Sr7Ge6, Ba7Ge6 and Ba3Sn2 –Three new binary compounds containing dumbbells and four-membered chains of tetrel atoms with considerable Ge–Ge π-bonding character

New Insights into the Crystal Chemistry of FeB-Type Compounds: The Case of CeGe

Several alkaline earth or rare earth binary monosilicides and -germanides possess complex bonding properties, such as polycation formation exceeding the scope of classical electron counting rules. In this study, we present characterization by powder and single-crystal diffraction and thermal analysis of CeGe, one of the few monogermanides crystallizing in the FeB-type structure. Comparative computational investigations for structure types experimentally observed for monogermanides and alternative structures with different structural motifs were performed to gain energetical insights into this family of compounds, underlining the preference for infinite germanium chains over other structural motifs. Formation enthalpy calculations and structural chemical analysis highlight the special position of FeB-type compounds among the monogermanides.

The germanides Er5Pd4Ge8 and Tm5Pd4Ge8 – 3D [Pd4Ge8] polyanions with Ge2 dumb-bells and Ge4 chains in cis-conformation

Tm5Pd4Ge8 was synthesized by melting of the elements in an arc-melting furnace. The new germanide was characterized by powder and single-crystal X-ray diffraction: own structure type, P21/m, a=574.3(1), b=1380.4(3), c=836.4(1) pm, β=107.57(2)°, V=0.6321 nm3, wR2=0.0578, 2533 F2 values, 86 variables. The palladium and germanium atoms built up a three-dimensional [Pd4Ge8]15− polyanionic network which contains a unique germanium substructure composed of the Zintl anions Ge2 6− dumb-bells and Ge4 10− chains in cis-conformation. The palladium atoms within the network have distorted square pyramidal germanium coordination. The three crystallographically independent thulium atoms have coordination numbers 15, 16 and 17 with partial motifs of the Frank-Kasper type polyhedra. The isotypic germanide Er5Pd4Ge8 forms only after annealing the arc-melted sample at 1070 K for 1 week: a=575.14(9), b=1386.3(3), c=838.4(1) pm, β=107.51(2)°, V=0.6375 nm3.

TrigermanidesAEGe3(AE= Ca, Sr, Ba): chemical bonding and superconductivity

The crystal structures of the trigermanidesAEGe3(tI32) (AE= Ca, Sr, Ba; space groupI4/mmm, for SrGe3:a= 7.7873(1),c= 12.0622(3) Å) comprise Ge2dumbbells forming layered Ge substructures which enclose embeddedAEatoms. The chemical bonding analysis by application of the electron localizability approach reveals a substantial charge transfer from theAEatoms to the germanium substructure. The bonding within the dumbbells is of the covalent two-center type. A detailed analysis of SrGe3reveals that the interaction on the bond-opposite side of the Ge2groups is not lone pair-like – as it would be expected from the Zintl-like interpretation of the crystal structure with anionic Ge layers separated by alkaline-earth cations – but multi-center strongly polar between the Ge2dumbbells and the adjacent metal atoms. Similar atomic interactions are present in CaGe3and BaGe3. The variation of the alkaline-earth metal has a merely insignificant influence on the superconducting transition temperatures in thes,p-electron compoundsAEGe3.

Synthesis, crystal structure, and bonding analysis of the hypoelectronic cubic phase Ca5Pd6Ge6

The title compound, Ca5Pd6Ge6, was obtained during a systematic investigation of the Ca-Pd-Ge ternary phase diagram. The crystal structure was determined and refined from single-crystal X-ray diffraction data. It crystallizes in a new structure variant of the Y4PdGa12-type structure (Im3̅m, a = 8.7764(4) Å) that features an arrangement of vertex-sharing body-centered cubes of calcium, Ca@Ca8, with a hierarchical bcc network, interpenetrating a second (Pd6Ge6) network consisting of Ge2 dumbbells surrounded by Pd in a strongly flattened octahedron with Pd(μ(2)-η(2),η(4)-Ge2)-like motifs. These octahedra are condensed through the Pd to form a 3D open fcc network. Theoretical band structure calculations suggested that the compound is hypoelectronic with predominantly multicenter-type interatomic interactions involving all three elements and essentially a Hume-Rothery-like regime of electronic stabilization. The similar electronegativity between germanium and palladium atoms has a decisive impact on the bonding picture of the system.