Short, strong halogen bonding in co-crystals of pyridyl bis-urea macrocycles and iodoperfluorocarbons

Co-crystals formed from pyridyl bis-urea macrocycles and iodopentafluorobenzene or diiodotetrafluoroethane show surprisingly short, strong halogen bonds. The shortest interactions were observed between the carbonyl oxygen and the iodide and were 78% of the sum of the van der Waals radii for O⋯I, with distances ranging from 2.719(2) to 2.745(2) A.