Synthesis, characterization and spectroscopic studies of nickel (II) complexes with some tridentate ONN donor Schiff bases and their electrocatalytic application for oxidation of methanol

Abstract

Some tridentate Schiff base ligands (L1–L5) and their nickel complexes [NiL (PR3)]; (where L1=N-salicyliden-2,3-diamino-cis-2-butenedinitrile, L2=3-methoxy-N-salicyliden-2,3-diamino-cis-2-butenedinitrile, L3=5-Bromo-N-salicyliden-2,3-diamino-cis-2-butenedinitrile, L4=5-nitro - N-salicyliden-2,3-diamino-cis-2-butenedinitrile, L5=5-methoxy-N-salicyliden-2,3-diamino-cis-2-butenedinitrile) were synthesized and characterized by different spectroscopic techniques. The geometry of [NiL2 (PPh3)] and [NiL5 (PPh3)] were determined by X-ray crystallography. Both of the structures show distorted square planer geometry. In addition, the optimized geometries of the ligands and complexes along with their IR spectra were calculated by the density functional theory (DFT). The time-dependent-density functional theory (TD-DFT) was employed to calculate the absorption spectra of the structures. The calculated IR and absorption spectra were compared with the corresponding experimental spectra to confirm the experimental results. The calculated IR and absorption spectra were assigned based on the theoretical calculations. Also, the nickel complexes were electrochemically dispersed onto multi-wall carbon nanotubes (MWCNTs) and their electrocatalytic activity for the oxidation of methanol have been studied by cyclic voltammetry. Based on the results, the nickel complexes were found to be active catalysts in the electro-oxidation of methanol.