Pressure-induced phase transition of 1,5-diamino-1H-tetrazole (DAT) under high pressure

Structural, vibrational and electronic properties of nitrogen-rich 2,4,6-triazide-1,3,5-triazine under high pressure

CONTEXT AND RESULTS

2,4,6-triazide-1,3,5-triazine (TAT) has received widespread attention for its great potential to synthesize or convert to nitrogen-rich high energy density materials (HEDMs). The TAT structure alteration in the compression process up to 30 GPa has characteristics as follows: (a) [N₃] groups straighten; (b) [N₃] groups gather toward the six-membered C-N heterocycles. At about 5 GPa, Raman peak split at 700 cm^-1 was observed both in calculation and in-situ Raman experiment, which is caused by pressure-induced intramolecular stress. Besides, the broad band of the amorphous two-dimensional C=N network (centered at 1630 cm^-1) occurred at about 12 GPa. Meantime, the study on electronic features suggests the pressure-induced deformation in TAT molecular structure cause the discontinuous change of band gap at about 4.5 GPa and 8.0 GPa, respectively.

COMPUTATIONAL AND THEORETICAL TECHNIQUES

The static compression process of TAT was explored in the range of 0-30 GPa by using dispersion corrected density functional theory (DFT-D) calculations combined with in-situ Raman experiment. The GGA/PBE+G06 method that has less errors than other calculation methods was used to predict the geometry structure, vibrational properties and electronic structure of TAT under pressure.

Compressive Symbol: A New Way to Evaluate the High-Pressure Behaviors of Energetic Tetrazole Materials

Energetic materials may transit to different phases or decompose directly under compression. Their reactivity in the explosions can be evaluated by their high-pressure induced behaviors, including polymorphism or phase transition. Here, we applied DFT methods to understand high-pressure behaviors of four typical tetrazole derivate crystals, including 5-aminotetrazole (ATZ), 1,5-aminotetrazole (DAT), 5-hydrazinotetrazole (HTZ), and 5-azidotetrazole (ADT), under the gradually increased pressure from ambient pressure to 200 GPa. In response to the extreme-high pressures, the performances are dominated by compressibility of crystals, reflected by compressive symbols on the basis of the molecular orientation in crystals. The crystal with weak compressibility (large symbol) generally dissociates, triggered by cleavage of weak bonds. However, the crystal with low compressive symbol is generally corresponding to a pressure-induced structural transformation or phase transition.

Chemistry of 2,5-diaminotetrazole

1,5-Diaminotetrazole is one of the most prominent high-nitrogen tetrazole compounds described in the literature. Interestingly the isomer 2,5-diaminotetrazole is nearly undescribed due to its challenging synthetic routes. 2,5-Diaminotetrazol (1) was successfully synthesized via amination of 5-aminotetrazole followed by various purification steps to separate it from isomeric 1,5-diaminotetrazole. In addition to the extensive characterization of 2,5-DAT further derivates by protonation, methylation and amination of the tetrazole ring were synthesized and characterized. The resulting tri-functionalized, ionic tetrazolium derivatives were combined with energetic anions (nitrate, perchlorate, azide, 5,5'-bistetrazole-1,1'-diolate (BTO^2-)) to adjust and tune the properties of each compound. All compounds were intensively characterized including IR and multinuclear NMR spectroscopy, thermal analysis through DTA, X-ray diffraction and sensitivity testing. The purity was verified by CHNO elemental analysis and the energetic properties were calculated using the EXPLO5 code and the calculated enthalpy of formation (CBS-4M).

Phase transition and chemical reactivity of 1H-tetrazole under high pressure up to 100 GPa

The pressure-induced phase transition and polymerization of nitrogen-rich molecules are widely focused on due to their extreme importance for the development of green high-energy-density materials. Here, we present a study of the phase-transition behaviour and chemical reaction of 1H-tetrazole up to 100 GPa using in situ Raman, IR, X-ray diffraction, neutron diffraction techniques and theoretical calculations. A phase transition above 2.6 GPa was identified and the high-pressure structure was determined with one molecule in a unit cell instead of two molecules as reported before. The 1H-tetrazole polymerized reversibly below 100 GPa, probably through carbon-nitrogen bonding instead of nitrogen-nitrogen bonding. Our studies update the structure model of the high-pressure phase of 1H-tetrazole, and present the possible intermolecular bonding route for the first time, which gives new insights to understand the phase transition and chemical reaction of nitrogen-rich compounds, and is of benefit for designing new high-energy-density materials.