SrNi2Ge and SrNi3Ge2 - Two Related Hexagonal Germanides

The strontium nickel germanides SrNi2Ge and SrNi3Ge2 were prepared by melting mixtures of the elements in an arc-furnace under an argon atmosphere. Single crystals were obtained by special heat treatment in welded tantalum ampoules. The compounds were investigated by X-ray diffractions both on powders and single crystals. SrNi2Ge crystallizes with the hexagonal GdPt2Sn structure with space group P6(3)/mmc, a = 4.128(1), c = 10.479(6) angstrom, wR2 = 0.105, 92 F-2 values, 9 variable parameters. In this structure the nickel and germanium atoms build two-dimensional [Ni2Ge] layers, which are separated by the Sr atoms. The crystal structure of SrNi3Ge2 can be described as a substitution variant of the YPtAs structure with space group P6(3)/mmc, a = 4.0511(1), c = 14.2187(6) angstrom, wR2 = 0.075, 117 F-2 values, 12 variable parameters. Two adjacent [NiGe] layers in this structure are interconnected by Ni atoms, forming [Ni3Ge2] blocks, which are separated by Sr atoms. The structure of SrNi2Ge and SrNi3Ge2 both are related to the A1B(2)-type structure. The crystal chemistry and chemical bonding in these structures is discussed in terms of group-subgroup relation, LMTO band structure calculation, and analysis using the Electron Localization Function (ELF).