CuSm3Se4[Se2]:: a new ternary copper(I) rare-earth(III) selenide with mono- and diselenide units

Single crystals of CuSm3Se6 develop by reaction of the elements (Cu, Sm and Se; molar ratio: 1:3:6) after 7 days at 973 K. As the formula indicates, the crystal structure of CuSm3Se4[Se-2] (orthorhombic, Pbcm; a = 709.53(6), b = 783.91(7), c = 1689.98(9) pm, Z = 4) contains both mono- (Se2-) and diselenide anions ([Se-2](2-)). The latter are surrounded by Six Sm3+ cations. If the diselenide units serve as one fragment, they form irregular {[Se-2]Sm-6}(16+) octahedra, which produce chains running along [010]. Together with [SeSm4](10+) tetrahedra they build up a two-dimensional layer parallel to (001) according to (2)(infinity){(Sm3Se[Se-2])(5+)}. Vertex-, edge- and face-shared [CuSe4](7-) tetrahedra compose chains running along [010] as well. Since the distance between the two central cations of a face-shared bitetrahedron (d(Cu-Cu) = 115 pm) is much too short, the copper position is only half occupied. A three-dimensional network is created by stacking (2)(infinity){(Sm3Se[Se-2])(5+)} layers and (1)(infinity){(CuSe3)(5-)} chains parallel to (001). (C) 2003 Elsevier Science (USA). All rights reserved.