Supramolecular Hierarchy among Halogen-Bond Donors

Through a combination of structural chemistry, vibrational spectroscopy, and theory, we have systematically examined the relative structure‐directing importance of a series of ditopic halogen‐bond (XB) donors. The molecular electrostatic potential surfaces of six XB donors were evaluated, which allowed for a charge‐based ranking. Each molecule was then co‐crystallized with 21 XB acceptors and the results have made it possible to map out the supramolecular landscape describing the competition between I/Br–ethynyl donors, perfluorinated I/Br donors, and I/Br–phenyl based donors. The results offer practical guidelines for synthetic crystal engineering driven by robust and directional halogen bonds. Joining the ranks: The halogen‐bonding strength of iodo and bromo analogues of ethynyl, perfluorinated, and phenyl‐based donors are compared theoretically, through the electrostatic potential surfaces of the donors, and experimentally, through the formation of co‐crystals by co‐grinding, in order to provide a “supramolecular ranking” of these moieties for crystal engineering applications (see graphic).