A(5)Fe3O6 (A = Rb, Cs), CsFeO2 and Cs-8Fe2O7: New oxoferrates of the heavy alkaline metals

摘要

The title compounds were synthesized at a temperature of 775 K via reaction of Fe2O3 with elemental cesium and rubidium alone or in combination with their hyperoxides AO(2) where required by stoichiometry. The structures of the dark-red crystals have been determined by single crystal x-ray diffraction (CsFeO2: cubic, space group Fd3m, a 839.2(2) pm, Z = 8, R1 = 0.0547 and A(5)Fe3O6 (A = Cs: orthorhombic, space group P2(1)2(1)2(1), a = 861.8(2), b = 870.7(2), c = 1658.7(3) pm, Z = 4, R1 = 0.0617 and A = Rb: tetragonal, space group I42d, a = 862.01(8), c = 1504.7(2) pm, Z = 4, R1 = 0.0334). These three compounds contain three-dimensional networks FeO2, in the case of the ideal stuffed cristobalite composed of corner-sharing tetrahedra FeO4/2, in the case of the new mixed valence compounds A(5)Fe3O6 formed by corner-sharing of tetrahedra (FeO4/2)-O-III and triangles (FeOO2/2)-O-II in a 1:2 ratio. The crystal structure of the cation rich compound Cs-8FeO7 (monoclinic, space group P2(1)/c, a = 722.32(12), b = 1789.0(3), c = 733.88(12) pm, beta = 118.976(3)degrees, Z = 4, R1 = 0.0287) exhibits di-ferrate anions Fe2O7(6-) composed of two corner-sharing (FeO4)-O-III tetrahedra with a linear Fe-O-Fe bridge.