Synthesis, characterization and electrochemical behaviour of some manganese and copper complexes with tetradentate Schiff base ligands

A series of symmetrical tetradentate Schiff bases derived from substituted salicylaldehyde and ethylenediamine were prepared and characterized by elem ental analysis, IR, UV-Visible and H-1 NMR spectroscopy. The interaction of these bases with MnCl2.4H(2)O and CUCl2.2H(2)O have been studied, leading to the preparation of manganese(II) and copper(II) complexes. Microanalysis , molar conductance, IR, UV-Visible spectroscopy, magnetic measurements and ESR spectra have been used to elucidate the stucture of the resultant comp lexes. The experimental data show that ail the Schiff base ligands N,N'-bis (2-hydroxybenzyl)ethylenediimine (H2L1), N,N'-bis(2-hydroxyacetophenyl)ethy lenediimine (H2L2) and N,N'-bis(2-hydroxypropiophenyl)ethylene (H2L3) yield 1:1 compounds except for the ligand H2L2 which gave a 2.1 compound with ma nganese(II). The spectral studies support the binding of the ligands with t wo N and two O donor sites to the metal(II) ion, giving an arrangement of N 2O2 donor groups. Magnetic and ESR data indicate that the manganese(II) ado pts a high spin configuration in the complexes studied and the covalent cha racter of the metal-ligand bonding in the copper(II) complexes increases wi th the increasing electron donating effect of the ligand substituents R. Th e electrochemical behaviour of the manganese(II) and the copper(II) complex es was determined by cyclic voltammetry which shows that the chelate struct ure and electron donating effects of the ligand substituents are among the factors influencing the redox potentials of the complexes.