Detection of the elusive cyclo-1,2-dihydrotetrazete (N₄H₂) in the gas phase

Nitrogen hydrides (N_nH_m) have attracted significant interest for their potential in developing high-energy-density materials. The synthesis of cyclic nitrogen hydrides is particularly challenging due to their inherently high strain energies. Here we report the preparation of the hitherto elusive trans- and cis-cyclo-1,2-dihydrotetrazete (2a and 2b, cyclo-N₄H₂) along with its open chain isomer azidamide (5a, N=N=N-NH₂) by exposing low temperature (5 K) ice of ammonia (NH₃) to high-energy electrons. These compounds were detected and discriminated in the gas phase during the temperature programmed desorption phase exploiting isomer selectivity soft photoionization reflectron time-of-flight mass spectrometry. The cyclo-1,2-dihydrotetrazete signifies a free gas phase species containing a tetranitrogen ring existing without recourse to high-pressure conditions or conjugative stabilization. Our approach may provide feasible strategies for designing higher-order nitrogen ring systems and for elucidating their chemical bonding and stability.