Ternary complexes of zn(ii)‎, cd(ii)‎, pb(ii)‎ and cu(ii)‎ with 2,2'-bipyridyl or 1,10 phenanthroline and some bidentate salicylamides

Abstract EN

The stability constants of Zn (II), Cd (II), Pb (II) and Cu (II) complexes containing 2, 2'-bipyridyl (bipy) or 1, 10-phenanthroline (phen) as the first ligand and N-(phenyl) salicylamide (PHS), N-(p-chloro phenyl) salicylamide (CPHS), N-(p-methyl phenyl) salicylamide (MPHS), or N-(p-methoxy phenyl) salicylamide (MePHS) as the second ligand were determined in 70 % (v / v) dioxane water medium at 30 ± 1 °C and 0.1 M (NaClO4) ionic strength in a nitrogen atmosphere.

The results give evidence that all these complexes have the same structure and therefore the binding sites of the ligands have to be imino nitrogen and oxygen of hydroxyl group.

The stability difference between the binary and the ternary complexes are in good agreement with this interpretation.

All the ternary complexes are more stable than would be expected on a statistical reasons, i.

e., the difference, log Km = log KMA MAL - log KM ML is negative (A = bipy / phen, L = PHS, CPHS, MPHS or MePHS).

In addition, the enhanced stability of the ternary complexes is discussed on the basis of the -acceptor qualities of heteroaromatic N-base and the occurrence of a cooperative effect due -systems of the two ligands bound with the same metal ion.

The ternary complexes formed with phen as ligand are less favoured than the corresponding complexes formed with bipy and is discussed on the basis of steric reasons.