Solid-state ¹⁷O NMR spectroscopy of hydrous magnesium silicates: evidence for proton dynamics

Griffin, J.M., Wimperis, S., Berry, A.J., Pickard, C.J. and Ashbrook, S.E. (2009) Solid-state ¹⁷O NMR spectroscopy of hydrous magnesium silicates: evidence for proton dynamics. Journal of Physical Chemistry C, 113(1), pp. 465-471. (doi: 10.1021/jp808651x)

Abstract

First-principles calculations of ¹⁷O quadrupolar and chemical shift NMR parameters were performed using CASTEP, a density functional theory (DFT) code, to try and interpret high-resolution ¹⁷O NMR spectra of the humite group minerals hydroxyl-chondrodite (2Mg2SiO4·Mg(OH)2) and hydroxyl-clinohumite (4Mg2SiO4·Mg(OH)2), which are models for the incorporation of water within the Earth’s upper mantle. The structures of these humite minerals contain two possible crystallographically inequivalent H sites with 50% occupancy. Isotropic ¹⁷O multiple-quantum magic angle spinning (MQMAS) spectra were therefore simulated using the calculated ¹⁷O NMR parameters and assuming either a static or dynamic model for the positional disorder of the H atoms. Only the dynamic disorder model provided simulated spectra that agree with experimental ¹⁷O MQMAS spectra of hydroxyl-chondrodite and hydroxyl-clinohumite. Previously published ¹⁷O satellite-transition magic angle spinning (STMAS) spectra of these minerals showed significant dynamic line-broadenings in the isotropic frequency dimension. We were able to reproduce these line-broadenings with at least qualitative accuracy using a combination of the same dynamic model for the positional H disorder, calculated values for the change in ¹⁷O quadrupolar NMR parameters upon H exchange, and a simple analytical model for dynamic line-broadening in MAS NMR experiments. Overall, this study shows that a combination of state-of-the-art NMR methodology and first-principles calculations of NMR parameters is able to provide information on dynamic processes in solids with atomic-scale resolution that is unobtainable by any other method.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Wimperis, Professor Stephen
• Authors: Griffin, J.M., Wimperis, S., Berry, A.J., Pickard, C.J., and Ashbrook, S.E.
• Subjects: Q Science > QD Chemistry
• College/School: College of Science and Engineering > School of Chemistry
• Journal Name: Journal of Physical Chemistry C
• Publisher: American Chemical Society
• ISSN: 1932-7447
• ISSN (Online): 1932-7455
• Published Online: 05 December 2008