Abstract

A. Mohan, K. Radha and M.Srinivas Mohan*

The formation and stability of binary and ternary Cu(ll) complexes containing 1,10-phenanthroline (PHEN), 2,9-dimethyl 1,10-phenanthroline (DPHEN) and 5-nitro 1,10-phenanthroline (NPHEN) was investigated potentiometrically and the formation constants are reported at 35.0 °C and u = 0.2 (KNO3) . In ternary complexes the second ligand used was glycine. α-alanine. serine, threonine,metheonine, phenylalanine, tryptophan, tyrosine or 3,4-dihydroxy phenylalanine. In order to assess the influence of the PHEN, DPHEN and NPHEN (L), the stability of the ternary complexes (MLA) were quantitatively compared with stability of the corresponding amino acid Cu(ll) binary complexes (MA) in terms of the parameter Δlog K. With respect to the primary ligand (L) the stability of the ternary complexes involving amino acids without an aromatic side chain increases in the order: PHEN > DPHEN > NPHEN. The extent of stacking interactions in ternary complexes involving amino acids with an aromatic side chain was quantitatively assessed in terms of the parameters Δ Δ log K, K, and (% MLA),,. In these stacks ternary complexes the stability with respect to the primary ligand ia DPHEN > NPHEN > PHEN. The influence of factors such as inductive effects of the substituents, metal dπ —> ligand pπ backbonding and metal ion mediated stacking interactions on the stability of the binary and ternary complexes are discussed.

Potentiometrically; Glycine; Quantitatively; PHEN; DPHEN

[ View HTML Full Text]