Li<sub>3</sub>[AlP<sub>2</sub>O<sub>7</sub>F(OH)](H<sub>2</sub>O)<sub>0.5</sub> and <i>A</i>[Al<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>F(H<

Three novel alkali metal fluoroaluminophosphates,\nLi<sub>3</sub>[AlP<sub>2</sub>O<sub>7</sub>F(OH)](H<sub>2</sub>O)<sub>0.5</sub> and <i>A</i>[Al<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>F(H<sub>2</sub>O)](<i>A</i> = K, Rb), were designed\nand\nsynthesized by using low-temperature flux methods. They crystallized\nin polar space groups <i>P</i><sub>4</sub> and <i>P</i>2<sub>1</sub>2<sub>1</sub>2<sub>1</sub>, respectively. Li<sub>3</sub>[AlP<sub>2</sub>O<sub>7</sub>F(OH)](H<sub>2</sub>O)<sub>0.5</sub> features a unique two-dimensional layered structure of fluoroaluminophosphate\n[AlP<sub>2</sub>O<sub>7</sub>F(OH)]<sup>3–</sup><sub><i>n</i></sub>, composed of alternately connected AlFO<sub>5</sub> octahedra and PO<sub>4</sub> tetrahedra. In contrast, with counter\ncations from Li<sup>+</sup> to K<sup>+</sup>/Rb<sup>+</sup>, two new\ncrystals of <i>A</i>[Al<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>F(H<sub>2</sub>O)](<i>A</i> = K, Rb) have been obtained.\nThey possess a distinct three-dimensional anionic framework, [Al<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>F]<sup>−</sup><sub><i>n</i></sub>, consisting of corner-sharing AlO<sub>5</sub> triangular\nbipyramids, AlFO<sub>5</sub> octahedra, and PO<sub>4</sub> tetrahedra,\nrevealing intersecting open tunnels along the [010], [001], and [111]\ndirections. Notably, both Li<sub>3</sub>[AlP<sub>2</sub>O<sub>7</sub>F(OH)](H<sub>2</sub>O)<sub>0.5</sub> and K[Al<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>F(H<sub>2</sub>O)] exhibit moderate second harmonic\ngeneration effects. Besides, porous material of K[Al<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>F(H<sub>2</sub>O)] exhibited remarkable ionic\nexchange properties with Cs<sup>+</sup>, implying its potential utility\nin the remediation of radioactive waste and offering a promising solution\nfor managing nuclear contaminants. This research reports on their\nsyntheses, topological structures, elemental analysis, thermal stability,\nIR Raman spectroscopy, UV–Vis diffuse reflectance spectroscopy,\nion exchange property, and nonlinear optical characteristics.