In situ synthesized 3D metal–organic frameworks (MOFs) constructed from transition metal cations and tetrazole derivatives: a family of insensitive energetic materials

Abstract

The combination of the hydrothermal method with in situ synthesis has been successfully employed to prepare a family of tetrazole-based energetic metal–organic frameworks (EMOFs) ([Ag(Mtta)]_n, 1; [Cd₅(Mtta)₉]_n, 2; [Pb₃(bta)₂(O)₂(H₂O)]_n, 3; and [Pb(tztr)₂(H₂O)]_n, 4) through [2 + 3] cycloaddition of azide anions and nitrile groups. All the synthesized EMOFs were characterized by single crystal X-ray diffraction, IR spectroscopy, elemental analysis (EA), different scanning calorimetry (DSC), and thermogravimetry (TG). Both complexes 1 and 4 consist of reticular two-dimensional (2D) layers that are linked by π–π overlap interactions between the ligands in neighbouring layers to form 3D supramolecular structures. In contrast, complexes 2 and 3 are 3D frameworks. The in situ formation of ligands bta and tztr has been described for the first time. Remarkably, thermogravimetric measurements demonstrated that the EMOFs 1–4 possess excellent thermostabilities with high decomposition temperatures up to 354, 389, and 372 °C for 1, 2, and 4, respectively. Sensitivity tests revealed that all the EMOFs are extremely insensitive.