Halogen and hydrogen bonding-driven self-assembly of supramolecular macrocycles and double helices from hydrogen-bonded arylamide foldamers

Abstract

Two hydrogen-bonded 3-mer arylamide foldamers 1 and 2, which bear two pyridine or iodobenzene subunits at the ends, have been designed and prepared. Compound 1 co-assembles with 1,4-diiodotetrafluorobenzene (3) to form 2 + 2 macrocycles through four (py)N⋯I halogen bonds, whereas compound 2 dimerizes into a macrocycle through two CO⋯I hydrogen bonds. Macrocycles formed by 1 and 3 stack to produce a supramolecular tube, with two neighboring macrocycles encapsulating one molecule of 3 through two CO⋯I halogen bonds. Through such a cross-layer connection, formally the two molecules also give rise to a new halogen-bonded supramolecular helix, and further stack alternately to afford a double helix. In contrast, the mixture of 1 and fumaric acid (5) did not produce a similar encapsulation-derived helix, even though they also formed a halogen-bonded 2 + 2 supramolecular macrocycle.