Constructing a 3D-layered energetic metal-organic framework with the strong stacking interactions of hydrogen-bridged rings: The way to an insensitive high energy complex

Energetic metal-organic frameworks (EMOFs) have drawn considerable attention due to their good energetic performances and acceptable sensitivity. Among these, 3D EMOFs show good thermal stability and mechanical insensitivity. Nevertheless, most of the 3D EMOFs have porous structures and relatively low crystal density, which is closely related to the energetic performances. This structural feature makes the preparation of 3D EMOFs with high density important and challenging. Herein, we present an efficient approach to construct 3D-layered EMOFs with strong stacking interactions, particularly the stacking of hydrogen-bridged rings, to solve the aforementioned contradiction. In this strategy, two EMOFs possessing layered structures with the same ligand and the metal center, named 1 and 2, were rationally designed and synthesized. EMOF 1 exhibits a 1D chain structure with a "head-to-tail"stacking mode, while EMOF 2 has a 3D architecture with a "head-to-head"stacking mode. The crystal structure and the molecular interaction analyses disclosed that the stacking of hydrogen-bridged rings in 2 are stronger than that in 1 and they play a more important role than π-stacking in the higher packing efficiency of 2. TG-DSC-MS-FTIR simultaneous tests showed that 2 has better thermal stability due to the improved structural reinforcement. As expected, 2 exhibits higher density, better energetic performance, and safety than 1 and possesses detonation velocity comparable to that of cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX). Our approach highlights the importance of the crystal packing architecture and the stacking interactions on the energetic properties of EMOFs and offers a new approach for the design and synthesis of high-performance insensitive energetic complexes.