A series of energetic metal pentazolate hydrates

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Singly or doubly bonded polynitrogen compounds can decompose to dinitrogen (N2) with an extremely large energy release. This makes them attractive as potential explosives or propellants1,2,3, but also challenging to produce in a stable form. Polynitrogen materials containing nitrogen as the only element exist in the form of high-pressure polymeric phases4,5,6, but under ambient conditions even metastability is realized only in the presence of other elements that provide stabilization. An early example is the molecule phenylpentazole, with a five-membered all-nitrogen ring, which was first reported in the 1900s7 and characterized in the 1950s8,9. Salts containing the azide anion (N3)10,11,12 or pentazenium cation (N5+)13 are also known, with compounds containing the pentazole anion, cyclo-N5, a more recent addition14,15,16. Very recently, a bulk material containing this species was reported17 and then used to prepare the first example of a solid-state metal–N5 complex18. Here we report the synthesis and characterization of five metal pentazolate hydrate complexes [Na(H2O)(N5)]·2H2O, [M(H2O)4(N5)2]·4H2O (M = Mn, Fe and Co) and [Mg(H2O)6(N5)2]·4H2O that, with the exception of the Co complex, exhibit good thermal stability with onset decomposition temperatures greater than 100 °C. For this series we find that the N5 ion can coordinate to the metal cation through either ionic or covalent interactions, and is stabilized through hydrogen-bonding interactions with water. Given their energetic properties and stability, pentazole–metal complexes might potentially serve as a new class of high-energy density materials19 or enable the development of such materials containing only nitrogen20,21,22,23. We also anticipate that the adaptability of the N5 ion in terms of its bonding interactions will enable the exploration of inorganic nitrogen analogues of metallocenes24 and other unusual polynitrogen complexes.

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Figure 1: Synthetic routes and single-crystal X-ray analysis of complexes 2–6.
Figure 2: Spectroscopic analysis of complexes 2–6.
Figure 3: Thermal analysis of complexes 2–6.
Figure 4: Decomposition behaviour of complex 2.

Change history

  • 23 May 2018

    In this Letter, under Methods subsection '[Na(H2O)(N5)]·2H2O (2)', the description "the intermediate product arylpentazole (5.000 g, 26.18 mmol)" should read "the intermediate product sodium salt of arylpentazole (5.000 g, 21.64 mmol)". In the legend of Fig. 3, we add that "All temperature points in the stability study were onset temperatures." to avoid misunderstanding. These corrections have been made online.


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This work was supported by the NSAF (U1530101) and the National Natural Science Foundation of China (51374131). We thank C. Zhang and B. Hu for co-exploring the rupture of C–N bonds in phenylpentazole at the beginning of the project, Z. Zhang for analysis of the crystal structures, L. Lu for analysis of Raman and NMR spectra, and L. Cheng for DSC measurements of decomposition kinetics.

Author information

Y.X., P.W. and M.L. conceived and designed the experiments. C.S. and Q.L. prepared N5 solid. Y.X. and Q.W. performed the crystal experiments. Y.X., Q.W. and P.W. performed the measurements and analysed the data. P.W. performed the DFT calculations. Y.X., P.W. and M.L. co-wrote the manuscript. All authors contributed to the overall scientific interpretation and edited the manuscript.

Correspondence to Pengcheng Wang or Ming Lu.

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Competing interests

The authors declare no competing financial interests.

Additional information

Reviewer Information Nature thanks K. O. Christe, T. M. Klapötke and H. Östmark for their contribution to the peer review of this work.

Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

An erratum to this article is available online at https://doi.org/10.1038/s41586-018-0142-y.

Extended data figures and tables

Extended Data Figure 1 High-resolution mass spectrum and 15N NMR spectra of 2.

a, Single mass and formula analysis of 2. b, 15N NMR spectra of 2 (in DMSO-d6, MeNO2 as external standard). c, 15N NMR spectra of NaN5 (15N labelled on N2) before column chromatography (in CD3OD, MeNO2 as external standard); inset, synthetic scheme for the preparation of 15N-labelled N5.

Extended Data Figure 2 Molecular structures of 2–6 shown by ORTEP representations.

a, b, Ball-and-stick packing diagrams of 2, viewed normal to (001) with hydrogen bonds (a), and normal to (010). (b). ce, Molecular structures of 35, respectively, viewed normal to (100), shown by ORTEP representations. fk, Ball-and-stick packing diagrams of 35, viewed normal to (001) (fh), and normal to (100) (ik). l, Hydrogen bonds in the packing of 6, and unit cell parameters. m, A unit cell of 6 viewed normal to (100), shown by ORTEP representation. n, Ball-and-stick packing diagram of 6 viewed normal to (001).

Extended Data Figure 3 XPS spectra of complexes 1–6.

af, Survey spectra of 16, respectively. gl, Narrow scan of the N 1s peak of 1 (g), 2 (h), 3 (j), 4 (k), 5 (l) and 6 (i). The experimental and fitting curves are shown in black and red, with the pyrrolic (N1), pyridinic (N2) and quaternary (N3) nitrogen curves shown in blue, pink and green, respectively.

Extended Data Figure 4 Theoretical simulation of complexes 2–6.

ae, Model deformation density maps of 2 (a), 3 (c), 4 (d), 5 (e) and 6 (b) in the plane defined by the N5 rings. Scale in a.u. The lone pair of electrons on N is attracted by H+, Mn2+, Fe2+ and Co2+. fk, Molecular orbital correlation diagrams for interactions between M2+ (M = Mn, Fe and Co) and N5 with and without H2O in complexes: Mn(N5)2 and Mn(H2O)4(N5)2 (f, g); Fe(N5)2 and Fe(H2O)4(N5)2. (h, i); Co(N5)2 and Co(H2O)4(N5)2. (j, k) The positive and negative phases of the molecular orbitals are shown in deep red and green; hydrogen, nitrogen, oxygen and metal atoms are shown in white, blue, red and brown respectively.

Extended Data Figure 5 DSC measurement of the decomposition kinetics of complexes 2–4 and 6, and their apparent activation energies.

ad, DSC curves of complexes at heating rates of 2, 5, 8 and 10 °C min–1: 2 (a), 3 (b), 4 (c), and 6 (d). e, Apparent activation energy Ea of the first exothermic peak of complexes 24 and 6, calculated using the Kissinger method. b, heating rate; Tp, peak temperature.

Extended Data Figure 6 TG–DSC–MS measurements of complexes 5 and 6.

a, b, TG–DSC–MS curves of 5 (a) and 6 (b); ions of m/z 14, 18, 28 and 42 are selected. Note explosion in a.

Extended Data Figure 7 IR spectra of complexes 3–6 after heating at different temperatures.

a, Complexes 36 after heating at 60 °C for 0.5 h, denoted as 3′–6′, respectively. cyclo-N5 remains after the partial loss of water, as shown in the highlighted regions. b, Complexes 36 heated at 110 °C for 0.5 h, denoted as 3″–6″, respectively. The signal for N3 indicates that cyclo-N5 decomposed under these conditions. ce, Temperature-dependent IR spectra of 46 in air. Significant decomposition of cyclo-N5 occurs at 95, 65 and 100 °C, respectively.

Extended Data Table 1 Crystallographic data for 2–6
Extended Data Table 2 Theoretical bond critical point data for 2–6, Co(CN)63–, and Co(NH3)5H2O3+
Extended Data Table 3 Hydrogen bonds of 2–6

Supplementary information

Supplementary Tables

This file contains Supplementary Tables 1-4. (PDF 163 kb)

Supplementary Data

This file contains crystallographic data for [Na(H2O)(N5)]•2H2O. (CIF 84 kb)

Supplementary Data

This file contains crystallographic data for [Mn(H2O)4(N5)2]•4H2O. (CIF 67 kb)

Supplementary Data

This file contains crystallographic data for [Fe(H2O)4(N5)2]•4H2O. (CIF 84 kb)

Supplementary Data

This file contains crystallographic data for [Co(H2O)4(N5)2]•4H2O. (CIF 11 kb)

Supplementary Data

This file contains crystallographic data for [Mg(H2O)6(N5)2]•4H2O. (CIF 12 kb)

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Xu, Y., Wang, Q., Shen, C. et al. A series of energetic metal pentazolate hydrates. Nature 549, 78–81 (2017) doi:10.1038/nature23662

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