Crystal Engineering with Iodoethynylnitrobenzenes: A Group of Highly Effective Halogen-Bond Donors

The benefits of employing a “double activation” strategy for promoting effective practical co-crystal synthesis through halogen bonding was explored in a systematic supramolecular synthetic study of iodoethynylnitrobenzenes. The positive electrostatic potential on the iodine atom was enhanced through a combination of an sp-hybridized carbon atom and one or more electron-withdrawing nitro groups. Three model compounds, 1-(iodoethynyl)-4-nitrobenzene (4N-I), 1-(iodoethynyl)-3-nitrobenzene (3N-I), and 1-(iodoethynyl)-3,5-dinitrobenzene (3,5DN-I) were synthesized and characterized, and calculated molecular electrostatic surface potential values on the halogen-bond donor site were about 20–40 kJ/mol higher than those observed for previously well-established halogen-bond donors. The ability of these molecules to drive co-crystal formation was evaluated through a total of 45 co-crystallization experiments with 15 different acceptor molecules. IR spectroscopic data for the resulting products showed that each reac...