Equilibrium studies on binary and ternary Cu(II) complexes containing ethylenediaminediacetic acid and a series of O?-O?, N-O? and N-N donor ligands

The formation constants for ternary metal complexes (MLA) where L = ethylenediaminediacetic acid (EDDA), M = Cu(II) and A = glycine, alanine, leucine, serine, threonine, methionine, proline, phenylalanine, tryptophan, histidine, aspartic acid, ethylenediamine, histamine, 2,2′-bipyridyl, 1,10-phenanthroline, imidazole, oxalic acid, malonic acid, pyrocatechol and nitropyrocatechol have been investigated by pH-metric method at 35°C andμ = 0.2 M (KNO₃). With respect to the donor atoms on ligand A, the stabilities of the ternary complexes increase in the order O⁻-O⁻ < N-O⁻≈N-N. The stabilities of the various ternary complexes decrease with the increasing number of carboxylate groups on the ligand in the order ethylenediamine (EN) < ethylenediamine monoacetic acid (EDMA) < EDDA. Various factors influencing the formation and stabilities of ternary complexes are discussed.