Structural Diversity in Oxoiridates with 1D IrnO3(n+1) Chain Fragments and Flat Bands

A previously unreported series of hexagonal-perovskite-based Rb-oxoiridates, Rb5Ir2O9, Rb7Ir3O12, and Rb12Ir7O24, have been synthesized and structurally analyzed via N-2-protected single-crystal X-ray diffraction (SC-XRD). These materials exhibit different 1D IrnO3(n+1) chain fragments along their c axes. IrO6 octahedra and RbOx (x = 6, 8, and 10) polyhedra are their basic building blocks. The IrO6 octahedra are linked via face-sharing, forming Ir2O9 dimers, Ir3O12 trimers, and Ir7O24 heptamers. The nonmagnetic RbOx (x = 6, 8, and 10) polyhedra serve as both bridging units and spacers. Temperature-dependent SC-XRD shows all three to display positive thermal expansion and rules out structural transitions from their triangular symmetries down to 100 K. Density functional theory results suggest semiconducting-like behavior for the title compounds. The flatness of the electronic bands and our structural analysis are of potential interest for understanding and designing 1D quantum materials.