Hard X‑ray-Induced Valence Tautomeric Interconversion in Cobalt‑o‑Dioxolene Complexes

Valence tautomeric interconversion (VTI) is a reversible process occurring in metal complexes in which an intramolecular metal–ligand electron transfer is accompanied by a change of metal ion spin state, creating two switchable electronic states (redox isomers). Herein, we describe the low-temperature, 30–100 K, single-crystal study of the [Co(diox)₂(4-CN-py)₂]·benzene complex (1) (diox = 3,5-di-t-butylsemiquinonate (SQ^•‑) and/or 3,5-di-t-butylcatecholate (Cat^2–) radical; 4-CN-py = 4-cyano-pyridine) using hard synchrotron X-ray radiation with different intensities. We demonstrate for the first time that hard X-rays can induce VTI, and that the interconversion molar fraction is dependent on both intensity and exposure time. This in turn shows that X-rays, as a probe, might be altering the very nature of many structures under investigation at low temperatures, and consequently their properties. Our findings add new perspectives to VTI studies and might be of significant interest to the entire community investigating photoresponsive complexes.