Tunable optical and thermodynamic properties: the ignition of energetic metal complexes with different crystal fields

Primary explosives are generally composed of a metal, energetic ligands and oxyacid anions, and are exploded by optical or thermal initiation pathways to provide energy. Nowadays, near-infrared (NIR) laser initiation is a safe way to ignite explosives to effectively avoid electromagnetic interference. Therefore, low NIR laser sensitivity and high thermal stability are the preconditions for applicable laser-initiated explosives. Here, metallic 1,5-diaminotetrazole perchlorate complexes, [M(DAT)₆](ClO₄)₂ (M²⁺ = Cr²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺), have been selected to understand the laser sensitivity and thermal stability of octahedral energetic complexes using time-dependent density-functional theory methods (TD-DFT) and Car-Parrinello molecular dynamics (CPMD) methods. Compared with the energetic complexes [M(1-AT)](NO₃)₂ (x = 2 or 3), which adopt a tetragonal/square crystal field, the optical properties are obviously influenced by the coordination field. In a departure from traditional viewpoints, the thermal safety is reflected not only by the stability of the thermal ignition stage, but also by the performance of the stable deflagration stage and the deflagration to detonation transition (DDT) stage. This work helps to enhance the NIR sensitivity of complexes by tuning the crystal field and to improve the thermal safety based on the metal-ligand interactions, which is valuable for the exploration and design of stable laser-ignited energetic materials.