Nickel(II) complexes of the unsymmetrical tetradentate Schiff base of methyl-2-(N-2′-aminoethane), (1-methyl-2′-aminoethane), (3-aminopropylamino)cyclopentenedithiocarboxylate: Synthesis, characterization, thermodynamic and computational studies

Five new unsymmetrical Schiff bases containing NNOS coordination sphere and their Ni(II) complexes, NiLX (where X = 1–5, and L1 = methyl-2-{N-[2-(acetone)triflourolidynenitrilo]ethyl}amino-1-cyclopentenedithi-ocarboxylate, L2 = methyl-2-{N-[2-(acetone)ethylidyneni-trilo]ethyl}amino-1-cyclopentenedithiocarboxylate, L3 = methyl-2-{N-[2-(acetone)phenylidy-nenitrilo]ethyl}amino-1-cyclopentenedithiocarboxylate, L4 = methyl-2-{[1-methyl-2-(ace-tone)ethylidynenitrilo]ethyl}amino-1-cyclopentenedithiocarboxylate, L5 = methyl-2-{[1-methyl-2-(acetone)ethylidynenitrilo]propyl}amino-1-cyclopentenedithiocarboxylate) were synthesized and characterized by different chemical techniques such as elemental analysis, infrared spectra, NMR, mass and UV–Vis spectroscopy. The formation constants and the thermodynamic free energies were measured using UV–Vis spectrophotometry titration for 1:1 complex formation at constant ionic strength 0.01 M (NaClO4), at 25 °C in DMF solvent. The trend of the complex formation of the nickel complexes is as follow: NiL2 > NiL3 > NiL1 and NiL4 > NiL2 > NiL5. Also, the gaussian03 program package was used for calculating of structural, electronic and orbital’s properties of the complexes. All calculations were done in gas phase. The DFT calculations supported the experimental formation constant.