Valence Tautomerism in a Cobalt Complex of a Schiff Base Diquinone Ligand

The cobalt(III) complex of a Schiff base diquinone ligand CoIII(Cat-N-BQ)(Cat-N-SQ) undergoes an entropy-driven valence tautomeric equilibrium in solution yielding the CoII(Cat-N-BQ)2 species. This suggestion is supported by variable temperature electronic and 1H NMR spectra, as well as by solution magnetic susceptibility data. The calculated thermodynamic quantities associated to the redox equilibrium are ΔH = 42.0(0.8) kJ mol-1 and ΔS = 140 (3) J mol-1 K-1.