Li[AlPOF(OH)](HO) and [Al(PO)F(HO)]( = K, Rb): Counter Cation Templates Derived Three Polar Alkaline Metal Fluoroaluminophosphates.

Three novel alkali metal fluoroaluminophosphates, Li[AlPOF(OH)](HO) and [Al(PO)F(HO)]( = K, Rb), were designed and synthesized by using low-temperature flux methods. They crystallized in polar space groups and 222, respectively. Li[AlPOF(OH)](HO) features a unique two-dimensional layered structure of fluoroaluminophosphate [AlPOF(OH)], composed of alternately connected AlFO octahedra and PO tetrahedra. In contrast, with counter cations from Li to K/Rb, two new crystals of [Al(PO)F(HO)]( = K, Rb) have been obtained. They possess a distinct three-dimensional anionic framework, [Al(PO)F], consisting of corner-sharing AlO triangular bipyramids, AlFO octahedra, and PO tetrahedra, revealing intersecting open tunnels along the [010], [001], and [111] directions. Notably, both Li[AlPOF(OH)](HO) and K[Al(PO)F(HO)] exhibit moderate second harmonic generation effects. Besides, porous material of K[Al(PO)F(HO)] 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.