Crystal structures of the ScCuSe2 and Sc3CuSn3Se11 compounds

The crystal structure of the ScCuSe2 compound was investigated using X-ray powder diffraction (space group P2, a = 0.67108(5) nm, b = 0.38949(3) nm, c = 1.27879(6) nm, β = 90.281(6)°, Pearson symbol mP16.08, RI = 0.0839). The structure of ScCuSe2 represents a distinctive 3a×a×2c superstructure of Er2/3Cu2S2. The Se atoms are stacked in a close-packed arrangement with layers in the sequence AB. The Sc atoms occupy half of the octahedral sites, the Cu atoms are located in 3/8 of the tetrahedral sites. The crystal structure of the Sc3CuSn3Se11 compound (space group Fd3m, a = 1.08827(4) nm, Pearson symbol cF52.48, RI = 0.0386) was also determined by means of X-ray powder diffraction. The Se atoms are stacked in a close-packed arrangement with layers in the sequence ABC. The Sc atoms and a statistical mixture M (Sc + Sn) are located in all octahedral sites, the Cu atoms in 1/8 of the tetrahedral sites.