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Preparation and Spectral Properties of [Pt(WS4)2] 2

A. M ü l l e r , M . C. Ch a k r a v o r t i , and H. D o r n f e l dInstitu te of Chemistry, U niversity of Dortmund

(Z. Naturforsch. 30 b, 162-164 [1975]; received December 12, 1974)

Preparation, Vibrational Spectra, Electronic Spectra

The stable com plex, [Pt(W S4)2] a~, has been prepared as the tetraphenyl phosphonium salt by the reaction of K 2[P tI6], (N H 4)2W S4 and (C6H 5)4PC1. Its vibrational and electronic spectra are reported. The [Pt(W S4)2] 2- ion has D 2h sym m etry with a planar P tS 4 chromo- phore. The vibrational frequencies have been assigned by a detailed analysis.

Recently we reported novel complexes wi h WS42-, WOS32-, W 02S22- and MoS42- as ligands1"6. In all such complexes the thio- or oxothiometal- late(VI) ions act as bidentate ligands with two sulphur atoms as donors. These compounds have been prepared only with 3d series of transition metals (Co11, Ni11 and also with Zn11) starting with their simple salts, except a mixed ligand complex7, [Nien2(WS4)], which was prepared starting with Ni(en)2Cl2. In the present communication we are reporting the isolation of a tetrathiotungstato(VI) complex of platinum(II) by reacting hexaiodopla- tinate(IV) with tetrathiotungstate(VI) in aqueous solution. I t seemed to be interesting to study the spectral properties of the complex having a ligand which is also a transition metal complex.

ExperimentalAmmonium tetrathiotungstate(VI) was prepared

by the method given in literature8. Potassium hexa- iodoplatinate(IV) used was of Messrs Degussa. Carbon, hydrogen and sulphur were estimated by standard micro chemical methods.

Magnetic susceptibility measurements were made by the Gouy method. Infrared spectra were scanned with an instrument of Perkin-Elmer (type 180). Raman spectra were recorded with a Coderg instrument (PHO; v = 15453.5 cm-1). The electronic absorption spectrum of acetonitrile solution was measured using a Perkin-Elmer EPS-3 T spectrophotometer.

R equests for reprints should be sent to Prof. Dr. A. M ü l l e r , Institu te of Chemistry, U niversity of Dortm und, D-4600 Dortmund, August-Schm idt-Straße, Postfach 500.

Preparation of [(C6H5)4P]2[Pt(WS4)2]. - Freshly prepared concentrated aqueous solutions of K 2[PtI6] (0.5 g) and (NH4)2WS4 (0.5 g) were mixed together and treated with an aqueous solution of [(C6H5)4P]C1 (0.3 g). The brown precipitate was immediately filtered and washed with water and acetone. I t was then extracted with nitro methane leaving a brown black residue. From the nitro methane solution the complex was precipitated with diethyl ether. I t was once more re crystallised in a similar manner. The yield was about 0.25 g.C48P40P2S8W2Pt

Found C 38.4 H 2.75 S 16.8,Calcd C 38.5 H 2.67 S 17.1.

Results and DiscussionTetraphenyl phosphonium bis(tetrathiotungstato)

platinate(II) is brown and insoluble in water, methanol, ethanol, acetone and diethyl ether. It is moderately soluble in nitro methane and less so in acetonitrile and chloroform. I t is stable at room temperature and diamagnetic. I t appears that WS42~ (as other thio ligands) reduces Pt(IV) in [P tl6]2- and thus a Pt(II) complex is obtained.The vibrational spectrum

The 27 normal coordinates of the [Pt(WS4)2]2- ion transform according to the irreducible representations of the point group D2h

r (D2h) = 5 Ag -j- 3 B ig 3 B2g -f- B3g -J- 2 A u -f- 4 BIU -f- 4 B2U -f- 5 B3U.

Whereas the gerade modes are only Raman active, the B1U, B2U and B3U modes are infrared active (rule of mutual exclusion).

A. MÜLLER E T A L. • PREPARATION AND SPECTRAL PROPERTIES OF [Pt(WS4)2]2- 163

The following structure of the [Pt(WS4)2]2- ion is proposed

S» Sb Sb s*

with the WS2t planes perpendicular to the WS2b planes.

The stretching frequencies can be classified according to the species

(r = 3 Ag -j- 2 Blg -j- B2g -f- B1U + 2 B2U -f- 3 B3U)as

r (WS1) = Ag -j- B2g -(- B1U b 3U (v i ) (v9) (vis) (»-23)

r (WSb) = Ag -(- Blg -f- b 2U + b 3UW i v e ) ( V 1 9 ) (V2 i )

r (PtS) = Ag -j- Blg -f- B2U -j- B3U (V») {v7) (v20) (V25)

which means that the number of IR or Raman active stretching vibrations of each type is two (ordering of the n in the usual way).

The bending vibrations can be classified according to the species

r (bending) = 2 Ag -f- Blg -f- 2 B,g ~\- B3g -j- 2 Au -f- 3 BIU -)- 2 B2U + 2 B3U

(six Raman active and seven IR active).

The four out-of-plane vibrations of the planar system WS2PtS2W

r (y) = Au (Tring) + 2 Blu[77(WS2Pt) and 77(S2PtS2)] + B2g [77(WS2Pt)]

should have wave numbers lower than about 50 cm-1.

A vibration which corresponds to a torsion of theW Sg group falls also under the species Au and is

both IR and Raman inactive. There is one ungerade vibration B2U involving mainly a deformation of the PtSg angles (which do not belong to the rings). This should also lie at very low wave numbers. In the corresponding gerade vibrations it is necessary that all PtS2 angles (that means also a ring deformation) are involved. I t thus means that one should find 4 IR and 5 Raman active fundamentals

r (bending rest:

164 A. MÜLLER E T AL. • PREPARATION AND SPECTRAL PROPERTIES OF [Pt(W S4)2] 2-

The vibrational spectra show that WS42- acts as a bidentate ligand. The four theoretically predicted IR and Raman active vibrations due to v(WSl) are observed. We could not measure strong Raman scattering mainly due to the brown colour of the substance so that only the most intense lines could be observed. I t is interesting to note that thev (WSl) modes give much more intense lines in the Raman spectrum than the v(WSb) vibrations according to the higher bond order in the terminal groups. I t is not easy to distinguish between the two u and the two g stretching vibrations of the bridging and terminal WS2 groups, i.e . v15/v23, vi»!vu> vi/v9 and v j v 6. However, the 500 cm-1 line with the highest intensity is definitely (Alg) (in phase vibration of the two symmetrical stretching vibrations of WS^)- Also the assignment given in Table I for the other WS stretching vibrations seems plausible as it is in agreement with the facts that a) a symmetric stretching vibration should be stronger/weaker than an asymmetric one in the Raman/IR spectrum; b) the WSn group belongs to the exceptions with vs > vas9 (for a review on transition metal chalcogen vibrations see10) ; c) corresponding vs (i. p.) and vs (o.p.) vibrations agree as well as Vas ( i-P -) and ^as (o.p.) (heavy masses of W and Pt!).

Due to the coordination of WS42- splitting of the degenerate modes v2(E) and y4(F2) of the isolated ion is also observed. Theoretically four bands are

expected in the IR as the torsion vibration is not IR active. Four bands are observed in the spectrum, but it is difficult to distinguish between pw(WSg), pr(WS*), ^(WSg) and A2g) should overlap with the strong charge transfer of the ligand. With A x ~ 26,000 cm-1 (for PtS4 chromophore13) and F2 = 600 cm-1 14 one gets Vi = 23,900 cm-1. In Pt[S2P(C6H5)2]2 the longest wave length d —>d transition vx occurs13 at 22,600 cm-1.

One of the authors (M. C. C.) thanks the “Alexander von Humboldt Foundation” for a fellowship. Thanks are also due to the “Fonds der Chemischen Industrie” and the “Deutsche Forschungsgemeinschaft” for financial assistance.

Table II. E lectronic spectrum [cm-1] and extinction coefficients (1 mole-1 cm -1).

[Pt(W S4)2] 2- (H S)2W S2a W S42-

23,300 (e ~ 1 0 4) \ b ~ 26,000 sh j

32,000 (e ~ 2 x 104)

23,000 \ b2 6 ,1 0 0 /36,100

Vl(lA x -* !T2)

v2(1A 1 -> !T2)

= 25,500 : tj -► 2e

= 36,100

a C2v sym m etry o f the chromophore S /W S .,2- as in [Pt(W S4)2] 2-. b Rough assignm ent: 7t(S) -> d(W).

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