Energetic Mn(II)/Ni(II) coordination compounds in catalyzing RDX and HMX decomposition and enhancing combustion

To develop energetic combustion catalysts for solid propellants, two novel energetic metal coordination compounds, Mn(AIM)₆(BF₄)₂ (Mn-ABF) and Ni(AIM)₆(BF₄)₂ (Ni-ABF), were successfully synthesized in this study. These compounds were prepared by coordinating Mn²⁺ and Ni²⁺ ions with the ligand 1-allylimidazole (AIM) and the tetrafluoroborate anion. Physicochemical characterization revealed that both compounds exhibit excellent safety performance (IS > 40 J, FS > 360 N) along with favorable energetic properties. Specifically, Mn-ABF and Ni-ABF lowered the decomposition temperature of RDX by 3.7 °C and 9.8 °C, and reduced its apparent activation energy by 32.1 kJ mol^-1 and 50.4 kJ mol^-1, respectively. For HMX, the decomposition temperatures were decreased by 3.8 °C and 18.3 °C, with corresponding reductions in apparent activation energy of 43.5 kJ mol^-1 and 137.7 kJ mol^-1, respectively. Combustion experiments based on these findings demonstrated that both compounds significantly promote the combustion process in RDX/AP/Al and HMX/AP/Al composite systems. They reduced the burning times of both AP/RDX/Al (from 33 s to 16 s and 6 s) and AP/HMX/Al (from 31 s to 13 s and 10 s), while also increasing the flame area and intensity. Quantum chemical calculations were conducted to analyze the Hirshfeld surfaces, interatomic interactions, and molecular electrostatic potential of Mn-ABF and Ni-ABF. These analyses revealed the intrinsic reasons, at the electronic structure level, for the superior catalytic performance of Ni-ABF over Mn-ABF. The results indicate that the synthesized Mn-ABF and Ni-ABF possess promising application potential as highly efficient combustion catalysts for solid propellants.