Synthesis, structure, and magnetic and electronic properties of Cs2Hg2USe5

The compound Cs2Hg2USe5 was obtained from the solid-state reaction of U, HgSe, Cs2Se3, Se, and CsI at 1123 K. This material crystallizes in a new structure type in space group P2/n of the monoclinic system with a cell of dimensions a = 10.276(6)angstrom, b = 4.299(2)angstrom, c = 15.432(9) angstrom, beta = 101.857(6)angstrom, and V = 667.2(6)angstrom(3). The structure contain (2)(infinity)[Hg2USe5] layers separated by Cs atoms. Within the layers are distorted HgSe4 tetrahedra and regular USe6 octahedra. In the temperature range of 25-300 K Cs2Hg2USe5 displays Curie-Weiss paramagnetism with mu(eff) = 3.71(2) mu(B). The compound exhibits semiconducting behavior in the [010] direction; the conductivity at 298 K is 3 x 10(-3) S/cm. Formal oxidation states of Cs/Hg/U/Se may be assigned as +1/+2/+4/-2, respectively. (C) 2009 Elsevier Inc. All rights reserved.