FeOH2n

FeOH2n is a generic term used in inorganic chemistry to describe a family of iron-containing hydroxide materials whose exact composition depends on the integer n. In this formulation, n indicates the level of hydration or polymerization and can vary with synthesis conditions. The concept stands for various solids in which iron centers are coordinated by oxide and hydroxide ligands, with hydroxide groups bridging between iron atoms and water molecules occupying interstitial sites. The iron may be in oxidation state +2 or +3, depending on preparation.

Structure and bonding: The solids typically feature FeO6 octahedra connected via shared edges or corners through hydroxide bridges, yielding layered or three-dimensional networks. Water and/or hydroxide balance charge and stability. The general formula does not pin down a single crystal structure; instead, it denotes a family including ferrihydrite-like, goethite-like, or lepidocrocite-like motifs depending on n and processing history.

Preparation and occurrence: FeOH2n materials are commonly prepared by hydrolysis of iron(II) or iron(III) salts under controlled pH, or by aging precipitates in aqueous media. As pH, temperature, and concentration change, the degree of hydration and polymerization changes, altering n. In nature, iron oxyhydroxide minerals form via weathering and biogeochemical cycling, examples include ferrihydrite, goethite, and lepidocrocite, which are related to the FeOH2n family.

Properties and applications: These compounds are typically poorly soluble in water and exhibit basic or amphoteric behavior. They can act as sorbents for contaminants and as precursors to iron oxides used as pigments, catalysts, and environmental remediation materials. Thermal treatment leads to dehydration and conversion to iron oxides.

Note: FeOH2n is not a single defined substance but a shorthand for a class of hydroxy-oxide materials whose precise composition is governed by synthesis conditions and the value of n.