Iron(II) oxide or ferrous oxide is the inorganic compound with the formula FeO. Its mineral form is known as

wüstite Wüstite ( Fe O) is a mineral form of iron(II) oxide found with meteorites and native iron. It has a grey colour with a greenish tint in reflected light. Wüstite crystallizes in the isometric-hexoctahedral crystal system in opaque to translu ...

. One of several iron oxides, it is a black-colored powder that is sometimes confused with

rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO( ...

, the latter of which consists of hydrated iron(III) oxide (ferric oxide). Iron(II) oxide also refers to a family of related

non-stoichiometric compound In chemistry, non-stoichiometric compounds are chemical compounds, almost always solid inorganic compounds, having elemental composition whose proportions cannot be represented by a ratio of small natural numbers (i.e. an empirical formula); m ...

s, which are typically iron deficient with compositions ranging from Fe_0.84O to Fe_0.95O.

Preparation

FeO can be prepared by the thermal decomposition of

iron(II) oxalate Ferrous oxalate, or iron(II) oxalate, is an inorganic compound with the formula FeC2O4 where is typically 2. These are orange compounds, poorly soluble in water. Structure The dihydrate FeC2O4 is a coordination polymer, consisting of chains of ...

. :FeC₂O₄ → FeO + CO₂ + CO The procedure is conducted under an inert atmosphere to avoid the formation of iron(III) oxide (Fe₂O₃). A similar procedure can also be used for the synthesis of manganous oxide and stannous oxide. Stoichiometric FeO can be prepared by heating Fe_0.95O with metallic iron at 770 °C and 36 kbar.Wells A.F. (1984) ''Structural Inorganic Chemistry'' 5th edition Oxford University Press

Reactions

FeO is thermodynamically unstable below 575 °C, tending to disproportionate to metal and Fe₃O₄: :4FeO → Fe + Fe₃O₄

Structure

Iron(II) oxide adopts the cubic,

rock salt Halite (), commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride ( Na Cl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, pi ...

structure, where iron atoms are octahedrally coordinated by oxygen atoms and the oxygen atoms octahedrally coordinated by iron atoms. The non-stoichiometry occurs because of the ease of oxidation of Fe^II to Fe^III effectively replacing a small portion of Fe^II with two thirds their number of Fe^III, which take up tetrahedral positions in the close packed oxide lattice. In contrast to the crystalline solid, in the molten state iron atoms are coordinated by predominantly 4 or 5 oxygen atoms. Below 200 K there is a minor change to the structure which changes the symmetry to rhombohedral and samples become

antiferromagnetic In materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules, usually related to the spins of electrons, align in a regular pattern with neighboring spins (on different sublattices) pointing in opposite directions. ...

Occurrence in nature

Iron(II) oxide makes up approximately 9% of the Earth's mantle. Within the mantle, it may be electrically conductive, which is a possible explanation for perturbations in Earth's rotation not accounted for by accepted models of the mantle's properties.

Uses

Iron(II) oxide is used as a

pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compou ...

. It is

FDA The United States Food and Drug Administration (FDA or US FDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food ...

-approved for use in cosmetics and it is used in some

tattoo A tattoo is a form of body modification made by inserting tattoo ink, dyes, and/or pigments, either indelible or temporary, into the dermis layer of the skin to form a design. Tattoo artists create these designs using several tattooing ...

inks. It can also be used as a phosphate remover from home aquaria.

References

External links

Wustite Mineral Data
{{oxygen compounds Iron(II) compounds Iron oxide pigments Non-stoichiometric compounds Transition metal oxides Rock salt crystal structure Glass dyes