Synthesis and experimental/theoretical evaluations on redox potentials and electronic absorption spectra for copper symmetric bis(thiosemicarbazone) complexes

Abstract

Two new bis(thiosemicarbazone) ligands 2-[1-(2-{3-[2-({2[(methyl)carbothioyl]hydrazono}-methyl)phenoxy]propoxy}phenyl)methylidene]-N1-(methyl)-1-hydrazinecarbothiamide (H2L5), 2-[1-(2-{3-[2-({2-[(methyl)carbothioyl]hydrazono}methyl)phenoxy]-2-hydroxypropoxy}-phenyl)methylidene]-N1-(methyl)-1-hydrazinecarbothiamide (H3L6), and their Cu(II) complexes were synthesized and characterized by physico-chemical and spectroscopic methods. Among eight DFT calculation methods PBE0/6-311+G(d,p)//B3LYP/6-31+G(d) method was the best method to predict one-electron reduction potentials (Ecalc) of these two new and four previously prepared copper complexes in DMF. The effects of solvation in DMF is incorporated as a self-consistent reaction field (SCRF) using the PCM solvent model. This model was capable to predict the experimental results with an error in the range of −0.200 to −0.002 V in comparison with experimental values (Eexp) derived from CV. The changes in solvation energy, ΔΔsolvG°, play important role and without considering the effects of solvation in the calculations, the results are more different from the experimental ones. The calculated one-electron reduction potentials correlated with the energies of both the LUMO of the CuII and the HOMO of the CuI complexes.