The new barium mercuride BaHg6 and ternary indium and gallium derivatives

The new binary barium mercuride BaHg6 and the derived ternary indium and gallium containing compounds BaIn1.2Hg4.8 and BaGa0.8Hg5.2 were synthesized from melts of the elements, which were slowly cooled from 500 to 200 °C. Their crystal structures have been determined by means of single crystal X-ray diffraction. The binary mercuride BaHg6 (Pnma, a = 1338.9(3), b = 519.39(13), c = 1042.6(4) pm, Z = 4, R1 = 0.0885) and the isotypic indium substituted compound BaIn1.2Hg4.8 as well as the structurally related gallium mercuride BaGa0.8Hg5.2 (Cmcm, a = 729.77(7), b = 1910.1(2), c = 507.48(5) pm, Z = 4, R1 = 0.0606) crystallize with new structure types. Common features of both structures are planar nets of five- and eight-membered Hg rings, stacked perpendicular to the shortest axes. According to their lengths, the Hg–Hg bonds can be classified into three groups: strong, short ones (I, 285–292 pm), which are only found inside the nets, and longer distances (II), still carrying bond critical points, around 300 pm. Further contacts (III) serve to complete the coordination spheres of Hg/M (320–358 pm). The overall coordination numbers of Hg/M range from 10 to 13. The Ba cations are positioned in the centers of the octagons of the Hg/M nets, thus exhibiting a 5:8:5, i.e. 18, coordination by Hg/M atoms. DFT calculations of the electronic band structure of pure BaHg6 and ordered models of the indium ′BaInHg5′ and the gallium ′BaGaHg5′ mercurides were performed using the FP-LAPW method. The calculated Bader charges show that indium as well as gallium are the positively charged bonding partners inside the Hg/M polyanions.

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► The new binary Hg-rich mercuride BaHg6 crystallizes with a singular structure type.
► Ternary In substituted compounds are isotypic, whereas Ga substituted compounds are only structurally related.
► Structure relation to other Hg-rich alkali and alkaline earth mercurides.
► Discussion of covalent and metallic bonding aspects, as found by structure features and band structure calculations.