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A new electron, six-electron, sulfide-bicapped trinuclear [Mo.sup.IV] cluster containing all sulfur coordination where each Mo atom is seven coordinated and retains the oxidation state of +14 is described. The formation of a binuclear tungsten(V) complex under identical reaction conditions with one electron oxidation of each [W.sup.IV] center and the redox chemistry of these complexes are rationalized.

Complexes analogous to the active site of dissimilatory nitrate reductase from Desulfovibrio desulfuricans are prepared. The NO evolution or nitrosylation to the Fe-S cluster is known from perplasmic nitrate reductase isolated from Pseudomonas dentrificans.

The synthesis, characterization and comparative chemical and structural analyses of a new series of dimeric bis(dithiolene) Mo(IV) and W(IV) complexes and one monomeric bis(dithiolene) tungsten bis(thiophenolate) complex are described. The pH-dependent interconversion has shown that even the pentacoordinated Mo(IV) and W(IV) bis(dithiolene) moieties are forced to dimerize and they can be reverted back to the corresponding monomeric complex.

The oxidized structure as [Mo(super IV)(OH(sub x))(S.Cys)(S2pd)(sub 2)] (x=1or 2) was established by X-ray crystallography. It is demonstrated that the nitrate is first bound to the molybdenum of the reduced cofactor with the formation of an enzyme substrate complex followed by the essential oxotransfer and the elimination of nitrite ion with the formation of oxidized oxomolybdenum cofactor [Mo(super IV)(O)(S.Cys)(S2pd)(sub 2)].

The article focuses on the chemistry of [Et4N][MoIV(SPh)(PPh3)(mnt)2] as an functional analogue of the active site for dissimilatory nitrate reductase of Desulfovibrio desulfuricans. It also reveals that the substitution of thiolate by chloride yielded structurally similar complex of [Et4N][MoIV(Cl)(PPh3)(mnt)2].

Review: 103 refs. [ABSTRACT FROM AUTHOR]