Structure and Bonding of Bi4Ir: A Difficult-to-Access Bismuth Iridide with a Unique Framework Structure

Crystals of Bi4Ir, a new intermetallic compound, were obtained by the reaction of an iridium-containing intermetallic precursor with liquid bismuth. X-ray diffraction on a single crystal revealed a rhombohedral structure [R3̅m, a = 2656.7(2) pm, and c = 701.6(4) pm]. Bi4Ir is not isostructural to Bi4Rh but combines motifs of the metastable superconductor Bi14Rh3 with those found in the weak topological insulator Bi14Rh3I9. The two crystallographically independent iridium sites in Bi4Ir have square-prismatic and skewed-square-antiprismatic bismuth coordination with Bi–Ir distances of 283–287 pm. By sharing common edges, the two types of [IrBi8] units constitute a complex three-dimensional network of rings and helices. The bonding in the heterometallic framework is dominated by pairwise Bi–Ir interactions. In addition, three-center bonds are found in the bismuth triangles formed by adjacent [IrBi8] polyhedra. Density functional theory based band-structure calculations suggest metallic properties.