Crystal structure, specific heat, and 119Sn Mossbauer spectroscopy of CeRu4Sn6:: A ternary stannide with condensed, distorted RuSn6 octahedra

CeRu4Sn6 was prepared from the elements by a reaction in an arc-melting furnace and subsequent annealing at 1123 K. It crystallizes with the tetragonal YRu4Sn6 type structure of space group I (4) over bar 2m: a=688.1(1), c=975.2(2) pm, V=0.4617(1) nm(3), wR2 = 0.0472, 554 F-2 values, and 19 variables. The cerium atoms in CeRu4Sn6 have coordination number 16 formed by 12 tin and 4 ruthenium atoms. These polyhedra are arranged in a tetragonal body-centered packing and are linked by common Sn1 atoms. The strongest bonding interactions are between ruthenium and tin atoms. The ruthenium atoms have 6 tin neighbors at distances from 256.9 to 276.8 pm in the form of a strongly distorted octahedron. Four of such octahedra are condensed via common edges and faces forming [Ru4Sn6] units. These groups are packed in a tetragonal body-centered arrangement. The cerium atoms occupy the space between the [Ru4Sn6] units. The [Ru4Sn6] substructure of CeRu4Sn6 is discussed in comparison with the structures of Ru2Sn3, LaRuSn3, and Ru3Sn15O14 which also contain condensed RuSn6 octahedra or trigonal prisms as characteristic structural motifs. Despite the two different tin sites the Sn-119 Mossbauer spectroscopic measurements show only one signal at delta=1.99 mm/s subjected to quadrupole splitting. Heat capacity measurements indicate that CeRu4Sn6 behaves like a heavy-fermion compound. (C) 1997 Academic Press.