The structure of qtz C 6 is shown in Fig. . A differentiation of carbon into two different sites was highlighted by resolving the initial C 6 structure (space group P6 5 22, No. 179) with unique (6a) sites into carbon atoms with (3c) and (3d) Wyckoff positions within space group P6 4 22, No. 181 as shown in Table . Such an elementary modification allowed to consider the binary compounds B 3 N 3 and Si 3 C 3 . The lattice parameters of the ground state structures are given in columns 3 to 5 of Table . The corresponding crystal structures are shown in Figs. with ball-and-stick and tetrahedral representations, the latter being characterized by corner sharing irregular tetrahedra (vide infra). The atoms are described with general Wyckoff positions, i.e., at (3c) ½, 0, 0 and at (3d) ½, 0, ½. Differences are observed in the volumes (total and atom-averaged) and in the interatomic distances, which increase along the series due to the increase in the respective atomic radii. If we look at the angles related to the constituent tetrahedra, they differ significantly from the regular tetrahedral one (109.47°), thus indicating the specificity of the qtz topology.