Indian Journal of ChemistryVol. 16A, August 1978, pp. 695-698

On the Nature of Tetrachloro(halosulphato)antimony(V)R. C. PAUL, R. C. KUMAR & RAJENDAR DEV VEIDdA

Department of Chemistry, Panjab University, Chandigarh 160014

Received 19 January 1978; accepted 25 Marcb 1978

Antimony(V) chloride forms SbCI.(S03X) on reaction with HS03X (X = F and CI). Themolecular weight and the vibrational spectrum of SbCI.(S03F) indicate it to be a dimer havingbridging fluorosulphate groups. SbCI.(S03X) forms 1: 1 adducts with pyridine, acetonitrileand tetramethylurea. Halosulphate groups behave as monodentate Ilgands in these adductsand antimony is hexa-coordinated. Tetramethylurea coordinates through its nitrogen atom.Ao values of SbCI.(S03X) in nitrobenzene and nitromethane indicate them to be strong Lewisacids.

INcontinuation of our studies on metal halosul-phatesv+, we now report the preparation andcharacterization of the compounds SbCI4(SOsX),

where X = Cl or F. SbCI,(SOsF) has been mentionedby Hayek et al.f' but lacks characterization. Thecompounds SbCI4(SOaX) have been characterizedfrom the vibrational spectral data. These halo-sulpha tes dissolve in organic solvents, such as acetone,nitro methane, nitrobenzene and acetonitrile. Semi-quantitatively, the Lewis acid strength of SbCI4(SOaX)has been determined by computing their Ao valuesin nitrobenzene and nitro methane. The donor-acceptor complexes of nitrogen bases with SbCI4-(SOaX) have also been prepared and characterized.

Materials and MethodsFluorosulphuric acid was prepared and purified

as described-. Chlorosulphuric acid (BDH) W2S usedas such. Antimony(V) chloride, pyridine, aceto-nitrile, tetramethylurea, acetone, nitromethane andother organic solvents were distilled before use.

Preparation of compounds - SbCI4(SOsF) andSbCI4(SOaCl) were prepared by heating a knownweight of antimony(V) chloride with excess offluorosulphuric acid and chlorosulphuric acid at 140°and 60° respectively. The heating was continuedtill the evolution of hydrogen halide ceased. Inboth the cases, white crystalline solids settled downon cooling from a clear solution. The white com-pounds were filtered under dry N2 atmosphere,washed with sulphuryl chloride followed bycarbon tetrachloride and finally dried under highvacuum.

Preparation of donor-acceptor complexes - The com-plexes of SbC14(SOaX) with pyridine and acetonitrilewere prepared by adding a solution of the respectivebase (1: 1 mole ratio) in CCI, to a suspension ofSbCl,(SOaX) also in CCl4. The contents were stirredfor 2 hr. The adducts formed were filtered, washedwith CCl, and finally dried in vacuo. The adduct oftetrarnethylurea (TMU) with SbCI4(S03Cl) was pre-pared by mixing the two components in 1: 1 mole

ratio in chloroform. Though SbCI,(S03Cl) is in-soluble in chloroform, yet a clear solution wasobtained on mixing the two components. On addirgpetroleum ether to this clear solution a white crysta l-.line compound W2S obta ired, which was filtered arddried. SbCI4(SOaF).TMU wr s obtained by mixirgthe two components in 1: 1 mcle ratio in nitro-methane, when a white solid we s formed. Bothtetra methylurea and SbCI4(S03F) ere soluble innitromethane.

Physical measurements - The IR spectra of thecompounds were recorded as nujol and hexachloro-butadiene mulls in silver chloride and polytheneplates, using Perkin-Elmer 621 grating spectro-photometer. The Raman spectrum of SbCI4(S03F)was obtained at the Chemistry Department, Univer-sity of Nottingham, UK.

For the measurement of the equivalent conduc-tance, a standard solution of SbCI,(SOaX) wasprepared in the respective solved and the measuredvolume of this was further diluted to a desiredstrength. Its conductance W2S measured on Philipstype PR 9500 conductivity bridge usirg a cor.dr c-tivity cell of cell constat 0·4 c t 25°± 0·1°. Tocover the whole range of cor.centra tior.s a rumberof standard solutior.s were prepared. The mole-cular weight of SbCl,(S03F) in nitroberzere We8-

determired cryoscopica lly. All the manipule tior swere either carried out in a dIY box Or ur der dryN2 atmosphere.

Results and DiscussionThe analytical data of the compour ds are given

in Table 1. SbF4(S03F) and SbCI4(OR) He poly-meric and dimeric respectively 6,7. Polymerizationin metal fluorosulpha tes he s been reported to occurvia bridging fluorosulpha te groups. SbCJ4(~03F)is a white compound having a molecule r weightof 726 in nitrobenzene. Its dimeric na ture ca nbe thought of to occur via bridgirg fluorosulpha tegroups as bidentate ligands and leading to hexa-coordina tion of antimony. The salient features

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PA UL el al.: TETRACHLORO(CHLORO/FLUORO-SULPHATO)ANTIMONY(V)

TABLE 1 - ANALYTICAL DATA OF TETR.\CHLORO(HALOSULPHATO) ..••NTlMO~Y(V) AXD THEIR COORDI~ATIO~ COMPLEXESWITH NITROGEN DONORS·

Found (%)t Reqd (%J------------------------- ---------------------------

Sb S Cl F ~ Sb S Cl F N

SbCl.(S03F) 34·45 9·21 39·12 5·84 33'56 8·82 3'),14 5·23

SbCl.(S03F).Py 27·98 7·45 33·13 4·48 3·29 27'56 7·24 32·14 4·30 3·17

SbCi.(S03F).CH3CN 31-12 7-84 36·12 4·91 3·35 30·15 7·92 35·17 4·70 3·46

SbCl.(SO.F).TMU 26·68 6·94 29·91 4·11 25·43 6·68 29·66 3·96

SbCi.(S03C1) 33·46 7·98 46·80 32·10 8·43 46·80

SbCl.(SO.Ci).Py 27·81 7-80 38-42 3·21 26·57 6·98 38'73 3·05

SbCi.(S03Cl).CH3CN 27·99 7·82 42042 3-48 28·97 7·61 42·23 3·33

SbCl.(SO.Cl).TMU 24'28 6·94 35·14 5·86 24·58 6·46 35'84 5·65

*Antimony was determined volumetrically by titrating it against N/10 sodium thiosulphate using starch as indicator.Sulphur was determined gravimetrically as BaSO. and chlorine was determined by Volhards method. Fluorine was deter-mined gravimetrically as (C6H.).SnF.

tSatisfactory C, H analyses have been obtained for the coordination complexes with nitrogen donors.

TABLE 2 - VIBRATIONAL SPECTRA OF SbCI.(S03F) AND ITs COORDINATION COMPLEXES WITH PYRIDINE, ACETONITRILEAND TETRAMETHYLUREA

SbCl.(S03F)(A)

IR Raman

1365 13601160 1170

1067 1070

830 835

675 650555 550

545 540448 448400 406

340320

A.Py A.CH3CN AssignmentA.TMU

1435 1415 1400 vI(E)

1225 1230 1300

1150 1160 1140 v1(A1)

790 770 760 "2(.1,)

670 660 615 v.(A1)

580 620 585

550 560 545 v3(A,)

410 v6(E)

385 380

350 360 v(Sb-CI)

340 340

426(403) 16b

630(601) 6a

1605(1578) Sa

2915(2944) vCH3

2315(2266) vCN

1365(1371) vCH.

930(920) vCC

1760(1650) vC=O

1460(1500) vC-N

940(1000) va(N-C=O)

650(740) vb(N -C=O)

Values in parentheses are of pure ligands.

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INDIAN J. CHEM., VOL. 16A, AUGUST 1978

-of the vibrational spectra * with tentative assign-ments of SbCl4(SOsF) are given in Table 2. Influorosulphate ion, SOsF-(Cav symmetry), the'VS S02 (VI) appears at 1081 and the doubly degenerate Vas mode ('.14) at 1290 (ref. 8). The latter modewould be split up into two components when thefluorosulphate group behaves as covalent mono- orbi-dentate ligand, in which case the symmetry islowered to Cs. The vibrational frequencies givenin Table 2 rule out the possibility of SOaF- ion. Thevibrational spectrum of SbCI4(S03F) is quite com-parable to those of the compounds where the.fluorosulphate group has been found to behave asbidentate bridging ligand", thus it can be representedby structure (I).

The position of the various vS-O in the vibrationalspectrum of SbCI,(SOsCI) (Table 3) also indicatesthe bidentate character of the chlorosulphate group.However, in the absence of the reliable molecularweight data, it is difficult to visualize its extent ofpolymeriza tion.

The region of the three vS- 0 modest? in the IRspectra of the coordination complexes of SbCI4(S03X)with pyridine, acetonitrile and tetramethylurea(Tables 2 and 3) indicate that the halosulphategroups behave as monodentate ligands in thesecomplexes.

The dominant pure pyridine vibrations appearingat 403 (an out-of-plane ring deformation) and at601 and 1578 (in-plane ring deformations) showsignificant shifts to higher frequency regions+ inSbCI4(SOaX),py (Tables 2 and 3) indicating co-ordination of pyridine to antimony.

The vC=O in pure tetramethylurea appears at1650 (ref. 12). It shifts to 1760 and 1750 in SbCl4~Sq3F) ..TMU and SbCI4(S03CI).TMU respectively,indicating that tetramethylurea coordinates to anti-mony through one of its nitrogen atoms rather thanthrough oxygen atom. The formation of the nitro-gen-antimony bond increases the electron demand by-donor nitrogen atom and blocks the resonance bet-ween this nitrogen atom and the carbonyl group. Thisbrings about increased double bond character andhence an increase in vCO. As a result of theformation of the N-Sb bond this nitrogen to carbonbond acquires more single bond character, whichIS reflected in the Cv-N to lower frequency region{Tables 2 and 3). Similar observations have beenmade by Mizushima et al.13 when nitrogen of ureaacts as a donor atom.

*IR vmax h crrr '.

TABLE 3 - VIBRATIONAL SPECTRA OF SbCI,(S03CI) ANDITS COORDINATION COMPLEXES WITH PYRIDINE,

ACETONITRILE AND TETRAMETHYLUREA

SbCI. B.Py B.CH3CN B.TMU Assign-(SO.CI) ments

B

1380 1400 1410 1410 v.(E)1230 1300 1300 13001210

1165 1050 1063 1080 v,tAl)

570 650 650 630 v.(E)570 590 570

550 550 555 550 v3(A,)

433 415 410 410 v2(A,)

404 400 v.(E)384 375 370 380

350 v (SiJ-CJ)340 340 320 340

430(403) 16b

630(601) 6a

1605(1578) 8a

2910(2944) vCH3

2310(2266) vC~

1360(1371) -cn,945(920) vCC

1765(1650) vC=O

1450(1500) vC-N

920(1000) va(N-C =0)

650(740) vb(N-C=O)

Values in parentheses are of pure Iigands.

The Lewis base character of acetonitrile can eitherarise by donation of the re-electron from C=N orfrom the lone pair localized on the nitrogen atom.II! ~he case of metal halide complexes with aceto-nitrile the bonding is of the later type14• Niobiumand tant,,!-lum chlorides and bromides and antimony(V) chloride form 1:1 adducts with acetonitrilel5,16.

The IR active vC-N which in acetonitrile appearsat 2266 shifts to 2315 and 2310 in SbCI4(SOsF).CHaCN and SbCl••(S03CI).CHsCN respectively (Tables2 and 3). Similar shifts of vC-N to higher regionhas been observed in BFs.CHsCN and AICla.CHaCN(ref. 17, 18).

.SbCI,(SOaF) dissolves readily in nitrobenzene,n~trometha?e a~d acetonitrile whereas SbCI4(SOaCI)dissolves III nitrobenzene and acetonitrile. Theresultant significant increase in the conductance ofthese solvents may be due to the presence of ions.The molar conductance values of the millimolarsolutions are well in the range expected for 1:1electrolytes.

The possibility of the formation of any additioncompound between these compounds with the sol-

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PAUL et al.: TETRACHLORO(CHLOROjFLUORO-SULPHATO)ANTIMONY(V)

vents nitrobenzene and nitromethane has been ruledout, since the parent compound separates out when1.n inert solvent like CCl, or n-pentane is addedto their saturated solutions in these solvents.However, this is not true in the cese of acetonitrilesolvent where the compounds of composition SbCI,(SOaX).CHaCN are obtained, suggesting thatacetonitrile gets coordinated and the conductanceof the solution in acetonitrile is due to the ionizationof solvated compound. However, in nitromethaneand nitrobenzene the parent compound gets dis-socia ted into the ions. The dissocia tion of SbCI,(SOsX) in nitrobenzene can be represented by Eq.(1)2SbCI4(SOaX)-*[SbCI4]+ +[SbCI.(SOaX)2J- ... (1)and the forma tion of ionic species of these compoundsin acetonitrile can be represented by Eq. (2)

2CH,CN2SbC14(SOaX)--+ 2SbCI4(SOaX) .CHaCN ~

[SbCI4(CHaCN)2J+ +[SbCI4(SOaX)2J- ... (2)The values of the equivalent conductance at ir.finitedilution (Ao) have been obtained by extrapolatingthe plots of y'C vs Ae and from the linea plots dCAe vs l/Ae in nitrobenzene and nitromethare ar:dare given below alongwith that of Sl;Cls in thesesolvents.

CompoundNitrobenzene Nitrornethane

SbCl4(SOaF)SbCl,(SOaC1)SbCJs

80·20, 78'90*32·00, 29·41 *33'40, 33'33*29·00 63·00

*.0 obtained from CAe vs 1Ae curves.

698

The comparable values of Ao of SbCl,(SOaX) andSbCIIS indicate that SbCI,(SOaX) act as strongLewis acids as SbClo and that the former dissociateto a large extent in these solvents, as shown above,

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