Highly porous aluminophosphates with unique three dimensional open framework structures from mild hydrothermal syntheses

Abstract

Crystals of three novel highly porous aluminophosphates, namely, α-NaAlPO₄(OH) (1), β-NaAlPO₄(OH) (2) and Al_3.5P_5.5O₁₉ (3), were synthesized through mild hydrothermal methods. Interestingly, among these three porous aluminophosphates, 1 is polar, whereas the other compounds are nonpolar and centrosymmetric. The 3D framework structure of 1 is built from AlO₆ octahedra and isolated PO₄ tetrahedra. 1D Al-chains are linked by PO₄ tetrahedra via sharing corners, forming the 3D framework, and 1D 8-membered ring (MR) tunnels were observed along the c-axis. Importantly, the material of 1 exhibits a moderate second harmonic generation (SHG) effect. 2 features a unique 3D anionic framework composed of corner-sharing [Al₂O₁₁] dimers and isolated PO₄ tetrahedra. Three intersecting tunnels along the axes can be observed; the small tunnels along the c-axis are based on 4-MRs, whereas the two 6-MRs are along the a- and b-axes. The structure of 3 displays a unique 3D framework based upon face-sharing [Al₂O₉] dimers and isolated PO₄ tetrahedra. The small tunnels along the a- and b-axes are based upon 4-MRs, whereas the 1D larger tunnels are based on 12-MRs along the c-axis. Here, the syntheses and topological structures of α-NaAlPO₄(OH) (1), β-NaAlPO₄(OH) (2) and Al_3.5P_5.5O₁₉ (3) as well as their elemental analysis, thermal stability, infrared spectroscopy, UV-vis diffuse reflectance and nonlinear optical (NLO) properties are also reported.