Upon removal of central carbon producing tet-C 3 with only C(tet) -cf. Table -, the charge density is modified, particularly for the carbon atoms pointing towards the empty space as shown by the larger red area. Such behavior resembling dangling bonds is in line with the low cohesive C 3 , allows expecting such nonbonding electron density to connect with interstitials. Indeed, the larger changes observed in C 6 (Fig. ) are exhibited with the charge density (dangling bonds in C 3 ) skewed towards tricarbon C(trig)-like with fat yellow charge density segments illustrating the C=C double bonds as in allene molecule. Therefore, we are presented with a decrease of the covalence from C 4 to C 6 brought by the introduction of trigonal carbon.