Stabilization of Cylindrical N₁₂ and N₁₈ by Phosphorus Substitution

Abstract

Molecules consisting entirely or predominantly of nitrogen are the subject of much research for their potential as high energy density materials (HEDM). The problem with many such HEDM candidates is their instability with respect to dissociation. For example, a low-energy dissociation path has been shown for a cylindrical cage isomer of N12. The instability is at least partially due to the ease of ring opening at triangles on either end of the molecule. In the current study, nitrogen cage molecules are examined to determine the stabilizing effect of substituting the triangle nitrogens with an element that more naturally forms triangles, namely phosphorus, which is valence isoelectronic with nitrogen. The cylindrical N12, and a larger analogue N18, form the structural basis for cage molecules of N6P6 and N12P6. Theoretical calculations using Hartree-Fock theory and perturbation theory (MP2 and MP4), along with the correlation-consistent basis sets of Dunning, have been carried out to determine dissociation energies along various pathways. The energies are discussed in terms of low-energy dissociation and the ability of the molecules to resist dissociation.

High-Pressure Photoinduced Synthesis of Polynitrogen in δ and ϵ Nitrogen Crystals Substitutionally Doped with CO

“…Experimentally, it is well-known that pressure favors the formation of nitrogen-rich materials, helping to overcome the energy barrier due to lone pair repulsion, as demonstrated by the employment of high pressure techniques in the synthesis of nitrides. − Some unsuccessful attempts to reduce the extreme pressure and temperature conditions for the synthesis of cg-N have been performed by using metallic catalysts or the azide ion as starting material instead of molecular nitrogen . On the other side, many computational studies searching for a convenient approach to reduce the instability of polynitrogen materials have reported the insertion of different heteroatoms (oxygen, , phosphorus, and carbon) into the polynitrogen framework to be efficient in relieving chain or ring strain in the case of several isolated molecular systems with different linear or cage , geometries, increasing both their thermodynamic and kinetic stability. In particular it has been found that for linear N x C 2 molecules the energy release properties vary linearly with the chain length and that the chains exhibit a good resistance to dissociation when terminated on both sides by CN groups .…”

From Tortoise-Shell-Like Molecular Segments to C4nH2nN2n (n = 3−8) Cages Stabilized by Alkenyl: A Theoretical Study

“…If they are further saturated by hydrogen only for those carbons in top and bottom polygons, a new series of C 4 n H 2 n N 2 n ( n = 3−8) cages in D nh ( n = 3−8) symmetry will be formed, as shown in Figure . During the investigation, some analogies of our title compounds, such as sunflower-like carbon−sulfur molecules, cylindrical N 18 and phosphorus substitution N 12 P 6 are found . To our knowledge, these designed title molecules have not been reported yet except a study of an analogy of C 24 H 12 N 12 molecule .…”

Chain or Ring: Which One Is Favorable in Nitrogen-Rich Molecules N6XHm, N8XHm, and N10XHm(X = B, Al, Ga,m= 1 and X = C, Si, Ge,m = 2)?

“…25−48 For instance, in addition to many synthesized stable azides, 25−36 a series of nitrogen-rich molecules containing N 7 , N 8 , N 10 , and N 11 nitrogen chain have been produced by introducing heteroatom C. 37−43 Theoretically, the nitrogen-rich cages were demonstrated to be more stable than the pure nitrogen cages when six nitrogen atoms were replaced by six phosphorus atoms in cylindrical N 12 and N 18 molecules. 49 In addition, a polymeric nitrogen chain encapsulated inside carbon nanotubes or fullerenes was also found to form new and stable hybrid molecules. 50,51 However, synthesizing more and more nitrogenrich molecule remains an active pursuit.…”