hydroxoiron

Hydroxoiron is a general term used to describe compounds containing iron atoms bonded to hydroxide ligands (OH⁻). These compounds are often intermediates in the formation of iron oxides and hydroxides, which are common in nature and industrial processes. The specific structure and properties of hydroxoiron species depend heavily on the oxidation state of the iron (typically Fe²⁺ or Fe³⁺) and the surrounding chemical environment, such as pH and the presence of other ions.

In aqueous solutions, hydroxoiron species can exist as simple aquoions, where water molecules are coordinated to the iron, or as various hydrolyzed forms where hydroxide ions replace water ligands. For instance, Fe³⁺ in water can form species like [Fe(OH)(H₂O)₅]²⁺, [Fe(OH)₂(H₂O)₄]⁺, and eventually precipitate as iron(III) hydroxide, Fe(OH)₃, or iron(III) oxide-hydroxide, FeO(OH). The exact speciation is sensitive to pH, with more neutral or alkaline conditions favoring the formation of higher-order hydroxoiron species and precipitates.

These compounds play roles in various fields. In environmental science, they are important in the fate and transport of iron in soils and water. In industrial chemistry, they are relevant in processes like water treatment and the production of pigments. The precise characterization of hydroxoiron species can be challenging due to their transient nature and tendency to polymerize or aggregate.