Self-assembly of Supramolecular Planar Macrocycle Driven by Intermolecular Halogen Bonding

Abstract

The design and synthesis of three kinds of arylamide molecules (compounds 1～3) containing halogen bonding donor and acceptor fragments, and the exploration and analyzation of different action modes of halogen bonding in solid phase were reported. Compounds 1 and 2 contain two tetrafluoroiodobenzene fragments, and compound 1 also contains a halogen receptor fragment-pyridine group. Isobutyl groups are introduced into the molecule to increase its solubility and crystallinity. And a pyrimidine fragment was introduced into compound 3, which has more aromatic rings. The two N atoms of the pyrimidine fragment can theoretically form intramolecular hydrogen bonds with the adjacent amide hydrogen atoms (-C(＝O)NH), so that the whole molecule has the properties of hydrogen-bonded arylamide foldamer. Moreover, trifluorobenzene fragments were selected in compound 3 to eliminate the repulsion between excess fluorine atoms and carbonyls. The crystal structures reveal that the three aromatic rings in compound 1 are twisted with each other for there is no intramolecular hydrogen bond, and a supramolecular DNA-like double helix was assembled controlled by intermolecular N…I and O…I halogen bonds arranged alternately. Compound 2 failed to form an intramolecular three-center hydrogen bonding due to the repulsion between the amide carbonyl groups and the two fluorine atoms in close proximity. As expected, in the solid phase of compound 3, an effective three-center hydrogen bond is formed between the terminal trifluoroiodobenzene and the benzene ring attached to it. Moreover, the two N-H bonds connected to the pyrimidine ring also form two effective three-center hydrogen bonds. The difference is that the participants of these two groups of three-center hydrogen bonds include two N atoms in the pyrimidine ring. The four aromatic rings in compound 3 are nearly coplanar driven by these intramolecular three-center hydrogen bonds. Two sets of strong intermolecular (pyridine ring) N…I halogen bonds control the formation of [1＋1] bimolecular supramolecular macrocycles with inner diameters of 1.36 nm and 1.07 nm in length and width. Moreover, the supramolecular macrocycle is near-planar due to the introduction of pyrimidine ring.