Solvothermal synthesis of potassium, rubidium, and cesium molybdenum oxyfluorides

Attention has recently been paid to oxyfluorides, one of the mixed anion materials, because they possess unique properties for many kinds of application fields. Because the general synthesis processes for oxyfluorides are based on troublesome methods, novel safe and facile processes are required. In this study, MoO₃ was solvothermally reacted with KF, RbF, and CsF at 200 °C to form potassium, rubidium, and cesium molybdenum oxyfluorides. The reaction of MoO₃ with KF and RbF led to the formation of K₃MoO₃F₃ and Rb₃MoO₃F₃ with a known structure, respectively, while the reaction of MoO₃ with CsF induced an unknown phase which should be Cs₃MoO₃F₃ with the similar structure to those of K₃MoO₃F₃ and Rb₃MoO₃F₃. A₃MoO₃F₃ (A = K, Rb, and Cs) has not been synthesized under liquid phase until now, and this research clarified this kind of the solvothermal reaction can lead to the formation of unique oxyfluorides at low temperature. In addition, Cs₃MoO₃F₃ was converted into Cs₃Mo₂O₆F₃ by treatment with methanol, suggesting the instability of Cs₃MoO₃F₃. This kind of conversion reaction from one oxyfluoride to the other oxyfluoride has not been reported, and the development of such chemical conversion may lead to the formation of new oxyfluorides.