Hydrazoic acid (HN(3))--potentially explosive, highly toxic, and very hygroscopic--is the simplest covalent azide and contains 97.7 wt % nitrogen. Although its molecular structure was established decades ago, its crystal structure has now been solved by X-ray diffraction for the first time. Molecules of HN(3) are connected to each other by hydrogen bonds in nearly planar layers parallel to (001) with stacking sequence A, B, ... The layer distance, at 2.950(1) Å, is shorter than that in 2H-graphite [3.355(2) Å]. The hydrogen bonds N-H···N are of great interest, since the azido group consists of three homonuclear atoms with identical electronegativity, but different formal charges. These hydrogen bonds are bifurcated into moderate ones with ≈2.0 Å and into weak ones with ≈2.6 Å. The moderate ones build up tetramers (HN(3))(4) in a nearly planar net of eight-membered rings. To the best of our knowledge, such a network of tetramers of a simple molecule is unique.
7:1 to nitrogen! Diazotization and subsequent dimerization of the triaminoguanidinium cation gave 1‐diazidocarbamoyl‐5‐azidotetrazole (see picture). The structurally and spectroscopically characterized binary CN compound shows great energetic performance and a high heat of formation, but also extremely high sensitivity to friction and shock.
1,5-Diaminotetrazole can be nitrated under very mild conditions by using nitronium tetrafluoroborate to result in 5-amino-1-nitriminotetrazole (1) in good yields. The same reaction can be performed with 1-amino-5-amino-4-methyltetrazole to yield 5-amino-4-methyl-1-nitriminotetrazole (2). Both compounds have been isolated and completely characterized by using vibrational spectroscopy, mass spectrometry, and differential scanning calorimetry. Additionally, X-ray diffraction measurements of the neutral compounds could be obtained; they indicated the structure of both compounds to be zwitterionic. Compounds 1 and 2 exhibit extremely high sensitivities to impact and friction and high positive heats of formation of 496 (1) and 453 kJ mol(-1) (2), respectively. Additionally, high-nitrogen-containing salts of 1 have been synthesized by metathesis reactions of silver 5-amino-1-nitriminotetrazolate with the corresponding halides so as to investigate the changes in sensitivity and thermal stability. All ionic compounds have been synthesized in good yields and characterized by means of vibrational and multinuclear NMR spectroscopy as well as X-ray diffraction measurements. Thermal stabilities have been evaluated by differential scanning calorimetry, whereas sensitivity measurements have been performed according to standardized Bundesanstalt für Materialforschung und -prüfung (BAM) tests. Theoretical calculations have been performed to investigate the heats of formation as well as the performance characteristics of the compounds.
Since 5‐Amino‐3‐nitro‐1H‐1,2,4‐triazole (ANTA) is known to be a thermally very stable secondary explosive, our goal in this contribution was the synthesis of thermally stable but more powerful energetic compounds based on ANTA. Hence, we utilized ANTA to synthesize 5‐nitramino‐3‐nitro‐1H‐1,2,4‐triazole (1) by nitration with a mixture of concentrated sulfuric acid and 100 % nitric acid. ANTA was also methylated with dimethyl sulfate to yield 5‐amino‐1‐methyl‐3‐nitro‐1,2,4‐triazole (2), which was then subsequently nitrated by using the method mentioned above to yield 1‐methyl‐5‐nitramino‐3‐nitro‐1,2,4‐triazole (3). All three compounds were characterized by IR and Raman as well as multinuclear NMR spectroscopy. Additionally, X‐ray crystallographic measurements of 1 and 3 were performed. The decomposition points of the compounds were found to be low for 1 (135 °C) and 3 (108 °C), despite the high thermal stability of ANTA (>220 °C) and 2 (294 °C). In order to increase the thermal stability of the compounds, nitrogen‐rich salts of 1 and 3 with the ammonium, hydrazinium, guanidinium, aminoguanidinium, and triaminoguanidinium cations were prepared and fully characterized by means of vibrational and NMR spectroscopy, DSC measurements, and X‐ray diffraction measurements. Additionally, the impact as well as friction sensitivities and the sensitivity against electrostatic discharge were determined by using standard BAM techniques. The standard heats of formation were calculated for selected compounds at the CBS‐4M level of theory, which reveals high positive heats of formation for all compounds.
The treatment of triaminoguanidinium chloride with two equivalents of sodium nitrite under acidic conditions, followed by the cyclization with stoichiometric amounts of either sodium hydroxide solution or solid sodium carbonate yielded 1-amino-5-azidotetrazole (1), 5-azido-1-diazidocarbamoyltetrazole (2), and 1-(aminoazidocarbamoyl)-5-azidotetrazole (3). The three novel compounds could be isolated by short-column liquid chromatography by using chloroform in reasonable yields. The mechanism of the formation as well as the decomposition pathway of the materials was investigated and a full characterization of all three compounds is presented. Compounds 1-3 have been characterized by means of Raman and IR as well as multinuclear NMR spectroscopy, mass spectrometry, and X-ray diffraction studies. Thermal stabilities have been evaluated by differential scanning calorimetry. Theoretical calculations have been performed to ensure the assignment of the vibrational modes obtained from Raman and IR measurements. The sensitivity values obtained from our measurements reflect the behavior of the compounds, which show an extremely high sensitivity toward mechanical as well as thermal stimuli.
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