Flux Growth, Crystal Structure, and Chemical Bonding of Yb(2)PdGe(3), an AlB(2) Superstructure within the Rare-Earth Series

[Image: see text] The complete structure revision of the RE(2)PdGe(3) (RE = rare-earth metal) series revealed that Yb(2)PdGe(3) is the only AlB(2) ordered superstructure. Good-quality single crystals of this compound were successfully grown from molten indium flux, enabling accurate single-crystal investigations. Yb(2)PdGe(3) crystallizes with the Ce(2)CoSi(3)-type structure in the hexagonal space group P6/mmm (no. 191) with lattice parameters a = 8.468(1) Å and c = 4.0747(7) Å. This structure is a four-order derivative of AlB(2), composed of planar (∞)(2)[PdGe(3)] honeycomb layers spaced by Yb species, located at the center of Ge(6) and Ge(4)Pd(2) hexagons. A superconducting transition is observed below the critical temperature of 4 K. A divalent state of Yb is deduced from magnetic susceptibility measurements below room temperature, which indicate an almost nonmagnetic behavior. A charge transfer from Yb to Pd and Ge was evidenced by the Quantum Theory of Atoms in Molecules (QTAIM) effective charges; polar four-atomic Ge–Pd/Yb and two-atomic Pd–Yb bonds were observed from the ELI-D (electron localizability indicator), partial ELI-D, and ELI-D/QTAIM intersections. The bonding interactions between Ge atoms within regular Ge(6) hexagons are found to be intermediate between single bonds, as in elemental Ge, and higher-order bonds in the hypothetic Ge(6)H(6) and Ge(6)(6–) aromatic molecules.