Controlled Light and Temperature Induced Valence Tautomerism in a Cobalt-o-Dioxolene Complex

This is the authors' abstract. We don't add key points for this paper.

The mononuclear cobalt complex of 3,5-di- tert -butylcathecolate and cyan-pyridine (Co( diox ) 2 (4-CN-py) 2 ) 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. In our work, we used single crystal X-ray diffraction as a probe for the light-induced VT in solid state and demonstrate the controlled use of hard X-rays via attenuation to avoid X-ray-induced VT interconversion. We report photoinduced VT in benzene solvated crystals of Co( diox ) 2 (4-CN-py) 2 illuminated with blue 450 nm light at 30 K with a very high yield (80%) of metastable hs -Co II states, and we also show evidence of the de-excitation of these photoinduced metastable states using red 660 nm light. Such high-yield light-induced VT had never been experimentally observed in molecular crystals of cobalt tautomers, proving that the 450 nm light illumination is triggering a chain of events that leads to the ls -Co III to h s-Co II interconversion.