Na₃[Al₂B₆P₄O₂₂(OH)₃](H₂O)₆ and Na₃[Al₂BP₂O₁₁](H₂O)_0.5: Two Remarkable Complex Aluminum Borophosphates

Two remarkable aluminum borophosphates (AlBPOs), namely, Na₃[Al₂B₆P₄O₂₂(OH)₃](H₂O)₆ (denoted as ABPO1) and Na₃[Al₂BP₂O₁₁](H₂O)_0.5 (denoted as ABPO2), have been designed and prepared by low-temperature flux syntheses. The exceptional open framework structure of ABPO1 is formed by a unique microanionic network [Al₂B₆P₄O₂₂(OH)₃]_n^3-, which contains three types of 8-, 12-, and 16-membered ring (MR) tunnels. Interestingly, these tunnels are featured by a type of super-nanocage as large as ∼1.753 nm × 1.753 nm × 1.753 nm, which is the first example of AlBPOs containing extra-large cages. Importantly, it was found that Na⁺ can be partially exchanged by K⁺, Sr²⁺, Cd²⁺, and Ni²⁺, which means that it is a potential ionic exchanger for removing radionuclides and toxic cations. The structure of ABPO2 features a unique 2D anionic AlBPO layer composed of corner-sharing AlO₆ octahedra and AlO₄, BO₄, and PO₄ tetrahedra. To the best of our knowledge, this is the first example of both AlO₆ octahedra and AlO₄ tetrahedra being contained in the structure. 9-MRs can be observed along the b-axis. Herein, the syntheses and topological structures of ABPO1 and ABPO2 as well as elemental analysis, thermal stability, infrared spectroscopy, UV-vis diffuse reflectance, structural properties, and ionic exchange properties are also discussed.