Spectroscopic characterisation of electrogenerated nickel(III) species.: Complexes with N2O2 Schiff-base ligands derived from salicylaldehyde

Several nickel(II) complexes with tetradentate N2O2 Schiff-base ligands (H2L) have been synthesized and their oxidative chemistry studied in dimethylformamide and in dimethyl sulfoxide. Electrochemical and EPR data for the oxidised solution revealed that in these strong co-ordinated solvents almost all nickel(II) complexes were oxidised to low-spin six-co-ordinate nickel(III) complexes, formulated as [(NiL)-L-III(solv)(2)](+), where solv stands for a solvent molecule. Upon addition of pyridine to fluid solutions of [(NiL)-L-III(solv)2](+) new species were formed which on the basis of their EPR spectra can be formulated as [(NiL)-L-III(py)(2)](+). Extensive electronic characterisation of the nickel(III) compounds was made by coupling of EPR and electronic spectroscopic data.