Near room temperature stepwise spin state switching and photomagnetic effect in a mixed-valence molecular square

Abstract

A two-step thermo-induced spin-state switching was observed in a cyanide-bridged [Fe₂Fe₂] molecular square complex, {[Fe(pzTp)(CN)₃]₂[Fe(L)₂]₂}[Fe(pzTp)(CN)₃]₂·4CH₃OH·2H₂O [1·4MeOH·2H₂O; pzTp = tetrakis(pyrazol-1-yl)borate and L = bis(1-ethylimidazol-2-yl)ketone (bik*)], which was characterized fully by single-crystal X-ray diffraction, (photo)magnetic measurements, and spectroscopic techniques. 1·4MeOH·2H₂O exhibited a two-step thermo-induced spin transition with T_1/2 (1) ↑ = 306 K and T_1/2 (2) ↑ = 370 K converting the low-temperature ground state, {[(Fe^III_LS)₂(Fe^II_LS)₂](Fe^III_LS)₂} into the high-temperature state, {[(Fe^III_LS)₂(Fe^II_HS)₂](Fe^III_LS)₂} via a stable intermediate phase. The desolvated phase, 1 also exhibited a gradual but reversible thermo-induced spin state change with a T_1/2 value of 190 K, significantly shifted to a lower temperature. It also exhibited photo-induced spin-state switching at 20 K with the T_LIESST value of 60 K.