SYNTHESIS, SPECTRAL AND ELECTROCHEMICAL STUDIES OF DIOXOTUNGSTEN(VI) COMPLEXES OF BINUCLEATING SCHIFF-BASES DERIVED FROM METHYLENE(SALICYLALDEBYDE) OR DITHIO-BIS(SALICYLALDEBYDE) AND VARIOUS HYDRAZIDES

The syntheses of binuclear dioxotungsten(VI) complexes of the type [(W O2)(2)L], where L is a flexibly bridged hexadentate tetraanionic schif f base derived from the condensation of methylene- or dithiobis(salicy laldehyde) with isonicotinoylhydrazide, benzoylhydrazide, p-nitrobenzo ylhydrazide and furoylhydrazide are reported. The IR and NMR spectral data suggest an oligomeric structure for these complexes in which each tungsten atom achieves a pseudo-octahedral structure via W - O-->W br idging. Cyclic voltammetric measurements indicate irreversible to quas ireversible reduction of the dioxotungsten(VI) complexes to oxotungste n(IV) with a cathodic reduction potential of - 1.0 to - 1.1 V vs SCE a t the scan rate of 500 mV/s. The bridging methylene (- CH2 -) or dithi o (- S - S -) group has very little effect on the thermodynamic stabil ity of the complexes.