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.