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 highly soluble in water, giving pale green solutions.
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| Names | |||
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| IUPAC names
Iron(II) chloride | |||
| Other names
Ferrous chloride | |||
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| ECHA InfoCard | 100.028.949 
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| Properties | |||
| FeCl2 | |||
| 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) | ||
| Boiling point | 1,023 °C (1,873 °F; 1,296 K) (anhydrous) | ||
| 64.4 g/100 mL (10 °C), 68.5 g/100 mL (20 °C), 105.7 g/100 mL (100 °C) | |||
| SolubilityinTHF | Soluble | ||
| log P | −0.15 | ||
| +14750·10−6 cm3/mol | |||
| Structure | |||
| Monoclinic | |||
| Octahedral at Fe | |||
| Pharmacology | |||
| B03AA05 (WHO) | |||
| Hazards | |||
| NFPA 704 (fire diamond) | |||
| NIOSH (US health exposure limits): | |||
REL (Recommended) |
TWA 1 mg/m3[1] | ||
| Safety data sheet (SDS) | Iron (II) chloride MSDS | ||
| 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). | |||
Hydrated forms of ferrous chloride are generated by treatment of wastes from steel production with hydrochloric acid. Such solutions are designated "spent acid," or "pickle liquor" especially when the hydrochloric acid is not completely consumed:
The production of ferric chloride involves the use of ferrous chloride. Ferrous chloride is also a byproduct from the production of titanium, since some titanium ores contain iron.[3]
Ferrous chloride is prepared by addition of iron powder to a solution of hydrochloric acid in methanol. This reaction gives the methanol solvate of the dichloride, which upon heating in a vacuum at about 160 °C converts to anhydrous FeCl2.[4] The net reaction is shown:
FeBr2 and FeI2 can be prepared analogously.
An alternative synthesis of anhydrous ferrous chloride is the reduction of FeCl3 with chlorobenzene:[5]
For the preparation of ferrocene ferrous chloride is generated in situ by comproportionation of FeCl3 with iron powder in tetrahydrofuran (THF).[6] Ferric chloride decomposes to ferrous chloride at high temperatures.
The dihydrate, FeCl2(H2O)2, crystallizes from concentrated hydrochloric acid.[7] The dihydrate 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]
FeCl2 and its hydrates form complexes with many ligands. For example, solutions of the hydrates react with two molar equivalents of [(C2H5)4N]Cl to give the salt [(C2H5)4N]2[FeCl4].[10]
The anhydrous FeCl2, which is soluble in THF,[2] is a standard precursor in organometallic synthesis. FeCl2 is used to generate NHC complexes in situ for cross coupling reactions.[11]
Unlike the related ferrous sulfate and ferric chloride, ferrous chloride has few commercial applications. Aside from use in the laboratory synthesis of iron complexes, ferrous chloride serves as a coagulation and flocculation agent in wastewater treatment, especially for wastes containing chromateorsulfides.[12] It is used for odor control in wastewater treatment. It is used as a precursor to make various grades of hematite that can be used in a variety of pigments. It is the precursor to hydrated iron(III) oxides that are magnetic pigments.[3] FeCl2 finds some use as a reagentinorganic synthesis.[13]
Lawrencite, (Fe,Ni)Cl2, is the natural counterpart, and a typically (though rarely occurring) meteoritic mineral.[14] The natural form of the dihydrate is rokühnite - a very rare mineral.[15] Related, but more complex (in particular, basic or hydrated) minerals are hibbingite, droninoite and kuliginite.
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