 The hydroxides of the transition metals and post-transition metals usually have the metal in the +2 (M = Mn, Fe, Co, Ni, Cu, Zn) or +3 (M = Fe, Ru, Rh, Ir) oxidation state.None are soluble in water, and many are poorly defined.One complicating feature of the hydroxides is their tendency to undergo further condensation to the oxides, a process called olation.