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Stabilization of hexazine rings in potassium polynitride at high pressure

Nature Chemistry volume 14, pages 794–800 (2022)Cite this article

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Abstract

Polynitrogen molecules are attractive for high-energy-density materials due to energy stored in nitrogen–nitrogen bonds; however, it remains challenging to find energy-efficient synthetic routes and stabilization mechanisms for these compounds. Direct synthesis from molecular dinitrogen requires overcoming large activation barriers and the reaction products are prone to inherent inhomogeneity. Here we report the synthesis of planar N62− hexazine dianions, stabilized in K2N6, from potassium azide (KN3) on laser heating in a diamond anvil cell at pressures above 45 GPa. The resulting K2N6, which exhibits a metallic lustre, remains metastable down to 20 GPa. Synchrotron X-ray diffraction and Raman spectroscopy were used to identify this material, through good agreement with the theoretically predicted structural, vibrational and electronic properties for K2N6. The N62− rings characterized here are likely to be present in other high-energy-density materials stabilized by pressure. Under 30 GPa, an unusual N20.75−-containing compound with the formula K3(N2)4 was formed instead.

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Fig. 1: Single-crystal X-ray diffraction data in compressed to 50 GPa and laser heated via direct coupling KN3 without a pressure medium.
Fig. 2: Raman spectra of X-ray-unexposed and -exposed KN3 before and after laser heating at around 50 GPa.
Fig. 3: Volumes per formula unit of K–N compounds investigated here.
Fig. 4: Vibrational frequencies of P6/mmm K2N6.
Fig. 5: Experimental data on I41/amd K3(N2)4 synthesized at 30 GPa by laser heating of KN3.

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Data availability

The datasets generated during and/or analysed during the current study are available at https://doi.org/10.6084/m9.figshare.19236573 (ref. 95), https://doi.org/10.6084/m9.figshare.19236609 (ref. 96) and https://doi.org/10.6084/m9.figshare.19228086.v1 (ref. 97). CSD 2022907 and 2094084 contain crystallographic data for the K3(N2)4 and K2N6 structures. These data can be obtained free of charge from FIZ Karlsruhe at www.ccdc.cam.ac.uk/structures. Source Data are provided with this paper.

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Acknowledgements

This work at ISSP was supported by the National Natural Science Foundation of China (grant nos. 11504382, 21473211, 11674330, 51672279, 11874361, 11774354 and 51727806), the CASHIPS Director’s Fund (grant no. YZJJ201705), the Chinese Academy of Science (grant nos. YZ201524 and YZJJ2020QN22) and a Science Challenge Project (no. TZ201601). This research at Carnegie and APS was sponsored by the Army Research Office and was accomplished under the Cooperative Agreement Number W911NF-19-2-0172. A.R.O., I.C. and A.I.S acknowledge funding from Russian Science Foundation (grant no. 19-72-30043). GeoSoilEnviroCARS (The University of Chicago, Sector 13), Advanced Photon Source (APS), Argonne National Laboratory is supported by the National Science Foundation—Earth Sciences (EAR-1634415). Use of the GSECARS Raman System was supported by the NSF MRI Proposal (EAR-1531583). The Advanced Photon Source is a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract no. DE-AC02-06CH11357. The theoretical calculations were performed using Arkuda and Oleg supercomputer of Skoltech.

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  1. Eran Greenberg

    Present address: Applied Physics Division SNRC, Yavne, Israel

Authors and Affiliations

  1. Key Laboratory of Materials Physics, Institute of Solid State Physics, HFIPS, Chinese Academy of Sciences, Hefei, China

    Yu Wang, Xiao Zhang & Shu-qing Jiang

  2. Earth and Planets Laboratory, Carnegie Institution of Washington, Washington, DC, USA

    Maxim Bykov, Elena Bykova & Alexander F. Goncharov

  3. Department of Mathematics, Howard University, Washington, DC, USA

    Maxim Bykov

  4. Skolkovo Institute of Science and Technology, Skolkovo Innovation Center, Moscow, Russia

    Ilya Chepkasov, Artem Samtsevich & Artem R. Oganov

  5. Center for Advanced Radiations Sources, University of Chicago, Chicago, IL, USA

    Eran Greenberg, Stella Chariton & Vitali B. Prakapenka

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Contributions

Y.W., M.B. and A.F.G. conceived the research and designed the experiments. Y.W., M.B., X.Z., E.G., S.C., V.B.P. and S.-q.J performed the experiment. E.B., Y.W., M.B. and A.F.G. analysed the data. I.C., A.S. and A.R.O. performed and analysed the calculations. A.F.G., Y.W., M.B. and A.S. wrote the manuscript. All authors reviewed and discussed the manuscript during preparation.

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Correspondence to Alexander F. Goncharov.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–11, Tables 1–5 and an ORTEP illustration of the crystal structures.

Supplementary Data 1

Crystallographic structure file for K2N6 (CCDC 2094084).

Supplementary Data 2

Crystallographic structure file for K3(N2)4 (CCDC 2022907).

Supplementary Data 3

Source data for Supplementary Figs. 5 and 6a,b, and uncompressed ascii data.

Supplementary Data 4

Source data for Supplementary Fig. 9 and uncompressed ascii data.

Supplementary Data 5

Source data for Supplementary Fig. 11 and ascii data.

Source data

Source Data Fig. 3

Uncompressed ascii data.

Source Data Fig. 4

Uncompressed ascii data.

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Wang, Y., Bykov, M., Chepkasov, I. et al. Stabilization of hexazine rings in potassium polynitride at high pressure. Nat. Chem. 14, 794–800 (2022). https://doi.org/10.1038/s41557-022-00925-0

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  • DOI: https://doi.org/10.1038/s41557-022-00925-0

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