Synthesis, crystal structure and thermal properties of the AlPO4 material UiO-12

The AlPO4 material UiO-12, [Al3P3O12(OH)](-)[CH3NH2CH3](+), is obtained hyd rothermally as a two-phase mixture with augelite and is isostructural with AlPO4-EN3 and some other AlPO4 materials. The crystal structure of the as-s ynthesized material, space group Pbca with a = 13.57920(1) Angstrom, b = 10 .3511(2) Angstrom and c = 17.4655(4) Angstrom, was solved from single cryst al X-ray diffraction data. The indicated decomposition of the tetramethylam monium template to dimethylammonium during synthesis was confirmed by C-13 MAS-NMR data which, in addition, showed small amounts of methylammonium. Th e P-31-MAS-NMR spectrum is consistent with three crystallographically non-e quivalent P-positions. UiO-12 undergoes complex structural rearrangements o n heating, and has at 500 degrees C transformed into a fully tetrahedral fr amework (UiO-12-500). The transformation involves the removal of encapsulat ed organic material and of bridging hydroxyl groups between five-coordinate d aluminum atoms. The structure of UiO-12-500, Al3P3O12, space group Pbca w ith a = 13.918(2) Angstrom, b = 9.663(1) Angstrom and c = 18.031(3) Angstro m at 298 K, was refined from powder X-ray diffraction data using a DLS opti mized four-coordinated variant of UiO-12-as as starting model. The structur e contains sheets of four-, six- and eight-membered rings linked via chains in a zigzag conformation. (C) 2000 Elsevier Science B.V. All rights reserv ed.