Calculations predict a stable molecular crystal of N8
Nitrogen, one of the most abundant elements in nature, forms the highly stable N2 molecule. However, only a few polynitrogen compounds made of nitrogen only are known, and no molecular crystal made of these compounds has been prepared to date. This work predicts the existence of a molecular solid of N8. The interactions that bind N8 molecules together are weak van der Waals and electrostatic forces; the monomers retain their structure and bonding pattern as in the gas phase. The predicted solid is metastable even at ambient pressure, the only chemical metastability being that of the N8 molecules. The solid is, according to calculations, more stable than previously predicted polymeric solids of nitrogen up to 20 GPa. It is computed to be highly energetic upon decomposition into nitrogen molecules. The structure, chemical bonding and properties of the N8 molecular crystal are discussed, and a possible preparation strategy is suggested.