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

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.

Synthesis of AgN5 and its extended 3D energetic framework.

The pentazolate anion, as a polynitrogen species, holds great promise as a high-energy density material for explosive or propulsion applications. Designing pentazole complexes that contain minimal non-energetic components is desirable in order to increase the material's energy density. Here, we report a solvent-free pentazolate complex, AgN5, and a 3D energetic-framework, [Ag(NH3)2]+[Ag3(N5)4]-, constructed from silver and cyclo-N5-. The complexes are stable up to 90 °C and only Ag and N2 are observed as the final decomposition products. Efforts to isolate pure AgN5 were unsuccessful due to partial photolytical and/or thermal-decomposition to AgN3. Convincing evidence for the formation of AgN5 as the original reaction product is presented. The isolation of a cyclo-N5- complex, devoid of stabilizing molecules and ions, such as H2O, H3O+, and NH4+, constitutes a major advance in pentazole chemistry.

A Symmetric Co(N5 )2 (H2 O)4 ⋠4 H2 O High-Nitrogen Compound Formed by Cobalt(II) Cation Trapping of a Cyclo-N5- Anion.

The reactions of (N5 )6 (H3 O)3 (NH4 )4 Cl with Co(NO3 )2 ⋅6 H2 O at room temperature yielded Co(N5 )2 (H2 O)4 ⋅4 H2 O as an air-stable orange metal complex. The structure, as determined by single-crystal X-ray diffraction, has two planar cyclo-N5- rings and four bound water molecules symmetrically positioned around the central metal ion. Thermal analysis demonstrated the explosive properties of the material.