ABSTRACT. Formation constant (Kf) values of Schiff base ligand, L = methyl-2-{[1-methyl-2-(aceton)ethylidynenitrilo]ethyl}amino-1-cyclopentenedithiocarboxylate, with Co(II), Ni(II), Cu(II) and Zn(II) ions has been determined spectrophotometrically for 1:1 complex formation at constant ionic strength 0.01 M (NaClO4), and at various temperatures in DMF solvent. Thermodynamic studies of the complexes have been carried out and their stability were found in the order CoL > CuL > NiL > ZnL. The enthalpy, entropy and Gibbs free energy changes of the complexation reaction have been evaluated from the temperature dependence of the formation constant. Our experimental results revealed that the complexation process is spontaneous, exothermic and entropically unfavorable. Also, B3LYP/(LANL2DZ and ‫)٭٭‪6-311G‬‬ level density functional theory is applied on the structure and stability of Schiff base ligand and their complexes. HOMO-LUMO and binding energies were calculated to obtained stability of the complexes. The theoretical results are compared with experimental data.

Sn NMR, IR and mass spectroscopy. IR spectral data show that the fifth coordination position of tin atom is occupied by an oxygen atom of Schiff base ligands. In the light of titled techniques, trigonal bipyramidal geometry around the tin atom is proposed for the synthesized complexes. The in vitro antibacterial activities of the complexes against Staphylococcus aureus and Escherichia Coli have been studied. It was found that they possess significant antibacterial activity. Also, DFT/B3LYP method was used to analyze the electronic structures and study of the geometries. The thermodynamic formation constants of the complexes were determined spectrophotometrically at 25 °C in DMF solvent.