Penta-valent ion in water?
Even the tetravalent cations (most of them) are heavily hydrolyzed and barely exist in water solutions. Pentavalent cation is even more of a challenge. Protactinium might be a possibility, but you can't have it anyway.

Speaking of anions, there is not even a trivalent single-atom anion that would not hydrolyze instantly and completely upon touching water.

On the other hand, polyatomic anions (and cations, for that matter) can have pretty much any charge you want.