Iron(II) fluoride or ferrous fluoride is an

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemis ...

with the molecular formula FeF₂. It forms a

tetrahydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was unders ...

FeF₂·4H₂O that is often referred to by the same names. The anhydrous and hydrated forms are white crystalline solids.Dale L. Perry (1995),
Handbook of Inorganic Compounds
, page 167. CRC Press.

Structure and bonding

Anhydrous FeF₂ adopts the TiO₂

rutile Rutile is an oxide mineral composed of titanium dioxide (TiO2), the most common natural form of TiO2. Rarer polymorphs of TiO2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest refractive indices at visib ...

structure. As such, the iron cations are octahedral and fluoride anions are trigonal planar. The tetrahydrate can exist in two structures, or polymorphs. One form is rhombohedral and the other is hexagonal, the former having a disorder. Like most fluoride compounds, the anhydrous and hydrated forms of iron(II) fluoride feature high spin metal center. Low temperature

neutron diffraction Neutron diffraction or elastic neutron scattering is the application of neutron scattering to the determination of the atomic and/or magnetic structure of a material. A sample to be examined is placed in a beam of thermal or cold neutrons to ob ...

studies show that the FeF₂ is

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. ...

Heat capacity Heat capacity or thermal capacity is a physical property of matter, defined as the amount of heat to be supplied to an object to produce a unit change in its temperature. The SI unit of heat capacity is joule per kelvin (J/K). Heat cap ...

measurements reveal an event at 78.3 K corresponding to ordering of antiferromagnetic state.

Selected physical properties

FeF₂ sublimes between 958 and 1178 K. Using Torsion and Knudsen methods, the heat of sublimation was experimentally determined and averaged to be 271 ± 2 kJ mole⁻¹. The following reaction is proposed in order to calculate the atomization energy for Fe⁺: :FeF₂ + e → Fe⁺ + F₂ (or 2F) + 2e

Synthesis and reactions

The anhydrous salt can be prepared by reaction of ferrous chloride with anhydrous hydrogen fluoride. It is slightly soluble in water (with

solubility product Solubility equilibrium is a type of dynamic equilibrium that exists when a chemical compound in the solid state is in chemical equilibrium with a solution of that compound. The solid may dissolve unchanged, with dissociation, or with chemical reacti ...

K_sp = 2.36×10⁻⁶ at 25 °C) as well as dilute

hydrofluoric acid Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water. Solutions of HF are colourless, acidic and highly corrosive. It is used to make most fluorine-containing compounds; examples include the commonly used pharmaceutical antidepres ...

, giving a pale green solution. It is insoluble in

organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ Chemistry * Organic matter, matter that has come from a once-living organism, is capable of decay or is the product ...

solvents. The tetrahydrate can be prepared by dissolving iron in warm hydrated

and precipitating the result by addition of

ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...

. It oxidizes in moist air to give, inter alia, a hydrate of iron(III) fluoride, (FeF₃)₂·9H₂O.

Uses

FeF₂ is used to

catalyze Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

some organic reactions.

References

External links

National Pollutant Inventory - Fluoride and compounds fact sheet
{{fluorine compounds Fluorides Metal halides Iron(II) compounds