PHOSPHATE COMPLEXATION OF OXOVANADIUM(IV) - EVIDENCE OF BIDENTATE CHELATION OF ORTHOPHOSPHATE

The interaction of VO(IV) with orthophosphate in aqueous solution has been investigated by EPR and electronic absorption. Monodentate coordination of dihydrogenphosphato and monohydrogenphosphato ligands is indicated below pH 4.5. Over the pH range 4.5-8.5 precipitation of VO(IV) orthophosphates depletes the solution of most of the vanadium ions. These are re-dissolved in more basic media to yield, besides polynuclear hydroxo-bridged species, a mononuclear bis-orthophosphate complex with bidentate chelation of the ligands. Finally, a species where the metal ion is chelated by a phosphate group and bound also to two terminal hydroxo groups is detected.