title: Metallic Borides, La2Re3B7 and La3Re2B5, Featuring Extensive Boron-Boron Bonding.
abstract: La2Re3B7 and La3Re2B5 have been synthesized in single-crystalline form from a molten La/Ni eutectic at 1000 °C in the first example of the flux crystal growth of ternary rare-earth rhenium borides. Both compounds crystallize in their own orthorhombic structure types, with La2Re3B7 (space group Pcca) having lattice parameters a = 7.657(2) Å, b = 6.755(1) Å, and c = 11.617(2) Å, and La3Re2B5 (space group Pmma) having lattice parameters a = 10.809(2) Å, b = 5.287(1) Å, and c = 5.747(1) Å. The compounds possess three-dimensional framework structures that are built up from rhenium boride polyhedra and boron-boron bonding. La3Re2B5 features fairly common B2 dumbbells, whereas La2Re3B7 has unique one-dimensional subunits composed of alternating triangular B3 and trans-B4 zigzag chain fragments. Also observed in La3Re2B5 is an unusual coordination of B by an octahedron of La atoms. Electronic band structure calculations predict that La2Re3B7 is a semimetal, which is observed in the electrical resistivity data as measured on single crystals, with behavior obeying the Bloch-Grüneisen model and a room-temperature resistivity ρ300 K of ∼375 μΩ cm. The electronic band structure calculations also suggest that La3Re2B5 is a regular metal.
authors.affiliation: Materials Science Division, Argonne National Laborator y, Argonne, Illinois 60439, United States.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Bugaris
authors.affiliation: Materials Science Division, Argonne National Laborator y, Argonne, Illinois 60439, United States.|Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Christos D
authors.initials: CD
authors.lastname: Malliakas
authors.affiliation: Materials Science Division, Argonne National Laborator y, Argonne, Illinois 60439, United States.
authors.forename: Duck Young
authors.initials: DY
authors.lastname: Chung
authors.affiliation: Materials Science Division, Argonne National Laborator y, Argonne, Illinois 60439, United States.|Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Mercouri G
authors.initials: MG
authors.lastname: Kanatzidis