A new sensitive structural motif inlaying the azides and tetrazole-based rigid 3D energetic MOFs: Highly sensitive primary explosives with excellent thermal stability

Although many primary explosives have been reported to date, there are three great challenges for researchers: 1) the persistent enhancement of the energetic properties of primary explosives, 2) the elucidation of sensitive structural motifs of the primary explosives, and 3) the establishment of the structural model of primary explosives with remarkable ignition performance and good thermostabilities. In this study, we employed the rigid tetrazole ligand to obtain two 3D energetic metal-organic frameworks (EMOFs) [Cu(N-3)(tz)](n) 1 and [Cd-3(N-3)(2)(tz)(3)(OH)](n) 2 (Htz = tetrazole). Due to the rigid and cheated 3D nitrogen-rich metal-organic frameworks, both of the two compounds exhibit decent thermostabilities (>180 degrees C), and good energetic performance. In particular, the thermal decomposition temperature (T-d(ec)) of 1 is high up to 265 degrees C, which is higher than those of all hitherto known cupper azide-based primary explosives, including copper azide@carbon (called MOFT-CA, T-d(ec), = 204 degrees C) and [Cu(N-3)(2)(MTZ)] (called Cu-MTZ, MTZ = 1-methyl-5H-tetrazole, T-dec, = 148 degrees C). Meanwhile, sensitivity tests reveal that the Impact sensitivy (IS) of 1 is <= 1.0 J, and the Friction sensitivity (FS) of 1 is <= 5.0 N, which is comparable with MOFT-CA (IS = 1 J, FS = 5 N), and superior to Cu(N-3)(2) with IS << 1 J, FS << 0.1 N. Theoretical calculations demonstrate that there exists the new sensitive structural motif of azide-based EMOFs, strong repulsive steric clashes between the tetrazole ligand and azide ions, which was revealed for the first time. In addition, structural anaysis deduces that the sensitive structural motif inlaying the rigid 3D framework constucts the new structural model, which provides guidance and reference in exploring advanced primary explosives with excellent thermal stabilities.