Besides N₂, What Is the Most Stable Molecule Composed Only of Nitrogen Atoms?

Abstract

Polynitrogen molecules have been studied systematically at high levels of ab initio and density functional theory (DFT). Besides N(2), the thermodynamically most stable N(n)() molecules, located with the help of a newly developed energy increment system, are all based on pentazole units. The geometric, energetic, and magnetic criteria establish pentazole (2) and its anion (3) to be as aromatic as their isoelectronic analogues, e.g., furan, pyrrole, and the cyclopentadienyl anion. The bond lengths in 2 and 3 are equalized; both have large aromatic stabilization energies (ASE) and also substantial magnetic susceptibility exaltations (Lambda). The C(s)() symmetric azidopentazole (14), a candidate for experimental investigation, is the lowest energy N(8) isomer but is still 196.7 kcal/mol higher in energy than four N(2) molecules. Octaazapentalene (12) with 10 pi electrons also is aromatic. The D(2)(d)() symmetric bispentazole (21) is the lowest energy N(10) minimum but is 260 kcal/mol higher in energy than five N(2) molecules. For strain-free molecules, the average deviation is +/-2.6 kcal/mol between the DFT energies and those based on the increment scheme. The increment scheme also provides estimates of the strain energies of polynitrogen compounds, e.g., tetraazatetrahedrane (8, 48.2 kcal/mol), octaazacubane (11, 192.6 kcal/mol), and N(20) (27, 294.6 kcal/mol), and is useful in searching for new high-energy-high-density materials.

Theoretical Insight into the Structure, Energetic Property and Thermal Stability of C6N6H12 Cages

“…Studies have proved that computational results of SE at the B3LYP/6-31G+(d,p) via homodesmotic process are reasonable [22,23,37,38,59] ) [61]. In the present work, the strain energies of C 6 N 6 H 12 cages are obtained by the homodesmotic reaction (1) and (2). For comparison, the following reactions are used to evaluate the SEs of hexaazaisowurtzitane and cubane, respectively: smaller the ring is, the greater distorted the molecule is, thus, the less the strain energy becomes.…”

“…A molecule Nx can undergo the reaction Nx→ (x/2) N2, a reaction that can be exothermic by more than 50 kcal/mol or more per nitrogen atom [1,2]. All-nitrogen molecules i.e., N 4 , N 5 , N 6 , N 7 , N 8 , N 10 , N 12 , N 18 , N 20 , N 24 , N 30 , and N 36 have been studied theoretically [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. There is also some research on nitrogen-rich molecules such as C x N y and O x N y species [22][23][24][25][26].…”

High‐Energy‐Density Materials: Synthesis and Characterization of N5+[P(N3)6]−, N5+ [B(N3)4]−, N5+ [HF2]−⋅n HF, N5+ [BF4]−, N5+ [PF6]−, and N5+ [SO3F]−

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] While most of the efforts were devoted to theoretical studies, the long-known existence of the stable azide anion (N 3 À ) [18] and the recent syntheses of stable salts of the pentanitrogen cation (N 5 + ) [1][2][3] have demonstrated the feasibility of experimentally pursuing polynitrogen-containing materials. The only known direct method for preparing N 5 + compounds is their synthesis from an [N 2 …”

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

“…[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 .…”