Amine-AlH₃ Adducts as Energetic Materials for a New Generation of Solid Fuels

Energetic materials, mainly propellants, explosives, and pyrotechnics, are crucial in various civilian applications, such as fuels for rockets and spacecraft. Current energetic fuels rely on highly toxic and polluting ammonium perchlorate (AP) or carcinogenic hydrazine derivatives, encouraging the search for greener and safer substitutes. This work demonstrates the first use of amine-AlH₃ adducts as potential solid fuels with promising hypergolic properties, high energy content, and without toxic derivatives. The herein presented four amine-AlH₃ adducts, AlH₃ coordinated with quinuclidine (Quin), triethylenediamine (TEDA), hexamethylenetetramine (HMTA), and tetraazatricyclododecane (TATD), illustrate a unique strategy to create new solid fuels by combining AlH₃ with an energy-rich nitrogen-containing molecule. The crystal structures of new compounds ([HMTA-AlH₃]_n and [TATD-AlH₃]_n) are determined from powder X-ray diffraction data. Differential scanning calorimetry-thermogravimetric analysis (DSC-TGA) of the samples combined with mass spectrometry (MS) evidence high thermal stability. The ultrashort ignition delays as low as one ms show an excellent hypergolic response. Four amine-AlH₃ adducts have higher combustion heat (> 29 kJ g^-1) than conventional hydrazine fuels (19.5 kJ g^-1). Finally, the successful mechanochemical syntheses of Quin₂AlH₃ and [HMTA-AlH₃]_n are introduced, showcasing a green chemistry approach to energetic materials.