Stabilization of hexazine rings in potassium polynitride at high pressure.

Polynitrogen molecules are attractive for high-energy-density materials due to energy stored in nitrogen-nitrogen bonds; however, it remains challenging to find energy-efficient synthetic routes and stabilization mechanisms for these compounds. Direct synthesis from molecular dinitrogen requires overcoming large activation barriers and the reaction products are prone to inherent inhomogeneity. Here we report the synthesis of planar N 6 2- hexazine dianions, stabilized in K 2 N 6 , from potassium azide (KN 3 ) on laser heating in a diamond anvil cell at pressures above 45 GPa. The resulting K 2 N 6 , which exhibits a metallic lustre, remains metastable down to 20 GPa. Synchrotron X-ray diffraction and Raman spectroscopy were used to identify this material, through good agreement with the theoretically predicted structural, vibrational and electronic properties for K 2 N 6 . The N 6 2- rings characterized here are likely to be present in other high-energy-density materials stabilized by pressure. Under 30 GPa, an unusual N 2 0.75- -containing compound with the formula K 3 (N 2 ) 4 was formed instead.