Aqueous tungstovanadate equilibria

Abstract

A combined equilibrium study of tungstovanadates involving potentiometry and ⁵¹V, ¹⁸³W and ¹⁷O NMR spectroscopy has been able to identify 11 main species, giving their formation constants and pK_a values where relevant. Tentative identification was also made of two other non-equilibrium species at lower pH values, in addition to those with a V-centred Keggin structure. The ⁵¹V shifts of the unprotonated hexametalate anions fall into a rational pattern, and the formation constants are all higher than those of the corresponding molybdovanadate species, where comparisons are possible.