Johannes Bender, Andreas Wohlfarth, Constantin Hoch
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.
Planare, isolierte Anionen SiP, SiAs, GeP und GeAs liegen in den Kristallen der dunkel metallisch glänzenden Titelverbindungen (Zintl‐Phasen) vor. Die 24‐Valenzelektronen‐Einheiten sind die ersten Beispiele für CO‐isostere Anionen, in denen Zentralatome und Liganden höheren Perioden angehören. Aus den gemessenen Bindungslängen lassen sich Bindungsordnungen (nach Pauling) von 1.22, 1.28, 1.12 bzw. 1.26 ableiten.