Die neuen Oxoarsenate(III) AAsO2 (A = Na, K, Rb) und Cs3As5O9. Darstellung, Kristallstrukturen und Raman-Spektren / The New Oxoarsenates(III) AAsO2 (A = Na, K, Rb) and Cs3As5O9. Synthesis, Crystal Structures and Raman Spectra

Abstract

The new alkaline metal arsenates(III) were synthesized at a temperature of 500 °C via reaction of stoichiometric mixtures of the elemental alkali metals A and As2O3. In the crystal structures of the four title compounds, which have been determined by single crystal x-ray diffraction, the As(III) atoms are in ψ-tetrahedral coordination by oxygen exclusively. In NaAsO2 (orthorhombic, space group Pbcm, a = 1429.6(9), b = 677.3(3), c = 509.1(2) pm, Z = 8) and the compounds AAsO2 (A = K/Rb, orthorhombic, space group Pbcm, a = 715.1(2)/729.7(5), b =748.0(1)/775.2(5), c = 539.20(17)/541.1(3) pm, Z = 4) the AsO3 ψ-tetrahedra are condensed to form zig-zag chains [AsOO2/2]−. In the Cs phase Cs3As5O9 with a lower alkaline metal content (trigonal, space group P31m, a = 845.5(3), c = 602.6(2) pm, Z = 1) the two crystallographically independent ψ-tetrahedra AsO3/2 and AsOO2/2 are connected in a 2:3 ratio to give polar sheets [As5O9]3−.