FeIII

FeIII (commonly written as Fe3+ or Fe(III)) denotes iron in the +3 oxidation state. In chemistry, iron frequently adopts the ferric state in oxides, hydroxides, and many salts. Common ferric species include iron(III) oxide (Fe2O3), iron(III) hydroxide Fe(OH)3, and ferric salts such as iron(III) chloride (FeCl3), iron(III) sulfate (Fe2(SO4)3), and iron(III) phosphate (FePO4).

In solution, the ferric ion is [Fe(H2O)6]3+ and acts as a Lewis acid. Fe3+ is usually high-spin and paramagnetic, with five unpaired electrons in many coordination environments. It readily hydrolyzes water, forming hydroxo complexes, and at modest pH forms insoluble Fe(OH)3 precipitates, often giving a yellow-brown to reddish solid. Solubility depends strongly on pH and ligands; it is relatively soluble under strongly acidic conditions and limited at neutral pH. Fe3+ is also a mild oxidizing agent, being reduced to Fe2+ in redox reactions.

Biology and environmental context features ferric iron in transport and storage: transferrin binds Fe3+ in blood, and ferritin stores iron as a ferric oxide-hydroxide core. Because Fe3+ is more prone to hydrolysis and precipitation than Fe2+, its solubility and bioavailability are highly pH-dependent, influencing mineral formation and nutrient cycles.

Applications include the use of ferric salts as coagulants in water treatment, pigments, and catalysts in various chemical processes. Safety: iron(III) compounds are generally of low toxicity but can be irritating or corrosive; standard safety precautions apply when handling ferric salts.