Electron transfer coupled spin transition in cyano-bridged mixed-valence {FeIII2FeII2} molecular squares.

The research on electron transfer coupled spin transition regulating the valence state and spin state transition of metal ions is promising and challenging. Herein, we report a cyano-bridged {FeIII2FeII2} molecular square complex, {[Fe(Tp)(CN) 3 ] 2 [Fe(bnbpen)] 2 }(ClO 4 ) 2 ·8CH 3 OH (1·8CH 3 OH, bnbpen = N , N '-bis-(2-naphthylmethyl)- N , N '-bis(2-picolayl)-ethylenediamine), and its free of solvents form (1). Combined single-crystal X-ray diffraction, temperature-dependent infrared (IR) spectra, magnetic measurements, and Mössbauer spectra reveal that 1·8CH 3 OH and 1 exhibit reversible one-step and two-step electron transfer coupled spin transition (ETCST) with temperature change, between the low-temperature state {Fe II,LS (μ-CN)Fe III,LS } 2 (LS = low spin, HS = high spin) and the high-temperature state {Fe III,LS (μ-CN)Fe II,HS } 2 , respectively.