Metal Coordination Compounds Base on Cyanoborohydride and 2-Imidazolidinone: Activity Fuels for Hypergolic and AP Composite Propellant Applications

To develop activity fuels for dual application propellant systems, two novel metal coordination compounds based on Cyanoborohydride (CBH) and 2-imidazolidinone (2-IO), Mn(2-IO)₄CBH₂ (CBH-1) and Co(2-IO)₄CBH₂ (CBH-2), were successfully synthesized. Their potential to serve as activity fuels for hypergolic propellants and AP composite solid propellants was systematically evaluated. Thermal analysis and energy testing revealed that CBH-2 possesses a lower thermal decomposition onset temperature (191.8 °C) and a higher energy density (E_v = 29.51 kJ·cm^–3), while both compounds exhibit low mechanical sensitivity and safety. In ignition tests with the liquid oxidizer WFNA, CBH-2 exhibited an ultrashort ignition delay time (8 ms), with a corresponding theoretical specific impulse of 241.4 s, significantly outperforming CBH-1 (26 ms, 190.9 s). Furthermore, when incorporated with ammonium perchlorate (AP) as a fuel component, CBH-2 exerts a more significant catalytic effect on the high-temperature decomposition of AP, reducing the peak decomposition temperature by 70.9 °C, and increasing the linear combustion rate of the composite system to 1.85 mm·s^–1, approximately 3.2 times that of the CBH-1 system. Theoretical calculations revealed the root cause of these performance differences at the microscopic level: CBH-2 exhibits stronger intermolecular interactions and a narrower energy gap, indicating that the Co²⁺ center confers higher electron transfer capacity and intrinsic reactivity.