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).