Li₃[AlP₂O₇F(OH)](H₂O)_0.5 and A[Al₂(PO₄)₂F(H₂O)](A = K, Rb): Counter Cation Templates Derived Three Polar Alkaline...

Three novel alkali metal fluoroaluminophosphates, Li₃[AlP₂O₇F(OH)](H₂O)_0.5 and A[Al₂(PO₄)₂F(H₂O)](A = K, Rb), were designed and synthesized by using low-temperature flux methods. They crystallized in polar space groups P₄ and P2₁2₁2₁, respectively. Li₃[AlP₂O₇F(OH)](H₂O)_0.5 features a unique two-dimensional layered structure of fluoroaluminophosphate [AlP₂O₇F(OH)]^3-, composed of alternately connected AlFO₅ octahedra and PO₄ tetrahedra. In contrast, with counter cations from Li⁺ to K⁺/Rb⁺, two new crystals of A[Al₂(PO₄)₂F(H₂O)](A = K, Rb) have been obtained. They possess a distinct three-dimensional anionic framework, [Al₂(PO₄)₂F]^-, consisting of corner-sharing AlO₅ triangular bipyramids, AlFO₅ octahedra, and PO₄ tetrahedra, revealing intersecting open tunnels along the [010], [001], and [111] directions. Notably, both Li₃[AlP₂O₇F(OH)](H₂O)_0.5 and K[Al₂(PO₄)₂F(H₂O)] exhibit moderate second harmonic generation effects. Besides, porous material of K[Al₂(PO₄)₂F(H₂O)] exhibited remarkable ionic exchange properties with Cs⁺, implying its potential utility in the remediation of radioactive waste and offering a promising solution for managing nuclear contaminants. This research reports on their syntheses, topological structures, elemental analysis, thermal stability, IR Raman spectroscopy, UV-Vis diffuse reflectance spectroscopy, ion exchange property, and nonlinear optical characteristics.