Valence tautomerism and delocalization in transition metal complexes of o-amidophenolates and other redox-active ligands. Some recent results

Abstract

The archetypal temperature-driven valence tautomeric process ‘CoIII(Cat)(SQ)’ ⇌ ‘CoII(SQ)2’ (spin state of cobalt changes from S = 0 to S = 3/2), where Cat2− and SQ·− are catecholato and semiquinonato redox-level, respectively, of the redox-active catecholate. Research on valence tautomerism has made notable advancement not only with new cobalt-catecholate systems but also with other metal ions and new redox-active ligands. The process is associated with changes in the charge distribution. Here some recent results on metal complexes of redox-active catecholates (only selected recent examples), o-amidophenolate and o-phenylenediamide ligands are presented.