Alternating-current polarographic study of the glycine, histidine, and citric acid coordination in copper(II) complex compounds

Alternating-current polarography and spectrophotometry were used to study the formation of copper(II) complex compounds CuLn2-n (n = 1, 2, 3, 4, 5, and 6) in the reaction with glycine or histidine and Cu(H2Citr)n2(1-n) (n = 1, 2, 3) in the reaction with citric acid in a 0.1 M NaClO4 solution at 20°C (pH 6.0). In the complexes containing the greatest possible number of ligands, the glycine and histidine anions (L-) are monodentate, while the H2Citr2- anion is a bidentate ligand. The copper(II) complexes are reduced in two electrochemical steps exhibiting different degrees of reversibility. The ratio of heights of the corresponding ac peaks accounts for the change in the ligand coordination mode upon the transition from one composition of the complex to the other. The calculated stepwise formation constant for Cu(H2Citr)34- is β = (5 ± 1.6) × 102 l/mol. © 1999 MAEe cyrillic signK "Hayκa/Interperiodica".