Selective Self-Assembly of Supramolecular Helices and Macrocycles Directed by Halogen Bonding

In this study, several hydrogen-bonded arylamide foldamers (compounds 1-5) with the same degree of polymerization were designed and synthesized. The polyfluoroiodobenzene or iodoethynyl polyfluoroiodobenzene segment was modified as a halogen donor at the end of the monomer, and pyridine or pyridine oxynitride served as the corresponding halogen acceptor segment. The crystal structure of compound 1 indicates that the supramolecular double helices were constructed by stacking a P helix and an M helix in an antiparallel manner in the direction of intermolecular I⋅⋅⋅^-O-N⁺ halogen bonding. The zig-zag-shaped linear structures of compounds 2 and 3 were generated under the induction of intermolecular I⋅⋅⋅N and I⋅⋅⋅^-O-N⁺ halogen bonds. [1+1] near-planar bimolecular supramolecular macrocycles in compounds 4 and 5 were formed by multiple groups of effective intramolecular three-center hydrogen bonding and strong I⋅⋅⋅N and I⋅⋅⋅^-O-N⁺ halogen bonds. Hirshfeld surface analysis and theoretical modelling of the halogen bonding energy were performed. The noncovalent interactions on the surface of the monomers and the halogen bonding energy were investigated in detail.