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Keywords:

  • Crystal structures;
  • Density functional calculations;
  • Energetic;
  • Heterocycles;
  • Nitrogen-rich compounds

Abstract

Isomeric 5-aminotetrazolate salts with the 1,4-dimethyl-5-aminotetrazolium (4) and the 1,3-dimethyl-5-aminotetrazolium (5) cations have been synthesized in high yields and purity by the metathesis reaction between silver 5-aminotetrazolate (3) and a suitable tetrazolium iodide salt (1 and 2). In addition we synthesized the free acid 1,4-dimethyl-5-iminotetrazole (7) by deprotonation of 1,4-dimethyl-5-aminotetrazolium iodide (1) using potassium hydroxide. 7 was alternatively used to synthesize 4. All three compounds (4, 5 and 7) were characterized using analytical and spectroscopic methods and the crystal structures of 4 and 7 were determined by low temperature X-ray measurements (4: Monoclinic, P21/n, a = 6.7422(4) Å, b = 9.8362(5) Å, c = 13.0637(8) Å, β = 97.985(5)°, V = 857.95(9) Å3, 7: Triclinic, P\bar{1}, a = 6.256(1) Å, b = 6.773(1) Å, c = 6.773(1) Å, α = 102.24(3)°, β = 97.96(3)°, γ = 100.39(3)°, V = 271(3) Å3). Due to the interest of nitrogen-rich compounds as energetic materials, the heats of formation of 4 and 5 were experimentally determined using bomb calorimetry and their validity was checked by means of quantum chemical calculations (MP2). Predicted detonation parameters for these materials are similar to commonly used energetic compounds and their low sensitivities make them interesting candidates as a new class of environmentally friendly insensitive ionic salts.