In general, the higher the oxidation state, the more is the covalent character of the oxide.

I₂O₇  &   I₂O₉do not exist.

I₂O₄is ionic in nature. It is in fact iodyl iodate${\left[IO\right]}^{+}{\left[I{O}_3\right]}^{-}$

. The only covalent oxide is I₂O₅

.