Ferrate loosely refers to a material that can be viewed as containing anionic iron complexes. The term ferrate derives from Latin ferrum 'iron'.
Examples include tetrachloroferrate (FeCl42−), oxyanions (e.g. FeO42−), and the organoferrates, including highly reduced tetracarbonylferrate ([Fe(CO)4]2−) salts.[page needed] Although rarely studied, ferrate(V) FeO43− and ferrate(IV) FeO44−) oxyanions of iron also exist. These too are called ferrates.
Ferrate(VI) is a strong oxidizer, used in water purification and battery technology.