The answer is Cl₂O₇.
That is the general formula for chlorine heptoxide is Cl₂O₇.
Chlorine heptoxide is also called dichlorine heptoxide .
Its chemical formula is Cl₂O₇.
This oxide is actually a anhydride of perchloric acid.
It is formed by distillation of perchloric acid in the presence of dehydrating agent.