Calculations predict a stable molecular crystal of N8

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Abstract

Nitrogen, one of the most abundant elements in nature, forms the highly stable N2 molecule in its elemental state. In contrast, polynitrogen compounds comprising only nitrogen atoms are rare, and no molecular crystal made of these compounds has been prepared. Here, we predict the existence of such a molecular solid, consisting of N8 molecules, that is metastable even at ambient pressure. In the solid state, the N8 monomers retain the same structure and bonding pattern as those they adopt in the gas phase. The interactions that bind N8 molecules together are weak van der Waals and electrostatic forces. The solid is, according to calculations, more stable than a previously reported polymeric nitrogen solid, including at low pressure (below 20 GPa). The structure and properties of the N8 molecular crystal are discussed and a possible preparation strategy is suggested.

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Figure 1: Crystal structure of the predicted N8 solid and bonding pattern in N8 molecules.
Figure 2: Structures and HOMOs of the components of the solid.
Figure 3: Thermodynamic stability of different forms of solid nitrogen.
Figure 4: Relevant energies (ΔHG, in kcal mol−1) of the N8 isomers and the barriers for decomposition (from ref. 10).
Figure 5: Calculated infrared spectrum of N8 molecular solid and normal modes corresponding to the most intense transitions.

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Acknowledgements

Research at the Hebrew University of Jerusalem was supported under the auspices of the Saerree K. and Louis P. Fiedler Chair in Chemistry (R.B.G.). A.I.K. acknowledges support from the Army Research Office (grant W911NF-12-1-0543). B.H. and R.B.G. wishes to thank S. Aflalo for her help with the artwork for the manuscript.

Author information

B.H. performed the calculations. A.I.K. provided advice on electronic structure calculations. R.B.G. proposed the research topic. B.H., A.I.K. and R.B.G. contributed to the interpretation of the results and co-wrote the manuscript.

Correspondence to R. Benny Gerber.

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Hirshberg, B., Gerber, R. & Krylov, A. Calculations predict a stable molecular crystal of N8. Nature Chem 6, 52–56 (2014) doi:10.1038/nchem.1818

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