Effect of counter-ion on packing and crystal density of 5,5′-(3,3′-bi[1,2,4-oxadiazole]-5,5′-diyl)bis(1H-tetrazol-1-olate) with five different cations

In energetic materials, the crystal density is an important parameter that affects the performance of the material. When making ionic energetic materials, the choice of counter-ion can have detrimental or beneficial effects on the packing, and therefore the density, of the resulting energetic crystal. Presented herein are a series of five ionic energetic crystals, all containing the dianion 5,5′-(3,3′-bi[1,2,4-oxadiazole]-5,5′-diyl)bis(1H-tetrazol-1-olate), with the following cations: hydrazinium (1) (2N₂H₅ ⁺·C₆N₁₂O₄ ²⁻), hydroxylammonium (2) 2NH₄O⁺·C₆N₁₂O₄ ²⁻ [Pagoria et al.. (2017). Chem. Heterocycl. Compd, 53, 760–778; included for comparison], dimethylammonium (3) (2C₂H₈N⁺·C₆N₁₂O₄ ²⁻), 5-amino-1H-tetrazol-4-ium (4) (2CH₄N₅ ⁺·C₆N₁₂O₄ ²⁻·4H₂O), and aminoguanidinium (5) (2CH₇N₄ ⁺·C₆N₁₂O₄ ²⁻). Both the supramolecular interactions and the sterics of the cation play a role in the density of the resulting crystals, which range from 1.544 to 1.873 Mg m⁻¹. In 5, the tetrazolate ring is disordered over two positions [occupancy ratio 0.907 (5):0.093 (5)] due to a 180° rotation in the terminal tetrazole rings.