Copolymerization of CO and N₂ to Extended CON₂ Framework Solid at High Pressures

Abstract

Synthesis of novel extended forms of nitrogen and nitrogen-rich materials has been a topic of interest in development of high-energy-density materials. Here, we present the formation of high-density (3.983 g/cm3) copolymer CON2, formed in crystalline form by laser heating of CO–N2 mixtures above 1700 K and 45 GPa—a substantially lower pressure–temperature condition than those required for converting pure nitrogen (above 110 GPa and 2000 K). It can be made even at lower pressures ∼20 GPa at ambient temperature for amorphous solid. According to the refined structure, the crystalline polymer is made of nitrogen-hybridized, eight-membered rings of singly bonded CON2 in a three-dimensional framework structure in the space group of P43, as one of the previously predicted structures. However, unlike the predicted structures, the present P43 solid converts back to ε-N2-like and δ-N2-like molecular phases as pressure unloads to 20 and 10 GPa, respectively.