New energetic compounds based on the nitrogen-rich 5,5′-azotetrazolate anion ([C2N10]2−)

Abstract

The metathesis reaction between sodium 5,5′-azotetrazolate ([Na]⁺₂ZT²⁻) pentahydrate and 1,3-dimethyl-5-aminotetrazolium iodide or semicarbazidium chloride in water leads to the formation of the corresponding ZT²⁻ salts as the hydrated species (2 and 4). The anhydrous derivatives (1 and 3) were synthesized by reaction of silver 5,5′-azotetrazolate with a suitable halogenide salt in methanol. Alternatively, the crystal water in the hydrated salts 2 and 4 was quantitatively removed under vacuum leading to a safe up-scalable synthesis for compounds 1 and 3, which does not make use of highly sensitive silver salts. The formation of the salts was confirmed by analytical and spectroscopic methods and, in addition, the crystal structures of 2 and 4 were determined using low-temperature X-ray measurements (2: monoclinic P2₁/n, a = 9.3101(3), b = 6.5383(2), c = 19.5637(5) Å; β = 90.48(1)°; V = 1190.84(6) ų and 4: triclinic P, a = 4.563(5), b = 7.362(5), c = 11.334(5) Å; α = 105.125(5), β = 90.48(1), γ = 102.871(5)°; V = 357.2(5) ų). Although the semicarbazidium salts 3 and 4 have relatively low thermal stabilities (<130 °C), the tetrazolium salts 1 and 2 decompose above 190 °C. All four compounds classify as insensitive, have high performances (1: P = 19.0 GPa and D = 7667 m s⁻¹; 2: P = 25.1 GPa and D = 8585 m s⁻¹; 3: P = 23.4 GPa and D = 8125 m s⁻¹ and 4: P = 20.0 GPa and D = 7694 m s⁻¹) and decompose giving (mainly) environmentally friendly gases. Lastly, the properties of salts 1–4 make them attractive for further studies as a new class of high performing, insensitive, environmentally more benign and, in the case of 1 and 2, also thermally stable energetic materials.