Near room temperature stepwise spin state switching and photomagnetic effect in a mixedvalence molecular square

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)center dot 4CH3OH center dot 2H(2)O [1 center dot 4MeOH center dot 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 center dot 4MeOH center dot 2H(2)O exhibited a two-step thermo-induced spin transition with T-1/ 2 (1) up arrow = 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)(FeII HS)(2)](FeIII 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.