MS22-P02 Experimental charge density for σ hole interactions Ulli Englert (Inorganic Chemistry, RWTH Aachen University, Aachen, Germany) Ruimin Wang (RWTH Aachen, Aachen, Germany) Daniel Hartnick (RWTH Aachen, Aachen, Germany) Shannon Potts (RWTH Aachen, Aachen, Germany) Irmgard Kalf (RWTH Aachen, Aachen, Germany)email: ullrich.englert@ac.rwth-aachen.deHalogen 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" [1], 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. [2] 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]. 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.

[1] Kieltsch, I., Eisenberger, P., & Togni, A. (2007). Angew. Chem. Int. Ed. 46, 754–757.

[2] Pinto De Magalhaes, H., Togni, A., & Lüthi, H. P. (2017). J. Org. Chem. 82, 11799–11805.

[3] Wang, R., Hartnick, D. & Englert, U. (2018) Z. Kristallogr. Cryst. Mater., submitted.
Keywords: intermolecular interactions, electron density, high resolution.