Structure and NMR assignment in calcined and as-synthesized forms of AlPO-14: a combined study by first-principles calculations and high- resolution ²⁷Al-³¹P MAS NMR correlation

Ashbrook, S.E., Cutajar, M., Pickard, C.J., Walton, R.I. and Wimperis, S. (2008) Structure and NMR assignment in calcined and as-synthesized forms of AlPO-14: a combined study by first-principles calculations and high- resolution ²⁷Al-³¹P MAS NMR correlation. Physical Chemistry Chemical Physics, 10(37), pp. 5754-5764. (doi: 10.1039/b805681a)

Abstract

The high-resolution ²⁷Al- and ³¹P- NMR spectra of two as-synthesized forms of the microporous aluminophosphate AlPO-14 and the corresponding calcined -dehydrated form were assigned using both "first-principles'' calculations of NMR parameters (GIPAW, as implemented in NMR-CASTEP) and a ²⁷Al-³¹-P heteronuclear correlation NMR experiment (MQ-<i>J</i>-HETCOR) that exploits Al-27 multiple-quantum coherences and J couplings to identify Al-O-P linkages. NMR parameters calculated from published AlPO-14 crystal structures, which are derived from powder X-ray diffraction (XRD) data, are in poor agreement with experiment and it was necessary to optimize the structure geometry using energy minimization before satisfactory agreement was obtained. Comparison of simulated powder XRD patterns from the experimental and the energy-minimized structures shows that the changes in relative atomic positions in the optimized structure are relatively small and yield only minor adjustments in the Bragg peak intensities. These results indicate that a combination of NMR spectroscopy and first-principles calculation of NMR parameters may soon be considered a generally useful step in the refinement of the structures of microporous materials derived from powder diffraction data.

• Item Type: Articles
• Keywords: AL-27 ALPO4-14 ANGLE COHERENCE COHERENCE-TRANSFER PATHWAYS CRYSTAL Crystal structure Crystal structures CRYSTAL-STRUCTURE CRYSTAL-STRUCTURES DIFFRACTION ENERGIES ENERGY INTEGER QUADRUPOLAR NUCLEI MAS NMR microporous materials MQMAS MULTIPLE-QUANTUM NMR P-31 NMR PARAMETERS POWDER DIFFRACTION POWDER DIFFRACTION DATA REFINEMENT RESOLUTION SOLID-STATE NMR SPECTRA SPECTROSCOPY SPECTRUM STEP STMAS NMR Structure X-RAY X-ray diffraction X-RAY-DIFFRACTION XRD
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Wimperis, Professor Stephen
• Authors: Ashbrook, S.E., Cutajar, M., Pickard, C.J., Walton, R.I., and Wimperis, S.
• College/School: College of Science and Engineering > School of Chemistry
• Journal Name: Physical Chemistry Chemical Physics
• Publisher: Royal Society of Chemistry
• ISSN: 1463-9076
• ISSN (Online): 1463-9084
• Published Online: 30 July 2008