Stability of nitrogen-oxygen cages N12O2, N14O2, N14O3, and N16O4

Abstract

Molecules consisting entirely of nitrogen have been studied extensively for their potential as high energy density materials (HEDM). However, many such molecules are too unstable to serve as practical energy sources. This has prompted many studies of molecules that are mostly nitrogen but which incorporate heteroatoms into the structure to provide additional stability. In the current study, cages of three-coordinate nitrogen are viewed as candidates for stabilization by insertion of oxygen atoms into the nitrogen framework. Cages of N12, N14, and N16 with four-membered rings are studied because four-membered rings have been previously shown to be a destabilizing influence. Insertion of oxygen atoms, which converts N-N bonds to N-O-N bonding groups, relieves ring strain and can potentially result in stable molecules. These molecules are studied by theoretical calculations, using Hartree-Fock and Moller-Plesset (MP3 and MP4) theories, to determine the dissociation energies of the molecules. The primary result of the study is that stable molecules can result from oxygen insertion but that oxygen-oxygen proximity destabilizes the insertion products.

Figure 1

The 0440 isomer of N₁₂ (D_2d point group symmetry). The molecule has two pairs of edge-sharing four-membered rings.

Figure 2

The 0441 isomer of N₁₄ (C_2v point group symmetry). The molecule has two pairs of edge-sharing four-membered rings.

Figure 3

The 0522 isomer of N₁₄ (C_2v point group symmetry). The molecule has five four-membered rings as an edge-sharing pair and a band of three.

Figure 4

The 0604 isomer of N₁₆ (D_2d point group symmetry). The molecule has six four-membered rings as two bands of three.

Figure 5

The N₁₂O₂ molecule that results when N₁₂ 0440 (Figure 1) has oxygen atoms inserted into bonds shared by four-membered rings. Symmetry-independent bonds in the molecule are labeled. The molecule has D_2d point group symmetry.

Figure 6

The N₁₄O₂ molecule that results when N₁₄ 0441 (Figure 2) has oxygen atoms inserted into bonds shared by four-membered rings. Symmetry-independent bonds in the molecule are labeled. The molecule has C_2v point group symmetry.

Figure 7

The N₁₄O₃ molecule that results when N₁₄ 0522 (Figure 3) has oxygen atoms inserted into bonds shared by four-membered rings. Symmetry-independent bonds in the molecule are labeled. The molecule has C_2v point group symmetry.

Figure 8

The N₁₆O₄ molecule that results when N₁₆ 0604 (Figure 4) has oxygen atoms inserted into bonds shared by four-membered rings. Symmetry-independent bonds in the molecule are labeled. The molecule has D_2d point group symmetry.