Terminal Fluorination of Ethylamine Cations Modulate Packing pattern for High-density Pentazolate Salts

Abstract

Introduction of fluorine substituent commonly is used to improve the density and stability of energetic materials. To clarify the effect of different number of fluorine substituents on the energy-related performances, 2-fluoroethylamine cation (FE), 2,2-difluoroethylamine cation (DFE) and 2,2,2-trifluoroethylamine cation (TFE) were assembled with pentazolate anion (cyclo-N5ˉ) to produce three corresponding salts (FEN, DFEN and TFEN). Their crystal structure reveal that terminal fluorination of ethylamine can altered the spatial arrangement of cations, further leading to the change in cyclo-N5ˉ anions stacking. The density of the corresponding pentazolate salts exhibited an increased trend, ranging from 1.42 to 1.72 g/cm³, as with fluorine substituents increase. The thermal stability analysis revealed that TFEN exhibits superior thermal stability (106.8 ℃) compared to FEN (87.5 ℃) and DFEN (103.7 ℃). These pentazolate salts display remarkable insensitivity properties, as evidenced by their impact sensitivity (≥40 J) and friction sensitivity (≥200 N) values. Notably, the incorporation of fluorine atoms presents a promising structural modification strategy for simultaneously enhancing both density and sensitivity in energetic material design. These results can provide a basis for the design of future energetic or fluorinated materials.