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 4,42-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 · · ·N intermolecular halogen bonding connecting bpe and dp with C6F4Br2 molecules into 1D infinite chains have been investigated and compared with the previously analyzed I · · ·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.