The ternary silicide ZrPd3Si3, a stacking variant of the alpha-FeSi2 and Re3B structure types

The ternary zirconium palladium silicide ZrPd3Si3 has been synthesized by a re-melting of the elemental components. It adopts a new structure type and crystallizes in the orthorhombic space group Cmcm with alpha = 3.8127(4) An gstrom, b = 15.551(1) Angstrom, c = 7.0390(5) Angstrom, and Z = 4 (Pearson symbol oC28). The structure can be regarded as being built up of Re3B-type slabs of composition "Pd3Si" alternating with alpha-FeSi2 slabs of composit ion "ZrSi2." Notable features include the presence of Sit pairs, square pyr amidal and tetrahedral coordination of Pd centers by Si atoms, an unusual d istorted cubic coordination of the Zr atoms by the Sit pairs, and an extens ive network of Zr-Zr, Zr-Pd, and Pd-Pd metal-metal bonds. ZrPd3Si3 is weakl y metallic with a room-temperature resistivity of 1.7 x 10(-3) Omega cm. Ex tended Huckel band structure calculations confirm the metallic behavior; su pport the simultaneous existence of strong metal-metal, metal-nonmetal, and nonmetal-nonmetal bonding; and suggest a reduced state for the Pd atoms re sulting from electron transfer from the Si atoms.