COMPLEXES OF AMINOPHOSPHONATES .9. COPPER(II) COMPLEXES OF CITRIC-ACID DERIVATIVES

Complex formation between copper(II) and 3-amino-3-phosphonoglutaric a cid (Apga), an ambidentate aminophosphonate or citric acid derivative, was studied in aqueous solution by pH-potentiometry and EPR and elect ronic spectroscopy. Complexation with the parent molecules citric acid and tricarballylic acid was reinvestigated. The stoichiometries and s tability constants of the complexes formed in these systems were deter mined at 25 degrees C at an ionic strength of 0.20 mol dm(-3) (KCl). S tability 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 aminophosphon ate-like (NH2, PO32-, CO2) coordination.