The nature of [N-Cl-N] super(+) and [N-F-N] super(+) halogen bonds in solution

Halonium ions are synthetically useful, transient species that may be stabilized by attachment to two electron donors. Whereas studies of [C-X-C] super(+)-type ions have greatly contributed to the fundamental understanding of chemical bonding and reaction mechanisms, investigations of the correspond...

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Bibliographic Details
Published in:Chemical science (Cambridge) 2014-06, Vol.5 (8), p.3226-3233
Main Authors: Karim, Alavi, Reitti, Marcus, Carlsson, Anna-Carin C, Graefenstein, Juergen, Erdelyi, Mate
Format: Article
Language:English
Subjects:
Asymmetry
Attachment
Bonding
Chemical bonds
Endothermic reactions
Entropy of formation
Halogens
Hydrogen bonds
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Summary:Halonium ions are synthetically useful, transient species that may be stabilized by attachment to two electron donors. Whereas studies of [C-X-C] super(+)-type ions have greatly contributed to the fundamental understanding of chemical bonding and reaction mechanisms, investigations of the corresponding [N-X-N] super(+) 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] super(+) and [N-F-N] super(+) 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] super(+) 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] super(+) bond is demonstrated to prefer asymmetric geometry analogous to the [N-H-N] super(+) hydrogen bond. However, the [N-F-N] super(+) system has a high energy barrier for interconversion, and due to entropy loss, its formation is slightly endothermic.
ISSN:2041-6520
2041-6539
DOI:10.1039/c4sc01175a