Dichlorine hexoxide is the chemical compound with the molecular formula Cl2O6, which is correct for its gaseous state.

However, in liquid or solid form, this chlorine oxide ionizes into the dark red ionic compound chloryl perchlorate [ClO2]+[ClO4]−, which may be thought of as the mixed anhydride of chloric and perchloric acids.

[1] It is produced by reaction between chlorine dioxide and excess ozone: It was originally reported to exist as the monomeric chlorine trioxide ClO3 in gas phase,[2] but was later shown to remain an oxygen-bridged dimer after evaporation and until thermal decomposition into chlorine perchlorate, Cl2O4, and oxygen.

The red color shows the presence of chloryl ions.

Although stable at room temperature, it explodes violently on contact with organic compounds[5] It is a strong dehydrating agent: Many reactions involving Cl2O6 reflect its ionic structure, [ClO2]+[ClO4]−, including the following:[6] It reacts with gold to produce the chloryl salt [ClO2]+[Au(ClO4)4]−:[7] Several other transition metal perchlorate complexes are prepared using dichlorine hexoxide.