Complexes of aminophosphonates .9. Copper(II) complexes of citric acid derivatives

Complex formation between copper(II) and 3-amino-3-phosphonoglutaric acid (Apga), an ambidentate aminophosphonate or citric acid derivative, was studied in aqueous solution by pH-potentiometry and EPR and electronic spectroscopy. Complexation with the parent molecules citric acid and tricarballylic acid was reinvestigated. The stoichiometries and stability constants of the complexes formed in these systems were determined at 25 degrees C at an ionic strength of 0.20 mol dm(-3) (KCl). Stability constant data and spectroscopic results revealed that in the acidic pH range Apga behaves as a citric acid derivative, forming the phosphonate-bridged dimeric species Cu(2)A(2)H(2), while in the basic pH range, with decreasing proton competition at the amino binding site, it rearranges to yield mononuclear complexes involving aminophosphonate-like (NH2, PO32-, CO2) coordination.