Crystal Engineering through Halogen Bonding: Complexes of Nitrogen Heterocycles with Organic Iodides

X-ray analysis has revealed that 4,4′-bipyridine, 1,2-bis(4-pyridyl)ethylene, and hexamethylenetetramine form donor - acceptor complexes with 1,4-diiodobenzene, 1,4-diiodotetrafluorobenzene, and tetraiodoethylene in which the N⋯I distance is longer than that for the corresponding I₂ complexes. As opposed to the corresponding I₂ complexes that are molecular adducts, these complexes have extended structures and longer N⋯I distances. Steric and electronic effects influence the strength of the N⋯I interaction and the crystal packing. An additional complex of 1,2-bis(4-pyridyl)ethane and 1,4-dibromotetrafluorobenzene has also been investigated for comparison of N⋯I and N⋯Br interactions.