Solid state NMR investigation of the structure of AlPO4-14A

The as-synthesized aluminophosphate framework material AlPO4-14A has a number of unique structural features related to the connectivities in the network of Al and P atoms. One tetrahedral Al atom is present that is linked, via Al-O(H)-Al bonds to two octahedral Al atoms and, consequently to only two P atoms. However, ail Al/P ratio of one is maintained as each of these octahedral Al atoms is connected to five P atoms in addition to the Al-O(H)-Al linkage. This connectivity network means that a framework made up of alternating Al and P atoms cannot be obtained by calcination. A variety of H-1, Al-27, and P-31 solid state NMR experiments have been employed to characterize the AlPO4-14A structure. A fast H-1 MAS experiment showed that the template was in the protonated form and a H-1 {Al-27} TRAPDOR experiment identified the resonance of the 'framework' proton. The Al-27 and P-31 resonances were completely assigned by the Al-27 -> P-31 INEPT heteronuclear correlation experiment and the quadrupolar parameters of the Al-27 signals determined from the Al-27 MQMAS experiment. Lastly, the complete assignment of both Al-27 and P-31 resonances made it possible to qualitatively determine the location and orientation of the template molecule within the framework from two-dimensional dipolar-based H-1 -> P-31 cross-polarization and H-1 -> Al-27 TEDOR heteronuclear correlation experiments. The data from these experiments confirm in detail the AlPO4-14A structure and will be useful benchmarks for the investigation of other structures for which diffraction data are limited. (c) 2005 Elsevier Inc. All rights reserved.