Nitrogen‐Rich Compounds in Pyrotechnics: Alkaline Earth Metal Salts of 5,5′‐Hydrazine‐1,2‐diylbis(1H‐tetrazole)

Abstract

AbstractAlkaline earth metal (2: Mg, 3: Ca, 4: Sr, and 5: Ba) salts with the nitrogen‐rich 5,5′‐hydrazine‐1,2‐diylbis(tetrazolate) anion (HBT2–) were synthesized in high purities and yields and fully characterized by spectroscopic and analytical methods. In addition, the crystal structures of the new compounds were determined by X‐ray diffraction techniques. Whereas the tetrazole rings in 2 are twisted with respect to one another, as reported for compounds with the same anion, in the heavier‐metal salts 3–5 there exists “apparent coplanarity” between the same rings due to disorder, which is discussed. A detailed description of the structures is given. The compounds, obtained as the hydrated species, are insensitive to friction, shock, and electrostatic discharge (BAM testing), but react vigorously in a flame upon loss of water to give the characteristic flame color for the metal atom. Differential scanning calorimetry (DSC) measurements showed strong bonding of the water of crystallization, which is lost at temperatures equal to or above 130 °C, and great thermal stabilities with decomposition points above 220 °C without melting. Additionally, loss of water was determined by using thermal gravimetry (TG). Lastly, due to the prospective interest in metal salts containing the HBT2– anion as energetic materials, their constant‐volume energies of combustion were measured experimentally by bomb calorimetry and their heats of formation were back‐calculated from these results. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)