inorganic chemistry - Formation of MnO2 vs [Mn(H2O)6]4+ in aqueous solution

I am looking for reasons why $\ce{Mn(IV)}$ wouldn't be stable as a hydrate. I know that from standard reduction potentials it exists as a ppt of $\ce{MnO2}$, but what is stopping it from being a hydrated $\mathrm{4+}$ aqueous cation? Is it that the water ligands would be too polarised and therefore $\ce{H+}$ dissociation would occur very easily? Are there other factors that make it a solid rather than a solvated ion, like lattice enthalpy etc.?