The chemistry of 5-(tetrazol-1-yl)-2H-tetrazole: an extensive study of structural and energetic properties.

5-(Tetrazol-1-yl)-2H-tetrazole (1), or 1,5'-bistetrazole, was synthesized by the cyclization of 5-amino-1H-tetrazole, sodium azide and triethyl orthoformate in glacial acetic acid. A derivative of 1, 2-methyl-5-(tetrazol-1-yl)tetrazole (2) can be obtained by this method starting from 5-amino-2-methyl-tetrazole. Furthermore, selected salts of 1 with nitrogen-rich and metal (alkali and transition metal) cations, including hydroxylammonium (4), triaminoguanidinium (5), copper(I) (8) and silver (9), as well as copper(II) complexes of both 1 and 2 were prepared. An intensive characterization of the compounds is given, including vibrational (IR, Raman) and multinuclear NMR spectroscopy, mass spectrometry, DSC and single-crystal X-ray diffraction. Their sensitivities towards physical stimuli (impact, friction, electrostatic) were determined according to Bundesamt für Materialforschung (BAM) standard methods. Energetic performance (detonation velocity, pressure, etc.) parameters were calculated with the EXPLO5 program, based on predicted heats of formation derived from enthalpies computed at the CBS-4M level of theory and utilizing the atomization energy method. From the analytical and calculated data, their potential as energetic materials in different applications was evaluated and discussed.