The effects of extraframework species on the structure-based prediction of 31P isotropic chemical shifts of aluminophosphates
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31P NMR spectroscopy is a valuable technique for the characterization of the local structure of aluminophosphates (AlPOs), capable of providing information on the number of crystallographic P sites, their relative populations, and the positions of any dopant atoms in the framework. Assigning the 31P spectra may, however, require multinuclear NMR experiments and/or density functional theory (DFT) calculations, which can be time consuming, computationally costly, and challenging in cases involving disorder or dynamics. To address the issue of computational cost, we recently demonstrated a simple relationship between the local structure around P (primarily in terms of the mean P-O bond length and P-O-Al bond angle) and the 31P isotropic chemical shift, δiso, calculated by DFT for a series of calcined AlPOs. Here, we extend this approach to as-made AlPOs where we show that, at least to a first approximation, the presence of framework-bound anions and/or guest species within the pores of AlPOs can be translated directly to a distortion of the local framework geometry without considering any additional structural parameters. This allows the prediction of a DFT-level 31P δiso even in cases where the structure may be highly disordered or partially incomplete (precluding the use of electronic structure calculations), and we investigate the minimal structural information required to provide meaningful results. The structure-spectrum relationship produced forms the basis for the geometry-based DIStortion COde (DISCO), which can rapidly (on the ms timescale) predict the outcome of a DFT calculation of 31P δiso to within 1.1 ppm.
Dawson , D M , Seymour , V R & Ashbrook , S E 2017 , ' The effects of extraframework species on the structure-based prediction of 31 P isotropic chemical shifts of aluminophosphates ' , Journal of Physical Chemistry C , vol. 121 , no. 50 , pp. 28065-28076 . https://doi.org/10.1021/acs.jpcc.7b09932
Journal of Physical Chemistry C
Copyright © 2017 American Chemical Society. This work has been made available online in accordance with the publisher’s policies. This is the author created accepted version manuscript following peer review and as such may differ slightly from the final published version. The final published version of this work is available at: https://doi.org/10.1021/acs.jpcc.7b09932
DescriptionSEA would like to thank EPSRC for computational support through the Collaborative Computational Project on NMR Crystallography (CCP-NC), via EP/M022501/1), the Leverhulme Trust (F/00 268/BJ) and the Royal Society and the Wolfson Foundation for a merit award. Dr David McKay is thanked for improving the DISCO compilation process.
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