SYNTHESIS AND STRUCTURE OF A NEW QUATERNARY RARE-EARTH SULFIDE, LA6MGGE2S14 AND THE RELATED COMPOUND LA6MGSI2S14

A new quaternary rare-earth sulfide has been isolated and identified, Crystals of La6MgGe2S14, as well as of the previously identified La6Mg Si2S14 have been grown from a mixed binary-halide eutectic flux, They both crystallize in the hexagonal space group C-6(6)-P6(3), with Z = 1 . The crystal structures of these compounds have been determined by si ngle-crystal X-ray diffraction techniques. Crystal data are La6MgGe2S1 4 - a = 10.367(1) Angstrom, c = 5.814(1) Angstrom (T = 298 K), V = 541 .09(8) Angstrom(3), R-w(F-2) = 0.050, R-1 (on F) = 0.018; La6MgSi2S14 - a = 10.363(2) Angstrom, c = 5.742(1) Angstrom (T = 298K), V = 534.1( 2) Angstrom(3), R-w (F-2) = 0.058, and R-1 (on F) = 0.022. Structurall y, these compounds belong to the Ln(6)M(2)M(2)'S-14 family (Ln = rare- earth, M = first-row transition metal or main-group metal, M' = main-g roup metal), Their structures are characterized by one-dimensional cha ins of MS6 face-sharing octahedra running parallel to the 6(3) axis, s urrounded by isolated M'S-4 tetrahedra aligned along the three-fold ax es. (C) 1997 Academic Press.