N•••Br halogen bonding:: One-dimensional infinite chains through the self-assembly of dibromotetrafluorobenzenes with dipyridyl derivatives

The N...Br halogen bonding drives the self-assembly of 1,4-dibromotetrafluorobenzene (1a) and its 1,3 or 1,2 analogues (1b,c, respectively) with dipyridyl derivatives 2a,b. The isomeric supramolecular architectures 3a-f are obtained as cocrystals that are stable in the air at room temperature. The solidstate features of these 1D infinite chains 3 have been fully characterized by single-crystal X-ray, Raman, and IR analyses. The occurrence of N...Br halogen bonding in solution has been detected with F-19 NMR spectroscopy. The N...Br halogen bonding is highly selective and directional and the geometry of the single strands of noncovalent copolymers 3 is programmed by the geometry of halogen-bonding donor and acceptor sites on the starting modules. The composition and topology of the instructed networks can be predicted with great accuracy. Experiments of competitive cocrystal formation established the strength of the N...Br interaction relative to other halogen bondings and the ability of different modules 1 to be involved in site-selective supramolecular syntheses.