Coordination Polymerization of 5,5′-Dinitro‑2H,2H′‑3,3′-bi-1,2,4-triazole Leads to a Dense Explosive with High Thermal Stability

High-energy coordination polymers (CPs) based on nitrogen-rich ligands are an emerging class of explosives. However, modulation of the energetic properties of high-energy CPs and the establishment of their structure–function relationship remain in their infancy. In the present study, the utility of coordination polymerization as a technique to modulate the application of critical energetic properties, such as density and thermal stability, of a secondary explosive, 5,5′-dinitro-2H,2H′-3,3′-bi-1,2,4-triazole (DNBT), is presented. Ni-DNBT is a discrete octahedral complex with density lower than that of DNBT. Cu-DNBT also contains octahedral metal coordination, similar to that in Ni-DNBT, as the building unit; however, the partial reduction of CuII to CuI ions during the reaction and their unique geometrical preferences lead to linking of the octahedral CuII complexes by tetrahedral CuI ions and render the resultant material a one-dimensional polymer with high density. In fact, Cu-DNBT has the highest density among all of the DNBT-based energetics. Furthermore, Cu-DNBT exhibits thermal stability superior to that of both Ni-DNBT and DNBT. Cu-DNBT is one of the two DNBT-based energetic materials and one of the few energetics that are stable at temperatures higher than 300 °C.