The formation of cyclotriazane (N3H3) from ammonia in contact with a silver-exchanged LTA zeolite: a reliable synthesis pathway?

Abstract

Sigma-catenated polynitrogen derivatives are scarce. Among polyazanes, the synthesis of derivatives of cyclotriazane (general formula N₃H₃) remains a challenge due to their very high reactivity. While several methods toward protected variants of cyclotriazane have been introduced, N₃H₃ itself has only been observed by Kim and Seff through the stoichiometric oxidation of ammonia on a (Ag⁺)-exchanged LTA zeolite followed by thermodesorption. Based on single-crystal XRD analysis of the crystal, they proposed the presence of cyclotriazane confined in the alpha cavity of the zeolite and in the sodalite cages. Since this 1977 publication by Kim and Seff, we could not find any other publications on this topic, and to the best of our knowledge, triazane has not yet been isolated. In the quest to decipher the mechanism of formation of cyclotriazane, we have studied the reactivity of silver-exchanged LTA zeolites with NH₃ by operando DRIFTS and XAS. In contrast to the conclusions of Kim and Seff, we could not detect any triazane, either in the pores of the zeolites or in the gas phase by temperature desorption. All alternative attempts to isolate this molecule through adduct formation with BH₃ also failed. No other species could be unambiguously identified by operando XAS and DRIFTS. XAS indicates that ammonia is adsorbed onto the 6 ring-centered Ag of the zeolite without the redox reaction. We can conclude that the formation of cyclotriazane by the auto-oxidation of ammonia is unlikely. Consequently, it seems highly unlikely that cyclotriazane synthesis could be carried out by NH₃ treatment of a silver-exchanged LTA zeolite. The synthesis and isolation of the highly reactive cyclotriazane molecule remain a quest for the future.