Terminal fluorination of ethylamine cations modulates the packing pattern of high-density pentazolate salts

Abstract

The introduction of fluorine substituents is commonly used to improve the density and stability of energetic materials. To clarify the effect of different numbers of fluorine substituents on energy-related performance, the 2-fluoroethylamine cation (FE), 2,2-difluoroethylamine cation (DFE) and 2,2,2-trifluoroethylamine cation (TFE) were assembled with the pentazolate anion (cyclo-N₅⁻) to produce three corresponding salts (FEN, DFEN and TFEN). Their crystal structures reveal that terminal fluorination of ethylamine can alter the spatial arrangement of cations, further leading to a change in cyclo-N₅⁻ anion stacking. The densities of the corresponding pentazolate salts exhibited an increased trend, ranging from 1.42 to 1.72 g cm⁻³, as the number of fluorine substituents increased. Thermal stability analysis revealed that TFEN exhibits superior thermal stability (108.5 °C) compared to FEN (89.5 °C) and DFEN (105.3 °C). 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 during energetic material design. These results can provide a basis for the design of future energetic or fluorinated materials.