Be3Ru: Polar Multiatomic Bonding in the Closest Packing of Atoms

The new phase Be₃Ru crystallizes with TiCu₃-type structure (space group Pmmn (59), a=3.7062(1) Å, b=4.5353(1) Å, c=4.4170(1) Å), a coloring variant of the hexagonal closest packing (hcp) of spheres. The electronic structure revealed that Be₃Ru has a pseudo-gap close to the Fermi level. A strong charge transfer from Be to Ru was observed from the analysis of electron density within the Quantum Theory of Atoms in Molecules (QTAIM) framework and polar three- and four-atomic Be−Ru bonds were observed from the ELI−D (electron localizability indicator) analysis. This situation is very similar to the recently investigated Be₅Pt and Be₂₁Pt₅ compounds. The unusual crystal chemical feature of Be₃Ru is that different charged species belong to the same closest packing, contrary to typical inorganic compounds, where the cationic components are located in the voids of the closest packing formed by anions. Be₃Ru is a diamagnet displaying metallic electrical resistivity.