F l u o r i n e Supply. 18 2 PRESSURE MEASUREMENT Note: A l l p r e s s u r e s quoted i n t h i s t h e s i s can be assumed t o be mm Hg, u n l e s s otherwise s t a t e d . 2.1 THE MODIFIED BOOTH-CROMER PRESSURE TRANSMITTER 2.1.1 D e s c r i p t i o n A c r o s s - s e c t i o n a l r e p r e s e n t a t i o n of the Booth-Cromer Pressure T r a n s m i t t e r i s shown i n f i g u r e 4. ( T h i s f i g u r e i s 9 reproduced from the Ph.D. t h e s i s of Dr. N. K. Jha.) T h i s d i a -phragm gauge was a s l i g h t l y m o d i f i e d v e r s i o n of the o r i g i n a l 76 Cromer T r a n s m i t t e r , T e f l o n being used as an i n s u l a t i n g m a t e r i a l . The T e f l o n r i n g p r o v i d e d both e l e c t r i c a l i n s u l a t i o n and a l e a k -t i g h t s e a l between the e l e c t r i c a l c o n t a c t and the n i c k e l diaphragm. The diaphragm gauge was connected through a s m a l l monel r e s e r v o i r to the vacuum l i n e . The instrument was^  used as a n u l l d e v i c e , by b a l a n c i n g the p r e s s u r e of gas being measured wi t h an equal p r e s s u r e of a i r on the upper s i d e of the diaphragm. The b a l a n c i n g p r e s s u r e of a i r was measured d i r e c t l y w i t h a U-tube manometer and mercury l e v e l s i n the manometer c o u l d be read e i t h e r from a meter s t i c k mounted behind the U-tube or, f o r g r e a t e r accuracy, w i t h a cathe-tometer r e a d i n g to-,± 0.005 mm. 2.1.2 Manual Oper a t i o n The e l e c t r i c a l c i r c u i t shown i n f i g u r e 4 i n d i c a t e d when the balance p o i n t was reached. The p o s i t i o n of the a d j u s t -a b l e c o n t a c t was f i x e d p r i o r t o use so that a s m a l l displacement (^0.05 mm) of the b a l a n c i n g air p r e s s u r e from the equal p r e s s u r e i n the r e s e r v o i r was s u f f i c i e n t to t u r n the l i g h t on or o f f . 19 A i r B a l a n c i n g Connection 1/4 i n . Monel Tube; *"u A d j u s t a b l e E l e c t r i c a l C ontact. T e f l o n Sleeve N i c k e l Diaphragm 1/4 i n . Monel Tube 110V . I n l e t f o r gas or vapour the p r e s s u r e of which i s to be measured. NE 51 F i g u r e 4. The Diaphragm Gauge. 20 Only i n f r e q u e n t re-adjustment of the p o s i t i o n of the movable cont a c t was r e q u i r e d . A two-way stopcock was used to admit or evacuate a i r , and care was taken to keep the pre s s u r e d i f f e r e n t i a l a c r o s s the diaphragm as s m a l l as p o s s i b l e . , 2.1.3 Semi-Automatic Oper a t i o n Continuous and automatic adjustment of the b a l a n c i n g a i r p r e s s u r e was accomplished u s i n g an e l e c t r i c a l c i r c u i t which connected the t r a n s m i t t e r to two s o l e n o i d v a l v e s and an e l e c t r i c a l r e l a y . The e s s e n t i a l f e a t u r e of the d e v i c e was the p a i r of s o l e n o i d v a l v e s which were a c t i v a t e d and d e - a c t i v a t e d by the e l e c t r o n i c r e l a y , upon the making and brea k i n g of the cont a c t between the a d j u s t a b l e e l e c t r i c a l c o n t a c t and the n i c k e l diaphragm of the t r a n s m i t t e r . One s o l e n o i d v a l v e (A) pe r m i t t e d entry of a i r t o the upper p a r t of the t r a n s m i t t e r w h i l e the other (B) per-m i t t e d e v a c u a t i o n of the a i r from the t r a n s m i t t e r . When the con t a c t was made, the c i r c u i t was a d j u s t e d such that A was open and B was c l o s e d , a l l o w i n g a i r t o enter the t r a n s m i t t e r . When the c o n t a c t was broken, B was open and A was c l o s e d , a l l o w i n g e v a c u a t i o n of the a i r from the t r a n s m i t t e r . Needle v a l v e s were connected i n s e r i e s t o the two s o l e n o i d v a l v e s t o permit manual c o n t r o l of the r a t e at which a i r flow through the s o l e n o i d v a l v e s when e i t h e r was open. With these needle v a l v e s s u i t a b l y a d j u s t e d , the s o l e n o i d v a l v e s opened and c l o s e d at r a t e s r a p i d enough t o keep the f l u c t u a t i o n of the b a l a n c i n g a i r p r e s s u r e to l e s s than ±0.01 mm. 21 2.2 HELICOID GAUGE A H e l i c o i d Test Gauge f o r oxygen s e r v i c e was used f o r r a p i d , reasonably a c c u r a t e (±2-3 mm) pressure measurements i n the pressure r e g i o n 0-1000 mm. 2.3 CROSBY HIGH PRESSURE GAUGE A Crosby gauge (0-600 p s i ) was used on the f l u o r i n e vacuum systems to measure f l u o r i n e p r e s s u r e s up to 400 p s i . A gauge s p e c i f i e d f o r oxygen s e r v i c e was s a t i s f a c t o r y f o r use w i t h f l u o r i n e . 2.4 THERMOCOUPLE AND IONIZATION GAUGES To measure p r e s s u r e s of l e s s than 0.1 mm, an NRC Thermocouple and an Emission r e g u l a t e d Ion Gauge C o n t r o l (NRC Equipment C o r p o r a t i o n , type 710 B) were used. The thermocouple -1 -3 gauge measured p r e s s u r e s of 10 to 10 mm, w h i l e the emission 3 —6 gauge measured p r e s s u r e s of l e s s than 10" mm (down to 10 mm). Both gauges were mounted on the m a n i f o l d of the good pumping system. The thermocouple gauge was used t o l o c a t e sources of leakage on the metal system by opening the suspected s e c t i o n of the system to the we l l - e v a c u a t e d m a n i f o l d . A sudden p r e s s u r e r i s e , as measured on the gauge, i n d i c a t e d a leak. The i o n i z a t i o n gauge was used to measure the l i m i t i n g p r e s s u r e i n the system by t u r n i n g i t on w h i l e pumping on the 22 system. The lowest a t t a i n a b l e p r e s s u r e , w i t h the metal p a r t of the system c l o s e d o f f from the m a n i f o l d , and the m a n i f o l d con--5 t i n u o u s l y evacuated, was 10 mm. Measurements with the thermocouple and i o n i z a t i o n gauges over a p e r i o d of time e s t a b l i s h e d t h a t , r o u t i n e l y , experiments were conducted w i t h p r e s s u r e s i n the evacuated system -3 of 1-5x10 mm. 23 3 EXPERIMENTAL TECHNIQUES  3.1. INFRARED SPECTROSCOPY 3.1.1 Gas C e l l The i n f r a r e d c e l l was c o n s t r u c t e d of monel and con-s i s t e d of a c a v i t y w i t h AgCl windows, ( f i g u r e 5) and a s m a l l (^20 ml c a p a c i t y ) r e s e r v o i r , separated from the c a v i t y by a v a l v e . A l e a k - t i g h t s e a l between the 1 mm t h i c k windows and the body of the c e l l c a v i t y was made by p r e s s i n g a p l a t e ("front p l a t e " i n f i g u r e ) a g a i n s t a T e f l o n r i n g which was mounted i n a groove on the t h i c k f l a n g e of the c e l l c a v i t y body. The T e f l o n r i n g c o u l d be r e p l a c e d when i t became deformed. The f r o n t p l a t e was hel d by a s e t of screws p a s s i n g through i t i n t o threaded h o l e s on a second p l a t e ("back p l a t e " i n f i g u r e ) , t h i s second p l a t e screwing onto the f l a n g e of the c e l l c a v i t y body. The assembled c e l l gave a path l e n g t h i n the i n f r a r e d beam of 7.5 cm. 3.1.2 I n f r a r e d Spectra of Gases I n f r a r e d s p e c t r a of gases at p r e s s u r e s as hig h as 2-3 atmospheres were obtained simply by f i l l i n g the evacuated c e l l to the d e s i r e d p r e s s u r e w i t h the gas and, having c l o s e d the v a l v e s on the c e l l to prevent i n g r e s s of a i r , running the spectrum i n the u s u a l way on the d e s i r e d instruments. A s p e c i a l h o l d e r , which f i t t e d snugly over the "back p l a t e " h e l d the c e l l i n the sample beam. The pre s s u r e of gaseous sample i n the c e l l c a v i t y c o u l d be v a r i e d by a d m i t t i n g more sample from the r e s e r -v o i r t o the c e l l c a v i t y , or by condensing some of the sample i n the c e l l c a v i t y i n t o the c e l l r e s e r v o i r . 24 AgCl window f r o n t p l a t e \ • i i ; back p l a t e T T e f l o n c e l l threaded f l a n g e r i n g c a v i t y (threads to r e c e i v e 19-*1 body back p l a t e ) O 74 15" 71 1 tt'M23 36 40 58 60 „ U l i l . A . l f y _ K 1 1 1 1 1 1—F U 60 * I 1 1 s i d e view d e p r e s s i o n f o r AgCl window f r o n t p l a t e back p l a t e threaded f l a n g e end views F i g u r e 5. I n f r a r e d Gas C e l l 3.1.3 Gas-Gas Reactions i n the I n f r a r e d C e l l The d e s i g n of the c e l l was a convenience i n f o l l o w i n g a r e a c t i o n between two gaseous m a t e r i a l s . Reactant A, a f t e r i t s spectrum was r e c o r d e d , i f d e s i r e d , was condensed i n t o the c e l l r e s e r v o i r and r e a c t a n t B was then taken i n t o the c e l l c a v i t y . The two m a t e r i a l s were then allowed to r e a c t , e i t h e r by condensing B onto A i n the c e l l r e s e r v o i r , or by a d m i t t i n g A ( i n p o r t i o n s , or a l l at once) to the c e l l c a v i t y from the r e s e r v o i r . The i n f r a -red s p e c t r a of the products and/or any remaining r e a c t a n t c o u l d then be recorded. The technique proved to be a p a r t i c u l a r l y s a t i s f a c t o r y method of o b t a i n i n g t h i n f i l m s of s o l i d r e a c t i o n products f o r s o l i d s t a t e i n f r a r e d s p e c t r a . 3.1.4 I n f r a r e d Spectrophotometers For r o u t i n e purposes, i n f r a r e d s p e c t r a were recorded on the Perkin-Elmer 137 NaCl and KBr Spectrophotometers, c o v e r i n g the ranges 4000-670 c m - 1 and 800-400 c m - 1 r e s p e c t i v e l y . For more a c c u r a t e measurement of a b s o r p t i o n f r e q u e n c i e s , and f o r i n c r e a s e d r e s o l u t i o n of a b s o r p t i o n peaks, the P e r k i n -Elmer 21 Spectrophotometer was used i n the range 4000-650 cm ^, and the Perkin-Elmer 421 Spectrophotometer i n the range 950-400 cm - 1. On o c c a s i o n , s p e c t r a were recorded i n the f a r i n f r a r e d r e g i o n (below 400 cm , down to 100 cm - 1) on the Perkin-Elmer model 301. F a r - i n f r a r e d Spectrophotometer. We acknowledge Dr. Wright of the B. C. Research C o u n c i l f o r p e r m i t t i n g us to use h i s instrument (the PE 301) and a s s i s t i n g i n r e c o r d i n g the s p e c t r a , and a l s o the U.B.C. i n f r a r e d s pectroscopy group f o r 26 p e r m i t t i n g us t o use t h e i r instrument (the PE 21) and a s s i s t i n g i n r e c o r d i n g the s p e c t r a . 3.2 X-RAY POWDER PHOTOGRAPHY 3.2.1 Sample P r e p a r a t i o n Samples f o r X-ray powder photographs were mounted i n 0.5 mm q u a r t z c a p i l l a r i e s (Pantak Company, Windsor, B e r k s , England). A sample l e n g t h of 5 mm i n the c a p i l l a r y was s u f f i c -i e n t , so powder photographs r e q u i r e d only s m a l l amounts of m a t e r i a l . Since most samples were m o i s t u r e - s e n s i t i v e , the samples were powdered (with an agate mortar and p e s t l e ) and loaded i n t o the c a p i l l a r i e s i n a drybox, and the ends of the c a p i l l a r i e s were s e a l e d w i t h a s m a l l hot flame immediately a f t e r removal of the c a p i l l a r i e s from the drybox. In g e n e r a l , X-ray powder photo-graphs of samples were obtained as soon a f t e r f i l l i n g the c a p i l -l a r i e s as p o s s i b l e , t o reduce the p o s s i b i l i t y of decomposition of the sample through a t t a c k on the s i l i c a . 3.2.2 Exposure and Measurement of Powder Photographs X-ray powder photographs of s o l i d s were obtained u s i n g a General E l e c t r i c powder camera of 14.32 cm diameter, w i t h Straumanis l o a d i n g . Cu K-oC X-ray r a d i a t i o n was used, w i t h an Ni f i l t e r to reduce K-^ r a d i a t i o n . The f i l m was I l f o r d " I l f e x s a f e t y base, f o r use without i n t e n s i f y i n g s c r e en", s u p p l i e d i n sheets 35.6 x 43.2 cm, which was cut i n t o s t r i p s 4cm x 43.2 cm f o r use i n the powder camera. 27 For f i l m s to be used f o r i d e n t i f i c a t i o n purposes only, when a shor t exposure time was d e s i r a b l e , a s l i t c o l l i m a t o r was used on the camera, but to o b t a i n photographs f o r measurement of l i n e s p o s i t i o n s a p i n h o l e c o l l i m a t o r was used, g i v i n g photo-graphs w i t h sharp low angle l i n e s . X-ray powder photographs were measured on a l i g h t box p r o v i d e d w i t h a meter s t i c k , to which was a t t a c h e d a measuring s l i d e assembly c o n t a i n i n g a v e r n i e r and a m a g n i f i e d c r o s s - h a i r f o r l o c a t i o n of the d i f f r a c t i o n l i n e . ("Film I l l u m i n a t o r and Measuring Device", type no. 52022/1, P h i l i p s E l e c t r o n i c s , Inc.) Measurement of a powder photograph of pure platinum w i r e (0.008" diameter, at a temperature of 25 ± 5°C) e s t a b l i s h e d that the s c a l e and measuring d e v i c e were a c c u r a t e to w i t h i n the e r r o r which has been a t t a c h e d to any c e l l parameters quoted i n t h i s t h e s i s . o 77 (Pt, a Q , measured, = 3.925 ± O.OOlS; a Q , 25 C, l i t e r a t u r e , = 3.923S.) A computer program (appendix 1, program 1) was w r i t t e n to convert the meter s t i c k r e a d i n g s to 1/d v a l u e s . 3.3 TENSIMETRIC TITRATION OF GASES A t e n s i m e t r i c t i t r a t i o n i s a means of e s t a b l i s h i n g the s t o i c h i o m e t r y of a product r e s u l t i n g from the r e a c t i o n of ( g e n e r a l l y ) two gases by a l l o w i n g the product to form from measured p r e s s u r e s of the r e a c t a n t s , the p r e s s u r e s being measured i n a system of known or f i x e d volume, f o l l o w e d by the measurement of the p r e s s u r e of unreacted gases i n the same system. 28 A l l measurements are made at the same temperature. The nature of the r e s i d u a l gas i s e s t a b l i s h e d by some s u i t a b l e technique, i f necessary. T e n s i m e t r i c t i t r a t i o n s can be performed q u i c k l y and e a s i l y , and o f t e n e l i m i n a t e the need f o r time-consuming a n a l y s e s of r e a c t i o n p r o d u c t s . In most of the t e n s i m e t r i c t i t r a t i o n s c a r r i e d out i n t h i s work, the s e c t i o n of the g e n e r a l purpose vacuum system 1 ( f i g u r e 2) between the i n l e t v a l v e s and the diaphragm p r e s s u r e gauge (between H, I and J , and D and E, wi t h F open, ( i n f i g u r e 2) was used as a system of f i x e d volume .("constant volume system") Two of the i n l e t v a l v e s were occupied by the storage c o n t a i n e r s of the two gaseous r e a c t a n t s , w h i l e the c o n t a i n e r (e.g., Kel-F t r a p or monel c o n t a i n e r w i t h removable l i d ) used f o r the r e a c t i o n was at t a c h e d to the t h i r d i n l e t . T h i s v e s s e l was not p a r t of the constant volume system. A f t e r the pr e s s u r e of one of the r e a c t a n t s was measured, i t was condensed i n t o the r e a c t i o n v e s s e l . T h i s c o n t a i n e r was then c l o s e d o f f from the constant volume system a g a i n and the p r e s s u r e of the second r e a c t a n t was measured, f o l l o w e d by i t s condensation i n t o the r e a c t i o n con-t a i n e r . A f t e r the r e a c t i o n had been allowed t o proceed under whatever c o n d i t i o n s were d e s i r e d - g e n e r a l l y , the r e a c t i o n v e s s e l was merely brought t o near room temperature w i t h a warm water bath and l e f t at room temperature f o r a p e r i o d of time -v o l a t i l e s p e c i e s were condensed from the r e a c t i o n c o n t a i n e r i n t o the constant volume system, by c o o l i n g the r e s e r v o i r of the diaphragm gauge. The p r e s s u r e of these gases i n the constant volume system was then recorded. As a matter of r o u t i n e or 29 n e c e s s i t y , i n f r a r e d s p e c t r a of the r e s i d u a l gases were then taken. 3.4 MEASUREMENT OF MAGNETIC SUSCEPTIBILITIES 3.4.1 Magnetic S u s c e p t i b i l i t y Apparatus Magnetic s u s c e p t i b i l i t i e s were measured by the Guoy technique w i t h an apparatus which provided f o r s u s c e p t i b i l i t y meaasurements*over the temperature range of -196° to + 100°C. The equipment-, has been d e s c r i b e d i n d e t a i l by C l a r k 35 and O'Brion . The apparatus c o n s i s t e d of a Dewar and h e a t i n g j a c k e t surrounding the sample c a v i t y to c o n t r o l temperatures, a microbala.nce to r e c o r d weight changes, and an electromagnet w i t h v a r i a b l e f i e l d s t r e n g t h . The r e f e r e n c e d e s c r i b e s these compon-ents i n d e t a i l . 3.4.2 Sample P r e p a r a t i o n and Experimental Techniques Samples were prepared by powdering the s o l i d i n the drybox and l o a d i n g i t i n t o a g l a s s or q u a r t z tube of 3-5 mm diameter. A sample l e n g t h of 9.4 cm was d e s i r a b l e , s i n c e , w i t h the u s u a l experimental arrangement, t h i s l e n g t h gave a sample which extended to a r e g i o n of e s s e n t i a l l y zero f i e l d s t r e n g t h . The tube, a f t e r removal from the drybox, was s e a l e d so as to g i v e a tube l e n g t h of 11.4 cm. Such a tube l e n g t h p l a c e d v:'„ the bottom of the tube Zt the c e n t e r of the pole, faces.; The sample was h e l d i n a b r a s s cap (of diameter such as to h o l d the tube snugly) and suspended i n the c a v i t y of the Dewar j a c k e t i n g arrangement by a b r a s s c h a i n which was a t t a c h e d to the microbalance. Weight changes of the sample w i t h the f i e l d 30 . on and o f f were then obtained at room temperature and over a range of temperatures from -196°C to room temperature, i f d e s i r e d . A f t e r the completion of the experiment, the weighed sample was removed from the tube by b r e a k i n g i t at the top end. A diamagnetic c o r r e c t i o n was obtained f o r the weighed empty tube by measurement of i t s weight change over a temperature range. Care was taken to i n s u r e that the bottom of the empty tube was at the same p o s i t i o n i n the f i e l d as i n the sample measurements, by i n s e r t i n g the d i s j o i n e d t i p i n t o the b r a s s holder ahead of the emptied tube. F i n a l l y , the tube constant was obtained by the room temperature measurement of the weight change of an HgCo(SCN)^ sample i n the same sample tube, w i t h the same sample l e n g t h as that of the compound measured. 3.4.4 Conversion of Weight Changes to S u s c e p t i b i l i t i e s and  Magnetic Moments The r e l a t i o n between the gram s u s c e p t i b i l i t y of a sample and i t s weight change i s given by a 2 g i A w _ L i . . . . ( 1 ) g H W where g = a c c e l e r a t i o n of g r a v i t y 1 = sample l e n g t h H = magnetic f i e l d s t r e n g t h (other symbols are d e f i n e d below) Since a value of H i s d i f f i c u l t to measure a c c u r a t e l y o a tube constant, C, d e f i n e d by C = 2gl/H , i s obtained by the measurement of the s u s c e p t i b i l i t y of HgCo(SCN)^ i n the manner described i n section 3.4.3. C i s then given by C = HM % X H = 16.44xl0" 6cgs at 20°C. M H g + 6 H g H g Hence, i n ( 1 ) X „ = X H O R HM— A W H g + 6 W where *v_ , = gram s u s c e p t i b i l i t i e s of sample and HgCo(SCN) 4, grams WHg, W = weights of sample and HgCo(SCN>4, grams AWHg, AW = weight changes of sample and HgCo(SCN)^ grams 6 = diamagnetic correction for sample tube, grams. ^ The molar s u s c e p t i b i l i t y i s obtained from the gram s u s c e p t i b i l i t y simply by m u l t i p l i c a t i o n by the molecular weight of the sample (% ^ = X g x M) and can be corrected for the diamagnetism of each atom i n the formula weight: ( ^ M * C O R R = ^ M" 5 + ^-DIAMAG' The magnetic moment i s given from the molar suscepti-b i l i t y by j x e t f = 2 . 8 3 7 ( % M T ) 2 where Jkkef± = e f f e c t i v e magnetic moment, Bohr magnetons o T = temperature, K. For substances following the Curie-Weiss law (1/?C M vs T plot i n a straight l i n e ) , the r e l a t i o n 32 /A.'eff = 2 . 8 3 7 [ X M ( T + © ) ] ^ , © = Weiss constant i s o f t e n used t o e v a l u a t e the magnetic moment. 3.5 ANALYTICAL AND PURIFICATION TECHNIQUES 3.5.1 A n a l y t i c a l Techniques ,Samples were commonly decomposed f o r a n a l y s i s u s i n g a p y r o h y d r o l y t i c technique. The weighed sample, contained i n a platinum boat i n a s i l i c a tube, was decomposed by p a s s i n g steam over the sample, the steam being c a r r i e d by a n i t r o g e n gas stream. The steam c o u l d be heated to 400°C by a tube furnace surrounding the s i l i c a tube. A condenser was at t a c h e d t o the end of the s i l i c a tube, and the end of the condenser dipped i n t o a f l a s k of water, to ensure that a l l HF from the decomposing sample was trapped. T r i a l experiments i n t h i s l a b o r a t o r y had e s t a b l i s h e d p r e v i o u s l y that t h i s technique r e s u l t e d i n no l o s s of HF through a t t a c k on the s i l i c a w a l l s . The d i s t i l l a t e c o l l e c t e d i n the f l a s k was analyzed 36 d i r e c t l y f o r f l u o r i d e by the PbCIF method . Often, the r e s i d u e i n the platirium boat was reduced o to a metal by r e d u c t i o n w i t h hydrogen at 400 C. In some i n s t a n c e s , samples were analyzed f o r metal content only by decomposition i n a platinum c r u c i b l e ( e i t h e r by the moisture of the a i r , or g e n t l e heating) f o l l o w e d by r e d u c t i o n of the r e s i d u e t o a metal w i t h hydrogen. ( c r u c i b l e heated w i t h a bunsen flame) 33 3.5.2 P u r i f i c a t i o n Techniques As a r o u t i n e and e a s i l y c a r r i e d out o p e r a t i o n , v o l a t i l e i m p u r i t i e s such as S i F ^ and CF^ were removed from samples merely by h o l d i n g the storage c o n t a i n e r at a temperature at which the substance to be p u r i f i e d was i n v o l a t i l e , and pumping. In some i n s t a n c e s , v o l a t i l e substances were p u r i f i e d by a t r a p - t o - t r a p d i s t i l l a t i o n , e i t h e r i n pyrex g l a s s or metal equipment. G e n e r a l l y , the i n i t i a l and t a i l f r a c t i o n s were d i s -carded. I n f r a r e d spectroscopy was used as the r o u t i n e method of checking the p u r i t y of v o l a t i l e s p e c i e s , although i n some cases the measurement of vapour p r e s s u r e at 0°C was a u s e f u l index to the p u r i t y of a substance. 3.5.3 " S p e c t r o g r a p h i c l y S t a n d a r d i z e d " Reagents The heavy metals used i n t h i s study (Re,Os,Ir,Pt) f o r the p r e p a r a t i o n of f l u o r i d e s and o x y f l u o r i d e s were obtained from Johnson, and Matthey Co., as s p e c t r o g r a p h i c l y s t a n d a r d i z e d powders. These powders were of high p u r i t y , the s p e c t r o g r a p h i c a n a l y s i s (provided w i t h each sample) showing the t o t a l amount of i m p u r i t i e s to be 10-15 ppm or l e s s . 3 4 CHAPTER I I I THE HEPTA- AND OXYPENTAFLUORIDES OF IODINE AND RHENIUM.MAGNETIC MEASUREMENTS ON XeF g I INTRODUCTION 1.1 SURVEY OF THE LITERATURE WORK 1.1.1 V i b r a t i o n a l S t u d i e s on IF-, IOF 5 and ReOFg 20 Lord and co-workers' v i b r a t i o n a l study on IF- i s the only one which has appeared i n the l i t e r a t u r e . They i n t e r -p r e t e d t h e i r i n f r a r e d and Raman data i n terms of a Dg n symmetry molecule, but the i n f r a r e d data c o l l e c t e d i n t h i s work f o r IOF 5 and IF- leave no doubt that there are e r r o r s i n t h e i r p u b l i s h e d 3 7 s p e c t r a . Recent Raman s t u d i e s of IOF_ by G i l l e s p i e s i m i l a r l y 5 i n d i c a t e mistakes i n the r e p o r t e d Raman spectrum of Lord et a l . , I0F_ Raman l i n e s being a s s i g n e d as IF_ l i n e s . G i l l e s p i e ' s Raman data i s c o n s i s t e n t w i t h the i n f r a r e d data c o l l e c t e d i n the present i n v e s t i g a t i o n . Some time a f t e r the p r e l i m i n a r y r e p o r t of i n f r a r e d 3 8 data f o r IOFg by B a r t l e t t and Levchuck, Smith p u b l i s h e d a paper on the complete v i b r a t i o n a l a n a l y s i s of I0F_. H i s s p e c t r a o were c o n s i s t e n t w i t h those which had been o b t a i n e d i n the pr e v i o u s two years work on t h i s t h e s i s . There have been no l i t e r a t u r e r e p o r t s on the v i b r a t -i o n a l spectrum of ReOFg. 35 19 1.1.2 F n.m.r. St u d i e s The n.m.r. spectrum of IF_ has been r e p o r t e d p r e v i o u s l y 22 by Gutowsky and Hoffman , but they were unable t o analyze t h e i r spectrum r i g o r o u s l y , s u g g e s t i n g only that the broad resonance s i g n a l they obtained was i n d i c a t i v e of s t r u c t u r a l l y nonequivalent f l u o r i n e atoms. Independent work ' p u b l i s h e d w h i l e our n.m.r. i n -v e s t i g a t i o n s were i n progress gave r e s u l t s i n agreement w i t h our own. A l l s e t s of r e s u l t s are c o n s i s t e n t w i t h the e a r l y spectrum of Gutowsky, but our i n t e r p r e t a t i o n (which i s the same 39 as M u e t t e r t i e s and Packer's ) of the r e s u l t s d i f f e r s . Two independent s e t s of r e s u l t s on the spectrum of IOF_ appeared w h i l e our work was i n pr o g r e s s . A l e x o s , Cornwall, 5 16 and P i e r c e o b t a i n e d a spectrum of IOFg i n an IF_-IOFj. mixture 15 which was similar t o ours and G i l l e s p i e and Q u a i l obtained a spectrum of IOFg i n IFg, w i t h the r e s u l t s a g a i n s i m i l a r to our own. 40 S e l i g and M u e t t e r t i e s have unpublished work on the n.m.r. spectrum of ReF-, as a neat l i q u i d and i n WFg s o l u t i o n . 19 There has been no work r e p o r t e d on the F n.m.r. spectrum of ReOFg. 1.1.3 Vapour Pressure Measurements Vapour p r e s s u r e r e s u l t s were r e p o r t e d f o r IF_ by 12 Ruff and Keim i n t h e i r o r i g i n a l p r e p a r a t i o n of IF^. They found l o g e P C M = 17.38 - 3781/T(-63 t o 0°C) and obtained a m e l t i n g p o i n t of 5-6°C. T h e i r measurements were made i n a qu a r t z system and hence the d i f f e r e n c e s between t h e i r r e s u l t s 36 and ours are probably due to t r a c e s of IOF_ i n t h e i r samples. 5 P r e l i m i n a r y vapour p r e s s u r e equations have been p u b l i s h e d p r e v i o u s l y f o r s o l i d I F 7 and IOFg, from t h i s l a b o r a t o r y ^ : I F ? l o g e P C M = 17.38 - 3781/T IOF 5 l o g e P C M = 18.31 - 3605/T. 1.2 -ACIDS AND BASES IN FLUORIDE SYSTEMS  1.2.1 D e f i n i t i o n s An a c i d i s a f l u o r i d e which a c t s as a f l u o r i d e i o n a c c e p t o r , e.g., A s F 5 , SbF 5, BF 3; XF + A s F 5 —y X +AsFg~. A base i s a f l u o r i d e which a c t s as a f l u o r i d e i o n donor, e.g., MF (M=alkali m e t a l ) , NOF, SF 4; NOF + Y —> NO +YF~. These d e f i n i t i o n s may be compared w i t h the Brb'nsted d e f i n i t i o n , i n which a c i d s and bases are c l a s s i f i e d a c c o r d i n g to a tendency to g a i n or l o s e a proton. From the viewpoint of the Lewis d e f i n i t i o n of a c i d s and bases, the base i n these a c i d - b a s e systems would be the 1 f l u o r i d e i o n and the a c i d s the s p e c i e s which compete f o r t h i s i o n . Thus N0 + and S F g + are a c i d s which l o s e a f l u o r i d e i o n to the s t r o n g e r a c i d s A s F & or SbF & i n a r e a c t i o n of the s o r t NOF + A s F 5 —> NO +AsF g~. Many f l u o r i d e s can a c t as both a c i d s and bases; the halogen f l u o r i d e s , XF^, are n o t a b l e examples, a c t i n g as bases to g i v e XFy_2 and a c i d s t o g i v e XFy+i-37 1.2.2 Acid-Base Behaviour of Species R e l a t e d to IF-, and  of I F ? The acid-base behaviour of most of the i n t e r h a l o g e n compounds has been i n v e s t i g a t e d . * C I F 4 1 " 4 3 , C l F g 4 4 - 4 6 , B r F g 4 7 , I F 3 4 8 , B r F 5 4 4 ' 4 9 , and I F g 4 7 have been shown to a c t as both a c i d s and bases, and BrFg and IF^ i n p a r t i c u l a r a c t as a c i d s and bases w i t h a wide range of compounds. The good s o l v e n t (and f l u o r i n a -t i n g - - e s p e c i a l l y BrF3 ) p r o p e r t i e s of these two f l u o r i d e s has 47 been e x t e n s i v e l y exploited;;, i o n i z a t i o n of the s o r t 2 M F x ^_-=± ^*x+l + ^ Fx-1 i s important i n these compounds. 45 IF- formed adducts w i t h s t r o n g a c i d s ( A s F 5 a n d SbFg, but not BFg) and f a i l e d t o g i v e adducts w i t h a l k a l i metal 19 f l u o r i d e s (NaF, KF, and RbF) at room temperature. (See a l s o I n t r o d u c t i o n i n chapter IV f o r comments on a c i d - b a s e p r o p e r t i e s ,50 ^ , 18, of IF-.) However, IF_ was r e p o r t e d t o exchange F r a p i d l y 18 w i t h H F i n the gas phase. An i n t e r m e d i a t e i n v o l v i n g i o d i n e i n a h i g h e r than seven c o o r d i n a t e s p e c i e s seems to be p o s s i b l e here; hence the one s e t of r e s u l t s on the f l u o r i d e i o n a c c e p t o r p r o p e r t i e s of IF- may not be d e f i n i t i v e . 51 ) TeFg has been found to form an adduct 2CsF*TeF 6 on h e a t i n g CsF under a p r e s s u r e of TeF . T h i s adduct may con-6 -2 t a i n the anion T e F Q , which would be i s o e l e c t r o n i c w i t h the o I F g - i o n . In many i n s t a n c e s , F~ d o n a t i o n or acceptance i n the adduct formed i s assumed, for m a t i o n of the adduct being the s o l e i n d i c a t i o n of an a c i d - b a s e r e a c t i o n . 38 XeFg shows both f l u o r i d e i o n donor and ac c e p t o r 52 53 54 p r o p e r t i e s . I t r e a c t s w i t h 3ci<hs such as AsFg , SbFg , PtFg 52 and BF3 , g i v i n g 1:1 adducts i n each case and a 2:1, and 1:2 adduct as w e l l w i t h SbFg. The XeFg-PtFg adduct has been charac-+ _54 t e r i z e d as the s a l t , XeF K PtF„ o 6 XeFg f o r m s 5 5 1:1 (MXeF ?) and 1:2 (M 2XeFg) adducts w i t h RbF and CsF and adducts w i t h NaF and KF as w e l l , probably the M 2XeFg s a l t s . The M 2XeFg s a l t s are the more s t a b l e , thermal-l y . There i s evidence of i n t e r a c t i o n w i t h BaFg• 1.2.3 The S t a b i l i t y of AMF V S a l t s as a F u n c t i o n of A 56 As a g e n e r a l r u l e , one f i n d s t hat the s t a b i l i t y of an a l k a l i metal f l u o r i d e , AMF V, decreases i n the order Cs > Rb ) K ) N a > L i wi t h change of A. (M=a t r a n s i t i o n a l or n o n t r a n s i t i o n a l element.). T h i s can only be a g e n e r a l t r e n d , of course; a change i n s t r u c t u r e of AMF X w i t h change of M c o u l d upset the t r e n d , f o r example. The tr e n d i s i n accor d w i t h what one would p r e d i c t from the f o l l o w i n g Hess c y c l e : AF(c) + M F y — ^ H r X > AMF X -U AF UAMF X A + ( g ) + F"(g) * A + ( g ) + M F x _ ( g ) A H M F v H = heat of r e a c t i o n U = l a t t i c e energy 1 Since the complex anion MF i s f a i r l y l a r g e compared to A +, ^AMF w i l l be approximately constant w i t h change of A and &*RX w i l l be most exothermic f o r the a l k a l i f l u o r i d e of s m a l l e s t l a t t i c e e n e r g y . ( i . e . , CsF). 39 N0 + i n a c r y s t a l o f t e n occupies a volume equal to that of K + ( i . e . , " r » , £ r + ) and the enthalpy of r e a c t i o n NCT K f o r the process ONF(g) — • N0 + + F~ (A/179 K i l c a l / m o l e ) i s between 57 the l a t t i c e e n e r g i e s of RbF and CsF . However, w i t h ONF there w i l l be an unfavourable entropy change compared to the a l k a l i f l u o r i d e s , s i n c e complex formation i n v o l v e s the gaseous ONF going t o the s o l i d phase. Hence one might expect NO + to l i e between Na + ( U N a F = 216 K i l c a l / m o l e ) and Rb + ( U R b F = 184 K i l c a l / m o l e ) on the above t r e n d i n s t a b i l i t y of AMF wi t h A v a r i a t i o n . A d d i t i o n of 15 K i l c a l to the computed 179 K i l c a l / mole, f o r example, g i v e s 194 K i l c a l / m o l e , c l o s e t o the l a t t i c e energy of KF ( Vrv = 191 K i l c a l / m o l e ) . J 40 2 EXPERIMENTAL 2.1 PREPARATIVE METHODS 2.1.1 The P r e p a r a t i o n of I F 7 IF- was prepared by the r e a c t i o n of IFg wit h F^• (a) The P r e p a r a t i o n of IF_': 5 For the i n i t i a l p r e p a r a t i o n s of IFg used i n t h i s work, powdered i o d i n e was f l u o r i n a t e d i n a monel r e a c t o r c o o l e d w i t h an acetone/C0 2 bath (-78°C), the purpose of which was to prevent the r e a c t i o n from proceeding too r a p i d l y . In a t y p i c a l prepara-t i o n , the i o d i n e began t o r e a c t (vigorous b o i l i n g of c o o l i n g bath) when the pr e s s u r e of f l u o r i n e i n the monel r e a c t o r reached 200 mm Hg and then proceeded smoothly with a f l u o r i n e p r e s s u r e of 50 mm. When the r a t e of r e a c t i o n began t o decrease ( b o i l i n g of c o o l i n g bath s u b s i d e d ) , the f l u o r i n e p r e s s u r e was r a i s e d g r a d u a l l y to 1000 mm Hg. F i n a l l y , the pr e s s u r e of f l u o r i n e was allowed to r i s e to about 30 p s i and the r e a c t o r was l e f t at room temperature f o r an hour. A f t e r removal of excess f l u o r i n e at -78°C, HF and other v o l a t i l e i m p u r i t i e s were pumped o f f w i t h the r e a c t o r coole<il to -10 C ( I F ^ has a vp of ^ 3 mm Hg at t h i s temperature; consequently pumping was continued f o r onl y 5 minutes or s o ) . The IF_ was then used f o r the I F 7 p r e p a r a t i o n . However, a more convenient method of p r e p a r a t i o n of IFg i n v o l v e d the p u r i f i c a t i o n of IF^ from a c y l i n d e r . A c y l i n d e r of IF^ (The Matheson Company), which had developed a leak, c o n t a i n e d IF^ contaminated w i t h Ig (brown c o l o u r i n IFg s o l u t i o n ) and, presumably, a x y f l u o r i d e s of i o d i n e . Impure samples of IFj- from the c y l i n d e r were e a s i l y p u r i f i e d by treatment w i t h 1-2 atmospheres of F at room temperature, f o l l o w e d by b r i e f pumping wi t h the monel c o n t a i n e r c o o l e d to -10°C. I n f r a r e d s p e c t r a o f IFy prepared from these IFg samples showed as l i t t l e or l e s s i m p u r i t y as samples from IFg prepared from i o d i n e . (b) The F l u o r i n a t i o n of I F C o To prepare IF^, IF,. (10-20 gm samples) was heated i n a 1.251 monel r e a c t o r w i t h a 50-100% excess of f l u o r i n e at 200-250°C f o r 5-18 hours, and the r e a c t o r was then allowed to c o o l to room temperature. Excess f l u o r i n e was removed w i t h the r e a c t o r c o o l e d i n l i q u i d n i t r o g e n . The p u r i t y of the IFy was r o u t i n e l y checked u s i n g i n f r a r e d s pectroscopy. The p r i n c i p a l i m p u r i t y , I0F_, c o u l d be e a s i l y d e t e c t e d by i t s i n t e n s e a b s o r p t i o n at 926 cm - 1. The i n t e n s i t y of t h i s peak i n i n f r a r e d s p e c t r a of IF^ at or near i t s vapour p r e s s u r e at room temperature ( r ^ l 5 0 0 mm Hg) i n d i c a t e d that the p r e s s u r e of IOFg i m p u r i t y was l e s s than 5 mm Hg. The amount of IOF_ i m p u r i t y was unchanged when IF„ samples were o i taken from l a r g e (1.25 1) r e a c t o r s ( p r e s s u r e s of up to 1000 mm), i n which the IFy was e n t i r e l y i n the gas phase, so the low q u a n t i t i e s of IOF^ seen i n the gas phase s p e c t r a are not a con-sequence of the lowering of i t s vapour p r e s s u r e by i t s d i s s o l u t i o n i n I F ? . IF^ samples were s t o r e d i n monel c o n t a i n e r s over anhydrous NaF. 42 2.1.2 The Preparation of IOF & (a) The Preparation of IF 7/IOF 5 Mixtures IOF_ was prepared by the reaction of IF, with pyrex 5 7 glass wool or with l i q u i d water. The reaction of IF_ with HglOg was also t r i e d as a route to IOF^. However, none of these reagents was? successful i n giving complete conversion of IF_ to the oxy-pentafluoride, mixtures of IF_ and IOF,. generally r e s u l t i n g , even 7 0 when an excess of oxygen containing reagent was used. Apparently the reaction of IOFg with the H 20,Si0 2 or HglOg competes with the reaction of IF_ with the same materials. The reaction with H20, i n p a r t i c u l a r was pursued with the intention of forcing the reaction IF7 + H 20 —y *0 F5 + ^HF to completion. A measured (by hyperdermic syringe) amount of water (^0.5-0.8 cc) i n a Kel-F trap, estimated to be equal to that required for complete hydrolysis of IF- to IOFg, was allowed/ to react with IF- condensed onto i t , by warming the Kel-F trap to room temperature. The r e s u l t s of many reactions so carried out were more or less the same. The IFj and IOF5 reacted to give two l i q u i d layers, both colourless, with the upper layer less i n bulk than the lower. There was no noticable ( i . e . Kel-F trap did not become warm) heat of reaction, except i n one experiment when a s l i g h t warming of the Kel-F trap was noted. Infrared spectra showed the presence of both IF^ and IOFj., each i n appreciable amounts. The lower l i q u i d layer was v o l a t i l e and could be transferred e a s i l y to a monel container codled i n l i q u i d nitrogen. The material transferred was an IFy-IOFg mixture. 43 The upper l i q u i d l a y e r c o ntained m a t e r i a l s having a room temperature vapour p r e s s u r e of l e s s than 0.1 mm. When t h i s l i q u i d was pumped through a Kel-F t r a p c o o l e d i n l i q u i d n i t r o g e n f o r 12 hours, i t separated i n t o a l i q u i d ( v o l a t i l e - passed to l i q u i d N 2 - c o o l e d t r a p ) and a s o l i d ( i n v o l a t i l e - remained be-hind i n Kel-F r e a c t i o n t r a p ) . Attempts at c h a r a c t e r i z i n g both the s o l i d and l i q u i d were u n s u c c e s s f u l ; r e p r o d u c i b l e a n a l y t i c a l r e s u l t s were not obtained w i t h samples from d i f f e r e n t h y d r o l y s i s r e a c t i o n s . Perhaps n e i t h e r i s a pure substance. In s e v e r a l experiments, the IFy/IOFg mixtures r e s u l t i n g from the i n i t i a l h y d r o l y s i s r e a c t i o n s were r e a c t e d w i t h f u r t h e r q u a n t i t i e s of water, q u a n t i t i e s i n excess of that r e q u i r e d f o r complete c o n v e r s i o n of the o r i g i n a l amount of I F 7 to IOFg. How-ever, i n f r a r e d s p e c t r a showed that the v o l a t i l e r e a c t i o n product was s t i l l a mixture of IFy and IOFg, w i t h no r e a d i l y d e t e c t a b l e (peak i n t e n s i t i e s i n IR) change i n the r a t i o of I0F_ to IF_. An experiment i n which IF^ i n the vapour phase, con-t a i n e d i n a l a r g e 1.25 l i t e r tank, was mixed w i t h a measured q u a n t i t y of HgO i n the tank was s i m i l a r l y u n s u c c e s s f u l , mixtures of IFy and IOF^ a g a i n r e s u l t i n g . The q u a n t i t i e s of reagents were such t h a t the HgO would have been e n t i r e l y gaseous i n the 1.25 1 r e a c t i o n volume at room temperature. IF^ l e f t i n c o n t a c t w i t h g l a s s wool or w i t h H^IOg g e n e r a l l y gave a product which was a mixture of IF^ and IOF^, even w i t h c o n t a c t times of s e v e r a l days. 44 (b) The P r e p a r a t i o n o f I F y - f r e e IOFg, I n two o r t h r e e o f t h e two d o z e n o r s o I F ^ r e a c t i o n s w h i c h w e r e c a r r i e d o u t , c o m p l e t e c o n v e r s i o n o f t h e I F _ t o IOF_ was o b s e r v e d . However c o m p l e t e c o n v e r s i o n s c o u l d n o t be r e l i a b l y o b t a i n e d , e v e n when e x p e r i m e n t s w e r e c o n d u c t e d w i t h c o n d i t i o n s a s n e a r l y i d e n t i c a l a s p o s s i b l e t o t h o s e w h i c h g a v e a f o r t u i t o u s c o m p l e t e c o n v e r s i o n . A r e l i a b l e m e t h o d o f p r e p a r i n g IOF_ f r e e o f I F , was 5 7 o b t a i n e d by u s i n g t h e r e a c t i o n o f I F _ w i t h SbF_: i 5 I F ? + S b F 5 — * I F ? ( S b F 5 ) x ( i n v o l a t i l e ) IOFg + S b F 5 : no r e a c t i o n . S b F ^ was p r e p a r e d by h e a t i n g SbgOg ( 5 - 1 0 gms) w i t h a 1 0 0 % e x c e s s o f f l u o r i n e a t 200-300°C f o r 10 h o u r s . I F 7 was s c r u b b e d o u t o f I F ^ / I O F g m i x t u r e s by h e a t i n g o them a t 125-250 C w i t h SbF- i n a 1.25 1 m o n e l c o n t a i n e r . The o d i s a p p e a r a n c e o f t h e I F ^ f u n d a m e n t a l a t 425 cm was u s e d t o show t h e s u c c e s s f u l e l i m i n a t i o n o f I F _ f r o m t h e I 0 F _ . I n some 7 5 i n s t a n c e s , s e v e r a l h e a t i n g p e r i o d s w e r e n e e d e d t o o b t a i n p u r e IOFg. P r e s u m a b l y , t h e r e was some d i f f i c u l t y i n o b t a i n i n g c o n d i -t i o n s u n d e r w h i c h t h e IF_-SbF,. i s n o t d i s s o c i a t e d a n d u n d e r w h i c h 7 o t h e c o m p l e x d o e s n o t f o r m a p a s s i v a t i n g s k i n on S b F g , w h i c h , a s w e l l known, i s a v i s c o u s r a t h e r i n v o l a t i l e l i q u i d . 2.1.3 The P r e p a r a t i o n o f R e F ? The p r e p a r a t i o n o f ReF^ i s d e s c r i b e d i n c h a p t e r V, s e c t i o n 2.1.3. 45 2.1.4 The P r e p a r a t i o n of ReOF_ o ReOFg was prepared i n a flow system, by the r e a c t i o n of rhenium metal (Johnson and Matthey, s p e c t r o g r a p h i c a l l y pure grade) w i t h an Fo/0n gas stream. The apparatus c o n s i s t e d of the « 2 pyrex g l a s s t r a p s and s i l i c a r e a c t i o n tube shown i n f i g u r e 6, which was j o i n e d to the metal vacuum system by a g l a s s - t o - m e t a l compression f i t t i n g . An oxygen c y l i n d e r was connected through a s u l p h u r i c a c i d bubbler to one of the i n l e t s of the metal vac-uum system, the bubbler being present to permit rough measurement of the oxygen flow r a t e . The f l u o r i n e system was m o d i f i e d s l i g h t l y at i t s p o i n t of attachment to the vacuum system (see f i g u r e 2 ) , the c o n n e c t i n g compression s t r a i g h t union being r e p l a c e d w i t h a compression tee, one arm of which c o n t a i n e d a copper tube l e a d i n g to a K e l - F t r a p of f l u o r o l u b e o i l . The o i l served the double purpose of p e r m i t t i n g crude measurement of the f l u o r i n e flow r a t e and p r o v i d i n g a s a f e t y blow-off, i n case of p l u g g i n g of the flow system d u r i n g the experiment. With Re (0.5-1.8 gm) metal i n n i c k e l boats i n the s i l i c a r e a c t o r , the system was evacuated and flamed out c a r e f u l l y , and was then pumped f o r 10-12 hours to o b t a i n a good vacuum. -3 (r*10 mm Hg), A f t e r the d r y i n g t r a p s (E and F) had been c o o l e d w i t h l i q u i d oxygen, the apparatus was again flamed out s e v e r a l times. The remaining t r a p s were then c o o l e d w i t h l i q u i d oxygen and the apparatus was f i l l e d w i t h n i t r o g e n gas, by r e p l a c i n g the oxygen c y l i n d e r w i t h a n i t r o g e n c y l i n d e r . The g l a s s stopcock was then opened and an approximate 5:1 ^2'^2 stream was obtained by making the bubble r a t e of F Q through the blow-off f i v e times g l a s s stopcock (Kel-F grease) / apparatus s e a l e d here after l o a d i n g boats i n t o s i l i c a tube / A B C D s i l i c a tube N i boats c o n t a i n i n g Re To F 2 , 0 2 s u p p l y To pump E F $J = graded s e a l , s i l i c a to pyrex 4 = break s e a l Figure 6. Flow Apparatus for Preparation of ReOF^. ^ 47 that of the oxygen through the a c i d bubbler. The gas stream was allowed to flow f o r 15 minutes a f t e r f l u o r i n e was i n i t i a l l y de-t e c t e d (KI paper) emerging from the downstream o u t l e t . The r e a c t -i o n was i n i t i a t e d by c a u t i o u s l y h e a t i n g the rhenium metal w i t h a smoky flame; once s t a r t e d , the r e a c t i o n u s u a l l y proceeded t o com-p l e t i o n without f u r t h e r h e a t i n g , although i n some cases the rhenium metal ceased burning i n the gas stream and needed to be r e - i g n i t e d . The metal burned f a i r l y q u i e t l y , w i t h a r ed glow and an o c c a s i o n a l b u r s t of flame. Some white fumes were seen and some g l a s s y t r a n s p a r e n t yellow s o l i d appeared on the w a l l s of the r e a c t o r . T h i s d e p o s i t disappeared as the r e a c t i o n proceeded, and was probably an o x y f l u o r i d e which s u f f e r e d f u r t h e r a t t a c k by the Fg-Cvj- A l i g h t y e llow product c o l l e c t e d i n the f i r s t two downstream t r a p s ( C and D). A f t e r the r e a c t i o n was complete, the downstream stopcock was c l o s e d , the gas stream was turned o f f and the system was evacuated. The product i n the /.u-. g l a s s t r a p s was l a t e r t r a n s f e r r e d t o a monel c o n t a i n e r f o r sto r a g e and subsequent o p e r a t i o n s . (In some experiments, a monel storage c o n t a i n e r was atta c h e d t o the p r e p a r a t i v e apparatus at H.) The ReOF_ ob t a i n e d i n t h i s way was p u r i f i e d by pumping 5 for»vl5 min. w i t h the monel c o n t a i n e r c o o l e d t o -15°C or, i n some cases, by t r a p - t o - t r a p d i s t i l l a t i o n i n a pyrex g l a s s system, i n i t i a l and t a i l f r a c t i o n s b e i n g d i s c a r d e d . Experience i n d i c a t e d t h a t the former method of p u r i f i c a t i o n gave m a t e r i a l of the same p u r i t y as the l a t t e r . I n f r a r e d spectroscopy and, e s p e c i a l l y , a vapour p r e s s u r e measurement a t 0°C were used as an index of p u r i t y . Vapour p r e s s u r e s of p u r i f i e d ReOF_ samples a t 0°C f e l l i n the 48 18 range 19-25 mm Hg. The r e p o r t e d value i s 22 mm. The p r i n c i p a l i m p u r i t y i n ReOF,- samples would be ReF^, 123 which i s almost i d e n t i c a l i n vapour p r e s s u r e to ReOF,. and which would, t h e r e f o r e , not be removed by f r a c t i o n a l d i s t i l l a t i o n . However, the experimental c o n d i t i o n s are such that s i g n i f i c a n t q u a n t i t i e s of ReF^ are not expected to form, the compound a r i s i n g 123 i n r e a c t i o n s i n only c l o s e d systems w i t h an excess of f l u o r i n e . ReF^ does not form i n the presence of rhenium metal and ReFg i s converted to ReF^ only on h e a t i n g . In the flow experiment, some ReF- i s formed (vp of u n p u r i f i e d m a t e r i a l i s high; peak i n IR b at 717 cm - ), but i t i s c a r r i e d q u i c k l y out of the heated zone by the gas flow. 2.2 INFRARED AND RAMAN SPECTROSCOPIC STUDIES I n f r a r e d s p e c t r a of IFy, ReOF,-, and IOFg i n the gas phase were obtained u s i n g the i n f r a r e d c e l l d e s c r i b e d i n s e c t i o n 3.1.1. Spectra were recorded w i t h gas p r e s s u r e s r a n g i n g from 1-2 mm Hg up to the room temperature vapour p r e s s u r e of the gas (^2 atm. f o r IOF 5 and I F ? ; rJ 90 mm f o r ReOFg) . 2.2.1 Iodine H e p t a f l u o r i d e , I F ? I n f r a r e d s t u d i e s were c a r r i e d out w i t h s e v e r a l samples of I F 7 from d i f f e r e n t p r e p a r a t i o n s . In a d d i t i o n , s i n c e i n f r a r e d s p e ctroscopy was used as a r o u t i n e method of checking the p u r i t y of IFy samples, many s p e c t r a were ob t a i n e d when i n f r a r e d s t u d i e s were not the p r i n c i p a l t o p i c of i n t e r e s t . Thus the r e s u l t s r e p o r t e d are based on »^50 s p e c t r a of I F 7 samples from f^lO 49 d i f f e r e n t IF7 makes, i n c l u d i n g r ^ i o s p e c t r a o f 4 d i f f e r e n t makes w h i c h w e r e o b t a i n e d s p e c i f i c a l l y f o r i n f r a r e d a n a l y s i s . I n f r a r e d s p e c t r a w e r e o b t a i n e d on ( i ) t h e P e r k i n E l m e r 137 N a C l and K B r S p e c t r o p h o t o -m e t e r s , c o v e r i n g t h e r a n g e s 4000-670 cm-"*" and 800-400 cm"""*" r e s p e c t i v e l y ; ( i i ) t h e P e r k i n E l m e r 21 C s B r S p e c t r o p h o t o m e t e r , c o v e r i n g t h e r a n g e 4000-650 cm ^; ( i i i ) t h e P e r k i n E l m e r 4 2 1 , c o v e r i n g t h e r e g i o n 950-400 cm" 1. See f i g u r e 7. 2.2.2 I o d i n e O x i d e P e n t a f l u o r i d e , I 0 F c 2 5 I n f r a r e d s p e c t r a o f IOFj. s a m p l e s w e r e o b t a i n e d on t h e same i n s t r u m e n t s a s t h o s e u s e d t o r e c o r d t h e s p e c t r u m o f I F ^ a n d , i n a d d i t i o n , t h e P e r k i n E l m e r m o d e l 301 F a r I n f r a r e d S p e c t r o p h o t o m e t e r . See f i g u r e 8. The f r e q u e n c y r a n g e b e l o w 400 cm down t o 200 c m - 1 , i s n o t shown i n t h e f i g u r e . The o n l y p r o m i n e n t p e a k s e e n i n t h i s r e g i o n was a b r o a d i n t e n s e b a n d a t 320 c m - 1 , p r e s u m a b l y a r i s i n g f r o m t h e o v e r l a p o f two o r more a b s o r p t i o n b a n d s . 2.2.3 R h e n i u m O x i d e P e n t a f l u o r i d e , ReOF^ I n f r a r e d s p e c t r a o f ReOFg w e r e o b t a i n e d on t h e same i n s t r u m e n t s a s t h o s e u s e d t o r e c o r d t h e s p e c t r u m o f I F y . See f i g u r e 9. 4000 1500 1400 1300 1200 1100 1000 900 800 700 600 500 Frequency, cm Figure 7. Infrared Spectrum of I F 7 (gas). 51 0 1842 Absorb oo < „ » no peakfe 1B50 1607 1565 1350 1392 1267 600 mm 4000 1800 1700 1600 l600 1400 1300 1200 oo 926 882 844 484 7Q9 .679 615 5^ 80 503 . 447 1200 1100 1000 900 800 Frequency, cm 700 600 500 400 -1 F i g u r e 8. I n f r a r e d Spectrum of IQFe (gas) 965 1987 1453 1367 1279 1110? 992 900? 74 2 711 6 40 4000 1500 1400 1300 1200 1100 1000 900 800 700 600 '400 -1 Frequency, cm Figure 9. Infrared Spectrum of R e O F 5 (gas). 53 2.3 THE ULTRAVIOLET SPECTRA OF I F ? AND IOF 5 2.3.1 Technique The u l t r a v i o l e t s p e c t r a were run i n a q u a r t z c e l l , of 10 cm l e n g t h and 2 cm diameter, w i t h the ends of the c e l l made of q u a r t z o p t i c a l p l a t e s . The c e l l connected t o the vacuum system v i a a Whitey v a l v e . The c e l l was evacuated f o r 18 hours and c a r e f u l l y flamed out p r i o r to i n t r o d u c t i o n of the sample. The samples were d r i e d over NaF f o r 12-18 hours b e f o r e admission to the c e l l . S p e ctra were run on a Cary 14 Spectrophotometer, from 3500 to 2000A. Blank s p e c t r a (scans made w i t h the evacuated c e l l i n the sample beam) were taken b e f o r e and a f t e r the sample s p e c t r a were recorded. 2.3.2 Iodine H e p t a f l u o r i d e , I F ? To prove that I F 7 c o u l d be handled without s i g n i f i c a n t decomposition i n the q u a r t z c e l l , a sample of IF^ was l e f t i n the c e l l f o r 12 hours and the i n f r a r e d spectrum was then recorded. The spectrum i n d i c a t e d t h a t , i n a d d i t i o n to 760 mm p r e s s u r e of I F 7 , t h ere was 20 mm p r e s s u r e of S i F 4 and l e s s than 5 mm pre s s u r e of I0F_. During the r e c o r d i n g of an u l t r a v i o l e t spectrum, a o sample of IF^ would be i n the c e l l f o r l e s s than 30 minutes. The u l t r a v i o l e t spectrum of IFy was taken at sample p r e s s u r e s r a n g i n g from 100 mm to l e s s than 0.1 mm. An i n f r a r e d spectrum of the sample at 60 mm p r e s s u r e , obtained by condensing the sample i n t o the i n f r a r e d c e l l a f t e r the u l t r a v i o l e t spectrum had been recorded, showed only peaks due to I F 7 . 54 Absorbance 2.0 p-I.SL 3500 blank 1-2^ mm J i i _ 3000 2500 Wavelength, ft <0.1 mm - J 1 2000 F i g u r e 10. The U l t r a v i o l e t Spectrum of IF, 50 1 i i i i i i 1 1 i 1 1 1 1 1 1 3500 3000 2500 2000 Wavelength, X F i g u r e 11. The U l t r a v i o l e t Spectrum of I0F_ 56 The u l t r a v i o l e t spectrum of IF^ i s shown i n f i g u r e 10. 2.3.3 Iodine Oxide P e n t a f l u o r i d e , I0F_ 5 IOFg s p e c t r a were recorded at sample p r e s s u r e s ranging from 20 mm to l e s s than 0.1 mm. F i g u r e 11. 2.4- F NUCLEAR MAGNETIC RESONANCE SPECTRA  2.4.1 Sample P r e p a r a t i o n (a) P r e p a r a t i o n of Compounds The p r e p a r a t i o n of ReF 7, ReOFg, I F 7 and IOFg has been d i s c u s s e d elsewhere i n t h i s t h e s i s . WFg was s u p p l i e d by the A l l i e d Chemical C o r p o r a t i o n and was used as s u p p l i e d . IF_ (60 gm), o from the Matheson Company, contaminated w i t h a l i t t l e i o d i n e , was t r e a t e d w i t h f l u o r i n e (2 atms.) at room temperature by shaking the impure m a t e r i a l i n a monel c o n t a i n e r (100 ml s i z e ) . A f t e r removal of excess f l u o r i n e at -196°C, the IFg was pumped b r i e f l y a t 0°C. 19 (b) P r e p a r a t i o n of the Samples f o r F n.m.r. Samples were made up i n tubes of pyrex or s i l i c a . The sample tubes (3 mm diameter) were connected to the vacuum system u s i n g a g l a s s - m e t a l compression f i t t i n g . Since IF^, i n the presence of even t r a c e s of moisture, a t t a c k s pyrex g l a s s or q u a r t z to g i v e IOFg, an. n.m.r. tube was f a b r i c a t e d from T e f l o n rod by t u r n i n g the rod to g i v e a tube w i t h a f l a n g e at the open end. The tube was connected to a b r a s s valve by a n u t - a n d - c o l l a r arrangement s i m i l a r t o that i l l u s t r a t e d f o r the Kel-F t r a p i n f i g u r e 1. I F 7 samples were run i n - t h i s tube, 57 as well as i n s i l i c a tubes. I F 7 and IOFg, l i q u i d s at room temperature, were run pure and i n a solvent (IFg), while ReF^ and ReOFg, which are s o l i d s at room temperature, were run only i n a solvent (WFg). 2.4.2 Nuclear Magnetic Resonance Spectra 19 F n.m.r. spectra were recorded and largely interpreted by Dr. E. J. Wells and Dr. L. W. Reeves. The spectra were obtained at 40 or 56.4 Mc/s using a Varian HR Spectrometer... Chemical s h i f t s and spin coupling constants were measured using sideband-cal i b r a t e d charts or, for sharp resonances, by superposition of sidebands on an o s c i l l i s c o p e trace. The sidebands were generated by a Hewlett-Packard o s c i l l a t o r and monitered by a Hewlett-Packard 522B frequency counter. Wherever possible, the sharp l i n e of SiF4 was used as i n in t e r n a l reference. Spectra, except where other-wise indicated, were run at room temperature. 2.4.3 Results Results are presented i n table 1 and figure 12a and b. The spectrum of I F 7 was obtained with samples i n both Teflon and quartz c e l l s . Figure 12-a shows the spectrum at 40 Mc/s i n a Teflon c e l l . The spectrum shows the ef f e c t of attack of the reactive IF„ on the Teflon. In addition to the broad 7 doublet IFy si g n a l , and the sign a l from the Teflon tube, resonance peaks due to IFg ( i d e n t i f i e d by comparison to the spectrum of IFg i n a pyrex tube) and to some un i d e n t i f i e d material(s) (? i n figure) can be seen. These compounds presumably arose from attack of the I F 7 on the Teflon; B a r t l e t t has suggested Table 1 F C h e m i c a l S h i f t s and C o u p l i n g s State (molar r a t i o given for solutions) C h e m i c a l s h i f t s (p. p. m. from SiF^) C o u p l i n g (c.p.s.) L i n e w i d t h (c.p.s.) Compound Equa t o r i a l A x i a l E q u a t o r i a l A x i a l I F 7 Pure l i q u i d 334±3 4,100+300 R e F 7 1:4 i n W F 6 510±1 65±2 IOF 5 Pure l i q u i d -236+1 -272+1 930+100 1,050±50 IOF 0 2:1 i n I F ? -236+2 -271+2 950±100 1,200±100 I O F 5 2:1 i n I F 5 -234.5+1 -272±1 = 280 170+30 R e O F 5 1:4 i n W F g r3£1.9±0.5 -159.6±0.5 JFF = 68.6+1 12+2 OsOFg 1:3 i n WFg Not seen -215+2 1,100+200 ^ 5 Pure l i q u i d -173.6+0.5 -222.2+0.5 Jpp = 85.0+0.8 5+2. W F 6 4:1 i n ReF 7 330.5±0.5 J183 w _ F = 4 3 . 8 + 0 . 5 (a) sample prepared by Dr. N. K. Jha (b) cf: reference 37 59 ? (1) i n T e f l o n c e l l (2-5) i n flamed s i l i c a c e l l F i g u r e 12-a. F Spectra of IF- at 40 Mc/s Figure 12-b. F Spectra of IOF at 56.4 M c . / s . that the u n i d e n t i f i e d m a t e r i a l may be IFgCFg. S i m i l a r l y , I F 7 s l o w l y a t t a c k e d i t s q u a r t z c e l l , decomposing i n time to IOF5 and S i F ^ . The numbers beside (2)-(5) i n f i g u r e 12-a are hours from time of sample p r e p a r a t i o n t o time of n.m.r. scan. These r e s u l t s are i n agreement w i t h those of independent s t u d i e s by s e v e r a l 15,16 groups of workers. The appearance of the IFy s i g n a l showed a temperature dependence, the two components of the doublet sharpening as the temperature was r a i s e d to 70°C. A l s o , the IF^ s i g n a l f o r IFy i n IFg (a 1:1 mole r a t i o ) , which at 28°C shows a doublet s t r u c t -ure i n a more complete stage of c o l l a p s e than pure IF^ ( s p l i t t i n g 3600 cps vs 4100 c p s ) , c o l l a p s e s t o a s i n g l e broad l i n e on c o o l i n g the s o l u t i o n . The spectrum of pure I0F_ ( f i g u r e 12-b shows the spec-trum at 56.4 Mc/s) showed two peaks w i t h no f i n e s t r u c t u r e and an i n t e n s i t y r a t i o .of 1:4. However, the spectrum i n IFg as a s o l -vent showed r e s o l u t i o n of these s i g n a l s , t o a doublet and a q u i n t e t , w i t h a c o u p l i n g of 280 cps (measured from the doublet s p l i t t i n g ) . The i n t e n s i t i e s were a f f e c t e d by second order per-t u r b a t i o n s . The spectrum of IOFg was unchanged when NaF was added t o remove HF. 19 The F spectrum of ReF ? i n WFg showed a s i n g l e sharp l i n e w i t h a l i n e width of 65 cps and a s h i f t of -510 ppm from i n t e r n a l SiF^,. I t s p o s i t i o n and width were temperature independ-ent . The spectrum of ReOF_ i n WF« showed a sharp doublet 5 0 and q u i n t e t . The q u i n t e t ( s i g n a l from a p i c a l f l u o r i n e of the 62 C4 V symmetry molecule - see d i s c u s s i o n ) was seen to be at(much) higher f i e l d than the doublet, the r e v e r s e of the s i t u a t i o n i n IOFg, which has i t s q u i n t e t t o a lower f i e l d than the doublet. (The d i f f e r e n c e i n s h i f t s of the doublet and q u i n t e t i s much l a r g e r i n ReOFg than IOFg.) 2.5 VAPOUR PRESSURE MEASUREMENTS  2.5.1 Technique Vapour p r e s s u r e measurements were made on samples of m a t e r i a l c o n t a i n e d i n the r e s e r v o i r of the Booth-Cromer t r a n s -m i t t e r (chapter I I , s e c t i o n 2.1). Pre s s u r e s were measured u s i n g the t r a n s m i t t e r on semi-automatic c o n t r o l . S i n c e o n l y p e r i o d i c adjustment of the bl e e d v a l v e s was r e q u i r e d t o m a i n t a i n continuous a c c u r a t e p r e s -sure measurement, l a r g e numbers of pr e s s u r e r e a d i n g s c o u l d be obtained i n a sh o r t p e r i o d of time. The temperature was measured w i t h a potentiometer ( G u i d e l i n e Instruments L t d . , type 3184-D) and a copper-constantan thermocouple w i t h an i c e bath as r e f e r e n c e . The accuracy was -t 0.1°C. The potentiometer was checked w i t h an a c c u r a t e (+ 0.05°C) thermometer over the temperature range 0-15°C. P r i o r t o be g i n n i n g a vapour p r e s s u r e measurement, the system was t r e a t e d w i t h f l u o r i n e and then evacuated f o r s e v e r a l hours and t h i s procedure was f o l l o w e d by treatment w i t h a sample of IF^ or IOFg and r e - e v a c u a t i o n . I n f r a r e d s p e c t r a of a sample of the IF_ or IOF K were recorded and the remaining m a t e r i a l was 63 condensed i n t o the r e s e r v o i r of the pressure gauge. The temperature of the r e s e r v o i r was c o n t r o l l e d w i t h a toluene s l u s h bath, i n i t i a l l y at -96°C. The f i r s t p r e s s u r e measurement was taken only a f t e r the gauge r e s e r v o i r had been evacuated b r i e f l y , w i t h the r e s e r v o i r and contents at -96°C. An a i r stream b u b b l i n g through the bath served the double purpose of keeping the c o o l i n g bath w e l l mixed and r a i s i n g i t s temperature sl o w l y enough that the I F 7 or IOFg i n the gauge r e s e r v o i r would always be i n e q u i l i b r i u m w i t h i t s vapour. Furthermore, the r a t e at which the a i r stream warmed the toluene bath decreased r a p i d l y w i t h i n c r e a s i n g temperature, as the temperature d i f f e r -ence between the bath and the room temperature a i r stream decreased. Thus at h i g h e r t e n p e r a t u r e s , when the vapour p r e s s u r e was h i g h e r and changing more r a p i d l y , a g r e a t e r l e n g t h of time was a u t o m a t i c a l l y a f f o r d e d t o keep the condensed phase i n e q u i l -i b r i u m w i t h i t s vapour. Vapour pressure measurements took about o 8 hours to cover the temperature range -70 t o +15 C and about 150 pressure-temperature r e a d i n g s were taken. At the end of the run, an i n f r a r e d spectrum was taken of the m a t e r i a l i n the gauge r e s e r v o i r . 2.5.2 Iondine H e p t a f l u o r i d e , I F 7 Three vapour p r e s s u r e runs were made, each w i t h I F 7 samples from d i f f e r e n t p r e p a r a t i o n s . The data f o r which the r e s u l t s are here presented i s b e l i e v e d to be the best s e t . T h i s c o n t e n t i o n i s based on examination of the i n f r a r e d s p e c t r a of the samples a f t e r the experiment, and on the m e l t i n g p o i n t s o btained from the vapour p r e s s u r e d a t a . ( S e t r e p o r t e d g i v e s 64 h i g h e s t m e l t i n g point.) The i n f r a r e d spectrum i n d i c a t e d t h at no a p p r e c i a b l e amounts of i m p u r i t i e s had a r i s e n d u r i n g the time of the run.(A s m a l l peak at 926 cm 1 i n d i c a t e d the presence of about 1mm Hg i n sample of p r e s s u r e 1000 mm; some unknown impuri t y had i n c r e a s e d the i n t e n s i t y of the IFy peak at 1257 cm"''' s l i g h t l y , r e l a t i v e t o the i n t e n s i t y of the other peaks.) See t a b l e 2. From the p l o t s of l ° g 1 0 P C M vs 1/T l o g 1 0 P C M ( s o l i d —> gas, -40 to +6.45°C) = -1,415/T + 6.971; o l o g 1 Q P C M ( l i q u i d —> gas, +6.45 to '15 C) = -1,244/T + 7.359; m e l t i n g p o i n t , from simultaneous s o l u t i o n of equations o = 6.4 C. The m e l t i n g p o i n t of t h i s IF^ sample was a l s o obtained v i s u a l l y , by condensing the m a t e r i a l , a f t e r vapour p r e s s u r e measurements, i n t o a Kel-F t r a p . The Kel-F t r a p was immersed i n a 5 1 beaker of water at 3°C, and the water bath was allowed to warm, w h i l e being s t i r r e d . The s o l i d melted s h a r p l y at 6.4-6.5°C. 2.5.3 Iodine Oxide P e n t a f l u o r i d e , IOF^ Two vapour p r e s s u r e runs were made, u s i n g samples from d i f f e r e n t p r e p a r a t i o n s . The data r e p o r t e d here i s f o r the set which gave the h i g h e r m e l t i n g p o i n t . The data o b t a i n e d from a p l o t of l o g i o P C M V S 1 / / T I S log^Q P^JJ ( s o l i d —y. gas; -40 to +4.6°C) = -1,543/T + 7.569 65 Table 2 Vapour Pressure Data f o r I F 7 Temp. °C Pressure mm Hg Temp. Pressure °C mm Hg Temp. °C Pressure mm Hg Temp. Pressure °C mm Hg -93 .2 1 . 56 -19 .5 245.42 +2 .4 689. 68 90 .9 1 .66 18 .5 258.76 2 .8 699. 86 88 .2 2 .12 17 .7 268.62 3 . 1 713. 82 83 .3 3 .541 16 .7 285.68 3 .4 723. 64 79 .5 4 .32 16 .0 293.72 3 .7 733. 16 76 .5 6 .64 15 .4 303.34 4 .0 741. 06 73 .6 7 .80 14 .5 313.50 4 .4 748. 90 71 .5 9 .02 13 .9 324.96 4 .5 756. 66 69 .3 12 .60 12 .9 341.26 4 .7 765. 26 68 .4 13 .62 10 .1 396.32 4 .9 773. 22 63 .6 17 .04 .9 12 409.70 5 .2 778. 86 60 .3 21 .86 8 .9 417.50 5 .3 783. 52 58 .9 24 .32 8 .2 426.96 5 .6 785. 44 57 .4 26 .76 7 .7 439.50 5 .9 792. 78 54 .4 32 .72 7 .1 454.94 6 .2 804. 42 52 .0 37 .86 6 .4 466.58 6 .6 816. 76 47 .9 49 .86 5 .8 480.26 6 .8 826. 32 46 .3 54 .32 5 .0 497.74 7 .4 841. 64 44 .9 59 .76 4 .3 511.50 8 . 1 867. 10 42 .9 67 .90 3 .7 527.20 8 .5 876. 12 39 .0 82 .82 3 . 1 541.66 9 .0 890. 92 36 .3 96 .90 2 .2 564.14 9 .2 900. 96 35 .0 104 .70 1 .4 579.62 9 .5 910 . 98 34 .3 112 . 14 1 .2 590.08 9 .9 922. 90 32 .3 126 .72 0 .9 595.96 10 . 1 931. 70 31 .3 134 .92 0 .7 601.48 10 .4 945. 74 29 .2 146 .32 0 .2 614.56 10 .6 950. 02 27 .6 159 .72 0 .0 621.72 11 .0 961. 06 26 . 1 175 .28 +0 .7 638.80 11 .4 980. 56 24 .3 189 .82 0 .9 646.06 12 .0 999. 12 23 .8 195 .00 1 .2 655.42 12 .5 1017. 50 22 .2 212 .84 1 .5 662.70 13 .0 1035. 62 21 .4 220 .96 1 .8 674.62 13 .5 1049. 82 20 .6 231 .44 2 . 1 680.80 14 .0 1068. 60 +14.3 14.6 14.9 1080.08 1090.32 1098.00 66 Table 3 Vapour Pre s s u r e Data f o r IOF Temp. Pressure Temp. Pressure Temp. Pressure Temp. Pressure C mm Hg °C mm Hg °C mm Hg °C mm Hg -95.4 0.32 -29 .9 169 .24 -11 . 1 479. 28 +3. 8 983. 88 88.6 0.51 29 .1 176 .66 10 .3 501. 20 3. 9 993. 96 76.2 4.14 28 .5 182 .86 9 .7 514. 16 4. 2 1007. 14 74.9 4.90 28 .0 188 .00 9 . 1 528. 58 4. 4 1015. 46 73.2 5.50 27 .4 194 .92 8 .9 537. 34 4. 8 1033. 16 71.2 8.04 26 .9 200 .36 8 .2 556. 22 5. 1 1042. 14 68.4 9.26 26 .4 206 .68 7 .6 575. 88 5. 3 1053. 94 66.7 11.16 25 .9 211 .76 7 .2 583. 22 5. 5 1063. 98 63.1 14.88 25 .4 218 .28 7 .1 587. 76 6. 0 1083. 22 62.2 16.38 24 .7 228 .00 7 .0 590. 40 6. 4 1102. 62 61.3 17.82 24 .2 234 .78 5 .5 635. 84 6. 5 1108. 48 60.2 19.62 23 .6 243 .84 4 .6 683. 34 7. 0 1120. 66 57.0 22.30 23 . 1 250 .26 4 .2 684. 26 7. 1 1128. 68 56.8 26.26 22 .6 257 .86 3 .6 694. 56 7. 3 1135. 26 55.5 28.28 22 . 1 265 .16 3 .2 709. 46 7. 4 1142. 54 52.8 37.32 21 .7 271 .98 2 .7 736. 96 7. 6 1148. 42 51.3 38.56 21 .25 278 .94 2 .0 753. 18 7. 7 1153. 66 50.0 43.98 20 .6 286 .96 1 .8 767. 86 7. 9 1162. 20 48.0 49. 86 20 .2 294 .34 1 .4 776. 62 8. 0 1165. 22 47.0 53.78 20 .0 301 .96 1 .3 783. 16 8. 1 1172. 94 46.2 57.42 19 .3 311 .78 1 .0 791. 12 8. 3 1178. 96 45.5 59.32 18 .7 320 .08 0 .7 800. 36 8. 5 1185. 56 45.0 62.26 18 .4 326 .86 0 .5 809. 46 8. 6 1191. 66 43.0 74.54 18 .0 333 .48 0 .4 818. 52 8. 8 1198. 66 41.2 79.96 17 .6 340 .40 0 . 1 829. 16 9. 0 1207. 44 40.8 83.46 17 .2 346 .78 0 .0 834. 26 9. 1 1214. 18 40.0 87.24 16 .9 353 .60 +0 .2 838. 96 9. 2 1219. 22 39.1 92.32 16 .6 360 .22 0 .6 852. 90 9. 3 1225. 66 38.4 99.92 16 .3 366 . 18 0 .8 862. 46 9. 6 1235. 30 36.6 109.08 15 .9 373 .96 1 .3 869. 40 9. 7 1242. 02 35.8 117.42 15 .4 382 .20 1 .4 886. 08 9. 8 1244. 84 34.3 130.28 15 .2 388 .42 1 .6 896. 66 10. 0 1252. 38 32.9 141.58 14 .6 397 .52 1 .8 901. 12 10. 2 1265. 76 30.8 149.40 14 . 1 411 .94 2 .4 928. 26 10. 7 1290. 78 30.4 161.76 12 .5 427 .96 2 .9 951. 04 10. 9 1293. 54 11 .9 479 .28 3 .2 963. 84 67 l o g 1 0 P C M ( l i q u i d —> gas; +4.6 to 11°C) = -1,250/T + 6.514. The m e l t i n g p o i n t obtained from the simultaneous s o l -u t i o n of the two equations i s 4 . 6 ° C 2.6 THE ACID-BASE PROPERTIES OF I F ? 2.6.1 The R e a c t i o n of I F 7 w i t h A c i d s : P F g , A s F 5 , SbF 5, BFg I F 7 d i d not form an adduct w i t h P F 5 at temperatures above -10°C. In one experiment, I F 7 and PFg, i n equimolar q u a n t i t i e s , were condensed together i n a pyrex g l a s s bulb ( w e l l evacuated and c a r e f u l l y flamed out p r i o r t o the experiment) and allowed to r e a c t by b r i n g i n g the bulb to room temperature. The p r e s s u r e of the r e s u l t i n g gas mixture was 250 mm, not s i g n i f i c a n t -l y d i f f e r e n t from the p r e s s u r e of 254 mm expected f o r no r e a c t i o n . In a second experiment, an equimolar mixture of I F 7 and PF^ gave o a p r e s s u r e of 266 mm w i t h a r e s e r v o i r on the system at 0 C, and a p r e s s u r e of 264 mm w i t h the same r e s e r v o i r at -10°C. The r e a c t i o n of I F 7 w i t h AsF^ and the c h a r a c t e r i z a t i o n and s t r u c t u r e of the r e s u l t i n g adduct a r e d e s c r i b e d i n chapter IV. A 1:1 adduct, IFg +AsFg~ was o b t a i n e d . I F 7 r e a c t e d w i t h SbFg to g i v e an adduct i n v o l a t i l e at room temperature. I F 7 i n IF7-IOF5 mixtures disappeared (as evidenced by complete disappearance of s t r o n g IR fundamental at 425 cm - 1) when the mixtures were heated w i t h SbF^. See s e c t i o n 2.1.2, d e s c r i b i n g the p u r i f i c a t i o n of I0F_ w i t h SbF-. 68 To p r e p a r e I F • ( S t f F - ) . . s a m p l e s f o r X - r a y powder s t u d i e s , 7 • '5 x , _ I a s a m p l e o f I F g A s F g was a l l o w e d t o r e a c t w i t h S b F 5 by c o n d e n s i n g e x c e s s S bFg o n t o t h e a d d u c t i n a q u a r t z t u b e a n d l e t t i n g t h e r e -a c t i o n p r o c e e d a t room t e m p e r a t u r e . I n f r a r e d s p e c t r o s c o p y i n d i -c a t e d t h a t t h e A s F g o f t h e o r i g i n a l I F g A s F g a d d u c t was d i s p l a c e d , t h e r e b e i n g a n i n t e n s e p e a k i n t h e g a s e o u s r e a c t i o n p r o d u c t s a t 800 c m - 1 . A s o l i d ( w h i t e ) r e m a i n e d a f t e r t h e A s F g a n d e x c e s s SbFg had b e e n r e m o v e d a t room t e m p e r a t u r e . H owever, X - r a y pow-d e r p i c t u r e s showed o n l y a few weak l i n e s a t l o w a n g l e , i n d i c a t i n g t h a t t h e p r o d u c t was p o o r l y c r y s t a l l i n e . The s o l i d was t h e n h e a t e d (50-6Q°G) o v e r n i g h t i n a p y r e x g l a s s t u b e , u n d e r c o n t i n u o u s e v a c u a t i o n . The h e a t e d p r o d u c t g a v e c o n s i d e r a b l y more l i n e s i n t h e X - r a y powder p h o t o g r a p h , b u t t h e l i n e s w e r e s t i l l i l l - d e f i n e d . C h a n g e s i n t h e powder p h o t o g r a p h w i t h f u r t h e r h e a t i n g i n d i c a t e d t h a t d e c o m p o s i t i o n o f t h e o r i g i n a l p r o d u c t o c c u r r e d u n d e r t h e a t t e m p t e d c r y s t a l l i z a t i o n p r o c e d u r e , a n d t h e a p p e a r a n c e o f t h e p h o t o g r a p h - a s e r i e s o f s t r o n g l i n e s , w i t h a n o t h e r s e r i e s o f w e a k e r b r o a d e r l i n e s b e t w e e n - i n d i c a t e d t h a t h e a t e d m a t e r i a l m i g h t be a m i x t u r e . No l i n e s due t o I F g A s F g w e r e e v i d e n t i n any o f t h e p h o t o g r a p h s . I n f r a r e d e v i d e n c e i n d i c a t e d t h a t I F 7 a n d BFg d i d n o t f o r m a s t a b l e a d d u c t a t room t e m p e r a t u r e . The p e a k s i n a n i n -f r a r e d s p e c t r u m o f I F 7 a t A/ 50 mm p r e s s u r e d i d n o t d e c r e a s e i n i n t e n s i t y on t h e a d d i t i o n o f BFg g r e a t l y (3-4 f o l d ) i n e x c e s s o f t h a t r e q u i r e d f o r t h e r e a c t i o n IF7 + BF3 — * I F 7 * B F g . 69 2.6.2 The R e a c t i o n of I F ? with Bases: NaF, ONF (a) I F 7 d i d not r e a c t w i t h NaF. I F 7 was s t o r e d f o r weeks or months at a time over an excess of NaF r e q u i r e d f o r the r e -a c t i o n NaF + I F 7 —> N a I F g w i t h no evidence f o r any l o s s of I F 7 through adduct formation. The amount of I F 7 recovered from the I F ^ ( l ) - NaF(s) mixtures was always, q u a l i t a t i v e l y at l e a s t , equal to the amount of I F 7 o r i g i n a l l y put i n c o n t a c t w i t h the s o l i d f l u o r i d e . Furthermore, the vapour p r e s s u r e of I F 7 i n c o n t a c t w i t h NaF was the same as that of I F 7 alone. (b) ONF? In an experiment of a p r e l i m i n a r y nature, ONF and I F 7 , each at 300 mm p r e s s u r e i n a constant volume system, were allowed to r e a c t (room temperature) i n a Kel-F t r a p . At room temperature, the Kel-F t r a p c o n t a i n e d a white s o l i d and, i n the gas phase, a yellow vapour.(NOg?)< The b l u i s h c o l o u r of the o r i g i n a l ONF r e a c t a n t , and the c o l o u r of the product vapours i n d i c a t e d the p o s s i b l e presence of a l i t t l e NOg. The s o l i d pro-o duct was v o l a t i l e , and t r a n s f e r r e d r e a d i l y t o a c o o l e d (-196 C) r e s e r v o i r on the constant volume system w i t h the other v o l a t i l e r e a c t i o n p r o d u c t s . The p r e s s u r e i n the constant volume system was l e s s than 400 mm.(cf; 600 mm f o r IF 7~0NF mixture) The p r e s s u r e dropped w i t h time, i n d i c a t i n g decomposition i n the monel system. A l l r e a c t i o n products were condensed back to the K e l - F t r a p , g i v i n g (at 25°C) a c o l o u r l e s s l i q u i d and a yellow vapour. The s o l i d d i d not form a g a i n , having e v i d e n t l y decompos-ed i n the h a n d l i n g p r o c e s s . A f t e r 8 hours of storage at -7C$Cj. the r e a c t i o n products i n the Kel-F t r a p (room temperature) c o n s i s t e d of a c o l o u r l e s s l i q u i d and a c o l o u r l e s s vapour. I n f r a r e d 70 spectroscopy i n d i c a t e d the presence of N0 2F, ONF, I F 7 and I F 5 at room temperature. IF^ a p p a r e n t l y f l u o r i n a t e d the N0 2 to N0 2F. 2.7 THE ACID-BASE PROPERTIES OF I 0 F e 2.7.1 R e a c t i o n w i t h A c i d s : AsF^, SbF^ IOFg and AsFg d i d not g i v e an adduct at room tempera-t u r e . An i n f r a r e d spectrum of IOFg at 1000 mm pr e s s u r e showed no change (no decrease i n i n t e n s i t y of peaks) on a d d i t i o n of AsFg . (^1000 mm pre s s u r e ) The AsFg was i d e n t i f i e d by i t s i n t e n s e fundamental at 800 cm-"'". IOFg does not form an adduct at room temperature w i t h SbFg. J O F J J w a s recovered unchanged (at 20°C) a f t e r h e a t i n g I F 7 / I 0 F 5 mixtures w i t h SbFg at temperatures up to 300°C f o r p e r i o d s of e i g h t hours or more.(See s e c t i o n 2.1.2, on the p u r i -f i c a t i o n of IOF5>.') 2.7.2 Rea c t i o n w i t h Bases: NaF 1 IOFc d i d not r e a c t w i t h NaF. IOF,. c o u l d be recovered 5 5 unchanged from NaF a f t e r c o n t a c t times of weeks or months. The amount of IOF5. recovered was e s s e n t i a l l y equal to the amount put i n c o n t a c t w i t h NaF. A l s o , the vapour p r e s s u r e of IOFg was not lowered when i n c o n t a c t w i t h NaF. 71 2.8 THE ACID-BASE PROPERTIES OF ReF ? AND ReOF^• 2.8.1 R e a c t i o n w i t h ONF The r e a c t i o n s of ReF_ and ReOF_ w i t h ONF are d e s c r i b e d i n 7 5 s e c t i o n s 2.2.4 and 2.2.5. 2.8.2 Attempted R e a c t i o n of ReF 7 wi^h AsFg A sample of ReF 7 i n WFg, remaining from the p r e p a r a t i o n 19 of an F n.m.r. sample, was used i n the attempted r e a c t i o n of ReF 7 w i t h AsFg. AsFg was condensed onto the WFg/AsFg mixture i n a pyrex g l a s s t r a p and the t r a p was brought to room temperature. No p r e c i p i t a t e formed ( a f t e r f i v e minutes at room temperature) and no r e s i d u e remained i n the t r a p when the AsFg,ReF 7 and WFg were removed. 2.9 THE REACTION OF ONF WITH I F C Since ONF a p p a r e n t l y gave a v o l a t i l e adduct w i t h I F 7 , a s i m i l a r r e a c t i o n was attempted w i t h IFg, to i n v e s t i g a t e the f e a s i -b i l i t y of p r e p a r i n g a s a l t c o n t a i n i n g the IF_ anion. b ONF (206 mm) and I F e (204 mm) i n a K e l - F t r a p at room temperature gave a yellow s o l u t i o n , w i t h no s o l i d p r e s e n t . The p r e s s u r e above the l i q u i d phase, however, was only 25 mm, i n d i c a -t i n g t h a t there was some i n t e r a c t i o n between the ONF and IFg. Presumably the l i q u i d phase was a s o l u t i o n of ONF i n IF_. When o more ONF was added to the r e a c t i o n mixture, a white s o l i d appeared on the w a l l s of the t r a p above the s o l u t i o n . T h i s s o l i d was s o l u b l e i n the l i q u i d phase. When more ONF was added, the amount of s o l i d i n the w a l l s i n c r e a s e d and s o l i d began to form i n the 72 l i q u i d phase,(The l i q u i d began t o s o l i d i f y . ) The pressure i n the gas phase was 50 mm. The white s o l i d was v o l a t i l e . When the Kel-F t r a p was evacuated, the s o l i d sublimed away, l e a v i n g the l i q u i d phase, which a l s o disappeared a f t e r a few minutes. A s m a l l amount of white s o l i d remained a f t e r the l i q u i d had vanished. X-ray photo-graphs were obtained, but i d e n t i f i c a t i o n of the s o l i d on the b a s i s of these photographs was not s u c c e s s f u l . 2.10 MAGNETIC MEASUREMENT ON XeF c 6 P r e p a r a t i o n of XeF~ *. In a t y p i c a l p r e p a r a t i o n , xenon b (1 atm. i n 1.25 1) was heated w i t h f l u o r i n e (5 atm. i n 1.25 1) at 250°C f o r 8 hours. At the end of t h i s h e a t i n g p e r i o d , s u f -f i c i e n t f l u o r i n e was added to the r e a c t i o n mixture to r a i s e the t o t a l p r e s s u r e t o 6 atmospheres and the r e a c t i o n mixture was again heated at 250°C. T h i s procedure was repeated u n t i l t here was no s i g n i f i c a n t p r e s s u r e drop d u r i n g a h e a t i n g p e r i o d and the amount of f l u o r i n e consumed approached t h r e e atmospheres. T y p i c a l l y , t hree h e a t i n g p e r i o d s were s u f f i c i e n t , g i v i n g a r a t i o of Xe used to Fg consumed of A; 1:3. I n f r a r e d spectroscopy confirmed t h a t these p r e p a r a t i v e c o n d i t i o n s y i e l d e d XeF . b Magnetic measurements were c a r r i e d out twice, on XeFg samples from two d i f f e r e n t p r e p a r a t i o n s . The r e s u l t s were the same i n both cases. The sample was co n t a i n e d i n a w e l l - f l a m e d 3 mm O.D. q u a r t z tube. P a r t i a l decomposition of the XeF f i o c c u r r e d through 73 a t t a c k of the XeFg on the q u a r t z , g i v i n g a mixture of XeFg and 58 XeOF4- The bulk of l i q u i d (XeOF 4 i s a l i q u i d at room temperature) to s o l i d (XeFg i s a s o l i d at room temperature) was roughly 1:1 i n one sample and much i n favour of the s o l i d phase (at l e a s t 2:1) i n the second, i n d i c a t i n g that each sample was predominantly XeF„. b I n f r a r e d s p e c t r a of m a t e r i a l r e covered from the s u s c e p t i b i l i t y tube a f t e r the magnetic measurements confirmed that i t was a mix-60 t u r e of XeFg and XeOF 4 > X e F g being i d e n t i f i e d by i t s band at 1 61' 1 520 cm" , XeOF 4, by i t s band a t 926 cm" . The XeOF 4 i n the s u s c e p t i b i l i t y tube was yellow-green, the c o l o u r presumably a r i s -i n g from d i s s o l v e d XeFg. XeOF 4 (pure) i s a c o l o u r l e s s l i q u i d - a n d 62 XeFg i s r e p o r t e d to have a green t i n g e i n the vapour s t a t e . (Our own experience c o n f i r m s t h i s o b s e r v a t i o n of the c o l o u r of XeFg vapour.) Magnetic measurements were c a r r i e d out on the XeOF 4/XeFg samples over a temperature range from -196°C to +15°C. In each case, the measured weight changes i n d i c a t e d a temperature indepen-dent diamagnetism f o r the XeOF 4/XeFg mixture. The observed weight change, f o r both samples, over the e n t i r e temperature range was -3.5 ± 0.5 mg. There was no s i g n i f i c a n t v a r i a t i o n i n the weight change w i t h temperature. 74 3 DISCUSSION 3.1 INFRARED AND ULTRAVIOLET SPECTROSCOPIC STUDIES  3.1.1 The I n f r a r e d Spectrum of I F 7 ( g ) The i n f r a r e d spectrum of I F 7 i n the r e g i o n 4000-400 cm 1 shows th r e e i n t e n s e bands, a t 744 cm - 1, 668 cm-1', and 425 cm - 1. These must be fundamental bands. Furthermore, s e v e r a l peaks i n the r e g i o n 1500-1000 cm-1" can be s u c c e s s f u l l y a s s i g n e d as combin-a t i o n bands i f 629 cm * i s chosen as the frequency of a fundamental mode. Indeed, s e v e r a l I F 7 s p e c t r a showed a shoulder on the i n t e n s e 668 c m - 1 peak at 635-630 cm - 1. With these f o u r f r e q u e n c i e s as fundamental modes, many of the observed peaks i n the spectrum can be a s s i g n e d . See t a b l e 4. 38 A comparison of our r e s u l t s and those of Smith w i t h 20 those of Lord et a l . r e v e a l s s e v e r a l e r r o r s i n Lord's i n f r a r e d spectrum: (1) IF^ peaks were r e p o r t e d at 360, 369 and 927 cm - 1. These a r e , however, fundamental modes of I0F_. Our work has o shown that IF^ does not absorb at 927 c m ~ ^ and the i n t e n s i t y of the 360 and 369 cm 1 peaks i n Lord's spectrum i s t h a t expected f o r IOF5 on the b a s i s of the i n t e n s i t y of the 927 cm 1 peak. (2) A peak was r e p o r t e d at 547 cm - 1. I F 7 shows no a b s o r p t i o n at t h i s frequency, even i n s p e c t r a w i t h sample gas p r e s s u r e s of 1-2 atmospheres. Lord et a l . r e p o r t e d an a b s o r p t i o n at pressures as low as 14 mm. We have no s u g g e s t i o n s as to the o r i g i n of t h i s peak. (3) A peak was r e p o r t e d at 1030 cm-1". T h i s peak i s l i k e l y due to a t r a c e of S i F ^ i n t h e i r I F 7 ; I F 7 shows no a b s o r p t i o n 75 Table 4 I n f r a r e d Data and Assignments, I F 7 ( g ) . -1 -1 fundamentals i 744 cm fundamental 629 cm (observed) 668 cm 1 ( p o s s i b i l i t y , suggested 425 cm~* from combination bands) sidebands frequency,observed cm -* 1417 1297 1257 1173 1097 1054 884 744 668 425 1389 1155 833 assignment 744 + 668 = 668 + 629 = 629 + 629 = 744 + 425 = 668 + 425 = 629 + 425 = fundamental fundamental fundamental 1412 1297 1258 1169 1093 1054 76 at 1030 cm - 1. (4) No peak was r e p o r t e d i n the r e g i o n of 744 cm-1". IFy has a very i n t e n s e fundamental at 744 cm * and the peak can be seen at sample p r e s s u r e s of 5 mm or l e s s . While our r e s u l t s are h a r d l y a complete v i b r a t i o n a l a n a l y s i s of I F 7 , they do favour a Dg h symmetry f o r the molecule. 63 The other p l a u s i b l e symmetries f o r I F ? ( C 2 , and C3 V) allow many more i n f r a r e d a c t i v e fundamentals (24, 20 and 14 r e s p e c t i v e -l y ) than does symmetry, which permits only f i v e . Our simple spectrum, w i t h r e l a t i v e l y few peaks i n the combination r e g i o n (above 1000 cm 1 ) , and w i t h only three d e f i n i t e l y e s t a b l i s h e d i n f r a r e d a c t i v e (the 629 cm * peak may be a Raman a c t i v e peak) fundamental modes, i n d i c a t e s a high symmetry. Indeed, as f i g u r e 13-a i n d i c a t e s , the spectrum of IF^ i s comparable i n s i m p l i c i t y t o that of an o c t a h e d r a l h e x a f l u o r i d e . ( e . g . , TeF„) S i g n i f i c a n t l y , 6 most of the combination bands can be a s s i g n e d i n terms of the f o u r fundamentals a l r e a d y chosen. A l s o , at comparable p r e s s u r e s , the IF^ spectrum does not show the complexity of the IOF5 (C^ v) spec-trum i n the 700-450 cm - 1 r e g i o n . Since symmetries C 7 y and D 7 h, which have fewer than f i v e i n f r a r e d a c t i v e fundamentals are not c h e m i c a l l y r e a s o n a b l e , symmetry emerges as the most l i k e l y model f o r the e x p l a n a t i o n of the v i b r a t i o n a l spectrum of I F 7 . The complete v i b r a t i o n a l spectrum of the o n l y other v o l a t i l e AX^ s p e c i e s , ReF 7, has been r e c e n t l y recorded and a n a l y -72 zed by C l a a s s e n and S e l i g . They concluded t h a t the D^ h model f o r ReF 7 f i t t e d t h e i r data b e t t e r than any of the other models 20 — 1 which L o r d * et a l . had suggested f o r I F 7 - I f the 425 cm band 0 0 product, >.~ ^- "W \ path length X V | / V / 1063Vr025 pressure = 4000cmxcm* J " 3+5 1+4 T e F 6 J (assignments 1/1/ 2+3 2+6 indicated) 1451 1425 371 / 509 439 / 481 •5 1392 / length x pressure =4500 / IOF ' 1 3 5 0 i U J r5 926 • • . . 709 | V j 1417 / 1173 1054 884 \ / / length x pressure =3750 U \ V I / 1297 \ 1/ IF 7 6 6 8 1 1 1 1 « 1—1 2000 1800 1600 1400 1200 1000 800 600 400 200 Frequency, cm * Figure 13-a. Infrared Spectra of TeFfi , IOE- , and IF 7 78 of IF^ coresponds to the 353 c m - 1 band of ReF^, a q u a l i t a t i v e comparison of our IF^ spectrum to C l a a s s e n and S e l i g ' s ReFy spec-trum supports our s u g g e s t i o n that IF^ i s D g h < Most s i g n i f i c a n t l y , I F 7 shows two i n f r a r e d a c t i v e fundamentals i n the 560-750 cm - 1 r e g i o n , where Claas s e n and S e l i g p o i n t out that two bands are y expected f o r ReF^ ( ° 5 n ) • (Only one band was a c t u a l l y seen i n ReF^, at 703 cm-"'"; i t was assumed to be the r e s u l t of two over-l a p p i n g fundamentals.) 3.1.2 The I n f r a r e d Spectrum of IOFg(g) The spectrum of IOFg i s compared w i t h t h a t of an o c t a -64 h e d r a l molecule, TeFg , i n f i g u r e 13-a. Since IOFg can be r e -garded as d e r i v e d from a s p e c i e s of 0^ symmetry by the r e p l a c e -ment of a f l u o r i n e atom by an oxygen atom, and s i n c e oxygen and f l u o r i n e are s i m i l a r i n s i z e and mass, some s i m i l a r i t y between the s p e c t r a of IOF and an o c t a h e d r a l s p e c i e s might be expected. 5 As f i g u r e 13-a i n d i c a t e s , t h i s c o n t e n t i o n i s borne out. Both the TeFg and the IOFg s p e c t r a show an i n t e n s e band i n the 700-750 cm - 1 r e g i o n , and both have t h e i r s t r o n g e s t combination bands i n the r e g i o n 1450-1250 cm \ The most s t r i k i n g d i f f e r e n c e i n the s p e c t r a i s the appearance of a very s t r o n g band a t 926 cm-''" i n the IOFg spectrum. Indeed, a c o r r e l a t i o n diagram between O^ and C^ y symmet-r i e s , and a comparison of our IOFg data to data f o r 0^ molecules was used i n our attempts at t e n t a t i v e l y a s s i g n i n g the IOFg spec-trum . Such comparison supplemented the i n f o r m a t i o n d e r i v e d from *We thank R. J . G i l l e s p i e f o r s u p p l y i n g us w i t h h i s unpublished IOFg Raman data. T h i s data, of course, proved i n v a l u a b l e i n h e l p -i n g us to a s s i g n our i n f r a r e d spectrum. 79 158 a comparison w i t h s p e c i e s such as SF5CI, which, a t the time, was the only v o l a t i l e AX5Y s p e c i e s f o r which i n f r a r e d assignments 61 were a v a i l a b l e , and XeOF^ (C4V symmetry). However, although reasonable frequency v a l u e s were obtained f o r most of the funda-mentals, assignment of s e v e r a l of the f r e q u e n c i e s to the v a r i o u s C^v symmetry modes has proved to be a somewhat a r b i t r a r y process w i t h our "pseudo-octahedral" approach. While our a n a l y s i s was s t i l l i n t h i s incomplete s t a t e , 38 Smith p u b l i s h e d h i s i n f r a r e d and Raman data on IOFg, together w i t h v i b r a t i o n a l assignments. U n f o r t u n a t e l y , the f i l e c o n t a i n i n g a l l the d e t a i l s of our t e n t a t i v e assignments has been misplaced and i s not a v a i l a b l e at the time of w r i t i n g of t h i s t h e s i s . Con-sequently a d e t a i l e d comparison of Smith's complete s e t of a s s i g n -ments w i t h our incomplete set cannot be presented here. However a b r i e f comparison of the two s e t s of data had r e v e a l e d no p o i n t s of c o n f l i c t , d i f f e r e n c e s i n assignments being c o n f i n e d to data f o r which our own-assignments were regarded as u n c e r t a i n . Our spectrum agrees w i t h t h a t of Smith, except f o r one 61 band. Smith r e p o r t s t h a t , i n a d d i t i o n to the IF a b s o r p t i o n at 5 640 cm - 1, there i s a b s o r p t i o n due to I0F_ at 640 c m - 1 and that 5 the i n t e n s i t y of a b s o r p t i o n , even f o r samples f r e e d of IFg, i s never l e s s than that of the 844 cm-'*" peak. We have found t h a t IOF does not absorb at 640 cm-"1"; presumably the a b s o r p t i o n seen 5 by Smith i s due to t r a c e s of IFg s t i l l i n h i s p u r i f i e d m a t e r i a l . Smith, who was a b l e to o b t a i n s p e c t r a w i t h path lengths of 54 cm, r e p o r t s many weak bands which we were unable to observe w i t h a 7.5 cm path l e n g t h . 80 Table 5 shows o u r i n f r a r e d d a t a , a l o n g w i t h t h e c o r r e s -p o n d i n g f r e q u e n c i e s o b s e r v e d by Smith, a n d Smith 's a s s i g n m e n t s . (Our own v a l u e s f o r t h e f u n d a m e n t a l s V - ^ , \)g a n d V g w e r e u s e d i n t h e a s s i g n m e n t s . ) Table 5 Infrared Data a n d Assignments, IOF,-(g) Frequency, observed, cm - Assignment, C, symmetry (Smith) Present work Smith tv 1842 1848 926 + 926 = 1852 (A x) 1607 1607 926 + 679 = 1605 (A x) 1565 1565 926 + 640 = 1566 (A x) 1392 1391 680 + 709 = 1389 (E) 1350 1350. 5 640 + 709 - 1349 (E) 1267 1260 926 + 342 = 1268 (E) 926 927. 3 fundamental (a-^) 882 882 679 + 205 = 884 (E) 844 844 640 + 205 = 845 (E) 709 710. 5 fundamental \>g (e) 679 680 fundamental \>2 (a-^) 615 621 (275) + 342 = 617 (E) 580 583 369+205=574(A j+Bj+Bg); 926-342= 584(E) 503 504 709+205-504(Ai+Bi+B^); 305+205= 510(E) 484 485 (275) + 205 = 480 (E) 447 447 640 _ 205 = 435 (E) 81 3. 1. 3 The Infrared Spectrum of ReOFg (g) The infrared spectrum of ReOFg i s compared with that of IOFg and OisOFg (the l a t t e r obtained by Dr. N. K. 9 Jha ) i n figure 13-b. The s t r i k i n g s i m i l a r i t y between the three spectra leaves no doubt that a l l three molecules have the same symmetry. Each spectrum has two intense bands, one i n the region 700-710 cm - 1, the other (PQR branched) i n the region 960-1000 cm"1. Also, each spectrum has a series of combination bands i n the region 1250-1450 cm - 1 and no peaks (exception: I0 Fg> a t high pressure) higher i n frequency than 1500 cm - 1, except for the overtone of the peak i n the 960-1000 cm~l region. P a r t i a l assignment of the ReOFg spectrum can be made on the basis of C4 V symmetry, by comparison with the spectrum of IOFg. The ReOFg 711 and 992 cm - 1 peaks obviously correspond to the 709 and 926 cm - 1 peaks of IOFg; hence the assignments \>(p) , 711 c m~ 1 ; V , ( a ), 992 cm - 1. 0 0 600 mm 1842 1/ / 1392 1 IOF 5 V 1 3 5 0 926 8 844 . 7C 2. 1 i t i 90 mm 1 9 8 7 145*3 13V67 ReOFg 1 1 640 200 mm 1405 1 I 1 1337 l\l 960 \» OsOF 5 I - l _ 1 l _ 1 . L - ! — 800 i 1/ 700 / 1 L J 2000 1800 1600 1400 1200 1000 800 600 400 200 Frequency, cm Figure 13-b. Infrared Spectra of IOFg, ReOFg, and OsOF 5. 83 Two other infrared active fundamentals are seen i n IOF c o in the region 600-750 cm" ( V 2 and V 3) and corresponding bands can be expected i n ReOFg. The peak seen at 640 cm - 1 i s obviously one of these; the peak at 742 cm"1" i s probably the other. The fact that the 1453 cm-"'" peak can be assigned as (742 + 711) sup-ports the choice of 742 cm"1 as the frequency of a fundamental mode. Rather a r b i t r a r i l y , on the basis of the available evidence, the 742 cm - 1 peak i s chosen a s V g ^ a ^ ) and the 640 cm"1 peak as "V3(a^). These choices give a better c o r r e l a t i o n of frequencies with the corresponding IOFg frequencies than would the reverse choice. A f i f t h assignment can be made with some degree of certainty. In I0F_, 640 cm - 1 i s chosen as the frequency of the b Raman active V g mode. Smith points out that the combination band V g + V g should occur strongly i n the infrared region. He attributes i t s absence i n the I0F_ spectrum to a coincidence i n 5 ; the\)g a n d V g frequencies. However, i n the ReOFg spectrum a ; strong band occurs at 1367 cmT^. If t h i s i s assigned to \ ) g+ V g > a frequency of 656 cm ^ i s derived f o r V g ( b ^ ) . The data for ReOFg i s given i n table 6. 3.1.4 Comparison of Frequencies The frequency of the t o t a l l y symmetric, stretching mode (the M-0 symmetric stretch) decreases i n the order ReOFg> OsOFg^ IOFg.(992, 960 and 926 cm"1) Since iodine i s l i g h t e r than the two t r a n s i t i o n metals, the eff e c t of mass would be to make the 1-0 stretching frequency higher than the Re-0 or Os-0 frequency. The difference i n mass of rhenium and osmium i s n e g l i g i b l e . 84 Table 6 Infrared Data and Assignments, ReOFc Fundamentals, C^ v symmetry observed cm * 992 V± (a x) 742 V 2 (a r) 0>3?) 711 \ ) 8 (e) 640 V 3 (a r) (Vg?) derived cm 656 V 5 (b]_) Frequency, observed, cm 1987 1453 1367 1279 ~1110? 992 965 (shoulder) rj 900? 742 711 646 -1 Assignments 992 + 992 = 1984 (A±) 742 + 712 = 1454 (E) 656 + 711 = 1367 (E) fundamental, (a^) fundamental, V 2 (a^) fundamental, \)g •(©••) fundamental, Vg (a-jO selection rules, symmetry: IR and R a^ ( - V4) e ( V 8 - V n ) R only b x (V>5, V 6 } >2 b n ( V 7 ) 85 Hence the observed order indicates a decrease i n the M-0 bond strength along the series ReOFg, OsOFg, IOFg. The decrease i n M-0 bond strengths from rhenium to osmium p a r a l l e l s the similar decrease i n M-F bond strengths i n 19 the hexafluorides. In the discussion of our F n.m.r. r e s u l t s i n a following section, the hypothesis that double bonding i s more important i n the t r a n s i t i o n metal oxyfluorides than i n IOFg i s advanced. In the extreme cases, the two bonding situations are regarded as M=0 (M=Re,Os) and I + — 0 ~ . If t h i s hypothesis i s correct, the frequencies observed for the stretching modes in d i e - -ate that the former type of bonding for the t r a n s i t i o n metals leads to stronger bonds than the l a t t e r type of bonding for iodine 3.1.5 The U l t r a v i o l e t Spectra of I F ? and IOFg The u l t r a v i o l e t spectra of I F 7 and IOFg showed intense maxima centred at s l i g h t l y less than 2000 X (IF 7) and at 2765 ft (IOF5). Molar extinction c o e f f i c i e n t s for the two vapours were 7 of the order of 10 liter/cm-mole. 3.2 1 9 F N.M.R. SPECTRA OF HEPTAVALENT FLUORIDES AND OXYPENTA-FLUORIDES 6 5 3.2.1 The Heptafluorides The 1 9 F n.m.r. spectra of ReF 7 (a single sharp line) and I F 7 (a broad doublet, s p l i t t i n g f i e l d independent) have been 65 interpreted by Reeves and Wells i n terms of the e f f e c t s of quadrupole coupling on a set of time-averaged magnetically equivalent f l u o r i n e n u c l e i , the equivalence of the nuclei a r i s i n g 86 from a rapid intramolecular rearrangement. The central nuclei, 1 2 7 I , 1 8 5 R e , and 1 8 7 R e a l l have spin 5/2 and hence possess, i n addition to a dipole moment, a quadru-p l e moment. In a sp h e r i c a l l y symmetric e l e c t r i c f i e l d , coupling between the spin 5/2 (general, n) nucleus and a set of equivalent nuclei of attached ligands s p l i t s the resonance l i n e of the set of nuclei into s i x (general, 2n+l) l i n e s . A s p l i t t i n g pattern corresponding to such an ef f e c t has been observed for some species of 0 h and T d symmetry. (I = 9/2, 9 3 N b F 6 ~ 6 6 , 7 3 G e F 4 6 7 ; 1=3/2, 1 1 B e F 4 ^ 6 8 ' 6 9 , 7 5 A s F 6 - 6 8 , SFg 7 0.) However, i n an asymmetrical e l e c t r i c f i e l d , rapid relaxation of the quadrupolar nucleus occurs and as a r e s u l t the set of equivalent nuclei gives a single sharp resonance, since the s p l i t t i n g due to spin-spin coupling disappears. In molecules close to 0^ symmetry, the f i e l d gradient can be expected to cause a p a r t i a l collapse of the spin-spin s p l i t -t i n g between the quadrupolar nucleus and the set of fl u o r i n e n u c l e i . The heptafluorides, which one expects w i l l have a mole-cular shape derived from symmetry by i n s e r t i o n of a seventh ligand with concomitant rearrangement of ligands, are l i k e l y to be i n t h i s intermediate category. Symmetries D 5 n ^ and C2y^ have both been suggested for the s t i l l - d i s p u t e d shape of the I F V molecule. The n.m.r. evidence i s consistent with a model of seven equivalent nu c l e i , the equivalence being due to a time-averaging of the nuclei by intramolecular exchange, with p a r t i a l l y 185 resolved spin-spin s p l i t t i n g . The quadrupole moments of Re and Re (2.8 and 2.6) are about four times larger than that of 87 (0.75), and the Re-F coupling i s expected to be smaller 65 19 than the I-F coupling. These ef f e c t s both cause the F signal i n ReFj to be more collapsed than i n IFy, as observed. Also, the IF^ doublet sharpens somewhat on increasing the temperature and tends to collapse to a single l i n e on lowering the temperature, consistent with the behaviour expected for a quadrupolar ef f e c t and opposite to the behaviour expected for an intermolecular ex-change e f f e c t . This picture of the quadrupolar mechanism means that the observed s p l i t t i n g of the IFy doublet i s due to I-F coupling, and leads to an estimated J of /v 1 Kc/sec. This implies that a l l 127 the fluorine nuclei have a l i f e t i m e on a given I nucleus of -4 more than 1.5 x 10 seconds, and indicates an intra-molecular averaging. A lower l i m i t on the rate of t h i s process i s .set by the absence of F-F coupling i n the sharp ReFy sign a l . Assuming th i s coupling to have a similar value to Jp_p i n ReOFg (68 cps) sets the maximum li f e t i m e of a given configuration of IFy or -3 ReF 7 at 2.5 x 10 sec. 3.2.2 Bonding i n the Oxypentafluorides The spectra of IOFg and ReOFg are consistent with C 4 v symmetry for the molecules, the doublet and quintet (intensity r a t i o 4:1.) being the pattern expected for a molecule containing one set of four equivalent fluorines and one unique f l u o r i n e . However, the differences i n d e t a i l of the spectra of the two oxyfluorides are of i n t e r e s t . (See schematic diagram 19 showing the 56.4 Mc/sec F n.m.r. spectra, figure 14.) IOFg has i t s quintet to s l i g h t l y lower f i e l d than i t s doublet, while IF 5 y I i i . i d . ReF7 1 • • « i • ReOFg 1 I • • » • » . i l u j OsOFj \ 1 • W F 6 1 1 , 1 . i 1 j -500 -400 -300 -200 Chemical Shift (ppm from SiF^) Figure 14. Schematic Diagram of 56.4 M c . / s e c . ^ F Spectra 89 ReOFg has i t s doublet to much lower f i e l d than i t s quintet. The doublet resonance of ReOFg i s shifted considerably downfield from the doublet and quintet signals of IOFg, and from the quintet signal of the ReOFg, the l a t t e r three signals occurring close together, r e l a t i v e to the i r separation from the ReOFg doublet. V o l a t i l e t r a n s i t i o n metal fluor i d e s generally have the i r resonance to lower f i e l d than corresponding nontransitional flu o r i d e s of similar stoichiometry. (cf., I F 7 and ReF 7; IOFg and WFg; IOFg 71 and ReOFg doublet; MoFg, WFg and SF g, SeFg, TeFg ) Hence the ReOFg quintet seems to be at an anomalously high f i e l d . These s h i f t s have been s a t i s f a c t o r i l y accounted for by Ba r t l e t t i n terms of dTT - pTT bonding between the central atom and the f l u o r i n e and oxygen ligands. The argument assumes that i n the tr a n s i t i o n element fluor i d e s the 5d o r b i t a l s are available for bonding, while i n the iodine flu o r i d e s they are not. IT-bonding w i l l reduce the p o l a r i t y of the f l u o r i n e - c e n t r a l atom bond and 19 cause the F resonance to be shi f t e d to lower f i e l d . Conversely, i f TT-bonding i s s l i g h t , or absent, a more polar bond w i l l r e s u l t 19 and the F resonance w i l l appear at higher f i e l d . In ReOFg, there i s a tendency towards double bond form-ation, by donation from the f i l l e d pTT-orbitals on the ligands into the d TT-orbitals of the rhenium. There are three d o r b i t a l s of TP-symmetry on the rhenium and each ligand can donate electron density into two of these. The oxygen and a x i a l f l u o r i n e , for example, can donate to the d x z and dy Z o r b i t a l s , but not to the d x y o r b i t a l . (The normal convention of choosing the unique axis to be the z axis i s used here.) In general, the ligand on axis 90 x i can overlap with the d x ^ X j and dx^x^ o r b i t a l s , but not with the d X j X k o r b i t a l . (x^,Xj,x k = x,y,z permutations) Since oxygen i s a better electron donor ligand than f l u o r i n e , the d x z and d v z o r b i t a l s w i l l be involved more in bonding with the oxygen than the fluorines. As a r e s u l t , l i t t l e or np dTT - plT bonding w i l l occur between the rhenium and the a x i a l f l u o r i n e , since the two dlT o r b i t a l s involved i n bonding to the oxygen are the only two which can If-bond with the a x i a l f l u o r i n e . The four equatorial fluo r i n e s , however, can s t i l l overlap with the d Y„ o r b i t a l , which cannot be used i n TT -bonding with the oxygen. The TT-bonding of the equatorial f l u o r i n e s decreases the diamagnetic shielding about the equatorial fluorines and th e i r resonance appears at low f i e l d , whereas the lack of TT-bonding of the a x i a l f l u o r i n e (a r e s u l t of the strong 7f-bonding of the oxygen) leaves i t s resonance i n the region expected for a f l u o r i n e i n a related non-t r a n s i t i o n a l f l u o r i d e . The 1 9 F n.m.r. spectrum of OsOFg (n.m.r. samples were 9 prepared by Jha ) i s consistent with B a r t l e t t ' s picture of TT-bonding i n a t r a n s i t i o n a l element oxypentafluoride. The spec-trum shows a single broad resonance to high f i e l d , i n the region where, by analogy to ReOFg, the quintet resonance of the a x i a l f luorine would be expected, and t h i s resonance may l o g i c a l l y be assumed to be the unresolved quintet of the equatorial f l u o r i n e s . Since OsOFg has a single nonbonding d electron, and since the oxygen ligand is'the strongest TT-bond donor, t h i s unpaired non-bonding d electron w i l l reside i n the d x v o r b i t a l , rather than t h e d x z o r d v z o r b i t a l s - (Note again that the d x z and d v z o r b i t a l s can TT-bond with the oxygen, while the d Xy cannot.) Since the d x y o r b i t a l can interact with the equatorial fluorines but not with the a x i a l f l u o r i n e s , the unpaired electron spin eliminates only the equatorial f l u o r i n e resonance. In IOFg, where Tf-bonding i s presumed to be absent, no downfield s h i f t of fl u o r i n e resonances occurs, and the resonance of the a x i a l and equatorial fluorines i s close together. 3.2.3 Oxidation State and Chemical Shift The schematic diagram of figure 14 shows that there i s a rela t i o n s h i p between oxidation state and chemical s h i f t . The compounds with the central atom i n the higher oxidation state and, hence, with the central atom carrying the higher p o s i t i v e charge have the i r resonances to lower f i e l d . (cf. , I F 7 and IFgJ ReF 7 and WFg) Since the compounds with the greater p a r t i a l p o s i t i v e charge on the central atom are expected to have the less polar M-F bonds, (a greater p a r t i a l charge on M implies greater 19 po l a r i z i n g power) the observed order of F resonance signals i s the anticipated one. Two f l u o r i n e atoms have a greater electron-withdrawing power than one oxygen atom and therefore the posit i v e charge on MFy i s expected to be higher than that on MOFg, i n spite of the fact that M has the same formal oxidation state i n both compounds. Thus the M-F bonds i n MF7 should be less polar than i n MOFg, and 19 the F resonance signal of the former should be to low f i e l d of that of the l a t t e r , as i s observed, (cf., I F 7 and IOFg; ReF 7 and ReOFg) 92 3.3 THE SHAPE OF THE I F 7 MOLECULE AND LIGAND INTERCONVERSION Although no d e f i n i t e conclusions on the shape of the IF 7 molecule have emerged from our infrared and nuclear magnetic resonance studies, the evidence strongly suggests a high symmetry for the molecule i n the l i q u i d and gaseous states. The s i m p l i c i t y of the infrared spectrum indicates that I F 7 has a high symmetry i n the vapour state, and D 5 N symmetry, or a symmetry which i s only a s l i g h t d i s t o r t i o n from Dc^ symmetry, seems l i k e l y for I F 7 . The stereochemically r i g i d model which Burbank proposed 19 for I F 7 i n the s o l i d cannot be used to explain the F n.m.r. spectrum of I F 7 ( 1 ) , since the expected difference of chemical s h i f t s for the two kinds of flu o r i n e atoms i n Burbank's model i s of the order of 20-100ppm , much larger than the maximum permit-73 * ted s h i f t difference (2 ppm ) consistent with the observed I F 7 n.m.r. spectrum. However, because of the rapid intramolecular exchange 19 occurring i n the l i q u i d , the F n.m.r. spectrum gave no informa-tion on the equilibrium configuration of I F 7 . The observed exchange process, however, i s in t e r e s t i n g . Apparently heptaco-74 75 ordinate I F 7 , l i k e many pentacoordinate species-PF5 i s perhaps the best known example- has a very low energy b a r r i e r for a process which interconverts the ligands i n the molecule. In pentacoordinate species, the process interconverting the With such a small permitted s h i f t difference, the fl u o r i n e ligands of I F 7 are at least approximately equivalent, and the discussion i n section 3.2.1 i s not affected. 93 ligands (between a x i a l and equatorial positions of D"3n symmetry) i s believed to be a d i s t o r t i n g vibration. While the process occurring i n I F 7 could be simply an interconversion of ligands i n one stereochemical modification, there i s a p o s s i b i l i t y that I F 7 i s interconverting between d i f f e r e n t stereochemical structures. 63 Claxton and Benson have pointed out the s i m i l a r i t y between the d i f f e r e n t possible arrangements of seven coordinate species. Possibly the energy difference between the most stable stereo-chemical modification of I F 7 and less stable modifications i s small indeed. 3.4 VAPOUR PRESSURE DATA FOR I F ? AND IOFg. ASSOCIATION IN THE  LIQUID AND SOLID STATES. Data derived from vapour pressure measurements of I F 7 and IOFg are presented i n table 7, along with that for several other compounds for comparison. The d i s s i m i l a r i t y of I F 7 and IOFg to the interhalogens and the s i m i l a r i t y to the hexafluorides i s evident. The high v o l a t i l i t y , low heats of vaporization and values of entropies of vaporization near 21 cal/mole a l l indicate the unassociated nature of I F 7 and IOF,- i n the l i q u i d phase. BrFg and IFg, which are known to a s s o c i a t e ^ 7 i n the l i q u i d state by the s e l f - i o n i z a t i o n 2MFX ^± MF ^ + MF X + 1, have high b o i l i n g points and heats of vaporization, and entropies of v a p o r i z a t i o a well above 21 cal/mole°. In the s o l i d phase, the data of table 7 again indicates 94 Table 7 Some Physical Data for I F 7 and IOF5, and Related Compound t r i p l e pt. b. °C p ,mm °i ,„ a I F 7 6.4 813 +4.8 (i I 0 F 5 a 4.6 1,010 -1.9 ( b B r F 3 8.7 B r F 5 C -60.5 I F 5 d 9.4 T e F 6 e -37.8 WF 6 6 2.0 413 HVAP q O SVAP HSUB SSUB HFUS cal/mole cal/mole° cal/mole cal/mole cal/mole I F ? 5,690 20.5 6,470 23.3 780 IOF 5 5,720 21.2 7,050 26.0 1,330 BrF3 10 ,200 25.7 13,070 2,870 BrF 5 7 ,310 23 9,070 1,760 IF 5 9,880 26.6 13,480 3,600 w 6 6,740 (1,900) WF6 6,330 21.8 7,750 23.3 420 q O bFUS 2.8 4.8 1.45 References: (a) present work; (b) 79; (c) 80; (d) 81; (e) 95 the r e l a t i v e l y small intermolecular forces acting i n I F 7 and IOFg. I F 7 and IOFg show sublimation pressure (both reach a sublimation pressure of 760 mm) and heats of sublimation more akin to the hexafluorides (e.g., TeF_ and WFe) than to the i n t e r -b b halogens such as IFg, BrFg and BrFg. This i s perhaps not surprising, since the Van der Waals forces i n s o l i d IOFg and I F 7 would be expected to be closer to those of the symmetrical hexa-12 flu o r i d e s than the lower-symmetry interhalogens. Ruff and Keim had concluded, on the basis of the i r vapour pressure data, that I F 7 was associated i n the l i q u i d and vapour states but t h e i r arguments do not seem to be v a l i d . The data presented here c e r t a i n l y leaves l i t t l e doubt that I F 7 and IOFg are e s s e n t i a l l y nonassociated molecular s o l i d s . The low values of the entropies of fusion for IOF_ and o I F 7 are in t e r e s t i n g ; again a comparison to the si m i l a r low values i n the hexafluorides can be made. In the t r a n s i t i o n 78 O metal hexaf luorides , the low values of Sj,^g have been assoc-iated with r o t a t i o n a l freedom of the MF„ molecules i n the s o l i d 6 at the t r a n s i t i o n point. The degree of rot a t i o n i n the s o l i d a,nd l i q u i d phases at the t r a n s i t i o n point i s about the same. Presumably, there i s a considerable degree of r o t a t i o n a l free-dom i n s o l i d IF„ and IOF,_ at th e i r melting points, as well. 7 5 96 3.5 THE ACID-BASE PROPERTIES OF IF, AND IOF-. : 7 5 Although a systematic study of the acid-base properties of I F 7 and IOFg was not undertaken during t h i s work, the inform'-ation which i s avail a b l e permits some comment on acid-base properties. The weak donor-acceptor properties of I F 7 and IOFg are apparent, but I F 7 may show weak, previously unrecorded, acceptor properties. 3.5.1 Adduct Formation with I F 7 and IOFg I F 7 acts as a base only towards strong acids such as AsFg and SbFg; no stable adducts at room temperature were iso l a t e d with BFg or PFg. That I F 7 i s indeed acting as a base (flu o r i d e ion donor) i n i t s adduct with AsFg i s proven i n chapter IV. Whether I F 7 w i l l act as an acid i n the presence of strong f l u o r i d e ion donors i s a matter of some doubt. It could be suggested that the v o l a t i l e compound which formed i n the ONF-I F 7 reaction mixture i s an IFg adduct, since IFg has been found i n the present work to form a v o l a t i l e adduct with ONF, and since traces of IFg were detected i n the 0NF-IF 7 gaseous reac-ti o n products. However, the apparent high v o l a t i l i t y of the adduct formed i n the ONF-IF_ reaction, and the presence of only 5 traces of IFg i n the 0NF-IF 7 system are not consistent with t h i s suggestion. It seems more l i k e l y that the IFg arose from a reaction between I F 7 and traces of N0 2 i n the ONF supply. Fur-ther work on the reaction i s obviously needed, both to prove conclusively that the adduct i s one of I F 7 and to es t a b l i s h the stoichiometry of the product. The problem i s worth pursuing; 97 the ONF-IF 7 adduct was v o l a t i l e at room temperature and grew rea d i l y into single c r y s t a l s suitable for X-ray analysis. The s t a b i l i t y of t h i s adduct can be contrasted with that of other ONF-(base) adducts. NOBF4, NOPFg and NOAsFg, for 83 example, are a l l stable s a l t s at room temperature. On the other hand, N0C1F2, formed as a white s o l i d 4 1 at -78°C, i s completely dissociated at room temperature. In a preliminary experiment conducted i n t h i s laboratory, before the observations on the ONF-IF 7 system were available, IF7 was not found to form an adduct when heated with CsF, the pres-sure of I F 7 being e s s e n t i a l l y the same before and a f t e r heating. However, i n view of the observations with ONF, and with the d i s -cussion of section 1.2 i n mind, one might expect an adduct between CsF and IF„. Such behaviour for IF- would p a r a l l e l that 7 7 of C1F. N0C1F2, as mentioned, decomposes at 20°C, but KC1F2, 42 RbClFg and CSCIF2 are a l l stable at room temperature. ( A l l were formed merely by heating the a l k a l i metal f l u o r i d e i n an atmosphere of C1F, with or without ONF as a catalyst.) The 51 -2 possible existence of the anion TeFg i n the adduct 2CsF-TeFg off e r s further encouragement. Repetition of the experiment with va r i a t i o n i n I F 7 pressure, temperature, or time of heating, or some other change i n technique would be worthwhile. IOF_ showed no evidence for acid-base properties, f a i l -5 ing to give adducts with AsF 5, SbF,. and NaF.(at room temperature) Thus t h i s pseudo-octahedral compound may be s i m i l a r i n i t s a c i d -base behaviour to SFg and SeFg but, i n view of the behaviour of i t s period neighbour, TeF f i, with CsF, further experiments with 98 IOF would be desirable before forming f i n a l conclusions on i t s f l u o r i d e ion acceptor properties. Its lack of reaction with SbFg indicates n e g l i g i b l e f l u o r i d e ion donor properties, SbFg being one of the strongest f l u o r i d e ion acceptors known. 3.5.2 Comparison of I F 7 to XeFg A comparison of the acid-base properties of I F 7 with those of XeF„ i s i n t e r e s t i n g . XeF c, which almost c e r t a i n l y has 6 ° a s t e r i c l y active lone pair, w i l l be pseudo-heptacoordinate and therefore might be expected to have acid-base properties s i m i l a r to I F 7 . In each case, loss of a f l u o r i d e ion would give a regu-l a r octahedral configuration of electron pairs about the central atom; the gain of a f l u o r i d e ion would give an "electron pair configuration" of greater than seven. However the i r acid-base properties are i n sharp con-t r a s t . As outlined i n the introduction, XeF., shows both acid 6 and base properties, forming adducts with AsFg, SbFg,BF3, the a l k a l i f l u o r i d e s , and BaFg. The apparent association of XeFg 84 85 i n the s o l i d state, as evidence by i t s low v o l a t i l i t y (rj 20 mm ' at 20°C) and the p o s s i b i l i t y that f l u o r i n e bridging might occur in complex cations of some of i t s adducts (e.g., The formation of an adduct such as 2XeFg-SbFg can be understood i f one assumes the existence of a complex cation XegF-j^*. ) o f f e r further con-t r a s t s i n behaviour between XeFg and I F 7 . Thus higher-than-seven coordination seems to be an important feature of the stereochemistry of Xe (VI). Possibly the s t e r i c requirement of the lone pair i n XeFg i s quite d i f f e r e n t from that of the seventh f l u o r i n e ligand i n I F 7 . 99 3.6 THE REACTION OF ONF WITH IF^ The X-ray powder photograph of the complex formed from 86 87 the reaction of KF with IFg, KIF g, i s known to be complex ; the pattern i s not related to those of other AMFg s a l t s with octahedral anions. The complexity suggests a nonoctahedral symmetry for the I F g anion. Since I F g i s i s o e l e c t r i c with XeF g, the shape of which has been much disputed, i t s shape i s of obvious i n t e r e s t . A non-octahedral arrangement would be expected i f the lone pair were s t e r i c l y active. The preparation of a v o l a t i l e adduct between ONF and IF^ in t h i s work, for which the most l i k e l y formulation i s NOIF g o f f e r s a possible method of attack on the problem. Growth of single c r y s t a l s for X-ray work should be possible, simply by subliming the adduct onto a suitably cooled surface, or by allowing the adduct to grow to single c r y s t a l s i n X-ray c a p i l -l a r i e s . The c a p i l l a r i e s would have to be of Kel-F or some other material inert to ONF, since the adduct has a f i n i t e vapour pressure at ambient temperatures. 3.7 MAGNETIC RESULTS ON XeF^. THE SHAPE OF THE XeFR MOLECULE. The shape of the XeF g molecule - whether i t i s or i s not regular octahedral i n i t s ground state - has been the subject Q O of much debate 0 0. Delocalized molecular o r b i t a l theory, as 89 applied to XeF 2 and XeF^ , predicts a regular octahedral shape for XeF g. On the other hand, many of the properties of XeF g, 90 84 85 such as i t s i n f r a r e d spectrum and low v o l a t i l i t y ' are 100 markedly d i f f e r e n t from those of other hexafluorides, known to be regular octahedral, and suggest a non-octahedral shape for 91 92 t h i s molecule. Indeed, recent electron d i f f r a c t i o n studies ' by two independent groups of workers have indicated that XeFg i s non-octahedral i n the vapour state. However, suggestions have been made 9 3 that XeFg has a low-lying t r i p l e t state above an octahedral (singlet) gound state. The p o s s i b i l i t y that such an . 94 arrangement of ele c t r o n i c states might account for anomolies i n the n.m.r. and e.p.r. spectra of XeFg/HF mixtures, and for the other properties of XeFg which are not explained by the 94 simple regular octahedral model was advanced . (This suggest-ion was made prior to the publication of the electron d i f f r a c -t i o n results.) The r e s u l t s of our magnetic measurements on XeFg are not consistent with the presence of a low-lying t r i p l e t state i n XeFg. Our observed weight changes for two XeFg-XeOF4 mixtures, one containing at least 50% XeFg, the other, at least 75% XeFg indicated a temperature independent diamagnetism for XeFg over the temperature range -196°C to +20°C. If the population of a Since i d e n t i c a l r e s u l t s were obtained for two mixtures con-taining d i f f e r i n g r a t i o s of XeFg to XeOF^, the r e s u l t s cannot be explained i n terms of a fortuitous cancellation of XeFg paramag-netism by temperature-dependent diamagnetism of XeOF4. Also, since our experience indicates that our s u s c e p t i b i l i t y tubes show a temperature independent diamagnetic weight change of 2.0 mg, and since the two experiments used tubes from d i f f e r e n t lengths of tubing, the fortuitous cancellation of XeFg paramag-netism by materials i n the quartz tube i s hardly possible. Experi-ments are planned using a Kel-F s u s c e p t i b i l i t y tube (eliminating decomposition of XeFg to XeOF4) i n order to obtain r e s u l t s which can be used to obtain a numerical value for the diamagnetic s u s c e p t i b i l i t y of XeFg. 101 t r i p l e t s t a t e were important at room temperature, XeFg should be paramagnetic at t h i s temperature, and should show a temperature dependent s u s c e p t i b i l i t y , as the t r i p l e t s t a t e becomes depopulated on d e c r e a s i n g the temperature. N e i t h e r the observed evidence of diamagnetism at room temperature, nor the independence of the s u s c e p t i b i l i t y of temperature are compatible w i t h a populated t r i p l e t s t a t e . Thus our magnetic s t u d i e s , even though they do not give • a numerical value f o r the diamagnetic s u s c e p t i b i l i t y of XeFg, r e i n f o r c e the view that the observed p r o p e r t i e s of XeFg can only be e x p l a i n e d i n terms of a model which a l l o w s that the molecule i s not r e g u l a r o c t a h e d r a l i n the ground s t a t e . A simple e l e c t r o n 95 96 p a i r r e p u l s i o n scheme, as developed by G i l l e s p i e and Nyholm ' , i s s a t i s f a c t o r y i n t h i s r e s p e c t ; i t a l l o w s that the lone p a i r i n XeFg i s s t e r i c l y a c t i v e and leads s t r a i g h t - f o r w a r d l y to a pre-d i c t i o n 9 ' of non-octahedral symmetry. However the extent of the d i s t o r t i o n from o c t a h e d r a l symmetry i n d i c a t e d by the e l e c -91 t r o n d i f f r a c t i o n r e s u l t s i s s a i d t o be l e s s than that expected on the b a s i s of the G i l l e s p i e - N y h o l m model. C e r t a i n l y i t i s apparent that the molecular o r b i t a l scheme which was s u c c e s s f u l l y used to e x p l a i n many of the p r o p e r t i e s of the lower xenon f l u o r -i d e s (XeF2 5- XeF 4) must be m o d i f i e d to accommodate XeFg. The 89 argument that the 5d o r b i t a l s of xenon cannot be used i n bonding i n XeFg because they are too high i n energy may not be v a l i d . I n c l u s i o n of s i g n i f i c a n t 5d o r b i t a l involvement i n a molecular o r b i t a l bonding scheme may l e a d to the s u c c e s s f u l p r e d i c t i o n of non-oetahedral symmetry f o r XeF f i• 102 CHAPTER IV  THE CHARACTERIZATION OF IF f l +AsF f i~ THE CRYSTAL STRUCTURE FROM POWDER DATA I INTRODUCTION Our interest i n the acid-base properties of I F 7 arose as a r e s u l t of our work®*' on the 1 9 F n.m.r. spectrum of the heptafluoride. As discussed i n the previous chapter, the n.m.r. work on I F 7 indicated that the fl u o r i n e ligands were undergoing a rapid intra-molecular exchange. The question then arose: would I F 7 act as a fl u o r i d e ion donor? The n.m.r. re s u l t s i n d i -cated l i t t l e tendency for I F 7 to exchange f l u o r i n e ligands with other I F 7 molecules or with the solvent (WFg) but B a r t l e t t sug-gested that the rapid rearrangement of the seven ligands i n I F 7 might indicate some l a b i l i t y and that, under the right conditions - that i s , i n the presence of a strong f l u o r i d e ion acceptor -I F 7 would show f l u o r i d e ion donor properties. Indeed, we found that I F 7 did give an adduct with AsFg. Subsequent search of the l i t e r a t u r e revealed that Seel and Detmer 4^, i n a general investigation of the reactions of SF 4, S0F 4, C1F 3, and I F 7 with BF^, AsFg, and SbFg, had isola t e d t h i s 1:1 adduct, among others. A l l were analogous to the acid-159 base complexes which B a r t l e t t and Robinson had reported p r i o r to the i r work. Seel and Detmer suggested that the adduct was the io n i c compound IFg +AsFg~, but they had no experimental evidence for t h e i r formulation. In view of the lack of evidence regarding the nature of t h i s adduct, we decided to proceed with our characterization. 103 Certainly we regarded the io n i c formulation as the most l i k e l y but we f e l t that d e f i n i t i v e evidence for t h i s formulation was desira-ble. In p a r t i c u l a r , we f e l t that extrapolation of the behaviour of species such as SF 4, BeF 4, CIF^ and the l i k e ( a l l generally accepted to behave as fl u o r i d e ion donors towards AsF^) to I F 7 , with a central atom i n a much higher oxidation state, might be questionable. In the absence of other experimental evidence, one could argue that the high p o s i t i v e charge on I(VII) would make i t a strong f l u o r i d e ion acceptor. The s t r u c t u r a l and infrared evidence presented i n t h i s chapter make the IFg +AsFg~ formulation a reasonable one, without recourse to other proper-t i e s of IF-,. 104 II EXPERIMENTAL 2.1 PREPARATION OF THE ADDUCT 2.1.1 Preparation of Reagents The preparation of I F 7 was described i n chapter III, section 2.1.1. AsF- was prepared by the reaction of either ASgOg ( B r i t i s h Drug Houses Ltd., a n a l y t i c a l reagent) or powdered arsenic metal (chemically pure grade or 99.999% s p e c i a l l y p u r i f i e d grade, l a t t e r from B r i t i s h Drug Houses Ltd.) with an excess of fl u o r i n e at temperatures ranging from 100-300°C for d i f f e r e n t preparations. AsFg was i d e n t i f i e d by i t s infrared spectrum, the c h a r a c t e r i s t i c feature of which was found to be a very intense absorption centred at 800 cm - 1, (At low pressures, 20 mm or less, two PQR branched peaks, p a r t i a l l y overlapping, with Q branches at 815 cm - 1 and 790 cm-"'", could be seen.) and by i t s reaction with ONF: ONF + AsF 5 y NOAsFg. X-Ray powder photography established that the white s o l i d from t h i s reaction was NOAsFg, which has been prepared by another route. (As 203 + BrFg + N0C1) 2.1.2 Preparation of the Adduct The adduct IF^'AsFg was prepared i n tensimetric t i t r a -tions c a r r i e d out i n the manner described i n section 3.3 of chapter II. The adduct formed as a fine white powder, i n v o l a t i l e at room temperature. A l l handling operations with the adduct were carr i e d out i n the drybox, since i t hydrolyzed rapidly i n moist a i r . The r e s u l t s of two tensimetric experiments are given i n table 8. Experiments carried out with an excess of either 105 reagent established that the 1:1 adduct was the only one stable i at room temperature, X-ray powder photography being used to prove that only the 1:1 adduct formed i n these reactions. Table 8 Tensimetric Results, I F 7 + AsFg Reaction IF7,mm AsFg,mm Residual,mm IF7:AsFs 998 995 20 1:1.02 374 376 27 1:1.08 2.2 THE INFRARED SPECTRUM OF IF f i +AsF f i" Infrared spectra of the s o l i d complex were obtained by allowing I F 7 and AsFg to react i n the cavity of the infrared c e l l , the i n s i t u reaction giving a deposit of f i n e l y divided white powder on the AgCl windows. Spectra of several deposits were obtained, spectra being run on the PE 137 NaCl and KBr instruments, and on the PE 421 instrument. See figure 15. The peak at 635 cm - 1 was due to a v o l a t i l e impurity, pro-i 61 bably IFg, ( V 7 of IFg = 640 cm - 1 ) a r i s i n g from slow attack of the complex on the c e l l windows. When the c e l l cavity was evacu-ated, or opened to the c e l l reservoir cooled to -196°C, t h i s peak disappeared, growing i n again when the c e l l was l e f t for f i v e to ten minutes without pumping or was closed off from the cooled reservoir. Figure 15. Infrared Spectrum of IFK AsF 107 2.3 X-RAY POWDER PHOTOGRAPHS OF IF f i +AsF f i~ X-Ray powder photographs of several preparations were obtained by the standard techniques outlined i n chapter II, section 3.2. A l l photographs were the same and were indexed on the basis of cubic symmetry, a Q = 9.4935 + 0.00058. Table 9 gives the 2 observed and calculated 1/d values, along with the v i s u a l l y estimated i n t e n s i t i e s . Two of the films, one of short exposure and one of long exposure, were selected for the determination of l i n e i n t e n s i t i e s . The films were scanned using a Hilger Recording X-Ray Microphoto-meter (model L-486) with a Hilger Power Supply (model Fa-17) and a Leeds and Northrup Recorder ("Speedomax", Type G Measuring Instrument) and the peak areas were then measured with a planimeter ("Aristo" planimeter). The long exposure f i l m was scanned twice, once under conditions of high s e n s i t i v i t y and small wedge and s l i t openings , a/id once under conditions of lower s e n s i t i v i t y with wider wedge and s l i t openings. The former scan gave large peaks, but also a high l e v e l of background noise, while the l a t t e r scan gave a low l e v e l of background noise, but smaller peaks. Composite data were obtained from the three sets of data by avera-ging the separately measured peak areas, or by s e l e c t i n g one or two of the three measurements i f the other(s) were obviously un-suitable, (e.g., Peak areas for the one or two completely black-ened l i n e s of the long exposure f i l m were unsuitable; peak areas * The microphotometer permitted v a r i a t i o n of l i g h t incident on the photometer tube by adjustment of a wedge, which controlled the height of the l i g h t beam, and a s l i t , which controlled the width of the l i g h t beam. 108 Table 9 X-Ray Powder Data for IF 6 +AsFg" N 1/d 2 (ft" 2) I/I OBS. CALC. OBS; o N i / d 2 ( r 2 ) OBS. CALC, I / I G OBS. 3 0.0343 0.0332 w 88 4 0.0455 0.0444 vvs 96 8 0.0902 0.0888 vs 100 11 0.1235 0.1221 w 104 12 0.1347 0.1331 ms 14 0.1571 0.1553 w 108 16 0.1792 0.1775 vvw 116 18 0.2022 0.1997 mw 19 0.2133 0.2108 w 120 20 0.2243 0.2219 ms 22 0.2462 0.2441 m 132 24 0.2685 0.2663 vs 26 0.2907 0.2885 w 136 27 0.3014 0.2996 w 32 0.3575 0.3551 ms " 140 35 0.3916 0.3883 w 36 0.4015 0.3994 vs 144 38 0.4237 0.4216 vvw 40 0.4462 0.4438 ms 148 44 0.4907 0.4882 ms 48 0.5349 0.5326 vw 51 0.5678 0.5659 w 52 0.5789 0.5770 ms 54 0.6018 0.5991 vvw cubi 56 0.6237 0.6213 s 59 0.6578 0.6546 vw 62 0.6905 0.6879 vw 64 0 .7118 0.7101 vw 68 0.7571 0.7545 ms 72 0.8002 0.7989 m 76 0.8452 0.8433 w 80 0.8902 0 . 8876 w 84 0.9334 0.9320 mw 0.9762 1. 1. 1. 1. 1. 1. 1, 1, 1. 1, 1. 1, 1. 1, 1, 1 1 1 1 0642 1089 1554 1561 1989 2880 2870 3328 3328 4649 4643 5098 5093 5538 5538 5978 5978 6422 6420 0. 9764 w 1. 0651 vw 1. 1096 mw 1. 1540 m 1. 1983 vw 1. 2870 m 1. 3315 mw 1. 4646 w 1. 5090 mw 1. 5534 mw 1. 5978 w 1. 6421 w 9.4935 + 0.0005 $ 109 for the weaker l i n e s of the low exposure f i l m were unsuitable, being poorly resolved; etc.) The separate sets of i n t e n s i t i e s were adjusted to the same r e l a t i v e i n t e n s i t y scale by multiplying the i n t e n s i t i e s i n each set by a factor K, chosen to make the sum of the i n t e n s i t i e s the same for a l l three sets. F i n a l l y , the composite set of photometered values were compared with the v i s u a l l y estimated set to ar r i v e at the set of in t e n s i t y values which were used i n the structure analysis. 110 III RESULTS ANALYSIS OF THE IFg +AsFg~ INTENSITY DATA 3.1 THE ARRANGEMENT OF THE IODINE AND ARSENIC ATOMS. The general pattern of i n t e n s i t i e s i n the IFg +AsFg~ photo-graph (plate) indicates d i r e c t l y the arrangement of the iodine and arsenic atoms in the unit c e l l . The pattern i s a series of strong l i n e s with a number of (generally) weaker l i n e s appearing between them. In fact, the strong l i n e pattern can be indexed on the basis of a simple cubic l a t t i c e , with a c e l l edge one-half of that needed to index a l l the l i n e s i n the photograph, i . e . , 4.747 X. Since the in t e n s i t y of the X-ray beam scattered by an atom i s a function of the square of the nuclear charge and since, therefore, the heavy arsenic and iodine atoms i n IFgAsFg w i l l dominate the scattering, the conclusion that the iodine arid arsenic atoms l i e on a sodium chloride array becomes obvious from t h i s general i n t e n s i t y pattern. In other words, there i s a face-centred arsenic array and a face-centred iodine array. A schematic representation of the powder photograph i s shown i n figure 16, the diagram being a representation of powder li n e i n t e n s i t y as a function of Bragg angle ©. The strong l i n e pattern arises from the set of planes hkl for which the iodine and arsenic face-centred l a t t i c e s scatter i n phase with each other. This reinforced scattering occurs for planes whose M i l l e r indices are a l l even. (N = h^ + k^ + l 2 i s a multiple of four.) Considerably weaker (in general) scattering occurs from the iodine-arsenic sodium chloride array when the scattered beam from the iodine l a t t i c e i s out of phase with that from the 0° 90 c 20 36 52 6<f 72 80 88 IOO to8 120 136 , m ,„Q II 19 21 35 SI 5 9 22 14 18 26 38 54 62 N = h 2 + k 2 + l 2 Figure 16. Schematic Representation of the IFg+AsFg~ X-ray Powder Photograph 112 arsenic l a t t i c e . Such i s the case for planes whose M i l l e r indices are a l l odd .(N = 3,11,19, and so forth - see figure 16) F i n a l l y , no scattering at a l l occurs from the As-I array when the M i l l e r indices are not a l l even or a l l odd, such planes v i o l a t i n g the condition that h + k = 2n, k+ 1 = 2n and k + 1 = 2n for net scattering from a face-centred array. The solution of the IFg +AsFg~ structure was simply a problem of placing the fl u o r i n e atoms i n t h i s face-centred array. 3.2 THE USE OF INTENSITY DATA IN THE LOCATION OF THE FLUORINE  ATOMS The observations regarding the in t e n s i t y of scattering from the iodine-arsenic face-centred array become important when one considers the placement of the fl u o r i n e atoms i n the struc-ture. Powder l i n e s which a r i s e from planes whose M i l l e r indices are mixed (not a l l odd or even) w i l l be due to scattering from the f l u o r i n e atoms alone. Hence, calculated i n t e n s i t i e s for such l i n e s w i l l be more sensi t i v e to the placement of the f l u o r -ine atoms than calculated i n t e n s i t i e s for l i n e s from planes with M i l l e r indices a l l odd, since these l i n e s contain some iodine-arsenic contribution. They w i l l be considerably more sensitive to f l u o r i n e placement than calculated i n t e n s i t i e s for l i n e s from planes with M i l l e r indices a l l even, since these l i n e s contain a strong iodine-arsenic contribution. However, since the scatter-ing from a l l planes w i l l contain (in general) some contribution from f l u o r i n e scattering, calculated i n t e n s i t i e s of a l l of the 113 l i n e s w i l l be a function of the f l u o r i n e atom position, and measured i n t e n s i t i e s for a l l l i n e s (not just fluorine-only ones) were used i n the analysis. 3.3 THE SPACE GROUP OF IFfi+AsFfi- PLACEMENT OF FLUORINE ATOMS  IN UNIT CELL. n o Only three cubic space groups^ are possible fcJr IFy-AsFg, o without increasing the c e l l edge over the value of 9.4935 A which was needed to index a l l the l i n e s i n the picture: Pa3, Pn3, and Pn3m. Pa3 was chosen as the most l o g i c a l group for analysis. Pn3m places the f l u o r i n e atoms i n special positions, (k) and was regarded as u n l i k e l y since i t required that two of the three f l u o r i n e coordinates be the same. Pn3, while allowing f l u o r i n e atoms to occupy general positions, gave a chemically less reason-able d i s p o s i t i o n of the atoms than did Pa3. Furthermore, Pa3 i s related to Ia3, the space group found for 02PtFg. As subsequent 34 analysis w i l l indicate IF7.ASF5, l i k e OgPtFg , i s made up of MFg groups. (OgPtFg also has an 02 + cation, of course.) If these groups (IFg + and AsFg ) were i d e n t i c a l , the space group of IFyAsFg would become Ia3. Figure 17 shows the unit c e l l of IFg +AsFg~. To solve the structure, MFg groups must be placed along the 3 axes i n d i c a -ted i n the figure. Symmetry requires that these groups be either regular octahedra or octahedra which have been distorted along the 3 axis, either by decreasing or increasing the angle 0 between t h i s axis and the M-F bond. The assumption i s made here, as, 114 115 indeed, i t was i n a r r i v i n g at a choice of the space group, that the f l u o r i n e atoms i n the structure are ordered. This assumption i s supported i n part by the appearance of seven fluorine-only l i n e s i n the powder photograph and, perhaps more s i g n i f i c a n t l y , by the success with which subsequent analysis of the structure proceeded with t h i s assumption. In the solution of the structure, the paramters 0, the angle between the 3 axis and the M-F bond; b Q, the M-F bond length; and a t h i r d parameter which was e s s e n t i a l l y <p, the angle of r otation of the MFg groups about the 3 axis were used to locate the f l u o r i n e atoms, i n preference to the cartesian coordinates x, y,z. The reason for t h i s was that these parameters are more ob-viously related to the chemically s i g n i f i c a n t ones - the bond lengths and angles of the MF groups - than are the cartesian co-6 ordinates. A computer program was used to calculate related values for the two sets of coordinates. A detailed explanation of the simple vector algebra and s o l i d state geometry used to r e l a t e (0, b Q, "^") to (x,y,z) i s given i n the appendices. 3.4 THE METHOD OF ATTACK USING X-RAY POWDER DATA The approach i s a t r i a l and error one. For any l i n e i n a powder photograph, IOBS <* A L P ( P l l F l l 2 + P 2 l F 2 l 2 + •••> exp(-B sin 20/A ) (1) where IQBS = observed i n t e n s i t y of l i n e k A = absorption factor of l i n e k Lp = Lorentz-Polarization factor of l i n e k 116 Pl>P2*** = m u l t i p l i c i t i e s for planes (h^ 1]_) , (h2 k2 I2)••• which contribute to the inten s i t y of l i n e k F1'F2'*° = calculated structure factors for planes < hl k l x l ) • • • > ( h2 k2 x2>••• exp( ) = exponential function, base e B = constant, taking account of temperature factors of atoms 0 = Bragg angle for l i n e k A. = wavelength of X-ray ra d i a t i o n used. The assumption i s made that the temperature factors for the i n d i v i d u a l atoms can be s a t i s f a c t o r i l y replaced by the ex-ponential expression used i n (1). This i s an assumption which has been empirically j u s t i f i e d . Inserting a constant of proportionality, C i n (1), tak-ing the square root and then the logarithm of both sides, and rearranging terms, one obtains i l o g [ l 0 B S / A L p C p ^ F i j S + p 2 |F 2| 2 + . . .) = (-B/2A)sin 20 + §log C Letting X = I 0 B S / A L P C P - J J F T J 2 + P 2| F2| 2 + •••) $ log X = (-B/2A) s i n 2 0 + J log C. One can see that for the correct structure, a plot of log X against s i n G should be a straight l i n e . The slope of thi s l i n e can be used i n (1) to obtain a set of calculated r e l a t i v e i n t e n s i t i e s , for comparison with the observed values. The procedure i s to guess values for the unknown para-meters (the f l u o r i n e coordinates i n the case of IFgAsFg), calculate the log X values for each powder l i n e , and then decide whether 117 the r e s u l t i n g set of log X values gives a better or worse scatter of points about a best straight l i n e than preceding sets. One continues changing the parameters u n t i l further changes f a i l to improve the scatter. 3.5 APPLICATION OF THE TRIAL-AND-ERROR METHOD TO IF f i +AsF f i~ VALUES OF FLUORINE COORDINATES In the analysis of the IFgAsFg structure, a computer program was used to calculate the sets of log X values (appendix 1, program 2) and about 200 choices of the f l u o r i n e parameters were made. The r e s u l t s from the i n i t i a l c a lculations were used to suggest the parameter changes made i n succeeding calculations. Table 10 shows the effect of v a r i a t i o n of bond lengths on the scatter of a set of log X values about the best straight l i n e i n the log X vs s i n ^ Q plot. The values of 0 and the para-meter related to <f have been fixed at values which are not s i g -n i f i c a n t l y d i f f e r e n t from those for the best set of data and the bond lengths have been allowed to take the values indicated i n the table. The expression log e(IQBS^ ICALC^ i s s i m P l y the difference (absolute value) between the calculated log X value for a given powder l i n e and the i d e a l s t r a i g h t - l i n e value for the same powder 1 l i n e : l o g e ( I 0 B g / I C A L C ) = log X C A L C - l o g X T D E A L . Thus, a set of log X values exactly on the best straight l i n e would give a £ A value of zero. The minimum value of £ A indicates the set of log X values with the least scatter about the best straight l i n e ; 118 Table 10 IFgAsFg Structure Determination. £ A as a Function of Bondlengths I-F ( 8 ) bond lengths -> 1.85 1.80 1.78 1.75 1.70 A s - F ( S ) 1.75 1.70 1.68 1.65 1.63 1.60 1.55 175 170 154 146 148 170 155 146 138 146 168 195 147 142 133 148 171 173 157 149 155 185 189 A = 100 x l o g e ( I 0 B S / I C A L C ) 119 o ^ o th i s minimum occurs for b A s_p - 1.67A and D T _ F = 1-75A. Similar analysis of sets of data i n which 0 and the ^  parameter were varied were used to arri v e at choices for these parameters. The fl u o r i n e atom coordinates and some of the chemi-c a l l y s i g n i f i c a n t interatomic distances are given i n table 11. (We thank the X-Ray Crystallography Group of U.B.C. for the use of their data r e s u l t s program to calculate the F-F interatomic d i s -tances . ) o Figure 18 compares the log X vs s i n 0 plots for the best set of data with another set, i n which the only s i g n i f i c a n t d i f f e r -ence i s the arse n i c - f l u o r i n e bond length, which has been increased to 1. 78ft (best value = 1.67A). Table 12 gives the observed and calculated i n t e n s i t i e s for the best set of data. The calculated i n t e n s i t i e s were scaled to make the sum of the calculated i n t e n s i t i e s equal to the sum of the observed i n t e n s i t i e s , the summation being r e s t r i c t e d to the powder l i n e s for which numerical values of observed i n t e n s i -t i e s were ava i l a b l e . o bond lengths (A) sin © x 100 Figure 18. Comparison of Log X vs Sin © P l o t s . 121 Table 11 Crystallographic Data for IFg +AsFg~ Space group Pa3 cubic a Q = 9.4935 + 0.0005 ft atomic parameters As i n 4(a) (0,0,0) I in 4(b) (4,i,4) F i n 24(d) (x,y,z) x = 0.0980; y = 0.1377; z =-0.0489 F i n 24(d) (x,y,z) x = 0.6001; y = 0.6431; z = 0.4411 bond distances and angles As-F = 1.67 A I-F = 1.75 ft F-As-F = 86.5 F - I - F = 90° intermolecular distances (3)F...F at 2.81 ft (3)F...F at 2.95 ft (3)F...F at 2.97 ft (3)F...F at 3.04 A 122 Table 12 Observed and Calculated Relative Intensities for IFg+AsFg -h 2+k 2+l 2 CALC. I OBSVD. I 3 11 - w 4 226 - vvs 8 172 180 vs 11 16 17 w 12 75 60 ms 14 20 22 w 16 8 - vvw 18 25 27 mw 19 16 19 w 20 87 79 ms 22 36 39 m 24 124 129 vs 26 19 21 w 27 13 18 w 32 62 67 ms 35 19 20 w 36 127 120 vs 38 12 15 vvw 40 74 75 ms 44 73 70 ms 48 24 24 vw 51 9 - w 52 66 60 ms 54 11 - vvw 56 6 vw 62 90 so 64 9 - vw 68 65 75 ms 72 43 50 m 76 19 20 w 80 31 30 w 84 41 - mw 88 20 - w 96 13 - vw 100 21 - mw 104 51 60 m 108 26 - vw 116 68 60 m 120 41 - mw 132 39 - w 136 69 - mw 140 69 - mw 144 55 - w 148 46 - w 123 IV DISCUSSION 4.1 THE INFRARED SPECTRUM OF IF f i +AsF f i~ The infrared spectrum i s consistent with the suggested formulation. Species of octahedral symmetry have s i x fundamental v i b r a t i o n a l modes and two of these, \) g and 's0^, (both symmetry T i u ) are infrared active. The t o t a l l y symmetric stretching vibration, \)-^ > the frequency of which could be d i r e c t l y correlated to the stretching force constant of the M-F bond, i s not active i n the infrared. With the exception of the l i g h t SFg molecule, and XeFg, which i s almost c e r t a i n l y non-octahedral, a l l the gaseous hexa-f l u o r i d e molecules have the V3 vibrati o n i n the region of 800-600 cm~^ and the \ ) 4 v i b r a t i o n i n the region of 400-200 cm - 1. Also, the spectrum of the s a l t K +AsFg has been recorded and peaks seen at 700 cm - 1 (\>3 of AsFg") and 400 cm"1 (\>4 o f AsFg"). Table 13 Infrared Assignments for IFg +AsFg~ Peak (cm 1) assignment (0 h symmetry) 795 v 3 > IFg+ 695 v 3 > AsFg 395 V 4 ' AsFg Table 13 shows the assignments made for the peaks i n the IFg +AsFg~ spectrum, on the basis of comparison to KAsFg and hexafluoride spectra. Presumably the V 4 fundamental of IFg + 124 l i e s below 390 cm ^, i n the region obscured by the absorption of the AgCl windows of our infrared c e l l . The s l i g h t asymmetry of the 695 cm"1 peak (V3) AsFg") may be due to interactions i n the s o l i d state. Table 14 compares the frequencies of the\>3 fundamental vibrations for some [MFg"] _ x species. There i s a regular trend within a period, t h e V g frequency increasing steadily with the increase i n the nuclear charge. In p a r t i c u l a r , the frequency of the IFg + cation i s i n the region expected ( i . e . >750 cm ^) on -3 extrapolation of the trend set from InFg to TeFg. Peacock and Sharp have pointed out that the trend i n — 2 — frequencies for the series SiFg , PF g , SF g(g) (V1 = 656, 741, and 770 cm - 1 respectively) followed the trend i n V 3 frequen-c i e s . Systematic Raman studies on the fluorocomplexes of the elements of the fourth and f i f t h periods have not been carried out, so there i s no di r e c t information on V ^-Vg trends. However, i t i s e n t i r e l y reasonable to suppose that the established c o r r e l a -tion of the t h i r d period (Si-P-S) can be extended to the fourth and f i f t h periods. If t h i s i s so, the data of table 14 indicates that the frequencies and hence the bond strengths increase across the series from InFg - to IFg +. Thus the bond strength increases with the increase in po s i t i v e charge on the central atom (nuclear charge i s increasing across the s e r i e s ) , the i n -creasing bond strength being a measure of the increasing a t t r a c t i o n between the central atom and the attached f l u o r i n e ligands. From the trends i n table 14 a frequency of ^ 820 cm"1 i s predicted for theVo fundamental of the as yet unprepared Table 14 Comparison of V j Frequencies for Some MFg Species Frequency of ^ 3 Fundamental Vibration, c m - 1 A1F 6 " 3 S i F 6 ~ 2 P F 6 SFg(gas) C 1 F 6 + 570(599?)a 726a 845a 939b 156(127 ?) 119 94 -3 2 + GaF 3 GeFg AsF g SeFg(gas) BrFg 464a 600a 695° 780b 136 95 85 InF g" 3 S n F 6 ~ 2 S b F 6 _ TeFg (gas) IFg + a a a h c 446 552 660 752D 795 106 108 92 43 (a) reference 99, and references cited therein; (b) referencelOQ and references cited therein; (c) present -work. to 126 BrFg + ion. The predicted frequency for C l F g + (also unknown) i s -1 ^1030 cm 4.2 THE STRUCTURE OF IF R+AsF^~ As the comparison between the observed and calculated i n t e n s i t i e s indicates, (table 12) the X-ray powder data for IF 7AsF 5 i s consistent with the IFg +AsFg~ formulation for the compound. The structure obtained from the powder data can be described by noting that i t i s derived from the OgPtFg struc-t u r e 3 4 ' 1 ^ 1 simply by removing the Og + cation and replacing one-half of the PtFg" ions with AsF g" ions (at (0,0,0)...) and the other half of the PtFg ions with IFg + ions (at (£,4,§)...). The MFg groups (IFg +, AsFg ) are arranged along the three-fold axes shown in the unit c e l l i n figure 17. The I F ~ + groups are regular b octahedral, but the AsFg groups are apparently s l i g h t l y compressed along the 3 axes, the F-As-F angle being reduced from 90° to o + <v86.5 . An a t t r a c t i v e feature of the structure i s that the IF„ 6 and AsFg" groups are "meshed". That i s , looking along the 3 axis from (2>£,i) to (0,0,0), the three fl u o r i n e s of the AsFg group at (0,0,0) which are above (0,0,0) are rotated by 60° from the three fl u o r i n e s of the IFg + group at (^,§,i) which are below In table 15, the bond lengths derived for IFg + and AsFg -o i n t h i s study (1.75 and 1.67 A, respectively, with errors of o /v + .05 A) are compared with bond lengths for a number of 127 Table 15 o M-F Bond Distances i n Isoelectronic MFg Species (A) A 1 F 6 3 _ - S i F 6 2 " PF 6" SF 6 C1F 6 + 1.71 1.59a 1.56 -1.58 GaF, 3- GeFg 2 &sFq~ S e F 6 BrF, 1.77 1.78 1.67 1.81 1.74 1.80 1.70 1.67 SnF, 2- SbF 6 1.87" 1.88 TeF, IF + 1.83 1.75 References: (a) 102; (b) present work; others 128 i s o e l e c t r o n i c species. The comparison indicates the bond lengths from t h i s study are rather short - the As-F bond length, i n o p a r t i c u l a r , i s of the order of 0.1 A less than that expected. However, no correction for thermal motion has been made for our o bond lengths and such a correction could be +0.1 A or more. A 102 recent paper by Copeland, Conner, and Meyers on the single c r y s t a l studies of pyridinium s a l t s of PFg~, AsFg" and SbFg" i l l u s t r a t e s t h i s point. The As-F bond length corrected for thermal motion was 1.777ft; the uncorrected value was only 1.65 ft. The shortest f l u o r i n e - f l u o r i n e intermolecular distance o i n IFgAsFg, 2.81 A, i s longer than twice Pauling's Van der Waals radius"*"*^ for f l u o r i n e , 2.70 ft, and considerably longer than the shortest d i s t a n c e 1 ^ 1 i n OvjPtFg, 2.56 ft. An increase i n the M-F bond lengths would decrease the Van der Waals distances. 129 CHAPTER V THE REACTIONS OF THIRD TRANSITION SERIES HEXAFLUORIDES AND OXYPENTAFLUORIDES, AND OF ReF y WITH NO AND ONF. I INTRODUCTION 1.1 THE CHEMICAL PREPARATION OF FLUORINE The extraordinary chemical r e a c t i v i t y of fl u o r i n e i s well known - with the exception of N 2, 0 2 and Kr, a l l of the elements forming chemical compounds w i l l combine d i r e c t l y with i t and numerous attempts have been made to reverse the process; that i s , to prepare f l u o r i n e i n a chemical reaction. A l l of the early claims to the successful production of f l u o r i n e i n a chemical reaction, other than by pyr o l y s i s , have been either refuted or seem un l i k e l y i n the l i g h t of present 104 105 knowledge. Ruff, for example, disproved Brauner's claim to have obtained f l u o r i n e by the decomposition of SKF.HF.PbF^ and Brauner himself was unable to duplicate his previous experiments. 1 0 7 Ginsberg and Holder decomposed K 2TiFg to ^ T i O F ^ i n a stream of dry a i r above 500°C and concluded that, since moisture was absent, f l u o r i n e must have been liberated. However, more recent-108 ly Schmitz-Dumont and Openhoff showed that the reaction only occurs i n the presence of moisture and, therefore, that HF, not fl u o r i n e i s evolved. This l a t t e r work also casts serious doubts 10$ on the production of f l u o r i n e by the decomposition of oxyfluor-ides of Zr, HF and T i i n oxygen. Si m i l a r l y , other work along these l i n e s has been unsuccessful or open to c r i t i c i s m , 130 p a r t i c u l a r l y regarding mistaking HF for f l u o r i n e . The thermal decomposition of higher f l u o r i d e s has been pursued with the intention of l i b e r a t i n g f l u o r i n e by decomposition to a lower f l u o r i d e , and a summary of some of the 110 attempts prior to 1950 i s given i n Mellor. More recent work f5 includes Seel's successful production of f l u o r i n e from I F 7 or i t s complexes with AsF^(IF7.ASF5) and SbF 5(IF 7.3SbF 5) by heating these i n the presence of KF at 200°C: KF + IF y.AsF 5 —> I F 7 + KAsFg I F ? ^ I F 5 + F 2 (*vl% d i s s o c i a t i o n at 200°C) IF,. + KF —> KIFg ( i n v o l a t i l e s o l i d ; displaces equilibrium to l e f t ) . In contrast, chemical reactions l i b e r a t i n g oxygen are well known. For example, the production of oxygen by the decomposition of KCIO^ with MnO^ as a catalyst i s a c l a s s i c laboratory exercise. The preparation of f l u o r i d e s by the reaction of oxides with f l u o r i n e or BrFg i s a standard prepara-t i v e method; oxygen i s liberated i n these reactions. 131 1.2 EVIDENCE FOR SEVEN AND EIGHT COORDINATION IN TRANSITION  METALS. Complexes of the type A yMF x where x=7 or 8, and A i s lo-an a l k a l i metal have been prepared for M=Zr,Hf,Nb,Ta,Mo,W,Ru,Rh and Re. The s t r u c t u r a l information which i s available supports the existence of complex ions of the sort MF7 (x=2,3) and MFg - 3. lia 113 Hampson and Pauling showed that previous evidence for the existence of NH^+, ZrFg" and F~ ions i n (NH^gZrF-y was unreasonable and that the structure could only be s a t i s f a c t o r i l y -3 interpreted i n terms of a ZrF 7 ion, disordered i n the l a t t i c e . They were able to obtain s a t i s f a c t o r y agreement between c a l c u l a t -ed and observed i n t e n s i t i e s i n X-ray powder patterns of -3 (NH4>3ZrF7 and I^ZrFy with a ZrF 7 ion constructed from an _o octahedral ZrFg ion by i n s e r t i n g a f l u o r i d e ion i n one of the faces, preserving one three-fold axis. 11M-However, Zachariasen disagreed with their detailed conclusions, although he agreed that the powder data required a -3 disordered Z r F 7 , ion, arranged i n the l a t t i c e i n some disordered 114-fashion. Zachariasen had obtained K3UF7 i n two c r y s t a l modifica-tions; one, body centred-tetragonal (a=9.22, c=18.34), the other, face centred cubic (a=9.22). The former showed an X-ray pattern nearly i d e n t i c a l i n l i n e i n t e n s i t i e s and clo s e l y similar i n l i n e 115 positions to that observed for K3UO2F5, which had been shown by -3 crystallographic studies to contain a pentagonal bipyramidal UO2F5 unit. Hence Zachariasen argued that K3UF7 contained a pentagonal -3 bipyramidal UF 7 group, i n both i t s tetragonal and cubic 132 modifications. Since (NH^gZrFy and KgZrF? were both i s o s t r u c t -u r a l (face centred cubic, Z=4) with the disordered KgUFy, he -3 -3 suggested that Z r F 7 , l i k e UF 7 , was a pentagonal bipyramid. 116 Hoard carried out single c r y s t a l studies on K^NbFy -2 and K 2TaF v and showed that they contained MF7 complex ions. These ions can be regarded as derived from a t r i g o n a l prism by in s e r t i n g a f l u o r i d e atom i n the centre of one square face. A 117 recent neutron d i f f r a c t i o n study on IGjNbFy confirmed the shape -2 which Hoard assigned to the NbF 7 anion. -2 Structural evidence for the existence of MFg corn-US plex ions comes from Hoard's single c r y s t a l study on Na^TaFg. -3 His evidence indicated that TaFg was an Archimedean antiprism, 119 possibly s l i g h t l y distorted. Koz'nin concluded from c r y s t a l -2 studies on KgReFg that ReFg was likewise an Archimedean a n t i -prism . 133 2 EXPERIMENTAL 2.1 PREPARATION OF STARTING MATERIALS  2.1.1 Preparation of ONF ONF was prepared by the reaction of NO with f l u o r i n e . The NO was supplied by The Matheson Company, and was used without further p u r i f i c a t i o n (minimum purity = 98.5%). NO (one to two atmospheres) i n a 1.25 l i t e r monel container was converted to ONF by adding successive small amounts of flu o r i n e to the mixture i n the container. The f l u o r i n e was admitted from the vacuum l i n e (figure 3) by b r i e f l y opening the container valve, the pressure of f l u o r i n e i n the l i n e being kept at f i v e to s i x atmospheres to prevent escape of the material i n the container upon addition of f l u o r i n e . Since the reaction NO + —F^ ^ ONF i s both appreciably exothermic ( & H R X = 37 2 Kilcal/mole) and rapid, caution was necessary i n adding fluorine, p a r t i c u l a r y i n the i n i t i a l stages of the reaction, when the NO was not d i l u t e d by ONF. After the addition of one aliquot of fl u o r i n e and before the addition of the next, the container was allowed to cool to room temperature. Fluorine was added i n stages u n t i l there was a s l i g h t excess. (Since one mole of NO gives one mole of ONF, the presence of flu o r i n e i n excess was indicated by a pressure increase i n the can upon addition of flu o r i n e . ) The excess f l u o r i n e was removed with the container o 1 2 1 at -196 C. Infrared spectra indicated that the only impurity i n the ONF was a small amount of NO2F, along with traces of CF4, 122 in some instances. In these preparations, ONF3 was not observed among the products. 134 2.1.2 The Handling of ONF i n the Vacuum System ONF was found to be a p a r t i c u l a r l y d i f f i c u l t gas to keep i n the monel system, slowly reacting to give N0 2. The decomposition could be minimized by pretreating the system with 400-500mm Hg of f l u o r i n e for periods of 1 to 24 hours, warming the l i n e with a luminous flame prior to removal of the f l u o r i n e , and f i n a l l y treating the system for about an hour with ONF. In t h i s way, tensimetrically measured samples of ONF could be obtained which were free of NOg. The presence of N0 2 i n the ONF was detected by the pale blue color which traces of N0 2 imparted to the ONF, which i s a pure white s o l i d at -196°C. It was customary practice to discard samples of ONF which had any blue coloration. However, i n spite of the steps taken to passivate the system to ONF, a slow decomposition of ONF i n the system and the presence of small amounts of N0 2 must be allowed for. In an experiment designed to check the pressure change of an ONF sample with time, ONF at 250 mm pressure was l e f t i n the thoroughly passivated system for 15 minutes. (This time includes a period of about 7 minutes i n which the ONF was confined to the Kel-F reactor at room temperature.) The pressure drop i n t h i s time was 25 mm, a 10% decrease. In a t y p i c a l tensimetric t i t r a t i o n , ONF samples were measured out and condensed into the reaction vessel i n a period of about 30 seconds. Subsequently, the ONF would be above l i q u i d nitrogen temperature only during the actual reaction (generally, 2-3 minutes) and during measure-ment of any excess ONF pressure (*v/l minute). 135 2.13 Preparation of the Metal Fluorides and Oxyfluorides. WFg (high purity grade) was supplied by the General Chemical D i v i s i o n of A l l i e d Chemicals and, aft e r drying over anhydrous NaF to remove HF, was used without further p u r i f i c a -t i o n . Infrared spectra of WFg from the cylinder, run at one to two atmospheres pressure, showed only peaks associated with WFg. ReFg and ReFy were prepared using a modification of 123 the procedure described by Malm and S e l i g . Pure ReF_ was obtained b by heating excess rhenium (Johnson and Matthey, spectroscopically standardized) with fl u o r i n e at 250-400°C for f i v e to eighteen hours, while ReFy was obtained by heating rhenium with a two or three-fold excess of f l u o r i n e under the same conditions. The purity of the two fluor i d e s was established from measurement of the i r vapour pressures at 0°C and from th e i r infrared spectra. ReFg free of both ReOFg and ReFy was obtained. The measured o vapour pressure at 0 C, for two d i f f e r e n t preparations, was 82 167.8 mm, and 164 mm, agreeing closely with the l i t e r a t u r e value of 167 mm, while the infrared spectra showed no absorption at 992 cm-^, and no shoulder on the low frequency side of the 716 (\)g) cm - 1 fundamental. See Table 17.) ReFy, however, always contained small amounts of ReOFg, i d e n t i f i e d by i t s absorption at 992 cm"-1-. The vapour pressure (0°C) was found to be 26 mm . 123 ( l i t e r a t u r e , 24.5 mm). ReOFg was always found i n ReFy samples, even when the Re metal and monel reactor were reduced at 400°C with one to two atmospheres of hydrogen prior to f l u o r i n a t i o n . Possibly the ReOFg arises from the reaction of the heptafluoride 136 Table 16 Intense Fundamental Absorptions of ReFg, ReF 7 and ReOFg. Compound(symmetry) Position of intense fundamentals, Reference cm ReFg (0 n) 716 ( V 3 > 123 ReF 7 (D 5 h) 703 (a 2"+ ex') 72,123 ReOF 5(C 4 v) 992, 711 ( V ^ V o ) present work with traces of oxygen containing materials i n the vacuum l i n e 72 and infrared c e l l . Other workers, studying the infrared spectrum of ReF 7, also found that ReF 7 samples contained a l i t t l e ReOFg, even after extensive p u r i f i c a t i o n steps. ReOF,. was prepared i n a flow system similar to that 17 used by Aynsley, Peacock and Robinson i n their preparation. The experimental d e t a i l s are described more f u l l y in chapter III, section 2.1.4. OsFg was prepared by the f l u o r i n a t i o n of osmium metal (Johnson and Matthey, spectroscopically standardized) with excess f l u o r i n e at 250-300°C for about s i x hours. The OsOFg used was a sample supplied by Dr. N. K. Jha, the preparation of which described i n his thesis. IrFg was prepared by the f l u o r i n a t i o n of Ir metal powder (Johnson and Matthey, spectroscopically standardized) with an excess of fl u o r i n e at 200-300°C for 5-10 hours. 137 lZ«f PtF was prepared by burning a platinum wire 6 (Johnson and Matthey, 0.03" diameter) in an atmosphere of f l u o r i n e . The fl u o r i n e was i n t i a l l y condensed into a K e l - F _ o trap on the vacuum system (L, i n figure 2 ), at -196 C. At t h i s temperature, f l u o r i n e i s a l i q u i d (vapour pressure M 300mm; density «v l . l gm/cc) and the volume of l i q u i d i n the trap served as a rough estimate of the amount of fl u o r i n e taken. A s l i g h t (*>10%) excess of that required for the reaction Pt + 3Fg —* PtFg was used. After the f l u o r i n e had been transferred from the Kel-F trap to the l i q u i d nitrogen-cooled reactor (of a design similar to that described i n the l i t e r a t u r e ) , the platinum wire was ignited by passing a current of 1.4 amperes through the c o i l . The walls of the reactor were kept at -196°C during the reaction to immediately quench the reaction product. Once started, the reaction proceeded vigorously, the l i q u i d nitrogen coolant b o i l i n g f u r i o u s l y and the current dropping to zero as the wire was burned through. The y i e l d of PtFg, based on the amount of platinum used, was 56% of t h e o r e t i c a l . The PtF„ was stored over NaF, to remove HF. 138 2.2 THE REACTIONS OF NO AND ONF WITH MO YF y  2.2.1 General Points. Tensimetric Data. The tensimetric t i t r a t i o n s were carried out using the procedure and apparatus described i n the section on general experimental techniques and the r e s u l t s of some of the tensimetric experiments have been presented i n Table 17. Other s a l i e n t features which could not be conveniently incorporated into t h i s table are given i n the description of each i n d i v i d u a l reaction, (sections 2.2.2 to 2.2.12) In Table 17, the f i r s t column indicates the reactants and the nature of the reaction. The common experimental tech-nique was to condense both the tensimetrically measured ONF (or NO) and the t r a n s i t i o n met&l,! (oxy)fluoride into the Kel-F trap and then warm the Kel-F trap up to room temperature with a warm (40-50°C) water bath. Since the NO and ONF were both considerably more v o l a t i l e than the other component i n the 125 o 1 2 6 o 62 reaction (b.pts.: NO = -152 C, ONF = -60 C; WFg (other (oxy)-f l u o r i d e s less v o l a t i l e ) = 17.1°C), they v o l a t i l i z e d much more quickly and the reaction which occurred was primarily one be-tween gaseous ONF (or NO) and the s o l i d (oxy)fluoride. Hence the reaction i s described as a solid-gas reaction i n the table. Of course, some gas-gas reaction might be expected as well, since a l i t t l e of the oxyfluoride could have sublimed as the temperature increase^. The observations made during these reactions support the above contention, i n general. As the reaction vessel was warmed, the NO or ONF sublimed and then the bulk of the s o l i d 139 Table 17 Tensimetric Data for NO and ONF Reactions REACTION ONF + WFg (gas-solid) ONF + ReFg (gas-solid) ON(F), mm 198 428 591 302 113 70 76 MOxFy, mm 411 211 204 98 53 82 160 Residues, mm 200 60 222 106 2 38 102 NOF:M0XFV Solid Prod. 1:1.07 , N0WF? 1.75:1 (N0)2WFg;N0WF7 1.81:1 (N0)2WF8;N0WF7 2.00:1 2.09:1 1.59:1 1.31:1 (N0) 2ReF g (N0) 2ReF g (NO) 2ReF g (NO) 2ReF 8 ONF + ReOFc 85 (gas-solid) 198 83 63 6 128 1:1.05 1.11:1 NOReOF 6 NOReOF, ONF + ReF 7 (gas-solid) 254 274 251 78 128 131 125 77 82 100 84 1.34:1 (NO)2ReF some(NO)ReO: 1.33:1 (NO) 2ReF g 1.34:1 unide n t i f i e d s o l i d phase(s) not (NO) 2ReF g 1.11:1 as above. ONF + OsFg (gas-solid) 204 140 106 144 87 20 1.10 :1 1.13:1 NOOsF. NOOsF. NOTE: No gaseous products detected i n r e a c t i o n s — s e e text. these 140 Table 17 (continued) REACTION ONF + OsFg (gas-gas) 0N(F) mm 202 410 208 MO F x y mm J 82 102 70 Residues, mm 80 280 134 NOF:MO F x y 1.49:1 1.27 :1 1.06:1 Solid Prod. N00sF c 6 N00sF 7; NOOsFg NOOsF-NO + ReFg (gas-splid) 99 98 1.05:1 NOReFg NO + ReF 7 (gas-solid) 150 150 46 1.44:1 NOReFg; (N0)'2ReFg NO + Re0F 5 142 (gas-solia) 140 1.02:1 NOReOF, NOTE: No gaseous products detected i n these r e a c t i o n s — s e e text. 141 (oxy)-fluoride transformed into the s o l i d reaction product, the transformation being indicated by a tendency for the product to peel away from the walls of the Kel-F trap and, often, by a color change. Sometimes a l i t t l e smoke formed towards the end of the reaction, when the Kfcl-F trap was at or near room temperature, and the bulk of the s o l i d (oxy)fluoride had apparently reacted. This was presumably material a r i s i n g from the reaction of the components i n the gas phase. In some instances, a modification of the experimental technique was used, so as to permit the ONF, i n the gas phase, to react with gaseous rather than s o l i d (oxy)fluoride (gas-gas  reaction). A tens i m e t r i c a l l y measured sample of the (oxy)fluor-ide, i n the Kel-F trap at room temperature, was allowed to react with a sample of ON(F) i n the l i n e by opening the valve separa-t i n g them (H,I or J i n figure 2). The NO(F) pressure i n the l i n e had to be a factor of two or three greater than that of the fl u o r i d e i n the Kel-F trap, so that the vapours would mix i n the Kel-F trap, depositing the product where i t could be recovered and preventing the vacuum l i n e from being contaminated with s o l i d . This procedure was thus not convenient for reactions i n which a 1:1 mole r a t i o of reactants was desired and suffered the further disadvantage that there was no opportunity to discard the measured sample of NO(F), should i t prove to contain NO . As a r e s u l t , gas-gas reactions were car r i e d out only when there was a possib-i l i t y that the gas-gas reaction did not give the same reaction products as the s o l i d -gas reaction. The r e s u l t s of gas-gas experiments indicated that there was no difference between the 142 gas-gas and gas-solid reactions. The r a t i o of ON(F) to (oxy)fluoride i n the reaction product (column 4) was determined aft e r running the infrared spectrum of the. residual vapours. In the instances where there was an excess of ONF, N0 2 and NOgF were always seen i n the i n -frared spectrum, along with ONF. It i s , however, reasonably certa i n that neither of these species arose i n the actual ONF + fl u o r i d e reaction. The N0 2 most l i k e l y arose from the decomp-o s i t i o n of the ONF i n the infrared c e l l and, to a much lesser extent (since the reaction system was always conditioned p r i o r to a reaction), from decomposition i n the reaction system during and afte r the reaction. S i g n i f i c a n t l y , the amount of NO was greatest i n instances where the infrared c e l l had not been just previously conditioned with ONE samples. The amount of N0 2F was never s i g n i f i c a n t l y greater than that expected on the basis of the known impurity of the ONF supply. Infrared spectroscopy established that no gaseous i species were present aft e r a reaction other than the s t a r t i n g reagents or t h e i r decomposition products. None of the reactions reported i n Table 17 gave a material having a detectable (greater than 0.5 mm Hg) vapour pressure at l i q u i d nitrogen temperature, except for the reactions involving an excess of NO (NO has a vapour pressure of rJ o.5 mm o at -196 C); these reactions had a pressure of products of less o than 1 mm Hg at -196 C. X-ray powder photography, combined with the tensimetric r e s u l t s , was used to i d e n t i f y the s o l i d reaction products 143 (column 6 of Table 17). In sections 2.2.2 to 2.2.12, experimental r e s u l t s and observations are given for each of the reactions studied. Ref-erence should be made to th i s section and Table 17 wherever pertinent. 2.2.2 The ONF + WFg Reaction Tensimetric t i t r a t i o n s established the existence of both 1:1 and 2:1 adducts and X-ray powder patterns were obtained for each s a l t . The powder data for N0WF7 i s presented i n Table 18, for (NO)2WF8, i n Table 19. Both N0WF7 and (NO)2WFg are white s o l i d s . 1 The N0WF7 photograph was indexed on the basis of cubic symmetry with a Q = 5.191 ± . 003A*. The impurity l i n e s seen i n the N0WF7 photograph at low angles (Table 18) l i k e l y a r i s e from decomposition of the N0WF7, perhaps from attack of the s a l t on the s i l i c a c a p i l l a r y . These l i n e s were also seen i n (NO)2WFg photographs (Table 19). in two of the i n i t i a l ONF + WFg experiments, t h i s minor phase showed up strongly and the cubic N0WF7 phase was absent, even though a 1:1 tensimetry had been obtained. However, both these photographs were of samples handled i n the Towers drybox (see chapter II, section 1.1.2) and l e f t for a week to ten days before obtaining the X-ray photograph. These observations are perhaps s i g n i f i c a n t with 127 regard to the work of Ogle et a l . , discussed below and i n section 144 Table 18 X-Ray Powder Data for NOWF- and NOOsF, N0WF7 NOOsF 7(with some NOOsFg, X) !+k 2+l 2 V d 2 ^ - 2) l / 1 o h 2+k 2+l 2 l / d 2 * •2> I / I G OES. CALC. OBS. CALC. p.03585 ms 1 0.03888 0.03778 vs 1 0.05843 0.03701 vs 0.05075 mw 0.04367 vvw 0.06987 w 0.04728 vw 2 0.07681 0.07556 vs 0.06287 vw X 0.07952 vw 0.07253 m 3 0.1149 0.1133 ms 2 0.07590 0.07402 vs X 0.1191 vw 0.07959 mw 0.1270 vw 3 0.1132 0.1110 ms 0.1463 w 4 0.1506 0.1480 w 4 0.1529 0.1511 mw 5 0.1879 0.1850 ms 0.1646 • w 6 0.2247 0.2221 s 0.1842 w 8 0.2989 0.2961 m 5 0.1905 0.1889 ms 9 0.3364 0.3331 ms 0.2220 w 10 0.3732 0.3701 m 6 0.2288 0.2267 s 11 0.4103 0.4071 mw X 0.2369 Iw 12 0.4465 0.4441 w 0.2401 J 13 0.4842 0.4811 mw 0.2593 w 14 0.5212 0.5181 mw 0.2778 w 17 0.6320 0.6291 w 0.2981 w 18 0.6689 0.6661 w 8 0.3039 0.3022 mw 19 0.7062 0.7032 vvw 9 0.3417 0.3400 ms 20 0.7439 0.7402 vvw X 0.3531 m 21 0.7800 0.7772 vw 0.3724 • w 10 0.3797 0.3778 m X 0.3911 vw Q 0.4100 w a = 5.198 ± .003 A 11 0.4166 0.4156 w from Nelson-Riley plot) X 0.4298 w 0.4473 w X 0.4661 vw from second f i l m : 13 0.4936 0.4911 vw a o = 5.197 + .004 A 14 0.5314 0.5289 mw a Q = 5.145 + 0.005 X (from Nelson-Riley plot) from second f i l m : a Q = 5.146 ± .004 8 145 Table 19 X-Ray Powder Data for (N0)2WFg and (N0) 2ReF g. (NO) 2 WFg (N0) 2ReF 8 ./d 2(A- 2) i/d 2(£- 2) I / d 2 ( S " 2 ) l/\ 0.0374a vs 0.3376c m 0.0371 s 0.0489?; vs 0.3494 . m 0.0394 vs 0.0577° w 0.3585 m 0.0499 s 0.0625° w 0.3681 m 0.0522 ms 0.0728° w 0.3759d : m 0.0894 s 0.0759c s 0.3877 m 0.103: ms 0.0799d w 0.3996 w 0.121 mw 0.0865 s 0.4076 vw 0.141 mw 0.0999 s 0.4116C vw 0.153 m 0.1069 vw 0.4192 m 0.160 m 0.1133C m 0.4258 w 0.173 mw 0.1204 m 0.4375 m 0.194 mw 0.1379 m 0.4494 m 0.207 mw 0.1421 w 0.4562 m 0.248 m 0.1500° m 0.4761 m 0.264 m 0.1581 m 0.4862° w 0.277 m 0.1692 m 0.5146 w 0.291 vw 0.1760 vw 0.5248d w 0.310 vw 0.1880d m 0.5351 w 0.330 m 0.1958 w 0.5472 vw 0.342 vw 0.2001 m 0.5676 w 0.362 W 0.2068 w 0.5771 w 0.370 w 0.2209 m 0.5860 w 0.381 w 0.2257 m 0.6146 vw 0.39*4 vw 0.2378 ms 0.6242 w 0.400 vw 0.2481 w 0.6339d w 0.433 w 0.2577 ms 0.6469 vw 0.471 w 0.2707 ms 0.6547 vvw 0.484 vw 0.2884 m 0.6652 vw 0.520 vw 0.2995d m 0.6859 vw 0.557 vw 0.3062 vw 0.7148 w 0.585 vw 0.3199 m 0.7339 w 0.638 vw 0.3259 m • . = doublet, unresolved; b = impurity, from attack on glass?; : = cubic N0WF7 and , probably, no (N0)2WFg l i n e ; d = cubic NOW] and, probably, an (>N0)2WF8 l i n e . 2 Q—6 Note: only 1/d values < 0.7500 A are given for (N0)2WFg li n e s 146 (NO)2WFg gave a complex, as yet, unindexed X-ray powder photograph. The photograph of (NO)2WFg always contained a weak cubic N0WF7 pattern and r a t i o s of ONF:WFg i n the products never exceeded 1.8:1. Pure (NO^WFg was not obtained even i n a reaction i n which a 3:1 mole r a t i o of WFg to ONF was used. (See tensimetric results.) 127 These r e s u l t s d i f f e r s i g n i f i c a n t l y from those of Ogle et a l . , who found that the ONF + WFg reaction gave only a 1:1 adduct having a complex X-ray powder photograph. Possibly t h e i r X-ray photographs were of the decomposition product of NOWF7. A sample of (NO)2WFg, X-ray pictures of which showed only a weak cubic pattern, was heated under vacuum at 80°C i n a Kel-F trap, for eight hours. Some of the material sublimed out of the heated zone,condensing as a white s o l i d on the upper unheated section of the Kel-F trap, while a roughly equal bulk of white s o l i d remained behind i n the bottom of the trap. An X-ray powder photograph of a mixture of the sublimed and unsub-limed s o l i d s showed a strong cubic N0WF7 pattern, and only a weak (NO)2WFg pattern. 2.2.3 The ONF + ReFfi Reaction Tensimetric t i r a t i o n s with 2:1 or 3:1 mole r a t i o s of ONF to ReFg gave pure (NO)2ReFg (results of tensimetric t i t r a t i o n s being taken as index of p u r i t y ) , white i n colour. (NO)2ReFg was found to be isomorphous with (NO)2WFg, although X-ray powder photographs of the (NO)2ReFg s a l t did not show l i n e s as sharp as those i n the (NO)2WFg photographs, and did not show l i n e s to as high a Bragg angle. Powder data for (N0) 9ReF R i s given i n table D9.. 147 Tensimetric t i t r a t i o n s with equimolar r a t i o s of ONF to ReFg, or with ReFg-rich r a t i o s were less s a t i s f a c t o r i l y character-ized. The s o l i d product was an inhomogenous mixture of yellow and white s o l i d s , and the tensimetric r e s u l t s indicated that the r a t i o of ONF to ReFg i n the s o l i d mixture was less than 2:1, but the X-ray photographs showed only l i n e s due to the phase i d e n t i f i e d as (NO^ReFg. The background of these photographas was clean, in d i c a t i n g the absence of any large amount of an amorphous phase. The yellow component of the mixture was probably unreacted, adsorbed ReFg. This would be consistent with the tensimetries of less than 2:1, and with the fact that the yellow colour faded on prolonged pumping (30 minutes) or on standing for one or two days. However the absence of l i n e s a t t r i b u t a b l e to ReFg i n X-ray photographs of samples which s t i l l retained a yellow colour i s puzzling. 2.2.4 The ONF + ReOFg Reaction ONF and ReOFg reacted to give only NOReOFg, even with an excess (3:1 mole r a t i o ) of ONF . NOReOFg i s a white s o l i d . The X-ray powder data i s given i n table 20. 2.2.5 The ONF + ReF 7 Reaction Several tensimetric t i t r a t i o n s gave 0NF:ReF7 r a t i o s of 1.33:1, but the s o l i d products were not the same i n a l l cases. Twice X-ray powder photographs, of a white s o l i d product, showed (NO^ReFg, while twice X-ray powder photographs, of a s o l i d pro-duct containing a yellow s o l i d , showed a complex pattern of, as yet, u n i d e n t i f i e d phases. In a l l reactions, the i n i t i a l reaction product appeared to be inhomogeneous, a mixture of pale yellow Table 20 X-Ray Powder Data for NOReOFg l / d 2 ( A " 2 ) I/Io 0.0373 s 0.0464 vs 0.0776 s 0.0827 s 0.0878 w 0.1223 m 0.1383 m 0.1488 m 0.1582 vw 0.1645 mw 0.1835 m 0.2106 vw 0.2197 w 0.2361 m 0.2491 vw 0.2577 w 0.2858 mw 0.3091 m 0.3187 m 0.3294 vw 0.3388 vw 0.3531 w 0.3602 w 0.3748 mw 0.4050 mw 0.4212 mw 0.4314 mw 0.4453 mw 0.4515 vw 0.4646 vw 0.4858 w 149 and white s o l i d s . When the s o l i d product was pumped for 30 minutes or so, or was l e f t standing for one or two days, the yellow colour faded and a white s o l i d , characterized as (N0) 2ReFg by i t s X-ray picture, was l e f t . However, i n instances where X-ray samples of the i n t i a l inhomogeneous material were run, the X-ray photograph was complex and showed no (N0) 2ReFg l i n e s . Gravimetric experiments were carr i e d out for the ONF + ReF 7 reaction i n an attempt to get quantitative r e s u l t s . The monel reactor described i n the experimental section on the ONF + p t F g reaction was used i n place of the Kel-F trap. A weighed quantity of ONF, i n excess of that required for a 2:1 reactant r a t i o , was allowed to react with ReF 7, i n one experiment, at room temperature and i n another experiment, at 50°C. In both cases the s o l i d product had an 0NF:ReF7 mole r a t i o well under 1:1. The observations made above on the s o l i d reaction products were confirmed. When the monel reactor was opened immediately aft e r removing the :excess of ONF (Infrared spectra showed the absence of any gaseous product-only ONF, N0r> and N0 2F peaks were seen.), the product was an inhomogeneous yellow and white s o l i d , the yellow material seemingly adsorbed on the surface of the white s o l i d . X-ray photographs showed the same complex phase as before, of an un i d e n t i f i e d material. After the s o l i d had been pumped at room temperature for about 2 hours, the yellow colour had faded and X-ray pictures of the white s o l i d remaining i d e n t i f i e d i t as (N0) 2ReF g. 150 2.2.6 The ONF + OsFg Reaction X-Ray powder photographs of the s o l i d reaction pro-ducts established that two phases, both cubic, were produced i n the reaction. The phase with the smaller unit c e l l , a white s o l i d , gave a pattern of l i n e s i d e n t i c a l i n position and i n t e n s i t y to NOOsFg. (The colour was determined by noting that reaction pro-ducts showing only t h i s phase i n the X-ray powder photographs were white.) The coincidence of l i n e s and correspondence of i n t e n s i -t i e s leaves absolutely no doubt that t h i s phase i s , i n fact, NOOsFg. The second phase, a yellow s o l i d , gave a cubic pattern, the l i n e p o sition i n d i c a t i n g a unit c e l l larger than that of NOOsFg. In reaction products which were mixtures of N00sF 7 and NOOsFg, the two cubic patterns were quite d i s t i n c t , the N00sF 7 pattern being inside the NOOsFg pattern. I d e n t i f i c a -t i o n of the larger cubic phase as N00sF 7 i s based on the close t o . . l : l tensimetries observed i n reactions i n which i t was the only s o l i d product, and on the r e l a t i o n of i t s unit c e l l size to that of i s o s t r u c t u r a l N0WF 7-(unit c e l l s l i g h t l y smaller, as expected - see discussion). The X-ray powder data for N00sF 7 i s given i n table 19. The pattern was indexed on the basis of a simple cubic Bravais l a t t i c e , with a Q = 5.145 ± .005 A*. In addi-tio n , there were l i n e s due to an u n i d e n t i f i e d impurity phase (or phases) i n several photographs. A sample of N00sF 7, heated to 105°C i n an evacuated Kel-F trap for eight hours, sublimed unchanged,in part, condensing as a yellow s o l i d on an unheated portion of the Kel-F trap. The remainder of the o r i g i n a l N00sF 7 had decomposed to NOOsFg. The 150. bulk of N00sF7 (sublimed s o l i d ) to NOOsFg (unsublimed s o l i d ) was, very roughly, 2:1. Examination of the gaseous materials from the ONF + OsFg reactions f a i l e d to e s t a b l i s h the existence of any fl u o r i n e (pressure i n system at -196°C was always 0 mm) or ONF3, (no peak in infrared spectra at 890 cnT^, the position of the most intense fundamental i n ONF3) except for one reaction i n which a trace of ONFg was found (small peak at 890 cm - 1). 2.2.7 The ONF + OsOFg Reaction The ONF + OsOFg reaction could not be studied tensime-t r i c a l l y with ease, because the reaction went to completion slowly, i n sharp contrast to those discussed hitherto, a l l of which proceeded to completion rapidly.(within the time required to warm the reaction mixture to ambient temperature) In one tensimetric t i r a t i o n which was attempted, a green s o l i d ( s o l i d OsOF^ i s lime-green) could s t i l l be seen i n the Kel-F trap a f t e r i t had been at room temperature for one or two minutes, i n spite of the fact that a 3:1 mole r a t i o of ONF to OsOFg had been used. The green s o l i d transferred to the con-stant volume system along with the other v o l a t i l e s i n the Kel-F trap. Only a small amount ( i n s u f f i c i e n t for X-ray samples) of white s o l i d remained i n the Kel-F trap. Two infrared spectra were taken of the material which had been transferred. I n i t i a l l y , the reservoir on the constant volume system was allowed to warm to room temperature and the vapours were expanded into the i n f r a -red c e l l . The spectrum of t h i s sample showed only ONF and N02-Then the reservoir of the constant volume system was pumped 152 b r i e f l y (^15-30 sec.) at -10°C and a second sample taken, by the aforementioned procedure. This sample showed OsOFg, i d e n t i -f i e d by peaks at 961, 700 and 640 cm - 1. (OsOFg has i t s strongest 9 l fundamentals at 960, 700 and 640 cm .) To confirm that the reaction between OsOFg and ONF took place slowly, i f at a l l , a reaction i n the infrared c e l l was studied. The infrared c e l l and reservoir were treated with f l u o r i n e and then with ONF. ONF (pressure ^ 1 atm.) was admitted to the infrared c e l l cavity and reservoir and the spectrum was ; recorded. The ONF was a very pale yellow and showed only a small 1618 cm - 1 peak; hence i t contained very l i t t l e NO . The ONF sample was condensed into the reservoir at -196°C. With the valve connecting the cooled reservoir to the c e l l cavity closed, a sample of OsOFg was admitted to the cavity. The spectrum showed that OsFg was absent but indicated the presence of a l i t t l e Os04. After the reservoir on the infrared c e l l had been warmed to room temperature, some ONF was admitted to the c e l l , the increase i n absorption at 765 cm - 1 ( V 3 1 2 1 of ONF = 765 cm - 1) serving to monitor the amount of ONF added. The spectrum was then scanned. Both ONF and OsOF,. co-existed i n the vapour phase but the gradual decrease i n i n t e n s i t y of the OsOFg fundamental at 700 cm - 1 i n d i -cated that the OsOF 5 was being consumed. The N02 peak at 1618 cm - 1 had increased s i g n i f i c a n t l y i n i n t e n s i t y . When more ONF was admitted to the c e l l and the spectrum scanned once more, the OsOF_ fundamental at 700 cm - 1 had disappeared completely, while 5 the NO2 1611 cm - 1 peak had increased further i n i n t e n s i t y . 153 A separate experiment i n which ONF was handled alone i n the infrared c e l l cast considerable doubt on the significance of the' growth of NOg during the reaction. After a sample of ONF had been l e f t i n the reservoir of the infrared c e l l for several minutes, and the infrared reservoir and c e l l for about 15 minutes, a 1611 cm - 1 peak had grown into the ONF spectrum, somewhat less i n i n t e n s i t y than that i n the spectrum of the ONF + OsOF^ react-ion products, but not so much less that the 1611 cm~^ peak i n the OsOFg + ONF reaction mixture could be d e f i n i t e l y taken as proof that the reaction ONF + OsOFg yielded N0 2 as a reaction product. 2.2.8 The ONF + I r F g Reaction This reaction was studied by the usual tensimetric technique. However, since one of the reaction products was a gas, noncondensable i n l i q u i d nitrogen, the pressure of the residual gases i n the constant volume system could not be obtained. The reason for t h i s , of course, was that the gas noncondensable i n l i q u i d nitrogen could not be condensed back into the constant volume system for pressure measurement. Similar d i f f i c u l t i e s were encountered i n studying the ONF + PtFg reaction, but an experimental procedure which overcame these d i f f i c u l t i e s was used to study t h i s reaction. (See the following section.) However, even with the presently described technique, the products of the ONF + IrFg reaction were established. These were: (1) NOIrFg. The white non-volatile s o l i d produced i n the reaction was i d e n t i f i e d by i t s X-ray powder picture, which 154 was cubic and i d e n t i c a l with photographs of authentic NOIrFg. (2) Fluorine. The gaseous product noncondensable at -196°C was i d e n t i f i e d by i t s pressure at that temperature (18, 26 and 24 mm i n three experiments) and by the orange discharge produced by a t e s l a c o i l . The only conceivable reaction products having a vapour pressure of more than one mm at .-196°C are F 2, 02, and N 2; and of these, only f l u o r i n e gives an orange gas discharge. More conclusive proof that the noncondensable gas produced i n the ONF + MFg (M = Ir, Pt) reaction was f l u o r i n e and only f l u o r i n e i s given i n the discussion of the ONF + P t F g reaction, for which an experiment of a quantitative nature was carried out. (3) ONF3. The infrared spectrum of the vapours condensa-ble i n l i q u i d N 2, run a f t e r pumping away the f l u o r i n e , showed peaks associated with ONF3. Peaks were observed at 1705 and 890 cm-"1", with the l a t t e r more intense. ONF3 has i t s two most intense fundamentals 1 2 2 at 1690 and 883 cm \ ( V 2 and V 4 respectively; \>4 more intense) A l l other peaks i n a l l the spectra could be assigned to known nitrogen species (N02, NOgF and ONF were seen i n one or more of the three experiments conducted), none of which are regarded as reaction products. Mr. J. Passmore, presently studying the preparation and properties of ONFg i n these laboratories, investigated the ONF + I r F g reaction as a possible method of preparation of ONF3. His experiments confirm that ONF3, F 2, and N0IrFg are the products of the reaction. 155 2.2.9 The ONF + PtF f i Reaction Since the tensimetric procedure employed i n the previous reactions was not suitable for obtaining quantitative r e s u l t s i n the ONF + MFg (M = Ir, Pt) reactions, and since quantitative r e s u l t s were c l e a r l y desirable i n these systems, the experimental apparatus and procedure was changed i n the study of the ONF + PtFg reaction. The Kel-F trap was replaced with small (about 10 cc capacity) monel container f i t t e d with a Hoke 431 valve, the tare weight of the container plus valve being less than 200 gms. The vessel could thus be weighed on an accurate a n a l y t i c a l balance. (Mettler "Gram-atic" Balance) Also the container had a remova-ble l i d so that the s o l i d reaction products could be handled i n the drybox, i f necessary. A leak-test p r i o r to the experiment -2 established that the container held a vacuum of less than 10 mm overnight. Furthermore, the reactor did not leak when cooled i n l i q u i d nitrogen. The entire system (as i n the tensimetric experiments, except that the Kel-F trap was replaced by the monel vessel) was treated with f l u o r i n e and ONF, as described i n the section on "The handling of ONF i n the vacuum system". Subsequently the only section of the system exposed to a i r for any length of time was the short (2") piece of monel tubing which connected the monel reactor to the vacuum system, the rest of the system being exposed only during the time required to evacuate t h i s section aft e r each weighing. After the tare weight of the reactor had been obtained, PtFg (*>1 gm) (from i t s container over NaF, which had been evacuated at -196°C to remove traces of a i r , just prior 156 to beginning t h i s experiment) was condensed into the l i q u i d nitrogen-cooled reactor, which was then reweighed. To remove moisture which tended to c o l l e c t on the metal container a f t e r i t had been cooled to -196°C, i t was washed with acetone and then dried i n a blast of compressed a i r . ONF i n s l i g h t excess of that required for the reaction ONF + PtFg —» NOPtFg + F 2 was then condensed into the reactor. A rough measurement of the ONF pressure i n a roughly known volume gave a crude estimate of the amount of ONF being used. The reactor was once again weighed and was then warmed to about 50°C for several minutes, to ensure complete reaction. The reactor was then cooled again to -196°C, (Note that the reactor was cooled i n l i q u i d nitrogen before i t was opened to the rest of the system; hence, the r a t i o of cooled surface to volume of vapours was f a i r l y high.) and any gases v o l a t i l e at -196°C were allowed to expand into an evacuated infrared c e l l , which had been attached to the system i n place of the PtFg storage container. Valve G of figure 3 was closed so as to obtain the maximum possible pressure i n the infrared c e l l . The spectrum of t h i s gas, and a subsequent experiment conducted i n the infrared c e l l , are described below. After the valve on the infrared c e l l had been closed, the remaining vapour was expanded (G opened) into the gauge, for pressure measurement. The pressure measured was 106 mm; the pressure of the gas sample i n the infrared c e l l would have been higher. The noncondensable gas i n the l i n e and monel reactor was then pumped away (monel reactor s t i l l at -196°). A t e s l a c o i l was held to a section of the glass manifold through which 157 these vapours passed and the orange colour of the gas discharge was noted. After the reactor had been weighed again, a sample of any vapours from materials v o l a t i l e at room temperature was taken into a second infrared c e l l and the remaining v o l a t i l e s were condensed into a storage vessel. The reactor was then weighed again. A l l weights have been recorded i n table 21. The infrared spectrum of the noncondensable gas showed no absorption i n the region 4000-400 cm * except for a very small PQR branched peak with the Q branch at 1275 cm"1. 128 This peak was considerably broader than the strong CF4 peak which occurs near t h i s frequency. After i t s spectrum had been recorded, the gas was allowed to expand into an evacuated pyrex bulb containing glass wool, which had been attached to the i n -frared c e l l i n place of the usual monel reservoir. After one hour, a substantial peak had grown into the spectrum at 1025 cm"^, 129 1 undoubtedly due to S i F 4 . The PQR branched peak at 1275 cm" had grown i n i n t e n s i t y and i s therefore l i k e l y associated with a species (fluorocarbon?) a r i s i n g from attack of the nonconden-sable gas on some material (Teflon?) i n the infrared c e l l , rather Table 21 Gravimetric Data for the ONF +.PtFg Reaction (1) tare weight of monel reactor 189.5908 gm (2) weight of reactor + PtFg 190.7359 gm (3) weight of reactor + PtFg + ONF 190.9300 gm (4) weight of reactor + PtFg + ONF - v o l a t i l e s at -196°C 190.8731 gm (5) weight of reactor + products i n v o l a t i l e at 25°C 190.8548 gm 158 than with some species from the ONF + ptFQ reaction. After the vapours had been i n contact with the glass for 10 hours, the 1025 cm - 1 peak had grown enormously, the absorption being off scale i n the region 1030-1020 cm - 1. Small peaks could also be seen at 1305 cm - 1 and 1275 cm - 1 (sharp); the l a t t e r presumably due to CF 4- The broad PQR branched peak at 1276 cm - 1 had d i a -appeared. No further changes were noted i n the spectrum aft e r an add i t i o n a l 24 hours contact. The infrared spectrum of the reaction species v o l a t i l e at room temperature but i n v o l a t i l e at -196°C showed only peaks at t r i b u t a b l e to N02F and ONF3. From the int e n s i t y of the peaks, the pressure of N02F was estimated to be less than 10 mm; of ONF3, less than 5 mm. The i d e n t i f i c a t i o n of the s o l i d reaction product of the ONF + PtFg reaction as N0+PtFg~ i s given i n the experimental part of chapter VI. Powder data for NOPtFg i s given i n table 22. 2.2.10 The NO + ReFg Reaction NO reacted with ReFg to give a 1:1 adduct, NOReFg. The X-ray pattern of the yellow s o l i d was indexed on the basis of a cubic unit c e l l , a Q = 10.151 + . 002A\ See table 22. 2.2.11 The NO + ReF ? Reaction NO and ReF 7 reacted to give an inhomogenous mixture of yellow and white s o l i d s . In one experiment, the reaction appeared to proceed i n two d i s t i n c t steps. I n i t i a l l y , a white s o l i d formed, the yellow ReF 7 seemingly transforming d i r e c t l y to the product. As the Kel-F trap became warmer (near room temperature), a yellow 159 Table 22 X-Ray Powder Data for NOReFg and NOPtFg. N0ReF6 •NOPtFg h 2+k 2+l 2 l / d 2 ( f t " 2 ) I/I h 2+k 2+l 2 l / d 2 ( f t " 2 ) I/I< OBS CALC OBS CALC 4 0 .0400 .0388 vs 8 0 .0794 .0777 vvs 12 0 .1186 .1165 m 14 0 .1376 vw 16 0 .1578 .1553 w 18 0 . 1767 .1747 vw 20 0 .1966 .1941 s 22 0 .2162 .2135 vw 24 0 .2353 .2330 vs 32 0 .3131 .3106 ms 36 0 .3527 .3494 s 40 0 .3911 • 3882 ms 44 0 .4306 .4271 m 48 0 .4698 .4659 w 52 0 .5081 .5048 m 56 0 .5483 .5436 s 64 0 .6254 .6212 vw 68 0 .6641 .6601 m 72 0 .7027 .6989 mw 76 0 .7409 .737 7 w 80 0 .7800 .7765 w 84 0 .8192 .8154 mw 88 0 .8573 .8542 w 96 0 .9350 .9319 w 100 0 .9744(«1) .9707 w 104 1 1 .0122 (<*1) .0120(<*2) 1.0095 m 108 1 1 .0505(c*l) .0501(o<2) 1.0483 w 116 1 .1277(0^1) 1.1260 m 1 . 1287 («2) 120 1 . 1671(C<L)' 1.1648 mw 1 . 1672 (<*2) 132 1 1 .2830(00.) .2821(6<2) 1.2813 mw 136 1 .3214 (0<1) 1.3201 mw 1 .3206(0*2) 140 1 .3606(0(1) 1.3590 mw 1 .3599(<X2) 144 1 1 .3991(00.) .3982(0(2) 1.3978 w 148 1 .4376(0(1) 1.4366 vw 152 1 .4762(0<1) 1.4754 m 1 .4765(0(2) 4 0 .0386 0 .0391 vs RHOMB 0 .0692 vw 8 0 .0783 0 .0782 vs RHOMB 0 .0945 vvw RHOMB 0 .1104 vvw 12 0 . 1181 0 .1173 m 14 0 . 1386 0 . 1369 vvw 16 0 . 1575 0 . 1564 mw RHOMB 0 . 1616 vvw 18 0 . 1774 0 .1760 vvw 20 0 . 1965 0 . 1956 ms 22 0 .2149 0 .2151 vw 24 0 .2356 0 .2347 s 32 0 .3140 0 .3130 m 36 0 .3536 0 .3521 ms 40 0 .3925 0 .3912 m 44 0 .4317 0 .4303 m 48 0 .4705 0 .4694 mw 52 0 . 5098 0 .5085 m 56 0 .5495 0 .5477 ms 68 0 .6672 0 .6650 m 72 0 .7058 0 .7041 mw 76 0 .7446 0 .7432 w 80 0 .7824 0 .7824 w 84 0 0 .8235(o(l) .8217 (*2) 0 .8215 w 88 0 .8607 0 .8606 vw 96 0 .9404 0 .9389 vvw 100 0 .9786 0 .9780 vvw 104 1 .0189 (o(l) 1 .0171 w 1 .0184 (C*2) vw 108 1 .0571 1 .0562 vvw 116 1 . 1363(00.) 1 . 1344 w 1 . 1361(0(2) vw 120 1 1 . 1744 (0(1) . 1755(CX2) 1 . 1736 vw vvw 132 1 .2919(0(1) 1 .2902 vw 1 .2929(0(2) vvw 136 1 .3313 (cxi) 1 .3301 vw 1 .3299(0<2) vvw 140 1 .3697 (<*l) 1 .3692 vw 1 .3696(0(2) vvw 144 1 .4093(0(1) 1 .4083 vw 1 .4092(o<2) vvw 160 Table 22 (continued) h 2+k 2+l 2 160 164 168 OBS N0ReF6 i / d 2 ( r 2 ) 1.5546(«1) 1.5921(<*1) 1.5921(<X2) 1.6308(C<1) 1.6357(0(2) CALC 1.5531 1.5919 1.6307 1/1, vw ms mw h 2+k 2+l 2 152 164 168 N0PtF6 i / d 2 ( r 2 OBS 1.4869(^1) 1.4866(«2) 1.6039(<*1) 1.6040(CK2) 1.6431(o<l) 1.6429(0(2) I/I. CALC o 1.4865 vw vvw 1.6039 w vw 1.6430 vw vvw a - 10.150 + .002 1 (from Nelson-Riley plot) RHOMB = l i n e of NOPtFg, rhombo-hedral modification from second f i l m : a Q = 10.152 + .003 A a Q = 10.112 ± .001 1 (from Nelson-Riley plot) 161 smoke formed, apparently from some gas-gas reaction, and se t t l e d on the walls of the Kel-F trap as a yellow coating. P a r t i a l separation of the two phases was possible i n the drybox, the upper portion of the Kel-F trap containing mostly the yellow s o l i d which had appeared from the gas phase, the lower, mostly the white s o l i d , with a coating of the yellow powder. X-ray pictures of the former showed a strong NOReFg pattern and a weak (NO)2ReFg pattern, while pictures of the l a t t e r showed the reverse - a strong (NO^ReFg and a weak NOReFg pattern. The reaction being discussed here i s the one for which tensimetric r e s u l t s are given i n table 17. 2.2.12 The NO + ReOF_ Reaction o NO and ReOFg gave a lime-green s o l i d , NOReOFg. The colour i s reminiscent of that of i s o e l e c t r o n i c OsOFg. The X-ray powder photograph was indexed on the basis of a tetragonal unit c e l l with a = 5.O83S, C = IO.OOQX. The powder data i s presented i n table 23, along with that for NOOsOFg, prepared by Dr. N.K.Jha and successfully indexed following the indexing of the NOReOFg photograph. The close s i m i l a r i t y i n the l i n e i n t e n s i t i e s and positions indicated that the two s a l t s are isomorphous. Powder 2 o-2 data for NOOsOFc i s given only to 1 /d s 0.52 A 162 Table 23 X-Ray Powder Data for NOOsOFg aad NOReOFg, NOOSOF5 l/d 2(S-2) NOReOFe 2, hkl c a l c . obs. I/I 001 0 .0093 — 002 0 .0372 0 .0375 vs 010,100 0 .0396 0 .0408 vs 011,101 0 .0489 0 .0497 vvs 110 012,102 0 0 .0792 .0768 0 .0786 vvs 003 0 .0837 111 0 .0885 0 .0929 s 112 0 . 1164 0 . 1170 s 013,103 0 . 1233 0 .1251 ms 004 0 . 1488 0 .1505 ms 020,200 0 .1584 0 . 1600 w 113 0 .1629 021,201 0 .1677 0 . 1711 ms 014,104 0 . 1884 0 .1915 ms 022 ,202 120,210 0 0 .1956 .1980 0 .1982 vvw 121,211 0 .2073 0 .2089 w 114 0 .2280 0 .2289 ms 005 122 ,212 0 0 .2325 .2352 0 .2359 ms 023,203 0 .2421 0 .2465 ms 015,105 0 .2721 0 .2732 vvw 123,213 0 .2817 0 .2832 ms 024,204 0 .3072 115 220 0 0 .3117 .3168 0 .3163 ms 221 0 .3261 006 0 .3348 0 .3349 w 214 222 0 0 .3468 .3540 0 .3514 w 300 0 .3564 301 0 .3657 106 0 .3744 0 .3770 w 205 0 .3909 302 310 0 0 .3936 .3960 0 .3963 ms 223 0 .4005 311 0 .4053 0 .4078 w 116 0 .4163 0 .4154 vw 215 312 0 0 .4305 .4332 0 .4321 vw hkl 001 010,100 002 011,101 110 012,102 111 003 112 013,103 020,200 004 021,20] 113 120,210 022,202 014,104 121,211 122,212 114 023,203 005 123 j213 015,105 220 204 221 115 222 030 ,300 214,214 006 031.301 130,310 032,302 016 ,106 131,311 223 025,205 132,312 116 033 .303 1/d calc. 0.0100 0.0387 0.0400 0.0487 0.0774 0.0787 0.0874 0.0900 0.1174 0.1287 0.1548 0.1600 0.1648 0.1674 0.1935 0.1948 0.1987 0.2035 0.2335 0.2374 0.2448 0.2500 0.2835 0.2887 0.3096 0.3148 0.3196 0.3274 0.3496 0.3483 0.3535 0.3600 0.3583 0.3870 0.3883 0.3987 0.3970 0.3995 0.4047 0.4274 0.4374 0.4382 ) obs. I/I 0 .0405 vvs 0 .0496 vvs 0 .0794 vvs 0 .0891 vs 0 . 1184 vs 0 . 1304 ms 0 . 1559 mw 0 . 1621 m 0 . 1661 ms 0 . 1946 w 0 .2004 m 0 .2052 vs 0 .2329 vs 0 .2386 vs 0 .2460 s 0 .2845 vs 0 .3086 m 0 .3127 w 0 .3307 w 0 .3482 m 0 .3534 ms 0 .3597 m 0 .3890 w • 0 .3979 m 0 .4064 0 .4288 mw 0 .4390 m 163 Table 23 (continued) NOOsOF5 l / d 2 ( A ~ 2 ) hkl c a l c . 303 0 .4401 007 0 .4557 224 0 .4656 313 0 .4797 107 0 .4953 206 0 .4932 304 0 .5052 320 0 .5148 321 0 . 5241 obs. 0.4397 0 .4501 0.4657 0.4837 0.4985 0.5142 0.5234 I/I ( vw w w w w w w tetragonal Bravais L a t t i c e a = 5.0258; c = 10.3.78 NOReOFg l/d 2(8 - 2) hkl est 1C 0 obs. I / I Q 125,215 0 .4434 0. 4452 mw 224 0 ^4696 0. 4687 mw 133,313 0 .4771 0. 4766 mw 007 0 .4901 230,320 0 .5031 0. 5001 mw 034,304 0 . 5092 0. 5087 mw 026,206 0 .5152 23 Xy321 0 .5130 017,107 0 . 5288 0. 5304 vw 232,322 0 .5431 0. 5397 vw 134,314 0 .5470 0. 5490 mw 126 ,216 0 . 5535 225 0 . 5596 117 0 .5674 0. 5695 233,323 0 .5931 0. 5901 035,305 0 . 5983 0. 5991 135,315 008 0 0 .6370 .6400 0. 6393 234,324 0 .6631 0. 6639 018,108 0 .6787 0. 6841 330 142.412 0 0 . 6966 . 6979 0. 6985 143',413 0 .7479 0. 7473 044,404 0 .7792 0. 7783 242,422 144,414 0 .8140 0. 8164 0 . 8179 128,218 037,307 0 0 . 8335 . 8383 0. 8358 029,209 0 .9648 " 050.500 0 .9675 • 0. 9651 340,430 0 .9675 0,10,0 ,10,00 129,219 1 1 .0000 .0035 1. 0021 151,511 1 .0162 0165 146 ,416 1 .0179 x. 229 1 . 1196 1. 1188 238 ? 328 1 . 1431 1. 1425 tetragonal Bravais L a t t i c e a - 5.O808; c = 10.00N8 164 III DISCUSSION 3.1 OXIDIZING PROPERTIES OF THE HEXAFLUORIDES AND RELATED  SPECIES 1 3 1 3.1.1 Trend i n oxidizing power of the hexafluorides The increase i n oxidizing properties of the hexafluorides of tungsten to platinum i n moving from l e f t to right i n the per-i o d i c table had been c l e a r l y indicated by previous work i n t h i s 9 laboratory. Dr. N. K. Jha had established t h i s trend from his study of the interactions of OsFg, IrFg and PtFg with NO; and 132 his f a i l u r e to make NO and WFg react confirmed the findings of Ogle and his coworkers. NO + WFg no reaction NO +- OsFg *- NOOsFg NO + IrFg *- NOIrFg + (NO)2Iz*Fg NO + PtFg *- NOPtFg + (NO) 2PtFg increasing tendency to oxidize NO Jha had also studied the i n t e r a c t i o n of oxygen with IrFg and PtFg: Og + * r F g R O reaction °2 + P t F 6 ' >" ° 2 P t F 6 • Together with the present author's observation that NO and ReFg react to give NOReFg, these reactions c l e a r l y established the trend: WFg ReFg OsFg IrFg PtFg increasing oxidizing power The products of the hexafluoride reactions with ONF are 165 also i n accord with t h i s trend, PtFg and IrFg once again showing extraordinary oxidizing properties. ONF + WFg ^NOWF? and (NO)2WFg ONF + ReFg (NO)2ReFg no oxidation of ONF. only adducts seen. ONF + OsFg *-N00sF 7 —»-N00sFg 1 some evidence that J NOOSF7 i s e a s i l y reduced, ONF + I r F 6 »-NOIrFfi + F 2 or ONF3 1 > ONF i s oxidized. ONF + PtFg *- NOPtFg + F 2 (+ONFg, trace) 133 Contrary to a very recent report which included a study of the ONF + PtFg reaction, no evidence was found to indicate that NOPtFg would interact with ONF to form (NO) 2PtF g + \ F 2• IrFg and P t F g both oxidize ONF to f l u o r i n e and/or ONF3, while WFg and ReFg form only adducts with ONF, the t r a n s i t i o n metal remaining i n the +6 oxidation state. OsFg exhibits behaviour si m i l a r to ReFg and WFg, forming an adduct, N00sF 7, but there i s evidence that osmium(VI) i s less stable i n t h i s compound than rhenium(VI) and tungsten(VI) i n t h e i r adducts. In several of the tensimetric experiments, X-ray powder photographs showed NOOsFg as one of the s o l i d phases; the data for two of these experiments i s shown i n table 17 of the experimental section. In contrast, NOReFg was never seen i n the ONF + ReFg reaction product, even though the rhenium adduct was prepared and handled under the same conditions as the ONF + OsFg product. Possibly some of the N00sF 7 was reduced by the presence of some weak ( i . e . , does not reduce (NO)2ReFg) reducing agent to which i t was exposed during the reaction or subsequent handling; 166 NOOsFy + X — N O O s F y + XF. A trace of ONF3 seen i n one of the reactions indicates that X i n some cases may be ONF. Clearly NOOsFy i s on the borderline of s t a b i l i t y . 3.1.2 Oxidizing Properties of ReOFg and OsOFc; ReOFg apparently has an oxidizing power similar to that of OsFg or ReFg, since i t oxidizes NO but does not oxidize ONF, giving instead a 1:1 adduct with the l a t t e r reagent: ONF + ReOF5 —9- NOReOFg. It i s anticipated ( s t e r i c factors apart) that rhenium(VII) w i l l be more powerfully oxidizing than rhenium(VI). OsOFg seems to be a weaker oxidizing agent than IrFg, since neither f l u o r i n e nor ONF3 was seen i n the slow ONF-OsOFg reaction. Apparently the removal of a nonbonding t 2 g electron plus replacement of a f l u o r i n e liga.nd by an oxygen ligand (Os^*Fg —>• Os^ I 1OFg) does not increase the ox i d i z i n g power of the central metal atom i n the complex as much as does the increase of nuclear charge plus addition of a t 2 g electron. (Os V IFg —»• VI Ir Fg.) Presumably t h i s i s a r e s u l t of both the poor shielding e f f e c t of a t 2 g electron and the poor electron withdrawing ef f e c t of oxygen r e l a t i v e to f l u o r i n e . That i s , one oxygen does not possess the electron withdrawing properties of two f l u o r i n e s and the loss of a t 2 g electron, (OsFg —•>> OsOFg) which has a shielding e f f e c t of less than one unit of efectronic charge, i s at least p a r t i a l l y compensated by the decreased p o l a r i z a t i o n of the Os-0 double bond r e l a t i v e to the Os-F single bond. 1 6 7 3 . 1.3 Estimated Electron A f f i n i t i e s of the Hexafluorides* As B a r t l e t t 3 3 ' 3 ' * pointed out i n discussing the 0 2 + PtFg reaction, the oxidizing power of the hexafluorides can be a t t r i -buted to t h e i r high electron a f f i n i t i e s and a Hess cycle can be used to place an upper l i m i t on t h e i r electron a f f i n i t i e s . Prior to the present work, the electron a f f i n i t y of IrFg was estimated to be greater than - 8 9 Kilcal/mole, on the basis of the observation that IrFg oxidates NO, giving NOIrFg. The reaction ONF + IrFg —> NOIrFg + J F 2 can now be used to revise the minimum electron a f f i n i t y of IrFg upwards. Consider the cycle ONF + IrFR NOIrF fi 4 ^ F, D(ONF) 6 I W I I £ 6 1 2 A 2 U(NOPtFg) 6 -NO + F »- NO+ + I (NO) i D(F-F) D ( O N F ) 1 2 0 = 5 5 ; I ( N O ) 1 3 4 = 2 1 4 ; £ D ( F - F ) 1 3 5 = 1 9 ; U(NOPtFg) = - 1 2 5 X 3 Q (from Kapustinskii's equation ). Units are Kilcal/mole. Since the reaction of ONF with I r F g was observed to take place spontaneously at or below room temperature, A H R X < 0 . In fact, since the entropy change i n the reaction i s unfavourable, (entropy increase - reaction involves gaseous reactants going to s o l i d products), and s i n c e the free energy i s the thermodynamic In t h i s section, the words "maximum", "minimum", "greater", " l e s s " etc., w i l l be used on the assumption that a l l numbers are read as absolute numbers. 168 function which must be negative for a spontaneous reaction, the enthalpy of reaction .( AH Rx) must be less than zero by at least enough to offset the unfavourable entropy change. Hence, from the above cycle, E ( I r F 6 ) + D(ONF) + I(NO) + U(NOPtFg) - ^D(F-F) = AH R X < O E(IrFg) < -125 Kilcal/mole. With such an electron a f f i n i t y , IrFg i s second only to PtFg as a powerfully oxidizing species. In table 24, the electron a f f i n i t y of IrF- i s compared with that estimated for the other b hexafluorides by the same type of arguments. Upper .limits were estimated from the observed lack of reaction of the hexafluoride with reagents as indicated i n the table. ( i . e . , No reaction implies A H R X < 0). Again Kapustinskii' s equation was used to g calculate the l a t t i c e energies, U. Pauling's univalent r a d i i for xenon and krypton were used along with an i o n i c radius of MF estimated from the c e l l edge of the cubic NOMF- s a l t . Ion-6 o i z a t i o n potentials were taken from the Handbook of Chemistry 134 and Physics. The maximum electron a f f i n i t i e s given for ReFg and OsFg cannot be revised downwards on the basis of the present experimental findings that the ONF + MFg (M = Re,0s) did not give NOMFg as a reaction product. In these systems, adduct formation occurs, and a l l that can be safely assumed i s that the In s e t t i n g upper l i m i t s , the i m p l i c i t assumption that there i s no appreciable k i n e t i c b a r r i e r to the reaction i s made. This assumption seems j u s t i f i e d i n view of the fact the oxidation reactions which do occur take place very r a p i d l y and at tempera-tures below room temperature. 169 Table 24 Estimated Electron A f f i n i t i e s of the Hexafluorides. (a) Reactions used to estimate minimum and maximum e. a f f i n i t i e s MF_ minimum electron a f f i n i t y maximum electron a f f i n i t y rx. with to give no rx. with WFg N0 a b ReFg NO NOReFg Xe OsFg C NO NOOsFg Xe IrFg ONFb NOIrFg + F 2 Xe c PtFg C 0 2 0 2 P t F 6 Kr (b) Estimated electron a f f i n i t i e s . Comparison to other species substance electron a f f i n i t y (Kcal/mole) min. max. WF„ - -90 6 ReFg -90 -170 OsFg -90 -170 I r F c -125 -170 6 Pt F e -170 -206 F -83.5 ± 2 CI -87 references: (a) 132, 9; (b) t h i s work; (c) 9. 170 enthalpy of reaction for the formation of N0MF- + hFn i s less b 2 (exothermic) than that for the formation of an adduct, which does not necessarily mean that the reaction ONF + MFg — > NOMFg + |F 2 i s endothermic, with A H R Y i 0. 3.2 THE OXIDATION OF ONF BY I r F g AND PtF f i: A FLUORINE LIBERATION  REACTION The most novel aspect of the experimental findings dealing with the i n t e r a c t i o n of the hexafluorides with ONF has been the discovery of the f l u o r i n e elimination reactions. U n t i l now, no f l u o r i n e elimination has been observed i n reactions between reactants which may be kept i n d e f i n i t e l y at 137 ordinary temperatures and pressures. Moisson's c l a s s i c a l electrochemical method ( e l e c t r o l y s i s of an anhydrous HF-KHF2 138 mixture, considerably modified technologically, of course) remains the sole commonly used method of i s o l a t i o n of the element. Certainly, chemical reactions l i b e r a t i n g f l u o r i n e can be quoted but these a l l involve the decomposition of a f l u o r i n e containing compound unstable under the conditions of the experiment. For 139 example, KrF2 i s thermally unstable at room temperature and 20°C decomposes, l i b e r a t i n g f l u o r i n e : KrF 2 *"* Kr + F 2; and PtFg, at temperatures above 145°C decomposes'*'24 slowly, l i b e r a t i n g f l u o r i n e i n the reaction PtFg —v P t F 4 + F 2. The uniqueness of the present ONF + PtFg (IrFg) reaction l i e s , then, i n the fact that f l u o r i n e i s liberated i n a reaction, 171 at room temperatures and belowjbetween two substances which are each, separately, stable at room temperature. (ONF i s thermo-120 dynamically stable with respect to NO and Fg and the afore-mentioned decomposition of PtFg occurs at a n e g l i g i b l e rate at room temperature.) That the reaction between ONF and PtFg does l i b e r a t e f l u o r i n e has been unequivocally established. The evidence that a sample of gas taken from the reaction_products at -196°C i s f l u o r i n e , i s as follows: (1) The gas had a vapour pressure i n excess of 100 mm Hg at -196°C. The only f e a s i b l e reaction products with such a vapour pressure are F 2, 0 2 and N 2• (2) The gas gave an orange gas discharge. F 2 has an orange gas discharge; 0 2 and N 2 do not. (3) The gas, at a pressure of greater than 100 mm, had no absorption i n the infrared region (4000-400 cm - 1). This lack of absorption indicates the absence of s i g n i f i c a n t quantities of species such as OF 2 ( v . p . 1 4 0 = 1 mm at -196°C) and NO ( v . p . 1 2 5 - 0.5 mm at -196°C), which might have been prevented from con-densing by the presence of some noncondensable gas. (4) The gas reacted with glass to produce s i g n i f i c a n t quantities of SiF^. This proves that the gas container s i g n i f i -cant quantities of f l u o r i n e . (5) The gas reacted completely with mercury. Mr. J. Pass-more found that a sample of the gas at 150 mm pressure i n a volume 3 of 100 cm was completely consumed afte r shaking with mercury (5 gms) for 24 hours at room temperature. This experiment proves 172 that the gas was e n t i r e l y f l u o r i n e and not, say, a mixture of fluo r i n e and oxygen. The experimental evidence also shows that the reaction proceeded largely according to ONF + PtFg — N O P t F g + §F 2 (1) (See table 25.) The observed r e s u l t s i n the table are obtained using the experi^ mental data of table 22, while the calculated figures are obtained from the amount of P t F g used i n the reaction, with the assumption that the reaction proceeded according to (1). However, the amount of fl u o r i n e produced was somewhat less (18%) than that required by equation (1). This i s not surprising, since the infrared spectrum of the reaction products condensable i n l i q u i d nitrogen showed that ONF^ was a reaction product. Unfortunately, since the infrared spectrum also showed the presence of NOgF, the amount of ONF^ produced i s not calculable. The appearance of ONF^ as a minor reaction product i n the ONF + PtFg reaction i s s i g n i f i c a n t . ONF3 i s not produced Table 25 Results for the ONF + PtF_ Reaction 6 observed calculated millimoles of ONF used 3.96 millimoles of PtF„ used 3.69 millimoles of NOPtFg produced millimoles of F 9 produced 3. 71 1.50 3.69 1.84 173 from the thermal reaction of elemental f l u o r i n e with ONF, under the conditions of temperature and pressure used i n the hexafluor-ide reactions. In the preparation of ONF i n t h i s work from NO and excess f l u o r i n e , no trace of ONFg has ever been see. Mr. J. Passmore, who i s presently investigating ONFg, found i n his more thorough studies of the subject that ONFg i s not produced from the room temperature reaction of ONF and f l u o r i n e . Hence the fact the ONFg arises i n small quantities i n the ONF + PtFg reaction indicates that perhaps fl u o r i n e atoms are released at some time during the reaction. One may speculate that the f o l -lowing occurs, with reaction (3) predominating over reaction (4): ONF + PtFg •» NOPtFg + F (2) F + F —*- F 2 (3) ONF + 2F —*- ONFg (4) Interestingly, while the ONF + PtFg reaction gave only a small amount of ONFg, the ONF + IrFg reaction gave a larger amount of ONFg, r e l a t i v e to the amount of f l u o r i n e . Indeed, t h i s q u a l i t a t i v e observation was confirmed by the work of Mr. Passmore, who investigated the reaction as a possible route to ONFg. He found that, i n the presence of ONF i n excess of that needed for the reaction ONF + IrFg —>- NOIrFg + 4 F2» ONFg was produced as the major oxidation product. Further comments on the nature of these i n t e r e s t i n g oxidation reactions are postponed u n t i l section 3.5, , a f t e r coordination numbers i n the (NO)xMOyF^ s a l t s have been discussed. 174 3.3 THE VARIATION IN ANION SIZES OF THE NO+ SALTS  3.3.1 Structural Studies on the Salts X-Ray powder photographs were obtained for a l l of the s a l t s prepared i n the course of t h i s work, and the Bravais l a t -t i c e on which each s a l t was indexed i s given i n table 26. The powder data for each s a l t has been given i n the experimental section. Table 26 also includes data for NOOsFg and NOIrFg, 9 obtained by Dr. Jha. NOReFg and NOPtFg both contained a strong l i n e pattern which could be indexed on the basis of a simple cubic unit c e l l o o with a Q = 5.076A and 5.056A respectively, but the presence of weaker r e f l e c t i o n s required a body-centred cubic unit c e l l with a Q = 10.151A* and 10.112A, respectively. The si m i l a r pattern of i n t e n s i t i e s i n the two s a l t s (NOOsFg and NOIrFg also have t h i s s i m i l a r pattern) indicates that they are probably i s o s t r u c t u r a l , and probably have the OgPtFg s t r u c t u r e 3 4 ' 1 0 1 . Hence Ia3 i s the probable space group 9 8. The N0WF7 and N00sF 7 films showed a strong l i n e , simple cubic pattern with no weak l i n e s between the strong ones. Thus powder photography indicates that the true unit c e l l i s simple cubic. Since seven f l u o r i n e atoms cannot be arranged i n a regular fashion about a tungsten atom so as to preserve cubic symmetry ( i . e . , r e t a i n the required four three-fold axes), the f l u o r i n e atoms must be disordered i n some way - perhaps the structure contains l i b r a t i n g or randomly arranged MFy~ groups. The absence of high angle l i n e s i n the powder photographs (no measurable l i n e s for a Bragg angle of greater than 55° on any photographs) i s consistent with a disordered structure, which 175 Table 26. Bravais L a t t i c e Parameters and E f f e c t i v e Molecular Volumes, NO+ Salts. s a l t Bravais l a t t i c e type Bravais l a t t i c e parameters(A) 1 mol. units per unit c e l l NOTaFg b. c. c. 10.220 8 NOReFg b. c. c. 10.151 8 NOOsFg b. c. c. 10.126 8 NOIrFg ' b. c. c. 10.114 8 NOPtFg b. c. c. 10.112 8 NOWE„ 6 cubic 5.197 1 NOOsF? cubic 5.145 \ 1 (NO)2WFg not indexed (NO) 2ReF g not indexed a c NOReOFg tetragonal 5.083, 10.0 Q 2 NOOsOFg tetragonal 5.025, 10.3 ? 2 e f f . mol.-: volume, A' 133.44 130.75 129.79 129.33 129.25 140.4 136 129 131 NOReOFg not indexed 176 would have a large apparent temperature factor, r e s u l t i n g i n a rapid decrease i n the i n t e n s i t y of d i f f r a c t i o n l i n e s with i n -creasing Bragg angle. There must be some thermal motion of the metal atoms. 127 Our r e s u l t s on NOWF7 d i f f e r - w i t h those of Ogle et a l . , who reported that ONF and WFg gave a 1:1 complex having a low symmetry. Possibly the complex pattern which they report i s for material containing some (NO^WFg; they did not comment on the existence of a 2:1 adduct. However, i f such i s the case, i t i s surpri s i n g they did not detect the cubic pattern of the 1:1 adduct i n th e i r complex photographs. Another possible explana-tion i s that they were examining the products a r i s i n g from the decomposition of N0WF7. Our experience indicates that unless NOWF7 i s handled under s t r i c t l y anhydrous conditions, i t de-composes r e a d i l y . The decomposition product gives a complex powder photograph. The X-ray powder photographs of NOReOF^ and NOOsOFg indicated that the s a l t s were isomorphous and they were both successfully indexed on the basis of tetragonal unit c e l l s . (NOReOF5, a = 5.083ft, c = 10.0Qft, NOOsOF5, a = 5.025A, c = 10.37ft). The approximate doubling of the c e l l edge c indicates that the atoms which dominate the scattering - the metal atoms -are displaced ( r e l a t i v e to the positions of the corresponding atoms i n a cubic NOMFg s a l t ) along the c axis. Presumably the MOFg" anions are arranged with t h e i r f o u r - f o l d axes along the fo u r - f o l d ( i . e . , d i r e c t i o n of c) axis of the tetragonal unit c e l l , and the doubling of the c e l l edge c i s a consequence of the 177 way i n which the F-M-0 groups are aligned. A possible arrange-ment i s i l l u s t r a t e d i n figure 19. For NOReOFg, the c e l l edge c i s s l i g h t l y less than | a, as would be expected for an arrangement as shown i n figure 19. The TT-bonding of the oxygen ligand w i l l make the M-0 bond shorter than the M-F bond, thus decreasing the a x i a l r a t i o below two. (The e f f e c t of the shorter M-0 bond on the a x i a l r a t i o ; w i l l be offs e t somewhat, however, by the larger Van der Waals radius of oxygen compared to fluorine.) The a x i a l r a t i o of s l i g h t l y greater than two for NOOsOFg may indicate a d i f f e r e n t arrangement of M0F5~ groups, but i t seems probable that i t i s due to a s l i g h t lengthening of the Os-O bond ( r e l a t i v e to Re-O), because of the adverse e f f e c t of the nonbonding t 2 g electron of osmium on TT-bonding by the oxygen ligand. 3.3.2 The Variation i n Anion Sizes i n Salts NOMOYFy The e f f e c t i v e molecular volume of a formula unit i n a c r y s t a l i s defined as the unit c e l l volume divided by the number of formula units i n the c e l l . In an i s o s t r u c t u r a l s e r i e s of compounds, the changes i n e f f e c t i v e molecular volumes can be taken to indicate corresponding changes i n the r e l a t i v e sizes of the ions or molecules of which the formula unit i s composed. This i s so because i n an i s o s t r u c t u r a l series the packing of the ions (molecules) i s the same for each compound, and the forces acting between ions (molecules) w i l l be constant across the s e r i e s . Thus, since the s a l t s of a given s t r u c t u r a l formula NOMOxF are i s o s t r u c t u r a l , the va r i a t i o n i n e f f e c t i v e molecular 178 Figure 19. Possible Unit C e l l of NOMOF 179 volumes with change of M can be attributed to a change i n the r e l a t i v e s i z e of the complex ions; the environment of the MOxFv~ ion i s the same for each ion i n the i s o s t r u c t u r a l series. The data i n table 27 shows c l e a r l y that the size of an ion MOxFy~ decreases st e a d i l y from l e f t to right of the periodic . 142 143 table, following, then, the trend set by the hexafluorides. 5 A plot of e f f e c t i v e molecular volume versus M i l l u s t r a t e s the changes graphically; (figure 20) the MFg~ series, s,ince i t i s complete but for WFg" shows the trend p a r t i c u l a r l y well. The molecular volume decreases slowly aft e r OsFg , an ind i c a t i o n that a l i m i t i n g size i s being reached. The volumes of NOOsOF^ and NOReOFg, however, are i n reverse order from that expected on the basis of the other trends. As mentioned i n section 3.3.1, the c/a r a t i o of NOOsOFg was, unexpectedly for the arrangement envisioned, greater than two. Perhaps the difference i s due to packing factors, but possibly the difference r e f l e c t s a lengthening of the Os-0 bond from the Re-0 bond length. ff-bonding may be less important for Os-0 than Re-0 because of the presence of a nonbonding t g g electron i n osmium(VII). The decrease i n anion si z e can be ascribed to the increase i n p o l a r i z i n g power of the central atom with increasing atomic number. Because of the poor screening properties of i electrons i n t 2 g o r b i t a l s , the e f f e c t i v e nuclear charge of the central atom increases from tungsten to platinum. Hence the at t r a c t i o n of the central metal for the surrounding electron density ( p o l a r i z i n g power) increases, and the electrons become 180 Table 27 o3 Ef f e c t i v e Molecular Volumes, NOMFx and MFg, A species Ta W Re Os Ir Pt MF ~ 133.44 130.75 129.79 129.33 129.25 6 MF?~ 140.4 136 MOF5~ 129 131 MF g,cubic 123.9 122.7 122.1 120.9 119.8 MF c,ortho. 108.5 106.6 1Q5.7 105/4 104.6 6 References: MFg, 142, 143; others, see table 26. Figure 20. Plots of E f f e c t i v e Molecular Volume vs M 181 more concentrated i n the region of space about the central atom. As a r e s u l t , the r e l a t i v e size of the ions decreases across the s e r i e s . Discretion must be exercised i n comparing e f f e c t i v e molecular volumes between s a l t s of d i f f e r e n t s t r u c t u r a l formula, since i s o s t r u c t u r a l s a l t s are not being compared. Thus the data i n table 27 does not imply that the difference i n size between OsF 7~ (disordered i n i t s s a l t , NOOsFy) and OsFg" (ordered i n i t s 03 s a l t , NOOsFg) i s 6 A . Indeed, since disorder generally causes an increase i n e f f e c t i v e molecular volume, (Compare, for example, the volumes of the low temperature ordered orthorhombic modifica-tions of the hexafluorides with room temperature disordered cubic modifications.) the difference i n r e l a t i v e sizes of OsF 7~ and o3 OsFg" i s probably considerably less than 6 A . The two ions may be nearly i d e n t i c a l i n s i z e . A small or no s i z e difference be-tween OsFg" and OsF 7" would be consistent with the small d i f f e r -ed 123 ence i n the sizes of ReFg ana" ReF 7 implied by the i d e n t i t y i n cubic unit c e l l sizes of the two compounds. S i m i l a r l y , almost 144 no difference i n unit c e l l sizes has been reported for the apparently isomprphous s a l t s KgUFg, K3UF7, KgUFg. Perhaps the addition of a seventh ligand to a hexacoordinate species merely d i s t o r t s the coordination s h e l l without expanding i t greatly, that i s , without increasing the radius of the sphere required to include a l l the coordinated ligands. S i g n i f i c a n t l y , the difference i n e f f e c t i v e molecular volumes of N00sF7 and OsFg (cubic) i s considerably less than 198^, the volume1^** usually assigned to a f l u o r i n e atom i n a 182 fl u o r i n e atom i n a f l u o r i d e structure. This seems to preclude the very u n l i k e l y p o s s i b i l i t y that N00sF 7 i s composed of N0+, OsFg, and F~ species. 3.4 A RATIONALE OF THE VARIATION IN NOMO F PROPERTIES — — — — . • A —y— The trends i n properties of the hexafluorides and related species, and th e i r s a l t s , can be reasonably r a t i o n a l i z e d and correlated. The v a r i a t i o n i n p o l a r i z i n g power of the central metal, and i t s e f f e c t on the bonding i n the hexafluorides and related species i s an important feature i n the r a t i o n a l i z a t i o n . The p o l a r i z i n g power of an atom i n a molecule can be defined as the a b i l i t y of the atom to a t t r a c t , i n p a r t i c u l a r , the bonding electron pairs i n the bonds which i t forms to other atoms i n the molecule. Q u a l i t a t i v e l y , the p o l a r i z i n g power of an atom i s measured by the e f f e c t i v e nuclear charge. This i s the actual 14fi nuclear charge less a screening constant which i s the amount by which the actual nuclear charge i s reduced because of the negative charge of the electron cloud surrounding the nucleus. 3.4.1 Bonding i n the Metal Hexafluorides Figure 21 represents the electron density about one — M-F bond i n a hexaf luoride. The general nature of the electron d i s t r i b u t i o n i s indicated i n the diagram. There i s an electron pair i n the region between the metal and f l u o r i n e nuclei and the nonbonding valence electrons of the f l u o r i n e atom extend out i n space away from the metal-fluorine nucleus bond axis. (These 183 Figure 21. Bonding i n a Metal Hexafluoride 184 valence electrons can be used i n IT -bonding with the central metal tgg o r b i t a l s . ) Any nonbonding electrons on the central metal are i n t 2 g o r b i t a l s . The cross-hatched spheres represent the core electrons of the f l u o r i n e and metal respectively and, for the purposes of the q u a l i t a t i v e picture being drawn here, can be considered to be spherical d i s t r i b u t i o n s centred at the f l u o r i n e and metal nuclei respecitvely. Thus, the f l u o r i n e nucleus and core electrons can be represented by a point charge of +7, and the metal nucleus plus core by a point charge of +6 (tungsten) to +10 (platinum). That i s , the s l i g h t p o l a r i z a t i o n e f f e c t s which w i l l a r i s e because of the fact that the core electrons are not i n a centrosymmetric f i e l d are ignored. The bonding electrons and the f l u o r i n e nucleus-core w i l l be screened from the metal nucleus-core by the nonbonding t 2 g electrons of the metal atom. Hence the e f f e c t i v e nuclear charge of the central metal nucleus-core w i l l be Z c - A > where ZQ i s the core charge (six, i n tungsten —> ten, i n platinum) and A i s the screening constant for the t 2 g electrons. Since the electron density of an electron i n a t 2 g o r b i t a l l i e s p r i n c i p a l l y i n regions of space between the ligand-central atom bond axes, (figure 22) t 2 g electrons w i l l be p a r t i c u l a r l y poorly screening \ for electron density on the bond axes. As a r e s u l t , the e f f e c t -ive nuclear charge w i l l increase i n moving from the hexafluoride of one metal to that of the metal with nuclear charge one greater, because the increase i n core charge (ZQ) by one unit w i l l not be completely cancelled by the i n s e r t i o n of an electron I 185 into a t 2 g o r b i t a l . An increase i n p o l a r i z i n g power from tungsten (VI) to platinum(VI) i s therefore expected. TT-bonding can occur i n the hexafluorides by donation of the nonbonding electrons of the f l u o r i n e ligands into the metal o r b i t a l s of TT-symmetry; that i s , the metal t 2 g o r b i t a l s . The donation of an electron pair into the tgg o r b i t a l s w i l l be i n h i b i t e d by the presence of noabonding metal electrons i n the t 2 g o r b i t a l s and the tendency for donation w i l l decrease from WFg to ReFg to OsFg. Since IrFg and PtFg have half or more than h a l f - f i l l e d t 2 g s h e l l s , -jr-donation from the f l u o r i n e ligands cannot occur without pair i n g of the metal electrons i n the t 2 g o r b i t a l s . ( t o avoid v i o l a t i o n of the Pauli p r i n c i p l e ) , Hence no TT-bonding i s expected i n I r F e and PtF~, and the trend i s b b WFg ReFg OsFg IrFg, PtFg y, decreasing TT-donation no |f -donation by F ligands 3.4.4 Q u a l i t a t i v e R a t i o n a l i z a t i o n of the Trends The trends which have been observed hitherto i n the hexafluorides and t h e i r s a l t s can a l l be r a t i o n a l i z e d i n terms of the concepts developed i n the previous section.- ' . ; . ' i ^ t , i • . The increase i n the ox i d i z i n g power of the hexafluoride from WFg to PtFg and the decrease i n anion sizes i n a series of i s o s t r u c t u r a l s a l t s are both a r e s u l t of the increasing tendency' for the central metal to; acquire negative charge. Thus the i n -creasing p o l a r i z i n g power of the central metal not only causes a decrease i n the size of the hexafluorides and related anions, i t also increases the exothermicity of any reaction i n which the 186 hexafluoride gains electrons , ( i . e . , acts as an oxidizing agent) However, the apparent d r i f t of electron density towards the central atom i s not matched, i n the hexafluorides, by a bond length decrease, electron d i f f r a c t i o n s t u d i e s 7 8 i n d i c a t i n g that the bond lengths remain e s s e n t i a l l y constant. The tendency for the ligand nuclei to move closer to the metal nucleus as the electron density s h i f t s i n that d i r e c t i o n i s presumably offset by the increased repulsion between the f l u o r i n e nucleus-core and central atom nucleus-core with the increase i n e f f e c t i v e nuclear change of the l a t t e r . The decrease i n frequencies 1*^ i n the hexafluorides from WFg to PtFg, and the s i m i l a r decrease from ReOFg to OsOFg established i n our laboratories - (chapter III) i s consistent with a d r i f t of electron density towards the central atom which i s not accompanied by a decrease i n bond length. The electron density i s s h i f t i n g away from the f l u o r i n e ligands and hence the f l u o r i n e nucleus-electron density a t t r a c t i v e force i s decreasing. Also, the ligand-ligand repulsive forces increase as the electron density about the ligands becomes concentrated i n a smaller region of space. The decrease i n TT-bonding i s also expected to r e s u l t i n a decrease i n the v i b r a t i o n frequency. 187 3.5 VARIATION IN THE COORDINATION NUMBERS OF THE COMPLEX IONS An examination of the compounds formed as a resul t of the NO and ONF reactions reveals a trend which can be interpreted by a v a r i a t i o n i n the tendency of the neutral compound to pick up a f l u o r i d e ion and form an ion of higher coordination number. The compounds is o l a t e d are shown i n table 28. 3.5.1 The MF7~ and MF R~ 2 Anions The general trend i s seen to be a decreasing tendency to form higher coordinate species from l e f t to right i n the t h i r d -2 t r a n s i t i o n s e r i e s . WFg and ReFg both formed octacoordinate MFg species, while OsFg formed an e a s i l y reduced OsF 7~ ion and IrFg and PtFg gave no stable MF7~ ion at a l l . NOOsFy i s the f i r s t s a l t prepared i n which osmium shows seven coordination i n a complex ion. There are apparently two opposing tendencies at work in the formation of hepta- and octa-coordinate species. The increasing p o l a r i z i n g power or electron a f f i n i t y of the central metal from tungsten to platinum makes the a c q u i s i t i o n of a f u l l y charged negative species, such as a fl u o r i d e ion, a more favour-able process. On the other hand, the decreasing size of the hexafluorides from l e f t to ri g h t makes the addition of a seventh or eighth ligand increasing unfavourable due to increasing s t e r i c crowding. There seems to be l i t t l e reason to doubt the existence of higher coordinate complex ions i n the s a l t s i s o l a t e d . The available ex-perimental evidence on e f f e c t i v e molecular volumes i s consistent with such a formulation (section 3.3.2) and the available l i t e r a -ture evidence indicates that seven and eight coordinate flu o r o -complex ions occur commonly. 188 Table 28 Higher -Coordinate Anions of the Third Transition Series Metals NO and ONF Reaction Products NO ONF WFg no reaction N0WF7;(NO)2WFg ReF g NOReFg (NO) 2ReF g ReOFg NOReOFg NOReOFg ReF 7 NOReFg + (NO) 2ReF g not characterized OsFg NOOsOFg (NOOsFg?); N00sF 7 OsOFg NOOsOFg not characterized IrFg . NOIrFg; (NO) 2IrF g NOIrFg + F 2 + ONFg PtFg NOPtFg; (NO) 2PtFg NOPtFg + F 2 + ONF3, trace Anions of +6 and +7 metals coord, no. WFg R e F 6 0 s F 6 I r F 6 P t F 6 6 - ReFg" OsFg" I r F 6 " p t F 6 ~ 7 WF7" - OsF 7~ 8 WFg - 2 ReFg - 2 -ReOFg 0 s 0 F 5 6 ReOF ~ OsOF^" o 5 7 ReOF~ 189 On the available evidence, s t e r i c crowding becomes the dominating factor with osmium, causing a seven coordinate anion, e a s i l y reduced, to be the highest coordinate species attainable. Iridium and platinum did not even form a stable seven coordinate anion. With tungsten and rhenium, there i s apparently a closer balance of the two competing influences, with the increased electron a f f i n i t y of rhenium r e l a t i v e to tungsten being more important than the increased s t e r i c crowding. ReFg forms only -2 - -2 ReFg , while WFg, i n contrastjforms both WFy and WFg , the heptacoordinate species apparently being somewhat favoured. (NOWFy could be formed without traces of (NO)2WFg; (NO)2WFg always contained NOWFy, even with ONF:WFg mole r a t i o s i n excess of 2:1.) Further evidence for the tendency of rhenium to adopt eight coordination i n preference to seven coordination came from the reaction of NO with ReFy. The reaction apparently proceeded according to 1 NO + ReFy NOReFy NOReFy »-(NO)2ReFg (white) + ReFg 3 NO + ReFg >-NOReFg (yellow) (steps 2 and 3 more rapid than 1) giving the observed o v e r a l l reaction 3N0 + 3ReF 7 — ( N O ) 2 R e F g + NOReFg + ReFy (excess). The seven coordinate species NOReFy, which might be expected to form i n i t i a l l y i n the reaction, was not i s o l a t e d . Only (NO)2ReFg and NOReFg were seen. The l a t t e r compound seemingly 190 precipitated from the gas phase, perhaps from ReFg liberated from an N0ReF7 intermediate. 3.5.2 The Reactions of ReOFg, OsOFg and ReF 7 with ONF The reaction of ONF with the oxide pentafluorides i s consistent with what would be expected on the basis of the d i s -cussion of section 3.5.1. ReOFg reacted r e a d i l y with ONF to form NOReOFg, but OsOFg reacted only very slowly. Probably the difference i n reaction rates i s a consequence of the d i f f i c u l t y of forming a seven coordinate species with OsOFg, which one might expect as the i n i t i a l intermediate i n any reaction and consequent-ly the a c t i v a t i o n energy for reaction i s high, and the reaction rate i s slow. The experiments i n t h i s work did not y i e l d quanti-t i e s of reaction product s u f f i c i e n t for X-ray studies or other characterization, so nothing can be said about the nature of the products forming i n the slow reaction which did occur. S i m i l a r l y , the nature of the reaction of ONF with ReF 7 i s s t i l l not s a t i s f a c t o r i l y resolved. Observations indicate that some reaction product (unidentified, since stoichiometries are not interpretable i n terms of any one compound) formed i n i t i a l l y which decomposed on pumping to (NO^ReFg. The i n i t i a l reaction products gave a very complex X-ray pattern which did not seem to include any l i n e s of (NO) 2ReFg. The f a i l u r e to e s t a b l i s h the existence of an eight coordinate anion of rhenium(VII) analogous to the eight coordinate anion of rhenium(VI) i s consistent with the greater s t e r i c crowding expected for the rhenium(VII) species. 191 3.5.3 The Reaction of IrF- and P t F c with ONF. Comments on b b Mechanism IrFg and PtFg showed no tendency to form stable MFy anions and, as discussed i n section 3.2, behaved as oxidizing agents towards ONF, l i b e r a t i n g F 2 or ONF3. However, i n the context of the present discussion, the mechanism suggested i n section 3.2 for the oxidation can be examined further. Presumably the f l u o r i n e atoms which arose during these reactions came from an intermediate involving the association of the hexafluoride with the ONF: ONF•MFg. A reasonable suggestion i s that t h i s intermediate involves a seven coordinate metal, which decomposes more or less r a p i d l y : ONF-MFg NOMF? *- F- + NOMFg. Spontaneous decomposition of such an intermediate would be consistent with the behaviour expected by extrapolation of the -2 -properties of the rhenium (forms ReFg ) and osmium (forms OsF 7 , easily"reduced) compounds. One would expect, i n view of the trend of s t a b i l i t i e s of higher coordinate species, that the intermediate would be more unstable^f oiu:M = Pt than Ir. F r a d i c a l s would thus be re-leased at a more controlled rate with M = Ir and there would be a greater opportunity for species such as ONFg to form. (The experimental observation was that the ONF + IrFg reaction could give large amounts of ONFg; the ONF + PtFg reaction gave only traces.) Presumably i n the ONF + PtFg reaction the decomposition of the intermediate i s nearly instantaneous and the F r a d i c a l s combine with each other, giving F_. 192 The observation that OsOFg reacted slowly with ONF i s important to the present discussion. This slow reaction was interpreted i n terms of the d i f f i c u l t y with which OsOFg forms a seven coordinate anion. If t h i s i s so,, sim i l a r , indeed greater, d i f f i c u l t y would be expected i n the formation of I r F 7 ~ and PtF 7~, on the basis of the l e f t - t o - r i g h t trends. However the ONF + (IrFg/PtFg) reactions: proceeded very: r a p i d l y P o s s i b l y , then, there i s only a tendency to seven coordination i n the ONF -(IrFg/PtFg) intermediate i n the reaction, with the ON-F bond weakening as the f l u o r i n e ligand i s drawn into the coordination s h e l l . The increased electron a f f i n i t y of IrF_ and P t F e r e l a t i v e 6 6 to OsOFg i s presumably the dr i v i n g force behind t h i s abstraction, while the s t e r i c crowding as t h i s seventh ligand enter*., the coordination s h e l l leads to i t s ejection, minus the electron pair which was involved i n the bond which i t had formed (or was forming) with the e l e c t r o p h i l i c iridium or platinum. 193 147 CHAPTER VI THE PREPARATION AND CHARACTERIZATION OF NO +PtFg~ THE MAGNETIC SUSCEPTIBILITY OF 0 2 +. I EXPERIMENTAL 1.1 THE PREPARATION OF THE SALTS. X-RAY POWDER PHOTOGRAPHS 9 Previous work i n t h i s laboratory had shown that the reaction between NO and PtFg was an unsatisfactory method for the preparation of NOPtFg, the reaction product being contamin-ated with (N0) 2PtFg. However, i n the present investigation, pure NOPtFg was prepared by the reaction of ONF with PtFg: ONF + PtFg >- NOPtFg + J F 2 (+ONF3, trace) In two separate experiments, PtFg ( «vl gm) and ONF (an amount estimated to be s l i g h t l y i n excess of that needed for the above reaction) were condensed into a monel metal reactor, which was then warmed to ^ 30°C and held at that temperature for several minutes to allow for complete reaction. After removal of materials v o l a t i l e at room temperature, the reactor was taken to the drybox for subsequent operations with the s o l i d product. (A d e t a i l e d description of a t h i r d ONF and PtFg reaction, i n an experiment designed to prove that f l u o r i n e was a reaction product, was described i n chapter V.) The v o l a t i l e reaction species were fl u o r i n e , i d e n t i f i e d by i t s v o l a t i l i t y at -196°C and i t s orange gas discharge, and, i n one experiment, a s l i g h t amount of un-reacted PtF~ , i n the second, a l i t t l e ONF, both i d e n t i f i e d by the i r infrared spectra. The s o l i d product from both experiments was a canary-yellow powder. A n a l y t i c a l r e s u l t s from both products 194 supported the formulation NOPtFg (table 29). OgPtFg was prepared by the reaction of oxygen with PtFg.' PtFg (1.8 gm) was condensed into a monel reactor of 400 cc capacity and the reactor was allowed to warm to room temperature. Oxygen (pressure, «^  latm.) was dried by passing through a U-tube cooled i n l i q u i d nitrogen and was then admitted to the reactor. The reactor was warmed for several minutes with a water bath at ^ 40-50°C to ensure complete reaction. Previous experience with t h i s reaction had indicated that a crust of OgPtFg formed on the PtFg and protected the PtFg underneath from attack by the oxygen. Using a reactor of f a i r l y large volume and warming the reactor helped overcome t h i s d i f f i c u l t y , by ensuring that a good portion of the PtF (<v.6 gm) was i n the vapour phase before the reaction, b and by increasing the vapour pressure of any unreacted PtFg which might have been trapped beneath a layer of the s o l i d pro-duct. After removal of the excess of oxygen, the reactor was pumped at room temperature for half an hour, to remove any traces Table 29 A n a l y t i c a l Results for NOPtFg element %,preparation 1 %,preparation 2 t h e o r e t i c a l , NOPtFg N - 3.73 a 4.13 Pt 56.3 57.3 a 57.5 F 3 2 . 4 a 32.5 a 33.6 A n a l y t i c a l Method: (a) Dumas, Schwarzkopff Microanalytical Laboratory; (b) thermal decomposition i n Pt c r u c i b l e + Hg reduction; (c) pyrohydrolysis i n steam + Hg reduction. 195 of unreacted PtFg. The X-ray photographs of the orange-red product were i d e n t i c a l with t h o s e 3 3 ' 3 4 of-0 2PtFg (cubic). No other l i n e s were seen i n the photograph. The sample from t h i s preparation was used i n magnetic s u s c e p t i b i l i t y studies. NOPtFg gave an X-ray pattern which was indexed on the basis of cubic symmetry, with a Q = 10.112 ± .002$. The powder data for NOPtFg i s given'in table 23, with that of isomorphous NOReFg. In addition to the l i n e s due to cubic NOPtFg, a few \ 9 weak l i n e s of the rhombohedral modification of NOPtFg were observed. A sample of NOPtFg, sealed i n an aluminum container f i l l e d with a screw cap and Teflon gasket, was sent to Brookhaven National Laboratory, Upton, N.Y., for neutron d i f f r a c t i o n spect-roscopy . 1.2 THE l INFRARED .: SPECTRUM OF N0PtF f i Two techniques were employed to obtain the infrared spectrum of s o l i d NOPtFg. One method involved the preparation of NOPtFg i n s i t u i n the i n f r a r e d c e l l . PtFg i n the infrared c e l l cavity was allowed to react with excess ONF which was admitted to the c e l l from the vacuum l i n e . The NOPtFg formed as a f i n e yellow powder from the gas phase reaction, s e t t l i n g on the windows and the body of the c e l l cavity. The infrared spectrum of the s o l i d deposit was obtained i n both the NaCl and KBr regions - see figure 23. No peak was detected i n the 'NO stretching region. The infrared 196 800 Absorbance (b) 700 635 600 Frequency 578 500 (a) V....--(a) NOPtFg i n fluorolube mull (b) ^  as (a), aft e r standing 6 hours 400 cm -1 800 700 600 Frequency 500 400 cm -1 Figure 23. Infrared Spectrum of NO PtFg 197 c e l l was disassembled i n the drybox and X-ray c a p i l l a r i e s were f i l l e d with material scraped from the body and windows of the c e l l . The X-ray powder photograph was i d e n t i c a l with that of rhombohedral NOPtFg, except for one weak l i n e at low angle, .possibly due to a small amount of NOgPtFg impurity and the much weaker pattern due to cubic NOPtFg. In experiments designed to check the r e s u l t s of other 133 workers , infrared spectra of NOPtFg were also obtained by running the s o l i d i n a mull, the NOPtFg (cubic) having been prepared i n bulk quantity previously, by the reaction of ONF with PtFg. Mulls with fluorolube (Hooker Chemical Corporation) as a mulling agent were prepared by adding one or two drops of fluorolube^to a small sample of f i n e l y powdered NOPtFg, followed by grinding to form a fin e paste, which was then squeezed between two s i l v e r chloride plates. The plates were sealed around the edge with e l e c t r i c a l tape and the spectrum scanned immediately afterward. The mull was then l e f t standing for 5-6 hours and the spectrum rescanned. See figure 23. Satisfactory spectra of the dry powder pressed between s i l v e r chloride plates were not obtained, presumably because the bulk of the" dry powder merely scattered the impinging infrared beam. 198 1.3 MAGNETIC SUSCEPTIBILITY STUDIES GN NOPtFg AND C^PtFg Magnetic s u s c e p t i b i l i t y data were obtained for NOPtFg and for OgPtFg using the apparatus and technique described i n the general experimental section. The samples were contained in pyrex sample tubes of 3 mm 0„D„ and magnetic measurements on the samples were made within 24 hours aft e r sealing the sample tubes. Duplicate readings of the weight changes at each tempera-ture were obtained and the s u s c e p t i b i l i t i e s were calculated separately for each reading. The molar s u s c e p t i b i l i t i e s c a l c u l a -ted (Xjj(obsvd.)) from the measured weight changes and the temperatures of measurement for NOPtFg and OgPtFg are given i n table 30. A diamagnetic correction"^ 4** of +10 x 10 ^ cgs for the N0 + cation has been applied to the "X jj(obsvd.) values for NOPtFg i n t h i s table. II RESULTS x'< i Analysis of the S u s c e p t i b i l i t y Data. Plots of 1/?^^(obsvd.) versus T were made for both OgPtFg and NOPtFg. A least squares program, provided by the X-ray Crystallography Group of U.B.C. and modified s l i g h t l y to accept our data, was used to obtain the best straight l i n e through the plotted points (figure 24). The s u s c e p t i b i l i t i e s obtained from these straight l i n e s (XJJ (ideal)) are given i n table 30 for comparison with the values of ^^(obsvd.). Both sets of data showed a Curie-Weiss behaviour over the temperature range 80-300°K. The Weiss constant for both o NOPtFg and OgPtFg was +32 . Here, the sign of the Weiss constant 199 I i 1 1 — J « « 1 0 100 200 300 K 0 100 200 300 Figure 24 1 / % M v s T Plots, N0 +PtF g~ and 0 2 + P t F 6 ~ 1..80r 1.40 1 1 1 1 0 100 200 300 °K Figure 25 JXeff v s T f o r NO^PtF, 200 Table 30 S u s c e p t i b i l i t i e s for NOPtFg and 0 2PtFg from 77°K to 300°K 0 2PtFg temp. M(obsvd) M ( i d e a l ) °K~ cgs x 10~ b cgs x 10" 77 . 1 3650,3630 3460 86 .0 3350,3280 3200 99 .7 2850,3000 2870 120 .9 2470,2440 2470 138 .4 2210,2210 2220 154 .4 1970,1980 2030 173 .7 1830,1780 1840 192 .0 1680,1670 1690 210 .8 1550,1530 1560 227 . 1 1410 1460 245 .3 1360,1350 1360 261 .6 1300,1280 1290 273 .2 1250,1230 1240 282 .7 1210,1200 1200 292 .8 1170,1180 1160 303 .0 1080,1160 1130 temp. jj(obsvd) jj(ideal) °K cgs x 10~ 6 cgs x 10" 77 . 1 7150 6650 87 .3 6070 6080 102 .4 5190 5400 106 .2 5220,5300 5250 123 .3 4620 4670 140 .4 4160,4160 4210 157 .7 3790,3890 3820 174 .6 3490,3480 3510 191 .9 3210,3220 3240 210 .9 3080,3000 2980 230 .3 2760,2740 2760 249 .9 2580,2570 2570 267 .0 2450,2440 2420 284 .4 2300,2270 2290 303 .2 2110,2110 2160 304 .7 2170,2190 2150 201 i s for the r e l a t i o n c/(T + 9), where 0 i s the Weiss constant. The magnetic moments calculated from the r e l a t i o n JJ<'eii = 2.84[X M(T + 0 ) ] ^ are 1.79 B.M. for the PtF 6 ~ ion and 2.41 B.M. for OgPtFg. The s u s c e p t i b i l i t y values taken from a smooth curve drawn through a X M ( ° b s v d * ) v s t P l o t f o r NOPtFg ( X M ( P t F g ~ ) , table 31) were corrected for the diamagnetism of the flu o r i n e 148 fi ligands by adding +40 x 10 cgs to each XJJ and were used to calculate e f f e c t i v e magnetic moments over a temperature l range according t o J U e f f = C X ^ T ) 2 . The e f f e c t i v e moments were plotted as a function of temperature (figure 25). The magnetic data for 02PtFg and NOPtFg can be used to estimate, at least approximately, the magnetic s u s c e p t i b i l i t y of the 0 2 + cation i n 0 2PtFg. NOPtFg, and 0 2PtFg are i s o s t r u c t u r a l and have nearly the same unit c e l l s i z e . Also, the Curie-Weiss behaviour shown by both s a l t s and the small value of the Weiss constant indicates absence of any appreciable i n t e r a c t i o n between the magnetic centers. Consequently, the s u s c e p t i b i l i t y of the PtFg" anion should be the same i n both s a l t s . For 0 2 P t F 6 : X M(0 2PtFg) = %M(02+) - X ^ P t F g " ) and X M ( P t F 6 ~ ) - X M(NOPtFg), with % M(N0PtFg) corrected for the diamagnetism of the N0 + cation. Hence: X M ( 0 2 + ) = X M « > 2 p t F 6 > " X M(N0PtFg). *X^(obsvd.) vs T plots were made for each s a l t , using the Xjj(obsvd.) values of table 30. (Note that the XjjCobsvd.) 202 values for NOPtFg include a correction for the diamagnetism of N0+.) Smooth curves were drawn through the two sets of plotted data and values of X M ( 0 2 P t F 6 ) and X M(NOPtFg) were obtained from these curves at temperature i n t e r v a l s of 30°K over the range 80-300°K. The difference between the two values was taken as XM(° 2 +) (table 31). The 0 2 + cation obeyed the Curie-Weiss law ) over the temperature range 80-300°K, the Weiss constant .being 38° (least squares a n a l y s i s ) . The magnetic moment calculated according to the r e l a t i o n j u ' e f f = (*% MCT + Ql)% i s 1.66 B.M. Values of the e f f e c t i v e magentic moment ( %. JJT) are also given i n table 31, calculated at temperature i n t e r v a l s of 40" over the range 100-300 K. E f f e c t i v e moments for NO are presented for comparison. Table 31 Molar S u s c e p t i b i l i t y Data for 0 2PtFg, NOPtFg and 0 2 + Temp.,°K % M , cgs x 10" units jXett 0 2 P t F g PtFg" 0 2 + 0 2 + N0n 80 6490 3590 2900 1.36 100 5500 2900 2600 1.42 140 4150 2160 1990 1.50 1.64 180 3400 1740 1660 1.55 1.71 220 2860 1470 1390 1.57 1.77 260 -2490 1290 1200 1.58 1.82 300 2170 1140 1030 1.57 1.86 203 III DISCUSSION 3.1 THE NOPtFg STRUCTURE. RELATIVE VOLUMES OF N0 + AND 0 2 + The s i m i l a r i t y of the pattern of i n t e n s i t i e s i n the powder photograph of NOPtFg (cubic) to that i n the photograph 3 4' 3** of 0 2PtFg indicates that the two s a l t s are i s o s t r u c t u r a l . Thus NOPtFg probably consists of a face-centred array of N0 + and PtFg" ions s i m i l a r to the arrangement of the corresponding ions i n 02PtFg. The space group i s Ia3 and a d i s t o r t i o n of the PtFg anion of NOPtFg along a 3 axis i s p o s s i b l e t h e anion may not be p e r f e c t l y octahedral. The arrangement of the NO+ cation i s probably the same as the disordered arrangement of 0 2 + used to best explain v the neutron d i f f r a c t i o n data of 0 2PtFg. Results from the neutron d i f f r a c t i o n study of NOPtFg are not yet available. Interestingly, the gas-gas reaction of ONF and PtFg gave the rhombohedral modification of NOPtFg as the major phase, while a l l the solid-gas reactions gave the aforementioned cubic modification of NOPtFg, with l i t t l e or none of the rhombohedral form (to l i m i t s of detection of X-ray method, <10%). Similar 9 behaviour was noted by Jha i n the reaction of NO with PtFg. The gas-gas reaction gave NOPtFg (rhomb.); the solid-gas reaction NOPtFg (cubic),(Both reactions gave, i n addition, (NO)2PtFg-)) There seems to be no obvious reason for the difference, * The neutron d i f f r a c t i o n data could not >-J unambiguously decide . between ordered and disordered 0 2 4. The disordered model was chosen because i t gave a more reasonable 0 2 + bond length. 204 Table 32 compares the e f f e c t i v e molecular volumes of NOPtFg and 0 2PtFg. Table 32 E f f e c t i v e Molecular Volumes of NOPtFg and 0 2PtFg cubic c e l l edge Z e f f e c t i v e molecular volume NOPtFg 10.112 ft 8 129.25ft 3 o o3 0 2PtFg 10.032 A 8 126.25 A The difference i n e f f e c t i v e molecular volumes can be taken as the difference i n r e l a t i v e sizes of the two cations, since i s o s t r u c t u r a l s a l t s are being compared. Thus 0 2 + i s about 3ft 3 smaller than N0 +. Apparently the increase i n size expected upon the addition of an antibonding electron (N0+—> 0g +) i s more than o f f s e t by the size decrease expected on the increase of the nuclear charge of one of the nuclei by one unit (N0 +—>-0 2 +). 150 A s i m i l a r e f f e c t i s seen i n the comparison of s o l i d f l u o r i n e ( ^-form 37.lft 3 ) with i t s s o l i d oxygen isomorph 1 5^ (tf-form 39.8ft 3). 3.2 THE INFRARED SPECTRUM OF NOPtFg. V g FREQUENCY OF P t F g " The in f r a r e d spectrum of NOPtFg obtained by depositing the s o l i d on the windows of the in f r a r e d c e l l showed a peak centred at 632 cm"^ ". This peak i s undoubtedly associated with the V3 v i b r a t i o n of the octahedral or near octahedral PtFg" anion. The frequency agrees well with that for PtFg" i n 205 0 2 P t F 6 3 5 (631 cm - 1) and XeFgPtFg 1 5 1 ( <^  640 cm - 1), and 152 KPtFg . Gortsema and Toeniskoetter u o reported that NOPtFg, N0 2PtFg and NgOsPtFg gave peaks at ~* 570 cm"1, which they assigned to the vibrat i o n of the PtFg" anion. Our experiments with NOPtFg i n a mull suggest that the 570 cm"1 peak i s prob-ably due to PtFg . (Gortsema and Toeniskoetter ran t h e i r spectra as Nujol mulls.) With fluorolube o i l as a mulling agent, spectra:were obtained which gave i n i t i a l l y , a peak centred at ^ 635 cm - 1. However, i n time (5-6 hours), t h i s peak disappeared completely and a broad peak with a maximum 1 = 99 153 centred at ro 570 cm" grew i n . Since PtFg i s known ' to give an absorption at 570 cm - 1, a reasonable explanation of our experiment i s that the PtFg" anion decomposed i n the . mull, probably reacting with traces of moisture i n the fluoro-lube or i n the a i r d i f f u s i n g into the mull, and that the product of decomposition i s the PtFg - anion. Gortsema and Toeniskoetter's reported absorption maxima are l i k e l y that for the same species, not that for PtFg". The \)3 frequency of PtFg" i s i n accord with that expected from a comparison to P t F g - 2 and PtFg(g)(table 33). Table 33 V 3 and V-j_ Frequencies of PtFg~ x PtFg~ x V>3, cm"1 V-p cm"1 PtFg(g) 705 a 655 a PtFg" 632 P t F g - 2 570 b 600 b(aq.sol'n) references: (a) 100; (b) 153. 206 For t h i s series of very similar species, one would reasonably expect thet V ±.frequency of PtFg" to l i e between that to PtFg and PtFg , giving a trend of frequencies s i m i l a r to the observed V 3 trend. The V 1 frequency trend would be P t F g - 2 PtFg" PtFg PtFg" = 635 cm - 1? — . >. increasing V 1 frequency The order of increasing infrared frequency i s the order of increasing p o l a r i z i n g power of the central atom, and i s thus i n a,ccord with the general observation that bonds strengthen ( \) ^  frequencies increase) as the ligands are more strongly attracted to the central atom. However, the trend i n \) 1 frequencies i n t h i s series i s opposite to that observed i n the series WFg —»-PtFg (chapter V) . In terms of the q u a l i t a -t i v e arguments used i n chapter V, i t i s not at all.obvious why the PtFg~ x trend should show normal behaviour; one would expect the p o l a r i z a t i o n e f f e c t s to be as extreme i n PtFg" as i n , say, WFg or ReFg. Perhaps a more rigorous approach to the problem, using molecular o r b i t a l theory, can resolve the apparent dilemma. 207 3.3 THE MAGNETIC MOMENTS OF NQPtFfi AND 0?+ The magnetic moment of NOPtFg i s close to 1.73 B.M. (jj!eff = 1.79 B.M.) and i s c e r t a i n l y consistent with a t 2 g configuration for the platinum atom. The moment i s close to the spin only value, as would be expected for an ion with a large spin o r b i t coupling constant. However, a closer examination of the r e s u l t s indicates that there a deviation from the detailed behaviour predicted 154 by Kotani's theory . The e f f e c t i v e magnetic moment (/Keff) i s only 1.69 B.M. at 300°K and drops to 1.54 B.M. at 100°K. Extrapolation to 0°K (figure 25) gives a moment of ~ 1.45 B.M. Kotani's theory predicts a moment of 1.73 B.M. at 0°K. While i t i s possible that there i s some in t e r a c t i o n between magnetic centres i n NOPtFg, i t seems more probable that the apparent deviation i s a r e s u l t of applying Kotani's theory (developed) for gaseous species) to the s o l i d state without modification. The suggestion that magnetic interactions oocur i n NOPtFg seems d i f f i c u l t to reconcile with the Cuxie=Weiss behaviour exhibited by NOPtFg (Weiss constant only 32°). Furthermore, 0 2PtFg, with both the cation and anion paramagnetic, would be expected to have stronger magnetic interactions than NOPtFg, whereas the experimental evidence (Curie-Weiss behaviour, Weiss constant 32°) indicates that such interactions are not s i g n i f i c a n t . Possibly a d i s t o r t i o n of the anion from 0 h symmetry i s a contributing factor to the deviation from Kotani behaviour.* * However, Ibers and Hamilton have concluded from t h e i r neutron diffraction data that the PtFg - d i s t o r t i o n was not experimentally significant. Their data indicates that 2\. F-Pt-F = 90 ± 0.5°. 208 The magnetic moment of 0 2 + i s compatible with the presence of one unpaired electron. JLk'eff i s 1.66 B.M. The reduction of the e f f e c t i v e magnetic moment ()U^ eff) below the spin-only value of 1.73 B.M. and i t s decrease with decreasing temperature i s compared with that of i s o e l e c t r o n i c 155 NO(g) , i n table 31. The moment of 0 2 + i s less than that of NO(g) at a given temperature, and i t s rate of decrease with temperature i s less than that of NO(g). Spin-orbit coupling w i l l change the magnetic moment of 0 2 + from the spin-only value, as i t does for NO, and the exact eff e c t of the coupling on the moment w i l l be complicated by the expected intermediate si z e of the coupling constant. Like NO 1^, Og can be expected to have a If ground state with spin-orbit coupling s p l i t t i n g t h i s into TT 3/2 and TT^ components, with a }} s p l i t t i n g of the order of kT. For NO(g), Van V l e c k 1 5 7 has derived a formula for the e f f e c t i v e magnetic moment as a function of the temperature and and the doublet s p l i t t i n g for the case where the s p l i t t i n g i s of the order of kT. His formula gave calculated moments agreeing very well with the experimental moments of N0(g).) However this .foriullla does not give calculated moments for 0 2 + which agree with the experimental values, regardless of the choice of doublet s p l i t -t i n g , although the best f i t s are obtained for a s p l i t t i n g greater than that of NO (NO s p l i t t i n g A; 120 cm - 1). This i s probably not * surpris i n g , since Van Vleck's formula was derived for the gas phase, However, the lower moments of 0 2 + compared to those of N0 + can probably be taken as an i n d i c a t i o n that the doublet s p l i t -t i n g i n 0 2 i s greater than that i n NO . j>0 I s C PROGRAM WRITTEN IN FORTRAN IV FOR IBM 7040 1 9 • 8 - C $JOB 15204 S P BEATON S I B F T C INDEXX 1 'o6iO . 11 C _ C CALC. OF 2*THETA»D(HKL)• 1/D*D»NELSON-RILEY FN.7NRFN) C SPACINGS FROM ARC ! | 0 44 C X1»X2=ARC READINGS* FROM FILM MOUNTED ON METER STICK C '*' . . . ^ . ' BN = 0. (SEE CHAP I ) "" - O i CN = 0. ' '- -SCP=0. • ' • SBP=0. > • 0 ' O -C •* C C CALC OF BEAM STOP CENTRE BPA=AV(X1+X2/2) DATA CARD WITH X1=X2=0 SIGNALS END OF DATA UJ !25 O X •: o 1 30 READ(5»30)X1.X2 FORMAT(2F10.3) v -BP=(X1+X2)/2. -M ; o SBP=SBP+BP IF(BP.EQ.O«. )G0 TO 3 " -BN=BN+1» 5U O Q gz ! o 3 GO TO 1 BPA = SBP/BN •' C - S 1— > ° C . C • 4 CALC OF COLLIMATOR CENTRE CPA=AV(X1+X2)/2 DATA CARD WITH X1=X2=0. SIGNALS END OF DATA READ(5 » 30)XI»X2 -f • 0 I CP=(X1+X2)/2. SCP = SCP+CP ""* IFtCP.EQ.O.)G0 TO 5 -1 ! O 5 CN=CN+1. GO TO 4 CPA=SCP/CN - o 75 C , WRITE(6,75) FORMAT(IX,10H XI ,20H 2THETA»20H D o CD -I IHKL *20H , 1/D*D »30H 2/ ) NRFN / / * 2 ll J — c o o o e n O l "*«J C O v O ^ 0 0 0 0 0 ^ Q O •<—e LU _ i z < o cc: < cc U J > o O 1— u < — r-< Q- O CO r -I < o <J- _ l r-1 • en • U J 1-1 11 O o U J Z r _ l < O — O z u_ o < — U J _ l < I II U J _ l o z < 0 3 X I W I 1 N I V U O « _ o r Q: o u Q U J I o < - U J u j cr 3 U J I X < r -> o x o z o c < O h -<NJ < d o o u . < o Q CM z < U J X CL LO < < < ct: up 0 ~ u_ to; X o 1 II l i - r H u u u APPENDIX [, PROGRAM DC U J O z < + < < o u_ o o z U J _ l < Z r H L9 X CO U ) M U -OS — II < r H L U CO U <"H C \ o <t r- r H H O O o o o o ep-os ON O 0> N O r -U J O • • r H <—I X X u. u_ O o o o o 1-1 r-• r-1— • o 11 < Q CO O O r H u. 2: -I < CM r-r-• vO o 11 < Q CD r H  O X II X < 1. m CM o r-o 11 < Q CD < rH  O X II o v 5 O o O CP • Z h -< _ J * • CM CM X < II h -CM U J < X I— h -U J — X U . vO CM < U J X t— r H I CM II CM O < r - r -U J O X CP r -O r H CM CM < < < LU LU X X — I/) CO r H II II < < t - h-U J U J x x U L0 X 10 < 11 11 o _ J t o v z X — LU X f— u < h -LU X t— u + < I— LU X I— L0 U J X I— u * < I— LU X I— © — • z u . cc O L0 CM _ i 1— x U J o X -h - CM * < CO I— CM U J 00 X CM t— m »• vO rH O 00 vO rH CO — II vO CM — < LU r - t -LU X ct: 01 co 1© in 4 18 FORMAT(1X»F10. 3 »10H »F10.3»10H fF10.5.10H 1 9 ' 8 1 70 »F10.6,20H GO TO 13 CALL S K I P TO (1) •F10.3/) i 6 ,H 17 GO TO 44 STOP END - f SENTRY *** -l . o ! - - -> 1 ! ° - • PPEND ! o X M I o • PROG ; o - : o i !:° • -! ° to I o - • i I o J Z . . r S C PROGRAM WRITTEN IN FORTRAN IV FOR IBM 7040 9 LQ 8 c $JOB 15204 S.P.BEATON SIB F T C FACTOR 6 OlQ II C C c CALC OF STRUCTURE FACTOR DATA,CUBIC XTALS FIRST SET OF CARDS...N I , NJ,NK • -z 1 ( I -C C C (1 CARD) ,NI=NO.OF SETS OF EQUIV ATOMS *. - - ' NJ=NO.OF PLANES (HKL) ' • ' • —-- % o -C C C NK=NO.OF POWDER LINES • SECOND SET OF CARDS...OBSI,PLOR,A o C C • C (NK CARDS) OBSI=OBSVD. INTENSITY OF LINE K PLOR=LOR.-POL. FACTOR FOR LINE K TD 51 D l-H o C C C A=ABS• FACTOR FOR LIN E K THIRD SET OF CARDS ... AH,AK,AL,PMULT • o C C C ( N J CARDS) AH,AK,AL=MILLER INDICES FOR PLANE J , PMULT = MUL T* OF PLANES J SO o o o -C . C c FOURTH SET OF CARDS...FA(I,K) " (NI*NK CARDS) s tSJ o c c c F A ( I , K ) = A T . SCATT. FACTOR, ATOM I + LINE K DATA- ORDER..F(1,1),F(2,1)...F(NI,1),F(1,2),F(2,2)... ON CARDS 1 2 NI NI+1 1 o c c c F I F T H SET OF CARDS ... X,Y,Z,RC»CC,AMULT (NI CARDS) -1 o c c c X,Y,Z=COORD OF ATOM I RC,CC=REAL+COMPLEX PARTS OF D I S P . CORR. AMULT=MULT. OF POSITION (XYZ) -to N> o c c c SIXTH SET OF CARDS... I TEST (1 CARD) • t-J o '1 - < c u 11 o i s . c c c , P U N C H I T E S T I N C O L . 1 I T E S T = 1 S I G N A L S E N D O F D A T A + NO S E T F O L L O W I N G I T F S T = 2 S I G N A L S E N D O F D A T A + A N O T H F R S F T F O L L O W I N G , 1 9 < 8 c c c C H A N G E I N S E T 5 V A L U E S O N L Y ( G I V E NEW S E T ) I T E S T =3 S I G N A L S E N D O F D A T A A N D A N O T H E R S E T F O L L O W I N G , C H A N G E I N O T H E R T H A N S E T 5 V A L U E S ( R E P E A T A L L S E T S O F V A L . ) ! 6 11 c C D E F I N I T I O N O F S O M E P R O G R A M S Y M B O L S C A X = M U L T I P L I C I T Y * ( G E 0 M E T R I C F A C T O R ) i ° C. AFAR»AFAC=REAL+COMPLEX P A R T S O F A T . S C A T T . F A C T O R W I T H C • C O R R . A P P L I E D C S F A C R , S F A C C = R E A L + C O M P L E X P T S . O F S T R U C T U R E F A C T O R D I S P -! o i C V A L U E = L O G ( X ) ( S E E T E X T , C H A P T E R I V ) C W R I T E ( 6 » 3 1 ) > 1 0 1 3 1 F O R M A T ( 2 X , 5 H H , K , L , 3 X , 2 3 H S T R U C T . F - R E A L , C O M P . P T S . , 4 X , 1 H N » 4 X , I///) D I M E N S I O N X ( 1 0 ) , Y ( 1 0 ) , 2 ( 1 0 ) , R C ( 1 0 ) , C C ( 1 0 ) , A M U L T ( 1 0 ) 6 H L 0 G ( X ) w a ; o D I M E N S I O N O B S I ( 1 0 0 ) , P L O R ( 1 0 0 ) , A ( 1 0 0 ) D I M E N S I O N A H ( 1 0 0 ) , A K ( 1 0 0 ) , A L ( 1 0 0 ) , P M U L T ( 1 0 0 ) D I M E N S I O N F A ( 1 0 » 1 0 0 ) M X M ! o D I M E N S I O N S F A C R ( 1 0 0 ) , S F A C C ( 1 0 0 ) D I M E N S I O N A X ( 1 0 , 1 0 0 ) , A F A R ( 1 0 , 1 0 0 ) , A F A C ( 1 0 , 1 0 0 ) , A M ( 1 0 0 ) . C o a ; 0 3 5 1 " R E A D ( 5 » l ) N I i N J i N K F O R M A T ( 3 I 1 0 ) . ~~~ " C ' '£ s o 1 1 1 2 D011K=1»NK R E A D ( 5 • 1 2 ) O B S I ( K ) » P L O R ( K ) , A ( K ) F O R M A T ( 3 F 1 0 . 4 ) 0 5 C D 0 5 J = 1 , N J R E A D ( 5 , 8 0 ) A H ( J ) , A K ( J ) , A L ( J ) , P M U L T ( J ) - ' o 8 0 F O R M A T ( 4 F 1 0 . 4 ) C D07K=1»NK to H 1 CO ! ° 6 D 0 7 I = 1 , N I R E A D ( 5 , 6 ) F A ( I » K ) F O R M A T ( F 1 0 . 4 ) | 0 ' j 3 4 D 0 4 I = 1 , N I z < 5 o J r O O O O O O ' O O O O O o r-4 u . cr o CM co < a CL => o cc e) LU U < a to o O Z Z II II *- ~) oo oo O O aai-iwn U I V U D *"I U <T ~> ~) ~) I ^ J < < < I I I - ) - > - ) V _ J X < < < II II II 3 3 3 APPENDIX I, rH CM 3 3 + + X > X < CM (NJ 0 . Q_ • CO CO vO O O II u u CM II | | M H I M r-H CM 2 2 + + X V < < * * CM CM o_ o_ a to to o o u u II II < f c n r-H CM 3 2 + + M X X V < < CM CM a a a. to to o o u u II II r- oo PROGRAM 2 00 + + CO — # — CM CO I— 3 * + r H ~ * * CO < r -* 3 CM 5 : I-. < a. 11 CO ~~> o -u -« 11 — ON x r - < 00 |CM < + CM < + CM •> X Z r H < . II II 1-~ ) — II CO > »— r H ~- O-O 2: C Q < C CO o ON o 2.4 I rH -> CM SI CM < CM I -CM + — >-V Z < II — > l i . V CM u — cr ~> + ->- — N ^ X z < < — — u II II cc u < < U_ L l . < < o II o II cc < to + - 5 cc < LL. < II rH " I II — -> CC o u rH < O Q r H - ) II — o 10 to cr < LL. CM CM t> =1 2 cn eo N to in f M 1 - • *o ' s 10 S F A C C ( J ) = A F A C < I , J ) + S F A C C ( J ) 9 \LQ : 8 C STRFA2=0. NKX = 0 ', 6 . iotO l l D 017J=1,NJ IF(J.EQ»1)GO TO 15 AKT=AM(J)-AM(J-1) ! Z I 15 I F ( A K T ) 2 5 , 1 5 , 2 5 NH= A H ( J ) K=AK(J) ' i i t o 16 L = A L ( J ) WRITE(6»16)NH,K»L»SFACR(J)»SFACC(J) FORMAT(IX,312»3X,2F10. 4) -> ; o / S T R F A 2 = S T R F A 2 + P M U L T ( J ) * ( S F A C R ( J ) * * 2 + S F A C C ( J ) * * 2 ) I F ( J . E Q . N J ) G O TO 45 GO TO 17 - • • X) fa M j 0 25 NKX=NKX+1 AMFAC=OBSI(NKX)/(A(NKX)*PLOR(NKX)) VALUE2=AMFAC/STRFA2 X M - I o VALUE=0.5*ALOG(VALUE2) M=AM(J-1) WRITE(6,19)M,VALUE X> O o o 19 FORMAT(35X,I3,F10.4//) STRFA2=0. ' GO TO 15 !> s to • o 45 NKX=NKX+1 AMFAC=OBSI(NKX)/(A(NKX)*PLOR(NKX)) VALUE2=AMFAC/STRFA2 \ o VALUE=0.5*ALOG(VALUE2) M= AM(J) -WRITE(6,19)M,VALUE to !' i o 17 CONTINUE C R E A D ( 5 , 3 2 ) I T E S T - r o 32 FORMAT(11) I F ( ITEST.EQ.1)GO TO 33 CALL S K I P TO (1) 0 h o WRITE(6,31) < X IU J _ t o c e o •£» O l CD N J CO CD ^ ^ n o O G O O O O O C M C~i o o LU LU IS) LO LU LU CL O Q r - Z LO LU LU APPENDIX I, PROGFAM 2 O O O O Q i l l W n N i v y D "1 216 > 2 r I " l 2 C T . o o r ^ i r > L r . 217 APPENDIX II In isolving the c r y s t a l structure of IFg +AsFg~, one of the problems was to f i n d a method of systematically choosing (x,y,z) parameters for the fluo r i n e s of the AsFg group and for + the flu o r i n e s of the IFg group i n space group Pa3. (a) Consider f i r s t the case of an octahedral group centred at (0,0,0)*, with the M-F bond length fixed at some value b Q . What values of (x,y,z) are required to describe a\ll possible orientations of the MFg group as i t i s rotated about the 3 axis? vector coordinates 41 + 1 +2 -3 -1 -2 -3 x ?y ,z z,x,y y ,z,x x,y, z 2, x, y y ,z,x these coordinates required by symmetry For an octahedral MFg group ( x - z ) 2 + (y - x ) 2 + ( z - y ) 2 = (x+z) 2 + (x+y) 2 + (y+z) 2 xz + yz + xy = 0 (1) Also, for an octahedral group, the angle between the vector (x,y,z) and the 3-axis, which i s the vector (1/73, 1/^5, l/i/3*) i s the same as the angle between one of the coordinate axes * Coordinates for the other MFg group, at ( J , ^ , J ) are obtained simply by adding (§,£,£) to the (x,y,z) coordinates for the corresponding group at (0,0,0) 218 and the 3 axis. The cosine of t h i s angle i s given by cos © = (1/V3 x 0) + (1/J3 x 0) + (l/>/3 x 0). The cosine of the angle between two vectors i n given by the cosine law: cos(A) = (V 1*V 2)/|V 1| |V2| ) |V|= length of vector V. Hence for the vectors (x,y,z) and (1/73, 1/^3, l/>[3) : cos 0 = l/>/3" = £ (!/#) x + (1/J3) y + (l/s[3) z ] /b Q x 1. Hence x + y + z = b Q (2). If x i s chosen to be an a r b i t r a r y value, x Q, (1) and (2) become x Q z + yz + x Qy = 0 x Q + y + z = 0. These two equations can be simultaneously solved to 9 2 give y and z i n terms of X Q and b Q . If A = - 3 X Q + 2 x 0 b 0 + b Q, then x = x Q y = ( b Q - x o ± A*)/2 z = ( b 0 - x Q + A^)/2. A must be a r e a l number and therefore x Q must l i e within the l i m i t s -1/3 b Q ^ x Q ~£ b Q . Indeed, because of the cubic symmetry, the choice of axes i s purely a r b i t r a r y and the v a r i a t i o n of x can be limited to 0 * x Q * 2/3 b Q to include a l l possible choices of coordinates (x,y,z). This allows for the fact that because of cubic symmetry, the choice (x',y',z') S <y',x',z'). (b) From a given orientation of an octahedral group with bond length b 0 and coordinates (x,y,z), the coordinates of an octahedral group i n the same orientation with any bond length 219 b are (kx,ky,kz), where k = b/b Q. (c) F i n a l l y , the problem of d i s t o r t i o n from octahedral symmetry by increasing or decreasing the angle between the 3 axis and the vector (x,y,z) must be considered. A r e l a t i o n can be derived between the coordinates (x,y , z ) defining the distorted group and the coordinates ( x ' , y , , z ' ) defining a regular octa-hedral group. Let both the distorted and undistorted groups have the same bond length, b Q, and l e t the vectors (x,y,z), (x',y',z') and (1/73, 1/73, 1/73) be i n the same plane. Equation of the common plane:Ax" + By" + Cz" = 0.—(3). Substituting for (x',y',z') and (1/73, 1/73, 1/73) i n (3) and choosing C = y'-x' gives, for the equation of the plane contain-ing the vector (x,y,z) (z*-y')x + (x'-z')y + (y'-x')z = 0 — (4). 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