Structural Diversity in Oxoiridates with 1D Ir n O 3( n +1) Chain Fragments and Flat Bands.

A previously unreported series of hexagonal-perovskite-based Rb-oxoiridates, Rb 5 Ir 2 O 9 , Rb 7 Ir 3 O 12 , and Rb 12 Ir 7 O 24 , have been synthesized and structurally analyzed via N 2 -protected single-crystal X-ray diffraction (SC-XRD). These materials exhibit different 1D Ir n O 3( n +1) chain fragments along their c axes. IrO 6 octahedra and RbO x ( x = 6, 8, and 10) polyhedra are their basic building blocks. The IrO 6 octahedra are linked via face-sharing, forming Ir 2 O 9 dimers, Ir 3 O 12 trimers, and Ir 7 O 24 heptamers. The nonmagnetic RbO x ( 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.