What are the roles of N3 and N5 rings in designing polynitrogen molecules?

A series of polynitrogen molecules composed by multiple cyclic-N(3) and/or cyclic-N(5) are systematically investigated by using DFT and MP2 methods. It is found that all energetically favored structures appear with a corner to corner connection between two rings for the cyclic-N(3) and/or the cyclic-N(5). Furthermore, straight interaction between the N(3)-rings would decrease the stability of cyclic-N(3) relative to the cyclic-N(3) radical and thus not favor the formation of a stable structure containing multiple cyclic-N(3), while the interaction between the N(5)-rings can improve the stability of cyclic-N(5) and tend to produce a stable structure composed by multiple cyclic-N(5). For the stable structure consisting of cyclic-N(3) and cyclic-N(5), the charge is transferred from cyclic-N(3) to cyclic-N(5), facilitating the stability of N(5), and the attacked site of the structure by the radicals is analyzed by condensed Fukui function. Finally, the stabilities of the structures N(3)(N(5))(3) and N(5)(N(5))(5) are investigated and demonstrated to be attributed to the charge transfer and the coordination number of N(3)-ring and N(5)-ring.