Cation size effect on photomagnetism and charge transfer phase transition of iron mixed-valence complexes with spiropyrans

Abstract

We have investigated the magnetic properties of a photoresponsive organic–inorganic hybrid system, (SP-R)[FeIIFeIII(dto)3] (SP=spiropyran; R=Me, Et, Pr; dto=C2O2S2), under hydrostatic pressures. At ambient pressure, (SP-Et)[FeIIFeIII(dto)3] and (SP-Pr)[FeIIFeIII(dto)3] undergo one and two ferromagnetic phase transitions corresponding to the high-temperature phase with the spin configuration of FeII(S=2)–FeIII(S=1/2), while (SP-Me)[FeIIFeIII(dto)3] undergoes two ferromagnetic phase transitions corresponding to the coexistence of the high-temperature phase and the low-temperature phase with the spin configuration of FeII(S=0)–FeIII(S=5/2). Under hydrostatic pressures, (SP-R)[FeIIFeIII(dto)3] (R=Et, Pr) undergo a new ferromagnetic phase transition corresponding to the low-temperature phase caused by the pressure-induced charge transfer phase transition.