Syntheses, crystal structures, and physical properties of the new thorium chalcogenides CuTh2Te6 and SrTh2Se5

摘要

Single crystals of CuTh2Te6 form by a stoichiometric reaction of the elements at 1000 degrees C. The compound crystallizes in the space group C-2h(2)-P2(1)/m with unit cell parameters a = 6.170(2) Angstrom, b = 4.332(1) Angstrom, c = 10.424-(3) Angstrom, beta = 98.85(1)degrees, and Z = 1 at 113 K. The structure was solved from single-crystal X-ray data. It consists of layers of (2)(infinity)[Th2Te6-] double chains joined by Cu+ cations. Each Th atom is coordinated to eight Te atoms in a bicapped trigonal prismatic arrangement. There are three crystallographically unique Te atoms. Each ThTe8 unit is bridged through one distinct Te atom, such that the capping Te atom of one unit forms the vertex of its neighbor. The two nonbridging Te atoms form infinite Te-Te chains along the exterior of the (2)(infinity)[Th2Te6-] layer. Copper atoms are coordinated to these Te atoms in a tetrahedral arrangement. Owing to the existence of Te-Te bonds of intermediate length, the assignment of formal oxidation states in this compound is not possible. Four-probe de electrical conductivity measurements of a single crystal of CuTh2Te6 indicate the compound is a semiconductor along [010]. Magnetic susceptibility measurements in the range 2-300 K show CuTh2Te6 to be paramagnetic with mu(eff) = 2.06 mu(B) at 300 K. Single crystals of SrTh2Se5 form from the reaction SrSe + Th + 3Sn + 3Se at 1000 degrees C. EDAX experiments show no tin present in several crystals analyzed. Transparent red blocks of SrTh2Se5 crystallize in the space group C-2h(5)-P2(1)/c with unit cell parameters a = 8.704(2) Angstrom, b = 7.861(2) Angstrom, c = 12.458(4) Angstrom, beta = 90.00(2)degrees, and Z = 4 at 113 K. The structure, which is related to that of U3S5, is a three-dimensional framework with Sr cations located in one-dimensional channels. There are two distinct Th environments, bicapped trigonal prismatic and distorted monocapped octahedral. There are no Se-Se bonds and so formal oxidation states of Sr2+, Th4+, and Se2- may be assigned. [References: 34]