Alkaline-earth tri-mercurides A(II)Hg(3) (A(II) = Ca, Sr, Ba): binary intermetallic compounds with a common and a new structure type

作者：Wendorff Marco; Roehr Caroline^*

来源：Zeitschrift fur Kristallographie-Crystalline Materials, 2018, 233(8): 515-529.

DOI：10.1515/zkri-2018-2054

• alkaline-earth
• amalgams
• bandstructure calculation
• crystal structure
• mercurides

The alkaline-earth tri-mercurides AHg(3) (A = Ca, Sr, Ba) were yielded from stoichiometric melts of the elements in pure phase (in the case of Sr with Sr11Hg54 as a by-product) and their structures were determined by means of single crystal X-ray data. As reported long ago from powder data, CaHg3 and SrHg3 crystallize in the Ni3Sn-type (P6(3)/mmc, a = 662.26(2)/689.39(3), c = 501.6/1(2)/510.38(3) pm, Z = 2, R1=0.0233/0.0306 for A= Ca/Sr). The structure consists of a hexagonal close packing of ordered layers AHg 3 or a dense packing of anti-cuboctahedra [AHg(12)] (as cation coordination polyhedra, CCP) and [Hg-6] octahedra fused via opposite faces to form columns along c. BaHg3 crystallizes in a unique structure type (P4/ncc, a = 1193.04(3), c = 958.02(5) pm, Z=12, R1= 0.0461). It contains three crystallographically different Hg atoms, which form layers of distorted flat square pyramids. In contrast to the layers of the BaAl4-type, 1/5 of the pyramids are 5 missing. Due to the 45 degree rotation of adjacent layers, the connection between the layers is not a 'apical-to-apical' one like in BaAl4, but is established by 'apical-to-basal' bonds. Compared to the Ca and Sr compound, the CCPs of the two different Ba atoms, which are embedded between the pyramid layers, are increased to 12+4 and 14 +2 (for Hg + Ba). For all title compounds and the Li phase LiHg3, which is isotypic to CaHg3, the electronic band structures were calculated within the framework of the FP-LAPW DFT method. Even though the compounds are metals and exhibit only very slight minima of the tDOS at the Fermi level, the electron transfer from the alkali/alkaline-earth element towards mercury is almost complete. Thus, Coulomb interactions and the optimized size and arrangement of the A CCPs, besides the flexible Hg-Hg bonding within the polyanion, determine the structure formation.

• 出版日期2018-8