Synthesis and crystal structures of BaLaSi2 with cis-trans Si chains and Ba5LaSi6 with pentagonal Si rings.

Prismatic single crystals of novel compounds BaLaSi2 and Ba5LaSi6 were synthesized from the elements with or without a Na flux. The crystal structures of the compounds were analyzed by X-ray diffraction. BaLaSi2, containing cis–trans ∞1[Si] chains, crystallizes in an orthorhombic cell (a = 4.6414(2) Å, b = 14.8851(7) Å, c = 6.7519(5) Å; space group, Cmcm (No. 63), Z = 4) and is isotypic with the low-temperature phase of LaSi. The crystal structure of Ba5LaSi6 (a = 17.1447(5) Å, b = 4.8767(1) Å, and c = 17.9102(4) Å; space group Pnma (No. 62), Z = 4) is a new type containing isolated anionic groups (0[Si5–Si]) of a pentagonal Si ring with a Si–Si stem. The electrical resistivities measured for the polycrystalline BaLaSi2 and Ba5LaSi6 sintered samples were 0.31 and 0.48 mΩ·cm, respectively, at 300 K and increased with temperature. The Seebeck coefficients of BaLaSi2 and Ba5LaSi6 were −7.6 and −11 μV·K–1, respectively, at 296 K.