CsCu2Sc3Te6 and CsCuY2Te4: Two new quaternary cesium copper rare-earth metal tellurides

The two new quaternary cesium copper(I) rare-earth metal(III) tellurides CsCu2Sc3Te6 and CsCuY2Te4 were prepared at 900 °C by reacting the elements copper, scandium or yttrium and tellurium together with CsBr as flux and cesium source for fourteen days in evacuated torch-sealed silica ampoules. Both compounds crystallize in space group C2/m of the monoclinic system with unit cells of the dimensions a = 1777.63(9), b = 414.20(2), c = 1033.51(5) pm, β = 113.032(4)° for CsCu2Sc3Te6 (Z = 2) and a = 3741.90(19), b = 432.73(2), c = 2087.62(11) pm, β = 107.357(4)° for CsCuY2Te4 (Z = 12). The crystal structure of the scandium compound contains [CuTe4]7− tetrahedra, which are cis  -edge connected in order to build up 1∞{[CuTe1/1tTe3/3e]3−} chains, and [ScTe6]9− octahedra, which share edges and vertices in forming corrugated 2∞{[Sc3Te6]3−} layers. These layers are separated from each other by [CuTe4]7− tetrahedra and Cs+ cations in trans-face bicapped square-prismatic Te2− coordination (CN = 10). The yttrium compound has a three-dimensional structure as well built up of [CuTe4]7− tetrahedra and [YTe6]9− octahedra. All three crystallographically independent Cu+ cations reside in an individual infinite 1∞{[CuTe2/1tTe2/2v]5−} chain, in which each [CuTe4]7− tetrahedron shares two vertices with neighbouring ones. The anionic framework 3∞{[Y2Te4]2−} and the copper-bearing 3∞{[CuY2Te4]−} one consist of sixteen-membered ring channels containing three different types of Cs+ cations (two in each channel) with bicapped trigonal prismatic (CN = 8) and monocapped cubic Te2− coordination (CN = 9). Thus there is no isotypy with the KCuGd2S4-type structure, characteristic for the lighter chalcogens (e. g. ACuM2Ch4; A = K–Cs, M = La–Er, Ch = S and Se).

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