Molten Ga as a solvent for exploratory synthesis. Preparation, structure, and properties of two ternary silicides MNiSi3 (M = Sm, Y)

Two ternary silicides, MNiSi3 (M = Sm, Y), have been synthesized from Sm, N i, and Si in molten Ga at 850 degrees C in sealed silica tubes. Both compou nds form black shiny crystals and are stable even in aqua regia. The struct ures, determined by single-crystal X-ray diffraction, are orthorhombic, Cmm m (No. 65) with Z = 4, and have lattice parameters a = 3.965(2) Angstrom, b = 21.144(2) Angstrom, c = 4.007(1) Angstrom for M = Sm and a = 3.930(2) An gstrom, b = 21.021(2) Angstrom, c = 3.960(1) Angstrom for M = Y, respective ly. Refinement based on F-o(2) yielded R-1 = 0.0319 and wR(2) = 0.0712 [I > 2 sigma(I)] for M = Sm and R-1 = 0.0267 and wR(2) = 0.0688 [1 > 2 sigma(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. V ariable temperature magnetic susceptibility data suggest that Sm is 3+ and Ni has no magnetic moment. SmNiSi3 has an antiferromagnetic transition at 1 2 K and follows the modified Curie-Weiss law above 12 K. Band structure cal culations using density functional theory, generalized gradient approximati on, full potential LAPW method, and also extended Huckel tight binding theo ry show that the materials are metallic and suggest that Ni is either neutr al or in a reduced oxidation state. Additional insight into the bonding was obtained by extended Huckel calculations carried out on the [NiSi3](3-) fr amework under the assumption that Y is mostly 3+. These results suggest tha t the Si zigzag chain contains single bonds with a partial double bond char acter.