Synthesis, spectral and electrochemical studies of dioxotungsten(Vl) complexes of binucleating schiff bases derived from methylene- or dithio-bis(salicylaldehyde) and various hydrazides

Abstract

The syntheses of binuclear dioxotungsten(VI) complexes of the type [(WO₂)₂L]. where L is a flexibly bridged hexadentate tetraanionic schiff base derived from the condensation of methylene- or dithiobis( salicylaldehyde) with isonicotinoylhydrazide,∙benzoylhydrazide, <i>p</i>-nitrobenzoylhydrazide 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 <i>via </i> W<img src='http://www.niscair.res.in/jinfo/threedot.gif' border=0>O->W bridging. Cyclic voltammetric measurements indicate irreversible to quasireversible reduction of the dioxotungsten(VI) complexes to oxotungsten(IV) with a cathodic reduction potential of - 1.0 to - 1.1V _<i>vs</i>SCE at the scan rate of 500 mV/s. The bridging methylene (- CH₂-) or dithio (- S- S-) group has very little effect on the thermodynamic stability of the complexes.