NiAs-derived cyanamide (carbodiimide) structures – a group-theoretical view

Abstract The cyanamide and carbodiimide anions are complex nitrogen-derived one-dimensional species of the type NCN2− (hence, resembling O2− but more covalently bonding) that form a huge number of salt-like phases with a variety of metal cations stemming from the whole Periodic Table. Depending on the coloring (binary, ternary and quaternary salts are known), the cationic size and charge as well as covalent contributions, different distortion (tilting in particular) and/or vacancy ordering variants of cyanamides/carbodiimides occur. Herein we summarize those cyanamide/carbodiimide structures that derive from the aristotype NiAs. The crystal chemistry is discussed on the basis of group-subgroup schemes (Bärnighausen trees).