Magnetic Bistability in a Cobalt Bis(dioxolene) Complex: Long-Lived Photoinduced Valence Tautomerism

The thermal- and photoinduced valence tautomerism of a cobalt bis(dioxolene) complex is described. The thermal conversion is precipitous, complete within 10 K, and is accompanied by a 5 K hysteresis loop (107 K < T1/2 < 112 K). Rapid thermal quenching (300 K → 10 K in ca. 5 s) and photoinduced valence tautomerism result in trapping of the metastable CoII-state at low temperatures through intermolecular hydrogen bonding. This lattice stabilization results in unmatched kinetic and thermal stability for a valence tautomer from 10−50 K, with residual hs-CoII persisting until about 90 K.