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 (T_d = 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.