Effect of counter-ion on packing and crystal density of 5,5'-(3,3'-bi[1,2,4-oxa-diazole]-5,5'-di-yl)bis-(1-tetra-zol-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-oxa-diazole]-5,5'-di-yl)bis-(1-tetra-zol-1-olate), with the following cations: hydrazinium () (2NH·CNO), hydroxyl-ammonium () 2NHO·CNO [Pagoria (2017). , , 760-778; included for comparison], di-methyl-ammonium () (2CHN·CNO), 5-amino-1-tetra-zol-4-ium () (2CHN·CNO·4HO), and amino-guanidinium () (2CHN·CNO). Both the supra-molecular inter-actions 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. In , the tetra-zolate ring is disordered over two positions [occupancy ratio 0.907 (5):0.093 (5)] due to a 180° rotation in the terminal tetra-zole rings.