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) 3 ] 2 [Fe(bik) 2 ] 2 }·[Fe(pzTp)(CN) 3 ] 2 ·4MeOH ( 1 ·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) 3 ] 2 [Fe(bik) 2 ] 2 }·[Fe(pzTp)(CN) 3 ] 2 ( 1 ). Both complexes exhibit thermo-induced spin-state switching behavior along with reversible SC-SC transformation, where the low-temperature [Fe III LS Fe II LS ] 2 phase transforms into a high-temperature [Fe III LS Fe II HS ] 2 phase. 1 ·4MeOH exhibits an abrupt spin-state switching with T 1/2 at 355 K, whereas 1 undergoes a gradual and reversible spin-state switching with a lower T 1/2 at 338 K. Astonishingly, 1 exhibits ON/OFF photo-induced spin-state switching with T LIESST = 67 K, whereas 1 ·4MeOH does not show such an effect.