Computational study of substituted 2,2′-bi-1H-imidazole as high energetic materials

Density functional theory (DFT) calculations were performed for a series of 2,2′-bi-1H-imidazole derivatives. The B3LYP and B3P86 functionals with 6-311G∗∗ basis set were used. The heats of formation (HOFs) were predicted through designed isodesmic reactions. Calculated results show that the HOFs decrease as the -NO2 groups being replaced by -NF2, but the HOFs increase as the -NO2 groups being replaced by -N3. When the -NO2 groups are replaced by -NH2, the HOFs initially decrease then increase. As for the isomeric compounds, the HOFs decrease following the increase of the number of hydrogen bonds for the different substituent position. At B3LYP/6-311G∗∗ level, the HOF of 4,4′-diamino-5,5′-dinitro-2,2′-bi-1H-imidazole is the smallest (125.2 kJ/mol), and the HOF of 4,4′,5,5′-tetraazido-2,2′-bi-1H-imidazole is the largest (1608.9 kJ/mol). The magnitudes of intramolecular group interactions were predicted through the disproportionation energies. The Edisproportion of 4,4′-diamino-5,5′-dinitro-2,2′-bi-1H-imidazole is −70.3 kJ/mol and is the smallest among the title compounds, but that of 4,4′,5,5′-tetranitro-2,2′-bi-1H-imidazole is the largest, which is 128.1 kJ/mol. Thermal stabilities were evaluated via bond dissociation energies (BDE) at the UB3LYP/6-311G∗∗ level. The BDEZPE value for C-NO2 bond, 270.0 kJ/mol in average, is the smallest compared to other types of bonds.