Electron transfer coupled spin transition in cyano-bridged mixed-valence {Fe III2Fe II2} molecular squares

Abstract

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 {Fe^III₂Fe^II₂} molecular square complex, {[Fe(Tp)(CN)₃]₂ [Fe(bnbpen)]₂}(ClO₄)₂·8CH₃OH (1·8CH₃OH, 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 1·8CH₃OH 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.