79/81Br nuclear quadrupole resonance spectroscopic characterization of halogen bonds in supramolecular assemblies

P Cerreia Vioglio; P M J Szell; M R Chierotti; R Gobetto; D L Bryce

doi:10.1039/c8sc01094c

^79/81Br nuclear quadrupole resonance spectroscopic characterization of halogen bonds in supramolecular assemblies

Chem Sci. 2018 Apr 30;9(20):4555-4561. doi: 10.1039/c8sc01094c. eCollection 2018 May 28.

Authors

P Cerreia Vioglio¹, P M J Szell², M R Chierotti¹, R Gobetto¹, D L Bryce²

Affiliations

¹ Department of Chemistry and NIS Centre , University of Torino , Via Pietro Giuria 7 , 10125 Torino , Italy.
² Department of Chemistry and Biomolecular Sciences & Centre for Catalysis Research and Innovation , University of Ottawa , 10 Marie Curie Private , Ottawa , Ontario K1N 6N5 , Canada . Email: dbryce@uottawa.ca ; ; Tel: +1-613-562-5800 ext. 2018.

Abstract

Despite the applicability of solid-state NMR to study the halogen bond, the direct NMR detection of ^79/81Br covalently bonded to carbon remains impractical due to extremely large spectral widths, even at ultra-high magnetic fields. In contrast, nuclear quadrupole resonance (NQR) offers comparatively sharp resonances. Here, we demonstrate the abilities of ^79/81Br NQR to characterize the electronic changes in the C-Br···N halogen bonding motifs found in supramolecular assemblies constructed from 1,4-dibromotetrafluorobenzene and nitrogen-containing heterocycles. An increase in the bromine quadrupolar coupling constant is observed, which correlates linearly with the halogen bond distance (d_Br···N). Notably, ^79/81Br NQR is able to distinguish between two symmetry-independent halogen bonds in the same crystal structure. This approach offers a rapid and reliable indication for the occurrence of a halogen bond, with experimental times limited only by the observation of ^79/81Br NQR resonances.