A2SbB3O8 (A = Na, K, Rb) and β-RbSbB2O6: two types of alkali boroantimonates with 3D anionic architectures composed of SbO6 octahedra and borate groups

Four new alkali metal boroantimonates, namely, A2SbB3O8 (A = Na, K, Rb) and β-RbSbB2O6, have been synthesized by high-temperature solid-state reactions. Isostructural A2SbB3O8 (A = Na, K, Rb) crystallizes in the monoclinic space group P21/c, with structures featuring a novel 3D anionic framework composed of SbO6 octahedra and linear B3O8 groups with 1D tunnels of Sb4B4 8-membered-rings (MRs) along the a-axis, which are filled by alkali metal ions. β-RbSbB2O6 crystallizes in the polar space group Cc, revealing novel 3D anionic networks composed of SbO6 octahedra chains and B2O5 groups with 1D tunnels of Sb4B2 6-MRs along the b-axis and 1D tunnels of Sb3B4 7-MRs along the c-axis. Studies on their optical properties and thermal stability, band structure calculations based on DFT methods and linear optical calculations have also been performed.