Carbon-free energetic materials: computational study on nitro-substituted BN-cage molecules with high heat of detonation and stability

Abstract

A new series of high-energy density materials (HEDMs) B 6 N 6 H 6Àn (NO 2 ) n (n ¼ 1-6) are studied at the M06-2X/6-311++G**, uB97XD/6-311++G** and B3LYP/6-311++G** levels. Analysis of the structural changes caused by substituting the NO 2 and the electronic structures, such as electron localization function (ELF), Wiberg bond index (WBI), charge transfer and bond dissociation energies (BDE), provide important insights into the essence of the chemical characteristics and stability. Moreover, the Born-Oppenheimer molecular dynamic (BOMD) simulation is performed to verify their stability, which suggests that only the BN-cage derivatives with one and two nitro groups bonding with boron atoms (NO 2 -1-1 and NO 2 -2-1) can remain stable under ambient conditions. To predict the detonation performance and sensitivity of these two stable BN-cage energetic molecules accurately, the density, gas phase enthalpy of formation, enthalpy of sublimation, detonation performance, impact sensitivity and BDE are calculated systematically. The calculation results show that both NO 2 -1-1 and NO 2 -2-1 have a higher heat of detonation, higher value of h 50 , and larger BDE of trigger bonds than CL-20.

Density functional theory studies of effects of boron replacement on the structure and property of RDX and HMX

“…For example, HMX-B4 has the lowest (N NO 2 ) average value in all five HMX-B compounds, it also has highest h 50 value and lowest sensitivity. Similar results were found in the boron-replaced CL-20, [5] whose sensitivity is lower than CL-20.…”

“…And the OB and HOF values would further increase and decrease with the increment of the amount of boron atoms, respectively. The negative effect of boron atoms on the HOF was also found in the previous study about the boron-replaced N 4 C 2 isomers [4] and CL-20 compounds [5] but just the opposite to that of the boron-replaced 1,1-diamino-2,2-dinitroethene (FOX-7), [3] while the positive effect of boron atoms on the OB was observed on the boron replaced FOX-7 [3] also. As a result, after the boron replacement, some designed molecules for high-energy compounds, indicating their combustion would be relatively complete and release heat as large as possible when detonated.…”

“…Finally, OB for designed compounds (C a H b O c N d B e ) was calculated by the Equation (1), the final combustion products are supposed to be CO 2 , H 2 O, N 2 , and B 2 O 3 . While the solid-phase density (ρ, Equation (2)) and impact sensitivity (h 50 , Equation (3)) were computed by the common methods for N NO 2 -based energetic compounds, which were performed at the same level used in the corresponding literature [5,9,10] :…”

“…First of all, for the density, since the boron atom is lighter than the carbon atom, the boron replacement would decrease the density in both RDX and HMX series usually, and the more the boron atom, the lower the density, this is similar to that of boron-replaced FOX-7 [3] and CL-20. [5] As a higher density value is helpful for improving the detonation performance of energetic compounds, the boron replacement would do harm to the detonation performance of both RDX and HMX. Interestingly, the changing trend of h 50 values is very similar to that of density, indicating that the boron atom also decreases the h 50 value of both RDX and HMX.…”

“…[1] The detonation velocity (D) and detonation pressure (P) of ammonia-(dinitramido)boranes were predicted to close that of one common high-energy compound pentaerythtritol tetranitrate and much better than that of trinitrotoluene. Some other boronbased energetic compounds including (E)-1,2-diamino-1,2-dinitrodiboron, [3] open-chain N 4 B 2 isomers [4] and nitrosubstituted BN-cage molecules B 6 N 6 H 6n (NO 2 ) n (n = 1-6) [5] were designed theoretically and they were estimated to have good detonation performance, good thermal stability, or low sensitivity. For instance, the calculated results show that two compounds in the series of B 6 N 6 H 6n (NO 2 ) n (n = 1-6) even have higher energy property and lower sensitivity than one famous energetic compound 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo[5.5.0.0.0]dodecane .…”