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, an 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 1H, 27Al, and 31P solid state NMR experiments have been employed to characterize the AlPO4-14A structure. A fast 1H MAS experiment showed that the template was in the protonated form and a 1H{27Al} TRAPDOR experiment identified the resonance of the ‘framework’ proton. The 27Al and 31P resonances were completely assigned by the 27Al→31P INEPT heteronuclear correlation experiment and the quadrupolar parameters of the 27Al signals determined from the 27Al MQMAS experiment. Lastly, the complete assignment of both 27Al and 31P resonances made it possible to qualitatively determine the location and orientation of the template molecule within the framework from two-dimensional dipolar-based 1H→31P cross-polarization and 1H→27Al 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.