Synthesis and Structure of a New Quaternary Rare-Earth Sulfide, La6MgGe2S14, and the Related Compound La6MgSi2S14

Abstract

A new quaternary rare-earth sulfide has been isolated and identified. Crystals of La6MgGe2S14, as well as of the previously identified La6MgSi2S14have been grown from a mixed binary-halide eutectic flux. They both crystallize in the hexagonal space groupC66-P63, withZ=1. The crystal structures of these compounds have been determined by single-crystal X-ray diffraction techniques. Crystal data are La6MgGe2S14−a=10.367(1) Å,c=5.814(1) Å (T=298 K),V=541.09(8) Å3,Rw(F2)=0.050,R1(onF)=0.018; La6MgSi2S14−a=10.363(2) Å,c=5.742(1) Å (T=298 K),V=534.1(2) Å3,Rw(F2)=0.058, andR1(onF)=0.022. Structurally, these compounds belong to theLn6M2M′2S14family (Ln=rare-earth,M=first-row transition metal or main-group metal,M′=main-group metal). Their structures are characterized by one-dimensional chains ofMS6face-sharing octahedra running parallel to the 63axis, surrounded by isolatedM′S4tetrahedra aligned along the three-fold axes.