Abstract. The centrosymmetric structure of Co 2 Al 9 (space group P2 1 /c, Pearson symbol mP22), the isotypic structures of Rh 2 Al 9 and Ir 2 Al 9 and the slightly distorted acentric structures of Rh 2 Ga 9 and Ir 2 Ga 9 (space group Pc) were reinvestigated from single crystal X-ray diffraction data. The structure of Rh 2 Ga 9 represents a new structure type. The difference between the aluminides and the galDer Strukturtyp Co 2 Al 9 erneut untersucht Inhaltsübersicht. Die zentrosymmetrische Struktur der Verbindung Co 2 Al 9 (Raumgruppe P2 1 /c, Pearson-Symbol mP22), die isotypen Strukturen Rh 2 Al 9 und Ir 2 Al 9 , sowie die leicht verzerrten azentrischen Strukturen Rh 2 Ga 9 und Ir 2 Ga 9 (Raumgruppe Pc) wurden auf der Basis der Einkristall-Röntgenbeugungsdaten erneut unter-

Structure D 2000 Preparation, Crystal Structure and Chemical Bonding Analysis of the New Binary Compounds Rh4Ga21 and Rh3Ga16. -Single crystals of the new title compounds are prepared in a Ga-rich self-flux containing Rh (150-300°C, 18 d). Rh4Ga21 crystallizes in the orthorhombic space group Cmca with Z = 4 and Rh3Ga16 in the orthorhombic space group Ccca with Z = 4. Bonding analysis indicates that the crystal structures of the compounds have to be considered as framework polyanions formed by covalently bonded Ga atoms with embedded Rh cations. -(BOSTROEM*, M.; PROTS, Y.; GRIN, Y.; J. Solid State Chem. 179 (2006) 8, 2472-2478; MPI Chem. Phys. fester Stoffe,

Ruthenium I 7800Preparation and Crystal Structure of Nanocrystalline RuZn3. -The new title compound is synthesized in nanocrystalline form by an isopiestic vapor pressure method exposing Ru to a constant vapor pressure of Zn at 963 K (12 d). RuZn3 crystallizes in the space group I4/mmm with Z = 4 as revealed by powder XRD. The Ru atoms are cubeoctahedrally coordinated by Zn atoms. The cubeoctahedra form layers by sharing square faces. -(BOSTROEM*, M.; GEMMI, M.; RICHTER, K. W.; J. Alloys Compd. 427 (2007) 1-2, 300-304; Eur. Synchrotron Radiat. Facil., F-38043 Grenoble, Fr.; Eng.) -W. Pewestorf

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5 . -The title compound is synthesized from the elements by a self-flux route (700°C, 10 h) and by solid state reaction (500°C, 10 d). The samples are characterized by single crystal XRD, magnetic measurements, and electronic band structure calculations employing FPLO, LMTO, and extended Hueckel tight-binding methods. The compound crystallizes in the tetragonal space group P4/mbm with Z = 2. The structure exhibits a three-dimensional Ga network made up of two crystallographically different types of Ga atoms. Mn2Ga5 exhibits a saturated magnetic moment of 2.71 µB per formula unit with TC ≈ 450 K. The nonmagnetic electronic structure of Mn2Ga5 reveals remarkably flat degenerate (superdegenerate) bands in the vicinity of the Fermi level. The resulting high density of states at the Fermi level is consistent with the Stoner condition for the observed itinerant electron ferromagnetism. -(KIM, S.-H.; BOSTROEM, M.; SEO*, D.-K.; J.