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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Christe, K. O. Polynitrogen chemistry enters the ring. Science 355, 351–353 (2017)
Hirshberg, B., Gerber, R. B. & Krylov, A. I. Calculations predict a stable molecular crystal of N8 . Nat. Chem. 6, 52–56 (2014)
Christe, K. O. Recent advances in the chemistry of N5+, N5− and high-oxygen compounds. Propellants Explos. Pyrotech. 32, 194–204 (2007)
Eremets, M. I., Gavriliuk, A. G., Trojan, I. A., Dzivenko, D. A. & Boehler, R. Single-bonded cubic form of nitrogen. Nat. Mater. 3, 558–563 (2004)
Steele, B. A. & Oleynik, I. I. Sodium pentazolate: a nitrogen rich high energy density material. Chem. Phys. Lett. 643, 21–26 (2016)
Steele, B. A. et al. High-pressure synthesis of a pentazolate salt. Chem. Mater. 29, 735–741 (2017)
Curtius, T., Darapsky, A. & Müller, E. Die sogenannten Pentazol-Verbindungen von J. Lifschitz. Ber. Dtsch. Chem. Ges. 48, 1614–1634 (1915)
Huisgen, R. & Ugi, I. Zur Lösung eines klassischen Problems der organischen Stickstoff-Chemie. Angew. Chem. 68, 705–706 (1956)
Huisgen, R. & Ugi, I. Pentazole, I. Die Lösung Eines Klassischen Problems der Organischen Stickstoffchemie. Chem. Ber. 90, 2914–2927 (1957)
Fehlhammer, W. P. & Beck, W. Azide chemistry – an inorganic perspective, Part I metal azides: overview, general trends and recent developments. Z. Anorg. Allg. Chem. 639, 1053–1082 (2013)
Haiges, R. et al. Polyazide chemistry: preparation and characterization of Te(N3)4 and [P(C6H5)4]2[Te(N3)6] and evidence for [N(CH3)4][Te(N3)5]. Angew. Chem. Int. Ed. 42, 5847–5851 (2003)
Crawford, M. J., Ellern, A. & Mayer, P. UN213−: a structurally characterized binary actinide heptaazide anion. Angew. Chem. Int. Ed. 44, 7874–7878 (2005)
Christe, K. O., Wilson, W. W., Sheehy, J. A. & Boatz, J. A. N5+: a novel homoleptic polynitrogen ion as a high energy density material. Angew. Chem. Int. Ed. 38, 2004–2009 (1999)
Vij, A., Pavlovich, J. G., Wilson, W. W., Vij, V. & Christe, K. O. Experimental detection of the pentaazacyclopentadienide (pentazolate) anion, cyclo-N5−. Angew. Chem. Int. Ed. 41, 3051–3054 (2002)
Östmark, H. et al. Detection of pentazolate anion (cyclo-N5−) from laser ionization and decomposition of solid p-dimethylaminophenylpentazole. Chem. Phys. Lett. 379, 539–546 (2003)
Bazanov, B. et al. Detection of cyclo-N5− in THF solution. Angew. Chem. Int. Ed. 55, 13233–13235 (2016)
Zhang, C., Sun, C., Hu, B., Yu, C. & Lu, M. Synthesis and characterization of the pentazolate anion cyclo-N5− in (N5)6(H3O)3(NH4)4Cl. Science 355, 374–376 (2017)
Zhang, C. et al. A symmetric Co(N5)2(H2O)4·4H2O high-nitrogen compound formed by cobalt(II) cation trapping of a cyclo-N5− anion. Angew. Chem. Int. Ed. 56, 4512–4514 (2017)
Klapötke, T. M. & Hammerl, A. in Comprehensive Heterocyclic Chemistry III (eds Katritzky, A. R., Ramsden, C. A., Scriven, E. F. V. & Taylor, R. J. K. ) 739–757 (Elsevier, 2008)
Butler, R. N., Stephens, J. C. & Burke, L. A. First generation of pentazole (HN5, pentazolic acid), the final azole, and a zinc pentazolate salt in solution: A new N-dearylation of 1-(p-methoxyphenyl) pyrazoles, a 2-(p-methoxyphenyl) tetrazole and application of the methodology to 1-(p-methoxyphenyl) pentazole. Chem. Commun. 1016–1017 (2003)
Schroer, T., Haiges, R., Schneider, S. & Christe, K. O. The race for the first generation of the pentazolate anion in solution is far from over. Chem. Commun. 1607–1609 (2005)
Choi, C., Yoo, H. W., Goh, E. M., Cho, S. G. & Jung, Y. Ti(N5)4 as a potential nitrogen-rich stable high-energy density material. J. Phys. Chem. A 120, 4249–4255 (2016)
Burke, L. A., Butler, R. N. & Stephens, J. C. Theoretical characterization of pentazole anion with metal counter ions. Calculated and experimental 15N shifts of aryldiazonium, -azide and -pentazole systems. J. Chem. Soc., Perkin Trans. 2 1679–1684 (2001)
Tsipis, A. C. & Chaviara, A. T. Structure, energetics, and bonding of first row transition metal pentazolato complexes: a DFT study. Inorg. Chem. 43, 1273–1286 (2004)
Perera, S. A., Gregusová, A. & Bartlett, R. J. First calculations of 15N–15N J values and new calculations of chemical shifts for high nitrogen systems: a comment on the long search for HN5 and its pentazole anion. J. Phys. Chem. A 113, 3197–3201 (2009)
Crawford, M. J. & Mayer, P. Structurally characterized ternary U–O–N compound, UN4O12: UO2(NO3)2·N2O4 or NO+UO2(NO3)3−? Inorg. Chem. 44, 8481–8485 (2005)
Malar, E. J. P. Do penta- and decaphospha analogues of lithocene anion and beryllocene exist? Analysis of stability, structure, and bonding by hybrid density functional study. Inorg. Chem. 42, 3873–3883 (2003)
Zhang, X., Yang, J., Lu, M. & Gong, X. Structure, stability and intramolecular interaction of M(N5)2 (M = Mg, Ca, Sr and Ba): a theoretical study. RSC Adv. 5, 21823–21830 (2015)
Bianchi, R., Gervasio, G. & Marabello, D. Experimental electron density analysis of Mn2(CO)10: metal–metal and metal–ligand bond characterization. Inorg. Chem. 39, 2360–2366 (2000)
Stowasser, R. & Hoffmann, R. What do the Kohn–Sham orbitals and eigenvalues mean? J. Am. Chem. Soc. 121, 3414–3420 (1999)
Zhang, C., Sun, C., Hu, B. & Lu, M. Investigation on the stability of multisubstituted arylpentazoles and the influence on the generation of pentazolate anion. J. Energ. Mater. 34, 103–111 (2016)
Frisch, M. J. et al. Gaussian 09, Revision A.02 (Gaussian, Inc., 2009)
Becke, A. D. Density functional thermochemistry. III. The role of exact exchange. J. Chem. Phys. 98, 5648–5652 (1993)
Lee, C., Yang, W. & Parr, R. G. Development of the Colle–Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B 37, 785–789 (1988)
Hay, P. J. & Wadt, W. R. Ab initio effective core potentials for molecular calculations. Potentials for K to Au including the outermost core orbitals. J. Chem. Phys. 82, 299–310 (1985)
Lu, T. & Chen, F. Multiwfn: a multifunctional wavefunction analyzer. J. Comput. Chem. 33, 580–592 (2012)
Cremer, D. & Kraka, E. Chemical bonds without bonding electron density — does the difference electron-density analysis suffice for a description of the chemical bond? Angew. Chem. Int. Edn 23, 627–628 (1984)
SAINT v7.68A (Bruker AXS Inc., 2009)
Sheldrick, G. M. SHELXL-2014/7 (Univ. Göttingen, 2014)
SADABS v2008/1 (Bruker AXS Inc., 2008)
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.
The authors declare no competing financial interests.
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
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−.
a, b, Ball-and-stick packing diagrams of 2, viewed normal to (001) with hydrogen bonds (a), and normal to (010). (b). c–e, Molecular structures of 3–5, respectively, viewed normal to (100), shown by ORTEP representations. f–k, Ball-and-stick packing diagrams of 3–5, viewed normal to (001) (f–h), and normal to (100) (i–k). 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).
a–f, Survey spectra of 1–6, respectively. g–l, 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.
a–e, 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+. f–k, 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.
a–d, 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 2–4 and 6, calculated using the Kissinger method. b, heating rate; Tp, peak temperature.
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.
a, Complexes 3–6 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 3–6 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. c–e, Temperature-dependent IR spectra of 4–6 in air. Significant decomposition of cyclo-N5– occurs at 95, 65 and 100 °C, respectively.
This file contains Supplementary Tables 1-4. (PDF 163 kb)
This file contains crystallographic data for [Na(H2O)(N5)]•2H2O. (CIF 84 kb)
This file contains crystallographic data for [Mn(H2O)4(N5)2]•4H2O. (CIF 67 kb)
This file contains crystallographic data for [Fe(H2O)4(N5)2]•4H2O. (CIF 84 kb)
This file contains crystallographic data for [Co(H2O)4(N5)2]•4H2O. (CIF 11 kb)
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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