Using tet-C 5 as a template, a new tetragonal C 6 allotrope was constructed with the modification of the central carbon position from ½, ½, ½ to ½, ½, z with z ~ 0.4, thus transforming it into a two-fold position (2f) in the primitive tetragonal space group P-4m2, No. 115. However, after full geometry optimization, and space group analysis, the (2e) and (2f) positions were merged by symmetry into a single four-fold position with body-center space group I-4m2, No. 119, as shown in Table . The topological analysis of the new allotrope revealed a tfa topology similar to that of the recently reported ultrahard C 6 allotrope called 'neoglitter' . The cohesive energy of the new tet-C 6 is E coh /atom = -1.73, which allows us to describe it as cohesive but less stable than tet-C 5 . The structure of tet-C 6 is shown in Fig. in three representations. Clearly, the tetrahedra are now connected by C2-C2 segments along two adjacent as in C 5 but also within the cell, thus exhibiting the higher symmetry compared to tet-C 5 .