Energetic 1 H-Imidazo[4,5- d]pyridazine-2,4,7-triamine: A Novel Nitrogen-rich Fused Heterocyclic Cation with High Density

Fused heterocyclic energetic cation was rarely reported despite the development of energetic cation has attracted increasing attention in recent years. In this work, a new 1H-imidazo[4,5-d]pyridazine-2,4,7-triamine was synthesized in a one-step reaction, which was used as a cation to prepare 1H-imidazo[4,5-d]pyridazine-2,4,7-triamine perchlorate. Interestingly, when the synthesis was accomplished in different conditions, two crystal forms of perchlorate α-4 and β-4 were obtained, which were further confirmed by X-ray single crystal diffraction, X-ray powder diffractograms, infrared and multinuclear NMR spectra. These salts showed high density (1.88-1.93 g cm^-3 at 293(2) K), moderate detonation performance (D, 8128-8437 m s^-1 P, 29.4-32.86 GPa) and good thermal stability (T_d: 272-274 °C). Compared with those known energetic perchlorates, the density and sensitivity (IS, 14-20 J; FS, 144-168 J) of 4 were also significantly improved. Through theoretical calculations and experiment results, the explanations for the differences in physicochemical properties of these two crystal forms were illustrated. Density overlap indicator (DORI) analysis was also employed to perform the necessary visualization and quantification of covalent and noncovalent interactions. It is evident that ionic bonds, hydrogen bonds, and π-πinteractions are responsible for the high density and excellent performance of 1H-imidazo[4,5-d]pyridazine-2,4,7-triamine perchlorate, indicating that as-synthesized new material is a very promising cation in the construction of low-sensitivity high-energy compounds.