Molten Ga as a Solvent for Exploratory Synthesis. Preparation, Structure, and Properties of Two Ternary Silicides MNiSi3 (M = Sm, Y)

Abstract

Two ternary silicides, MNiSi3 (M = Sm, Y), have been synthesized from Sm, Ni, and Si in molten Ga at 850 °C in sealed silica tubes. Both compounds form black shiny crystals and are stable even in aqua regia. The structures, determined by single-crystal X-ray diffraction, are orthorhombic, Cmmm (No. 65) with Z = 4, and have lattice parameters a = 3.965(2) Å, b = 21.144(2) Å, c = 4.007(1) Å for M = Sm and a = 3.930(2) Å, b = 21.021(2) Å, c = 3.960(1) Å for M = Y, respectively. Refinement based on Fo2 yielded R1 = 0.0319 and wR2 = 0.0712 [I > 2 σ(I)] for M = Sm and R1 = 0.0267 and wR2 = 0.0688 [I > 2σ(I)] for M = Y. The compounds adopt the SmNiGe3 structure type with zigzag Si chains and Si dimers and exhibit metallic p-type electrical conductivity. Variable temperature magnetic susceptibility data suggest that Sm is 3+ and Ni has no magnetic moment. SmNiSi3 has an antiferromagnetic transition at 12 K and follows the modified Curie−Weiss law above 12 K. Band structure calculations using density functional theory, generalized gradient approximation, full potential LAPW method, and also extended Hückel tight binding theory show that the materials are metallic and suggest that Ni is either neutral or in a reduced oxidation state. Additional insight into the bonding was obtained by extended Hückel calculations carried out on the [NiSi3]3- framework under the assumption that Y is mostly 3+. These results suggest that the Si zigzag chain contains single bonds with a partial double bond character.