1979 1251Preparation and Characterization of Tetrafluorophosphonium(v) Hexa-decafluorotriantimonate(v), [ PF4] [SbsF16], the Adduct Arsenic Penta-fluoride-Trifluorophosphine (1 /I ), and the Redox Reactions of Trifluoro-phosphine with Arsenic, Antimony, and Bismuth PentafluorideBy Grace S. H. Chen and Jack Passmore,' Department of Chemistry, University of New Brunswick, P.O. Box4400, Fredericton, New Brunswick, Canada E3B 5A3Phosphorus pentafluoride and SbF5 form a 1 : 3 adduct the vibrational spectrum of which is consistent with theformulation [PF,][Sb,F,,]. The 1 : 1 donor-acceptor adduct formed at -130 "C between PF, and AsF, hasbeen characterized by Raman spectroscopy. The adduct is in equilibrium with its dissociated components between-130 and -78 'C; however, a redox reaction occurs at 2-78 "C.Phosphorus trifluoride also undergoes redoxreactions with antimony and bismuth pentafluorides.COMPLEXES between phosphorus trifluoride and transi-tion metals are well known; l-3 PF, also forms weakcomplexes with strong main-group Lewis acids, e.g.PF,-BH, , 2v PF,*B( BF,), , and PF,*AlCI,.Various two-co-ordinate phosphorus cations havebeen reported.'-1° Thomas et aZ.ll have prepared salts of[P(NMe,),]+ and [PCl(NMe,)]+, but attempts to identify[PF(NMe,)]+ and [PF,]+ were not successful. However,other workers l2 reported that PF,*AsF, and PF,*SbF,were stable at -78 "C and room temperature, respect-ively, and these adducts were formulated as [PF,]-[AsF6] and [PF,] [SbF,] , with cation-anion inter-action, on the basis of their vibrational spectra.Thelatter systems have been reinvestigated and the resultsare presented below.In an attempt to determine the nature of the solidproduced in the reaction of PF, with SbF,, PI;, wasfound to react with SbF, to form a 1 : 3 adduct formu-lated as [PF,] [Sb,F16]. Phosphorus pentafluoride'sability to act as a fluoride-ion acceptor is well known; 1,however, since its discovery by Thorpe l4 in 1875 therehave been no reports of it acting as a Lewis base. Apreliminary account of part of this work has beenreported .15EXPERIMENTALReagents and Apparatus .-Unless otherwise stated,apparatus and materials and techniques were as given inrefs. 16-18, and starting materials purified and character-ized by routine methods.Raman spectra were obtainedusing a Spex Ramalab RS2 spectrometer with the green5 145 A exciting line and a slit width of 4 cm-l, unless other-wise specified. Low-temperature Raman spectra wererecorded using a variable-temperature assembly. Theinterior of the non-silvered Dewar was first cooled to a tleast - 100 "C, and then the sample, at - 196 "C, was quicklyintroduced.Reaction of PF, with AsF, at -78 "C.-Phosphorus tri-fluoride and AsF, (50 cm3, 2 atm) were condensed sepa-rately into a Kel-F vessel, and warmed to -78 "C. In 30min the vapour pressure was 1 atm in 60 cm3, and thevolatiIes were PF,, PF,, and AsF,. In a series of separateexperiments, double the amounts of PF, and AsF, were1 mmHgw13.6 x 9.8 Pa.f Throughout this paper: 1 atm = 101 325 Pa;allowed to react for 7 inin, 1, 6.75, and 9.25 h, a t -78 "C.Volatiles a t -78 "C were removed and the AsF, residueidentified. The reduction of AsF, to AsF, was found to be70, 80, 94, and loo%, respectively, based on the weight ofPF, added and AsF, produced.The reaction was also followed by lQF n.m.r.spectroscopyin SO,F, and S0,ClF solvents. A redox reaction wasobserved t o proceed a t -60 to -55 OC, after 0.5 h, andincreased with time.Gas-phase Reaction between PF, and AsF, at RoomTemperature.-Phosphorus trifluoride (0.17 atm in thevolume of the line and i.r. cell) was condensed and isolatedin the side arm of the i.r. cell. An equal amount of AsF, wasintroduced into the cell, and its spectrum taken.The valveseparating the AsF, and PF, was opened. The spectrum ofthe reaction products was immediately taken and showedthe presence of PF,, AsF,, PF,, and AsF,. The conversionwas ca. 50, 95, and 100% in 7 min, I , and 3 h, respectivelybased on calibration of the i.r. absorption intensity of PF, atknown concentrations.Preparation of Raman Samples of PF,-AsF,.-Thesamples were prepared by condensing pre-weighed stoicheio-metric amounts of PF, and AsF, into sample tubes whichwere flame-sealed under vacuum. The components weremixed by warming gradually from - 196 to - 78 "C (briefly),with mixing. The sample was then stored a t -196 "C.The compound was a solid at - 130 "C and a solid-liquidmixture a t -78 "C.Reaction of PF, with SbF,.-In a typical reaction, PF,(0.26 g) was condensed onto SbF, ( 1 g) in a Kel-F tube.In1 h the vapour pressure had decreased from 760 t o 645mmHg at room temperature in a volume of 63 cm3. Thecompounds PF, and PF, were present in the gas phaseand the relative amount of the latter increased with time.After 2 d the volatiles (700 mmHg) were removed bypumping for 10 min. The white solid left had a weightdecrease of 6% relative to that of SbF, added, and onlyhad a broad intense i.r. absorption at 500-700 cm-' in theSb-F stretching region.Reaction between PF, and SbF, in S02F2 at -45 "C.-Phosphorus trifluoride ( 1.68 g) was condensed onto amixture of SbF, (4.87 g) and S02F2 (9.24 g), then themixture was kept a t -45 "C for 3 d. The volatiles at-45 "C (PF,, SO,F,) were distilled off leaving a white pastewhich had a weight increase of 0.18 g relative to SbF, addedand had some vapour pressure at room temperature.Thevolatiles contained PF, and S02F2, but no PF,. The i.r.spectrum of the white paste had a weak absorption a1252 J.C.S. Dalton1 160 cm-l, indicating formation of [PF,][Sb,F,,] (seebelow), and a very intense peak in the Sb-F stretchingregion.Reaction between PF, and SbF, in WF,.-Phosphorustrifluoride (0.25 g) was condensed onto a mixture of SbF,(4.87 g) and WF, (7.89 g) and stirred at room temperature.The volatile contained PF, and WF,, but no PF, after 18 h.The sample was evacuated to constant weight. A Ramanspectrum of the white solid residue (1.13 g correspondingt o SbF, : SbF, = 1.0 : 1.0) showed peaks in the Ramancorresponding to SbF,.SbF, (form A) of Gillespie et al.19v20A ttempted Identification of PF,-SbF, by Raman Spectro-scopy.-Phosphorus trifluoride (0.06 g) was condensed ontoSbF, (0.63 g) in the form of a thin film on the wall of thesample tube, and flame-sealed.The Raman spectrumtaken at room temperature, 10 min after the sample wasremoved from liquid N a , showed peaks attributable t o[PF,][Sb3F16] a small amount of SbF,, and probablySbF,(SbF,),.1a-23Vapour Pressure of [PF,] [Sb,F,,] .-The vapour pressureabove [PF,] [Sb,F,,] was measured using a Validyne APlOpressure gauge with 0-100 and 0-1 000 mmHg trans-ducers calibrated for direct read out from a model CDtransducer indicator.Pressures were obtained as thetemperature was increased. The data for 0-23 "C werefitted by least squares yielding equation ( 1 ) . The measuredlog,,(P/mmHg) = 11.4 - (2 740/T) (1)pressures were, for example, 139 f 2, 24 f 1, and 16 & 1mmHg a t 23, 0.1, and -23 "C, respectively. The experi-ment was repeated and the same results obtained withinexperimental error.Attempted Preparations of Adducts PF,-BiF,, -NbF,,and -TaF,, and AsF,-SbF, and -BiF,.-The systemsPF,-BiF,, -NbF,, -TaF,, AsF,-SbF,, and AsF,-BiF, weresimilarly investigated. The vapour pressure was constantduring the reaction, and the products were found t o be thesame as the starting materials.I I I J1500 1200 900 600 300 50S / c m - lFIGURE 1 Raman spectra of solid PF,*AsF, a t ca.-162 "CA Raman spectrum of PF, : SbF, = 3.4 : 1, taken a t-135 "C after standing a t -45 "C for 8 d, showed peaksattributed t o the starting material, as did that of PF,:SbF, : S0,F2 = 2.5 : 3 : 1 held a t -45 "C for 8 d.Reaction of PF, with BiF,.-In a typical experiment,PF, (1.07 g) was condensed onto BiF, (1.55 g) in a Monelvessel. The vapour pressure remained constant and after3 d the volatiles contained only PF,. The reaction vesselwas then heated for 5 d a t 80 "C with the upper part of thevessel cooled with air. The gaseous product containedPF, and PF,. Volatiles were removed leaving BiF, (1.37 g) .Preparation of [PF,] [Sb,F,,].--In a typical experimentPF, (3.62 g, 28.74 mmol) was condensed onto SbF, (4.65 g,21.45 mmol) in a Pyrex glass bulb (60 cm3).The mixturewas repeatedly thermally cycled between room temperatureand -196 "C. After 2.5 cl the excess of PF, was removedby pumping, with the reactor held at -78 "C. The weightof solid (5.62 g) corresponded to the formation of an adductwith mol ratio PF, : SbF, = 1 : 2.8, assuming the weightincrease was the amount of PF, consumed. The com-pounds PF, and SbF, were separated by fractional distill-ation in a closed system recovering 6.70 mmol of PF, and21.70 mmol of SbF,. The experiment was repeated tentimes with various ratios of starting materials (PF, alwaysin excess) including one carried out in a Parr bomb (50cm3; SbF,, 5.38 g ; PF,, 38.44 g). Adducts of PF, : SbF,ratio cu. 1 : 3 were obtained in all cases.Preparation of Ranian Samples of PF,-SbF,.-A Ramansample of [PF,][Sb,F,,] was prepared in situ as above.The weight of the sample corresponded to PF, : SbF, =1 : 2.9.The Raman spectrum was recorded on a Cary model82 spectrometer.The polarization measurements were obtained from asample of ratio PF, : SbF, = 1 : 8 which was prepared bycondensing the stoicheiometric amounts into a sample tube.A homogeneous liquid sample was obtained by gentleheating. A sample of SOF,*3SbF5 was similarly prepared,and Raman spectra obtained using a Spex 1400 spectro-meter.RESULTS AND DISCUSSIONRaman Spectrum of PF,*AsF5.-The Raman spectrumof solid PF,*AsF, obtained a t ca. -162 "C is given inFigure 1. The assignments given in Table 1 are madeby comparison with the vibrational spectra of PF3,24PF,*BH,,25 [Ni(PF,),] ,26 SC1F,,27d29 S(CF,)F,,27 SeC1F5,30TeC1F5,3l M~CN-ASF,,~~ and other L-AsF, 33 (L =POF,, COF,, SOF,, or SO,F,) adducts.The local symmetry of the P-AsF, moiety in PF,*AsF,is considered to be C4v.27p32933 For the purpose ofcomparison and convenience, we follow the descriptiongiven for SeClF, by Christe et aZ.,O for the P*AsF,moiety.The peaks at 605, 663, 736, and 763 cm-l ar1979 1253readily assigned as v,, v2, vl, and va, respectively, ofP-AsF,, by comparison with the Raman spectra ofrelated species. vg and vl0 are assigned at 381 and 291cm-l; however, the assignments could be reversed as1027100395376373672866360551938136533829 1263TABLE 1Raman spectrum (cm-l) a of PF,*AsF,Species AssignmentsPF, asym str.PF, sym str.AsF, asym str.AsF' str.?AsF, sym str.AsF, sym out-of-phasePF, sym def.F'AsF, wagAsF, sym out-of-planePF, asym def.AsF, sym in-plane def.AsF, asym in-plane def.?str.def.208 (16)) PF, rock155 ASP str.PAsF, wag191 (12)Relative intensities (0-100) are given in parentheses.b Vibrations in parentheses are those referred to P-AsF,moiety (C4t, symmetry) only.discussed by Byler and S h r i ~ e r , , ~ vSym(PF3) (A,) andV,,~,(PF,) ( E ) are assigned at 953 and 1003, 1027 cm-l.The splitting of the E mode may be attributed to thelower symmetry in the solid state.The increase ofv(PF,) in the adduct, relative to that in PF, 24 (vsym at892, vasym a t 840 cm-l), is consistent with an increase ofthe positive character on phosphorus accompanyinglone-pair donation from phosphorus to arsenic and anincrease in P-F bond strength.I t is possible that inPF,*AsF, there is no back donation of electron densityaccounting for the higher V,~~,V,,~~-(PF,) stretchingfrequencies relative to those observed for simple transi-tion-metal PF, complexes.1*26The symmetric P-Ni stretch in the stable [Ni(PF,),] 26occurs at 195 cm-l; therefore it is reasonable to assignv4 to the weaker P-As stretch in the labile PF,*AsF5adduct as the band a t 155 cm-l. The medium intensityof this peak also supports the assignments, since otherpeaks in the region observed for related species are weak.The Raman spectrum is therefore consistent with thedonor-acceptor formulation PF,*AsF, rather than[PF,] [AsF,] .I2Behaviour of PF,*AsF, above -130 "C.-The Ramanspectrum of a sample of ratio PF,: AsF, = 1 : 1 at-130 "C showed peaks attributable t o the adduct only;however, a t -112 and -78 "C the individual com-pounds PF, and AsF5 were present, the dissociationincreasing with increase in temperature. A sample ofratio PF, : AsF, = 1 : 3 was kept at -78 "C for 3 h.The Raman spectrum showed a mixture of PF,, AsF,,AsF,, and the adduct PF,*AsF,. Therefore, the follow-ing equilibrium takes place between -130 and -78 "C,and a redox reaction occurred at 2 -78 "C, the extentof reaction increasing with time :between -130and - 7 8 O CPF, + AsF, PF,*AsF, +> -78°C -PF, + AsF,It appears that AsF, is a poorer acceptor toward PF,than either B,H6 or AlCl,!FIGURE 2 Infrared spectrum of [PF,][Sb,FIJ1 1 1 1 1 1 1 1 1 1 1 1 11200 800 400 0? / cm"FIGURE 3 Raman spectrum of [PF,][Sb,F,,] solidThe Raman results showing a redox reaction betweenPI?, and AsF, at 3 -78 "C are supported by the 19Fn.m.r.experiments, the large-scale reactions, and thereaction carried out between PF, and AsF, in an i.r.cell at room temperature. It was previously reported l2that PF,*AsF, was stable a t -78 "C, and dissociatedinto its constituents at room temperature. The redoxreaction involving components in their standard andother states is allowed (AH = -356 kJ mol-l at25 "C).34-38PF3-SbF, System.-The salt [PF,] [Sb,FI6] wasobserved in the Raman spectrum of a sample of PF3-SbF, obtained 10 min after removal from liquid N,,indicating that a redox reaction occurs at room temper-ature or below1254Raman spectra of PF,-SbF, and PF,-SbF,-SO,l~,taken at -135 "C after being held at -45 "C showedpeaks attributable to the starting materials.Thissuggests the absence of formatior of ' PF,*SbF, ' a t thistemperature and is further evidence for the lack of anextensive redox reaction under these conditions. Evi-dence for the reported [PF2][SbF6] l2 was notobtained. However, a redox reaction occurs betweenPF,(g) and SbF,(l) at room temperature. The redoxreaction yielding SbF,(s) and PF,(g) is allowed 35936938-40(AH = -207 kJ mol-1 at 25 "C).The reaction is,J.C.S. Daltonparticularly at lower temperatures where the experi-mental points were not fitted by equation (1). The lowvalue of AH is consistent with the observation thatexcess of PF, was needed for the reaction to go to com-pletion. We were unable to obtain evidence for [PF41-[SbF,] or [PF,] [Sb,F,,].V'ibrational Spectra of [PF,][Sb,F,,] .-The i.r. andRainan spectra of the title compound are shown inFigures 2 and 3 and a Raman spectrum of a sample ofratio PF, : SbF, = 1 : 8 is shown in Figure 4. The assign-ments are given in Table 2.~II____ L---L -.-_Ipl---_l-r -L--I-I,_1.1200 800 400Rainaii spectra of a liquid sample of ratio PV, : SbF, = 1 : S$/crn-I1600FIGURE 4however, complicated by the further reaction of theproducts with SbF,(l) to form [PF4][Sb,F,$ and SbF,-( SbF,),.19-23Preparation of [PF,] [Sb,F16] .-This salt is preparedquantitatively from SbF, and excess of PF, at roomtemperature according to equation (2).The white solidhas a vapour pressure of PF, of 139 & 2 mmHg at 23 "C.pF5(g) + :(sbF5)n(1) [PF41[Sb3F16j (s) (2)The compounds PF5 and SbF, were quantitativelyrecovered by fractional distillation. The value forAH (dissociation) of 52 & 3 kJ mol-1 can be obtainedfrom equation (1) and presumably is associated withequations (3), (4), (5), and (6) and others that aresimilar.4[pF41 [Sb3F161 - pF5(g) + 3[pF41 LSb4F2115[pF41 [Sb4F211 - pF5(g) + 4[PF41 iSb51'2$(3)('12[SbnF5, + 11 - ---t[SbnFsn + 11 - - [Sbn - 1FS(n - 1) + 11- + [ S h 4 1F5(n + 1) +1]- (5)[Sbn - 1F5(n - 1) + 11 - + 6 (SbF5) n (1) (6)It is noted that the Raman spectrum of PF,-SSbF,(Figure 4, Table 2) is not dissimilar to a superposition of[PF4][Sb3Fl,] and (SbF5)n(l).Inhomogeneity and solidi-fication of SbF, at 8.3 "C also complicate the systemAssignments of [PF4]+ are made by comparison withthe isoelectronic tetrahedral SiF,,42*.43 [NF4]+,44 CF 4, 42945and [BF4]-42>44 of T d symmetry. The strong i.r.TABLE 2Vibrational spectra (mi-1) of [PF,] [Sb,F1,]=1:8 Tentative[l'Fa] [Sb3FI6] PF, : SbF,7 - 71 170vwRaman I.r.e Raman assignments160vw} 1 160s,br 1 165 [dp] v3(F2) PF asym str.908s 908 [p] vl(Ai) PF sym str.800vvw II7 :33sh717 [PI670s 670 [PI6 5 7 ~ s 657 [PI609m 608 [dpl709 (sh) 707 (sh)703vs 690s,br 701 [p] s,+ str.Sb-F-Sb bridging str.5 2 0 - 520-380vw.br 450n1,br 380360vwi:: !!:) Sb-F bendings and def.lattice vibration342vw 342 [p]29711-1 294 [dPl281w271w24Om188vw125w70w2 2 2w 220 [dPlIt is possible that the compound might well have lost PF,on sample preparation and the i.r. may be that of [PFJ-[Sb,F,,].xSbF,. a Polarization measurement uncertain1979 1255absorption at 1 160 cm-1 is in the P-F stretching region Notwithstanding the difficulty of assigning the [Sb,-which is assigned as v3(F2). The weak doublet at 1 170 peaks, the vibrational evidence suggests thatand 1 160 cm-l (broad, singlet, depolarized in the liquid [PE,]+ is essentially ionic, and therefore PF, acts as aphase) in the Raman supports this assignment.The fluoride-ion donor toward SbF,. Various other lessintense, well polarized, Raman peak at 908 cm-l in the acidic fluorophosphonium(v) salts 46759-62 have alsoP-F stretching region is assigned as vI(A1). The P-I; been prepared. I t is noted that SOF, containing formallystretching frequencies were similar in intensity, but a t SvI is a better donor than PF, containing Pv. ThisTABLE 3Fundamental vibrational modes (cm-1) of tetrahedral [PF4]+, [NF,]', SiF,, CF,, and [BF,]-Tetrahedral[PFd 'species Ref. Activity v1 (-41) v2 (El v3 (FA VP (F2)1170vw1 160vw1 160s44 Raman 849s 450m 1185w 613s1153w"Fd"613s 1.r. 1162sSiF, 42,43 Raman 800s 268w 1 OlOW 390w1.r. 1031vs 391sCF4 42,45 Raman 908.5s 435m 1234w 631.2mThis work Raman 908s1.r.1.r.1.r.[BFaI - 42,44 Raman 778mhigher energy, than the corresponding bands of SiF,, andare similar to those of [NF,]+ (see Table 3).The P-F stretching frequency is the highest so faro b s e r ~ e d .~ ~ - ~ ~ , ~ ~ The isoelectronic [SOF,] + containsvery strong S-0 and S-F and exists as adiscrete ion in solid [SOF,![ASF,].~ The ionic formul-ation [PI!,]+ is therefore favoured although we cannotrule out the possibility of some weak anion-cationbridging.I t is expected that v2 and v4 of [PF4]+ would occur atca. 300 and cn. 400 cm-l, at slightly higher frequenciesthan those of the isoelectronic SiF442743 which areobserved at 268 and 390 cm-l (Table 3). After a carefulcomparison of both the position and relative intensitiesof vibrational spectra of the [Sb,F,,]- anions in saltscontaining the counter ions [IF6]+,49 [ReF6]+,50 and[SOF3]+ (see Table 4) we were unable to assign v2 and v,with any confidence.TABLE 4liaman spectrum (cm-") a of [SOF,] !Sb,F1,]1 5d2w 7 12111 531w 235ni1 265w 702s 505mw 2 19wI 06'4w 690m 436vw 186vw1 0 5 7 ~ 676niw 384mw 140w9 0 t h 662vs 290mw 126vw85Ovw 607m 266w 1 12vwItalicized bands are assignable t o [SOF,]+ (see ref.47).I t is possible that [SOF,][Sb,F,,] may be the average com-position of the sample and the spectrum may be a super-imposition of an equilibrium mixtureof [SOF,][SbF,], [Sb,F;,]-,[Sb,Fltj]-, [Sb,F,J-, etc.Raman bands at <700 cm-l are similar, but not identi-cal to, those of [Sb,F,,]- 18951-55 and may be due to thetrans-bridged [Sb,F,,] - isomer, previously found in[Br,][Sb,F,,].56957 It is also possible that [PF,][Sb,F,,]has a tetrameric structure similar to that of BiF,-(SbF5),,16758 however, with very weak interaction be-tween + and the cis-bridged [Sb,F,,]-.1241.2s 631.3m1063s 529s358w 1065vw 535wmay in part be due to the stability of the [SOFJk ionarising from the x-bond energy associated with the SObond.,7p48We thank Drs.H. L. Paige and R. Kaiser for leF n.ni.r.spectra, Dr. N. Bartlett for his suggestion in 1973 that[PF,][Sb,FI6] may have a cis-bridged ring structure, andthe National Research Council of Canada for support.[8/86l Receiucd, 9th May, 19781REFERENCEST.Kruck, Atig~w. Chem. Intevnat. Edn., 1967, 6, 53.J . F. Nixon, Adv. Inovg. Chem. Hadiochem., 1970, 13, 363.0. Stelzer, Topics Phosphovus Chem., 1977, 9, 1.R. W. Parry and T. C. Bissot, J . Amev. Chem. Soc., 1956, 78,B. G. DeBocr, A. Zalkin, and D. H. Templeton, Inovg. Chem.,E. R. Alton, R. G. Montemayor, and R. \\'. Parry, Inovg.I<. Dimroth, Topics Cuvrcnt Cfirm., 1973, 38, I .S. Fleming, R1. K. Lupton, and K. Jekot, Inovg. ChcnL., 1973,0. J..Scherer and G. Schnabl, Chem. Bey., 1976, 109, 2996.lo E. Niecke and R. Kroher, Angew. Chem. Ititernat. Edn.,1976, 15, 694".l1 M. G. Thomas, C. W. Schultz, and R. \V. Parry, Inovg. Chewi.,1977, 16, 994 and refs. therein.l2 R. D. W. Kernmitt, V. M. McRae, K. I). Pcacock, and I . L.Wilson, .I. Inovg. Nuclear Chem., 1969, 31, 3674.1, M. Webster, Chrm. Rev., 1966, 66, 87.l4 T. E. Thorpc, Chem. News, 1875, 32, 232.G. S. H. Chcn and J. Passmore, J.C.S. C h ~ i i i . C'omn., 1973,l 6 G. S . H. Chen, J . Passmore, P. Taylor, and '1'. K. Whidden,1524.1969, 8, 836.Chem., 1074, 13, 2267.11, 2534.559.Inorg. Nzdeav Chem. Lcttevs, 1976, 12, 943.J . Passmore and P . Taylor, J.C.S. Dalton, 1976, 804.l8 C . Lau and J . Passmore, J.C.S. Dalton, 1973, 2528.l9 T. Birchall, I-'. A. W. Dean, B. Della Vallc, and R. J .2o R. J . Gillespie, D. R. Slim, and J. E. Vekris, J.C.S. Dalton,21 0. Ruff and W. Plato, Bcr., 1904, 37, 674.22 A. J. Edwards and D. R. Slim, J.C.S. Chem. Comm., 1974,178.23 A. J . Hewitt, J . H. Holloway, and B. Frlec, J . FluorineChem., 1975, 5, 169.24 H. S. Gutowsky and A. D. Liehr, J . Chcm. Phys., 1952, 20,1652.Gillespie, Canad. J . Chem.. 1973, 51, 667.1977, 971 and refs. therein