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 [Fe 2 Fe 2 ] molecular square complex, {[Fe(pzTp)(CN) 3 ] 2 [Fe(L) 2 ] 2 }[Fe(pzTp)(CN) 3 ] 2 ·4CH 3 OH·2H 2 O [1·4MeOH·2H 2 O; 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·2H 2 O 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, {[(FeIIILS) 2 (FeIILS) 2 ](FeIIILS) 2 } into the high-temperature state, {[(FeIIILS) 2 (FeIIHS) 2 ](FeIIILS) 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.