STABILITY OF TERNARY COPPER AND NICKEL-COMPLEXES WITH 1,10-PHENANTHROLINE

This work presents a comparative analysis of the behavior of copper(II) and nickel (II) towards the formation of mixed-ligand complexes with 1,10-phenanthroline as primary ligand. Secondary ligands were acetylacetonate, salicylaldehydate (O-O donors), glycinate, or tyrosinate (O-N donors). The formation of hexacoordinate complexes was observed in the case of nickel. Stability enhancement compared to statistical expectations is found for complexes where the secondary ligand is an O-O donor and for tyrosinate. These observations are explained in terms of a hardness increase in the species M(phen)2+, as compared to M2+, due to the well-known pi-acceptor behavior of aromatic imines, which makes the first species more attractive to harder ligands as oxygen donors. In the case of tyrosinate, increase in stability is attributed to a hydrophobic interaction between the phenolic group and 1,10-phenanthroline.