Tricyclic compounds with 1,4,2,5-dioxadiazine bridged triazoles and pyrazoles as potential energetic materials

In this study, two energetic molecules with 1,4,2,5-dioxadiazine as a bridge were created by adding triazoles and pyrazoles to the oxazine skeleton. The structural characteristics, thermal behavior, and explosive properties of the obtained compounds 3,6-bis(1-nitro-1H-1,2,4-triazol-3-yl)-1,4,2,5-dioxadiazine (4a) and 3,6-bis(1-nitro-1H-pyrazol-3-yl)-1,4,2,5-dioxadiazine (4b) were investigated using experimental and theoretical techniques. To further elucidate the structure-property relationship, this study conducted calculations and analyses of quantum chemistry, such as the Hirshfeld surface analysis, the electrostatic potential (ESP) surface analysis, and the localized orbital locator (LOL) calculation. Compounds 4a and 4b have higher detonation velocities (4a: D_v ​= ​8328 ​m ​s⁻¹; 4b: D_v ​= ​7681 ​m ​s⁻¹) than the conventional explosive 2,4,6-trinitrotoluene (TNT; D_v ​= ​6881 ​m ​s⁻¹) according to an energetic evaluation. Moreover, the thermal properties and sensitivities of 4a (T_d ​= ​155 ​°C, IS ​= ​15 ​J, FS ​= ​288 ​N) and 4b (T_d ​= ​192 ​°C, IS ​= ​20 ​J, FS ​= ​216 ​N) were greatly improved compared with the previously reported energetic furazan-1,4,2,5-dioxadiazine derivatives N,N'-((1,4,2,5-dioxadiazine-3,6-diyl)bis(1,2,5-oxadiazole-4,3-diyl))dinitramide (i; T_d ​= ​106 ​°C, IS ​= ​4.5 ​J, FS ​= ​100 ​N) and 3,6-bis(4-nitro-1,2,5-oxadiazol-3-yl)-1,4,2,5-dioxadiazine (ii; T_d ​= ​148 ​°C, IS ​= ​2.2 ​J, FS ​= ​116 ​N). The excellent sensitivities and acceptable detonation velocities of compounds 4a and 4b make them good candidates for potential mechanically low-sensitive explosives. These findings will enrich the further application of nitrogen heterocycle 1,4,2,5-dioxadiazine in the field of energetic materials.