Some new symmetrical diimino tetradentate Schiff base ligands were synthesized by the reaction of 3,4-diaminobenzophenone with salicylaldehyde derivatives, such as [3,4-bis(((2-hydroxy-4-methoxyphenyl)methylene)amino)phenyl]phenylmethanone (L 1 ), [3,4-bis(((2-hydroxy-5-methoxyphenyl)methylene)amino)phenyl]phenylmethanone (L 2 ), [3,4-bis(((5-bromo-2-hydroxyphenyl)methylene)amino)phenyl]phenylmethanone (L 3 ) and [3,4-bis(((2-hydroxy--5-nitrophenyl)methylene)amino)phenyl]phenylmethanone (L 4 ). Additionally, a tetradentate Schiff base ligand [3,4-bis(((2-hydroxy-3-methoxyphenyl)methylene)amino)phenyl]phenylmethanone (L 5 ) was synthesized. All the Schiff bases and their Ni(II), Cu(II) and Zn(II) complexes were characterized using elemental analysis and infrared, electronic, mass and 1 H-NMR spectroscopy. The formation constants of the complexes were measured using UV-Vis spectroscopic titration at constant ionic strength 0.10 M (NaClO 4 ), at 25 °C in dimethylformamide (DMF) as solvent.
64ASADI, SEPEHRPOUR and MOHAMMADI veral metal chelates of the ONNO donor class of Schiff bases were studied as oxygen carrier and they were found to be useful models for bioinorganic processes. 6,7 Schiff bases are effective inhibitors and could be adsorbed on the surface of metals. 8 Symmetric tetradentate Schiff base complexes have been extensively used as macrocycle models. 9 These compounds have received considerable attention because of their potential use as catalysts, 10-14 and their antibacterial, 5,15,16 antifungal, 17 antitumour 18,19 and herbicidal activities. 20 The main goals of this study were the synthesis and characterization of some new tetradentate Schiff bases and their complexation with Ni(II), Cu(II) and Zn(II) metals. These compounds were characterized by elemental analysis, and FT-IR, 1 H-NMR, mass and UV-Vis techniques. In addition, the formation constants, K f , were determined spectrophotometrically and the free energy changes, ΔG , at 25 °C, were calculated for the complexes. The effects of the electronic and steric nature of substituents on the Schiff base type ligands on the formation constants and free energy changes resulting from complex formation were studied.
