Of Cl_2O_7", chlorine heptoxide"Cl2O7, chlorine heptoxide................or "perchloric anhydride"perchloric anhydride...........
Explanation:
This is the anhydride of perchloric acid, HClO_4HClO4, i.e. O_3Cl-O-ClO_3O3Cl−O−ClO3; we have Cl(VII)Cl(VII), i.e. the maximum Group oxidation number is expressed.