Anion–Cation Bonding and Structure–Property Relationships of Three cyclo-Pentazolate Compounds

Abstract

The all-nitrogen cyclo-pentazolate (c-N5 –) anion has attracted considerable attention because of its potential applications in high-energy density materials. However, achieving comprehensive insight into the chemical properties of c-N5 – is challenging because of its complex chemical behavior. To elucidate this behavior, we stabilized the c-N5 – anion by forming its triaminoguanidinium (1) and 4-nitro-(3,4-diamino-1,2,4-triazolium-5-yl)-1H-pyrazolium (2) salts and its cocrystal (3) of a 1:1 ratio of 3,3-dinitroazetidinium pentazolate to 3,3-dinitroazetidine. X-ray single-crystal analysis confirmed that the c-N5 – anion combined with a sterically hindered cation exhibits a highly active π-system. This is characterized by the intermolecular p−π, intramolecular π–π, and intermolecular nitro−π interactions, arising from the binding of the π-face of c-N5 – to the amino group, electron-rich aromatic ring, and nitro group, respectively. In combination with hydrogen bonds, these interactions synergistically sustain the stability of the c-N5 – derivatives. Electronic structure calculations provided additional information on the physicochemical properties of these compounds. Remarkably, the predicted detonation velocity of 1 is higher than that of RDX among the new materials. This study broadens the understanding of the bonding of c-N5 – with its counterions and sheds more light on the structure–property relationships of pentazolate compounds.

Synthesis, characterization, and comparison of explosive hexaamminecobalt(III) and nitropentamminecobalt(III) cyclopentazolate (cyclo‐N5−) salts

“…[4] The stability of cyclo-N 5 À anions is influenced by different coordination modes, and recent research has confirmed that π-π interactions and hydrogen bonding are crucial for stabilizing cyclo-N 5 À anions. [5] The cyclo-N 5…”

Synthesis and characterization of cyclo-pentazolate salts of iron(iii) and aluminum(iii)

“…5a-f) represent areas of high and low close contacts, respectively. 31,32 Of the six crystal environments of cyclo-N 5 − anions in compound 1 (named 1i- 1vi), 1i, 1ii, 1iv, and 1v are stabilized by five hydrogen bonds with water molecules, and 1iii and 1vi are stabilized by four hydrogen bonds with water molecules. The Hirshfeld surfaces of 1i, 1ii, 1iv, and 1v are pentagonal, with areas of high close contact mainly distributed at the edges of the surfaces, while those of 1iii and 1vi have an irregular block shape, with an uneven distribution of areas of high close contact.…”

A molecular dynamics simulation study of thermal transport in hydrazinium cyclo-pentazolate

“…From the published physicochemical properties, the cyclopentazolate salts (CPSs) have exhibited substantial difference from the conventional HEDMs, e.g. trinitrotoluene (TNT), Royal Demolition Explosive (RDX) and High Melting Explosive (HMX), in terms of the decomposition temperature and density, together with the formation heat and the detonation velocity [11,12]. To understand these differences, computational work is quickly followed, employing the DFT calculation [7,13] and ab initio calculations [14] based on the single-crystal structures of CPSs, which leads to a better understanding of the noncovalent interaction between molecules and the energy change after bond-breaking [15].…”