Here we report a series of energetic-energetic cocrystals that incorporate the primary explosive diacetone diperoxide (DADP) with a series of trihalotrinitrobenzene explosives: 1:1 DADP/1,3,5-trichloro-2,4,6-trinitrobenzene (TCTNB), 1:1 DADP/1,3,5-tribromo-2,4,6-trinitrobenzene (TBTNB), and 1:1 DADP/1,3,5-triiodo-2,4,6-trinitrobenzene (TITNB). Acetone peroxides are attractive for their inexpensive and facile synthesis, but undesirable properties such as poor stability, intractably high sensitivity and low density, an indicator for low explosive power, have limited their application. Here through cocrystallization the density, oxygen balance, and stability of DADP are dramatically improved. Regarding sensitivity, in the case of the DADP/TCTNB cocrystal, the high impact sensitivity of DADP is retained by the cocrystal, making it a denser and less volatile form of DADP that remains viable as a primary explosive. Conversely, the DADP/TITNB cocrystal features impact sensitivity that is greatly reduced relative to both pure DADP and pure TITNB, demonstrating for the first time an energetic cocrystal that is less sensitive to impact than either of its pure components. This dramatic difference in cocrystal sensitivities may stem from the significantly different halogen-peroxide interactions seen in each cocrystal structure. These results highlight how sensitivity is defined by complex relationships between inherent bond strengths and solid-state properties, and cocrystal series such as that presented here provide a powerful experimental platform to probe this relationship.

A unique approach to alter the properties of existing energetic materials through cocrystallization is presented. The structure and properties of 17 new cocrystals of the benchmark energetic material 2,4,6-trinitrotoluene (TNT) are elucidated. The donor-acceptor π-π interaction represents a reliable supramolecular synthon for the formation of cocrystals with this aromatic energetic material. When present, amine-nitro interactions direct secondary packing in these crystals. A detailed study of the cocrystals formed reveals an alteration of key properties including density, packing coefficient, melting point, and decomposition temperature. Cocrystallization provides the opportunity to tune properties of existing energetics to create superior materials and provides a complementary alternative to traditional methods that focus primarily on the synthesis of new compounds and/or the discovery of polymorphs with the most attractive properties.

The detoxification of nitric oxide (NO) by bacterial NO reductase (NorBC) has gained much attention as this reaction provides a paradigm as to how NO can be detoxified anaerobically in cells. However, a clear mechanistic picture of how the heme/non-heme active site of NorBC activates NO is lacking, mostly as a result of insufficient knowledge about the properties of the non-heme iron(II)–NO adduct. Here we report the first biomimetic model complexes for this species that closely resemble the coordination environment found in the protein, using the ligands BMPA-Pr and TPA. The systematic investigation of these compounds allowed us to gain key insight into the electronic structure and geometric properties of high-spin non-heme iron(II)–NO adducts. In particular, we show how small changes in the ligand environment of iron could be used by NorBC to greatly modulate the properties, and hence, the reactivity of this species.

Energetic materials (energetics), including explosives, propellants, and pyrotechnics, are an important class of materials for which performance depends critically on solid-state properties such as density and stability. Cocrystallization is emerging as a strategy to enhance materials properties of new and existing energetics; however, few examples exist where the principles to enable the successful engineering of such cocrystals have been delineated. To address this need, the cocrystallization of 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX), a powerful and widely used explosive, was investigated. Seven cocrystals of HMX were structurally elucidated using single crystal X-ray diffraction. These cocrystal structures, in addition to three previously reported structures, reveal at least three distinct structural motifs by which HMX cocrystals form, each dictated by the electronic character and size of the cocrystal former. From these structures, general trends emerge having direct implications for cocrystal properties including density, packing coefficient, sensitivity to impact, and thermal behavior. In addition, these impact-insensitive energetic cocrystals can be restored to sensitive δ-HMX upon gentle heating, demonstrating the potential for these cocrystals to function as smart explosive materials.

Irreconcilable differences: Electron‐rich diacetone diperoxide is paired with the electron‐deficient rings of trichloro‐ and tribromotrinitrobenzene to form energetic cocrystals by design. Though the two cocrystals are isostructural, the former is very stable while the later exhibits a rare metastability and favors separation.