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

Abstract

Two remarkable aluminum borophosphates (AlBPOs), namely,\nNa₃[Al₂B₆P₄O₂₂(OH)₃](H₂O)₆ (denoted as ABPO1)\nand Na₃[Al₂BP₂O₁₁](H₂O)_0.5 (denoted as ABPO2), have been designed and\nprepared\nby low-temperature flux syntheses. The exceptional open framework\nstructure of ABPO1 is formed by a unique microanionic network [Al₂B₆P₄O₂₂(OH)₃]_n^3–, which contains three types of 8-, 12-,\nand 16-membered ring (MR) tunnels. Interestingly, these tunnels are\nfeatured by a type of super-nanocage as large as ∼1.753 nm\n× 1.753 nm × 1.753 nm, which is the first example of AlBPOs\ncontaining 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\npotential ionic exchanger for removing radionuclides and toxic cations.\nThe structure of ABPO2 features a unique 2D anionic AlBPO layer composed\nof corner-sharing AlO₆ octahedra and AlO₄, BO₄, and PO₄ tetrahedra. To the best of our knowledge,\nthis is the first example of both AlO₆ octahedra and AlO₄ tetrahedra being contained in the structure. 9-MRs can be\nobserved along the <i>b</i>-axis. Herein, the syntheses\nand topological structures of ABPO1 and ABPO2 as well as elemental\nanalysis, thermal stability, infrared spectroscopy, UV–vis\ndiffuse reflectance, structural properties, and ionic exchange properties\nare also discussed.