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 coordi nation of dihydrogenphosphato and monohydrogenphosphato ligands is ind icated 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. T hese are re-dissolved in more basic media to yield, besides polynuclea r hydroxo-bridged species, a mononuclear bis-orthophosphate complex wi th bidentate chelation of the ligands. Finally, a species where the me tal ion is chelated by a phosphate group and bound also to two termina l hydroxo groups is detected.