Azo-linked four-heterocyclic energetic molecule and its complexes: Exploring the important influence of conjugated planar structure on their crystal arrangement and stability

Abstract

Using two routes, this study designed and synthesized a novel azo-linked four-heterocyclic compound, 1,2-bis(5-(1H-tetrazol-5-yl)-4H-1,2,4-triazol-3-yl) diazene (3, H4BTTD), with high yields. It corroborated that large conjugated planar energetic molecules in energetic compounds, exemplified by H4BTTD, contribute to the formation of layered crystal stacking based on abundant hydrogen bonds and interlayer π-π interactions. This markedly diminishes the mechanical sensitivities of energetic compounds. Single-crystal X-ray diffraction (XRD) experiments revealed the presence of layered structures in H4BTTD hydrate, as well as its magnesium-based complex [Mg2(BTTD)(H2O)8] (4) and calcium salt [Ca(H2O)7] (H3BTTD)2(5). Based on these structural data, this study analyzed the causes of these layered structures. Furthermore, this study systematically characterized the compounds’ physical and chemical properties, including mechanical sensitivities (IS ≥ 20 J, FS > 360 N), thermal stability (Td = 253.7–287.8 °C), and detonation performance (D = 6808–8253 m⋅s−1), confirming the influence of molecular structures on the macroscopic properties of energetic materials through crystal stacking. Additionally, pyrotechnic formulas based on compounds 3 and 5 exhibited the most intense light emission within a wavelength range of 658.6–689.8 nm, underscoring the potential application of both compounds as promising candidates in preparing high-purity red pyrotechnic formulation.