Synthesis and Characterization of cyclo-Pentazolate Salts of NH4+, NH3OH+, N2H5+, C(NH2)3+, and N(CH3)4

Chen Yang; Chong Zhang; Zhansheng Zheng; Chao Jiang; Jun Luo; Yang Du; Bingcheng Hu; Chengguo Sun; Karl O Christe

doi:10.1021/jacs.8b05106

Synthesis and Characterization of cyclo-Pentazolate Salts of NH₄⁺, NH₃OH⁺, N₂H₅⁺, C(NH₂)₃⁺, and N(CH₃)₄

J Am Chem Soc. 2018 Dec 5;140(48):16488-16494. doi: 10.1021/jacs.8b05106. Epub 2018 Nov 16.

Authors

Chen Yang¹, Chong Zhang¹, Zhansheng Zheng¹, Chao Jiang¹, Jun Luo¹, Yang Du¹, Bingcheng Hu¹, Chengguo Sun^{1

2}, Karl O Christe^{1

3}

Affiliations

¹ School of Chemical Engineering , Nanjing University of Science and Technology , Nanjing , Jiangsu 210094 , China.
² School of Chemical Engineering , University of Science and Technology Liaoning , Anshan , Liaoning 114051 , China.
³ Loker Hydrocarbon Research Institute and Department of Chemistry , University of Southern California , Los Angeles , California 90089-1661 , United States.

PMID: 30392354
DOI: 10.1021/jacs.8b05106

Abstract

A breakthrough in polynitrogen chemistry was recently achieved by our bulk synthesis of (N₅)₆(H₃O)₃(NH₄)₄Cl in which the cyclo-pentazolate anions were stabilized extensively by hydrogen bridges with the NH₄⁺ and OH₃⁺ cations. Significant efforts have been carried out to replace these nonenergetic cations and the Cl^- anion by more energetic cations. In this paper, the metathetical syntheses of cyclo-pentazolate salts containing the simple nitrogen-rich cations NH₄⁺, NH₃OH⁺, N₂H₅⁺, C(NH₂)₃⁺, and N(CH₃)₄⁺ are reported. These salts were characterized by their crystal structures; vibrational, mass, and multinuclear NMR spectra; thermal stability measurements; sensitivity data; and performance calculations. It is shown that the cyclo-pentazolates are more energetic than the corresponding azides but are thermally less stable decomposing in the range of 80 °C to 105 °C. As explosives, the hydrazinium and hydroxyl ammonium salts are predicted to match the detonation pressure of RDX but exhibit significantly higher detonation velocities than RDX and HMX with comparable impact and friction sensitivities. Although the ammonium salt has a lower detonation pressure than RDX, its detonation velocity also exceeds those of RDX and HMX. As a rocket propellant, the hydrazinium and hydroxyl ammonium salts are predicted to exceed the performances of RDX and HMX. The crystal structures show that the cyclo-pentazolate anions are generally stabilized by hydrogen bonds to the cations, except for the N(CH₃)₄⁺ salt which also exhibits strong cation-π interactions. This difference in the anion stabilization is also detectable in the vibrational spectra which show for the N(CH₃)₄⁺ salt a decrease in the cyclo-N₅^- stretching vibrations of about 20 cm^-1.