Halogen Bonding-Directed Supramolecular Quadruple and Double Helices from Hydrogen Bonded Arylamide Foldamers.

Halogen bonding has been used to glue hydrogen bonded short arylamide foldamers to achieve new supramolecular double and quadruple helices in the solid state. Compounds 1-3, which bear one pyridine at one end and one CF2I or fluorinated iodobenzene group at the other end, are induced by head-to-tail N⋅⋅⋅I halogen bonding to form one-component supramolecular P and M helices, which further stack to afford supramolecular double-stranded helices. Double helix formed by 3 can further dimerize to form a G-quadruplex-like supramolecular quadruple helix. Symmetric compound 4, which bears two pyridines at the ends, is revealed to bind to ICF2CF2I (5) through N⋅⋅⋅I halogen bonding to form two-component supramolecular P and M helices, with one turn consisting of four (2+2) molecules. Half of the molecules of 4 in two P helices and two M helices are found to stack alternately to form another supramolecular quadruple helix. Another half of the molecules of 4 in such quadruple helices stack alternately with counterparts from neighbouring quadruple helices, leading to unique quadruple helical arrays in the two-dimensional space.