Formation constants and thermodynamic parameters of bivalent Co, Ni, Cu and Zn complexes with Schiff base ligand: Experimental and DFT calculations

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.