Solid-state dynamics in the closo-carboranes: A11B MAS NMR and molecular dynamics study

Ahumada, H., Kurkiewicz, T., Thrippleton, M. J. and Wimperis, S. (2015) Solid-state dynamics in the closo-carboranes: A11B MAS NMR and molecular dynamics study. Journal of Physical Chemistry B, 119(11), pp. 4309-4320. (doi:10.1021/acs.jpcb.5b00043) (PMID:25710751)

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Abstract

This work explores the dynamic behaviour of the three closo-carborane isomers (formula C2B10H12) using modern solid-state magic angle spinning (MAS) NMR techniques and relates the experimental measurements to theoretical results obtained using molecular dynamics simulations. At high temperatures and at B0 = 9.4 T, the 11B MAS linewidths are narrow (40-90 Hz) for the three isomers. The rotational correlation times (tauc) calculated by molecular dynamics are on the picosecond timescale, showing a quasi-isotropic rotation at these temperatures, typical for liquid systems. For all three isomers, the values of the 11B spin-lattice relaxation times (T1) show discontinuities as the temperature is decreased, confirming the phase changes reported in the literature. At low temperatures, the 11B MAS spectra of all three isomers exhibit much broader lines. The simulations showed that the molecular reorientation was anisotropic around different symmetry axes for each isomer, and this was supported by the values of the reduced quadrupolar parameter PQeff derived from “dynamic shift” measurements using 11B MQMAS NMR spectroscopy. The behaviour of PQeff as a function of temperature for para-carborane suggests that molecular reorientation is about the C5 symmetry axis of the molecule at low temperatures and this was supported by the molecular dynamics simulations.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Ahumada, Dr Hernan and Wimperis, Professor Stephen and Thrippleton, Dr Michael and Kurkiewicz, Miss Teresa
Authors: Ahumada, H., Kurkiewicz, T., Thrippleton, M. J., and Wimperis, S.
College/School:College of Science and Engineering > School of Chemistry
Journal Name:Journal of Physical Chemistry B
Journal Abbr.:J. Phys. Chem. B
Publisher:American Chemical Society
ISSN:1520-6106
ISSN (Online):1520-5207
Copyright Holders:Copyright © 2015 American Chemical Society
First Published:First published in Journal of Physical Chemistry 119(11):4309-4320
Publisher Policy:Reproduced under a Creative Commons License

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
426181Satellite-transition MAS - a new technique for high-resolution quadrupolar NMRStephen WimperisEngineering & Physical Sciences Research Council (EPSRC)GR/T23824/01CHEM - CHEMISTRY