Chains of condensed RuSm6/2 octahedra in Sm3RuMg 7 - A ternary ordered version of the Ti6Sn5 type

Abstract

The magnesium-rich intermetallic compound Sm3RuMg7 was synthesized by induction melting of the elements. Single crystals were grown by slow cooling of the polycrystalline sample. The structure was characterized by powder and single-crystal X-ray diffraction: ordered Ti6Sn 5 type, P63/mmc, Z = 2, a = 1034.1(2), c = 611.3(1) pm, wR2 = 0.0216, 399 F2 values and 19 parameters. The ruthenium atoms have slightly distorted octahedral samarium coordination. These RuSm 6/2 octahedra (Ru-Sm 279 pm) are condensed via common faces leading to chains in the c direction which are arranged in the form of a hexagonal rod packing. Between these rods the Mg2 atoms build chains of face-sharing trigonal prisms. Alternately these prisms are centered by Mg3 or capped by Mg1 atoms on the rectangular faces. Within the magnesium substructure the Mg-Mg distances range from 303 to 335 pm. The Mg3 site shows slight mixing with samarium, leading to the composition Sm3.16RuMg6.84 for the investigated crystal. The compounds RE3RuMg7 (RE = Gd, Tb) are isotypic. © 2011 Verlag der Zeitschrift fur Naturforschung.