Binary and ternary complexes of copper(II) containing some potentially tridentate ligands
The multiple equilibria involved in some new ternary systems of general formula CuII–A–B [A =DL-2,3-diaminopropionic acid (dapa) or DL-2,4-diaminobutyric acid (daba); B = daba, DL-ornithine (Orn), DL-3-aminobutyric acid (3-aba), or DL-4-amino-3-hydroxybutyric acid (ahba) for the systems with A = dapa, and B = Orn, DL-2-aminobutyric acid (2-aba), 3-aba, or ahba for the systems with A = daba] have been studied pH-metrically at 37 °C and I= 0.15 mol dm–3(Na[ClO4]). Auxiliary data, such as the acid dissociation constants of dapa, daba, Orn, and ahba and their binary stability constants with CuII, have also been obtained under identical conditions. The results suggest that dapa, daba, and ahba bind in a tridentate manner in their 1 : 1 binary complexes. However, Orn appears to co-ordinate in a glycine-like mode both in the binary and ternary systems. The probable structures for the various binary and ternary complexes in this study are discussed in terms of their stability-constant data. In general, the results suggest that CuII prefers to have one five- and one six-membered chelate ring rather than two rings of the same size in its co-ordination sphere.