Halogen bonding is a close to linear, noncovalent interaction between an electrophilic halogen X (I, Br, Cl or F) and an electron donor. The interaction shows strong resemblance with hydrogen bonding. Whereas the symmetry of N-H-N and O-H-O hydrogen bonds has been extensively studied for decades, the investigation of the behaviour of the analogous [N-X-N]+ halogen bonds in solution is still in an early stage. To get an insight of the [N-X-N]+interactions in solution may be of importance for the development of new halogenating agents, and for the understanding of reaction mechanisms.We have determined the symmetries of [N-I-N]+ and [N-Br-N]+ halogen bond complexes in CH2Cl2 solution by using the NMR technique isotopic perturbation of equilibrium (IPE) based on 13C detection and the observation of deuterium isotope effects (Carlsson et al. Chem. Commun., 2012 , 48, 1458; JACS, 2012 , 134, 5706). In our model systems the positive halogen(I) is bound between the nitrogen donors of two identical pyridines. For the IPE NMR studies, the complexes investigated were selectively deuterium labelled. By measuring the temperature dependence of the isotope effects we could determine whether the halogen was located in the middle between the two N-donors ([N���X+���N]), or was jumping between them in a rapid, low-barrier equilibrium ([N+-X���N] ? [N���X-N+]). The former represents a static, symmetric geometry with two equivalent N���X bonds, whereas the latter describes an asymmetric geometry with one covalent N-X bond and one conventional halogen bond. Both experimental and computational studies showed that our [N-I-N]+ and [N-Br-N]+ model systems preferred to exist as static, symmetric geometries in CH2Cl2. Recently, we have studied how the [N-X-N]+ halogen bond symmetry is affected upon changes of the chemical environment. Results based on NMR experiments and DFT calculations will be presented.

[N-X-N]<sup>+</sup> Halogen bond symmetry in solution

248th National Meeting (2014)

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[N-X-N]+ Halogen bond symmetry in solution

[N-X-N]⁺ Halogen bond symmetry in solution