High-Pressure Synthesis of a Nitrogen-Rich Inclusion Compound ReN₈ ⋅x N₂ with Conjugated Polymeric Nitrogen Chains

A nitrogen-rich compound, ReN₈ ⋅x N₂ , was synthesized by a direct reaction between rhenium and nitrogen at high pressure and high temperature in a laser-heated diamond anvil cell. Single-crystal X-ray diffraction revealed that the crystal structure, which is based on the ReN₈ framework, has rectangular-shaped channels that accommodate nitrogen molecules. Thus, despite a very high synthesis pressure, exceeding 100 GPa, ReN₈ ⋅x N₂ is an inclusion compound. The amount of trapped nitrogen (x) depends on the synthesis conditions. The polydiazenediyl chains [-N=N-]_∞ that constitute the framework have not been previously observed in any compound. Ab initio calculations on ReN₈ ⋅x N₂ provide strong support for the experimental results and conclusions.