Synthesis and Crystal Structure of a 6H Hexagonal Fluoro-Perovskite: RbMgF3

RbMgF3, a perovskite halide, serendipitously crystallized from a reaction between MgCl2 and TiO2 in molten RbCl/RbF eutectic flux (melting point = 546 °C) and was characterized by single crystal X-ray diffraction. RbMgF3 crystals can also be grown directly in higher yield using a molten RbCl–RbF flux layered over MgCl2 or MgF2 contained in a silver tube at 575 °C. RbMgF3 crystallizes in the hexagonal space group P63/mmc in the 6H hexagonal perovskite structure type with lattice parameters a = 5.8368(2) A and c = 14.2087(5) A. The crystal structure exhibits face-sharing Mg2F9 octahedra connected via corner-sharing MgF6 octahedra. Elemental composition for RbMgF3 was semi-quantitatively confirmed by energy dispersive spectroscopy (EDS). X-ray diffraction quality single crystals of RbMgF3 were grown from a molten RbCl/RbF eutectic flux at 850 °C and used for structure determination using single crystal X-ray diffraction. The compound crystallizes in the hexagonal space group P63/mmc in the 6H hexagonal structure type.