BaIr ₂ Si ₉ : A Hybrid Structure Bridging Sodalite, Clathrate, and Skutterudite Patterns

The cage compound BaIr 2 Si 9 adopts the BaRh 2 Si 9 structure type with space group C 2/ c (Pearson symbol mC 48, a = 6.230(1) Å, b = 21.409(3) Å, c = 6.232(1) Å, β = 90.30(1)°). The atomic arrangement features fragmented sodalite cages that are interrupted along [010] by puckered Ir–Si layers showing the pentagonal Cairo‐Tiling motif. The compound melts incongruently at 1180°C and is obtained as a single‐phase after annealing at 800°C for 3 days. Electric transport measurements reveal that BaIr 2 Si 9 is a p ‐type semiconductor, consistent with band structure calculations indicating a bandgap of 0.5 eV. Quantum chemical calculation confirms positively charged Ba atoms accompanied by Ir atoms with negative charges. The charge distribution of silicon is heterogeneous as Si atoms bonded to Ir exhibit positive charges while those forming merely Si–Si contacts are negatively charged.