Crystal structures of new alkali metal-rich oxometallates: Rubidium aluminate tetrahydroxide, Rb_9(AlO_4)(OH)_4, rubidium orthogallate, Rb_5GaO_4, Cesium bis-chromate(IV) oxide, Cs_(10)(CrO_4)_2O, and cesium diindate, Cs_8In_2O_7

摘要

Several new alkali metal oxometallates with anions built up from tetrahedral [MO_4] units were obtained in reactions aimed at the formation of alkali metal suboxometallates or by thermally decomposing the latter. Rubidium orthoaluminate tetrahydroxide Rb_9(AlO _4)(OH)_4 crystallizes with a new structure type (space group P2_1/c, a = 13.116(1), b = 6.9266(5), c = 18.934(2) ?, β = 92.05(1)°, V = 1719.0(3) ?~3, Z = 4, R1 = 0.0352) and contains orthoaluminate anions [AlO_4]~(5-) and isolated hydroxide anions. Rubidium orthogallate Rb_5GaO_4 crystallizes with the Na_5GaO_4 structure type (space group Pbca, a = 6.9318(5), b = 21.309(2), c = 11.740(1) ?, V = 1734.2(3) ? ~3, Z = 8, R1 = 0.0423) with isolated orthogallate anions [GaO _4]~(5-). Cesium chromate oxide Cs_(10)(CrO _4)_2O adopts the Cs_(10)(GeO_4) _2O structure type (space group P2_1/c, a = 12.903(1), b = 11.4523(8), c = 19.074(3) ?, β = 127.903(8)°,V = 2223.9(4) ?~3, Z = 4, R1 = 0.0326) with orthochromate(IV) anions [CrO _4]~(4-) and isolated oxide anions. In all orthometallates the anions [MO_4]~(n-) deviate only slightly from ideal tetrahedral symmetry. Cesium diindate Cs_8In_2O_7 crystallizes with the Cs_8Fe_2O_7 structure type (space group P2_1/c, a = 7.4307(6), b = 18.6181(14), c = 7.2639(6) ?, β = 119.225(8)°, V = 877.0(1) ?~3, 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.