Recent advances in the syntheses and properties of polynitrogen pentazolate anion cyclo-N₅⁻ and its derivatives

Abstract

The pentazolate anion, or cyclo-N5-, which is a five-membered ring composed solely of nitrogen atoms, has a unique structure among polynitrogen compounds. Cyclo-N5- is receiving ever-increasing levels of attention because of its potential ability to store large amounts of energy compared to the azide ion, its environmentally friendly decomposition products, and its carbon- and hydrogen-free composition, which are promising characteristics for advancing the field of high-energy-density materials (HEDMs), that include explosives, oxidisers, and propellants in closed environments. In this review, we provide a detailed introduction to cyclo-N5- and cover the following topics: (1) substituted pentazoles as precursors of cyclo-N5-, with a focus on the syntheses and stabilities of substituted pentazole derivatives; (2) routes to cyclo-N5- through cleavage of C-N bonds in substituted pentazoles, during which competitive reactions between pentazole decomposition and C-N bond cleavage need to be considered to ensure a successful outcome; (3) complexes of cyclo-N5-, summarising recent progress toward producing cyclo-N5--based complexes through the assembly of isolated cyclo-N5- with both metallic and nonmetallic components; and (4) interactions between cyclo-N5- and metal cations and non-metal species, as well as factors that influence the stability of these complexes; in particular, the thermal stabilities of prepared cyclo-N5- salts are discussed. This review summarises recent studies and is intended to improve the understanding of polynitrogen chemistry while supporting further research into its potential application as an efficient, safe, and environmentally friendly HEDM.

Coplanar Fused Heterocycle‐Based Energetic Materials

“…Figure 2 shows that the structures of two large conjugated anions were all nearly planar. The physicochemical and energetic properties of nitroamino-functionalized 1,2,4-Triazole[4,3-b] [1,2,4,5] tetrazines and their salts were showed in Table 2. The density of 2 was 1.76 g · cm À 3 , while its ionic derivatives show higher densities of 1.76-1.80 g · cm À 3 .…”

“…The modern energetic materials were required to focusing on more integrated properties in order to meet the demands of military and civilian development [1][2][3]. The key demands include high energetic performance, mechanical insensitivity, thermal stability, decomposition products environmentally-benign and so on [4][5][6][7][8].…”

Pentapnictogen heterocyclic monoanions: Structure, stability, and aromaticity

“…All‐inorganic aromatic clusters have been hotly pursued for many years . Among them, the planar pentapnictogen ring anions are unique because they are isoelectronic analogs of the cyclopentadienyl anion (Cp − ), promising their potential considerable aromaticity.…”

“…All-inorganic aromatic clusters have been hotly pursued for many years. [1,2] Among them, the planar pentapnictogen ring anions are unique because they are isoelectronic analogs of the cyclopentadienyl anion (Cp − ), promising their potential considerable aromaticity. In particular, many efforts are devoted to the cyclopentazole anion (cyclo-N 5 − ), because polynitrogen compounds are potential high-energy-density materials although their synthesis and isolation are rather challenging.…”

“…In particular, many efforts are devoted to the cyclopentazole anion (cyclo-N 5 − ), because polynitrogen compounds are potential high-energy-density materials although their synthesis and isolation are rather challenging. [2] Theoretical calculations revealed that planar cyclo-N 5 − is stable with large aromatic stabilization energy and considerable barrier for fragmentation, and could be isolated in an inert matrix at low temperature. [3] It was detected first in gas phase and recently in solution.…”