Metallation of tetradentate N2O2 Schiff base with Mn(II), Co(II), Cu(II) and Zn(II): synthesis, characterization and formation constants measurement

Four Schiff base ligands, salabza-H-2 = N, N'-bis(salicylidene)-2-aminobenzylamine, were synthesized by condensation of one mole of 2-aminobenzylamine and two moles of salicylaldehyde and/or two moles of substituted salicylaldehyde (5-OMe, 5-Br, 5-NO2). All the four Schiff bases and their Mn(II), Co(II), Cu(II) and Zn(II) complexes are characterized by UV-Vis, FT-IR, H-1 NMR spectroscopy, mass spectrometry and elemental analysis. The formation constants and the Gibbs free energies were measured spectrophotometrically for 1: 1 complexes in methanol in constant ionic strength (I = 0.1 mol dm(-3) NaClO4) and at 25 degrees C. The data refinement was carried out with the SQUAD program. The trend of formation constants of H2L1 with M(II) follows the order: Mn(II) (3.97) < Zn(II) (4.30) < Co(II) (4.89) < Cu(II) (5.73) Also, the trend of formation constants of ligand toward a given metal (for example Mn) is as follows: H2L1 (rho-OMe) (3.97) > H2L2 (rho-H) (3.65) > H2L3 (rho-Br) (3.37) > H2L4 (rho-NO2) (3.04)