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 (l^1), n,nˊ-bis(2-quinolylmethylidene)-4-methy-1,2-phenylenediimine (l^2), n,nˊ-bis(2-quinolylmethylidene)-4-chloro- 1,2-phenylenediimine (l3), n,nˊ-bis(2-quinolylmethylidene)-4-carboxylic-1,2-phenylenediimine (l^4), n,nˊ-bis(2-quinolylmethylidene)-4- nitro-1,2-phenylenediimine (l^5), 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: l^2 > l^1 > l^3 > l^5 > l^4. the trend for complex formation of the metal ions with a given ligand is as follows: zn(ii) > cu(ii) > ni(ii).