Ternary cobalt complexes with amino acids: potentiometric study, modelization and solid-state investigation

Abstract

A study in solution of new ternary complexes of cobalt (II) with the tetradentate ligand Schiff base (N,N’-bis (2-hydroxy acetophenone) ethylenediimine; H2L) as primary ligand and the amino acid (histidine or tryptophan) as the secondary one has been realized by potentiometry. The stability constants of the complexes have been determined with the calculation program SIRKO. It has been found that the ternary complexes are more stable than the corresponding binary ones. The study has been completed by modelization of all the species found in solution by molecular mechanics with the program EMO (Energy of Molecule).
The complexes isolated in powdered form were characterized by elemental analysis, molar conductance, IR spectra, magnetic and electronic spectra. The spectral results support the binding of H2L with two N and two O donor sites to cobalt ion and the binding of histidine or tryptophan by monodentate maner with O donor site, giving an octahedral geometry.
Magnetic and Electronic results show that the Cobalt (II) has been oxidized to Co(III) and has a low spin configuration.