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

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)], 1; [Cd(Mtta)], 2; [Pb(bta)(O)(HO)], 3; and [Pb(tztr)(HO)], 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.