SINGLE-CRYSTAL STRUCTURE OF BASM2S4

Nonstoichiometric barium samarium sulfide, Ba1-xSm2S4-x (x = 0.10), M(r) = 549.43, orthorhombic, Pnma, a = 12.262 (3), b = 4.121 (3), c = 14.713 (2) angstrom, V = 743.5 (6) angstrom3, Z = 4, D(x) = 4.91 g cm-3, lambda(Mo K-alpha) 0.71069 angstrom, mu = 218.74 cm-1, T = 296 K, F(000) = 947.2, R = 0.027, wR = 0.037 for 736 observed unique reflections [I > 3-sigma(I)]. X-ray single-crystal structure results confirm that the title compound crystallizes in a CaFe2O4-type structure, which is built up from edge-sharing, double octahedral, infinite chains. The structure also contains BaS8 polyhedra, which can best be described as bicapped trigonal prisms (b.t.p). The two capping S(2) atoms adopt much longer Ba-S bond distances. This is attributed in part to the nonstoichiometry of the Ba and S(2) site. The same structure type is also adopted by other heavier rare-earth metal ternary sulfides and selenides, e.g., A(RE)2Q4 (Q = S and Se), where RE = Tb-Lu for A = Sr and RE = Nd-Lu for A = Ba.