Cobalt(II), Nickel(II), Copper(II) and Zinc(II) Complexes with New Tetraaza Schiff Base Ligands: Synthesis, Characterization and Thermodynamic Studies

New complexes of Co(II), Ni(II), Cu(II) and Zn(II) with four new tetraaza Schiff base ligands, N,N'-bis(2-quinolylmethylidene)-1,2-ethanediimino (L1), N,N'-bis(2-quinolylmethylidene)-1,2-propanediimino (L2), N,N'-bis(2-quinolylmethylidene)-1,3-propanediimino (L3), N,N'-bis(2-quinolylmethylidene)-4-nitro-1,2-phenylenediimine (L4), were synthesized and characterized by elemental analysis, IR, 1H NMR, and UV-Vis spectroscopy. The thermodynamic formation constants of the complexes were measured spectrophotometrically, at the constant ionic strength 0.1 M (NaClO4), at 25 °C in MeOH solvent. The trend of the complex formation of a given metal ion with the ligands was found to be as follows L2 > L1 > L3 > L4 and the trend of a given ligand with the metal ions was Co(II) > Ni(II) > Cu(II) > Zn(II).