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

A two-step thermo-induced spin-state switching was observed in a cyanide-bridged [FeFe] molecular square complex, {[Fe(pzTp)(CN)][Fe(L)]}[Fe(pzTp)(CN)]·4CHOH·2HO [1·4MeOH·2HO; 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·2HO exhibited a two-step thermo-induced spin transition with (1) ↑ = 306 K and (2) ↑ = 370 K converting the low-temperature ground state, {(FeIIILS)(FeIILS)} into the high-temperature state, {(FeIIILS)(FeIIHS)} a stable intermediate phase. The desolvated phase, 1 also exhibited a gradual but reversible thermo-induced spin state change with a value of 190 K, significantly shifted to a lower temperature. It also exhibited photo-induced spin-state switching at 20 K with the value of 60 K.