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Preparation and properties of metal difluorophosphates Tan, Thiam Hock 1970

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PREPARATION AND PROPERTIES OF METAL DIFLUOROPHOSPHATES by , THIAM HOCK TAN B . S c , N a n y a n g U n i v e r s i t y , S i n g a p o r e , 1965 A T H E S I S SUBMITTED IN P A R T I A L FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF "' MASTER OF S C I E N C E i n t h e D e p a r t m e n t o f C h e m i s t r y We a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE U N I V E R S I T Y OF B R I T I S H COLUMBIA A u g u s t , 1970 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and Study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of CHENiSrty The University of British Columbia Vancouver 8, Canada ( i i ) Abstract Twenty-seven difluorophosphates are successful ly prepared by the displacement reactions of anhydrous chlorides or arylcarboxylates with p u r i f i e d difluorophosphoric ac id . V ib ra t iona l spectra are obtained for these d i f l uo ro -phosphates and assignments made. The effects of cation-anion in teract ions on the v i b r a t i o n a l frequencies of the PC^*^ 2 r o u P a r e a ^ - s o examined. Mossbauer parameters for f ive d i a l k y l t i n bis-difluorophosphates are reported and compared with those of analogous f luorosulfa te de r iva t ives . E l e c t r i c a l conduct iv i ty , nuclear magnetic resonance and density studies of solut ions of some metal difluorophosphates i n difluorophosphoric acid are made i n an attempt to obtain a bet ter understanding of so lu t ion behaviour i n difluorophosphoric ac id . ( i i i ) TABLE OF CONTENTS Abstract ( i i ) L i s t o f Tables (vi) L i s t of Figures ( v i i ) Acknowledgements - ( v i i i ) Chapter I : GENERAL INTRODUCTION ' '; 1 A. B r i e f Review of Difluorophosphate Chemistry 2 B. Out l ine of Present Work 6 Chapter I I : PREPARATION OF DIFLUOROPHOSPHATES : ; • 8 • •— A. Introduction 8 B. Experimental ' 10 • 1. Mater ia ls used 10 2. Reaction of Anhydrous Chlorides with Difluorophosphoric Ac id 11 3. Other Preparative Methods 12 4. Chemical Analyses 18 C. Discussion 18 Chapter I I I : VIBRATIONAL SPECTRA OF DIFLUOROPHOSPHATES AND RELATED COMPOUNDS 25 ; A . Introduction 25 B. Experimental 26 1. Infrared Spectra 26 2. Raman Spectra 27 (iv) . TABLE OF CONTENTS (cont.) C. Results and Discussion 27 1 . A l k a l i Metal Difluorophosphate, M P O ^ 27 2. Metal Bis-Difluorophosphates, M ( P 0 2 F 2 ) 2 29 3. D i a l k y l t i n Bis-Difluorophosphates 36 . 4. Tetraphenylarsonium and tetraphenyl-phosphoniura Difluorophosphates 39 5. Relation Between v n r i and v n „ i n XYP(0)F P O P F Molecules 39 6. Relation Between v n_ and P o l a r i z i n g Power r r of the Cation 46 7. Comments on the Linear Relationship Between P-0 Stretching Force Constants and Bond Order Proposed by G i l l e s p i e and Robinson 50 Chapter IV: MOSSBAUER SPECTRA OF DIALKYLTIN BIS-DIFLUOROPHOSPHATES 52 A. Introduction 52 B. Experimental 53 C. Results and Discussion 53 Chapter V: SOLUTIONS IN DIFLUOROPHOSPHORIC ACID 58 A. Introduction 58 B. Experimental . 59 1 . E l e c t r i c a l Conductivity 59 (V) TABLE OF CONTENTS (cont.) 2. Nuclear Magnetic Resonance 60 3. Density 60 C. Results and Discussion 60 1. E l e c t r i c a l Conduct ivi ty 60 2. Nuclear Magnetic Resonance 66 3. Density 72 Bibl iography 74 (vi) LIST OF TABLES TABLE . PAGE I Reaction of Anhydrous Chlorides with Difluorophosphoric Ac id 13 II A n a l y t i c a l Resul ts , Colors and Mel t ing Points of Di f luoro-phosphates 19 I I I V i b r a t i o n a l Spectra of (a) Ammonium and A l k a l i Metal Difluorophosphates 28 (b) A l k a l i n e Earth Metal Difluorophosphates 30 (c) Transi t ion-Metal and Other' Bis-Difluorophosphates 32 (d) D i a l k y l t i n Bis-Difluorophosphates 37 (e) Tetraphenylarsonium and Tetraphenylphosphonium Difluorophosphates 1 40 IV v p Q and v p p for XYP(0)F Molecules .. 43 V Ca l cu l a t i on of the Cation Po la r i z ing Powers 47 VI Mossbauer Parameters of R 2 S n ( P 0 2 F 2 ) 2 55 VII Mossbauer Parameters of (CH 3 ) 2 Sn(S0 3 X) and (CH ) 2 Sn(P0 2 F 2 ) 55 VIII Spec i f i c Conduct iv i t ies of Difluorophosphates and Chlorides i n HP0 2 F 2 at 25°C 61 IX lH and 1 9 F Chemical Shif ts for Solutions of Di f luoro -phosphates i n HP0 2 F 2 67 . X Densi t ies and Molar Volumes of Solutions i n HP0oF_ at 25°C 73 ( v i i ) LIST OF FIGURES F I G U R E PAGE 1 . Structures of (a) Difluorophosphoric Ac id 5 (b) Difluorophosphate Anion i n i t s Potassium Sal t 5 2. Infrared Spectra of (a) Potassium Difluorophosphate 34 (b) Beryl l ium Difluorophosphate ' - 34 (c) Magnesium Difluorophosphate 34 (d) Iron (II) Difluorophosphate 34 (e) Cobalt (II) Difluorophosphate (blue) 34 (f) Cobalt (II) Difluorophosphate (pink) 34 (g) Copper (II) Difluorophosphate 34 3 . Re la t ion Between v p Q and v p p i n XYP(0)F Molecules 45 4. Re la t ion Between v p p and Po l a r i z ing Power of Cation 49 5. . Comparison of Mossbauer Parameters of D i a l k y l t i n B i s -Difluorophosphates and Fluorosulfates 57 6. S p e c i f i c Conduct iv i t ies of Difluorophosphates and Chlorides i n HP0 2 F 2 at 25°C 63 7. J H NMR Chemical Shif ts for Some D i f luorophosphates i n H P O ^ 69 8. 1 9 F NMR Chemical Shif ts for Some Difluorophosphates i n HPO„F_ 70 { v i i i ) ACKNOWLEDGEMENTS The author wishes to express h i s sincere grati tude to Dr. R.C. Thompson for h i s invaluable guidance and assistance throughout the period of th i s work. . Thanks are due to Dr. F. Aubke for generous g i f t s o f various t i n ch lor ides , for al lowing use of the Model 221B universa l br idge, and for many useful d iscuss ions , to Mr. C.T. Wong for supplying cobalt (II) m-bromobenzoate, to Miss B . F . E . Ford and Mr. J . Scott for obtaining the Mossbauer Spectra, _ to Miss P. Watson for obtaining the *H nmr spectra, to Mr. R. Burton for obtaining the ^^F nmr spectra, to Mr. P. Borda for the carbon and hydrogen microanalyses, to Mr. Steve Rak and Mr. Josef Molnar for constructing the glass apparatus. F i n a l l y , the author wishes to express h is deepest grat i tude to h i s fiancee for encouragement. CHAPTER I GENERAL INTRODUCTION The l i t e r a t u r e p r i o r to 1965 on the chemistry of difluorophosphoric ac id and i t s der iva t ives has been extensively reviewed by R e e d ^ , S c h m u t z l e r ^ , and White and P u p p ^ 3 \ Since then a number of papers have appeared dealing with the preparations of difluorophosphate d e r i v a t i v e s ^ and studies on these which include v i b r a t i o n a l (1,11-14,16) . (1, 17-19) j , spectroscopy , x-ray c rys ta l lography v ' J , and nuclear (20-22) magnetic resonance spectroscopy . The purpose of t h i s chapter i s to give a b r i e f review of difluorophosphate chemistry, and to out l ine the purpose of the present work and the contents of t h i s t hes i s . A more de ta i led discussion of the l i t e r a tu r e which i s relevant to the present work i s given i n the in t roduct ion to each chapter. - 2 -A. B r i e f Review of Difluorophosphate Chemistry Difluorophosphoric ac id , HP0 2 F 2 , i s a mobile, co lo r l e s s , c lear (3) l i q u i d which fumes strongly i n moist a i r . I t i s a strong monobasic acid i n water and i s slowly hydrolyzed with the formation of monofluoro-phosphoric a c i d ^ 2 " ^ . • . HP0 2 F 2 + H 2 0 -> H 2 P0 3 F + HF (1) In s u l f u r i c ac id , HP0 2 F 2 has been shown to behave as a base with a d i s soc ia t ion constant, estimated by conductometric t i t r a t i o n with H 2 S 2 0 _ , of 1 x 1 0 " 3 ^ ) . As difluorophosphoric acid i s a base of the s u l f u r i c acid system, i t i s reasonable to conclude that i t s proton-donating power i s less than that of the i soe lec t ron ic HSO^F which was shown to behave as an acid i n s u l f u r i c a c i d . Evidence that HP0 2 F 2 i s s trongly associated i n the l i q u i d state i s extensive . I ts b o i l i n g point of 116°C i s high compared to that of POFg (b.p. - 39 .8°C) , an observation which can be accounted for only by assuming extensive molecular associa t ion i n l i q u i d H P 0 2 F 2 ^ 2 ^ . The very high b o i l i n g point of H 2 S 0 4 , (317°C) as compared to that of HS0 3F, (162.7°C) has been a t t r ibuted to a higher degree of molecular associa t ion i n the (27) l i q u i d form . I t has been found that the OH st re tching frequencies of a number of hydroxylie acids sh i f ted to lower frequencies on going from f 28) monomers i n the vapor phase to the associated l i q u i d phase . The extent of the monomer to l i q u i d frequency sh i f t has been used as a measure of the r e l a t i v e strengths of hydrogen-bonding present i n the l i q u i d s ta te . In the fol lowing acids s tudied, HNOj, HC10 4, HS0 3F, CH 3S0 3H and H P O ^ , i t was (29) found that the OH frequency sh i f t i s greatest for HP0 2 F 2 . Evidence - 3 -for hydrogen-bonding can also be obtained from proton magnetic resonance studies . The 1 H NMR chemical sh i f t s are usual ly displaced to lower f i e l d s by the formation of hydrogen bonds. Consistent with t h i s , the lli (25) resonance of l i q u i d HP0 2 F 2 occurs at -3.35x^ j , lower f i e l d even than that for H^SO^. F i n a l l y , consistent with a high degree of molecular associa t ion i n the l i q u i d , both the v i s c o s i t y and the Trouton constant of (31) (31) HP0 2 F 2 are h igh , being 5.31 centipoise^ J and 24 J r e spec t ive ly . On the basis of the known near-tetrahedral configurat ion of (32) phosphoryl f luor ide and other phosphoryl hal ides , and also of the (17-19) difluorophosphate anion i n i t s a l k a l i metal and ammonium sa l t s , the molecular shape of monomeric HP0 2 F 2 may be assumed to be approximately te trahedral (Figure la) with C g point group symmetry. Chackalackal and Stafford have assigned the IR spectrum of H P 0 2 F 2 , both i n l i q u i d and vapor (29) s ta tes , according to th i s symmetryv . Some recent work involv ing reactions of HP0 2 F 2 has included the preparation of the a l k a l i metal difluorophosphates by the react ion of the appropriate . metal chlor ide with the a c i d ^ ' 2 ^ ' ' ' ' ^ ' ' and the preparation of pyrophosphoryl tetraf luoride, P 2 0 3 F 4 > by the react ion of C1S02NC0 with HPG"2F2 . The ac id and dimethylaminothiophosphoryl d i f l uo r ide have been shown to react at 70° to produce POF^, (SPF 2 ) 2 0 and a mixture of (33) dimethylaminothiophosphoryl and phosphoryl d i f luor ides . The compound, F 2P(0)N(H)P0C1 2 has been obtained by the react ion of difluorophosphoric ac id with F 2 P(0)N:PC1 3 at 65 o(34) Reed has invest igated the chemical and physical properties of solut ions i n H P O ^ , , ^ ' 2 ^ . Physical measurements on solut ions included e l e c t r i c a l conduc t iv i ty , nuclear magnetic resonance, density and v i s c o s i t y s tud ies . The resu l t s indicated that the acid i s a poor solvent for - 4 -e lec t ro ly te s and that ion-pa i r ing i s extensive i n th i s solvent . Metal difluorophosphates (reaction 2 ) , ch lor ides^n i t ra tes , and carbonates (react ion 3) , organic amines and some organic nitro-compounds and carboxyl ic acids (reaction 4 ) , which d issolve i n HPO2F2 producing the.solvent anion, ^®2?2~' D e n a v e a s bases: M P 0 2 F 2 J M + + P 0 2 F 2 " (2) MX + H P 0 2 F 2 + M + + P 0 2 F 2 ~ + HX (3) B + H P 0 2 F 2 + BH + + P 0 2 F 2 ~ (4) On the other hand, H^SO^, HSO^F (reaction 5) and SbF^ (reaction 6) , behave as acids as they produce the solvent ca t ion , H 2 P 0 2 F 2 + . HA + H P 0 o F o -> H o P 0 „ F + + ' A" (5) 2 2 -<- . . 2 2 2 SbF 5 + 2 H P 0 2 F 2 J H 2 P 0 2 F 2 + + S b F 5 P 0 2 F 2 (6) Conductometric t i t r a t i o n of these ac id i c solut ions by a base, say K P 0 2 F 2 , y ie lded insoluble K H S 0 4 , KSOjF and K S b F 5 P 0 2 F 2 . X-ray powder photographs indicated that , apart from the l i t h ium and probably the sodium s a l t s , the other a l k a l i metal and ammonium difluorophosphates are isomorphous with the corresponding p e r c h l o r a t e s ^ , (351 many of which have the barium sulfate s t ruc tu re v . This suggestion was l a t e r proved by x-ray s ingle c r y s t a l s tructure studies of the d i f l u o r o -phosphates of K + ( - 1 7 ' ) , C s + , R b + ( - 1 8 - ) and N H ^ 1 9 - * . The structure of the P 0 2 F 2 ~ anion i n i t s potassium s a l t i s shown i n Figure l b . The d i f l u o r o -phosphate anion has C 2 v symmetry wi th in experimental e r ror . The short FIGURE 1 STRUCTURES OF DIFLUOROPHOSPHORIC ACID DIFLUOROPHOSPHATE ANION IN ITS POTASSIUM SALT*-1 7"1 F F 0 108.6 122.4 - ^ ^ P b P-0 length i n P02p2~ compared with e i ther the Schomaker-Stevenson^"^ o o single-bond length of 1.71A or the value 1.76A obtained from the sum of the Pau l ing covalent r a d i i v indicates considerable n-bonding. The o o P-F bond length of 1.575A compared with 1.74A for the sum of the o Pauling covalent r a d i i and the value 1.65A for the Schomaker-Stevenson length, suggests that there i s also some mul t ip le bonding between the phosphorus and f luor ine atoms i n th i s i o n . A d i s t o r t i o n of the valency-angles from the regular tetrahedral value was noted, and explained i n terras of the va lence-she l l e lectron repuls ion theory . The resu l t s of crystal s t ructure studies of potassium, rubidium and cesium difluorophosphates showed that the l a t t i c e parameters and i n t e r i o n i c distances of these - 6 -(18) difluorophosphates increase with the radius of the cat ion . The c r y s t a l s tructure of an addi t ion compound, Ca(P02p2)2' 2CH2C00C2H,. has also been d e t e r m i n e d . The compound belongs to the class of coordination polymers having a cha in - l i ke double-bridge s t ructure . The study of the properties of potassium difluorophosphate has a t t racted much a t ten t ion . Some of i t s phys ica l proper t ies , including f8 39) s o l u b i l i t y , density and molar volume have been determined 5 . The P-F s t re tching frequency of KPO2F2 has been used i n an inves t iga t ion of the v a r i a t i o n of v p p with the e lec t ronega t iv i ty of atoms bonded to phosphorus No l i n e a r r e l a t ionsh ip was found between these two parameters for KPO2F2, Pr 4NPSOF 2 and C s P S ^ . Kreshkov et a l . have invest igated an accurate and rapid poten-t iometr ic t i t r a t i o n of t r i a lky l s i l y ld i f l uo rophospha t e s by sodium methoxide i n methanol . B. Outl ine of Present Work In order to invest igate the general a p p l i c a b i l i t y of the react ion of anhydrous chlor ides with H P 0 2 F 2 as a preparative route to d i f l u o r o -phosphate de r iva t ives , the reactions of t h i r t y -n ine d i f ferent chlorides with the acid have been s tudied. The resu l t s of t h i s study are given i n Chapter I I . Chapter I I I i s concerned with the v i b r a t i o n a l spectra of difluorophosphates. In the present work, the infrared spectra for some univa len t , d iva lent and t r i v a l e n t difluorophosphates are reported. Since the nature of the difluorophosphates prepared i n th i s work vary from the essen t i a l ly ion ic (C^H^)^As + s a l t to more covalent der ivat ives such as the d i a l k y l t i n bis-difluorophosphates and a lso , presumably, B e ( P 0 2 F 2 ) 2 , i t was possible to extend previous work on the effect of cation-anion interact ions on the v ib ra t iona l spectrum of the P 0 2 F 2 ~ * o n * T ^ e o n l v R a m ^n (421 spectrum previously reported for a difluorophosphate was that of KP0 2 F 2 . Raman spectra of some difluorophosphates prepared here are also reported. . An approximately l i nea r re la t ionsh ip between v p^ and v p p i n compounds of the type XYP(0)F i s described, and a c r i t i c a l comment on the l i nea r re la t ionsh ip between force constant and v p ^ proposed by G i l l e s p i e and (43) - :' Robinson i s also made i n t h i s chapter. - . :' Mossbauer parameters for d imethyl t in der ivat ives of some (44) (45) monobasic su l fonic acids and other d i a l k y l t i n b i s - f luorosu l fa tes were obtained recent ly . As part of a general comparison of the properties of difluorophosphates and f luorosul fa tes , Mossbauer parameters were obtained for the f ive d i a l k y l t i n bis-difluorophosphates prepared here. This work i s described i n Chapter IV. In order to invest igate further the behavior of various e lec t ro ly te i n H P 0 2 F 2 , e l e c t r i c a l conduct iv i ty , 1 H and 1 9 F NMR, and density studies have been made on solut ions i n HP0 2 F 2 of some of the compounds prepared i n th i s work. The resul ts are given and discussed i n Chapter V. CHAPTER II PREPARATION OF DIFLUOROPHOSPHATES A. Introduction Derivat ives of difluorophosphoric acid known before 1965 have been reviewed by S c h m u t z l e r ^ and R e e d ^ . Since then new der ivat ives have been reported, prepared by ( i ) he t e ro ly t i c cleavage of the P-O-P bond of pyrophosphoryltetrafluoride by su i tab le nucleophiles; ( i i ) react ion between t r i a l k y l s i l y l c h l o r i d e s or d i a l k y l s i l y l d i c h l o r i d e s and ammonium difluorophosphate i n organic media at t he i r b o i l i n g points ; ( i i i ) d i rec t f l uo r ina t i on of metal dichlorophosphates; ( iv) displacement react ion of anhydrous chlorides with difluorophosphoric ac id ; and (v) react ion of 2-haiogenoidoperfluoroisopropoxide anion with phosphorylbromidedifluoride. (4) Method ( i ) has been used to prepare 1-aziridium difluorophosphate , N H4 P O2 F2 ( 1 0' ,> C 2 H 5 OPOF 2 , ( C H 3 ) 3 S i P 0 2 F 2 , S i ( P 0 2 F 2 ) 4 and ( n - C ^ ) 3 S n ( P O ^ ) 0 -I t i s in te res t ing to note here that apparently the react ion of nucleophiles with pyrophosphoryltetrachloride does not y i e l d dichlorophosphates . Method ( i i ) has been applied to the preparation of t r i a l k y l s i l y l d i f l u o r o -(5 71 phosphates, R ^ R ^ i P O ^ v ' . The analogous reactions of d i a l k y l -s i l y l d i c h l o r i d e s , R 1 R 2 S i C l 2 , with NH 4 P0 2 F 2 d id not. y i e l d d i a l k y l s i l y l b i s - d i f luorophosphates, R ^ S i (P0 2 F 2 ) 2 , but gave instead compounds of the type R ^ R 2 S i F 2 and mixed f luor ide d i f l u o r o p h o s p h a t e s ^ . Method ( i i i ) has (131 been used to prepare difluorophosphates of Fe(III), In(III) and Al(I I I ) . Thompson and Reed conveniently used method (iv) to prepare ammonium, f ive a l k a l i metal and two a lka l ine-ear th metal d i f l u o r o p h o s p h a t e s ^ ' . Using method (v) , Lus t ig reported the synthesis of a series of u-oxo-fluorophosphorus compounds, inc luding (CF ) C(CN)OP(0)F (CF )„C(N ) -OP( .0 )F 2 , (CF 3 ) 2 C(NCS)OP(0)F 2 , and ( C F 3 ) ^ ( S C N ) O P ( 0 ) F 2 C 1 2 ) . Besides the above react ions , KP0 2 F 2 has been synthesized according to the r e a c t i o n : KPF, + -(KP0_) -> 3KP0_F„ . (7) o n 3 n 2 2 Cesium difluorophosphate has been reported to be formed from the react ion (91 between cesium f luor ide and phosphoryl f l u o r i d e v J : 2CsF + 2PF 30 + CsP0 2 F 2 + CsPF 6 (8) Two dif ferent addi t ion compounds of ethyl acetate and calcium difluorophosphate have been repor ted^*^ . The compound C a ( P 0 2 F 2 ) 2 ' 2CH3COOC2H5 was prepared by react ing H P O ^ with C a C l 2 i n C H ^ O O C ^ , while Ca (P0 2 F 2 ) 2 -CH 3 C00C 2 H 5 was obtained by allowing C a ( P 0 2 F 2 ) 2 ' 2CH3COOC2H^ to stand over phosphoric oxide. - 10 -B. Experimental For t h i s work, care was taken at a l l times to minimize exposure of dif luorophosphoric acid solut ions and react ion products to the atmosphere. A l l manipulations were carr ied out i n a dry box. A l l apparatus used inc luding the double d i s t i l l a t i o n apparatus, react ion vessels , and vacuum f i l t r a t i o n apparatus were flamed under vacuum and f i l l e d with dry a i r before use. • • • ' _ • '. 1. Mater ia l s Used. ... Difluorophosphoric A c i d : Difluorophosphoric ac id , obtained from the Ozark-Mehoning Chemical Company, was p u r i f i e d by d i s t i l l a t i o n at 9 cm Hg and 45 - 49°C i n a d o u b l e - d i s t i l l a t i o n apparatus described p r e v i o u s l y ^ ' . Two to three d o u b l e - d i s t i l l a t i o n s were required to obtain acid of sui table pu r i ty for preparations. The f i n a l d i s t i l l a t i o n was always done d i r e c t l y into the react ion vesse l . Thionyl Chlor ide : Reagent Grade th iony l chlor ide was d i s t i l l e d at 7 5 - 78°C and used immediately. Ethanol : Reagent Grade 100% ethanol was treated with me ta l l i c sodium and d i s t i l l e d twice at 7 8 ° C . Methanol: Reagent Grade methanol was treated with me ta l l i c sodium and d i s t i l l e d twice at 65°C. Chlor ides : A l l chlorides used were obtained commercially. Detai ls of the i r o r i g i n a l states and prel iminary treatments are given i n Table I . - 11 -Ether and Petroleum Ether: They were commercial Reagent Grade and were used d i r e c t l y without any further p u r i f i c a t i o n . . Cobalt(II)m - bromobenzoate: This compound was provided by Mr. C.T. Wong of th i s Department. Copper(II) o_ - methylbenzoate: This was provided by Dr. R.C. Thompson of th i s Department. 2. Reaction of Anhydrous Chlorides with Difluorophosphoric A c i d . The general a p p l i c a b i l i t y of the method of preparing d i f luo ro -phosphates by the react ion of anhydrous chlorides with difluorophosphoric a c i d , • . • • . MCI '+ xHPCLF + M(PO F ) + xHCl (9) has been tested i n the present work. The procedure used was to d i s t i l l excess difluorophosphoric acid onto the anhydrous chlor ide contained i n a 100-ml f lask equipped with a B19 ground-glass j o i n t . For those chlorides, which reacted r ap id ly with HPO2F2 (as evidenced by effervescence due to HCl evolu t ion) , excess acid and HCl were removed on a general purpose vacuum l i n e and the i n v o l a t i l e products examined. Where chlorides appeared not to react with the acid at room temperature or reacted only very s lowly , the suspension of chlor ide i n HPO2F2 was refluxed for several hours at 9 cm Hg pressure. Insoluble mater ial was vacuum f i l t e r e d from the HPO2F2 and examined, and the f i l t r a t e was evaporated to dryness and i n v o l a t i l e s remaining were examined. Deta i l s of procedures used i n each preparation are summarized i n Table I . S o l i d products were transferred to a dry box, - 12 -ground to f ine powders, transferred to v i a l s and stored over phosphoric oxide i n a vacuum desiccator . 3. Other Preparative Methods. Inspection of Table I shows that not a l l of the chlor ide reactions y ie lded sa t i s fac tory products. Other preparative methods t r i e d i n the present work are described below. -Attempted preparation of tetraethylammonium difluorbphbsphate: The preparation of tetraethylammonium difluorophosphate by the react ion of ethylphosphorodifluoridate, C2HJ-OPOF2, with t r iethylamine has been ( 4 7 48") reported ' . As described e a r l i e r attempts to obtain (C2H^) 4 NP02p2 by evaporation of a so lu t ion of tetraethylammonium' chlor ide i n HPO2F2 were unsuccessful. On cooling the so lu t ion to dry- ice temperature, a s o l i d product was observed to c r y s t a l l i z e ; i t could not, however, be i so la t ed by f i l t r a t i o n as the so lu t ion was too viscous at low temperatures. Other workers have successful ly p rec ip i ta ted chlorosulfate sa l t s from ( 4 9 ) ch lo rosu l fu r ic acid by adding th iony l chlor ide to the so lu t ion . Ex-periments i n which solut ions of tetraethylammonium chlor ide i n HPO2F2 were d i lu t ed with th iony l chloride or d i e thy l ether f a i l e d to resu l t i n the p r e c i p i t a t i o n of the required s a l t . The preparation of tetramethylammonium difluorophosphate by the metathetical react ion i n water of tetramethyl-ammonium n i t r a t e with ammonium difluorophosphate.has been reported elsewhere We attempted, without success, to obtain the tetraethylammonium sa l t by.the same method. - 13 -TABLE I Reaction of Anhydrous Chlorides with Difluorophosphoric Acid Drying** Reagent* Procedure Remarks 1. L i C l •" a In a l l cases the chlor ide reacted r ead i ly with the acid to give a c lear 2. NaCl ' a so lu t i on . Evaporation of the so lu t ion to dryness yie lded the products as 3. KC1 " a powders, with the exception of the zinc chlor ide react ion where the product i s 4. RbCl a best described as a g lass . The a l k a l i metal and ammonium difluorophosphates 5. CsCl a have been prepared previously by th i s method and were i d e n t i f i e d here by 6. NHLCI . b comparison of t he i r infrared spectra with-published data CI>14). The remain-7. MgCT2 a ing products were i d e n t i f i e d as difluorophosphates by elemental analyses 8. MgCl 2 -6H 0 • d (Table I I ) . During the preparation of - the ferrous compound, care was taken 9. CaCl *6H_0 a to ensure a nitrogen atmosphere above both so lu t ion and product. A l l d i f luoro 10. , S r C l 2 - 6 H 2 0 d phosphates prepared are white with the exception of Fe(P02F2)2 which i s pale 11. BaCl -2H_0 2 2 a blue and Co(P02F2)2 which i s pink. 12. MnCl 2*6H 0 d 13. F e C l 2 c 14. C o C l 2 ."• c 15. ZnCl 2 -xH 2 0 d 16. ( C H 3 ) 2 S n C l 2 c 17. ( C 2 H 5 ) 2 S n C l 2 c 18. ( n C 3 H 7 ) 2 S n C l 2 c continued on next page - 14 -TABLE I (cont.) Reagent'' Drying** Procedure Remarks 19. ( n C 4 H 9 ) 2 S n C l 2 20. ( n C g H 1 7 ) 2 S n C l 2 21. (C 6 H 5 ) 4 PC1 22. ( C 6 H 5 ) 4 A s C l b The chlorides reacted r ead i ly with the a c i d , however, the products were not very b soluble i n H P O 2 F 2 and clear solut ions were not obtained. The react ion was considered complete when effervescence due to HCl evolut ion ceased. The products, obtained as white powders, after removal - of excess ac id , were dissolved i n methanol, p rec ip i t a t ed with d i e t h y l ether, and i d e n t i f i e d by elemental analyses. ~ 23. BeCl, 24. FeCl 3 -6H 2 0 25. N i C U 26. CdCl 2 -2^H 2 0 27. PbCl„ a These chlor ides were found to react ex-tremely slowly with the a c i d . The d suspension of the chlor ide i n HP0_F_ was refluxed with s t i r r i n g for several Hours c at a pressure of 9 cm of Hg. Unreacted chlor ide was removed by vacuum f i l t r a t i o n d and the f i l t r a t e was evaporated to dry-ness y i e l d i n g the corresponding d i f l uo ro -a phosphates, i d e n t i f i e d by elemental analyses. Except for n i c k e l ( I I ) difluorophosphate which i s ye l low, a l l these difluorophosphates are white. 28. CrCl 3 «6H 2 0 d These chlorides were found to be iner t to react ion with HP0„F„. After re f lux ing 29. CuCl 2 -2H 2 0 d the suspended chlor ide i n HP0 2 F 2 for several hours and f i l t e r i n g , the insoluble 30. AgCl c materials were found to contain chlor ide but no s i gn i f i c an t amount of d i f l uo ro -31. H g C l 2 a phosphate evident i n the infrared spectrum ' •'• . and the f i l t r a t e y ie lded no i n v o l a t i l e 32. (C-Ht-) SnCl c products on evaporation to dryness. continued on next page - 15 TABLE I (cont.) Reagent Drying** Procedure Remarks b The chlorides reacted read i ly with the ac id forming clear so lu t ions , but on c pumping at room temperature, or at s l i g h t l y elevated temperatures, only viscous o i l s c were obtained. No attempts at character iz ing these o i l s were made. In the case of the tetramethyl ammonium s a l t , a s o l i d product was obtained by heating the o i l to 125°C, but i t d id not analyze as the expected difluorophosphate. 36. (CgH^gCCl c Both of these chlorides dissolved to give c lear so lu t ions , co lor less i n the 37. (CH^jSnCl c case of t r ime thy l t i n ch lor ide , and yellow to golden i n color depending on concentra-t i on i n the case of triphenylmethyl ch lo r ide . The so lu t ion containing t r i -. methyl t in chlor ide reduced to a viscous o i l on pumping. The so lu t ion containing triphenylmethyl chlor ide could not be pumped to dryness without heating, while A at s l i g h t l y elevated temperatures, a brown s o l i d was obtained. Elemental carbon analysis on the product was i n poor agreement with that expected for t r i pheny l -. . methyl difluorophosphate. 33. (CH 3) 4NC1 34. (C 2 H 5 ) 4 NC1 35. (nC 4 H 9 ) 4 NCl 38. S n C l 2 b These compounds reacted slowly with the acid under ref lux condi t ions . After 39. (C^Hj.) 2 SnCl 2 c f i l t r a t i o n and reducing the f i l t r a t e to dryness the products of the t i n and 40. (C^H 4 CH 2 ) 2 SnCl 2 c d iphenyl t ind ich lor ide reactions were found to contain both chlor ide (AgNO, test) and difluorophosphate (infrared spectrum). The product of the d ibenzy l t ind ich lo r ide react ion d id not contain ch lor ide ; however, analyses showed i t was not a pure com-pound. * A l l chlorides used were Analar or Reagent Grade chemicals with the exception continued on next page - 16 -TABLE I (cont.) of d i - n - b u t y l t i n d i c h l o r i d e which was Technical Grade and was r e c r y s t a l -l i z e d from petroleum ether before use. P r io r to react ion with difluorophosphoric ac id a l l chlorides were dr ied . The method used i n each case i s given i n th i s column. (a) heated i n oven at 120° for several days and pumped on under vacuum immediately p r i o r to use. (b) heated to 70° under vacuum for several hours. (c) pumped on under vacuum at room temperature for several hours. (d) ref luxed with f reshly d i s t i l l e d th iony l chlor ide for 2 - 3 hours (chromic chlor ide was ref luxed for about 24 hours) with a dry ' ' (4 ni t rogen b leed . Excess th iony l chlor ide was removed under vacuum - 17 -Attempted Preparation of S i l v e r ( I ) Difluorophosphate: S i l v e r ( I ) difluorophosphate has apparently never been prepared. This compound could be a useful s t a r t ing material i n the preparation, by metathetical reactions with chlor ides , of other difluorophosphates. A l l of the reactions described here f a i l ed to y i e l d the desired product. In view of the l i g h t s e n s i t i v i t y of s i l v e r ( I ) compounds, react ion vessels were wrapped i n aluminum f o i l during a l l experiments. As described previous ly , s i l v e r chlor ide i s iner t to react ion with difluorophosphoric ac id . As w i l l be discussed below some success has been achieved i n the preparation of t rans i t ion-metal difluorophosphates by the react ion of t rans i t ion-meta l aryl-carboxylates with HPG^F,,. Unfortunately, l i k e AgCl , s i l v e r benzoate i s e s s en t i a l l y iner t to react ion with the ac id . S i l v e r t r i f luoroace ta te has been prepared by the react ion of s i l v e r n i t r a t e with sodium t r i f luoroace ta te ' i n water followed by ext rac t ion of the product in to e the r^"^ . ' In an analogous reac t ion , s i l v e r n i t r a t e and potassium difluorophosphate were added i n equimolar amounts to water and the so lu t ion extracted overnight with ether. Upon separation and evaporation of the ether (521 layer , no i n v o l a t i l e product was obtained. F i n a l l y , Woolf v J reported that a number of metal acetates dissolved i n anhydrous acet ic acid p rec ip i t a te from solu t ion as the corresponding f luorosulfa te upon addi t ion of f luorosu l fu r i c a c i d . S i l v e r acetate i s only s l i g h t l y soluble i n acet ic acid and when HPO2F2 was added, the s i l v e r acetate dissolved completely and no p rec ip i t a te was obtained on standing. Preparation of Copper(II) Difluorophosphate: As described previously copper(II) chlor ide i s ine r t to react ion with difluorophosphoric a c i d . Copper (I I) °_-methylbenzoate • J was found to d issolve slowly i n the acid y i e l d i n g a pale yellow s o l u t i o n . Excess HPCLF9 was removed under vacuum - 18 -at room temperature and o-methylbenzoic acid was sublimed at 100°C under vacuum from the residue. The product remaining was pale green and was i d e n t i f i e d as copper(II) difluorophosphate by elemental ana lys i s . Preparation of Cobal t(II) Difluorophosphate: Although cobal t ( I I ) difluorophosphate may be obtained r ead i ly by. the react ion of cobal t ( I I ) ch lor ide with difluorophosphoric acid (see above), i t was of in teres t to see whether the type of react ion described above for the preparation of copper(II) difluorophosphate was appl icable to the preparation of the cobal t ( I I ) compound. Cobal t ( I I ) m-bromobenzoate dissolved rap id ly i n difluorophosphoric ac id y i e l d i n g a pink so lu t ion and undissolved m-bromobenzoic ac id . After vacuum f i l t r a t i o n , the f i l t r a t e was pumped to dryness. The infrared spectrum of the product showed contamination by m-bromobenzoic ac id which was then removed by vacuum .sublimation at 150°C. The f i n a l product was blue i n color and analyzed as Co(P02F2)2» . 4 . Chemical Analyses. Ana ly t i ca l , data are l i s t e d i n Table I I , together with colors and melt ing points of the difluorophosphates prepared i n th i s work. Carbon and hydrogen analyses were obtained i n the microanaly t ica l laboratory at the Unive r s i ty o f B r i t i s h Columbia, f luor ine and phosphorus analyses were obtained i n the A. Bernhardt microanaly t ica l laboratory, Germany. A l l difluorophosphates l i s t e d i n Table II gave negative tests for chlor ide (AgNO^ t e s t ) . C. Discussion This chapter describes the successful preparation of twenty-seven TABLE II Ana ly t i ca l Resul ts , Colors and Melt ing Points of Difluorophosphates A n a l y t i c a l Results (%) C H P F No. Compound Calc . Found Calc . Found Calc . Found Calc . Found Color M.P.(°C)* 1 L i P 0 2 F 2 _ - - - - - - white 360 2 NaP0 2 F 2 - - - - 24.99 24.72 30.65 30.64 white 210 3 KP0 2 F 2 • - - - - - - white ' 263 (>220) 4 RbP0 2 F 2 • _ ' _ - - white 160 • £ . C s P 0 2 F 2 . ^ - - - white 286 6 N H 4 P 0 2 F 2 ' - - - - white 213 (213) 7 B e ( P 0 2 F 2 ) 2 - - \ - . 29.37 29.14 36.02 35.85 white ;>400 d 8 MgCPO F ) - . - - . 27.38 27.28 33.59 33.29 white 200 9 C a ( P 0 2 F 2 ) 2 - . - ' . / - - 25.60 25.35 31.40 31.68 white • d (>260) softening 345 V 10 S r ( P 0 2 F 2 ) 2 - 21.40 21.61 26.24 26.58 white ca 250 d softening 96-200 11 B a ( P 0 2 F 2 ) 2 - - - - . 18.26 18.54 22.40 22.66 white >400 12 M n ( P 0 2 F 2 ) 2 - - - - 24.12 23.95 29.58 29.69 white 184 13 F e ( P 0 2 F 2 ) 2 ' - - - 24.03 24.07 29.48 29.17 pale blue 180 d continued on next page TABLE II (cont.) Ana ly t i ca l Results (%) C H P F No. Compound . Calc . Found Ca lc . Found Calc . Found Calc . Found Color . M.P.(°C)* 14 F e ( P 0 2 F 2 ) 3 • - - 25.90 25.71 31. 77 31. 90 white >400 15a C o ( P 0 2 F 2 ) 2 - - - 23.75 23.58 29. 13 29. 03 blue 173 15b C o ( P 0 2 F 2 ) 2 - - 23.75 23.95 29. 13 29. 23 pink 173 16 N i ( P 0 2 F 2 ) 2 • - - • - 23.77 23.90 29. 16 29, 03 yellow >400 d at 255 17 C u ( P 0 2 F 2 ) 2 - - 23.34 23.16 28. 62 28. 71 pale green 265 d 18 Z n ( P 0 2 F 2 ) 2 - • - • - '. 23.18 23.05 28. 43 28. 26 white * * .19 C d ( P 0 2 F 2 ) 2 • - - 19.71 19.87 24. 17 24. 01 white . 245 d 20 21 P b ( P 0 2 F 2 ) 2 . ( C 6 H 5 ) 4 A s P 0 2 F 2 59.50 59.56 4. 13 4. 16 15.14 6.40 15.07 6.52. 18. 7. 58 85 18. 7. 69 84 white white 189 334 d d 22 ( C 6 H 5 ) 4 P P 0 2 F 2 65.45 65.23 4. 55 4. 50 14.09 14.28 8. 64 8. 71 white 350 d 23 24 * CCH 3 ) 2 Sn(P0 2 F 2 ) 2 ( C 2 H 5 ) 2 S n ( P 0 2 F 2 ) 2 6.85 12.68 5.93 12.53 1. 2. 72 66 2. 2. 62 71 — - white white 204 262 d d 25 ( n - C 3 H 7 ) 2 S n ( P 0 2 F 2 ) 2 17.71 17.47 17.84 17.64 3. 47 3. 3. 3. 43 47 44 15.23 15.36 15.35 18. 68 18. 18. 81 68 white 245 d continued on next page TABLE II (cont.) Ana ly t i ca l Results (%) H P . N o . - . Compound Calc . Found Calc . Found Calc . Found Calc . Found Color M.P.(°C)* 26 ( n - C 4 H g ) 2 S n ( P 0 2 F 2 ) 2 22.09 22.09 4.17 4.05 - - - - white 235 d 27 ( n - C g H 1 7 ) 2 S n ( P 0 2 F 2 ) 2 35.12 35.42 6.26 6.25 - - - - white 114 * Mel t ing points i n parenthesis are from reference 50. ** Z n ( P 0 2 F 2 ) 2 i s a glassy s o l i d . I ts m.p. i s probably around room temperature, d Indicates melting with decomposition. anhydrous difluorophosphates. Nine of these, NH^*, L i + , N a + , K + , Rb + , QS+(1,14)^  _ a2+^ B a 2 + ^ ^ \ and F e + 3 ^ ^ d i f l u o r o p h o s p h a t e s have been reported prev ious ly . The r e a c t i v i t y of chlorides towards difluorophosphoric acid requires more comment. Ionic chlorides as exemplified by NH^Cl, (C^H^.)^PCl, (CgH,.)^AsCl, the. a l k a l i metal chlorides and, with the exception of BeCl^, the a lka l ine -ea r th metal chlorides react r ead i ly with HPO2F2. Beryl l ium ch lo r ide , which has the most covalent metal-chlorine bonds of the a l k a l i n e -earth metal chlorides reacted only slowly with the ac id . The r e a c t i v i t y of divalent t rans i t ion-metal chlorides towards HPO2F2 appears re la ted to the l a t t i c e energy of the chloride involved. In the series M n C l 2 , F e C l 2 , C o C l 2 , N i C l 2 , C u C l 2 and Z n C l 2 , copper(II) chlor ide has the highest l a t t i c e energy and was found to be .inert to react ion with HPO2F2, while N i C l 2 having the next highest l a t t i c e energy reacted only s lowly. The other divalent chlorides reacted read i ly with the ac id . The same trend appears evident for the t r i v a l e n t t rans i t ion-metal ch lor ides . Of the two chlor ides tested, FeCl^ and C r C l ^ , the chromium compound has the higher l a t t i c e energy and was found to be ine r t to react ion with HPO2F2, while the i ron compound reacted s lowly . A de f in i t e trend i s also observable i n the r e a c t i v i t y of the divalent Group (II)B chlorides towards difluorophosphoric ac id . . Z i n c chlor ide reacts read i ly with the a c i d , cadmium chlor ide only s lowly , and mercuric chlor ide i s i ne r t to react ion with the a c i d . Both of the Group (IV) divalent chlorides s tudied, S n C ^ and P b C ^ reacted slowly with difluorophosphoric ac id . The preparation of a number of dimethyl t in der ivat ives of mono-basic sulphonic acids by the react ion of dimethylt indichlori .de with the (44) appropriate acid has been reported previously . In the present work - 23 -we have successful ly prepared f ive d i a l k y l t i n bis-difluorophosphates by the react ion of d i a l k y l t i n d i c h l o r i d e with difluorophosphoric ac id . Attempts to extend the react ion to the preparation of the a ry l -de r iva t ives ( C 6 H 5 ) 2 S n ( P 0 2 F 2 ) 2 and ( C ^ C H ^ n ( P O ^ ) 2 were, however, unsuccessful. The react ion of t r ime thy l t i n chlor ide with difluorophosphoric acid y ie lded only (44) a viscous o i l . I t i s in te res t ing to note that previous authors have reported that the react ion of, t r i m e t h y l t i n chlor ide with a s l i g h t l y greater than two-fold excess of a monobasic su l fon ic acid y ie lds a dimethyl t in der iva t ive according to the reac t ion : • ' -\ • (CH 3 ) 3 SnCl •"+ 2HS03X + (CH^) 2 Sn (SC^X) + CH 4 + HC1 (10) No evidence for an analogous react ion with HP0 2 F 2 was obtained i n the present work. Woolf reported the preparation of a number of t ransi t ion-metal f luorosulfates by heterogeneous displacement reactions of t rans i t ion-metal (521 sa l t s with f luorosul fonic acid . A number of in te res t ing comparisons between the previous work i n the f luorosul fonic acid system and the present work may be made. Transi t ion-metal f luorosulfates are insoluble i n f luo rosu l fu r i c a c i d . Hence, during the react ion of, for example, t r a n s i t i o n -metal chlorides with HSOjF the react ing chlor ide becomes coated with the insoluble product f luorosu l fa te , necess i ta t ing prolonged re f lux ing i n the ac id . In the difluorophosphoric ac id case most products are soluble i n HP0 2 F 2 and may be eas i ly recovered by evaporation to dryness. Woolf also reported that carboxylate sa l t s reacted with HS03F more r ead i ly than ch lor ides . The same trend was observed i n the present work with difluorophosphoric ac id . Q u a l i t a t i v e l y , cobal t ( I I ) m-bromobenzoate reacts more rap id ly than cobal t ( I I ) - 24 -ch lo r ide . The trend i s more obvious i n the case of the preparation of copper(II) difluorophosphate; copper(II) chlor ide i s iner t to react ion with H P O 2 F 2 , while copper(II) o-methylbenzoate reacts r a p i d l y . Two forms of Co(PC>2F2)2 were prepared i n the present work. They have different, colors and IR spectra (Chapter I I I ) . The pink Co(P02F 2 ) 2 could be converted to blue by simply heating to 140 - 150°C under vacuum. - 25 -< > CHAPTER I I I VIBRATIONAL SPECTRA OF DIFLUOROPHOSPHATES AND RELATED COMPOUNDS A . Introduction The f i r s t v i b r a t i o n a l spectrum reported for a difluorophosphate (53") was that o f Corbridge and Lowe J who recorded the infrared spectrum of NH 4 P0 2 F 2 over the range 5,000 - 600 c m - 1 . Buhler and Bues^ 4 2^ invest igated the v i b r a t i o n a l spectra of fluorophosphate melts and c ry s t a l s . The IR and Raman spectra of c r y s t a l l i n e K P 0 2 F 2 , KPF^ a n c * ^PO^F were reported, assignments made, and the force constants and bond orders i n these and i n re la ted anions were discussed. The only IR study on difluorophosphoric acid i s that of (29) Chackalackal and Stafford who reported and assigned the IR spectra in the range 4,000 - 400 c m - 1 of l i q u i d and of associated and monomeric gaseous acid according to C g point symmetry. The IR spectra of (CH3) ^SiPO,^, , , (n-C 4 H g ) 3 S n P 0 2 F 2 , and S i ( P 0 2 F 2 ) 4 have been r e p o r t e d b u t only assignments - 26 -were made to the t r i m e t h y l s i l y l s a l t . Weidlein obtained the IR spectra of the difluorophosphates of A l ( I I I ) , Fe(III) , and I n f i l l ) , and the frequencies associated with v ibra t ions of the P 0 2 F 2 g r o u P s were assigned according to symmetry. In an attempt to invest igate the effect of cation-anion in teract ions on the v ib ra t i ona l frequencies of the difluorophosphate anion, fl4) ~ • Thompson and Reed v studied the IR spectra of ammonium and f ive a l k a l i metal difluorophosphates. They found that symmetric P 0 2 , asymmetric PF 2 and symmetric PF 2 s t re tching frequencies decrease s tead i ly as the s i ze of the a l k a l i metal cat ion increases. The difluorophosphate anion, P0 2 F~, has C 2 v symmetry and for a f ive atom species with th i s symmetry, there are nine fundamental modes of v i b r a t i o n , eight of which, (the exception being the tors ion mode v ^ ) , are expected to be IR ac t ive . I f the difluorophosphate group i s engaged i n bonding to other atoms through both oxygen atoms i n an equivalent manner, the symmetry i s not reduced. However, i f the bonding v i a the two oxygen atoms i s not i n an equivalent manner or i f only one of the oxygen atoms i s engaged i n bonding, the symmetry i s reduced to C and a l l nine fundamental s modes are IR ac t ive . B. Experimental 1. Infrared Spectra. A l l spectra, unless otherwise s tated, were obtained as nujol mulls of f i n e l y powdered samples of the s a l t s . The mulls were contained between KRS-5 plates and the spectra recorded on a Perkin Elmer 457 Double Beam Spectrophotometer i n the range 4,000 - 250 c m - 1 . A l l spectra were ca l ibra ted - 27 -using polystyrene. 2. Raman Spectra. A l l spectra were taken with a Cary Model 81 Raman Spectrophotometer i n which a helium-neon gas laser o s c i l l a t i n g at 6328A was used for exc i t a t ion . The mater ia ls were examined as f i ne ly divided powders i n sealed Pyrex tubes. C. Resul ts and Discussion 1. A l k a l i Metal Difluorophosphates, MP0 2 F 2 . Infrared data for the a l k a l i metal difluorophosphates and ammonium d i f luorophosphates have been reported p r e v i o u s l y ^ 1 ' 1 4 - 1 and are given, with assignments, i n Table I I I ( a ) . Infrared spectra obtained i n the present work agreed with the published data for a l l compounds with the exception of sodium difluorophosphate, where an extra band at 900 cm - 1 was observed i n the present work. This band i s t en ta t ive ly assigned to the combination + v ^ . I t i s not at a l l c lea r why the band was not observed i n the previous work. Raman frequencies obtained here are tabulated i n Table I I I (a) and serve to confirm the assignments made prev ious ly . The t o t a l l y symmetric A^ s t re tch-ing modes appear as strong bands i n the Raman spectrum. The symmetric A^ bending modes, which appear weak or not at a l l i n the IR spectra, appear as (42) s trong to medium in tens i ty bands i n the Raman spectra. Biihler and Bues have reported the Raman spectrum of K P 0 2 F 2 > The Raman spectrum obtained for KP0 2F 2 i n the present work agreed we l l with th i s previous work except that we were able to observe the rocking band at 503 cm - 1 but not the band at 277 cm - 1 which Biihler and Bues assigned to 6 . 2 TABLE I I I (a) VIBRATIONAL SPECTRA OF AMMONIUM AND ALKALI METAL DIFLUOROPHOSPHATES ( c m _ 1 ) + * Na + K + Rb + Cs + N H 4 + Assignment IR IR** IR R IR R IR R IR R IR , R V 2 + V 9 ]" - • - 1332s - • 1330s - 1321s - - -as 2 1 6 1273s 1309s 1309s - 1310s 1314w 1310s - 1299s • . - 1292s -v s P 0 2 ( A 1 ) v 1 1164s 1152s 1152s 1170s 1148s 1144s 1145s 1142s 1137s 1138vvs 1138s 1137s V 3 + V4 - 900s 900s - - ; - ' - - ' -•' - - • v a s P W v 8 > • 940s- 868s 868s - 850s - .846m - • 843m 832w 860m -v s P F 2 ( A l ) v 2 890s . 844s 844s 851s 832s 825s 827s 819s 818s 812s 842s 835s P0 2 bending(Aj) \>j 525s - 531m - 518m - 514m - 511s - 518m rocking ( B ^ v ^ rocking ( B 2 ) v 9 498s 420s 502s 458m 502s 458m .."504w . 503s 49Ss 503w 505m . 492s 500w 503m 489s 499m . 500s 505w • PF 2 bending (A^)v 4 , 350s 360w . 360w 360m 356m -' 354m - 352s - 354s * for abbreviations see Table H I (c) ** from reference (14) f used KBr windows for obtaining IR spectra 0 3 - 29 -Attempts to obtain the Raman spectra of powdered samples of L i P 0 2 p 2 and most of the metal bis-difluorophosphates, described i n the next sec t ion , were unsuccessful. This may have been due to too much scat ter ing of the exc i t i ng rad ia t ion or fluorescence from the sample, although, the reasons for t h i s are not understood. 2. Metal bis-difluorophosphates, M(P02p2)2-Infrared data for the metal bis-difluorophosphates and for F e t P C y ^ j are given i n Table 111(b), ( a lka l ine earth metal difluorophosphates) and Table 111 (c ) , ( t ransi t ion-metal and other bis-dif luorophosphates) . Some t y p i c a l spectra are shown i n Figure 2 with that of KPO2F2. The most s t r i k i n g feature o f these spectra are t h e i r increased complexity over those of the a l k a l i metal difluorophosphates. The p o s s i b i l i t y does exis t that some of the bands, p a r t i c u l a r l y those i n the region 1,000 - 1,200 cm" 1 are due to phosphate impur i t i e s . This seems u n l i k e l y , however, i n view of the ana ly t i c a l data and also i n view of the fact that repeated preparations of both B a(P02p2)2 a n d the pink form of C o(P02p2)2 gave i d e n t i c a l spectra. Further, i d e n t i c a l spectra were also obtained for d i f ferent samples of Mg(P02p2)2 prepared from anhydrous MgC^ and hydrated MgC^ after treatment with t h iony l ch lo r ide . Moreover, i t was found that M g f P O , ^ ^ dissolved i n cyanomethane gave a simple spectrum with bands at 1,280 cm"1 (PO^ asym. s t r e t ch ) , 1,170 ( P 0 2 sym. s t r e t ch ) , 890 (PF 2 asym. s t r e t ch ) , 860 (PF 2 sym. stretch) and a broad band at 500 cm - 1 (bending and rocking modes), and no detectable bands i n the 1,000 - 1,100 cm"1 region. I t i s concluded, there-fore , that the complexity of the spectrum i s a consequence of the s o l i d s tate s tructure and does not a r i se through the presence of impur i t ies . TABLE I I I Cb)' VIBRATIONAL SPECTRA OF ALKALINE EARTH METAL DIFLUOROPHOSPHATES (cm'-.1)* Assignment V 2 + V 9 . V a s P ( V B l ) V 6 V 2 + V 4 V S P 0 2 C A 1 ) V 1 overtones and combinations of bending and rocking modes v PF„(B_)v Q as 2 V 2J 8 B e + + IR 1291s 1205s 963s Mg++ IR 1337s 1307s 1179sh 1166) J7J 115 1127m 1077 A 1055' 982m 949, 937'' m Ca + H III 1342s 1292s 1 1 5 2 l s 1137J . 950| S 930 ; S r + + IR 1300-1250 s,br 1144s Ba"1 1063m 924s IR 1270s, br 1250s 1209sh,vw •1150i 1140i S 1112sh, vw 938sh 920 1298s 1183s 1140m 930m continued on next page TABLE:III (b) cont. B e + + M g + + C a + + S r + + : B a + + • Assignment IR IR IR IR IR R V3 + V4 897sh, 885s 892s %J *"T s , v s P F 2 ( A 1 ) v 2 963s ,887 > 885s 878s 835s 842s - 810vvw - • - - -vBe-0 . 725sh> - - - •- -685 s - - . -P0 2 bend ( A ^ V j 523sh 557m 532s ^ 528s 535s -2v 5 - 524sh - - • 517sh • -rocking ( B ^ v ^ 505s • 507m 520s 490s 502s -- 487m - - -rocking ^ J v g 455s 472s 502s 469s 493sh -PF^endCAi) v 4 345w 380| 348w 360w 350w 365s j w » - 360J - • . - - -300s - i -* for abbreviations, see Table I I I .(c) TABLE I I I (c) INFRARED SPECTRA OF TRANSITION METAL AND SOME DIVALENT DIFLUOROPHOSPHATES (cm - 1 ) t o Assignment Mn +2 Fe +2 FeH + 3 F e + 3 ' Co + 2 (b) Co + 2 (p ) N i + 2 Cu 1 Zn+2 Cd +2 Pb +2 V 2 + V 9 as 2 1' 6 V 2 + V4 W W overtones and combinations of bending and rocking modes - a s P F 2 ( B 2 ^ 8 1350-1250 s vbr 1144s 1067-1050 m br 975m 935s 1326s -1276s 1237s 1242s 1149 i 1126sh 1068 1051sh 975m 946 937 m 965s 965s 1272s 1145s 1172shv 1173s 1129s 944s 1333s 1280s 1291s 1143s 1133s 1072| 1074m fm-s 1050 980m 960wsh 9471 938 > 941s 1289sh 1263s 1222i 1212 i m 1167^ I s 1145-' 1285s 1150s 1065m 974sh.N 930s S 953 i 1300-1250 s vbr 1140-1110 s vbr 925s 1300sh,br 1232s 1127s 934s Continued on next page TABLE I I I (c) (cont.) Assignment Mn + 2 F e + 2 Fe + 3 , F e + 3 * Co + 2 (b) Co + 2 (p) N i + 2 C u + 2 Z n + 2 * * C d + 2 Pb +2 V 3 + V 4 v s P F 2 ( A 1 ) v 2 2 x \>r rocking (B^v . , rocking ( B 2 ) v g PF 2 bend(A 1 )v 4 to r s ion v_ 880s P0 2 bend(A 1 )v 3 342m-s 517sh 500m-s 487m 470s 375 345 891sh, 884 ) 905s ' 914s 889s 548m 585m 570m 546s 514m 496m-s 481m 471s \ 3 7 9 \ J W 346*W 497m-s 528m-s 485sh 493m 375w 262m 262m 510sh 495s 898sh> S 882 ) 887s 804vvw 555> 545 >s 535 J 557m 516sh 517sh -500s 491m-s 473sh 468s 469m , ' , 380i 380-350 370w,br 7 r f > f W , ' 350' w br 904s 878s 870s | 2 g S ^ j m 535m 545sh - - 525s 497m 505sh 500sh 495s 480s 881s 860s 528s 513m 502m 485s 35 Ow * from reference ** used KBr windows b : blue (13) br : broad m: medium p: pink s: strong sh: shoulder v : very w: weak - 35 -Unfortunately, structures of none of these compounds are known, and explana-t ions of the complexity of the spectra given below are speculat ive. I t i s poss ible that difluorophosphate anions are present i n more than one chemical environment. Extra bands may also ar i se through combinations and overtones of fundamental frequencies, combinations of l a t t i c e modes with fundamental frequencies or the s p l i t t i n g of fundamentals due to anion-anion in te rac t ions . (491 f54 551 S imi la r complex spectra of ch lo rosu l fa t e v J and hypophosphite^ ' J anions i n some of t h e i r sa l t s have been reported previously with many bands assigned to combinations and overtones. The assignments shown i n Tables 111(b) and (c) are very ten ta t ive . In some cases the fundamental modes appear to be s p l i t , a feature which could a r i se through coupling of the v ibra t ions of two separate anions. The infrared spectrum of B e ( P 0 2 F 2 ) 2 shows a broad band at 685 cm" 1 with a shoulder at 725 cm In view of the fact that B e ( P 0 2 F 2 ) 2 probably has a considerable degree of covalent character i n the metal-oxygen bond, t h i s band could be due to the B'e-0 s t re tch ing . Beryllium-oxygen s t re tching frequencies around th i s region have been reported for some bery l l ium complexes, for example, 754 c m - 1 i n bery l l ium acetate and 745 c m - 1 i n bery l l ium f o r m a t e . The infrared spectrum of the only t r i v a l e n t difluorophosphate studied i n th i s work, F e ( P 0 2 F 2 ) 3 , merits some comment. The frequencies observed i n th i s work are compared i n Table I I I (c) with those obtained for th i s fl31 compound by Weidlein ' . The agreement i s qui te good except that we observed a shoulder on the band and an addi t iona l weak band at 375 cm" 1 which we fl31 assign to the PF 2 bending mode. The band at 262 cm"1 assigned by Weidlein } to P F 2 bending could be the to rs ion mode or a l a t t i c e mode. I f i t i s the to rs ion mode, then the symmetry of the difluorophosphate anion must be - 36 -reduced to C g for which th i s mode i s IR ac t ive . The pink and blue forms of cobal t ( I I ) difluorophosphate obtained in th i s work gave completely d i f ferent IR spectra . The blue form gave a simple spectrum of the kind observed for monovalent difluorophosphates, while the pink form gave a more complex spectrum t y p i c a l of most of the other divalent difluorophosphates. 3. D i a l k y l t i n Bis-Difluorophosphates. The infrared spectra of the d i a l k y l t i n bis-difluorophosphates were compared with those of the corresponding d i a l k y l t i n d ich lor ides i n order to determine those bands a r i s i n g from vibra t ions i n the difluorophos-phate groups. Infrared and Raman frequencies are given i n Table 111(d) with assignments 'for the PC^*^ v ib ra t i ons . For the ser ies of d i a l k y l t i n bis-difluorophosphates s tudied, the absorption frequencies due to the ?0^?^ groups are r e l a t i v e l y in sens i t ive to the nature of the a l k y l group. I t i s in te res t ing to note that the PF^ s t re tching frequencies (around 905 cm - 1 ) are s i g n i f i c a n t l y higher than those o f the a l k a l i metal difluorophosphates (potassium s a l t : 841 c m - 1 ) . A s i m i l a r observation with regard to the SF s t re tching frequencies was also (57) found in analogous f luorosulfa te system . On going from KSO^F to (CH^)^Sn(SO^F)2 the S-F bond length decreases with a concomitant increase in v s p • By analogy, a shorter P-F bond length i n the d i a l k y l t i n b i s -difluorophosphates compared to the a l k a l i metal difluorophosphates would account for the differences i n the v • frequencies observed. P-F The bands around 600 c m - 1 i n the IR spectra and 535 cm"1 i n the Raman spectra were assigned to the asymmetric and symmetric Sn-C stretches TABLE I I I (d) VIBRATIONAL SPECTRA OF DIALKYLTIN BIS-DIFLUOROPHOSPHATES R 2 Sn(P0 2 ' F 2 ) 2 * (cm"!) R = CH 3 R = C 2 H 5 . R = n - C 3 H 7 R = n-• C4 H9 R = n - C 8 H 1 7 Assignment IR R IR R IR R IR IR R 1298sh 1370sh 1424w 1370sh 1425w 1356vw 1422vw 1370sh 1330sh 1330sh 1333w 1290w 1290sh 1300sh 1278sh v a s P W v 6 12S8s 1218w 1230w 1267s 1235vw . 1210w 1270s 1207w. 1184w 1162sh 1197s 1260s 1200vw 1180w 1258s 1227vw 1220vw v s P 0 2 ( A 1 ) v 1 1168s .1128sh 1169m 1158s 1128sh ' 1158s 1080s 1165m 1079w 1157s 1089m 1175s 1150s 1050vw 1027m 1027sh 1028s 1053'vvw 1138sh 1018vw 1007vw 978m 1010s 1033m ' 1113sh 1047w 1027w 987w tfas P W V 8 928s 927w 926s 918s 920s 922s Continued on next page TABLE I I I (d) (cont.) Assignment R = CH. IR R C 2 H 5 IR R = n - C 3 H y IR R R = n - C . H n  4 9 IR R = n - C 8 H 1 7 IR R v s P F 2 ( A l ) v 2 v SnC„ as 2 v SnC-s 2 P0 2 bend (A^v-j rocking ( B 1 ) v y rocking (B2)v g, PF 2 bend ( A 1 ) v 4 888s 8S8vw 808s 887m 886s 890m 885s 883s 740vw 725vw 603m 540m 506m 485s 350m 535s 725w 700m 670vw 560w 510sh 493s 350w 500s 812m (738sh l725w (694s I670sh 638m 600vw 536m 517m 490s 350w 600ws 506w 36 5w 884s 7.72vw 752vw |723w ^693s 644w 533m 501w 484s 882s 851w 830w 770w <737sh V20m (693s '670vw 64 5w 584w 532m 502w 487s 350w 88 7vw 534s * for abbreviations see Table I I I (c) - 39 -One exception appears to be the compound (n-C^H^)2Sn(P02p2)2 where the symmetric s t re tching frequency i s at 600 c m - 1 . The observation of only one s t re tching frequency i n each of the IR and Raman spectra indicates the dimethyl t in group i s l i n e a r . 4. Tetraphenylarsonium and Tetraphenylphosphonium difluorophosphates. As for the d i a l k y l t i n bis-difluorophosphates, the IR spectra of tetraphenylarsonium and tetraphenylphosphonium difluorophosphates were compared with those of the,corresponding chlor ides and assignments were made to the absorption frequencies due to the P0 2 F 2~ a n i ° n * ^ n e r e s u l t s are given i n Table IIICe). As can be seen from th i s tab le , the two d i f l u o r o -phosphates gave almost i d e n t i c a l spectra. Furthermore, there appears to be no s p l i t t i n g of the PF2 s t re tching frequency into symmetric and asymmetric modes and the value of v p p i s the lowest of a l l difluorophosphates s tudied. i 5. Rela t ion Between v p Q and v p p i n XYP(0)F Molecules. The v a r i a t i o n of the frequency of the PO s t re tching v i b r a t i o n , (V PQ) i n approximately tetrahedral XYZP=0 molecules as a resu l t o f changing the chemical nature of the substituents on phosphorus has been a subject of considerable d i scuss ion . The va r i a t i on has been ascribed to changes i n the m a s s a n d changes i n the electronegat ivi t ies(29,61-65) q ^ ^ g s u | 3 S t ^ t u e n t groups. B e l l et a l . J established-a l i n e a r re la t ionsh ip between vPQ and the sum of the group e lec t ronega t iv i t i e s of the substituents d i r e c t l y attached to the phosphorus atom, the higher frequencies always being associated with higher e l ec t ronega t i v i t i e s . A poss ib le explanation for th i s re la t ionsh ip i s - 40 -* TABLE I I I (e)* VIBRATIONAL SPECTRA OF TETRAPHENYLARSONIUM AND TETRAPHENYLPHOSPHONIUM DIFLUOROPHOSPHATES (cm - 1 ) 4 A s P 0 2 F 2 (C 6H 5) 4 P P ° 2 F 2 Assignment IR R IR R 1328s 1316sh 1328s •:-1316sh. 1190w ;-1148sh 1190m 1170m 1190w 1148sh 1192m 1170m v s P 0 2 ( A 1 ) v 1 1136s 1136m 1135s 1134m 1083s 1086m 1110s 1101s 1023m 1028s 1028w 1031s 998s lOlOvvs 995s 1004vvs V 992sh 992sh 980vw ..' 980vw 964vw 964vw 954w 952w 918w 922vw 885w 88 5w V a s P W v 8 | 850m • 852m 852vw v s P F 2 ( A l ) v 2 J 801s 746s 800m 800s 760sh 753s 800w Continued on next page - 41 -TABLE I I I (e) (cont.) Assignment ( C 6 H 5 ) 4 A s P 0 2 F 2 IR F ( C 6 H 5 ) 4 P P 0 2 F 2 IR R P0 2 bend ( A ^ V j rocking (B^)v^ rocking ( B 2 ) v g PF 2 bend (Aj )v 4 728sh 690s 687sh 500sh 495s 478s 460 350sh 340s 673s 615m 351m 276w 256m 237vs 728sh 725s 690s 675sh 530s 500sh 495s 450s 350sh 340s 683m 615m 312w 253m for abbreviat ions, see Table I I I (c) - 42 -that an increase i n the e lec t ronegat iv i ty of the groups bonded to phosphorus resu l t s i n a lowering i n energy of i t s 3d o rb i t a l s and an increase i n the strength of the IT bond between phosphorus and oxygen. I f , i n tetrahedral molecules containing both P-0 and P-F bonds, there i s s ign i f i can t ir bonding (17) between phosphorus and f luor ine (as has been suggested elsewhere ) , then the P-F s t re tching frequencies would be expected to increase with increasing e lec t ronega t iv i ty of the groups bonded to phosphorus and a cor re la t ion between v..- and v n „ should e x i s t . A search of ,the l i t e r a tu r e y ie lded infrared PO PF ' data for some for ty " te t rahedral" molecules o f the type XYP(0)F (note that X and Y may also be f l u o r i n e ) . Table IV l i s t s the compounds together with VpQ and Vpp values. Where more than one f luor ine atom i s present, Vpp i s ca lcula ted from Lehmann's "average r u l e " , ^ a ^ : v D n = - [ v + ( x - l ) v ] (11) PF x L s as . J Examination of Figure 3 shows that a cor re la t ion does indeed ex is t between v p o and Vpp i n molecules of t h i s type. Also included on the graph (shown as f u l l c i r c l e s ) are points for the p 0 2 F 2 ~ i o n i n t J i e ^C6H5-^4A s + a n c l ^ C6H5-*4 P + s a l t s . Data for the other difluorophosphates l i e outside the cor re la t ion shown, the values of Vp^ for these compounds are s i m i l a r to those of the (C ( .H 5 ) 4 As + and ( C ^ H 5 ) 4 P + sa l t s but the values of v p p are greater. I t i s concluded that due to the large s i ze of these cat ions , cation-anion interact ions are weak and the difluorophosphate ions i n these sa l t s are e s sen t i a l l y "free" unperturbed ions and so f i t the co r re l a t ion established for the "free" tetrahedral molecules. For the other difluorophosphates, the cation-anion in terac t ions which may be described as a p o l a r i z a t i o n of the anion by the cat ion affects the v n _ values more than i t does the v„„ values. PF PO - 43 -TABLE IV -v p o AND v p F FOR XYP(0)F MOLECULES (cm-1) No. Molecule X XYP(0)F Y VPO V PF References 1. F F 1418 954 66 2. F C l . 1358 922 67,68,69 3. F Br 1340-60 914 67,68,69 4. C l C l 1331 894 67,70 5. Br Br 1303 880 67,70 6. C l Br 1319 890 69,70,71 7. C H 3 F 1334 909 72 8. C1CH2 F 1332 923 72 9. C 2 H 5 . . F 1328 893 72 10. n - C 4 H g F 1333 893 72 11. n - C 6 H l l F ... 4 1332 883 . 72 12. (C6H5)CH=CH F 1321 900 72- ' 13. C 6 H 5 .. F 1335 890 72 14. C 1 C 6 H 4 - F 1337 890 72 15. C H 3 C 6 H 4 F . 1330 890 72 16. CCH 3 ) 2 CHC 6 H 4 F 1336 891 72 17. CH 3 CH 3 1250 808 72 18. n - C 4 H 9 n " C 4 H 9 1260 819 72 19. CH 3 C 6 H 5 1258 807 72 Continued on next page - 44 -TABLE IV (cont.) Molecule XYP(Q)F No. X Y VP0 VPF References 20. C 6 H 5 C 6 H 5 1256 835 72 21. BrCH 2CH 20 CH 3 1289 849 73 22. (CH 3) 2CH0 C H 3 1280 840 73,74,75 23. C 2 H 5 CH 30 1295 858 • 76 24. (CH 3) 2CH0 C 2 H 5 1290 850 77 25. (CH 3) 2CH (CH3) 2CH0 1258 848 73 26. C 6 H 5 n-C.H-0 4 9 1287 845 78 27. CH 3 C 0 H C S 1250 828 73 28. CH 3 (CH 3 ) 2 N , 1269 815 73 29. CH30 CH 30 1308 864 76 30. C 2 H 5 0 C 2 H 5 ° 1278 845 76 31. (CH 3) 2CH0 (CH 3) 2CH0 1299 865 73 32. (CH 3 ) 2 N (CH 3 ) 2 N 1255 847 73,79,80 33. OP(0)F 2 F 1405 946. 33 34. (CF 3 ) 2 C(CN)0 F 1408 965 12 35. (CF 3 ) 2 C(N 3 )0 F 1389 940 12 36. (CF„) 0C(SCN)0 F . 1399 968 12 (CF 3) 2C(NCS)0 F 760 800 " 840 880 920 960 vpp (cm- 1) 1000 As discussed i n the fol lowing sec t ion , the value of V p p for d i f l u o r o -phosphate i s re la ted to the po l a r i z ing power of the cat ion. 6. Rela t ion Between v n t ? and P o l a r i z i n g Power of the Cat ion. r r The p o l a r i z i n g power of a cat ion may be defined as • V 5 z 1 - 2 7 P =; \ C7T77J-) ( H a ) where z i s the charge of the ca t ion , r* the ion ic r a d i i , and I the i o n i z a -f81) t i o n p o t e n t i a l . The f i r s t factor i s the i o n i c po ten t ia l and the second, f 82) the sh ie ld ing e f f ic iency for the ca t ion ic species. The ca l cu la t ion of P for various metal cations i s shown i n Table V, together with the average PF s t re tching frequencies of the corresponding difluorophosphates, and a graph of Vpp against p o l a r i z i n g power, P, i s given i n Figure 4. The r e l a t i o n for the a l k a l i metal sa l t s i s almost l inea r and i t levels of f with an increasing scat ter of the points for compounds of metals with high po l a r i z ing powers. S imi la r var ia t ions i n s t re tching frequencies with cation p o l a r i z i n g power have been found i n f luorosulfates and n i t ra tes Two points are worth mentioning. Data for the . ( C ^ F y ^ A s * and (C^H^) 4 P + s a l t s are included i n the Figure, by assuming the (C^I-y^As* and {C^H^)ions to have p o l a r i z i n g powers of zero. The points f i t the r e l a t i o n very we l l supporting the conclusion reached i n the previous sect ion that cation-anion in t e rac t ion i n these sa l t s i s smal l . Further, data for the d i a l k y l t i n bis-difluorophosphates are also included, using the p o l a r i z i n g 2 power of Sn + ca t ion . Again the data f i t the re la t ionsh ip we l l ind ica t ing +2 2 that the R„Sn groups are behaving as Sn + cations with regard to t h e i r - 47 -TABLE V CALCULATION OF THE CATION POLARIZING POWERS No. Cation I (vol t ) r CX) 5 Z 1 . 2 7 r V 2 I Z r P v * PF (cm"1) 1. L i + . 5.363 0.60 1.20 1.67 2.00 915 2. Na + 5.120 0.95 1.00 1.05 1.05 856 3. K + 4.318 1.33 1.00 0.752 0.752 841 .4 . Rb + 4.159 1.48 0.988 0.676 0.668 837 5. Cs + 3.870 1.69 0.994 0.592 0.589 831 6. D +2 Be 18.12 0.31 1.19 6.45 7.68 963 7. M g + 2 14.96 0.65 0.999 3.07 3.07 918 8. Ca +2 11.82 0.99 1.03 2.02 2.08 915 9. S r + 2 10.98 1.13 1.03 1.77 1.82 904 10. B a + 2 9.950 1.35 1.04 1.48 1.54 882, 886** 11. M n + 2 15.70 0.80 0.858 2.50 2.15 908 12. F e + 2 16.18 0.75 0.860 2.67 2.30 915 13. C o + 2 17.30 0.72 0.821 2.78 2.28 917t, 913tt 14. N i + 2 18.15 0.69 0.799 2.90 2.32 914 15. C u + 2 20.34 0.72 0.698 2.78 1.94 934 16. Z n + 2 17.89 0.74 0.783 2.70 2.11 904 17. C d + 2 16.84 0.97 0.727 2.06 1.50 898 18. S n + 2 14.50 0.93 0.862 2.15 1.85 902*** 19. pb+2 14.96 1.21 0.732 1.65 1.21 897 20. I n + 3 27.90 0.81 0.803 3.70 2.97 936ttt 21. F e + 3 30.64 0.64 0.822 4.69 3.86 935 22. A l + 3 28.31 0.50 1.01 6.00 6.06 945ttt average PF stretching, frequencies of the corresponding difluorophosphates observed i n IR spectrum Raman spectrum Continued on next page - 48 -TABLE V (cont.) *** VPF d i - n - p r o p y l t i n bis-difluorophosphate t blue cobalt ( I I ) difluorophosphate t t pink cobalt ( I I ) difluorophosphate (13) t t t from Reference p in te rac t ion with the PC^*^ 2 r o u P s ' I t i s poss ible to give a chemical in te rpre ta t ion of the v „ „ vs P Pr re la t ionsh ip i n terms of dn-pTr bonding between the 3d o rb i t a l s on phosphorus and the 2p o rb i t a l s on f l uo r ine . As the p o l a r i z i n g power of the cat ion increases electron density i s withdrawn from the phosphorus atom increasing i t s e f fec t ive pos i t i ve charge and decreasing the energy of i t s d o r b i t a l s . This r e su l t s i n a greater Tr-bond strength between phosphorus and f luo r ine . I t does not, however, explain the lack of a s i m i l a r r e l a t i o n between Vp^ and P. , The explanations for the trends i n v„n and v n T , values described FO PF i n th i s sect ion and i n the previous sect ion have ignored mass effects and the effects of coupling between these v ibra t ions and other v ibra t ions i n - - • the molecules. While t h i s i s an obvious weakness i n the treatment, i t i s f e l t that iT-bonding i n both P-0 and P-F bonds i s important and the in terpre ta-t i on of the trends i n terms of var ia t ions i n the degree of TT bonding i s at least q u a l i t a t i v e l y correc t . 7. Comments on the Linear Relat ionship Between P-0 Stretching Force Constants and Bond Order Proposed by G i l l e s p i e and Robinson. Using Cruickshank's Tr-bond theory which assumed that only the 3 d x 2 - y 2 and 3dz 2 o rb i t a l s on phosphorus are ava i lab le for TT bonding i n tetrahedral molecules, that i s , a maximum Tr-bond order of two i s achieved, f43) G i l l e s p i e and Robinson assumed that the Tr-bond order of the P-0 bonds i n the ions PO^ and PO^F^" are 0.5 and 0.67 respec t ive ly . Using these values and the corresponding P-0 s t re tching force constants derived from IR data, together with the force constant for a P-0 s ingle bond, they established - 5 1 -a l i n e a r re la t ionsh ip between these three sets of values. In view of the discussions i n the previous sections of th i s Chapter, i t i s f e l t that there are weaknesses i n the re la t ionsh ip described by G i l l e s p i e and Robinson which should be pointed out. F i r s t l y , the assumption of 0.67 TT bond order i n PO^F 2 - car r ies with i t the assumption of zero Tr-bonding i n the P-F bond, contrary to the conclusion above that IT bonding between phosphorus and f luor ine i s important. Secondly, the assignment of f i n i t e ir-bond orders i n anions, independent of the cat ion involved i s not consistent with the present work and the work of other f83-85) authors ~. which showed a de f in i t e dependence of s t re tching frequencies (and therefore Tt-bond orders) on the p o l a r i z i n g power of the ca t ion . - 52 -CHAPTER IV MOSSBAUER SPECTRA OF DIALKYLTIN BIS-DIFLUOROPHOSPHATES A. Introduction . Mossbauer Spectroscopy presents a convenient too l for the inves t iga t ion of bonding i n t i n compounds. Two parameters, isomer sh i f t 6 and quadrupole s p l i t t i n g A g ive , respec t ive ly , a measure of the s electron density on t i n and the asymmetry i n the e lec t ron ic enviroment around t i n . This Chapter reports for the f i r s t time, Mossbauer data on difluorophosphate (451 de r iva t ives . The parameters are compared to those obtained by other workers on analogous f luorosulfa te compounds i n an attempt to obtain information on the structure and bonding propert ies of the difluorophosphate group. - 53 -B. Experimental (87) The Mossbauer spectrometer has been described previously The powdered absorbers (approximately 0.5 mm i n thickness) were contained i n brass c e l l s with Mylar windows and Teflon spacers. Measurements were made with the absorber at 80° or 295°K and. the B a 1 1 9 m S n 0 3 source at room temperature. The v e l o c i t y scale was ca l ib ra ted with an NBS standard sodium ni t ropruss ide absorber. A l l isomer sh i f t values are reported r e l a t i v e to an Sn0 2 absorber at 80°K. The r e l a t i v e p rec i s ion of the Mossbauer parameters i s ± 0.03 mm/sec. C. Results and Discussion - . • — The Mossbauer data, isomer s h i f t , 6, quadrupole s p l i t t i n g , A, and the l i n e widths at half-peak-height , and T2, for R 2Sn(P0 2F2)2 where R = C H 3 , C 2 H 5 , n C 3 H 7 , n C 4 H g and n C g H 1 7 are l i s t e d i n Table V I . As can be seen, the isomer sh i f t s f a l l i n the range ~ 1 . 5 0 to 1.70 mm/sec. with reference to Sn02 and quadrupole s p l i t t i n g s from 5.0 to 5.1 mm/sec. Before discussing the Mossbauer parameters, i t i s convenient to discuss the probable structures of the compounds under considerat ion. A l l of the compounds are considered to have a structure analogous to that of ( C H 3 ) 2 S n ( S 0 3 F ) 2 , recent ly determined by Lerbscher and T r o t t e r ^ 8 8 ^ . In t h i s compound, the Sn atoms are bonded covalent ly by trans CH 3 groups. The l i nea r Sn(CH 3 ) 2 groups are bridged, each by four dif ferent SOjF" groups, g iv ing a two-dimensional layer type l a t t i c e . The compounds, R 2 S n ( P 0 2 F 2 ) 2 , are bel ieved to have an analogous structure owing to the fol lowing observations: ( i ) only one Sn-C s t re tching frequency i s observed i n the - 54 -IR spectra consistent with a l i nea r C-Sn-C arrangement, ( i i ) the v i b r a t i o n a l spectra indica te the presence of only one type of PO^F^~ group, and the P-F s t re tching frequencies are i n the range observed for compounds with strong metal-oxygen in t e rac t ion (see Chapter I I I ) , ( i i i ) the compounds are almost non-conducting i n HPO2F2 ( Chapter V) suggesting polymeric s t ructures , and, (iv) the Mossbauer data are s i m i l a r to those observed for ( C H ^ ^ S n ^ O ^ F ^ , where the large quadrupole s p l i t t i n g s indicate two a l k y l groups bonded to t i n i n a trans configurat ion . , Mossbauer parameters of some dimethyl t in der ivat ives of monobasic (44) sul fonic acids have been obtained previously . They are given i n Table VI together with those of d imethyl t in bis-difluorophosphate. The compounds are arranged i n order of decreasing 6 value and i f i t i s assumed that t h i s i s the order of r e l a t i v e base strengths of the anions involved, i . e . SO^F" < S 0 3 C F 3 " <S0 3 C1" < F 0 2 F 2 " < S 0 3 C H 3 " , then the resu l t s may be explained as fo l lows . The f luorosulfa te der iva t ive i s the most i o n i c or polar of the compounds studied and i n i t the electron density around t i n most c lose ly approximates sp hybr id iza t ion (bonds to the two CH 3 groups). As the base strength of the surrounding anions increases to that of SO^CHj - , the s electron density diffuses more in to the Sn-0 bonds and so decreases around t i n . Note too the trend i n the A values. Considering the Sn(CH )_ part 3 ^ of the molecule as e s sen t i a l l y covalent and the Sn-0 bonds more po la r , the asymmetry i n the e lec t ron ic environment around t i n decreases as the anion becomes more bas ic and th i s i s re f lec ted i n the decreasing A values. Care must be taken not to accept the above order of base strengths too l i t e r a l l y , however, since the accuracy of the Mossbauer parameters i s only ± 0.03. A general conclusion that the base strength of the P02F2 * o n * s - 55 -TABLE VI MOSSBAUER PARAMETERS OF R 2Sn ( P O ^ ) 2 Compound Temperature (°K) 6 (mm/sec) A (mm/sec) F l F2 ( C H 3 ) 2 S n ( P 0 2 F 2 ) 2 80 1.533 5.132 0.898 0.921 • 295 1.486 4.956 - ' -( C 2 H 5 ) 2 S n ( P 0 2 F 2 ) 2 80 1.669 4.906 1.096 1.094 ( n - C 3 H 7 ) 2 S n ( P 0 2 F 2 ) 2 80 1.636 5.000 0.967 0.954 ( n - C 4 H 9 ) 2 S n ( P 0 2 F 2 ) 2 80 1.674 5.027 1.045 1.061 ( n - C 8 H 1 7 ) 2 S n ( P 0 2 F 2 ) 2 80 "1.620 4.793 1.009 1. 262 TABLE VII MOSSBAUER PARAMETERS OF (CH^nCSO^) 2 AND (CH 3)2Sn(P0 2F 2) 2 AT LIQUID NITROGEN TEMPERATURE Compound (mm/sec) A (mm/sec) Reference ( C H 3 ) 2 S n ( S 0 3 F ) 2 ( C H 3 ) 2 S n ( S 0 3 C F 3 ) 2 ( C H 3 ) 2 S n ( S 0 3 C l ) 2 ( C H 3 ) 2 S n ( P 0 2 F 2 ) 2 (CH 3) 2Sn(S0 3CH 3) 2 1.82 1.79 1.75 1.53 1.52 5.54 5.51 5.20 5.13 5.05 44 44 44 this work 44 " 56 comparable to that of CH^SO^" ion and measurably greater than the base strength of the SO^F" ion does seem v a l i d . Moreover, th i s conclusion i s (24) consistent with the work of Barr, G i l l e s p i e and Robinson J who demonstrated, by e l e c t r i c a l conduct ivi ty studies i n s u l f u r i c acid so lu t ions , that f luoro-s u l f u r i c ac id i s a stronger ac id than e i ther methylsulfonic acid or d i f l u o r o -phosphoric a c i d . Mossbauer parameters of some other d i a l k y l t i n b i s - f luorosu l fa tes ( 4 5 ) have been obtained r ecen t ly v ' . Figure 5 compares graphica l ly these values with those of the corresponding difluorophosphates obtained i n th i s work. Note that both 6 and A are cons is tent ly higher i n a l l cases for the f luorosulfa te compounds compared to the difluorophosphate compounds., consistent with the weaker base strength of SO^F - compared to P 0 2 p 2 ~ as explained above. , • The effect of increasing the a l k y l chain length on the values of the parameters i s s i m i l a r i n both the f luorosulfa te and difluorophosphate de r iva t ives . In p a r t i c u l a r , the effect of going from -CH^ to -Ch^CH^ ( i . e . replacing one H on the CH^ bonded to t i n by a CH^ group), causes an increase i n 6 and a-decrease i n A. The increase i n 6 i s understood i n terms of the greater electron donor power of CF^CH^ r e l a t i v e to that of CH^, as re f lec ted i n the pKa values of CH^OOH ( 4 . 7 5 ) , and CH3CH2COOH ( 4 . 8 8 ) / 9 0 - 1 . There seems no obvious explanation for the decrease i n A unless you assume that the increase i n donor power of the a l k y l group feeds more electron density in to the Sn-0 bonds and so makes the e lec t ron ic environment around Sn more symmetrical. The effect of further increasing the a l k y l chain length i s less s i gn i f i c an t as the carbon atoms effected are not bonded d i r e c t l y to the t i n atom. - 57 -FIGURE 5 COMPARISON OF MOSSBAUER PARAMETERS OF DIALKYLTIN BIS-DIFLUOROPHOSPHATES AND FLUOROSULFATES 2.0 1.9 o m 6 o 1.8 1.7 1.6 1.5 5.6 t> 6 o 5.4 5.2 5.0 -/ ,,o- . S 0 3 F - /' / / / -* o" -• p-- / / * P 0 2 F 2 d CH 3 C 2»5 n - C 3 H 7 1 n - C 4 H 9 L -S0 3F -Q \ \ xcr"'" -~-C -P ° 2 F 2 - 58 -CHAPTER V SOLUTIONS IN DIFLUOROPHOSPHORIC ACID A. Introduction Reed studied the e l e c t r i c a l conduct iv i t ies of solut ions of (25*) a l k a l i metal difluorophosphates i n HPO2F2 . The solut ions are rather weakly conducting compared to those of the corresponding f luorosulfates i n (911 (92) HSO^F^ and hydrogen sulfates i n ^ S O ^ . Moreover, the a l k a l i metal difluorophosphates were found to give conduct iv i t ies which, at the same value of concentration, decreased i n the order L i >Na >K >Rb >Cs. This order was interpreted i n terms of incomplete d i s soc ia t ion of the a l k a l i metal difluorophosphates i n HPO2F2 wi th the degree of d i s soc i a t i on decreasing with increasing cat ion s i z e . Further evidence supporting th i s was the - 59 -observation that tetraphenylarsonium chlor ide gave s i g n i f i c a n t l y higher conduct iv i ty values than the a l k a l i metal s a l t s . In the present work, we have extended the study of sa l t s with large cations to include (C^H^) 4AsPC>2F2 ( C , H r ) , C C l and (C-H_).NC1. o o o ^ b 4 Reed also found that Ba ( ^ 0 ^ 2 ) 2 gave more conducting solut ions than Ca(PC>2F2)2> suggesting that i n the a lka l i ne earth series the r e l a t i v e order of d i s soc i a t i on i s opposite to that observed for the a l k a l i metal se r i e s . The series of a lka l ine earth metal difluorophosphates i s completed here with the study of solut ions of be ry l l ium, magnesium and strontium difluorophosphates. Nuclear magnetic resonance and density studies on solut ions of a l k a l i metal difluorophosphates i n HPO2F2 were also reported by Reed and an extension of this, work i s described i n th i s chapter. B. Experimental . 1 . E l e c t r i c a l Conduct iv i ty . The design of the conduct ivi ty c e l l has been given p r e v i o u s l y d » 2 ^ ) The electrodes were plated with platinum black as described by Jones and f931 B i l l i n g e r , and the c e l l constants of two c e l l s used i n th i s work, deter-f941 mined using aqueous potassium chlor ide so lu t ion , were approximately 6 and 21 c m - 1 . Before each measurement, the c e l l was cleaned with chromic ac id and r insed with deionized water, and the tubes holding the electrodes were successively cleaned with n i t r i c ac id , water, saturated potassium hydroxide so lu t ion and f i n a l l y deionized water. The procedure used for measuring the conduct ivi ty of difluorophosphoric acid solut ions has been 60 -(25 911 described previously ' . Measurements were made i n an o i l thermostat (951 at 25 ± 0.01°C with a p rec i s ion a .c . bridge using a 2,000 c/s o s c i l l a t o r ^ , or with a Model 221B Wayne-Kerr universa l bridge. Electrode po l a r i za t i on effects were not serious as per iodic checks of so lu t ion resistances at 4,000 c/s were found to be i n sa t i s fac tory agreement with those obtained at 2,000 c / s . 2. Nuclear Magnetic Resonance (nmr). The procedure for preparing samples for nmr studies was the same (251 19 as that described by Reed •. The F chemical s h i f t s , r e l a t i ve to the pure solvent , were measured with a Varian HA 100 high-resolu t ion spectrometer, operating at 94.07 Mc/s , using the field-frequency lock provided with the instrument. Proton chemical sh i f t s were measured with a Varian T-60 high reso lu t ion spectrometer operating at 60 Mc/s . 3. Density . " Density measurements were made at 25 ± 0.01°C using a 10-ml s p e c i f i c g rav i ty bo t t l e ca l ib ra ted with mercury. C. Results and Discussion 1. E l e c t r i c a l Conduct iv i ty . The resu l t s of the e l e c t r i c a l conduct ivi ty studies on solut ions of some difluorophosphates and chlorides i n HPO2F2, at 25°C, are given i n Table VI I I and presented graphica l ly i n Figure 6. Throughout th i s Chapter 61 -TABLE VIII SPECIFIC CONDUCTIVITIES OF DIFLUOROPHOSPHATES AND CHLORIDES IN HP0 2 F 2 AT 25°C ioV 10 4K 10 4K 10^m (ohm - 1 cm"1) 102m (ohm - 1 cm"1) 102m (ohm~1cm-(n-C 4 H 9 ) 2 S n ( P 0 2 F 2 ) 2 ( C 2 H 5 ) 2 S n ( P 0 2 F 2 ) 2 ( C H 3 ) 2 S n ( P 0 2 F 2 ) 2 0.000 2.512 0.000 2.502 0.000 2.464 1.042 2.707 .1.596 2.796 1.151 2.603 2.208 2.888 3.012 3.016 2.810 2.967 3.436 3.082 4.671 3.266 4.681 3.275 4.636 3.262 6.023 3.454 6.538 3.620 5.937 3.407 7.402 3.638 9.168 4.034 6.710 3.486 9.267 3.869 11.13 4.617 7.531 3.577 10.99 4.078 13.13 5.917 8.124 3.640 12.47 4.236 16.31 6.610 14.05 4.477 (n-C 3 H 7 ) 2 S n ( P 0 2 F 2 ) 2 15.47 4.678 (C 6 H 5 ) 4 A s P 0 2 F 2 17.50 4.874 0.000 2.433 18.47 5.027 0.000 2.477 1.174 2.645 20.17 5.302 0.6174 3.625 2.738 2.882 21.77 5.512 1.366 5.391 4.449 3.126 22.73 5.601 2.149 7.452 5.702 3.271 24.42 5.892 2.864 9.396 7.142 3.427 3.548 11.27 8.749 3.571 4.542 14.13 L0.42 3.706 5.117 15.74 L1.98 3.971 5.152 15.97 Continued on next page _ 62 _ TABLE VII I (cont.) 1 0 4 K 1 0 4 K . 104< 102m (ohm"1 cm"1) 102m (ohm - 1 cm"1) 102m (ohm - 1 cm' B e ( P 0 2 F 2 ) 2 (C 2 H 5 ) 4 NC1 •Mg(P0 2 F 2 ) 2 0.000 2.413 0.000 2.652 0.000 2.427 1.601 2.518 2.095 4,967 5.012 4.917 2.866 2.695 4.496 7.259. 10.29 7.372 4.027 3.133 7.326 12.58 15.73 9.439 5.277 3.663 11.58 20.61 19.80 10.78 6.146 4.432 14.75 27.25 24.94 12.32 6.893 4.877 18.26 35.11 30.68 13.87 7.711 5.379 21.08 41.85 37.11 15.51 23.50 47.80 41.75 16.63 (C 6 H 5 ) 3 CC1 • 27.57 57.75 Sr (P0_F„) 9 31.31 67.80 0.000 2.521 34.39 75.94 0.000 2.432 0.3846 2.822 38.96 87.78 2.836 4.812 0.9877 3.936 5.810 7.686 2.048 7.201 9.834 11.23 2.810 8.432 13.26 14.02 3.643 10.54 18.04 17.32 4.614 13.80 22.18 20.33 5.194 14.67 26.08 22.82 5.996 17.13 29.79 25.56 6.888 19.14 FIGURE 6 SPECIFIC CONDUCTIVITIES OF DIFLUOROPHOSPHATES AND CHLORIDES IN H P O ^ . AT 25°C 10 K(ohm-1cm"1) - 64 -concentrations are given i n units of moles of solute per kilogram of solvent (m)• Included i n Figure 6 are the resu l t s obtained by Reed for C a ( P 0 2 F 2 ) 2 , B a ( P 0 2 F 2 ) 2 , and ( C ^ ) 4 A s C l ^ 2 S j . Of the compounds studied here, M g ( P 0 2 F 2 ) 2 , S r ( P 0 2 F 2 ) 2 and R 2 S n ( P 0 2 F 2 ) 2 , (with the exception of ( n - C g H 1 7 ) 2 S n ( P 0 2 F 2 ) 2 ) , are soluble i n HP0 2 F 2 over the concentration range s tudied. The compounds (C 6 H, . ) 4 PP0 2 F 2 and ( n - C g H ^ l j S n ^ O ^ ) 2 are e s sen t i a l l y inso lub le while B e ( P 0 2 F 2 ) 2 and (C^Hj-^AsPO,^ d issolve slowly and only to an extent of approximately 8 x 10~,2m. Of a l l the d i f luorophosphates s tudied, (C^H^I^AsPO^,, gave the most highly conducting solut ions i n difluorophosphoric ac id . Moreover, other sa l t s containing large ca t ions , such as ( C ^ H ^ ^ C d and ( C ^ H ^ ^ N C l , also gave more h ighly conducting solut ions i n HP0 2 F 2 than did solut ions of metal difluorophosphates. I t i s unreasonable to assume that these high conduct iv i t ies are due to the (C^H^-I^As*, (CgH,.) 3 C + and (C 2H r .") 4N + cations having greater m o b i l i t i e s than the a lka l i ne earth metal cations for example, and hence the greater conduct iv i t ies of the former group of compounds must be due to a larger degree of d i s s o c i a t i o n ' - ^ ' 1 as suggested e a r l i e r by Reed. (251 Ionic chlorides have been found to undergo complete s o l v o l y s i s to the corresponding difluorophosphates and HCl according to equation 9. After measuring the e l e c t r i c a l conduct iv i t ies of solut ions of some chlorides i n HP0 2 F 2 and comparing these values with those of the. corresponding difluorophosphates, Reed concluded that the HCl produced has very l i t t l e effect on the measured conduct ivi ty at low concentrations, but at high concentrations the HCl causes a change i n the properties of the so lu t ion and affects the conduct iv i t ies measurably. In the present study on (C^H 5 ) 4 AsP0 2 F 2 and (C^H^^AsCl i t was found that the difluorophosphate - 65 -gave s l i g h t l y higher conduct iv i t ies than the ch lo r ide . As can be seen from Figure 6, the conduct iv i t ies of the a lka l ine earth metal difluorophosphates i n HPO2F2 decrease i n the order Ba >Sr >Ca >Mg >Be, confirming the e a r l i e r conclusion, based on studies of Ba (PC>2F2)2 and C a(P02p2)2 so lu t ions , that i n the a lka l ine earth se r i e s , the degree of d i s soc i a t i on increases as the cat ion s i ze increases. A s i m i l a r trend ( 9 7 1 has been found i n the ch lorosu l fu r ic acid system . The resu l t s may be explained as fo l lows . I f we assume that HPO2F2 has a r e l a t i v e l y low d i e l e c t r i c constant and ion-pa i r ing is important over the concentration range studied, then the d i s soc ia t ion constant, K, for the formation of free ions i s determined by the i on i za t ion constant for the formation of i on -pa i r s , K i , and the d i s soc i a t i on constant, Kd, for the d i s soc ia t ion of ion-pairs in to free ions, MX K i ( M + . . . . . X - ) : , +• . ' solv K i = _ . [ (M+. . . X-)] [MX] ( 1 2 ) Of Kd solv M . + X" • solv solv K d " [(M + X-)] t l 3 ) Therefore, MX + M + , + X" , —<- solv solv KiKd (14) Thus the r e l a t i v e order of d i s soc ia t ion i s dependent on both Ki and Kd, which i n turn depend on, respec t ive ly , the degree'of covalency of the s a l t s tudied and the so lva t ion energies of the ions produced. The value of K i would be expected to increase with increasing cat ion s i ze while Kd would be expected to decrease with increasing cat ion s i z e . As discussed i n - 66 -Chapter I I I the a l k a l i metal sa l t s are e s sen t i a l l y i o n i c so l ids and hence i t i s not unreasonable to assume that for th i s series values of K i are large.and of the same order of magnitude for a l l the compounds. The r e l a t i v e values of K are then determined by the va r i a t i on in Kd. For the a lka l ine earth difluorophosphates, however, covalent bonding i s more important and here the effect of the v a r i a t i o n i n K i values outweighs the effect of the v a r i a t i o n i n Kd. A l l four d i a l k y l t i n bis-difluorophosphates are almost non-conducting when dissolved i n H P O 2 F 2 , suggesting that they are not i o n i c sa l t s and are probably covalent compounds with polymeric structures as described i n Chapter IV. . . . 2. Nuclear Magnetic Resonance. 1 19 The H and F chemical sh i f t s r e l a t i v e to an external reference of H P O 2 F 2 for solut ions of some difluorophosphates i n H P O 2 F 2 are summarized i n Table IX and i n Figures 7 and 8. Since the app l ica t ion of bulk diamagnet s u s c e p t i b i l i t y c o r r e c t i o n s s i m p l y s h i f t the curves shown i n Figures 7 and 8 to s l i g h t l y higher f i e l d they do not a l t e r the nature of the resul ts (25) obtained . Thus, the uncorrected curves w i l l be used i n the d iscuss ion . The four d i a l k y l t i n bis-difluorophosphates gave roughly the same resu l t s 19 and are represented by a s ingle curve. The F resonances appeared as doublets due to coupling with phosphorus and chemical sh i f t s were measured form the centre of the doublets. Consider f i r s t the *H nmr r e s u l t s . The r e l a t i v e sh i f t to high f i e l d caused by d i s so lu t i on of the a lka l ine earth metal difluorophosphates i s i n the order Ba >Sr >Ca >Mg >Be compared to the order L i >Na >K >Rb >Cs - 67 -TABLE IX 19 ' H AND F CHEMICAL SHIFTS FOR SOLUTIONS OF DIFLUOROPHOSPHATES IN H P O ^ Chemical Sh i f t (ppm) Chemical Shi f t (ppm) 1,, 19„* 1,, 19^* 10 ra H F 10 m H F (n -C 4 H g ) 2 Sn(P0 2 F 2 ) 2 B a ( P 0 2 F 2 ) 2 6.038 -0.09633 -0.07707 14.77 +0.03867 -0.2687 10.81 -0.1175 -0.1300 24.43 +0.07000 -0.4643 26,91 -0.3483 -0.3210 32.53 +0.08867 -0.5411 35.38 -0.4483 * * - 51.69 +0.1008 -0.9424 ( n C 3 H 7 ) 2 S n ( P 0 2 F 2 ) 2 . S r ( P 0 2 F 2 ) 2 -8.345 -0.06833 -0.1018 13.71 +0.01767 -0.1850 16.48 -0.2300 ' -0.2009 20.49 +0.02167 -0.2600 23.96 -0.3150 -0.2666 26.19 +0.02917 -0.3221 28.45 -0.3342 -0.3779 32.28 +0.03833 -0.3779 ( C 2 H 5 ) 2 S n ( P 0 2 F 2 ) 2 . C a ( P 0 2 F 2 ) 2 3.003 -0.04000 -0.02658 9.612 -0.02833 -0.1026 7.307 -0.07416 -0.1100 22.79 -0.06583 -0.1929 24.47 -0.3142 -0.2615 36.67 -0.08083 -0.2915 35.25 -0.4452 -0.4146 52.22 -0.1030 -0.3747 Continued on next page - 68 -TABLE IX (cont.) Chemical Shi f t (ppm) ' , ' Chemical Shi f t (ppm) 102m . i H 1 9 F * 102m ' .  lH " 1 9 F * ( C H 3 ) 2 S n ( P 0 2 F 2 ) 2 M g ( P 0 2 F 2 ) 2 11.23 -0.1617 -0.1690 11.69 -0.03833 -0 . 08770 19.33 -0.2588 -0.1866 .21.47 -0.06583 -0 . 1488 25.66 -0.3317 -0.2697 27.20 -0.08250 -0 . 1781 30.67 -0.3517 -0.3264 41.75 -0.08417 -0 . 2397 ( C 6 H 5 ) 4 A s P 0 2 F 2 44.19 -0.09867 -0 . 2567 5.407 -0.03983 -0.1164 B e ( P 0 2 F 2 ) 2 11.45 -0.1000 -0.2551 6.631 -0.09333 -o. 00584' 18.45 -0.1430 ** 12.00 -0.1312 -0 . 01807 20.29 -0.1525 ** 20.78 -0.1963 -0 . 04093 * average values ** p r e c i p i t a t i o n occurred - 69 -FIGURE 7 *H NMR CHEMICAL SHIFTS FOR SOME DIFLUOROPHOSPHATES IN HP0 2F' 2 0.10 r - ——' O 0.05 0.00 -0.40 ffl,0 •. ffl O B a ( P 0 2 F 2 ) 2 0Sr(PO2F2)2 © C a ( P 0 2 F 2 ) 2 | M g ( P 0 2 F 2 ) 2 B e ( P 0 2 F 2 ) 2 (C 6H 5 ) 4 A s P 0 2 F 2 • ( n - C 4 H 9 ) 2 S n ( P 0 2 F 2 ) 2 0 (n-C 3H 7 ) 2 Sn(PO 2 F 2 ) 2 S(C 2H 5 ) 2 S n ( P 0 2 F 2 ) 2  Fl fflCCH5)2Sn(P02F2)2 10 20 30 40 50 60 - 70 _ 19 6 PL, LU FIGURE 8 NMR CHEMICAL SHIFTS FOR SOME DIFLU0R0PH0SPHATES IN H P O ^ B e ( P 0 2 F 2 ) 2 -0.25 -0.45 -0.50r-3 M g ( P 0 2 F 2 ) 2 e • s ffl ,© o C a ( P 0 2 F 2 ) 2 ( n - C 4 H 9 ) 2 S n ( P 0 2 F 2 ) 2 ( n - C 3 H 7 ) 2 S n ( P 0 2 F 2 ) 2 ( C 2 H 5 ) 2 S n ( P 0 2 F 2 ) 2 ( C H 3 ) 2 S n ( P 0 2 F 2 ) 2 S r ( P 0 2 F 2 ) 2 B a ( P 0 2 F 2 ) 2 ( C 6 H 5 ) 4 A s P 0 2 F 2 - 71 -found by Reed for the a l k a l i metal s e r i e s . The order i n both series p a r a l l e l s the degree of d i s soc ia t ion as found by the conduct ivi ty s tudies . I t i s we l l known^ 9 8 100) ^hat ca t ions , by v i r tue of t he i r so lva t ion , cause . a break-up of the hydrogen bonded structure of protonic solvents r e su l t i ng i n a sh i f t to high f i e l d of the *H resonance. Anions, on the other hand, cause a downfield s h i f t as a r e su l t of so lva t ion v i a hydrogen bonding to solvent m o l e c u l e s ( ^ a ) _ j £ w e a s s u m e that i n HPO2F2 the upf i e ld s h i f t caused by cat ion so lva t ion outweighs the downfield sh i f t caused by anion so lva t ion then the most d issocia ted sa l t s w i l l give the largest upf i e ld s h i f t as i s observed. I t i s in te res t ing to note that {C^U^)^ksPO^F2 causes a large downfield s h i f t . In t h i s case the large (C^H^-I^As4" cat ion would be expected to be only weakly solvated and the downfield sh i f t caused by so lva t ion of p 02 F 2~ ^ o n s outweighs the upf i e ld s h i f t caused by so lva t ion of the ( C 6 H 5 ) 4 A s + ca t ion . The solutes R 2 S n ( P Q 2 F 2 ) 2 cause a downfield s h i f t i n the *H resonance. These compounds are e s sen t i a l ly non-electrolytes i n HPO2F2 and are presumably present as neutral molecules solvated v i a hydrogen bonds to solvent molecules r e su l t i ng i n the observed downfield s h i f t i n the *H resonance. In contrast to the ''"H nmr r e s u l t s , the r e l a t i v e sh i f t to high 19 f i e l d i n the F resonance caused by d i s so lu t ion of the a lka l ine earth metal and a l k a l i metal difluorophosphates p a r a l l e l the r e l a t i v e i o n i c r a d i i of the cations involved and not the degree of d i s soc i a t ion of the s a l t s . Shif ts to high f i e l d for the a l k a l i metal ser ies are i n the order (25") L i >Na >K >Rb >Cs and for the a lka l ine earth metal ser ies Be >Mg >Ca >Sr >Ba. This trend i s explained i f i t i s assumed that the effect of increasing the p o l a r i z i n g power o f the cat ion i s to decrease the P-F*bond - 72 -length i n the surrounding molecules of solvent or ^^2^2" * o n s ^ n t n e c a s e 19 of neutral molecules or ion-pairs) with a concomitant sh i f t of the F resonance to high f i e l d . A decrease i n the P-F bond length with increasing po la r i z ing power of the cat ion i s consistent with the trends i n P-F stretching frequencies reported i n Chapter I I I for metal difluorophosphates. It should also be pointed out that , consistent with the above, (C£rL_.)4AsPC>2F2 which has a very weakly p o l a r i z i n g cat ion produces the 19 largest downfield sh i f t i n the F resonance. 3. Dens i t ies . Densit ies of some difluorophosphoric ac id solut ions have been measured i n the present work and the resul ts are given i n Table X. Included i n t h i s Table are values of the apparent molar volume of the solute , <j>, and of the ca t ion , $ + , calculated as described previously(25,101) _ The value of <j>+ for Mg(P02p2)2 appears to be s i g n i f i c a n t l y smaller than those for Sr(PC>2F2)2 and Ba(PC>2F2)2 and probably r e f l ec t s a greater +2 +2 +2 degree of so lva t ion of Mg r e l a t i v e to Sr and Ba . This agrees with the idea that smaller cations tend to have larger so lva t ion n u m b e r s , i n (25) the a l k a l i metal se r i es , Reed J found no s i g n i f i c a n t differences i n the <f>+ values. I t i s in te res t ing to note that the values of <f>+ for the two d i a l k y l t i n bis-difluorophosphates s tudied, are pos i t i ve and large , ind ica t ing rather weak so lva t ion of the species i n so lu t ion . - 73 -TABLE X DENSITIES AND THE MOLAR VOLUMES OF SOLUTIONS IN HP0 2 F 2 AT 25°C 102m d 2 5 (g m l - 1 ) <Ji (mis) Mean cf> (mis) Mean <j>+ (mis) M g C P ° 2 F 2 ) 2 0.000 1.5826(10.0001) 10.96 1.5939 (±0.0004) 101 99(±3) -29 (±3) 30.63 1.6173(±0.0004) 96 S r C P Q 2 F 2 ) 2 11.18 1.6042(±0.0004) 105 106 (±1) -22(±1) 29.'79* 1,6384(±0.0001) 106 . . . . Ba ( P Q 2 F 2 ) 2 * * 23.05 1.6406(±0.0008) 110 108 (±2) -20(±2) 29.95 1.6599(±0.0005) 106 ( C 2 H 5 ) 2 S n ( P 0 2 F 2 ) 2 12.00 1.5986(***) 185 184(±2) +56(±2) 20.88 1.6112(***) 182 . 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