Characterization of non-classical C-Br⋯π interactions in (E)-1,3-dibromo-5-(2-(ferrocenyl)vinyl)benzene and related derivatives of ferrocene

Amongst the halogens, the involvement of bromine atoms in various types of intermolecular interactions is comparatively the least studied. In this manuscript, we report the formation of Csingle bondBr⋯π interactions, with the π-rings being the cyclopentadienyl (Cp) rings of a ferrocene molecule in a newly synthesized compound (E)-1,3-dibromo-5-(2-(ferrocenyl)vinyl)benzene. We have also performed a detailed quantitative analysis on Csingle bondBr⋯π interactions observed in the synthesized molecule and in several related molecules found in the Cambridge Structure Database (CSD) showing the presence of these interactions. A topological analysis based upon QTAIM theory and electrostatic potential ESP mapped on the Hirshfeld surface of these molecules confirm that these interactions are better described as “halogen bonds” wherein the electropositive region (σ-hole) on the Br-atom interacts with the electronegative region over the Cp-ring of the ferrocene. Further, the electronegative region on the bromine atom (perpendicular to the Csingle bondBr bond) was observed to be involved in the formation of highly directional Csingle bondH⋯Br interactions with the ∠Csingle bondBr⋯H close to 90°. Thus the bromine atom is acting as both a “halogen bond donor” and “hydrogen bond acceptor” in the crystal packing with the two interactions being mutually orthogonal.
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