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

The ternary selenides LnCuSe2 (Ln=La, Ce, 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 LaCuS2, crystallize with four formula units in the space group <f>P21/c</f> of the monoclinic system. The structure may be thought of as consisting of layers of CuSe4 tetrahedra separated by double layers of LnSe7 monocapped trigonal prisms along the a-axis. Cell constants (A˚ or deg) at 153 K are: LaCuSe2, 6.8142(5), 7.5817(6), 7.2052(6), 97.573(1)°; CeCuSe2, 6.7630(5), 7.5311(6), 7.1650(6), 97.392(1)°; PrCuSe2, 6.740(1), 7.481(1), 7.141(1), 97.374(2)°; NdCuSe2, 6.7149(6), 7.4452(7), 7.1192(6), 97.310(1)°; SmCuSe2, 6.6655(6), 7.3825(7), 7.0724(6), 97.115(1)°. There are no Se–Se bonds in the structure of LnCuSe2; the formal oxidation states of Ln/Cu/Se are 3+/1+/2−. [Copyright &y& Elsevier]