Li3[AlP2O7F(OH)](H2O)0.5 and A[Al2(PO4)2F(H2O)](A = K, Rb): Counter Cation Templates Derived Three Polar Alkaline Metal Fluoroaluminophosphates

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 P 4 and P212121, respectively. Li3[AlP2O7F(OH)](H2O)0.5 features a unique two-dimensional layered structure of fluoroaluminophosphate [AlP2O7F(OH)]3- n , 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]- n , 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.