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Symmetric halogen bonding is preferred in solution.

Authors
  • Carlsson, Anna-Carin C
  • Gräfenstein, Jürgen
  • Budnjo, Adnan
  • Laurila, Jesse L
  • Bergquist, Jonas
  • Karim, Alavi
  • Kleinmaier, Roland
  • Brath, Ulrika
  • Erdélyi, Máté
Type
Published Article
Journal
Journal of the American Chemical Society
Publisher
American Chemical Society
Publication Date
Mar 28, 2012
Volume
134
Issue
12
Pages
5706–5715
Identifiers
DOI: 10.1021/ja301341h
PMID: 22384818
Source
Medline
License
Unknown

Abstract

Halogen bonding is a recently rediscovered secondary interaction that shows potential to become a complementary molecular tool to hydrogen bonding in rational drug design and in material sciences. Whereas hydrogen bond symmetry has been the subject of systematic studies for decades, the understanding of the analogous three-center halogen bonds is yet in its infancy. The isotopic perturbation of equilibrium (IPE) technique with (13)C NMR detection was applied to regioselectively deuterated pyridine complexes to investigate the symmetry of [N-I-N](+) and [N-Br-N](+) halogen bonding in solution. Preference for a symmetric arrangement was observed for both a freely adjustable and for a conformationally restricted [N-X-N](+) model system, as also confirmed by computation on the DFT level. A closely attached counterion is shown to be compatible with the preferred symmetric arrangement. The experimental observations and computational predictions reveal a high energetic gain upon formation of symmetric, three-center four-electron halogen bonding. Whereas hydrogen bonds are generally asymmetric in solution and symmetric in the crystalline state, the analogous bromine and iodine centered halogen bonds prefer symmetric arrangement in solution.

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