[(C ₄N ₂H ₁₂) ₃·H ₂O][(Al ₂P ₃O ₁₂) ₂]: A new anionic open-framework aluminophosphate with helical chains and multi-directional intersecting twelve-ring channels

A new three-dimensional (3D) anionic interrupted open-framework aluminophosphate [(C ₄N ₂H ₁₂) ₃· H ₂O][(Al ₂P ₃O ₁₂) ₂] (denoted AlPO-JU88) with an Al/P ratio of 2/3 was hydrothermally synthesized by using piperazine as a structure directing agent. The structure was determined by single-crystal X-ray diffraction structural analysis and was further characterized by X-ray powder diffraction, elemental (CHN), thermogravimetric (TG), and NMR analyses. The strict alternation of Al-centered tetrahedra (AlO ₄) and P-centered tetrahedra (PO ₂(O) ₂ and PO ₃(O)) via bridging oxygen atoms resulted in a 3D open-framework featuring a new type of super-cage of 4 ⁶12 ⁸. Six racemic helical (3 ₁ or 3 ₂) chains were linked together to form a twelve-ring (12R) channel along the [0 0 1] direction, forming a multi-directional intersecting 12R channel system together with the 12R channels run along [2 4 1], [2 -2 1], and [- 4 - 2 1] directions. The negative charge of the framework was balanced by doubly protonated piperazine molecules. Ion exchange experiment suggested that 22 mol% of the protonated piperazine can be exchanged by Na cations, showing a better ion exchange property for the 3D interrupted open-framework aluminophosphates.