Thiomolybdate anions

Cyclic voltammetric investigation4,26,52,53 of [M(MoO S4 )2]2- (M = Ni, n = 0-2 M = Pd, Pt, n = 0) complexes has shown that each can be reduced reversibly in a one-electron process and a further one-electron reduction is possible for some of the complexes. The first reduction is primarily centred on the d8 metal but the second reduction is not so easily described, since the nature of it shows a sensitivity to both the nature of M and the thiomolybdate(VI) anion.26 The electrochemical behaviour of [Co(MoS4)2]3- has also been investigated and two reversible processes, assigned to the 2-/3- and 3-/4- couples, have been observed.21... 

The infrared, Raman, visible and ultraviolet spectra of the thiomolybdate and thio-tungstate species have been examined in detail and are given in several of the papers cited. The Mo-S and W-S stretching frequencies in these compounds are in the vicinity of 480—450 cm-1. The infrared and Raman spectra of some thiochalco-genide anions reported by Muller200 are given in Tables 10 and 11. 

An early example involved mononuclear thiomolybdates and excess cyanide (227). In related studies, Muller and co-workers (i 75,228-230) have isolated and characterized a variety of polynuclear cyano anions of Mo(IV) and Mo(III). These complexes feature and jug-thio ligands,... 

Analytically pure crystalline samples of these thiomolybdates undergo no measurable oxidation or hydrolysis after several weeks in air at room temperature. However, solutions of the anions [Mo Sg] " and [Mo S,] " completely oxidize and hydrolyze after standing under air for several days at ambient temperature. Solutions of [MojSg] ", [MojS,] ", and [MojS,] " oxidize and hydrolyze much faster (within a few hours) at elevated temperatures ( 100°C) under air. Therefore, solutions of these complexes should be handled under an inert atmosphere. The (Ph4P) salts of these thiomolybdates are very soluble in DMF ( lg 50mL" ) and much less soluble in MeCN. 

The resin in the chloride form exchanges chloride against tungstate and thiomolybdate. In the case of tungstate the equation is idealized, because in reality isopolytungstates are present Sodium ions as well as the anions silicate, phosphate, and arsenate are not retained and pass the column. The pH is too high for heteropolytungstate formation with these anions. 

Binary Thiomolybdates and Tertiary Oxo/thiomolybdates A. The (MoS,04-,) Anions Binary Thiomolybdates Tertiary Oxo/thiomolybdates... 

The reactions of oxomolybdates [(Mo04) or (M07O24) ] with H2S or CNH4)2S t under basic conditions give thiomolybdate products that, depending on reaction times or conditions, contain Mo=S and Mo=0 units in various combinations (42). The chemistry and spectroscopic properties of the tetrahedral (MoS 04 anions have been reviewed (43-45) and the structures of various thiomolybdates have been determined (46). 

The thiomolybdate(VI) anions [MoO S4 ] (n = 0-3) have been prepared by a number of methods and, with the exception of [MoOsS] ", act as versatile ligands to a wide variety of metal ions (see Table 1). In each of the compounds listed in this table, the [MoO S4- p ion acts as a bidentate ligand to the metal and the resultant structural versatility has been clearly demonstrated for copper(I) (Table 2). In addition, thiomolybdate(VI) anions are of interest since they have special relevance to aspects of bioinorganic chemistry. Thus, [MoS4] has been widely used in the synthesis of Fe—Mo—S clusters, examples of which serve as spectroscopic analogues for the iron-molybdenum cofactor of the nitrogenases (see Section 36.6.2), and Cu—Mo—S aggregates, which are relevant to the copper deficiency induced by molybdenum in ruminant animals. 

There are several explanations for the high sensitivity of ruminants to increased dietary molybdenum and sulfur, the most plausible being the role of thiomolybdates. Thiomolyb-dates are con wunds formed by the progressive substitution for sulfur and oxygen in the molybdate (MoO ) anion when hydrogen... 

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