Synthesis and crystal structure of tischendorfite, Pd8Hg3Se9

Abstract

The synthetic analogue of the mineral tischendorfite, Pd 8 Hg 3 Se 9 , was prepared using the silica glass tube technique and its crystal structure was solved and refined from powder X-ray diffraction data. The structure is orthorhombic, space group Pmmn , with a = 7.1886(2), b = 16.8083(5), c = 6.4762(2) A, V = 782.51(4) A 3 and Z = 2. There are three Pd, two Hg and four Se independent positions. Tischendorfite crystallizes in a framework structure, where Pd atoms show two types of coordination by Se atoms: [PdSe 4 ] squares and [PdSe 5 ] pyramids. The [PdSe 5 ] pyramid shares two opposite Se–Se edges with adjacent pyramids forming linear isolated chains running along the a -axis, whereas [PdSe 4 ] squares are paired via one common Se–Se edge. The paired squares and chains of pyramids form characteristic slabs parallel to (010). Both types of slabs alternate along the b -axis. The Hg atoms occupy the anti-cubooctahedral voids formed by Se atoms. The structure is stabilized by a system of Pd–Hg and Pd–Pd metallic bonds.