Sulfur complexes, charge-transfer bands

A chemistry of cobalt-sulfide-thiolate molecular clusters comparable with that of iron systems has also begun to emerge. Treatment of [Co4( -SPh)6(SPh)4]2- with HS- in acetone affords the octanuclear cluster [Co8(ji4-S)6(SPh)8]4 isolated as its Pr4N+ salt.988 In MeCN solution the complex is red-purple with intense sulfur-core charge transfer bands which obscure the Co" d-d transitions. This behaviour contrasts with that of both mono- and poly-nuclear cobalt"-thiolate complexes, which all display LMCT bands below 440 nm and have well-developed v2 and v3 features. The [Co8(/j4-S6)]4+ core sustains reversible one-electron oxidation and reduction (E]l2 = —0.54, — 1.18 V, MeCN) and chemical reduction with sodium acenaphthylenide in THF gives [Co8(/r4-... 

Energies of the Maxima of the First Charge-Transfer Bands of Complexes of Sulfur Compounds with Tetracyanoethylene (A) and Chloranil (B) in Chloroform177... 

Dithiophosphinate complexes [V(S2PX2)3] (X = F, CF3, Me, Ph, OEt) were reported293 and the structure where X = OEt has been determined.294 The six sulfur atoms form a trigonally distorted octahedron around vanadium with the average V—S distance 2.45 0.02 A. Visible spectra (in CH2C12 or an oriented crystal) show four bands a charge-transfer band is observed at 22700 and 23 300 cm-1 in the solution and crystal. The others at 12 820, 18080 and 26 400 cm-1 (13 200, 18 400 and 26 400 in the crystal) are the expected transitions for octahedral V111. 

In the extreme class III behaviour,360-362 two types of structures were envisaged clusters and infinite lattices (Table 17). The latter, class IIIB behaviour, has been known for a number of years in the nonstoichiometric sulfides of copper (see ref. 10, p. 1142), and particularly in the double layer structure of K[Cu4S3],382 which exhibits the electrical conductivity and the reflectivity typical of a metal. The former, class IIIA behaviour, was looked for in the polynuclear clusters of copper(I) Cu gX, species, especially where X = sulfur, but no mixed valence copper(I)/(II) clusters with class IIIA behaviour have been identified to date. Mixed valence copper(I)/(II) complexes of class II behaviour (Table 17) have properties intermediate between those of class I and class III. The local copper(I)/(II) stereochemistry is well defined and the same for all Cu atoms present, and the single odd electron is associated with both Cu atoms, i.e. delocalized between them, but will have a normal spin-only magnetic moment. The complexes will be semiconductors and the d-d spectra of the odd electron will involve a near normal copper(II)-type spectrum (see Section 53.4.4.5), but in addition a unique band may be observed associated with an intervalence CuVCu11 charge transfer band (IVTC) (Table 19). While these requirements are fairly clear,360,362 their realization for specific systems is not so clearly established. 

Irradiation of the charge transfer band of complexes of 2,2,3,3-tetraarylthiiranes 178 and tetracyanoethylene results in C-C bond cleavage of the intermediary sulfur radical cation [327] to give 179, which is an example of a distonic radical cation. 

When sodium lignosulfonate or sulfur lignin are compounded, for instance, with iodine or bromine, complexes supposedly form (16-17). These systems are conductors with mixed ionic and electronic nature. Presumably they are charge transfer complexes, since the electronic conductivity predominates (18-19). These compounded materials form charge transfer structures (20). Water is supposed to introduce ionic conductivity to the system. Impurities affect conductivity, too (21). In any case, the main models of conductivity are probably based on the band model and/or the hopping model. 

The UV/visible absorption spectra of [MoO S4 ]2 (n = 0-2) complexes are dominated by the sulfur-to-metal charge transfer transitions of the anion and these bands often serve to characterize the particular system, even though these absorptions may be correlated with those of the parent anion.4 The reduction in symmetry due to complex formation often leads to a broadening or splitting of the bands and, in the majority of the d transition metal complexes, the lowest energy band is red-shifted by an amount which is dependent both upon the nature of the transition metal and the number of such metals bound per MoviO S4 group. 

---