Vibrational spectra of dimethyl sulfoxide complexes of antimony (III) and bismuth (III) halides

SpeotFoohimioa Act+ Vol. HA, pp. 669 to 669. Pergamon Prwa 1970. Printed in Northern Ireland

Vibrational spectra;of dimethyl sulfbxide complexes of antimony (III) and bismuth (IIl) halides* R~cnmm P. OE~TEL Department of Chemistry, Cornell University, Ithace, New York, 14860 (Receiued24 Febrwy

1969)

Ab&ac&Complexea of the typea -(DIMSO), and Bi&(DMSO), (DMSO = dimethyl adfoxide; M = Sb, Bi; X = Cl, Br) have been prepared and invcstigatcd spcctroecopically. Inframd and Raman assignmentsfor the eolidaare discussed, with apccialemphssia on metalligand vibrations. All DMSO molecule arc shown to bc coordinatedthrough oxygen. Structural considerationasrc prcacntedfor the solid-state species.

vibration frequencies for mixed complexes of Sb(II1) and Bi(II1) halides are few in the chemical literature. Raman spectra of complexes of SbCl, and SbBra with aromatio organio molecules reveal several new bands in the F&halogen stret&ing region which are absent in speotra of the Sb(III) halides themselves [l, 21. Infrared spectra have been reported for SbCl,(CH,),PO and SbCQ2(CH,),PO and, although complete sssignments are lacking, several frequencies fall reasonably within the Sb-0 and Sb-Cl stretohing regions [3]. The majority of relevant studies, however, oonsider only internal ligand vibrations [4-71. The present paper reports the in&red and Raman spectra of several dimethyl sulfoxide (DMSO) complexes of the form MXa(DMSO), and BiXJDMSO), (M = Sb, Bi; X = Cl, Br). This series of compounds offers an excellent opportunity to (1) distinguish metal-DMSO from metal-halogen vibration frequenoies, (2) correlate both sets of frequencies with coordination number and (3) draw structural aonolusions from spectral evidence. Of these compounds, only SbClJDMSO), has been reported previously [8]. W&~G~D

EXPERIMENTAL

Prepamtkm and characterkztim of compkxe8 AU chemicals were reagent grade. The complexes were prepared and subsequently handled in a dry-nitrogen atmosphere. In general, the oomplexes were crystallized from a methanolic solution of the appropriate metal trihalide to whioh DMSO had been added in the following mole ratios (DMSO :metal) : Sb(II1) complexes, 5 : 1; * Support from National Science Foundation Grant GP-8126 is gretefully acknowledged. [I] [2] [3] [4]

SE. SE. Run, Dokl. Akad. Nauk SSSR l%j, 646 (1968). A. T. Ko-, opt. spectry 18, 189 (1965). M. ZAU~SSON and K. I. ALDEN, Aota Chem. Scmd. 14, 994 (1900). D. S. BYS~OV et al., PTOO.Symp. Chem. Coodmdon Compoun&, Agra, Indie, Pt. 2, p. 128 (1969); Cbm. Abs. 55,704Ob (1901). [6] F. WATARI end S. -, SC&.Rep. &a. In&. Tohoku Univ. Ser. A. 13, 330 (1961); C?wwa. Abs. 66, 9694a (1962). [6-j D. J. PHILLIPSand S. Y. Tnam, J. Am. Chem. Sot. S&1806 (1961). [7] J. GERBIERand V. LOREN-, Cmpt. Rend. 264B, 690 (1967). [S] I. LINDQVI~T md P. EINAB~~ON, Acta Chem. &and. 18,420 (1969). [S] R. P. oER= and R. A. -, Itwg. Ohem. 6, 1960 (1967). 669

660

Rmww

P. 0~~5

BiCls(DNSO),, 2: 1; BiCl,(DMSO),, 7: 1; BiBr,(DMSO),, 15: 1 or 1: 1. The complex BiBre(DMSO), ctouldbe prepared only by slowly evaporating a solution of BiBr, in DMSO. In all cases, the crystals were washed with ether and dried in 2racuoat room temperature. An interesting observation is that the tris-DMSO complexes are transformed into bis complexes upon standing in air for several days and are reformed upon exposure of the bis oomplexes to a DMSO-rich atmosphere for several weeks. X-ray powder di8raction and miorosoopy studies indicate that crystals of BiCl,(DMSO),, BiBr,(DMSO), and SbBr,(DMSO), are isomorphous; SbCl,(DMSO), is definitely not isomorphous with these three compounds. It is difficult to draw a conclusion oonoerning the possible isomorphism of the BiX,(DMSO), complexes, Table 1. Analytical data, melting points and molar conductaces Compound SbCI,(DMSO), SbBr,(DMSO), BiCl,(DMSO), BiC&(DMSO), BiBrJDMSO), BiBq&DMSO),

Calculated %C %H 12.49 9.27 10.16 13.10 7.93 10.64

3.12 2.31 2.64 3.27 1.99 2.64

Found %C %H 12.64 9.24 9.87 13.06 7.76 10.77

3.24 2.27 2.64 3.26 1.96 3.03

Melting point (“C) es.&-7o”t 103-106° 107.6-109.6° 90-9ff 134-136’ 94-96’

* Concentration in nitroben~e at 26.0’ N 2 x lo-8 M. electrolytes normally exhibit A, w 20-30 P1 cm* mokl. t Literature value [S], 70’.

Molar conductance* Ab6 (W1 cmBmole+) 0.66 1.8 1.1 1.1 2.1 2.7

Under similar conditions, 1: 1

because, despite the close correspondence between powder patteims, crystals of these two compounds possess different shapes. Only the Sb(II1) complexes are au&Gently soluble in nitrobenzene for molecular weights to be measured cryoscopioally (301 found vs. 384calo. for monomerio SbCl,(DMSO),; 443 found vs. 518 caltlct. for monomerict SbBr,(DMSO),). Table 1 presents analytical data, melting points and molar conduutances measured in nitrobenzene at 25.0”. Vibrationd spectra Raman spectra ( 11200 cm-l) of all crystalline oomplexes except SbBr,(DMSO), were obtained using a Gary 81 spectrophotometer with 4358 A mercury excitation for the colorless solids and 5481 A mercury excitation for BiBr,(DMSO), below ~500 om-l. Complete spectra of BiBr,(DMSO), and SbBr,(DMSO), were reoorded using a Jarrell-Ash laser Raman spectrophotometer with 6328 and 6145 A rare gas souroes, respeotively. Frequencies of sharp bands are considered accurate to f2 cm-l. A Perk&Elmer 621 grating speotrophotometer was used to measure iufrared spectra of Nujol mulls between silver ohloride (4000-500 cm-r) and polyethylene (BOO-260 om-l) plates. The instrument was purged with dry air and aalibrated with both indene and polystyrene. Frequencies are oonsidered actcurateto f2 om-l. RESULTS AND DI~~TJ~~I~N

The conduotance and moleoular weight data, together with spectral evidence that all DMSO molecules are aoordinated to the metal (u&k?in&), point towed

Vibration4 epeotre of dimethyl eulfoxide complexes

661

monomeric five- and six-coordinate solid-state species, MXJDMSO), and BiXJDMSO),, respectively. Polymeric solid-state species which could be broken down in nitrobenzene solution are ruled out by both the low and systematic melting points and the simplioity of the vibrational spectra of the solid oompounds (described below). Since in nitrobenzene solution there is dissociation of halide and probably DMSO, structural spectrosoopio studies should be most meaningful if carried out using the solid oomplexes. Infrared and Raman spectra were examined of the solids as Nujol mulls and crystalline powders, respectively. For each compound, the absenoe of infrared absorption over the range 3000-4000 cm-l served to rule out the presence of water or hydroxyl groups. The region of greatest interest in both infrared and Raman spectra lies below 1200 om-l. Frequencies found in this region are presented in Tables 2 and 3, together with assignments based on the work of HORROCKS and COTTON [lo]. Table 3 also includes data for DMSO. Intern421&and frequ4mciea In the infrared and Raman spectra of uncoordinated DMSO, the band at 1045 cm-l represents almost equal contributions from two different types of molecular motion: S-O stretching and CR, rocking [lo]. The direction of frequency shift of this band upon oomplexation oan be used to distinguish between oxygen- and sulfurbound DMSO: a decrease in frequenoy acoompanies oxygen coordination, whereas sulfur bonding leads to a frequenoy increase [ 11, 121. For oxygen-coordinated DMSO complexes, however, there is disagreement in assigning this band, because it falls near several others in the CH, rooking region and very likely represents strongly coupled motions [13]. Since it is difficult to make unequivocal assignments, this spectral region is Iabeled “@-O), CH, rook” in Tables 2 and 3. Of most significance is the absenoe of bands above 1046 cm-l; clearly, all of the complexes in the present study oontain only oxygen-bound DMSO. There are some obvious spectral differences between the five (his)- and six (tris)coordinate DMSO oomplexes of Bi(II1) : (1) infrared bands appearing in the 9001060 cm-r region for the tris compounds are much broader than for the bis oompounds ; (2) a doublet is seen at ~1020 cm-l in infrared spectra of the tris complexes, whereas only one band appears here for the bis oompounds; (3) in both infrared and Raman speotra, G-S stretching frequencies at ~700 cm-r are lower for the tris complexes; (4) the higher C-S stretching fiequenay appears as a doublet in infrared speatra of the tris oomplexes, but only as a single band for the bis compounds; (5) and finally, the separation between the two G--s-O deformation frequencies is greater for the tris oomplexes (~36 om-r tris vs. ~25 cm-r bis) and approaches the value of ~50 om-l in uncoordinated DMSO. Broadness and multiplicity of certain bands in spectra of the tris-DMSO complexes probably arise from a oombination of ligand coupling and crystal symmetry effects. The fact that frequencies of the C-S stretching and C-S-O deformation bands in the tris complexes are shifted, relative to frequencies for the bis oomplexes, toward the values for unbound DMSO [lo] [ll] [12] [13]

W. D. HORROCXS, JR. and F. A. CO'ITON, &ectrochim. Acta 17, 134 (1961). F. A. COTTONet aZ., J. Phy.s. Ch. 64, 1634 (1960). M. J. BENNET,F. A. COTTONand D. L. WEAVER,Nature ZU, 286 (1966). R. S. DR&IO and D. MEEK,J. Phy8. Chem. 65, 1446 (1961).

336 w 317 w 219 va 204 8 IS@ ma 146 m 129m saw 5Qsh 42 va 24va

937 mw 920 mw 903 w 720 mw 660 m 422 w

975 mw

1022w

4118 331 m 302 m 271 m -260 a

1027m 980 m 973 w 936 w 997 w 908 s 723 w -683 VW

196 w 146 VW 122 mw 82 w 80 w 66 w

337 w 318 mw 273 PB 243a

974 mw 937 w 926 mw 906 w 72a mw 684 m 423 m

1023 w

Bi~~(DMSO)~ IR R-&A

408 8 329 m 301 m

1022m 977 m 972 w 984 w Q23w 908 0 720w -680 VW 332 w 810 VW1 181 s 179 va 167 VB 118 w 102 w 81 w 63 VW 49 m 37 m I

1014VW 977 w \ 940~ 928 w 909 VWI 721 mw 683 m 411 m

RiBr&MdSO), Rem&Xl IR

complexes*

CH, rook

deform&ion + tattiae m&

v@--O) f

Desoriptiont

* Infmred speotraobtsined ofsolida 88Nujol mulls, Rsman speaM as arys&lline powders. s, &rong; m, medium; w, wet&g v, very; ah, shoulder; b, broad. t v, etxeta~ Vibration; 8, deformation.

211 w 162 VW 144VW 133w 86 w 62 w

897 B 722 w -683 VW

918 ma 719 ma 683 B 420 VW 406 VW 342 VW 316w t 301 va 24s mw

942 w 926 I 913 s 721 w -688 VW 424 a 406 a a41 * 330 m,ah 360sfb g.260 8 406s 329 m 300m

1025m 979 m 976 w 936 w

1028vw 977 m

SbBr~(D~SO)~ IR l&man

1028m 982 B

SbCl~(DMSO)* IR Raman

Table 2. Vibrational tiequenoies (om--l) for MX,(DMSO),

t

670 8

383 w 334 m 308 w

687 m

332 8 3a2 a &iO6 w,&

m s,b s,b

In

.--%o

E

PO36 8SM% 343 B 303 m

717 w 711 m

1029 1020 994 930 II B VW a

239 0 219 m 102 m -81 w Mvw

269 va

677 W 403 mw a98 wls5 3Mm 310 mw

989 940 908 714

X027 w

BiCl,(D&IBO), IR B&m&n

m m IJ s,b

404 394 237 303

8 % a m

VW 8 a vw I m

eh vn B m w mw I

1

II, ntroq;

m,

+ CIq m&K for rouk for DMSO

far DWO

complexeat;OH,

V(s-0)

speaks aa orystallins powdem.

188 176 160 148 ~83 -70

341 mw 310 mw

-393 w&k

1 678 8 407 mw

1018 934 934 90s 714

“v(S-0)”

Desoriptiont

complexes and DMBQ*

RiBr,(DM80), Rsmatl

716 w 710 m

1027 10X6 979 929

IR

* Infrared speotra obt&.ned af solid complexes as Nujol mulls, RW medium; w, wenk: v, very; sh, nhoulcler; b, bmd. t V, nket&ing vibration, 8, deform&ion.

7OOm

954 8 931 m a97 w 7001,

962 vw

1046m

1046 vu

1028 vu

R5m6n

IR

DMSO(1iq)

Table 3. Vibrational frequencies (cm-l) for BiX,(DMBO),

664

RIUEIAED P. O~WL

Bi CI,(DMSO),

Bi Br,(DMS0)3

Frequency,

cm“

Fig. 1. Low-frequency infrared speotre of solid complexes MX,(DMSO), BiX,(DMSO), in Nujol mulls.

and

must be related to the lower polarizing ability of Bi(II1) as its effective charge is reduoed by the third DMSO ligand. H&l-ligand

frequencies and

solid-date structures

Low-frequency infrared (250-500 ctm-1) and Raman ((600 om-l) speatra of the oomplexes MXJDMSO), and BiXJDMSO), are displayed in Figs. 1-3. The striking correspondence among the speotra of BiCl,(DM.SO),, BiBrJDMSO), and SbBrJDMSO),, especially in the infrared region, is strong support for the oonclusion that these oompounds are isomorphous, and presumably isostrurAura1.Dissimilarities

Vibrational spectra of dimethyl aulfoxide complex88

86%

between these spectra and those of Sb~~(DMSO)* are consistent with the latter compound’s not being isomorphous with the other bis complexes. Spectra of the BiX,(DMSO)s compounds are very similar to one another and indicate that, even if the crystals are not isomo~ho~ (see experimental section), the molecular structures are probably identical.

I

400

I

I

300 200 Frequency,cm“

I

too

Fig. 2. Low-frequency Raman spectra of solid complexes MXe(DMSO), line powder&

&ecryetal-

Bands found near 400 cm-x are ascribed to ~bratio~al modes invoking predominantly M-O stretching. Similar assignments have been made for related

RIG-

666 I

I

P. OEBTJSL

r

I

I

Bi CIJDMSO),

Frequency, cm-’

Fig. 3. Low-frequency Raman spectra of solid complexes BiX,(DMSO), aa cryatal-

line powders. For BiCl,(DMSO),, single slit wa used in the region below 200 cm-l and double slit above 200 cm-l.

species [14, 161 and are substantiated

by a recent

normal coordinate

analysis

of

DMSO complexes of uranyl halides [16]. For the compounds examined here, there is no evidence of any significant influence of the M-O or M-X stretching vibrations on one another, e.g., there is no abrupt shift in the M-O frequency in comparing Of the two M-O stretching bands which appear chloride with bromide complexes. in both infrared and Raman spectra of the six-coordinate complexes BiX,(DMSO),,

the higher-frequency band is more intense in the Raman, while the lower-frequency band is stronger in the infrared spectrum. The higher one is therefore assigned to the symmetric and the lower one to the antisymmetric stretching mode. A similar situation appears to hold for the five-coordinate complexes. For SbCl,(DMSO), the higher-frequency Raman band is stronger and is assigned to the symmetric stretching [la] C. V. BERNEY and J. H. WEBER, Inwg. C&m. 7,283 (1968). [IS] R. A. WUNN, Inorg. Chm., 7,640 (1968). and M. J. F. LEROY, BUZZSot. Chim. France 3770 (1966). [la] G. KA-

Vibrational ape&n of dimcthyl &oxide

complexes

667

mode; for the remainiug three bis-DMSO oompounds, the higher-i?equency band is only Raman active and the lower one only infrared active. Table 4 summtiea these data which illustrate the shift toward lower frequenoy as the coordination number increases from five to six. Intense Raman bands located within the range 160-300 om-l oan be assigned to M-X stretohing vibrations. Lower-frequency Raman bands are due to deformation and lattioe vibrations. For complexes with metal-DMSO stretching frequencies near 420 cm-l, metal-DMSO deformation modes have been associated with d.iEirse infrared features at ~260-280 om-l [14]. These bands are not observed in the present infrared speutra and are also probably too weak to be seen in the Raman speotra. The assignment of M-X stretohing vibrations for each compound will now be disoussed in greater detail. Table 4. Metal-oxygen strct&ing frcqucncieg(cm-l) Compound SbCl,(DMSO), SbBr,(DMSO), BiCI,(DMSO), Bi13r,(DMS0)8 BiCI,(DMSO), BiBr,(DMSO),

%ym(~--O) IR R8mlWI 424 403 404

420 422 423 417 406 407

%ym(M--0) IR REman 406 406 411 408 394 394

405 395 398

SbCl,(DMSO),. The intense Raman peak at 301 om-l which is assigned to the symmetrio &-Cl stret&ing mode closely matches the strong 290 om-l band similarly assigned for five-coordinate SbC15a- [17]. Both bands are looated between symmetrio stretching frequenoies found for supposed three-coordinate SbCl, (~346 om-l) [18] and six-coordinate SbCl,s- (267 cm-l) [19]. Of the two bands at 249 and 211 cm-l, only the first can be assigned with oertainty to the antisymmetric Sb-Cl stretching mode; the second band is considered too weak and its frequency too low. It should be noted that symmetio and antisymmetrio Sb-Cl stretching vibrations are both infrared and Raman active. Judging from the X-ray structures of SbCl,a- [20] and SbCla~t(C,H,)&sO [21], it appears that five-coordinate species oontaining Sb(II1) and ohloride most often exist as a distorted square pyramid with a stereoohemiaally active eleotron pair occupying a sixth position. In the arsine oxide adduct, the oxygen atoms are in cis positions in the base of the pyramid and the Sb-Cl bond opposite the electron pair is shorter than the two Sb-Cl bonds in the base. The vibrational spectra described herein are oonsistent with a similar structure for SbCl,(DMSO),. Symmetrio and antisymmetrio Sb-0 stretohing modes are both infrared and Raman aotive, as [l?] H. A. SZYMBNSKI et al., J. Ch-em.P&s. 47, 1877 (1967). [IS] P. D. SIIUOVA and R. ANQELOVA, Izv. Bdgar. Akd. Nauk, Otdd. F&z. Mat. TekL Nauk, Ser. Fiz. 7, 333 (1969); Ohma.Abe. 54, 170488 (1980). [19] T. BARROWet a;l., J. Chem. Sot. A 1810 (1967). [20] M. EDSTRAND, M. hQE_ and N. INURI,Ada, C??wn.Scund. 9,122 (1956). [21] I. LINDQ~I~T, Inorganic Adduct Mokch of Oxo-Compounds,p. 71. Springer-Verlag(1963):

068

RIOEABD P. Onmm

expeoted for a bent SbO, subunit. Only two of the three infrared- and Ramanallowed Sb-Cl stretohing bands predicted by this symmetry (0, for the SbCl, subunit) are observed; the third is probably made inaocessible in the infrared by the 260 cm-l cutoff, while in the Raman spectrum it is presumed too weak or almost aoincident with one of the other bands. SbBrJDMSO),. For this complex, the strong Raman band at 219 om-l whioh is assigned to the symmetrio Sb-Br stretihing mode oocurs at a frequenoy lower than the analogous band in SbBr, (at -243 em-i) [22], as expected. The two bands at 204 and 189 om-l can be thought to result from removal of the degeneraoy of the antisymmetrio stretching vibration in pyramidal SbBr, owing to complexation. Comparison with the five-coordinate speoies SbBQ- is of doubtful value, sinoe this ion (in the bispyridinium salt) consists of distorted ootahedra bridged by bromine atoms [23]. BiCl,(DMSO), and BiCl,(DMSO),. The bands at 273 om-l for the five-ooordinate and at 269 om-l for the six-coordinate oomplex are assigned to symmetrio B&Cl stretching vibrations. These frequenuies are in quite olose agreement with those for the symmetrio stretching mode in the solid-state speoies BiCl,s- (~270 om-i) [S, 241 and BiCb3- (~268 om-l) [9, 19, 241. Antisymmetrio Bi-Cl stretching occurs at 246 cm-l for the bis complex ; the bands at 239 and 219 cm-l for the tris oomplex can be oonsidered to arise from removal of the degeneracy of the antisymmetrio stretching mode of pyramidal BiCI,. The symmetric Bi-Cl stretching modes of both oompounds and the antisymmetric mode of BiCl&DMSO), are both infrared and Raman aotive. BiBrJDMSO), ati BiBrJDMSO),. The Raman speotrum of the five-ooordinate oompound in the Bi-Br stretohing region is remarkably similar to that of solid BiBr, [26]. Frequenoies for the tris oompound are somewhat lower, as expeoted. As in the ease of BiB4, the highest-frequenoy band (191 om-l in the bis, 176 cm-l in the tris oomplex) is ascribed to the symmetrio Bi-Br stretohing mode. The hiihfrequency shoulder on the 176 om- 1 band of BiBra(DMSO)a is of unoertain origin, although it might be due to a small amount of the bis compound. It is reasonable to pioture the two remaining strong peaks for each oompound as resulting from splitting of the degeneraoy of the antisymmetrio stretching mode of pyramidal BiBr, upon complexation. Whereas the symmetrio Bi-Cl stretohing mode of BiCl,(DMSO), (269 cm-l) almost coincides with the analogous vibration of BiCl,B- (268 am-l), this is not true for BiBr,(DMSO), (176 om-l) oompared with BiBr,*- (166 cm-l) [9, 241. The greater repulsion among six bromine atoms in BiBr,s- must be responsible for the lower fcequenoy for this speoies. The three isomorphous oompounds MXJDMSO), possess a less certain struoture than does SbCl,(DMSO)I, although several comments can be made. In oontrast to SbCl,(DMSO),, a bent MO, subunit is ruled out by the laok of infrared-Raman 1221 J. C. Evms, J. Mol. &e&y 4, 435 (1960). [23] W. G. b%d?BEESON and E. A. MIWE.BS,J. ph98. Chtm. 78,532 (1988). 1241R. A. WALTON, Spectrochim. Acta 9&l, 1527 (1968). 1261R. P. OUZEL and R. A. Prmm, Inorg. C&m. 8,1188 (1969).

Vibrational aptwtra of dimethyl sulfoxide complexees

669

coincidence of M-O stretching bands. Also, a strictly planar MX, subunit with DS1, symmetry is probably absent for three reasons : (1) three M-Br stretohing vibrations appear in the Raman spectra of the bis bromo compounds, (2) the symmetrio stretching vibration is in&red active for BiClJDMSO), and (3) Yap > vspmis usually found for Dsn symmetry, but is not observed here [26]. The most plausible structure is based on an o&ah&on with trans DMSO groups and one position occupied by a non-bonding electron pair. Since it is established that six-coordirmte halide complexes of Bi(II1) are octahedral, it is most reasonable to assume that the oompounds BiX,(DMSO), possess pseudo-octahedral symmetry, either in the cis or trans form. Selection rules for the stretching modes are as follows: cis, 2Bi-0 and 2Bi-X, all infrared and Ram&n active ; tram, 3Bi-0 and 3Bi-X, all infrared and Raman active. While Raman spectra of both compounds reveal three Bi-X stretching bands, the 250 cm-l infrared spectrometer cutoff allows observation of only the highest B&Cl band for BiCl,(DMSO),. Lsrgely owing to the Raman evidence, trans symmetry is more likely correct. The separation between the two infrared- and Raman-active Bi-0 bands is ~10 cm-l; a third Bi-0 band could either be very week or poorly resolvable. The postulate of trans symmetry for the complexes BiXJDMSO), is consistent with the proposedlinear structure for the BiO, subunit in the complexesBiX,(DMSO),, since this structural similarity would favor the observed transformation between tris and bis forms. [26] K. NABIAMOTO, Infrared John Wiley (1963).

16

Spectra of Inm-ganio and Coordinutim

Compoun&

pp. 90, 117.