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

We have investigated the magnetic properties of a photoresponsive organic inorganic hybrid system, (SP-R)[(FeFeIII)-Fe-II(dto)(3)](SP = spiropyran; R = Me, Et, Pr; dto = C2O2S2), under hydrostatic pressures. At ambient pressure, (SP-Et)[(FeFeIII)-Fe-II(dto)(3)] and (SP-Pr)[(FeFeIII)-Fe-II(dto)(3)] undergo one and two ferromagnetic phase transitions corresponding to the high-temperature phase with the spin configuration of Fe-II(S = 2)-Fe-III(S = 1/2), while (SP-Me)[(FeFeIII)-Fe-II(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 Fe-II(S = 0)-Fe-III(S = 5/2). Under hydrostatic pressures, (SP-R)[(FeFeIII)-Fe-II(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. (C) 2013 Elsevier Ltd. All rights reserved.