All-nitrogen solids, if successfully synthesized, are ideal high-energy-density materials because they store a great amount of energy and produce only harmless N 2 gas upon decomposition. Currently, the only method to obtain all-nitrogen solids is to apply high pressure to N 2 crystals. However, products such as cg-N tend to decompose upon releasing the pressure. Compared to covalent solids, molecular crystals are more likely to remain stable during decompression because they can relax the strain by increasing the intermolecular distances. The challenge of such a route is to find a molecular crystal that can attain a favorable phase under elevated pressure. In this work, we show, by designing a novel N 16 molecule (tripentazolylamine) and examining its crystal structures under a series of pressures, that the aromatic units and high molecular symmetry are the key factors to achieving an all-nitrogen molecular crystal. Density functional calculations and structural studies reveal that this new all-nitrogen molecular crystal exhibits a particularly slow enthalpy increase with pressure due to the highly efficient crystal packing of its highly symmetric molecules. Vibration mode calculations and molecular dynamics (MD) simulations show that N 16 crystals are metastable at ambient pressure and could remain inactive up to 400 K. The initial reaction steps of the decomposition are calculated by following the pathway of the concerted excision of N 2 from the N 5 group as revealed by the MD simulations.
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A practical way to enhance the synthesis of N 8 − from an N 3 − precursor, studied by both computational and experimental methods
Polymeric nitrogen (PN) belongs to a general family of materials containing all-nitrogen molecules or clusters. Although it is rare and challenging to synthesize PN members, they are attracting increasing scientific attention due to their high energy storage capacity and possible use as a green catalyst. A few theoretical calculations predicted the possible PN phases from N 2 gas, but they all require extremely high pressures and temperatures to synthesize. In this work, a practical way to synthesize N 8 polymeric nitrogen from an N 3 − precursor is elucidated using density functional theory calculations. The detailed mechanism, , is determined. The calculated energy barriers indicate that the first step is the rate-limiting step. This result guides us to rationally synthesize N 8 under UV (254 nm) irradiation, chosen based on the calculated absorption spectrum for the azide anion. As expected, UV irradiation enhances N 8 yields by nearly four times. This provides an interesting route to the scalable synthesis of high energy density N 8 compounds.
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- Award ID(s):
- 1804949
- PAR ID:
- 10290665
- Date Published:
- Journal Name:
- Physical Chemistry Chemical Physics
- Volume:
- 23
- Issue:
- 29
- ISSN:
- 1463-9076
- Page Range / eLocation ID:
- 15713 to 15718
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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