Halogen bonds direct the solid state architectures of a multivalent iodopropargylcalix[4]arene

The iodoalkynyl group is a ditopic synthon, able to act as a halogen bond (XB) donor through the iodine atom and as an XB acceptor on the C≡C triple bond. With the aim of exploring the self-assembly properties via XB of calix[4]arene macrocycles containing this synthon, we synthesized and characterized a tetra(iodopropargyl)calix[4]arene (3). In the solid state, all the iodoalkynyl units of 3 are involved in intermolecular XB interactions as both donors and acceptors, resulting in a two-dimensional network of calixarene double layers. On the contrary, in the cocrystal of 3 with 4,4′-bipyridine, a bidentate XB acceptor, the iodine atoms are halogen bonded to the pyridine nitrogen atoms forming a one-dimensional ribbon of calixarenes alternated by two 4,4′-bipyridine units. These supramolecular architectures are the first example of solid-state networks of calixarene derivatives where the self-assembly is mostly driven by XBs.