Integrating three types of structure reinforcements abounding in heat-resistant explosives to construct a 3D solvent-free EMOF with superb stability

Abstract

With the consecutive development of space missions, deep wells, and other specialized applications, the creation of new-generation heat-resistant energetic materials bearing high stability to satisfy the harsh requirements of the above application scenarios is crucial. Inspired by three types of structure reinforcements abounding in heat-resistant explosives, namely, weak interaction, azo moiety, and coordination, we attempted to simultaneously integrate them within one molecule to improve stability. Consequently, we employed the 5,5′-diamino-3,3′-azo-1H-1,2,4-triazole (H₂DAAT) ligand to obtain a 3D solvent-free energetic metal–organic framework (EMOF) [Cd(DAAT)]_n (1). Structurally, both N atoms of the azo moiety in the DAAT²⁻ ligands simultaneously coordinated with Cd(II) ions to form a bis-five-membered ring by the μ₂-bridged trans-coordination style, which was rarely reported before in the territory of EMOFs. This intriguing trait may enhance the stability of the two EMOFs by reducing the probability of metal ions coordinating with the solvent molecules. Surprisingly, the thermal decomposition temperature of 1 (T_d = 404 °C) is 117 °C higher than that of the ligand (T_d = 287 °C). Besides, 1 manifests superb chemical stability (intact in aqueous solutions with pH 1–14 for 15 days), and mechanical stability (IS > 40 J, FS > 360 N). The calculation results show that 1 has a detonation pressure of 33.25 GPa and a detonation velocity of 7941 m s⁻¹. The possible decomposition products were probed by a TG-DSC-MS-IR test. Overall, this work lends concrete support to the design and synthesis of a new-generation of heat-resistant energetic materials.