Alkalimetall-Arsenide A3As7 Und Aas (A = K, Rb, Cs). Synthesen, Kristallstrukturen, Schwingungsspektren / Alkaline Metal Arsenides A3As7 and AAs (A = K, Rb, Cs). Preparation, Crystal Structure, Vibrational Spectroscopy

Abstract

The title compounds were synthesized from the elements and characterized via single crystal x-ray studies and Raman spectroscopy. In the Zintl phases A3As7 (A = K, Rb, Cs) the As atoms form nortricyclene-analogous anions As3 7 with As-As distances ranging from 230 to 254 pm. The three compounds crystallizewithdifferent newstructure types containing different packings of theAs7 anions:K3As7 (orthorhombic, Pbca; a=1291.9(8), b = 2544.1(9), c=1537.7(16) pm) shows a double hexagonal close packing (ABAC stacking of planes of hexagonal close packed anions), Rb3 As7 (monoclinic, P21/c, a = 757.3(5), b = 1310.2(8), c = 2692.7(18) pm , β= 91.972(12)°) hows a hexagonal close packing (AB) and the Cs compound (orthorhombic, Pbca, a = 1022.8(5), b = 1317.6(7), c = 2195.2(11) pm) a cubic close packing (ABC) (also present in theHT-forms of the three compounds) respectively. The alkaline metalmonoarsenides AAs (A = K, Rb) crystallize with the NaP structure type (A = K/Rb: orthorhombic, P212121; a = 661.7(5) / 658.1(8), b = 688.8(6) / 691.6(8), c = 1197.3(10) / 1204.7(10) pm, Z = 8) with approximate fourfold screw axes 41 of As$ chains, whereas the crystal structure of CsAs (hexagonal, P¯62m, a = 1219.7(3), c = 1046.3(2) pm, Z = 18) contains three crystallographically independent three membered rings As3 3 with As-As distances of 243.0 to 247.5 pm