Issue 8, 2014

The nature of [N–Cl–N]+ and [N–F–N]+ halogen bonds in solution

Abstract

Halonium ions are synthetically useful, transient species that may be stabilized by attachment to two electron donors. Whereas studies of [C–X–C]+-type ions have greatly contributed to the fundamental understanding of chemical bonding and reaction mechanisms, investigations of the corresponding [N–X–N]+ halogen bond complexes are only at an early stage. Herein we present solution NMR spectroscopic and theoretical evidence for the nature of [N–Cl–N]+ and [N–F–N]+ complexes, and we discuss their geometries and stabilities in comparison to their iodine and bromine-centered analogues as well as the corresponding three-center [N–H–N]+ hydrogen bond. We show the chlorine-centered halogen bond to be weaker but yet to resemble the symmetric geometry of the three-center bond of heavier halogens. In contrast, the [N–F–N]+ bond is demonstrated to prefer asymmetric geometry analogous to the [N–H–N]+ hydrogen bond. However, the [N–F–N]+ system has a high energy barrier for interconversion, and due to entropy loss, its formation is slightly endothermic.

Graphical abstract: The nature of [N–Cl–N]+ and [N–F–N]+ halogen bonds in solution

Supplementary files

Article information

Article type
Edge Article
Submitted
22 Apr 2014
Accepted
27 May 2014
First published
28 May 2014

Chem. Sci., 2014,5, 3226-3233

Author version available

The nature of [N–Cl–N]+ and [N–F–N]+ halogen bonds in solution

A. Karim, M. Reitti, A. C. Carlsson, J. Gräfenstein and M. Erdélyi, Chem. Sci., 2014, 5, 3226 DOI: 10.1039/C4SC01175A

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