Preparation and structure of the light rare-earth copper selenides LnCuSe2 (Ln = La, Ce, Pr, Nd, Sm)

The ternary selenides LnCuSe(2) (Ln- La, Cc, Pr, Nd, Sm) have been synthesized by the reaction at 1173 K of Ln, Cu, and Se in a KBr or KI flux. The compounds, which are isostructural with LaCuS,, crystallize with four formula units in the space group P2(1)/c of the monoclinic system. The structure may be thought of as consisting of layers of CuSe4 tetrahedra separated by double layers of LnSe(7) monocapped trigonal prisms along the a-axis. Cell constants (Angstrom or deg) at 153 K are: LaCuSe2, 6.8142(5), 7.5817(6), 7.2052(6), 97.573(1)degrees; CeCuSe2, 6.7630(5), 7.5311(6) 7.1650(6), 97.392(1)degrees, PrCuSe2, 6.740(1), 7.481(1), 7.141(1) 97.374(2)degrees; NdCuSe2, 6.7149(6), 7.4452(7), 7.1192(6) 97.310(1)degrees; SmCuSe2, 6.6655(6), 7.3825(7), 7.0724(6), 97.115(1)degrees. There are no Se-Se bonds in the structure of LnCuSe(2),; the formal oxidation states of Ln/Cu/Se are 3 +/1 + /2-. (C) 2003 Elsevier Inc. All rights reserved.