Synthesis and crystal structure of a new quaternary chalcoantimonide:: KLa2Sb3S9 and KSm2Sb3Se8

Silver-needle shaped crystals of KLa2Sb3S9 from K2Sx flux and KSm2Sb3Se8 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 P2(1)2(1)2(1) (No. 19) with a unit cell of a = 4.220(3) Angstrom, b = 24.145(2) Angstrom, c = 14.757(5) Angstrom and Z = 4. KSm2Sb3Se8 crystallizes in the orthorhombic space group Pnma (No. 62) with a unit cell of a = 16.719(3) Angstrom, b = 4.1236(8) Angstrom, c = 22.151(4) Angstrom 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 Gd2S3-type fragments. KLa2Sb3S9 also contains building fragments similar to those of KSm2Sb3Se8, however, there are chalcogen-chalcogen bonds in the Gd2S3-type fragment. The formula of KLa2Sb3S9 can be described as (K+)(La3+)(2)(Sb3+)(3)(S2-)(7)(S-2(2-)).