Mg3Ir3Si8, ein neues Magnesium‐Iridium‐Silicid mit Tetraedern und gekappten Tetraedern aus Silicium‐Atomen

Abstract

AbstractMg3Ir3Si8, a New Magnesium Iridium Silicide with Si4 Tetrahedra and Si12 Truncated TetrahedraThe ternary silicide Mg3Ir3Si8 (cubic, a = 1221.4(1) pm, space group $F{\bar 4}{\rm 3}m$, 8 formula units per unit cell) was prepared by reaction of the elemental components in a sealed molybdenum container (1000 °C, 1 d, cooled with 100 °/h). The crystal structure was determined from single crystal data. Short distances in the three‐dimensional iridium silicon network indicate strong Ir‐Si‐bonding (d(Ir‐Si) = 240.5(2) and 245.6(1) pm). In addition, homonuclear bonding seems to be important, resulting in the formation of Si4‐tetrahedra (d(Si‐Si) = 257(1) pm), and Mg centered Si12‐polyhedra with the shape of truncated tetrahedra (d(Si‐Si) = 241(1) and 261.0(9) pm). Furthermore, Mg4‐tetrahedra with Mg‐Mg‐distances of 355(2) pm are formed. The structure may be derived from the structure of the isotypic compounds Mg5Pd10Si16 and Mg5Pt10Si16 by adding a Mg siteset and subtracting a platinum metal siteset. It can be described by an expanded cubic “close” packing of MgIr6‐octahedra in which Si4‐tetrahedra reside in the octahedral holes while Mg4‐tetrahedra and MgSi12‐units occupy one half of the tetrahedral holes each.