  Polynitrogen molecules represent the ultimate high energy-density materials
as they have a huge potential chemical energy originating from their high
enthalpy. However, synthesis and storage of such compounds remain a big
challenge because of difficulties to find energy efficient synthetic routes and
stabilization mechanisms. Compounds of metals with nitrogen represent promising
candidates for realization of energetic polynitrogen compounds, which are also
environmentally benign. Here we report the synthesis of polynitrogen planar N6
hexazine rings, stabilized in K2N6 compound, which was formed from K azide upon
laser heating in a diamond anvil cell at high pressures in excess of 45 GPa and
remains metastable down to 20 GPa. Synchrotron X-ray diffraction and Raman
spectroscopy are used to identify this material, also exhibiting metallic
luster, being all consistent with theoretically predicted structural,
vibrational and electronic properties. The documented here N6 hexazine rings
represent new highly energetic polynitrogens, which have a potential for future
recovery and utilization.
