Selective binding by a divanadium complex of arsenate over phosphate: A computational study

Density functional theory (M06-2X) calculations on divanadium complexes [(VO)2(bpbp)(A)]2+ of the oxo anions formate, phosphate, and arsenate (A = HCOO−, H 2 PO 4 - , H 2 AsO 4 - ) as well as the diaquo complex [(VO)2(bpbp)(OH2)2]3+ indicate increased binding in the series H2O < HCOO− < H 2 PO 4 - < H 2 AsO 4 - . Aqueous solvation enhances the experimentally observed selective recognition of arsenate over phosphate indicating differences in hydration enthalpies of the respective complexes as the main reason for the surprising differentiation between dihydrogenphosphato and dihydrogenarsenato by the divanadyl complex [(VO)2(bpbp)(OH2)2](ClO4)3·H2O. Deprotonation of the dihydrogenphosphato/arsenato complexes to [(VO)2(bpbp)(HXO4)]+ further increases preferential solvation of the arsenato over the phosphato complex.