ON/OFF Photo(switching) along with Reversible Spin-State Change and Single-Crystal-to-Single-Crystal Transformation in a Mixed-Valence Fe(II)Fe(III) Molecular System.

A mixed-valence Fe(II)Fe(III) molecular system, {[Fe(pzTp)(CN)][Fe(bik)]}·[Fe(pzTp)(CN)]·4MeOH (·4MeOH) (bik = bis-(1-methylimidazolyl)-2-methanone, pzTp = tetrakis(pyrazolyl)borate), exhibits single-crystal-to-single-crystal (SC-SC) transformation while increasing the temperature and is converted into {[Fe(pzTp)(CN)][Fe(bik)]}·[Fe(pzTp)(CN)] (). Both complexes exhibit thermo-induced spin-state switching behavior along with reversible SC-SC transformation, where the low-temperature [FeFe] phase transforms into a high-temperature [FeFe] phase. ·4MeOH exhibits an abrupt spin-state switching with at 355 K, whereas undergoes a gradual and reversible spin-state switching with a lower at 338 K. Astonishingly, exhibits ON/OFF photo-induced spin-state switching with = 67 K, whereas ·4MeOH does not show such an effect.