Growing catenated nitrogen atom chains.

Within the field of materials science, high-nitrogen compounds represent an important class of energetic materials. As a result of the existence of a large number of inherently energetic N N or N=N bonds within the molecules, highnitrogen compounds possess very high positive heats of formation, thereby making them intrinsically high-energy materials. The energy of most compounds with high-nitrogen content mainly derives from the transformation of nitrogencontaining bonds. Such transformations are always accompanied by the release of enormous amounts of energy, which originates from the breaking and rearrangement of the highly energetic bonds, including N N (160 kJmol ), N=N (418 kJmol ), and N N (954 kJmol ) bonds, during the explosion. In general, the higher nitrogen content means a higher heat of formation, which in turn leads to a higher energetic performance. From the viewpoint of organic chemistry, the design and synthesis of new high-nitrogen structures which can challenge or overcome the limit of the nitrogen content of existing compounds has unquestionably attracted significant interest from the academic community. With this background, continuing and dedicated efforts have been devoted to developing new strategies for high-nitrogen structures. However, in most cases, high nitrogen content and stability tend to be mutually exclusive, thereby making the synthesis and isolation of such highly energetic materials an interesting and enormous challenge. In the early studies on high-nitrogen compounds, scientists mainly focused on the synthetic strategy of incorporating one or more azido groups into the nitrogen-rich molecular backbone, with the aim of achieving an ultrahigh nitrogen content. Since organic polyazide-substituted compounds have very high heats of formation, as one azido group adds approximately 87 kcalmol 1 of endothermicity to the molecule, this class of high-nitrogen compounds has been at the forefront of high-energy research. By virtue of this strategy, a number of polyazido compounds with very high nitrogen content have been reported. Of these, tetraazidomethane is a well-known polyazido compound that was synthesized and isolated successfully with the highest nitrogen content (93.33% N). Indeed, most high-nitrogen polyazides possess very high positive heats of formation and, therefore, display excellent explosive performance. However, most of them are notorious for their extreme sensitivity toward external forces such as heat, shock, friction, and electrostatic discharge, which significantly limits their application potential for use on a large scale. Recently, in pursuit of new high-nitrogen structures, a fascinating class of compounds containing long catenated nitrogen atom chains has been reported. Tartakovskii and coworkers as well as Klapçtke et al. have successfully designed and synthesized a 1,3-bis-(nitroimido)-1,2,3-triazolate anion (1, Scheme 1), which has a chain of seven catenated