Switchable cobalt coordination polymers: Spin crossover and valence tautomerism

Abstract

Electronically labile, or switchable, cobalt coordination polymers exhibit reversible spin crossover (SCO) or valence tautomeric (VT) transitions upon the application of an external stimulus, such as temperature variation. Spin crossover transitions at pseudo-octahedral cobalt(II) centers with an appropriate ligand field involve a heating-induced transition from the low-spin to high-spin electronic configurations. Valence tautomeric transitions are most commonly observed for cobalt-dioxolene systems, which undergo an intramolecular electron transfer and concomitant spin transition at the cobalt center, from low-spin-cobalt(III)-catecholate at low temperature to high-spin-cobalt(II)-semiquino..