MS22-P02 Experimental charge density for σ hole interactionsHalogen bonds and σ hole interactions do not only play an important role in crystal engineering but are also relevant for understanding chemical reactivity.
3,3-dimethyl-1-(trifluoromethyl)-1,3-dihydro-1 λ3,2-benziodoxole, 1, commonly known as "Togni reagent" , is used for the electrophilic transfer of the trifluoromethyl group by reductive elimination. The σ hole associated with the hypervalent iodine atom is essential for this reactivity.  Based on high resolution X-ray diffraction, we have determined the experimental electron density for 1. In the crystal, it interacts with a neighbouring molecule via O···I contacts of 2.9809(6) Å. We compare 1 with two cocrystals 2 and 3 (see Scheme) in terms of electrostatic potential and QTAIM properties in the bond critical point (bcp) for the σ hole interaction. In 2, tetrafluorodiiodobenzene (TFDIB) interacts with two molecules of dimethylaminopyridine (DMAP); the N···I halogen bond is as short as 2.6622(4) Å. With respect to its electronic properties, it resembles a coordinative bond . 3 consists of infinite chains in which diaminobicyclooctane (DABCO) and TFDIB alternate; the N···I contacts are significantly longer but still much shorter than O···I in the case of the Togni reagent. The bcps for the halogen bonds in 3 fall in the range of electron depletion associated with the σ hole on iodine; consequently, the electron density in the bcps is surprisingly small.
In conclusion, the three examples documented in this contribution underline the very wide range of σ hole interactions.References:
 Kieltsch, I., Eisenberger, P., & Togni, A. (2007). Angew. Chem. Int. Ed. 46, 754–757.
 Pinto De Magalhaes, H., Togni, A., & Lüthi, H. P. (2017). J. Org. Chem. 82, 11799–11805.
 Wang, R., Hartnick, D. & Englert, U. (2018) Z. Kristallogr. Cryst. Mater., submitted. Keywords: intermolecular interactions, electron density, high resolution.