Nickel coordination chemistry of bis(dithiocarbazate) Schiff base ligands; metal and ligand centred redox reactions

Abstract

The tetradentate N₂S₂ Schiff base ligands derived from condensing S-methyl or S-benzyl dithiocarbazate with acetylacetone have been found to be versatile chelators for copper and able to stabilise unusually high oxidation states. Herein we report their Ni coordination chemistry and a variety of products ensue depending on the reaction conditions. Unusual examples of linkage isomerism have been observed upon complexation with nickel acetate and these asymmetrically and symmetrically coordinated Ni^IIN₂S₂ complexes have been characterised both crystallographically and in solution by NMR. These compounds react rapidly with dioxygen and the ligands are particularly susceptible to oxidation which lead to various products including dinuclear Ni^II complexes derived from radical homocoupling reactions. These dinuclear Ni^II complexes are also redox active and spectroelectrochemistry has revealed new electronic transitions from their formally Ni^III/Ni^II mixed valent state.