A theoretical study on the structure, intramolecular interactions, and detonation performance of hydrazinium dinitramide

Delocalization quantitatively mapped for prototypic organic nitroanions as well as azidoform anions

Delocalization of occupied orbitals impacts the chemical bonding in the simplest known pernitroanions [(NO2)3C]- (1) and [(NO2)2N]- (2) as well as other functionalized organic anions. By quantitatively mapping it onto molecular backbones of 1, 2, [CH2NO2]- (3), [CH3NNO2]- (4) and [C(N3)]- (6) anions (all modeled by QM calculations), the Weinhold's NBO analysis refines their chemical structure, enabling to explain and even predict their essential chemical behaviour. In detail, the HOMO of 1 and 2 is associated with the central atom to the degree of 70.7% and 80.4%, respectively, while the HOMO localization on O atoms for 3 and 4 is 85.3% and 81.1%, respectively. Predomination of C-alkylation for 1 and that of O-alkylation for 3 in non-coordinating solvents thus becomes clear. The important news is that the easiness of homolytically disrupting the N-N bond in 2, a constituent of inexpensive powerful explosives, is because of the occupancy of the related σ*orbital increases with stretching this bond. The same is true for electrocyclic extrusion of NO3- from this molecule. This antibonding effect may be assumed to be the common cause of the proneness of aliphatic nitro compounds to decompose. Pyramidal anion 6 is a highly localized carbanion. Its isomer of molecular symmetry CS has a unique chemical structure of its azido substituents: each of them is represented by one high-weight resonance structure, e.g., N-N[triple bond, length as m-dash]N. The prediction is that the dinitrogen-eliminating decomposition of this isomer is more facile than of the isomer of C3 symmetry. In summary, this study affords three novel particular insights into the chemical structure and reactivity of these anions: chemically telling delocalization-augmented molecular structures, a reasonable hypothesis of the common cause of thermally triggered instability of aliphatic nitro compounds, and discovered one-resonance structure azido groups.

A DFT-D study on the stability and intramolecular interactions of the energetic salts of 3,6-dihydrazido-1,2,4,5-tetrazine

Structures of the salts I–IV formed by 3,6-dihydrazido-1,2,4,5-tetrazine with HNO3, HN(NO2)2, HClO4, and HC(NO2)3, respectively, were studied using dispersion-corrected density functional theory. The intramolecular hydrogen bond energies of I–IV were estimated using the quantum theory of atoms in molecules. The total hydrogen bond energies (EH,tot) have the order of I (65.60 kcal/mol) > II (46.24 kcal/mol) > III (39.13 kcal/mol) > IV (19.68 kcal/mol). In addition, the charge transfer (q), binding energy (Eb), lattice energy (HL), dispersion energy (Edis), and second-order perturbation energy (E2) were evaluated for studying the intramolecular interactions between the cation and anion. Linear relationships exist between any two of EH,tot, qtot, Eb, and E2,tot. HLs have the same variation trend as h50s (characteristic height) and may be used as the indicator of impact sensitivity. The HOMOs and LUMOs of I–IV are derived from the HOMOs of the isolated anions and the LUMOs of the isolated cations, respectively. Ultraviolet spectra of I–IV have the strongest absorptions at around 442, 445, 427, and 587 nm, respectively. The excitations HOMO→LUMO to HOMO–7→LUMO play important roles in the first three excited states.

Theoretical studies on the stability of salts formed by 3-substituted 6-nitraminotetrazines with different cations

A series of energetic salts based on the cations NH4 (+), NH3OH(+), N2H5 (+) and C(NH2)3 (+) and the anions of 6-nitraminotetrazine and its 3-substituted derivatives of -NH2, -N3, -ONO2, -NF2 or -NO2 was studied using dispersion-corrected density functional theory (DFT-D). In comparison with salts of unsubstituted 6-nitraminotetrazine, -NH2 substitution strengthens the hydrogen bonding interaction and other intramolecular interactions (such as charge transfer, binding energy, second-order perturbation energy and dispersion energy), -N3 has tiny effects on these interactions, and other groups weaken these interactions, with weakening decreasing in the order -NO2 > -NF2 > -ONO2. The ability of the cations to produce strong intramolecular interactions decreases in the order NH3OH(+) > N2H5 (+) > NH4 (+) > C(NH2)3 (+), which is contrary to the order of the basicity of bases. Stronger intramolecular interactions lead to more stable salts. All substituent groups improved the chemical stability except -ONO2, while cations had no effect on chemical stability. All substituent groups were helpful in improving aromaticity, in the sequence -ONO2 > -NF2 > -NO2 > -N3 > -NH2.

A DFT-D study on the stability and intramolecular interactions of the salts of 1,2,3- and 1,2,4-triazoles

Nitrogen-rich 1,2,4-triazole (1) and 1,2,3-triazole (2) react as bases with the oxygen-rich acids HNO3 (a), HN(NO2)2 (b), and HClO4 (c) to produce energetic salts (1a, 1b, and 1c and 2a, 2b, and 2c, respectively) potentially applicable to composite explosives and propellants. In this study, these salts were studied with the dispersion-corrected density functional theory. For the isomers such as 1a and 2a, the more negative ΔrGm of the formation reaction leads to a higher thermally stable salt. The ability to form intramolecular hydrogen bonds predicted with the quantum theory of atoms in molecules has the order of 2 > 1. Different hydrogen bonds result in different second-order perturbation energies, redshifts in IR, and electron density differences. The charge transfer, binding energy, dispersion energy, lattice energy, and energy gap between frontier orbits in the salts of 1 are larger than those of 2, which is helpful for stabilizing the former, and 1 is more obviously stabilized than 2 by formation of salts. Different conformations of 1 and 2 hardly affect the frontier orbital distributions. Base 1 is a more preferred base than 2 to form salts.

A theoretical study on the stability and intramolecular interaction in 5-nitrotetrazolates with the DFT and DFT-D methods

Two new salts 3,5-diazido-1,2,4-triazolium 5-nitrotetrazolate and 1-methyl-3,5-diazido-1,2,4-triazolium 5-nitrotetrazolate were designed based on the structures of experimentally synthesized 3-azido-1,2,4-triazolium 5-nitro-tetrazolate and 1-methyl-3-azido-1,2,4-triazolium 5-nitro-tetrazolate, to explore new promising candidates for energetic materials and to investigate the influences of the substituents (- CH 3 and - N 3) and solvent (water) on the intramolecular interactions and properties. The intramolecular hydrogen bonding interactions were investigated by the natural bond orbital (NBO) and the quantum theory of atoms in molecules (QTAIM) analyses using the density functional theory (DFT) and the dispersion correction DFT (DFT-D) methods. The low-lying singlet electronic transitions were estimated using the time-dependent DFT. All four examined salts exist as ionic structures in aqueous solution while acid–base molecular complexes form in gas phase. The hydrogen bond energy (E H ) obtained with the DFT-D method is larger than that obtained with the DFT method, but the trend is consistent, i.e. - N 3 increases while - CH 3 decreases E H . In addition, the position of the strongest electronic absorption peak has a little correlation with the number of - N 3 and - CH 3 groups. 3,5-diazido-1,2,4-triazolium 5-nitrotetrazolate is a valuable energetic salt with the highest nitrogen content, oxygen coefficient and density and the second highest heat of formation and chemical stability.