Ternary lanthanoid ruthenium gallides with a high gallium content: Ln(2)Ru(3)Ga(10) (Ln = Yb, Lu) with a new structure type and LnRu(2)Ga(8) (Ln = La-Nd) with CaCo(2)Al(8)-type structure.

Abstract

The title compounds were prepared by reaction of the elemental components at high temperatures. The compounds Yb(2)Ru(3)Ga(10) and Lu(2)Ru(3)Ga(10) crystallize with a new structure type, which has been determined from the single-crystal X-ray data of Yb(2)Ru(3)Ga(10): P4/mbm, Z = 2, a = 881.9(1) pm, c = 632.5(1) pm. In this structure the gallium atoms form two-dimensionally infinite double layers that extend perpendicular to the tetragonal axis. They contain two-thirds of the ruthenium atoms. The other ruthenium and the ytterbium atoms are situated between the gallium double layers. The structure is closely related to that of Mn(2)Hg(5). The latter compound may be written with the formula Mn(2)Mn(2)(square)Hg(10), thus indicating that its structure may be regarded as a defect-variant of the presently reported structure of Yb(2)Ru(3)Ga(10). The four gallides of the series LnRu(2)Ga(8) (Ln = La-Nd) crystallize with the orthorhombic CaCo(2)Al(8)-type structure (Pbam, Z = 4). This structure has been refined from single-crystal X-ray data of the cerium and neodymium compounds. Slight deviations from the ideal composition for one of the two ruthenium sites resulted in the formulas CeRu(1.913(4))Ga(8) and NdRu(1.858(4))Ga(8). Magnetic susceptibility measurements with a SQUID magnetometer indicate diamagnetism for LaRu(2)Ga(8), which is partially compensated by the expected Pauli paramagnetism. The cerium atoms in CeRu(2)Ga(8) show mixed or intermediate valent behavior, and PrRu(2)Ga(8) follows the Curie-Weiss law with no magnetic order down to 4 K.