Condensed (Ru_4Sn_6) Units in the Stannides LnRu_4Sn_6 (Ln=La, Pr, Nd, Sm, Gd)-Synthesis, Structure, and Chemical Bonding

摘要

The stannides LnRu_4Sn_6 (Ln = La, Pr, Nd, Sm, Gd) were prepared by reaction of the elements in an arc-melting furnace and subsequent annealing at 1120 K. The praseodymium, the neodymium, and the samarium stannide were obtained for the first time. The LnRu_4Sn_6 stannides were investigated by X-ray diffraction both on powders and single crystals. They adopt the YRu_4Sn_6 type structure which was refined from single crystal X-ray data for the samarium and the gadolinium compound: I42m, a = 686.1 (1), c = 977.7 (2) pm, wR2 = 0.0649, 483F~2 values for SmRu_4Sn_6, and a = 685.2 (1), C = 977.6 (3) pm, wR2 = 0.0629, 554 F~2 values for GdRu_4Sn_6 with 19 variables for each refinement. The striking structural motif of these stannides are distorted Ru_4Sn_6 octahedra with Ru-Sn distances ranging from 257 to 278 pm. Four of such octahedra are condensed via common edges and faces forming [Ru_4Sn_6] units which are packed in a tetragonal body-centered arrangement. The rare-earth atoms fill the voids between the [Ru_4Sn_6] units. Based on an extended Huckel calculation, strong bonding interactions were found for the Ru-Sn and the various Sn-Sn contacts.