Condensed [Ru4Sn6] units in the stannides LnRu(4)Sn(6) (Ln = La, Pr, Nd, Sm, Gd) - Synthesis, structure, and chemical bonding

The stannides LnRu(4)Sn(6) (Ln = La, Pr, Nd, Sm, Gd) were prepared by react ion of the elements in an are-melting furnace and subsequent annealing at 1 120 K. The praseodymium, the neodymium, and the samarium stannide were obta ined for the first time. The LnRu(4)Sn(6) stannides were investigated by X- ray diffraction both on powders and single crystals. They adopt the YRu4Sn6 type structure which was refined from single crystal X-ray data for the sa marium and the gadolinium compound: I (4) over bar 2m, a = 686.1(1), c = 97 7.7(2) pm, wR2 = 0.0649, 483 F-3 values for SmRu4Sn6, and a = 685.2(1), c = 977.6(3) pm, wR2 = 0.0629, 554 F-2 values for GdRu4Sn6 with 19 variables f or each refinement. The striking structural motif of these stannides are di storted RuSn6 octahedra with Ru-Sn distances ranging from 257 to 278 pm. Fo ur of such octahedra are condensed via common edges and faces forming [Ru4S n6] units which are packed in a tetragonal body-centered arrangement. The r are-earth atoms fill the voids between the [Ru4Sn6] units. Based on an exte nded Huckel calculation, strong bonding interactions were found for the Ru- Sn and the various Sn-Sn contacts.