Isotope pairs in different states at room temperature? Does any pair of isotopes exist which are in different states at room temperature—either in isolation or as part of an otherwise-identical compound?
It’s not exactly room temperature but it’s probably the closest you can get to two isotopes having different states so that they can be separated by physical means:

At very low temperatures (below $1~\mathrm{K}$) liquefied helium will separate into a superfluidic helium-4 phase and a normal liquid phase containing mostly helium-3. The superfluid and the normal liquid can be considered different phases and are immiscible.