Die Undecaarsenide A3As11 (A = Rb,Cs) — Synthesen und Kristallstrukturen

Alkaline Metal Arsenides A₃As₁₁ (A = Rb, Cs): Preparation and Crystal Structures Rb₃As₁₁ and Cs₃As₁₁ were synthesized from the elements and the crystal structures of the ordered room temperature form were characterized via single crystal x‐ray studies. In the Zintl phases the As atoms form chiral ufosan‐anions As with As‐As distances ranging from 238 to 248 pm. Like K₃As₁₁ Rb₃As₁₁ crystallizes with the Na₃P₁₁ structure type (orthorhombic, space group Pbcn, a = 1108.2(2), b = 1533.5(3), c = 1060.1(2) pm, Z = 4), whereas the Cs compound (monoclinic, space group C2/c, a = 1324.5(7), b = 1524.5(9), c = 1937.2(11) pm, β = 95.29(1)°, Z = 8) forms a new structure type. The crystallographic relationship between the two structure types and the anion packings in the plastic crystalline high temperature forms are discussed.