Isostructural Energetic Coordination Compounds Based on 1,2-Dimethylimidazole and Cyanoborohydride toward...

Area of Science:

• Materials Science
• Chemistry
• Aerospace Engineering

Background:

• Spacecraft propulsion demands hypergolic materials with high energy density, short ignition delay, and low sensitivity.
• Traditional unsymmetrical dimethylhydrazine (UDMH) has limitations including low energy density, storage challenges, and carcinogenicity.
• Energetic coordination compounds (ECCs) offer potential as advanced hypergolic materials by combining energetic organic components with metal centers.

Purpose of the Study:

• To synthesize and characterize novel isostructural hypergolic ECCs for spacecraft propulsion.
• To investigate the structure-property relationships influencing ignition delay (ID) time in these ECCs.
• To evaluate the performance of new ECCs against traditional hypergolic fuels like UDMH.

Main Methods:

• Synthesis of two isostructural ECCs: [Cd(DMI)4(CBH)2] (1) and [Ni(DMI)4(CBH)2] (2), using 1,2-dimethylimidazole (DMI) and cyanoborohydride (CBH-).
• Measurement of volumetric energy density (Ev), ignition delay (ID) time upon contact with red fuming nitric acid (RFNA), and material sensitivity.
• Theoretical calculations to elucidate the electronic structure and interaction mechanisms governing ignition delay.

Main Results:

• Both synthesized ECCs exhibit high energy density, short ID times, and low sensitivity.
• The Ni-based ECC (2) demonstrates superior performance with a higher Ev (31.97 kJ·cm-3) compared to UDMH (25.60 kJ·cm-3) and other ZIF-based materials.
• Compound 2 shows a significantly shorter ID time (14 ms) than compound 1 (19 ms), attributed to its higher HOMO energy level and more electron-rich Ni center.

Conclusions:

• The Ni-based ECC, [Ni(DMI)4(CBH)2], is a highly promising hypergolic material due to its excellent energy density and rapid ignition characteristics.
• Theoretical analysis confirms that electronic structure, particularly the metal center's properties, dictates ignition delay, providing insights for designing future hypergolic materials.
• These findings pave the way for developing safer, more efficient hypergolic propellants for advanced spacecraft applications.