Penta-valent ion in water?

I would like to have a solution with a pentavalent positive ion. I need something that, preferably in water: $\ce{XY -> X^5+ + Y^5-}$. What can XY be?

• I don't think this is too broad, considering that as far as I know, no such compound exists. – orthocresol Feb 28 '17 at 22:52
• If you consider a small polymer chain with eg 5 amine groups it can exist, but 5+ is a very high charge, so you need some really strong stabilization mechanism if you want to concentrate it to a single group or small molecule. – Greg Mar 1 '17 at 0:44
• You won't get a +5 charge on a single atom (or even a small molecule) in water. It will be heavily coordinated by water/hydroxo/oxo ligands. – bon Mar 1 '17 at 8:29
• Just to back this up there aren't a huge amount of single atom tetravalent simply hydrated ions that come to mind, let alone pentavalent, if it is single atoms you are looking for. For the cation Cerium, Thorium and Uranium are possibilities that come to mind, but without looking them up I can't be sure. – Ian Bush Mar 1 '17 at 9:00

One five-charge anion you might see is tri(poly)phosphate, as in the sodium salt $\ce{Na_5P_3O_10}$. See https://en.wikipedia.org/wiki/Sodium_triphosphate.