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

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 (NiN2S2)-N-II 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.

Automated summary

The tetradentate N2S2 Schiff base ligands show versatile chelating behavior for copper and stabilize high oxidation states. The Ni coordination chemistry of these ligands leads to a variety of products, including dinuclear Ni-II complexes derived from radical homocoupling reactions. These complexes are redox active and exhibit new electronic transitions in spectroelectrochemistry.