High-Pressure Synthesis of a Pentazolate Salt

Abstract

The pentazolates, the last all-nitrogen members of the azole series, have been notoriously elusive for the last hundred years despite enormous efforts to make these compounds in either gas or condensed phases. Here we report a successful synthesis of a solid state compound consisting of isolated pentazolate anions N − 5 , which is achieved by compressing and laser heating cesium azide (CsN 3 ) mixed with N 2 cryogenic liquid in a diamond anvil cell. The experiment was guided by theory, which predicted the transformation of the mixture at high pressures to a new compound, cesium pentazolate salt (CsN 5 ). Electron transfer from Cs atoms to N 5 rings enables both aromaticity in the pentazolates as well as ionic bonding in the CsN 5 crystal. This work provides a critical insight into the role of extreme conditions in exploring unusual bonding routes that ultimately lead to the formation of novel high nitrogen content species.

Pentazole and Ammonium Pentazolate: Crystalline Hydro-Nitrogens at High Pressure

“…High pressure substantially modifies the potential energy surface thus promoting unusual chemical bonding in the condensed phase. Recently, several N 5 -ring containing crystals have been predicted [12][13][14] and one of them, CsN 5 , has been synthesized at high pressures 15 .…”

Amorphous polymerization of nitrogen in compressed cupric azide

“…For example, Steele et al successfully synthesized cyclo ‐N salt by compressing cesium azide (CsN 3 ) mixed with N 2. In fact, metal azides are prominent precursors for synthesizing polymeric nitrogen. The azide anion N was firstly reported by Curtius in aqueous solutions of HN 3 in 1890 .…”

Self-assembled energetic coordination polymers based on multidentate pentazole cyclo-N5−

“…Unfortunately, owing to the unstable bonding interactions with other anions, further developments of N 5 + ion have been limited. The pentazole anion cyclo-N 5 -was first detected in 2002 via mass spectrometry (MS) [18,19] and was not adopted for bulk production until recently [20][21][22][23][24][25][26]. However, the anhydrous pentazole sample NaN 5 [21] and CsN 5 [22] were only observed under extreme high pressure and the metal-pentazole hydrates [24][25][26] decomposed in the range of 100-110°C.…”