SYNTHESIS AND ELECTROCHEMICAL STUDIES OF NI(II) COMPLEXES WITH TETRADENTATE SCHIFF-BASE LIGANDS

A series of tetradentate Schiff base ligands; [1,2-bis(naphthylideneim ino)ethane, 1,3-bis(naphthylideneimino)propane, 1,4-bis(naphthylidenei mino)butane, and 1,5-bis(naphthylideneimino)pentane] and their Ni(II) complexes have been synthesized. The properties of these ligands and t heir Ni(II) complexes have been characterized by elemental analysis, I R, MMR, UV-vis spectra, molar conductance, and thermogravimetric analy sis. The mole ratio of Schiff base to Ni(II) metal was found to be 1:1 . The electrochemical redox process of the ligands and their Ni(II) co mplexes in DMF and DMSO solution containing 0.1 M tetraethyl ammonium perchlorate (TEAP) as a supporting electrolyte have been investigated by cyclic voltammetry, chronoamperometry, differential pulse voltammet ry, and controlled potential coulometry at glassy carbon electrode. Th e redox process of the ligands was highly irreversible, whereas redox process of Ni(II) complexes were observed as one electron transfer pro cess in quasi-reversible and diffusion-controlled reaction. The electr ochemical redox potentials of the Ni(II) complexes were affected by th e chelate ring size of ligands. The diffusion coefficients of Ni(II) c omplexes containing 0.1 M TEAP in DMSO solution were determined to be 5.7-6.9 X 10(-6) cm(2)/sec. Also the exchange rate constants were dete rmined to be 1.8-9.5 X 10(-2) cm/sec. These values were affected by th e chelate ring size of ligands.