Structure refinement of (NH(4))(3)Al(2)(PO(4))(3) prepared by ionothermal synthesis in phospho­nium based ionic liquids – a redetermination

After crystallization during ionothermal syntheses in phospho­nium-containing ionic liquids, the structure of (NH(4))(3)Al(2)(PO(4))(3) [tri­ammonium dialuminum tris­(phosphate)] was refined on the basis of powder X-ray diffraction data from a synchrotron source. (NH(4))(3)Al(2)(PO(4))(3) is a member of the structural family with formula A (3)Al(2)(PO(4))(3), where A is a group 1 element, and of which the NH(4), K, and Rb forms were previously known. The NH(4) form is isostructural with the K form, and was previously solved from single-crystal X-ray data when the material (SIZ-2) crystallized from a choline-containing eutectic mixture [Cooper et al. (2004 ▸). Nature, 430, 1012–1017]. Our independent refinement incorporates NH(4) groups and shows that these NH(4) groups are hydrogen bonded to framework O atoms present in rings containing 12 T sites in a channel along the c-axis direction. We describe structural details of (NH(4))(3)Al(2)(PO(4))(3) and discuss differences with respect to isostructural forms.