Anion–Cation Bonding and Structure–Property Relationships of Three <i>cyclo</i>-Pentazolate Compounds
Chen Yang, Lei Chen, Siyuan Chen, Wenkang Wu, Wanli Yuan, Jie Yao, Chong Zhang, Chengguo Sun, Yang Du, Bingcheng Hu
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.