Abstract

Tridentate Schiff base ligands, <TEX>$SIPH_2$</TEX>, <TEX>$SIPCH_2$</TEX>, <TEX>$HNIPH_2$</TEX>, and <TEX>$HNIPCH_2$</TEX> were prepared by the reactions of salicylaldehyde and 2-hydroxy-1-naphthaldehyde with 2-aminophenol and 2-amino-p-cresol. Ni(II) complexes of those ligands were synthesized. The structures and properties of ligands and their complexes were studied by elemental analysis, <TEX>$^1H$</TEX>-NMR, IR, UV-visible spectra, and thermogravimetric analysis. The mole ratio of Schiff base to the metal of complexes was found to be 1:1. Ni(II) complexes were contemplated to be hexa-coordinated octahedral configuration containing three water molecules. The redox process of ligands and complexes in DMSO solution containing 0.1 M TBAP as supporting electrolyte was investigated by cyclic voltammetry and differential pulse voltammetry with glassy carbon electrode. The redox process of the tridentate Schiff base ligands was totally irreversible. The redox process of Ni(II) complexes were quasi-reversible and diffusion-controlled as one electron by one step process Ni(II)/Ni(I). The reduction potentials of the Ni(II) complexes shifted in the positive direction in the order [<TEX>$Ni(II)(HNIP)(H_2O)_3$</TEX>]>[<TEX>$Ni(II)(SIP)(H_2O)_3$</TEX>]>[<TEX>$Ni(II)(SIPC)(H_2O)_3$</TEX>]>[<TEX>$Ni(II)(HNIPC)(H_2O)_3$</TEX>] and their dependence on ligands were not so high. Consequently the [<TEX>$Ni(II)(HNIPC)(H_2O)_3$</TEX>] complex among the synthesized Ni(II) complexes was found to be most stable in the DMSO solution.