Explosive Soccer: Nitrogen Fullerene
A 60-atom molecule made entirely of nitrogen would store a tremendous amount of energy. According to Riad Manaa, a theoretical chemist in CChED, it might be possible to join six 10-atom nitrogen molecules into a soccer-ball-shaped molecule, akin to the carbon based buckminsterfullerene.
The interest in creating some form of polynitrogen other than the diatomic orm N2 and the highly explosive anion N3, lies in the fact that such species (say a four atoms pyramidal or a cube-shaped molecule composed of eight atoms) are metastable and are prime candidates for new high explosives or a novel high-performance propellant.
C60 Exists, Why Not N60?
Discovered in 1985, icosahedral C60 is a new allotropic form of carbon (in addition to the known diamond and graphite phases)
- In C60 electrons delocalization give rise to a pentagonal bond
R = 1.43 Å > the bond shared in the 6 member rings R = 1.39 Å
- Could the three-dimensional bonding in C60 be extended to other elements that exhibit similar bonding (nitrogen, boron?)
- For N60, electron delocalization would have to give way to a weaker singly bonded N-N
Polynitrogen: Prelude to Unusual Properties
N2 and N3 are the only known forms of nitrogen, discovered >100 years
- Radical and ionic species, N3 , N3+ and N4+ have linear structures and are very short lived
- Same group elements, phosphorus and arsenic, have other phases than the diatomic (e.g. P4)
- Inconclusive evidence for Tetrazete (N4) generated in electric discharge of nitrogen plasma (CPL, 328, 227, 2000)
- Direct lab synthesis seems to have been successful in producing the N5+ ion as a complex with AsF6 (1999)
- N = N triple bond is one of the strongest covalent bonds, D0 = 228 kcal/mol
Recently: Optical evidence for nonmolecular phases of nitrogen above 150 Gpa (PRL, 85,1262, 2000) and a semiconducting non-molecular phase at 240 Gpa (Nature, May 10, 2001)
- N-N single bond is weak D0 ~ 40 kcal/mol, and the N = N double bond is D0 ~ 100 kcal/mol
- For nitrogen, energy of 3 single bonds < one triple bond. However, for carbon the opposite is true.
Polynitrogen Are Potential High-Energy Density Materials
- Calculations show that Tetraheadral N4 is metastable with dissociation energy (N4 > 2N2 ) = 186 kcal/mol. The energy barrier to decomposition is 61 kcal/mol (long lived and could be trapped)
- N8 should be metastable having a dissociation energy
(N8> 4N2) = 423 kcal/mol.
Stability of Energetic Molecules
Kinetic stability guarantees that decomposition is sufficiently slow at ambient conditions that the molecule is long lived.
Nonadiabatic effects might play a significant role in the stability of N4 and N8.
The spin-forbidden dissociation for N8 was predicted with a barrier of ~ 20 kcal/mol.
We use multiple quantum chemical methods to determine the structure and spectroscopy of bicyclic N10.
Equilibrium structure is not planar. The bond is a hybrid of single and double bond character.
Dipentazole (N10) is suspected to be the most likely species to exist:
D0(N10 > 5N2) = 260 kcal/mol
The bridging bond is very strong:
D0(N10 > 2N5) = 93 kcal/mol
Both N5+ and N5 (pentazole ions) are predicted to be stable planar species and long lived
|Gas-phase detection of ionic N5 is planned
(P5 has been detected in appreciable quantity)
The infrared spectrum of bicyclic N10 shows strong bands at 1000 and 1100 cm1.
The planar structure of bicyclic N10 is a transition state structure 4 kcal/mol above the equilibrium, orthogonal structure.
|The bridging bond is quite strong, yet flexible enough to allow transformation between the two structures
Caculations showed the absence of any other barrier between the two structures > facile movement
Calculations show that N60 is purely single bonded with NN = 1.43 Angstrom, and has three active IR bonds.
|The pentagonal and 6-member ring bond lengths switched, with R1 = 1.43 and R2 = 1.44 Angstrom
In C60, R2 is delocalized pie type shorter bond. In N60 R1 and R2 are of a p-type orbital
Three IR bands show at 68 (56), 701 (94), 1153 (4) cm1
HUMO-LUMO gap = 7.4 eV!
Pending more accurate results (in parallel):
D0(N60>30N2) = 2400 kcal/mol!!
Equal bond lengths
From N10 to N60
Consider the pressure-induced process:
N60: a super-high-energy molecule
C59N has been produced in bulk quantities
The possibility and stability of N60
Molecular dynamics simulation are underway to determine the feasibility of the process
Calculations on the adiabatic and nonadiabatic stability of N10 units
Ab initio based electronic structure calculations to study properties of solid N60
Similar calculations are underway for boron analogues
Contact: Riad Manaa, firstname.lastname@example.org
Related Website: Explosive Soccer: Nitrogen Fullerene
Related Publication: LLNL S&TR Article, This Nitrogen Molecule Really Packs Heat