Bottom-up design of high-energy-density molecules (N2CO)n (n = 2–8)

Abstract

Seeking high-energy-density materials (HEDMs) with balanced huge energy release and good stability has remained quite a tough task for both experimentalists and theoreticians. The current HEDM design mostly concentrates on the chemical modification of either the skeletons or ligands. To increase the number of HEDM candidates, a novel design strategy is highly desired. In this paper, we computationally proposed a bottom-up strategy, i.e., a suitable HEDM seed (e.g., cyc-N₂CO) can form novel HEDMs while retaining good stability and good performance. Starting from the experimentally known diazirinone (cyc-N₂CO) as a “seed” and by considering various bond-addition channels (2 + 2/2 + 3/3 + 3 cyclo-addition at the NN/CO/C–N bonds), we found that the cyc-N₂CO dimer isomer 1 (i.e., (N₂CO)₂ containing a COCO ring with an exocyclic side-N₂ at each C-atom) possess the rate-determining barrier of 29.9 kcal mol⁻¹ and exothermicity of 168.7 kcal mol⁻¹ into 2N₂ + 2CO at the composite CBS-QB3 level. Moreover, the trimer and tetramer of cyc-N₂CO each possess high rate-determining barriers of 25.8 and 30.3 kcal mol⁻¹, respectively, at the CBS-QB3 level. Even higher oligomers with n = 5–8 have rate-determining barriers around 25 and 34 kcal mol⁻¹. The spiral skeletons were shown to have a contribution to their good inherent kinetic stability. By comparing the detonation properties with some known HEDM compounds, the oligomers of cyc-N₂CO may well deserve future synthetic trials for novel HEDMs. Our designed (N₂CO)_n with all the untouched NN bonds differed sharply from the recently reported high-pressure polymerized forms, in which all the double bonds have been transformed into single bonds. The present bottom-up strategy from an HEDM seed (i.e., cyc-N₂CO) to novel oligomeric HEDMs confirmed by the CBS-QB3 calculations seems to be quite promising and may open a new way of designing in the HEDM realm.