Synthesis, Crystal Structure, and Solid-State NMR Spectroscopy of a New Open-Framework Aluminophosphate (NH₄)₂Al₄(PO₄)₄(HPO₄)·H₂O

A new three-dimensional open-framework aluminophosphate (NH4)2Al4(PO4)4(HPO4)·H2O (denoted AlPO-CJ19) with an Al/P ratio of 4/5 has been synthesized, using pyridine as the solvent and 2-aminopyridine as the structure-directing agent, under solvothermal conditions. The structure was determined by single-crystal X-ray diffraction and further characterized by solid-state NMR techniques. The alternation of the Al-centered polyhedra (including AlO4, AlO5, and AlO6) and the P-centered tetrahedra (including PO4 and PO3OH) results in an interrupted open-framework structure with an eight-membered ring channel along the [100] direction. This is the first aluminophosphate containing three kinds of Al coordinations (AlO4, AlO5, and AlO6) with all oxygen vertexes connected to framework P atoms. 27Al MAS NMR, 31P MAS NMR, and 1H → 31P CPMAS NMR characterizations show that the solid-state NMR techniques are an effective complement to XRD analysis for structure elucidation. Furthermore, all of the possible coordinations of Al and P in the aluminophosphates with an Al/P ratio of 4/5 are summarized. Crystal data: (NH4)2Al4(PO4)4(HPO4)·H2O, monoclinic P21 (No. 4), a = 5.0568(3) Å, b = 21.6211(18) Å, c = 8.1724(4) Å, β = 91.361(4)°, V = 893.27(10) Å3, Z = 2, R1 = 0.0456 (I > 2σ(I)), and wR2 = 0.1051 (all data).