Synthesis and crystal structure of a new quaternary chalcoantimonide: KLa₂Sb₃S₉ and KSm₂Sb ₃Se₈

Silver-needle shaped crystals of KLa₂Sb₃S ₉ from K₂S_x flux and KSm₂Sb ₃Se₈ from NaCl/KCl flux reactions were obtained and their crystal structures were determined by the single crystal X-ray diffraction method. KLa₂Sb₃S₉ crystallizes in the orthorhombic noncentrosymmetric space group P2₁2₁2 ₁ (No. 19) with a unit cell of a = 4.220(3) Å, b = 24.145(2) Å, c = 14.757(5) Å and Z = 4. KSm₂Sb₃Se ₈ crystallizes in the orthorhombic space group Pnma (No.62) with a unit cell of a = 16.719(3) Å, b = 4.1236(8) Å, c = 22.151(4) Å and Z = 4. Both structures have three-dimensional tunnel frameworks filled with K⁺ ions. KSm₂Sb₃Se₈ is an ordered version of ALn_{1 ± x}Bi_{4 ± x}S ₈, and it is made up of NaCl-type and Gd₂S ₃-type fragments. KLa₂Sb₃S₉ also contains building fragments similar to those of KSm₂Sb ₃Se₈, however, there are chalcogen-chalcogen bonds in the Gd₂S₃-type fragment. The formula of KLa₂Sb ₃S₉ can be described as (K⁺)(La ³⁺)₂(Sb³⁺)₃(S^2-) ₇(S₂^2-).