Modification of crystalline energetic salts through polymorphic transition: Enhanced crystal density and energy performance

Crystal engineering plays a vital role in the development of energetic materials. In this study, the polymorphs of 3-nitramino-4-(4,5-diamino-1,2,4-triazole-3-yl)-furazan (3) were investigated and confirmed by single crystal X-ray diffraction. α-3 can easily transform to the β-form by controlling temperature. Examination of their crystal structures reveals that α-3 exhibits a face-to-face stacking, while two desirable stacking types, face-to-face and wavelike types, are integrated within β-3. The results of NCI and Hirshfeld surface analyses suggest that β-3 possesses more extensive hydrogen bonding interactions than α-3. Therefore, compared with α-3, β-3 exhibits a higher crystal density and higher detonation performance. Meanwhile, similar molecular stability can be observed in the two polymorphs of 3. This work offers a novel and effective route to improve the properties of energetic salts.