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The element iron in its +3 oxidation state / From Wikipedia, the free encyclopedia

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In chemistry, iron(III) refers to the element iron in its +3 oxidation state. In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe3+.

Ferric oxide, commonly, though not precisely, called rust.

The adjective ferric or the prefix ferri- is often used to specify such compounds, as in ferric chloride for iron(III) chloride (FeCl3). The adjective ferrous is used instead for iron(II) salts, containing the cation Fe2+. The word ferric is derived from the Latin word ferrum, meaning "iron".

Iron(III) metal centres also occur in coordination complexes, such as in the anion ferrioxalate, [Fe(C2O4)3]3−, where three bidentate oxalate ions surrounding the metal centre; or, in organometallic compounds, such as the ferrocenium cation [Fe(C2H5)2]+, where two cyclopentadienyl anions are bound to the FeIII centre.

Iron is almost always encountered in the oxidation states 0 (as in the metal), +2, or +3. Iron(III) is usually the most stable form in air, as illustrated by the pervasiveness of rust, an insoluble iron(III)-containing material.