Iron(II) fluoride

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Iron(II) fluoride
CAS number 7789-28-8 N= ?
13940-89-1 (tetrahydrate)
PubChem 522690
ChemSpider 74215 YesY
Jmol-3D images Image 1
Molecular formula FeF2
Molar mass 93.84 g/mol (anhydrous)
165.k90 g/mol (tetrahydrate)
Appearance red-violet transparent crystal
Density 4.09 g/cm3 (anhydrous)
2.20 g/cm3 (tetrahydrate)
Melting point 970 °C (anhydrous)
100 °C (tetrahydrate)[1]
Boiling point 1100 °C (anhydrous)
Solubility in water 165 g/100 mL
Solubility insoluble in ethanol, ether;
dissolves in HF
Crystal structure Rutile (tetragonal), tP6
Space group P42/mnm, No. 136
Main hazards Causes severe skin burns & eye damage;
Hazardous decomposition products formed under fire conditions- Iron oxides[2]
Flash point not applicable[2]
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 noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Iron(II) fluoride (also ferrous fluoride) is a chemical compound with formula FeF2. It is a green crystalline solid that melts at about 1000 °C.[3] It is used in ceramics and as a catalyst in some organic reactions.[3]

The anhydrous salt can be prepared by reacting the elements.[4] It has the TiO2 rutile structure where the iron atoms are octahedrally coordinated and the fluoride ions three coordinate.[4]

Physical Properties[edit]

Through neutron diffraction studies at low temperatures, Iron(II) fluoride is antiferromagnetic.[5] Heat capacity was measured over a temperature range 12-300 K. At temperature 78.3 K a thermal anomaly occurred. This thermal anomaly can be explained as Iron(II) fluoride passing from its disordered paramagnetic state to a more ordered antiferromagnetic state.[6]

The vapor species were identified between 965 and 1149 K. Using mass spectrometry the heat of sublimation was experimentally determined and averaged to be 75.56 ± 0.23 kcal. mole−1.[7] The following reaction was proposed in order to calculate the atomization energy for Fe+:

FeF2 + e → Fe+ +F2(or 2F) + 2e[7]

Crystal Structure[edit]

It is slightly soluble in water[4] (Ksp = 2.36 × 10−6)[8] and can be crystallized from it as a colorless tetrahydrate, FeF2·4H2O, (CAS Number 13940-89-1). The latter exists in two crystal structures, one rhombohedral and one hexagonal, the former having a disordered[9] The tetrahydrate oxidizes in moist air to a hydrate of iron(III) fluoride, 2FeF3·9H2O.[9]

To determine impurities in previous crystal structuring of the FeF2 the compound was first melted and then through spectrochemical analysis the percent of impurities could be determined.[10]

Though calculations using the lattice constants, found through X-ray crystallography, the bond lengths[10] were determined as follows:

d1(Fe-F): 2.03 ± 0.07 Å
d2(Fe-F): 2.10 ± 0.04 Å
d (F-F): 2.59 ± 0.13 Å

External links[edit]


  1. ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
  2. ^ a b Sigma-Aldrich. "Material Safety Data Sheet". Sigma-Aldrich. Retrieved 5 April 2011. 
  3. ^ a b Iron (II) Fluoride in the Chembok site. Accessed on 2011-01-16.
  4. ^ a b c Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0080379419. 
  5. ^ Erickson, R. (June 1953). "Neutron Diffraction Studies of Antiferromagnetism in Manganous Fluoride and Some Isomorphous Compounds". Physical Review 90 (5): 779–785. doi:10.1103/PhysRev.90.779. 
  6. ^ Stout, J.; Edward Catalano (December 1953). "Thermal Anomalies Associated with the Antiferromagnetic Ordering of FeF2, CoF3, and NiF2". Physical Review 92 (6): 1575–1575. doi:10.1103/PhysRev.92.1575. 
  7. ^ a b Kent, Richard; John L. Margrave (November 1965). "Mass Spectrometric Studies at High Temperatures. VIII. The Sublimation Pressure of Iron(II) Fluoride". Journal of the American Chemical Society 87 (21): 4754–4756. doi:10.1021/ja00949a016. 
  8. ^ Ksp solubility constant for common salts. Solubility of things site. Accessed on 2011-01-16.
  9. ^ a b Penfold, B. R.; Taylor, M. R. (1960). "The crystal structure of a disordered form of iron(II) fluoride tetrahydrate". Acta Crystallographica 13: 953–956. doi:10.1107/S0365110X60002302. 
  10. ^ a b Stout, J.; Stanley A. Reed (Nov 5, 1954). "The Crystal Structure of MnF2, FeF2, CoF2, NiF2 and ZnF2". Crystal Structures of Anhydrous Fluorides: 5279–5281.