Nitrogen‐Rich Energetic Ionic Liquids Based on the N,N‐Bis(1H‐tetrazol‐5‐yl)amine Anion – Syntheses, Structures, and Properties

Abstract

AbstractN,N‐Bis(1H‐tetrazol‐5‐yl)amine anions (HBTA–/BTA2–) were used as suitable nitrogen‐rich components for the construction of energetic ionic liquids. Seven ionic liquids, namely, 1,3‐dimethylimidazolium (1, [C1mim]HBTA), 1‐ethyl‐3‐methylimidazolium (2, [C2mim]HBTA), 1‐butyl‐3‐methylimidazolium (3, [C4mim]HBTA), 1‐hexyl‐3‐methylimidazolium (4, [C6mim]HBTA), 1‐methyl‐3‐octylimidazolium (5, [C8mim]HBTA), and 1,2,3‐trimethylimidazolium (6, [C1mmim]HBTA) cations with the HBTA– anion and di‐1,2,3‐trimethylimidazolium N,N‐bis(1H‐tetrazol‐5‐yl)amine (7, [C1mmim]2BTA), were synthesized. All materials were fully characterized by IR and NMR spectroscopy, elemental analysis, and high‐resolution mass spectrometry. The crystal structures of 1 and 7 were determined by single‐crystal X‐ray diffraction [1: monoclinic, P21/n, a = 14.0653(4) Å, b = 6.9507(2) Å, c = 22.4699(7) Å, β = 93.996(3)°, V = 2191.38(12) Å3, Z = 8, ρ = 1.511 g cm–3; 7: monoclinic, P21/c, a = 17.5869(3) Å, b = 12.8757(2) Å, c = 21.9203(6) Å, β = 125.0580(10)°, V = 4063.15(15) Å3, Z = 8, ρ = 1.221 g cm–3]. The nitrogen contents of 1–7 exceed 40 %, and 1 has the highest value of 61.78 %. The ionic liquids 1–7 are thermally stable to 220 °C, and 2–5 are room‐temperature ionic liquids. The heats of formation of 1–7 obtained by both experimental and theoretical methods are all positive. The ionic liquids 1–7 are insensitive towards impact (>40 J) and friction (>360 N). They can be ignited in air. These new energetic ionic liquids contain only C, H, and N and are of interest as potential propellants with high energy, high thermal stability, low sensitivity to impact and friction, and environmentally friendly decomposition gases.