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 (C(6)F(4)Br(2)), 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 C(6)F(4)Br(2) 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.