Thio complexes, molybdenum

In the anaerobic digester environment, one would thus expect sulfide reactions to dominate the Mo chemistry since the oxy-anions of the more reduced forms of this metal are relatively unstable (Tucker et al, 1997). For Facility J, total dissolved Mo concentration in the anaerobic digester supernatant was high (47 /rg/l Fig. 3) but the Mo(VI)/(total dissolved Mo) ratio was only 0.15, showing substantive formation of soluble species other than molybdate in the system. The dominant form of molybdenum present in the digester supernatant is unknown and is believed to be molybdenum sulfides. Formation of thio-complexes is also suggested by the ratio... 

The first thionitrosyl complex was discovered by chance during an attempted synthesis of molybdenum nitrido complexes in the presence of a source of sulfur, tetrathiuram sulfide.168 This work of Dilworth and Chatt was reported in 1974 and ultimately led to the syntheses of a range of Mo, Re and Os thionitrosyl complexes starting with the respective nitrido complexes.143,164 Nitrosyl complexes, like carbonyls, had been known for decades, and the more recent syntheses of thio-carbonyl complexes forebode the advent of thionitrosyl complexes. However, convenient synthetic routes based on analogies with syntheses of NO complexes were generally not available because the requisite precursors did not exist or were inconvenient to handle. Sulfiliminato complexes (M=N=SR2) of transition metals are as yet unknown. The chemistry of thionitrosyl complexes was the subject of a recent review.179... 

The electrochemical reversibility of the M(VI)/M(V) couple for the complexes with sterically hindered ligands contrasts with the reported behavior of the [MoO(SPh)4] complex, which exhibited electrochemical irreversibility for the Mo(V)/Mo(VI) step but a reversible Mo(IV)/ Mo(V) couple. The sterically hindered aromatic substituent groups stabilize the molybdenum(VI) complex and decrease relative to the thiophenol derivative. The molybdenum(VI) species can also be isolated by chemical oxidation. [MoO(PFTP)4] was prepared by chemical redu-tion of [MoO(PFTP)4] . The presence of the electron-withdrawing substituents on the aromatic thiolate increases E ei relative to the thio-phenolate derivative. Evidently the properties of these last complexes are influenced primarily by the electron-withdrawing characteristics of the fluorine substituents rather than by steric factors (33). 

MOLYBDENUM(II) CARBONYL COMPLEXES CONTAINING THIO LIGANDS AND ACETYLENE... 

Ccrvilla, A., Domenech, A., Llopis, E., Vicente, E, and Tamarit, R. 1994b. Molybdenum complexes with slcrically-hindcrcd thio-carboxylate ligands. Electrochemical properties of the anionic complex bis(2,2-diphenyl-2-mercaptoethanoate) dioxomolybdatefVI) in protic solvents. Inorganica ChimicaActa 221, 117-124. 

S- and Se-Donor Ligands. Molybdenum(vi) and tungsten(vi) thio- and seleno-halide complexes are described on p. 153. 

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