Halogen bonds, attractive intermolecular interactions between perfluoroalkyl bromides and bromide ions, are present in cocrystals of (-)-sparteinium hydrobromide (1) and (S)-1,2-dibromohexafluoropropane (2; shown schematically), and result in enantiopure and infinite supramolecular helices. The perfluorocarbon-hydrocarbon self-assembly allows the resolution of racemic 2.

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It is well known [1] that carbon-bound halogen atoms (frequently iodine and bromine, but also chlorine and even fluorine) can act as electron acceptors and form short contacts with different species (both neutral and negatively charged) that possess an ability to act as an electron donor. [2] These noncovalent interactions can be strong enough to control the aggregation of organic molecules in solid, [3] liquid, [4] and gas [5, 6] phases and the term ªhalogen bondingº [2, 6] has been suggested in order to emphasize the similarity with hydrogen bonding. While metal-ion coordination [7] is frequently the key feature in inorganic supramolecular systems, hydrogen bonding [8] is by far the most frequently used tool to assemble organic molecules in solid, liquid, or gas phases, and it plays an important role in stabilizing supramolecular aggregates even in water.Here we show that when the recognition pattern controlling the self-assembly process can be based on either hydrogen or halogen bonding, the latter can dominate over the former and, under appropriate conditions, will single out the molecules that will be involved in the construction of supramolecular architectures. We have already described specific I´´´N intermolecular interactions occurring between a,w-diiodoperfluoroalkanes and dinitrogen hydrocarbons. [9±11] These interactions are strong enough to overcome the low affinity [12] that exists between perfluorocarbons and hydrocarbons to assemble them into oligomeric structures in the liquid phase [4] and into crystalline 1D networks in the solid phase. [9±11] methacrylate as a comonomer. The copolymer 1 was shown to have good film-forming properties on a solid substrate. The fluorescence of the polymer was effectively quenched by photochemically generated acid and afforded finely resolved fluorescent images on a solid substrate. Experimental Section4: Potassium carbonate (82.9 g, 0.60 mol) and benzyl bromide (136.8 g, 0.80 mol) were added to a solution of 5-fluoro-2-nitrophenol (3) (94.3 g, 0.60 mol) in DMF (200 mL). The resulting mixture was stirred at 100 8C for 3 h, filtered, and the filtrate diluted with diethyl ether. The organic layer was washed with water and dried with anhydrous magnesium sulfate. Concentration, followed by vacuum distillation (142 ± 146 8C, 0.

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