Controlled light and temperature induced valence tautomerism in a Cobalt-o-Dioxolene complex

The mononuclear cobalt complex of 3,5-di-tert-butylcathecolate and cyan-pyridine is a very versatile compound that displays valence tautomerism (VT) in the solid-state which is induced by temperature, light and hard X-rays and modulated by solvent in the crystal lattice. Here, we demonstrate the photo-induced valence tautomerism in benzene solvated crystals of such complex with a very high yield of metastable states using 450nm light, and also show evidence of the de-excitation of these photo-induced metastable states using red 660nm light. In our work we use single crystal X-ray diffraction as a probe for the VT and demonstrate the controlled use of hard X-rays using attenuated X-ray beams in order to control the X-ray induced VT interconversion. Our results point to a larger efficiency in the VT interconversion when d-d transitions are excited in comparison with charge transfer promotion.