Tungsten(VI) and mixed tungsten,molybdenum(VI) complexes of tartaric acid

A number of studies of species formed in the tungsten(VI) oxide-R,R-(+)-tartaric acid-water system have been carried out(^1–3). While various species have been proposed, it is generally accepted that three main ones predominate. Two have tungsten: (+)-tartaric acid [(+)-tartH₄] ratios of 11 and the third has the same ratio of 12. This latter species cannot be that proposed by Avaloset al.⁽³⁾ since both ligands in their structure would have to be present as unidentates.Recently we have shown⁽⁴⁾ that high resolution¹H and¹³C n.m.r. studies were particularly useful in delineating the complexes formed in aqueous solution in the analogous molybdenum(VI) system. Thus, we turned our attention to the corresponding tungsten(VI) complexes, especially in view of the controversy surrounding the nature of the species formed in aqueous solution with (+)-tartH₄. The results of our studies, presented below, indicate that only a few species are formed, and that these are quite analogous, as might be expected, to the previously described molybdenum(VI) species⁽⁴⁾. In addition we have observed the formation of a mixed dimeric species [MoWO⁴{(+)-tart}₂]^4–, whose structure is akin to the mono-metallic complexes, as well as the well-characterized antimony(III) and arsenic(III) dimers of (+)-tartH₄⁽⁵⁾.