Nitrate anions embedded in rigid and cationic 3D energetic MOFs constructed by the chelating ligand towards insensitive energetic materials

Abstract

Balancing the conflict between energy and mechanical sensitivities is still one of the most challenging issues in the field of energetic materials (EMs). The NO₃⁻ anion has attracted widespread attention in the preparation of EMs because of rich oxygen contents and excellent energy densities. In this work, a 3D energetic metal–organic framework (EMOF) {[Zn₂(μ₂-OH)(datz)₂(H₂O)](NO₃)}_n1 (Hdatz = 3,5-diamino-1,2,4-triazole) was constructed by chelating the nitrogen-rich Hdatz ligand and NO₃⁻ anions. The structural analysis demonstrates that the Hdatz ligand chelated with surrounding binuclear metal centers to construct [Zn–O–Zn] structural units, resulting in the formation of highly stable five-membered fused rings, which contribute to the construction of a 3D cationic framework. Additionally, free NO₃⁻ anions are encapsulated by the cationic 3D frameworks and stabilized by robust hydrogen-bonding interactions in the channels. The values of enthalpy of formation (Δ_fH°) and heat of detonation (ΔH_det) of 1 are high up to 3478 kJ mol⁻¹ and 5.316 kJ g⁻¹. In addition, compound 1 has a relatively good thermal decomposition temperature of 161 °C and excellent low impact (IS > 40 J) and friction (FS >360 N) sensitivities. These results demonstrate that 1 can serve as a potential insensitive EM. This unique structural feature also presents an effective reference for developing advanced EMs.