Non‐Covalent Interactions of Organic Halogen Compounds with Aromatic Systems – Analyses of Crystal Structure Data

Abstract The Cambridge Structural Database showed in mid 2002 about 20.000 structures containing halogen atoms and aryl rests with distances d between the aryl center and the halogen atom, which would allow both hydrogen bonds with the aromatic hydrogens and/or van der Waalsinteractions with the π‐cloud. The latter are characterized by short distances d and by small angles α between the vector along the aryl centroid–halogen line and the perpendicular vector originating in the aryl center (the plane normal). The cases with d 60° (about 40 % of the fragments), with only very few cases close to linear hydrogen bonds (then with α = 90°). Compounds containing metal–halogen bonds were omitted in view of possible strong orientational interferences. The structures were screened with four different halogen binding modes, all of them containing the halogen attached to a carbon atom, but with different hybrizations at the connecting carbon centers. The results show only small differences in the distance distributions, with a slight preference for smaller α values for sp 2 frameworks. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)