Crystal Structures of New Alkali Metal-rich Oxometallates: Rubidium Aluminate Tetrahydroxide, Rb₉(AlO₄)(OH)₄, Rubidium Orthogallate, Rb₅GaO₄, Cesiumbis-Chromate(IV) Oxide, Cs₁₀(CrO₄)₂O, and Cesium Diindate, Cs₈In₂O₇

Several new alkali metal oxometallates with anions built up from tetrahedral [MO4] units were obtained in reactions aimed at the formation of alkali metal suboxometallates or by thermally decomposing the latter. Rubidium orthoaluminate tetrahydroxide Rb9(AlO4)(OH)4 crystallizes with a new structure type (space group P21/c, a = 13.116(1), b = 6.9266(5), c = 18.934(2) A , β = 92.05(1)°, V = 1719.0(3) Å3, Z = 4, R1 = 0.0352) and contains orthoaluminate anions [AlO4]5− and isolated hydroxide anions. Rubidium orthogallate Rb5GaO4 crystallizes with the Na5GaO4 structure type (space group Pbca, a = 6.9318(5), b = 21.309(2), c = 11.740(1) Å, V = 1734.2(3) Å3, Z = 8, R1 = 0.0423) with isolated orthogallate anions [GaO4]5−. Cesium chromate oxide Cs10(CrO4)2O adopts the Cs10(GeO4)2O structure type (space group P21/c, a = 12.903(1), b = 11.4523(8), c = 19.074(3) Å , β = 127.903(8)°,V = 2223.9(4) Å3, Z = 4, R1 = 0.0326) with orthochromate(IV) anions [CrO4]4− and isolated oxide anions. In all orthometallates the anions [MO4]n− deviate only slightly from ideal tetrahedral symmetry. Cesium diindate Cs8In2O7 crystallizes with the Cs8Fe2O7 structure type (space group P21/c, a = 7.4307(6), b = 18.6181(14), c = 7.2639(6) Å , β = 119.225(8)°, V = 877.0(1) Å3, Z = 2, R1 = 0.0349). A single-crystal structure investigation at r. t. has shown linear diindate units, but the temperature dependence of the libration angles from TLS studies for the bridging oxygen atom suggests a slightly bent and dynamically disordered diindate anion.