What prompted you to investigate this topic? Energetic materials are fascinating compounds that attract attention not only because of the enormous amount of energy that they can store and release, but also because of the inherent "power-safety" contradiction that often hampers their practical applications. Ethylenedinitramine (EDNA) is ap owerful explosive, but its deployment is limited due to its sensitivity and chemical instability .W ew anted to establish if our expertise in basic co-crystal technology could be successfully employed in order to minimize or eliminate these drawbacks.

The benefits of employing a 'double activation' strategy for promoting effective practical cocrystal synthesis through halogen bonding was explored in a systematic supramolecular synthetic study of iodoethynylnitrobenzenes, where the positive electrostatic potential on the iodine atom was enhanced through a combination of an sp-hybridized carbon atom and one or more electronwithdrawing 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 reaction in the formation of a co-crystal driven by either C-I···N or C-I···O halogen bonds. The analogues bromo-compounds displayed a 60% success rate whereas the chloro-analogues did not yield any co-crystals, emphasizing the importance of the magnitude of the electrostatic aspects of halogen bonding for practical supramolecular synthesis. Ten new crystal structures are presented and the outcome (in terms of stoichiometry and connectivity) is largely predictable. A comparison of I···acceptor distances found in these structures with relevant data from the CSD shows that iodoethynylnitrobenzenes consistently give rise to a larger reduction of combined van der Waals radii (for C-X···acceptor) than do other well-known halogen bond donor moieties.

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A convenient, effective, and scalable protocol for stabilizing volatile liquid chemicals is reported. Through the use of halogen-bond driven co-crystal synthesis, several examples of liquid iodoperfluoroalkanes are transformed into crystalline materials with low-vapor pressure, considerable thermal stability, and moisture resistance. The target compounds can subsequently be re-generated through simple solvent-extractions.