Iron(II) fluoride

Iron(II) fluoride

Identifiers
CAS Number	7789-28-8 anhydrous N 13940-89-1 (tetrahydrate) N
3D model (Jmol)	Interactive image
ChemSpider	74215 Y
ECHA InfoCard	100.029.232
PubChem CID	522690
InChI InChI=1S/2FH.Fe/h2*1H;/q;;+2/p-2 Y Key: FZGIHSNZYGFUGM-UHFFFAOYSA-L Y InChI=1/2FH.Fe/h2*1H;/q;;+2/p-2 Key: FZGIHSNZYGFUGM-NUQVWONBAX
SMILES [Fe+2].[F-].[F-]
Properties
Chemical formula	FeF2
Molar mass	93.84 g/mol (anhydrous) 165.902 g/mol (tetrahydrate)
Appearance	colorless transparent crystals
Density	4.09 g/cm3 (anhydrous) 2.20 g/cm3 (tetrahydrate)
Melting point	970 °C (1,780 °F; 1,240 K) (anhydrous) 100 °C (tetrahydrate)
Boiling point	1,100 °C (2,010 °F; 1,370 K) (anhydrous)
Solubility in water	165 g/100 mL
Solubility	insoluble in ethanol, ether; dissolves in HF
Magnetic susceptibility (χ)	+9500.0·10−6 cm3/mol
Structure
Crystal structure	Rutile (tetragonal), tP6
Space group	P42/mnm, No. 136
Hazards
Main hazards	Causes severe skin burns & eye damage; Hazardous decomposition products formed under fire conditions- Iron oxides
Flash point	not applicable
Related compounds
Other anions	iron(II) oxide, iron(II) chloride
Other cations	manganese(II) fluoride, cobalt(II) fluoride
Related compounds	iron(III) fluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

Iron(II) fluoride or ferrous fluoride is an inorganic compound with the molecular formula FeF₂. It forms a tetrahydrate FeF₂·4H₂O that is often referred to by the same names. The anhydrous and hydrated forms are white crystalline solids.

Anhydrous FeF₂ adopts the TiO₂rutile 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 studies show that the FeF₂ is antiferromagnetic.Heat capacity measurements reveal an event at 78.3 K corresponding to ordering of antiferromagnetic state.

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⁺:

The anhydrous salt can be prepared by reaction of ferrous chloride with anhydrous hydrogen fluoride. It is slightly soluble in water (with solubility product K_sp = 2.36×10⁻⁶ at 25 °C) as well as dilute hydrofluoric acid, giving a pale green solution. It is insoluble in organic solvents.

The tetrahydrate can be prepared by dissolving iron in warm hydrated hydrofluoric acid and precipitating the result by addition of ethanol. It oxidizes in moist air to give, inter alia, a hydrate of iron(III) fluoride, (FeF₃)₂·9H₂O.

FeF₂ is used to catalyze some organic reactions.