Synthesis of 1-(2H-tetrazol-5-yl)-5-nitraminotetrazole and its derivatives from 5-aminotetrazole and cyanogen azide: A promising strategy towards the development of C-N linked bistetrazolate energetic materials

A series of C-N linked bistetrazolate nitramino compounds, i.e., 1-(2H-tetrazol-5-yl)-5-nitraminotetrazole (2) and its energetic salts (3-8), were successfully prepared from readily available 5-aminotetrazole. All new energetic compounds were fully characterized by IR and NMR spectra and elemental analysis, and six of them (1, 3-7) were further determined by single-crystal X-ray diffraction analysis. The nitrogen contents of these energetic bistetrazolate compounds, ranging from 59.3% (3) to 74.8% (7), are much higher than those of the commonly used high explosives such as RDX (N: 37.8%), HMX (N: 37.8%) and CL-20 (N: 38.3%). And theoretical calculations by using the Gaussian 09 program package demonstrate that compounds 1-8 have high positive heats of formation, of which the heats of formation of ammonium salt 4 (3.60 kJ g^-1), aminonitroguanidinium 5 (3.11 kJ g^-1) and dihydrazinium salt 7 (3.25 kJ g^-1) are approximately eight times higher than those of RDX (0.39 kJ g^-1) and HMX (0.39 kJ g^-1), and four times higher than that of CL-20 (0.83 kJ g^-1). The high nitrogen contents and high heats of formation have endowed these energetic compounds with prominent detonation performance. It is noteworthy that compound 7 exhibits an excellent calculated detonation velocity of 9822 m s^-1 superior to that of CL-20 (9730 m s^-1), while the impact and friction sensitivities of 7 (IS = 8 J, FS = 192 N) are comparable to those of HMX (IS = 7 J, FS = 112 N). The good detonation properties with moderate sensitivities demonstrate that compound 7 is a promising candidate for application as a high-performance energetic material.