Sensitive structural motifs separately distributed in azide-based 3D EMOFs: a primary explosive with an excellent initiation ability and enhanced stability

Abstract

Azide-based energetic metal–organic frameworks (EMOFs) with a remarkable initiation capability are expected to replace lead-based primers (lead azide, LA; lead styphnate, LS). However, most of them are not stable enough in the field of primary explosives. Developing primary explosives with excellent energetic performances and stabilizing sensitive structural motifs with acceptable mechanical sensitivity remain great challenges. In this work, two EMOFs, namely the 3D [Cu₃(N₃)₄(bmttz)₂]_n1 and 2D [Cd₇(N₃)₁₀(bmttz)₄]_n2 based on azides and Hbmttz ligands (Hbmttz = 1,3-bis(1-methyltetrazol-5-yl)triaz-1-ene), were successfully prepared. The thermal decomposition temperature (T_dec) of 1 was 216 °C, which was higher than most of Cu(N₃)₂ (CA)-based primary explosives, such as CA (T_dec = 205 °C) and Cu-MTZ (T_dec = 148 °C, [Cu(N₃)₂(MTZ)]_n, MTZ = 1-methyl-5H-tetrazole), and the T_dec value of 2 was up to 281 °C. The lead plate explosive tests showed that the initiation ability of 1 was more effective than those of LA, [Ni(N₂H₄)₃](NO₃)₂ (NHN) and the reported Cu-TZ ([Cu(N₃)(tz)]_n, Htz = tetrazole). In particular, the detonation charge of 1 was only 1/20th of that of NHN to attain a similar effect for initiating 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX). Sensitivity tests indicated that the mechanical sensitivities of 1 and 2 were comparable with that of commercial LA. Furthermore, structural analyses and theoretical calculations demonstrated that the sensitive structural motifs were separately distributed by bmttz⁻ ligands in the 3D framework, which promoted 1 to possess higher mechanical and thermal stabilities than those of CA and Cu-MTZ. This work presents unique types of molecular architectures with good detonation performances and suitable stabilities.