Charge transfer induced cubic gauche nitrogen from azides

Abstract

Cubic gauche nitrogen (cg-N) with a three-dimensional network of N-N single bonds attracted lots of attentions in last decades, since it theoretically has five times larger energy than TNT. While, extreme environments of high pressure or plasma treatment were required in traditional routes. Quite recently, in vacuum or protective gas environments, a one-step synthesis route relying solely on heating is reported giving the highest cg-N content. However, corresponding mechanism is missing, which hinders the improvement of yield and the development of simpler methods. Here, by treating KN3 in different gas environments, we find that moisture can prevent the transition from KN3 to cg-N. In a dry air environment at 260 ~ 300°C, KN3 decomposes into K and N2, and charge transfer from K to KN3 can induce cg-N. Furthermore, by grinding or loading pressure on the mixture of KN3 with Li, Na, K, Cs, Ca, Mg and Al, we find that elements with higher electronegativity, higher pressure and temperature conditions are needed to induce cg-N, while grinding alone is sufficient for alkali metals even without heating, thus confirming the charge-transfer mechanism. These findings provide guidance for the synthesis of cg-N under ambient conditions through metal-catalyzed polymerization of various azides.