Theoretical Study On Structure And Properties Of 1,2,4,5 - Tetrazine Derivatives

S-tetrazines are high nitrogen-containing heterocycle compounds with high positive enthalpy of formation(EOF), good thermal stability and low sensitivity. Because of their high nitrogen, low carbon and hydrogen contents in their structures, they are easy to reach oxygen balance and have high densities. All these features are necessary for high energetic density materials(HEDM). It is well known that the experiments of energetic compounds are expensive, time-consuming, dangerous and inefficient, moreover, there are many influential factors which cannot be forecasted. Therefore, theoretical studies on the relationship between structures and properties of tetrazines are significant.In this paper, using DFT-wB97/6-31+G** method in Gaussian09 package, we systematically studied four types s-tetrazine derivatives which is 23 kinds of energetic group substituted 1,2,4,5-tetrazine derivatives,30 kinds of 1,2,4,5-tetrazine derivatives with tetrazoles,30 kinds of 1,2,4,5-tetrazine derivatives with furazans and 14 kinds of 1,2,4,5-tetrazine derivatives with polycyclic. Fully optimized geometries of each derivative have been obtained. Vibrational frequencies showed that optimized structures were the minima on their potential energy surfaces since there are no imaginary frequencies. The EOF and volume were calculated by using atomization scheme and Monte-Carlo methods, respectively. Based on the EOF and volume, the detonation properties (detonation velocity and detonation pressure) of the derivatives were estimated by Kamlet-Jacobs equation. The Wiberg bond order was obtained through natural bond orbital(NBO) analysis and the possible trigger bond was identified according to the theory of the minimum bond order. The bond dissociation energy with weaker bond was calculated to judge the thermal stability of the title compounds. The thermodynamic properties of some representative compounds at different temperatures from 200K to 800K were calculated by statistic thermodynamics. In the same kinds of the title compounds, the influence of N atom numbers to EOF and detonation properties was investigated, moreover, the relationship between structures and properties was discussed.Theoretical studies on the structures and properties of s-tetrazine derivatives shows:(1) Besides -NH2 and -CN, other groups -N2H、-NO2、-NHNH2、-N3 and -N=N- are all conductive to improve EOF and detonation properties of tetrazine derivatives. (2) tetrazole and furazan rings are directly connected with tetrazine ring which is helpful to increase EOF and detonation properties of tetrazine derivatives, and indirect connections through -N=N-or introduce -NO2 and -N=N-N02 in the tetrazole and furazan rings further significantly increase EOF and detonation properties of tetrazine derivatives. (3) NN bond numbers and N atom numbers of 1,2,4,5-tetrazine derivatives with polycyclic are all beneficial improve EOF and detonation properties of tetrazine derivatives. (4) The values of Cp、Sm and Hm of all derivatives gradually increase with the temperature. Compared with the traditional explosives RDX and HMX, ten s-tetrazine derivatives with excellent performance are selected as high energy density materials candidates. These results establish theoretical foundation and provide valid data for the molecular design of HEDM.