4d and 5d series metals generally do not form stable cationic species.state reasons
d-block elements have variable oxidation states. Number of oxidation states increases from d1 to d5 then gradually decreases. Manganese has seven oxidation states (+1 to +7). Stability of higher oxidation states decreases along a period. So transition metals show variable oxidation states, some of the oxidation states are more stable than other.