Our computational study suggests thus that the highest iridium oxidation state that has a realistic chance of experimental observation is Ir⁺ⱽᴵᴵ. The experimentally known highest 5d oxidation states for groups 9, 10, and 11 are Os⁺ⱽᴵᴵᴵ, Pt⁺ⱽᴵ, and Au⁺ⱽ, respectively. Adding the computational predicted Hg⁺ᴵⱽ and Ir⁺ⱽᴵᴵ states suggests that the trend for the later 5d metals should become a linear decrease. All in all there is a linear increase up to Os and after Os there is a linear decrease down to Hg. This trend is a new observation for the 5d transition metals.