STRUCTURAL INFLUENCE ON THE STABILITY OF MIXED-LIGAND COMPLEXES OF COPPER(II) WITH ALIPHATIC DIAMINES AND AMINO-ACIDS

The stabilities of mixed ligand complexes of Cu(II)-diamine(A)-amino acid(B) systems, where diamine refers to 1,2-diaminopropane (dp) or 1,3-diaminopropane (tp) and amino acid to DL-2-aminobutyric acid (2-aba), DL-3-aminobutyric acid (3-aba), 4-aminobutyric acid (4-aba) or DL-4-amino-3-hydroxybutyric acid (ahba) have been studied by computer based analysis of the pH-metric data at 37-degrees-C and I = 0.15 mol dm-3 (NaClO4). In the Cu(II)-dp(A)-2-aba, 3-aba and 4-aba (B) systems only CuAB type of ternary species is detected, while in the corresponding tp(A) systems in addition CuABH is also present. The tendency of mixed complex formation decreases in the order 3-aba > 2-aba > 4-aba in the former systems, while in the latter systems the order is 2-aba > 3-aba > 4-aba. These trends are explained on the basis of the chelate ring size. In the Cu(II)-dp/tp(A)-ahba (B) systems only CuAB type of ternary species has been detected. In this species ahba(B) ligand binds the metal in a bidentate manner, though it is tridentate in its binary species with Cu(II).