SPECTROELECTROCHEMISTRY OF NICKEL(II) COMPLEXES OF N,N'-BIS(SALICYLALDEHYDE)-O-PHENYLENEDIAMINE AND BIS(2-HYDROXY-1-NAPHTHALDEHYDE)-O-PHENYLENEDIAMINE USING AN OPTICALLY TRANSPARENT THIN-LAYER ELECTRODE

The Schiff base nickel(II) complexes of N,N'-bis(salicylaldehyde)-o-ph enylenediamine and bis(2-hydroxy-1-naphthaldehyde)-o-phenylenediamine provide an opportunity for the spectroelectrochemical investigation of the azomethazine and transition-metal chromosphores using a gold-mesh optically-transparent thin-layer electrode (OTTLE) in protic solvents . Cyclic voltammetry of these compounds showed a well ordered electroc hemical behaviour with reductions in both the metal and ligand. All co mplexes showed two well defined electrode couples, Ni-I/Ni-II and Ni-I I/Ni-III. The dependence of the electrochemical parameters on the solv ent, supporting electrolyte, scan rate and the nature of the ligands i s discussed. Application of the OTTLE cell technique to the study of t he redox chemistry of the nickel(II) pigments tested proved efficient for the spectral and electrochemical characterization of the various o xidation states. The spectropotentiostatic experiments provided redox potentials, n values, close to those obtained by controlled potential coulometry and in agreement with those values predicted from the bulk cyclic voltammetry. The estimated standard electrode potential (E(0)) values agreed well with those obtained by Nernstian analysis, and faci litated the acquisition of E and n values, which are not readily obtai ned by conventional techniques. This was possible even for quasi-rever sible reactions where the peak separation does not yield accurate n va lues. Exhaustive electrolysis of the small volume of solution in the O TTLE ensured the quantitative generation of a particular redox state w ithout interference from extraneous redox reactions. The effect of an additional aromatic ring is to provide an additional redox couple. The electrochemical and spectral behaviours were in good agreement, which suggests that the phenomenon of colour fading in the complex and elec trochemical changes produce similar trends.