Temperature- and photo-induced phase transition in rubidium manganese hexacyanoferrate

This article describes a temperature- and photo-induced phase transition in rubidium manganese hexacyanoferrate, RbMn[Fe(CN)6]. This compound displays a drop in the magnetic susceptibility at 225 K (=T1/2↓) and an abrupt increase in the magnetic susceptibility at 300 K (=T1/2↑) in the cooling and warming processes, respectively. This phase transition is accompanied by a structural change from cubic (F4¯3m) to tetragonal (I4¯m2). The high-temperature (HT) and low-temperature (LT) phases are composed of MnII(S = 25)NCFeIII(S = 12) and MnIII(S = 2)NCFeII(S = 0), respectively. A metal-to-metal charge transfer from MnII to FeIII and a Jahn–Teller distortion of the produced MnIII ion cause this phenomenon. The magnetic transition entropy and enthalpy of the LT phase indicate that this phase shows a three-dimensional Heisenberg-type ferromagnetic lattice for the MnIII sites with a Tc of 11.0 K, which is due to a valence delocalization mechanism. Ferromagnetic magnetization of LT phase in Rb0.91Mn1.05[Fe(CN)6]·0.6H2O is reduced by irradiation with only one-shot of laser pulse and the quantum yield is above one and reaches 4.5. This photomagnetic effect is caused by a photo-induced phase transition from the LT phase to the HT phase.