All-Nitrogen Cages and Molecular Crystals: Topological Rules, Stability, and Pyrolysis Paths

Abstract

We combined ab initio molecular dynamics with the intrinsic reaction coordinate in order to investigate the mechanisms of stability and pyrolysis of N4 ÷ N120 fullerene-like nitrogen cages. The stability of the cages was evaluated in terms of the activation barriers and the activation Gibbs energies of their thermal-induced breaking. We found that binding energies, bond lengths, and quantum-mechanical descriptors failed to predict the stability of the cages. However, we derived a simple topological rule that adjacent hexagons on the cage surface resulted in its instability. For this reason, the number of stable nitrogen cages is significantly restricted in comparison with their carbon counterparts. As a rule, smaller clusters are more stable, whereas the earlier proposed large cages collapse at room temperature. The most stable all-nitrogen cages are the N4 and N6 clusters, which can form the van der Waals crystals with densities of 1.23 and 1.36 g/cm3, respectively. The examination of their band structures and densities of electronic states shows that they are both insulators. Their power and sensitivity are not inferior to the modern advanced high-energy nanosystems.

Stability of neutral molecular polynitrogens: energy content and decomposition mechanisms

“…This barrier is comparable to those presented by N 8 ( C 2v )-B and N 8 ( O h ) isomers which, together with a large energy released upon full dissociation (DE), makes N 10 ( D 5h ) the most attractive polyN within the N 10 structures according to our calculations. The just published study employing reaction dynamics 89 obtained a similar transition state, but the B3LYP reported energy barrier is substantially lower (13 kcal mol −1 ). Since the B3LYP functional is well known to underestimate barrier heights, 90,91 with a MUE about four times higher than the functionals employed here, 76 our AE value should be more realistic.…”

“…Our proposed isomerization pathway agrees with the results of ref. 66 , 68 and 89 . After isomerization, N 8 ( O h ) may readily follow the N 8 ( C 2v )-B decomposition path already discussed and presented in Fig.…”

Molecular and Electronic Structures of Neutral Polynitrogens: Review on the Theory and Experiment in 21st Century

“…It is expected that this will open up great prospects for the study and application of nitrogen nanofibers, because, according to [ 88 ], nitrogen-containing nanotubes should be environmentally friendly. Publications of the last decade [ 89 , 90 ] concerned the problems of the topology of polynitrogens, from tetranitrogen N 4 to eicosahectanitrogen N 120 .…”