Iron(II) oxideorferrous oxide is the inorganic compound with the formula FeO. Its mineral form is known as wüstite.[3][4] One of several iron oxides, it is a black-colored powder that is sometimes confused with rust, the latter of which consists of hydrated iron(III) oxide (ferric oxide). Iron(II) oxide also refers to a family of related non-stoichiometric compounds, which are typically iron deficient with compositions ranging from Fe0.84O to Fe0.95O.[5]
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| Names | |
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| IUPAC name
Iron(II) oxide | |
| Other names
Ferrous oxide,iron monoxide | |
| Identifiers | |
3D model (JSmol) |
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| ChEBI | |
| ChemSpider |
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| ECHA InfoCard | 100.014.292 
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| 13590 | |
PubChem CID |
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| UNII | |
CompTox Dashboard (EPA) |
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| Properties | |
| FeO | |
| Molar mass | 71.844 g/mol |
| Appearance | black crystals |
| Density | 5.745 g/cm3 |
| Melting point | 1,377 °C (2,511 °F; 1,650 K)[1] |
| Boiling point | 3,414 °C (6,177 °F; 3,687 K) |
| Insoluble | |
| Solubility | insoluble in alkali, alcohol dissolves in acid |
| +7200·10−6cm3/mol | |
Refractive index (nD) |
2.23 |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards |
can be combustible under specific conditions[2] |
| NFPA 704 (fire diamond) | |
| 200 °C (392 °F; 473 K) | |
| Safety data sheet (SDS) | ICSC 0793 |
| Related compounds | |
Other anions |
Iron(II) sulfide Iron(II) selenide Iron(II) telluride |
Other cations |
Manganese(II) oxide Cobalt(II) oxide |
| Iron(II,III) oxide Iron(III) oxide | |
Related compounds |
Iron(II) fluoride |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
FeO can be prepared by the thermal decomposition of iron(II) oxalate.
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.[6][7]
Stoichiometric FeO can be prepared by heating Fe0.95O with metallic iron at 770 °C and 36 kbar.[8]
FeO is thermodynamically unstable below 575 °C, tending to disproportionate to metal and Fe3O4:[5]
Iron(II) oxide adopts the cubic, rock salt 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 FeII to FeIII effectively replacing a small portion of FeII with two-thirds their number of FeIII, which take up tetrahedral positions in the close packed oxide lattice.[8]
In contrast to the crystalline solid, in the molten state iron atoms are coordinated by predominantly 4 or 5 oxygen atoms.[9]
Below 200 K there is a minor change to the structure which changes the symmetry to rhombohedral and samples become antiferromagnetic.[8][10]
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.[11]
Iron(II) oxide is used as a pigment. It is FDA-approved for use in cosmetics and it is used in some tattoo inks. It can also be used as a phosphate remover from home aquaria.
