The Ternary Silicide ZrPd₃Si₃, a Stacking Variant of the α-FeSi₂ and Re₃B Structure Types

The ternary zirconium palladium silicide ZrPd3Si3 has been synthesized by arc-melting of the elemental components. It adopts a new structure type and crystallizes in the orthorhombic space group Cmcm with a = 3.8127(4) Å, b = 15.551(1) Å, c = 7.0390(5) Å, and Z = 4 (Pearson symbol oC28). The structure can be regarded as being built up of Re3B-type slabs of composition “Pd3Si” alternating with α-FeSi2 slabs of composition “ZrSi2.” Notable features include the presence of Si2 pairs, square pyramidal and tetrahedral coordination of Pd centers by Si atoms, an unusual distorted cubic coordination of the Zr atoms by the Si2 pairs, and an extensive network of Zr−Zr, Zr−Pd, and Pd−Pd metal−metal bonds. ZrPd3Si3 is weakly metallic with a room-temperature resistivity of 1.7 × 10-3 Ω cm. Extended Hückel band structure calculations confirm the metallic behavior; support the simultaneous existence of strong metal−metal, metal−nonmetal, and nonmetal−nonmetal bonding; and suggest a reduced state for the Pd atoms resulting from electron transfer from the Si atoms.