For C 6 N 8 (Fig. ) the projection onto the basal plane was chosen to show an extended plane around the unit cell exhibiting the vacancies at C1 at 0,0,0 and C2 at ½,½,0. The charge density is clearly localized on N, following the difference in the electronegativity between C and N, alike in boron nitride. Both binary compounds can be qualified as polar-covalent chemical systems, oppositely to purely covalent C 16 and diamond.