Complexes of transition metals with Schiff bases and the factors influencing their redox properties. Part II. Nickel and cobalt complexes of some terdentate chelating ligands containing the donor atom set N₂S

The syntheses of some nickel and cobalt complexes containing terdentate Schiff base ligands (L), having the donor atom set N₂S, are described. The ligands are derived from pyridine- or pyrrole-2-carbaldehyde and o-aminobenzenethiol, or thiosemicarbazide or its 4-methyl analogue. The complexes are of the type [NiLCl], [Ni₂L₂], or [NiL₂](in which only two donor atoms, probably N, in each ligand are co-ordinated to the metal), and [CoL₂]⁺(in which all three donor atoms of the ligand are co-ordinated to the metal). Attempts to prepare binuclear complexes of the type [Co₂L₂] are described. The complexes were characterised by electronic, mass, and n.m.r. spectroscopy; these data were used to predict their structures.

The electrochemical properties of the complexes were investigated in dimethylformamide by polarography and cyclic voltammetry. The nickel complexes generally underwent one oxidation, and at least one, and more often two reduction processes, which were usually irreversible. The cobalt complexes could be reduced polarographically in a reversible one-electron step giving [CoL₂]⁰.