N5+: A Novel Homoleptic Polynitrogen Ion as a High Energy Density Material

Abstract

Only the third known example of a homoleptic polynitrogen species besides N2 and N3−, the N5+ ion possesses surprising stability and can be isolated on a macroscopic scale as its AsF6− salt. The assigment of the C2v‐symmetric structure (shown schematically) predicted by calculations was supported by IR and Raman as well as 14N and 15N NMR spectroscopic studies of the isotopically labeled product.

A theoretical study of the nitrogen clusters formed from the ions N3−, N5+, and N5−

“…This should be compared to the experimental 14 at the B3LYP and CCSD͑T͒ levels of theory. The present CASPT2 results were obtained with the five orbitals active.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] Besides their theoretical interest, these structures have attracted interest because of their possible use as high energy-density materials ͑HEDM͒, i.e., the large ratio between the energy released in a fragmentation reaction and the specific weight. Since 1999 there is exciting new experimental interest in these compounds: Christe et al 14 described the synthesis of N 5 ϩ as a salt with AsF 6 Ϫ . The cation is the first new all-nitrogen species to be isolated in more than a century, and only the third known besides N 2 and N 3 Ϫ .…”

Backbone NxH compounds at high pressures

“…There are numerous reports on synthesis of complex energetic materials containing chains of nitrogen atoms: N5, N8, and even N10 [6][7][8] and complex "salts" such as TAG-MNT [9], but these materials require other elements for stabilization and their synthesis remains quite challenging. Rich in nitrogen N-H systems appear to be the most attractive as they would be the most energy-density efficient and because hydrogen tends to stabilize low bond order nitrogen compounds (e.g., hydrazine).…”

Stability of Nitrogen—Oxygen Cages N12O2, N14O2, N14O3 and N16O4

“…Cage isomers of N 8 and N 12 have also been shown 7-10 by theoretical calculations to be unstable. Experimental progress in the synthesis of nitrogen molecules has been very encouraging, with the N 5 + and N 5 − ions having been recently produced 11,12 Figures 1-4, respectively. These molecules are subjected to oxygen insertion to relieve ring strain in the four-membered rings, and the stability of the oxygen insertion products is determined to identify which ones may be viable high energy density materials.…”