Vibrational spectra and structures of some thiosulphate complexes

Sp&mchimica Acta, Vol.27A,pp.1456to 1466.Pergamon Pm6 1071.Printed inNorthern Ireland

Vibrational spectra and structures of some thiosulphate complexes A. N. FREEDMAN and B. P. STRAU~HAN Department, of Inorganic Chemistry, Umversity of Newcastle upon Tyne, Englmd (Received 20 July 1970) Ab&&---The m. spectra of 9 thiosulphate complexes, mth known crystal structures, have been exmed m detail and criteria have been proposed for distmgmshmg between the different ways in which the thiosulphctte amon can co-ordinate to metal atoms. The cnteria have been used to elucldat,e the structures of several other complexes which are less well characterised. Fin&y, It appears that no examples of solely oxygen co-ordm&ion m tluosulphate complexes have been reported previously. We now propose the first examples of this type of co-ordmatlon.

INTRODUCTION COMPLEXESof thiosulphate with a number of metal salts have been characterised but until recently little work has been carried out on their molecular structures. Stereochemistries have been postulated with little or no basis, and the i.r. spectra of several complexes have been misinterpreted because of a lack of knowledge of the effect on the spectra of the different possible types of thiosulphate co-ordination. Nine crystal structures of thiosulphate complexes have been reported [l-9] and they indicate some of these possibilities. Anhydrous sodium thiosulphate as well as sodium and magnesium thiosulphate hydrates [2, 31 (which also contain hydrated metal cations) possess ionic structures. In contrast, single sulphur to metal coordination has been found for zinc tristhiourea thiosulphat,e, [4] [Zntu,S,O,]H,O (tu = thiourea throughout) (l), b arium selenopentathionate, [5] BeSe(S,O,),2H,O and ammonium telluropent&hionate [6] (NH,),Te(S,O,),. A third possibility which involves a sulphur atom in a bridging position occurs in Na4,[Cu(NH,),],[Cu(S,o,),,1, [7] (2) while bidenbate sulphur/oxygen co-ordination has been shown for nickel tetrathiourea thiosulph&e [8] [Nitu&O,]H,O (3). Finally barium thiosulphate, BaS,O,H,O, contains both bidentate sulphur/oxygen and bidentate oxygen/oxygen co-ordinated thiosulphate groups [9] (4). The purpose of this paper is to discuss the i.r. spectra of these complexes in the

light of their crystal structures, and to establish reliable criteria from i.r. data which will enable the type of thiosulphate co-ordination to be distinguished for complexes of unknown structure. Furthermore it appears that no examples of solely oxygen co-ordination in thiosulphate complexes have been reported previously. We have examined this possibility using our criteria and now propose the first examples of this type of co-ordination. [l] E. SANDOR and L. CSORD~S, Acta Cq8.t. 14, 237 (1961). [2] P. G. TAYLOR and C. A. BEEVERS, Acta Cm&. 5, 341 (1952). [3] M. NARDELLI, G. FAVA and G. GIRALDI, Acta Cry&. 15, 227 (1962). [4] G. D. ANDREETTI, L. CAVALCA, P. DO~A.NO and A. MUSATTI, Rzc. SW 38, 1100 (1968). [B] 0. Foss and 0. TJOMSLAND, Acta Ch.twn.Scad 8, 1701 (1954). [S] 0. Foss and P. A. LARSSEN, Acta Chem. Scad 8, 1042 (1954). [7] A. FERRARI, A. BRAIFUXTI and A. TIRIPICOHIO,Acta Cryat. 21, 605 (1966). [S] G. F. GASPARRI, A. MUSATTI and M. NARDELLI, Acta Cry&. B25, 203 (1969). [Q] M. NARDELLI md G. FAVA, Acta Cry&. 15, 477 (1962).

1455

1466

A. N.

and B. P. STRAWGHAN

F'REEDMAN

l

I -Ag

s-cu

4-s

/

---s-s-o

= Thloureo

7 \

\

“\\

so3 so3

(7)

(3) sp3

4y

/i\

/P3

ss/cd\sf

o

cd\so

3

3

I

RESULTSmu DISCUSSION The spectrum of anhydrous sodium thiosulph&e was chosen 8s the standard for the comparison of the spectra of the other thiosulphata complexes. The low interaction between the sodium and thiosulphate ions (stability constant = 4.8 compared with 213.8 for barium thiosulphate) [IO] together with the lack of hydrogen [ lo] Oheva. Sot. Speoml Publ. 7.

Vibrational

spectra and structures of some thlosulphate

complexes

1467

bonding and the known structure of the complex make it suitable for this purpose. The free thiosulphate ion with C,, symmetry has six fundamental modes of vibration: symmetric (al) and antisymmetric (e) stretching and bending vibrations, a sulphur-sulphur stretch (al) and a rocking mode (e). A complication which arises in the spectrum of Na,S,O, (and also in the spectra of the other solid complexes) may be attributed to the effects of the crystal lattice (see Table 1 and Fig. 1). The latter causes splittings of the free thiosulphate ion fundamentals to occur, but the splittings can be readily predicted using a factor-group analysis for the complexes with known space groups. The magnitude of the splitting appears to be most serious for the v,(SO) and 6,(SO) modes of the ligand but it does not seriously mask the frequency shifts caused by electronic changes for different types of co-ordination (see Fig. 1). The crystal structures of the sodium and magnesium thiosulphate hydrates show the presence of hydrated cations and the effects of hydrogen-bonding can be recognised in the spectra by a lowering and a broadening of particularly the sulphuroxygen stretching modes compared with their positions in anhydrous Na,S,O,. The effect of hydrogen bonding is even more pronounced in (NH,),S,O, as can be seen in Fig. 2. As expected, the Y(NH) stretching frequency of the ammonium cations shows a marked lowering due to hydrogen bonding. We consider now some complexes which have been shown by X-ray crystallography to involve S or S/O co-ordination to a metal. For sulphur co-ordination (e.g. [Zntu,S,O,]H,O) the spectra exhibit a lowering of the Y(SS) with a corresponding increase in the v,(SO) and Y,(SO) frequencies compared with the fundamental frequencies of Na,S,O,. In contrast, oxygen co-ordination would be expected to cause frequency shifts in the opposite direction. The effects of both S and 0 co-ordination can be seen in the spectrum of the nickel oomplex, where the YJSO) band has two components one above and one below the frequency of 1130 cm-l found for Na,SaOs The shifts in Y(SO) due to sulphur co-ordination are more pronounced in the sulphurbridged copper complex (2) than in the zinc complex (1). It is important to remember, however, that these frequency shifts due to the different types of co-ordination may be superimposed on hydrogen-bonding effects and thus the presence of -NH, groups in the nickel thiosulphate complex (3) may account for the low value of the Y,(SO) frequency in the spectrum of this complex. We have carried out normal co-ordinate analyses on some 1: 1 complexes involving M-S co-ordinate bonds and the analyses indicate that while the Y(SO) and 6(SO) vibrations of the free anion remain relatively pure modes of vibration on co-ordination, the Y(SS), Y(MS) and p(S0) become highly mixed and are of little diagnostic use. The positions of the &SO) vibrations do not appear to give a simple indication of the type of co-ordination involved but the positions of the Y, and Y,S-0 stretching modes provide a useful criterion for distinguishing between the different types of thiosulphate co-ordination. The trends in the frequencies relative to anhydrous Na,S,Os for complexes involving different types of co-ordination are indicated in the line diagram (Fig. 1). It is clear from the latter that Y(SO) moves to higher wave number positions for S-co-ordination and to lower wave number positions for Oco-ordination. There is a small tendency for the reverse trend to apply to the symmetric deformation mode. The splittings due to the crystal lattice are also

and 254* 235*

338 w

655 m 535 m

680 ah 1002 s 668 8

1160 sh 1130 s

~%S,Os

[ll] G A. NEWMAN, J. Mol. Stmct. 5, 61 (1970). [12] C. D. FLINT and M. GOODCUME, J. Ghan. Sot. (A), 1718 (1967). [13] F. A. MILLER, G. L. CARLSON,F. F. BENTLEY and W. H. JONES, Spctrochwn. (1960).

* These values from Ref. [12]. t These values from Ref. [ 131.

v(M-S) r(SS0)

360 w* 358 w* 325 VW*

530 m

546 m 632 m

USC)

446 w i 436 w

647 s 1006 s

659 s 1012 s

USG) %(SG)

Other bands wmch wdl include v(S-S),

1108 8 1142 s

1177 s 1137 8

ZntusS,Os.H,O

%(SG)

Na,,[Cu(NHs)al,.[Cu(S,O,l,,l,

16,136

450t 430 wt

536 m

660 s 998 s

1120 a, br

WW,O),S,Os

535

665 971

1162 1090

Nltu&S,O,.H,O (Ref. 11)

compounds of known structure

Acta

Table 1. Infrared frequencies (cm-l) for some metal-tmosulphate

u

556

? m E s

324 w 276 260

td

s

366 w 352 w

468 m 450 w 398 ah

E

;

988 * 676 s 1007 I

638 1 m 508

?

1120 1105 I 8 1075

BaS,O,H,O

Vlbratlond spectra and structures of some thlosulphate complexes

1459

obvious from this diagram. In general, one can conclude that Y,(SO) occurs at: > 1175 cm-l (for S-bridging systems); 1130-1176 cm-l (for M-S co-ordination) ; ~1130 cm-l (for ionic thiosulphate groups); and ~1130 cm-l (for M-O co-ordination). The corresponding regions for Ye occur at > 1000 cm-l for S co-ordination and < 1000 cm-l for O-co-ordination.

v,= II

I,

III

s,so

8, so

v, so

I

I

I

!

1 , I.

II

!

I

I

IV

I

I

\ V

1

i

VI

I:,,

VII /

I 11 I

1200

I

1

1100

I I i 1000

700

I. I

I

600

500

cm-’ I

CH&O,,

II

Na,, [cu(NH~~,[cu,(%o,),,]

IV Na,S,O,, V Mg(H,OI,~O,.

III Zn(td3 s203~~0

2,

VI NI (tdq~03.

Hz0 ; VII

BcEg.0,. H,O

Fig. 1.

Using these criteria as a basis, one can now propose structures for other thiosulphate complexes from an examination of their spectra. Copper

silver and gold complexes

The positions of the fundementsls for a number of copper, silver and gold complexes are given in Table 2. The spectra for some of these complexes have been reported previously by MURUULESCUet al. [14] but we have discounted their results because parts of their analytical data were found to be in error and their frequency values differ substantially from our own. The frequencies given in Table 2 can be interpreted satisfactorily using the criteria discussed above. The spectra of the two silver complexes and the gold complex are very similar and the Y(SO) frequencies fall within the range for single sulphur-tometal co-ordination by the thiosulphete group. The copper complexes present a more complicated picture. Although the positions of the Y(SO) fundamentals for all three complexes are indicative of sulphur coordination, the very high YJSO) frequency of 1190 cm-l for the 1: 1 complex suggests a sulphur bridging situation. In the 1: 2 complex this vibration occurs at 1147 cm-l [14]

I. G. Mu~cw~~scu, V. E. SAHINI, M. SEQAL and M. DABCASCHIN, Rev. Rowname 29 (1964).

Chwn. 9,

A. N. F'REEDMAN and B. P. STRAUGHAN

1400

I

No,S,O,

,

II

(NH,),

3500

S,O,

3000

2500

cm-’

Fig. 2.

suggesting single sulphur-to-copper co-ordination whereas in the 2 : 3 complex the YJSO) vibration is observed as a split band with components at 1185 and 1146 cm-l which may indicate the presence of both bridging and single sulphur-to-metal coordination. Possible structures are shown in [5], [6] and [7]. When ammonium replaces sodium as the cation in the copper and silver complexes, a broadening and lowering of some bands is observed. We have ascribed these affects to hydrogen bonding and no variations in their structures need be invoked. The spectra of (NHo)2MaS20,12 (M = Cu’, AgI) have been reported by NEWMAN [15]. The Y,(SO) mode appears as a triplet in both cases with components at 1193, [15] G. A. NEWMAN,

Chem. Ind. 614 (1968).

642 s

636 m

USO)

&(SO)

1186 s 1146 s 1023 sh 1014 s 64Q sh 629 s 648 m 639 m -

NG!WS,O,WH,O

* Probably due to Impunties.

-

1020 s

v,(SO)

v(SS)

1190s

%(SO)

NWu(%Odl-H,O 1150s 1018 8 645 s 555 m 640 m 420 w

1160 s 1010 8 650 s 637 m

1147 s 1016 s 662 s 633 m 420 VW

Na[Ag(S,O.J].2H,O

Na-JAg(S,O,),I~BH,O

NaWu(S,0s)&2H,0

Table 2 Infrared frequencies (cm-l) for some copper, silver and gold complexes

656 s 646 sh* 640 m 630 m 450 w

1209 sh* 1175 s 1150 sh* 1013 8

N~[Au(S,O,),].~H,O

1462

A. N. FREEDMAN and B. P. STRAUIJH~LN

1167 and 1122 cm-l in the silver complex and at 1204, 1177 and 1132 cm-l in the copper complex. The v,(SO) mode appears at 1000 cm-l in the silver and at 1008 cm-l in the copper complex. NEWMAN interpreted these spectra in terms of structure [8]. An alternative explanation of the spectra, which we prefer on the basis of our criteria, can be made by postulating a sulphur bridged system as shown in [9]. This structure is consistent with the high frequency component of the Y,(SO) mode, while the presence of hydrogen bonding from the ammonium ion would be expected to give rise to the lower frequency components. Lead thiosulphate complex The i.r. frequencies of lead thiosulphate PbS,O,, a white insoluble solid, are shown in Table 3. The presence of two components above and below 1130 cm-l for the Y,(SO) fundamental suggest the possibility of both sulphur and oxygen co-ordination Table 3. Infrwcd

frequencw

VJSO) PbS,O, K&d(SsOs)si

1140s 1116 s 1223 1 1210 s ’ br 1162 s

988 s 1019 I 1007 s

(cm-l)

for lead ad

4JSO)

&(SO)

645 s 624 s

541 s 516 s

cadmnun thlosulphates Other bands mcludmg

v(SS)

434 m, 358 m, 332 m 428 VW, 410 VW, 370 VW, 344 VW, 326,313, 242 VW

The r,(SO) frequency at 988 cm-l also supports oxygen co-ordination. When both sulphur and oxygen co-ordination occurs, the effect of the latter is likely to be predominant on the y,(SO) vibration as it directly affects the S-O bond. The bond will only be affected indirectly by co-ordination of the terminal sulphur atom. The band at 434 cm-l could be assigned to the Y(SS) vibration and the low position compared with the corresponding frequency in anhydrous sodium thiosulphate (455 cm-l) would then be indicative of sulphur co-ordination. However, a normal coordinate analysis for this type of system indicated that the mixing of vibrations in this region of the spectra becomes serious and hence the assignments of specific modes of vibration become meaningless and the frequency values are no longer diagnostic. Thus the band at 434 cm-l may also involve the Y(Pb0) stretching mode and the band at 516 cm-l may contain a major contribution from the Y(SS) vibration. The spectrum of the lead salt below 600 cm-r shows a general increase in the intensity pattern for the low frequency modes. This pattern has also been observed in BaS,O,H,O, which has been shown to involve both S/O and O/O co-ordination and the trend indicates the involvement of oxygen as well as sulphur co-ordination to the metal. Thus we propose the presence of bidentate S/O co-ordination of thiosulphate groups to lead. Ca&nium thiosulphate complex The i.r. spectrum of the complex K,[Cd(S,O,),] is shown in Table 3. The r,(SO) mode is split into two components, a high frequency component suggestmg bridging

Vibrationalspectraand structuresof some thiosulphatecomplexes

1463

sulphur co-ordinstion and a second component in the single sulphur-to-metal coordination range. In addition, the v,(SO) band has two components, one 11 cm-r higher than the other which again suggests only sulphur co-ordination. The spectra can be interpreted therefore in terms of a structure involving both bridging and single sulphur-to-metal co-ordination [lo]. The weak intensity pattern of the bands below 600 cm-i also support this conclusion. Metal oxycation complexes Although both O/O and O/S co-ordination have been shown by X-ray studies to be present in barium thiosulphate, and O/S co-ordination has been proposed for lead thiosulphate snd nickel tetrsthiourea thiosulphate, no exclusively oxygen coordinated or oxygen bridged thiosulphate complexes have been reported. One possible rationslisation arises from the strong reducing properties of the thiosulphate reagent itself. The metals are reduced to a low oxidation state (e.g. Cu’r + CuI) before the complex&ion takes place. The metal in this state then behsves as a soft acid centre and it is able to form r-bonds with the empty available “d” orbit& of the sulphur atom. An alternative way of stabilising the low oxidation state of a metal is to supply electrons from other ligands in the complex (e.g. Zn(tu),S,O,H,O). With these ideas in mind, a possible source of oxygen co-ordination to a metal is via the hsrd acid centre in the oxycations UOz2+or Zr02+. Ursnyl thiosulphate has been prepared previously by ICLY~IN and KOLYADA[16] who carried out solubility studies on it. Zinconyl thiosulphate has not been previously reported, but the complex was prepared during the course of this work. Both complexes exhibit strong absorption bands between 860 and 1100 cm-l and the bands can be assigned to v(M0) and Y(SO) vibrations as shown in Table 4. The very low Y(SO) frequencies Table 4. Infraredfrequencies(cm-l) for zlrconyland uranylthiosulphate

UO,S,O,*H,O

ZrOS,0s.8H,0

v(SO)

v(U-0)

998s 971s 886s

924s

1125w 1010s

&SO)

830ah

640m 532w 510w

925a, br

626m, br

Otherweak bandsmcludmg v(SS),v(M-O), rock 447,390, 310, 214 184, 172, 150, 132 108,60 460, 349, 333, 314, 269,234,211

compared with the positions for all the other thiosulphate complexes examined suggest oxygen-bridged co-ordination. Bridging oxygen co-ordination would also allow for the higher co-ordination numbers preferred by the uranyl and zirconyl ions, A co-ordination number of eight has been observed in some uritnyl crystal structures and ZrOCl,SH,O contains oxygen-bridged links from the OH groups of the water molecules [17]. Thus a polymeric structure involving considerable cross linking by bridging oxygen atoms would seem to be the most likely structure for the thiosulphate complexes and the presence of such structures would be in accord with the insoluble [16] [17] 16

A. E. KLYUIN and N. S. KOLYADA, RUM. J. Inorg. C?mn. 6, 663 (1960). XELD and P. A. VAUGHAN, Actu Cryst. 9, 565 (1956). A. CLEARE

1464

A. N. FREEDUN

and B. P. STRATJQHAN

Thus one may conclude that there is no reason why nature of these complexes. thiosulphate groups cannot co-ordinate to metals via the oxygen atoms alone and the uranyl and zirconyl complexes appear to be the 6rst examples of this particular type of co-ordination. EXPERIMENTAL Preparation of com$exes Sodium thiosulphate pentahydrate and ammonium thiosulphate were obtained from commercial sources. Zntu,S,O,H,O [IS]; Na4,[Cu(NH,),],[Cu,(S,o,),,1, [7]; K,[Cd(S,O,),] [19] and UO$,O,H,O were all prepared by literature methods and the analytical data were in good agreement with the published results. Attempts to repeat the preparation of Nitu,S,O,*H,O using the method of NARDELLI and CHIERWI [lS] were unsuccessful and so we have relied on previously published i.r. data [ll] for this complex. Anhydrous sodium thiosulphate remains when an evaporating basin containing crystals of the hydrated salt is left in an oven overnight at a temperature of just above 100°C. Found: i&.0,, 70~3O/~Calc. for Na,S,O,: S,O,, 7O-9o/o. Magnesium and barium thiosulphates were prepared by the slow evaporation of an equimolar mixture of the metal salt and sodium thiosulphate in aqueous solution. Found: S,O,, 46.1 Calc. for Mg(H,O),S,O,: S,O,, 459%. Found. S,O,, 42.3% Calc. for BaS,O,H,O: S,O,, 41.9%. Lead and zirconyl thiosulphates were prepared by mixing in 1: 1 proportions aqueous solutions of lead nitrate or zirconium oxydichloride and sodium thiosulphate. The complexes precipitated immediately and they were filtered, washed with water and dried. Found: S, 10.7. Calc. for PbS,O,: S, lO*1o/o. Found: ZrO, 28.5; S,O,, 31.1%. ZrOS,0,8H,O requires ZrO, 29.5%; S&O,, 30.8%. The 1: 1 silver complex was prepared by BAINES method 1201. The 1: 2 complex was prepared by dissolving a suspension of one equivalent of freshly prepared silver chloride in an aqueous solution of two equivalents of sodium thiosulphate and filtering the resultant solution into ethanol from which the complex precipitates. The copper complexes were prepared by mixing aqueous solutions of cupric salts with aqueous solutions of sodium thiosulphate in appropriate proportions. The 1: 1 complex was precipitated by pouring into ethanol; the 1: 2 and 2 : 3 complexes precipitated from solution. The gold complex was prepared from HAuCl, by addition of NaI which left a precipitate of AuI. This was washed and then dissolved in an aqueous solution of two equivalents of sodium thiosulphate and the complex was precipitated by pouring into ethanol. The analyses of the freshly prepared complexes were carried out immediately and infrared spectra were also run without delay. Satisfactory analyses were obtained Found: S,O,, 43-O. Calc. for Na[Ag(S,O,)]H,O: for the silver and gold complexes: S,O,, 51.3%. S,O,, 42.9%. Found : S,O,, 51.5. Calc. for Na,[Ag(S,0,),]2H,O: [18] M. NAFLDELLI and I. CHIERICI, Razz. Chum. Ital. 88, 832 (1958). [19] M. S. NOVAKOVSKII and A. P. RYAZANTSEVA, C&m. Abs. 52, 50981 (1968). [20] H. B_uhTEs, J. Chern. Sot. 1763 (1929).

Vibrational spectra and structures of some thiosulphate complexes

1465

Found: S,O,, 40.7.Calc. for Na,[Au(S,0,),]2H,O: S,O,, 42.6%. The copper complexes persisted in giving unsatisfactory analytical results and previous workers [21] have apparently experienced similar difficulties for these psrticular copper compounds. The spectra of the copper and silver complexes showed no signs of impurity bsnds but the spectra of the gold complex showed shoulders on the sides of the main bands. The shoulders are probably due to decomposition products because their intensities increased with time. I .r. spectra

Infrared spectra were recorded on Perk&Elmer models 125 and 457 spectrophotometers. The samples were examined either as Nujol or hexachlorobutadiene mulls or as KBr or CsI discs. KBr plates were used down to 400 cm-l and CsI or polythene windows were used in the range 400 to 250 cm-l. Spectra in the range 400-20cm-l were measured using an R.I.I.C. Fourier spectrophotometer (F.S. 520) with s, melinex beam divider. The samples were examined as Nujol mulls between polythene plates and the spectra were recorded at approximately liquid nitrogen temperature. Acknowledgements-We thank S.R.C. for a researchstudentship (to A. N. F.). [21] H. BASSETTand R.

G. DURANT,J.Chm. Sot.1279 (1923).