Iron(II) chloride

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Iron(II) chloride
structure of anhydrous ferrous chloride (purple = Fe, green = Cl)
structure of tetrahydrate
IUPAC names
Iron(II) chloride
Iron dichloride
Other names
Ferrous chloride,
3D model (JSmol)
ECHA InfoCard 100.028.949
EC Number 231-843-4
RTECS number NO5400000
Molar mass 126.751 g/mol (anhydrous)
198.8102 g/mol (tetrahydrate)
Appearance tan solid (anhydrous)
pale green solid (di-tetrahydrate)
Density 3.16 g/cm3 (anhydrous)
2.39 g/cm3 (dihydrate)
1.93 g/cm3 (tetrahydrate)
Melting point 677 °C (1,251 °F; 950 K) (anhydrous)
120 °C (dihydrate)
105 °C (tetrahydrate) [1]
Boiling point 1,023 °C (1,873 °F; 1,296 K) (anhydrous)
64.4 g/100 mL (10 °C),
68.5 g/100mL (20 °C),
105.7 g/100 mL (100 °C)
Solubility in THF soluble
log P -0.15
+14,750·10−6 cm3/mol
octahedral at Fe
B03AA05 (WHO)
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
US health exposure limits (NIOSH):
REL (Recommended)
TWA 1 mg/m3[2]
Related compounds
Other anions
Iron(II) fluoride
Iron(II) bromide
Iron(II) iodide
Other cations
Cobalt(II) chloride
Manganese(II) chloride
Copper(II) chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Iron(II) chloride, also known as ferrous chloride, is the chemical compound of formula FeCl2. It is a paramagnetic solid with a high melting point. The compound is white, but typical samples are often off-white. FeCl2 crystallizes from water as the greenish tetrahydrate, which is the form that is most commonly encountered in commerce and the laboratory. There is also a dihydrate. The compound is also soluble in water; aqueous solutions of FeCl2 are highly transparent and pale green in color.


Hydrated forms of ferrous chloride are generated by treatment of wastes from steel production with hydrochloric acid. Such solutions are designated "spent acid," especially when the hydrochloric acid is not completely consumed:

Fe + 2 HCl → FeCl2 + H2

The spent acid requires treatment before its disposal. It is also byproduct from titanium production, since some titanium ores contain iron.[3]

Sample of hydrated ferrous chloride.

Laboratory preparation[edit]

The dihydrate crystallizes from concentrated hydrochloric acid.[4]

Anhydrous FeCl2[edit]

Ferrous chloride is conveniently prepared by addition of iron powder to a solution of methanol and concentrated hydrochloric acid under an inert atmosphere. This reaction gives the methanol solvate, which upon heating in a vacuum at about 160 °C gives anhydrous FeCl2.[5] FeBr2 and FeI2 can be prepared analogously.

Fe + 2 HCl → FeCl2 + H2

An alternative synthesis of entails the reduction of FeCl3 with chlorobenzene:[6]

2 FeCl3 + C6H5Cl → 2 FeCl2 + C6H4Cl2 + HCl

FeCl2 is soluble in tetrahydrofuran (THF). In one of two classic syntheses of ferrocene, Wilkinson generated FeCl2 by heating FeCl3 with iron powder in THF.[7] Ferric chloride decomposes to ferrous chloride at high temperatures.


The dihydrate, FeCl2(H2O)2, is a coordination polymer. Each Fe center is coordinated to four doubly bridging chloride ligands. The octahedron is completed by a pair of mutually trans aquo ligands.[8]

Subunit of FeCl2(H2O)2 lattice.


FeCl2 and its hydrates form complexes with many ligands. The anhydrous FeCl2 is a standard precursor in organometallic synthesis. Solutions of the hydrates react with two molar equivalents of [(C2H5)4N]Cl to give the salt [(C2H5)4N]2[FeCl4].[9]


Ferrous chloride has a variety of niche applications, but the related compounds ferrous sulfate and ferric chloride enjoy more applications. Aside from use in the laboratory synthesis of iron complexes, ferrous chloride serves as a reducing flocculating agent in wastewater treatment, especially for wastes containing chromate. It is the precursor to hydrated iron(III) oxides that are magnetic pigments.[3] Ferrous chloride is employed as a reducing agent in many organic synthesis reactions.


  1. ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
  2. ^ "NIOSH Pocket Guide to Chemical Hazards #0346". National Institute for Occupational Safety and Health (NIOSH). 
  3. ^ a b Egon Wildermuth, Hans Stark, Gabriele Friedrich, Franz Ludwig Ebenhöch, Brigitte Kühborth, Jack Silver, Rafael Rituper “Iron Compounds” in Ullmann’s Encyclopedia of Industrial Chemistry Wiley-VCH, Wienheim, 2005.
  4. ^ K. H.. Gayer; L. Woontner (1957). "Iron(II) Chloride 2-Hydrate". Inorg. Synth. 5: 179–181. doi:10.1002/9780470132364.ch48. 
  5. ^ G. Winter; Thompson, D. W.; Loehe, J. R. (1973). "Iron(II) Halides". Inorg. Synth. 14: 99–104. doi:10.1002/9780470132456.ch20. 
  6. ^ P. Kovacic and N. O. Brace (1960). "Iron(II) Chloride". Inorg. Synth. 6: 172. doi:10.1002/9780470132371.ch54. 
  7. ^ G. Wilkinson (1963). "Ferrocene". Org. Synth. ; Coll. Vol., 4, p. 473 
  8. ^ Morosin, B.; Graeber, E. J. (1965). "Crystal structures of manganese(II) and iron(II) chloride dihydrate". Journal of Chemical Physics. 42: 898–901. doi:10.1063/1.1696078. 
  9. ^ N. S. Gill, F. B. Taylor (1967). "Tetrahalo Complexes of Dipositive Metals in the First Transition Series". Inorg. Synth. 9: 136–142. doi:10.1002/9780470132401.ch37. 

See also[edit]