The new Hg-rich barium indium mercurides BaInxHg7−x (x=3.1) and BaInxHg11−x (x=0–2.8)

Abstract

Abstract The title compounds BaInxHg7−x (x=3.1(1)) and BaInxHg11−x (x=0–2.8) were synthesized from stoichiometric ratios of the elements in Ta crucibles. Their crystal structures have been determined using single crystal X-ray data. BaInxHg7−x (x=3.1(1)) crystallizes in a new structure type (orthorhombic, oC16, space group Cmmm: a=512.02(1), b=1227.68(3), c=668.61(2) pm, Z=2, R1=0.0311). In the structure, the atoms of the three crystallographically different mixed In/Hg positions form planar nets of four-, six- and eight-membered rings. These nets are shifted against each other such that the four-membered rings form empty distorted cubes. The cubes are connected via common edges, corners and folded ladders, which are also found in BaIn2/BaHg2 (KHg2 structure type) and BaIn (α-NaHg type). The Ba atoms are centered in the eight-membered rings and exhibit an overall coordination number of 20. The [BaM20] polyhedra and twice as many distorted [M8] cubes tesselate the space. BaIn2.8Hg8.2 (cubic, cP36, space group Pm 3 ¯ m , a=961.83(1) pm, Z=3, R1=0.0243) is the border compound of the phase width BaInxHg11−x of the rare BaHg11 structure type. In the structure, ideal [M8] cubes (at the corners of the unit cell) and BaM20 polyhedra (at the edges of the unit cell) represent the building blocks comparable to the other new In mercuride. In accordance with the increased In/Hg content, additional M-pure regions appear: the center of the unit cell contains a huge [Hg(1)M(2)12M(3,4)32] polyhedron, a Hg-centered cuboctahedron of In/Hg atoms surrounded by a capped cantellated cube of 32 additional M atoms. For both structure types, the bonding situation and the ‘coloring’, i.e. the In/Hg distribution of the polyanionic network, are discussed considering the different sizes of the atoms and the charge distribution (Bader AIM charges), which have been calculated within the framework of FP-LAPW density functional theory.