The ternary rare earth ruthenium gallides R3Ru 4Ga 15 ( R=Y, Tb–Er) with a new structure type, a further example of a recently recognized large family of structures

Abstract

The title compounds were prepared by reaction of the elemental components at high temperature. They crystallize with a new orthorhombic structure type which was determined from single-crystal diffractometer data of Ho 3Ru 4Ga 15: Pnma, a=871.7(1) pm, b=956.4(1) pm, c=1765.9(3) pm, Z=4, R=0.040 for 1039 structure factors and 114 variable parameters. The structure may be viewed as consisting of two kinds of atomic layers, although atomic bonding within and between the layers is comparable strength, as can be judged from the near-neighbor environments, where all of the 15 atomic sites have high coordination numbers. One kind of atomic layers ( A) contains all of the holmium and additional gallium atoms in the ratio Ho:Ga=3:5 with a unit mesh content of 2Ho 3Ga 5; these layers are flat. The other layers ( B) consist of sheets of corner- and edge-sharing condensed RuGa 6 octahedra, which are extremely compressed resulting in a hexagonal close-packed, puckered net with a Ru:Ga ratio of 2:5 and a unit mesh content of 4Ru 2Ga 5. These nets alternate in the sequence ABAB, ABAB, thus yielding the formula 4Ho 3Ga 5·8Ru 2Ga 5=4Ho 3Ru 4Ga 15. Similar layers are observed in the structures of Y 2Co 3Ga 9, Gd 3Ru 4Al 12, Er 4Pt 9Al 24, CeOsGa 4, CaCr 2Al 10, and the four stacking variants with the compositions TbRe 2Al 10, DyRe 2Al 10, YbFe 2Al 10, and LuRe 2Al 10.