Oxovanadium(IV) complexes of di- and triphosphate

The interaction of oxovanadium(IV) ion with diphosphoric and triphosphoric acids in aqueous solution was investigated over the measurable pH range by means of potentiometry, electronic absorption and EPR measurements. The results show that both diphosphate and triphosphate, partially or fully deprotonated depending on pH, are able to chelate the metal ion to yield several mononuclear species. With triphosphate, there is no evidence for the formation of a species analogous to the already reported and well-characterized trinuclear complex formed by diphosphate acting as a chelating and bridging ligand through the four unshared oxygen atoms.