new tetraaza schiff base ligands and their complexes: synthesis, characterization and thermodynamic studies

some new symmetrical tetraaza schiff base ligands containing 2-quinolinecarboxaldehyde moiety formed from condensation reaction of 2-quinolinecarboxaldehyde and o-phenylenediamine derivatives, such as n, nˊ-bis(2-quinolylmethylidene)-4-methoxy-1, 2-phenylenediimine (l1), n, nˊ-bis(2-quinolylmethylidene)-4-methy-1, 2-phenylenediimine (l2), n, nˊ-bis(2-quinolylmethylidene)-4-chloro-1, 2-phenylenediimine (l3), n, nˊ-bis(2-quinolylmethylidene)-4-carboxylic-1, 2-phenylenediimine (l4), n, nˊ-bis(2-quinolylmethylidene)-4-nitro-1, 2-phenylenediimine (l5), and their ni(ii), cu(ii), zn(ii) complexes, have been synthesized. the ligands and their metal complexes have been characterized by molar conductance, elemental analysis, ir, 1h-nmr and uv-vis spectroscopy. the formation constant and the free energy of the complexes were determined using electronic spectroscopic titration at constant ionic strength 0.1 m (naclo4), at 25°c in meoh solvent. the comparison of the formation constants and the thermodynamic parameters show that the trend of complex formation toward a given ligand is as follows: l2 > l1 > l3 > l5 > l4 .the trend for complex formation of the metal ions with a given ligand is as follows: zn (ii) > cu (ii) > ni (ii).