High-Density Cd/Na Mixed-Metal Energetic Coordination Polymer Constructed via In Situ Tetrazole Formation

The development of heat-resistant energetic materials that simultaneously combine high thermal stability, acceptable detonation performance, and low mechanical sensitivity remains a major challenge in energetic materials research. Herein, we report a highly dense heterometallic Cd/Na metal energetic coordination polymer (ECP), [Cd3NaCl(C3H6N18O)]n, constructed through a unique in situ tetrazole-forming strategy, in which tetrazole generation and framework assembly occur concurrently, enabling effective immobilization of Cadmium ions within a rigid three-dimensional energetic framework. The ECP exhibits an exceptional crystal density of 3.03 g cm−3 and a high decomposition temperature of 361 °C, demonstrating remarkable thermal endurance. Furthermore, the material shows acceptable detonation performance (VOD = 6940 m s−1; DP = 29.8 GPa) together with low mechanical sensitivity (IS = 40 J; FS = 360 N), achieving a favorable balance between energetic performance and safety. Single-crystal analysis reveals that the cooperative Cd/Na coordination environment and dense supramolecular packing play a crucial role in enhancing the framework rigidity and thermal stability. The enhanced stability and energetic behavior arise from the synergistic effects of in situ generated tetrazole ligands, strong Cd−N coordination, heterometallic assembly, and efficient crystal packing. This work demonstrates that combining in situ heterocycle formation with mixed-metal coordination polymer engineering is an effective and underexplored strategy for developing thermally robust energetic materials with reliable performance and low mechanical sensitivity.