Experimental and Theoretical Study of the Br•••N Halogen Bond in Complexes of 1,4-Dibromotetrafluorobenzene with Dipyridyl Derivatives

The electron density distributions of two halogen-bonded complexes, that is, (E)-1,2-bis(4-pyridyl)ethylene (bpe) or 4,4'-dipyridyl (dp) With 1,4-dibromotetrafluorobenzene (C6F4Br2), have been obtained from accurate single-crystal X-ray diffracted intensities collected at 90 K and analyzed through the Bader's quantum theory of atoms in molecules. The experimental results have been compared with theoretical densities resulting from DFT calculations on both gas-phase isolated complexes and periodic crystal structures. The topological features and the energetics of the underlying Br center dot center dot center dot N intermolecular halogen bonding connecting bpe and dp with C6F4Br2 molecules into ID infinite chains have been investigated and compared with the previously analyzed I center dot center dot center dot N halogen bond. The analysis provides a quantitative evaluation of the differences observed between the involved halogen species, in addition to pointing out the basic features shared by the investigated halogen bond interactions.