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 a cid(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-a mino-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 C uAB type of ternary species is detected, while in the corresponding tp (A) systems in addition CuABH is also present. The tendency of mixed c omplex formation decreases in the order 3-aba > 2-aba > 4-aba in the f ormer 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 s ize. 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 m etal in a bidentate manner, though it is tridentate in its binary spec ies with Cu(II).