A multinuclear NMR study of six forms of AlPO-34:structure and motional broadening

Dawson, Daniel M. and Griffin, John Matthew and Seymour, Valerie R. and Wheatley, Paul S. and Amri, Mahrez and Kurkiewicz, Teresa and Guillou, Nathalie and Wimperis, Stephen and Walton, Richard I. and Ashbrook, Sharon E. (2017) A multinuclear NMR study of six forms of AlPO-34:structure and motional broadening. The Journal of Physical Chemistry C, 121 (3). pp. 1781-1793. ISSN 1932-7447

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We report a study of the CHA-type aluminophosphate AlPO-34, prepared with six different structure-directing agents (SDAs): piperidine (pip), morpholine (mor), pyridine (pyr), 1,4,8,11-tetraazacyclotetradecane (cyclam), 1,3 dimethylimidazolium (dmim) chloride and 1-ethyl-3-methylimidazolium (emim) bromide. Using a combination of solid-state NMR spectroscopy, periodic density functional theory (DFT) calculations and synchrotron X-ray diffraction, we show that, even in crystallographically well-ordered materials such as AlPO-34 with dmim as the SDA, local disorder may be present. For such disordered structures, where it is challenging to use DFT to assign NMR spectra, we show that the 31P isotropic chemical shift can be predicted accurately using the mean P-O bond length and P-O-Al bond angle, in an extension of previous work. Variable-temperature 27Al NMR reveals the presence of microsecond-timescale dynamics in all forms of AlPO- 34, with two different motional regimes observed, depending on whether structural H2O is also present. H2O is detected in AlPO-34 prepared with mor as the SDA, although this material was previously reported as anhydrous, suggesting that this form of AlPO-34 may be hygroscopic despite the presence of the SDAs within the pores.

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Journal Article
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The Journal of Physical Chemistry C
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This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry, copyright ©2017 American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.6b11908
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05 Jan 2017 14:06
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22 Nov 2022 04:15