Iron (II) chloride

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Crystal structure
Structure of iron (II) chloride
__ Fe 2+      __ Cl -
Surname Iron (II) chloride
other names
  • Ferrous chloride
  • Iron dichloride
  • Iron chloride
  • Ferrum chloratum
Ratio formula FeCl 2
FeCl 2 · 4 H 2 O
Brief description

white crystals, as tetrahydrate blue-green, monoclinic, deliquescent crystals

External identifiers / databases
CAS number
  • 7758-94-3
  • 16399-77-2 (dihydrate)
  • 13478-10-9 (tetrahydrate)
EC number 231-843-4
ECHA InfoCard 100,028,949
PubChem 24458
ChemSpider 22866
Wikidata Q407867
Drug information
ATC code

B03 AA05

Molar mass
  • 126.75 g mol −1 (anhydrous)
  • 198.83 g mol −1 (tetrahydrate)
Physical state


  • 3.16 g cm −3 (anhydrous, 20 ° C)
  • 1.93 g cm −3 (tetrahydrate)
Melting point

677 ° C
105–110 ° C (release of crystal water)

boiling point

1023 ° C


good in water (644 g l −1 at 10 ° C)

safety instructions
Please note the exemption from the labeling requirement for drugs, medical devices, cosmetics, food and animal feed
GHS labeling of hazardous substances
05 - Corrosive 07 - Warning


H and P phrases H: 302-314
P: 280-305 + 351 + 338-310
Toxicological data

450 mg kg −1 ( LD 50ratoral )

As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Iron (II) chloride (FeCl 2 ) is a chemical compound of iron (II) - and chloride - ion . Iron (II) chloride belongs to the group of iron halides . There is also an iron (II) chloride tetrahydrate containing water of crystallization . Iron (II) chloride tetrahydrate cannot be converted into anhydrous iron (II) chloride by heating, as it decomposes when heated and iron (II) oxide is formed.

Iron (III) chloride (FeCl 3 ) also falls under the name iron chloride .


Iron (II) chloride occurs naturally in the form of the mineral rokühnit (hydrate).

Extraction and presentation

Iron (II) chloride can be prepared by reducing iron (III) chloride with hydrogen at 300 to 350 ° C (above this temperature, reduction to iron easily occurs).

Iron (II) chloride can also be produced by reacting iron with dry hydrogen chloride gas , although this reaction is less recommended because of the high temperatures required.

On the other hand, anhydrous iron (II) chloride cannot be produced by dissolving iron in hydrochloric acid and then precipitating it . This creates the hydrous iron (II) chloride tetrahydrate FeCl 2 4 H 2 O and molecular hydrogen :

However, if the synthesis is carried out under a nitrogen atmosphere in methanol , the hexamethanol solvate can be prepared and isolated with concentrated aqueous hydrochloric acid , which is then thermally decomposed to form anhydrous chloride:

A relatively simple representation of anhydrous iron (II) chloride in the laboratory is the reaction of chlorobenzene with anhydrous iron (III) chloride at 130 ° C:

It is also a by-product of the production of titanium dioxide using the chloride process . When pickling of iron sheets and parts, as a preparatory step of galvanizing , incurred large amounts.

The greenish tetrahydrate of iron (II) chloride. The brown color comes from contact with oxygen in the air.


Iron (II) chloride is a white, hygroscopic powder that can be sublimed in a stream of HCl at around 700 ° C. The tetrahydrate has a light blue color in its pure state. Even a small amount of oxidation turns it green. As oxidation by atmospheric oxygen progresses, it quickly changes to a rusty-brownish color. Both are easily soluble in water and in alcohol. Iron (II) chloride has a crystal structure of the cadmium (II) chloride type with the space group R 3 m (space group no. 166) (a = 360.3 pm, c = 1753.6 pm). The tetrahydrate crystallizes monoclinically , space group P 2 1 / c (No. 14) , lattice parameters a = 588.5 pm, b = 718 pm, c = 851.4 pm, β = 111.1 °. The dihydrate also crystallizes monoclinically, space group C 2 / m (No. 12) , lattice parameters a = 735.5 pm, b = 854.8 pm, c = 363.7 pm, β = 98.18 °. Template: room group / 166Template: room group / 14Template: room group / 12


In the laboratory and in synthetic chemistry, iron (II) chloride is an important starting material for the production of other iron compounds such as iron (III) chloride.

In the wastewater it serves as felling - and flocculants . Sewage treatment plants , for example, often use iron (II) chloride to eliminate phosphates , i.e. to precipitate phosphates (detergent or dishwashing detergent components). The best results are achieved with simultaneous precipitation.

In the case of long sewer lines and sewer pressure pipes, there are always odor problems in the warmer seasons. The cause is the formation of hydrogen sulfide . This formation can be prevented with iron (II) chloride.

Biogas plants also have to struggle with the formation of hydrogen sulfide. Here, iron (II) chloride is used for biogas desulphurisation .

In addition to the solid form, iron (II) chloride is supplied as an aqueous solution in rubberized tank trucks or in cans from chemical dealers.

Individual evidence

  1. a b c d e f g Entry on iron (II) chloride in the GESTIS substance database of the IFA , accessed on January 10, 2017(JavaScript required) .
  2. Entry on iron chlorides. In: Römpp Online . Georg Thieme Verlag, accessed on May 30, 2014.
  3. a b c data sheet iron (II) chloride (PDF) from Merck , accessed on January 19, 2011.
  4. a b Georg Brauer: Handbook of preparative inorganic chemistry . 3., reworked. Edition. tape III . Enke, Stuttgart 1981, ISBN 3-432-87823-0 , pp. 1641 .
  5. G. Winter: Iron (II) halides . In: Aaron Wold and John K. Ruff (Eds.): Inorganic Syntheses . tape 14 . McGraw-Hill Book Company, Inc., 1973, ISBN   07-071320-0  ( defective ) , p. 101-104 (English).
  6. Peter Kovacic and Neal O. Brace: Iron (II) chloride . In: Eugene G. Rochow (Ed.): Inorganic Syntheses . tape 6 . McGraw-Hill Book Company, Inc., 1960, pp. 172-173 (English).
  7. M. Wilkinson, JW Cable, WC Koehler: Neutron diffraction investigations of the magnetic ordering in FeBr 2 , CoBr 2 , FeCl 2 and CoCl 2 . In: Physical Review , 1959 , 20 , pp. 421-423. doi : 10.1103 / PhysRev.113.497
  8. ^ JJ Verbist, WC Hamilton, MS Lehmann, TF Koetzle: Neutron Diffraction Study of Iron (II) Chloride Tetrahydrate, FeCl 2 · 4 H 2 In: Journal of Chemical Physics , 56, 1972, pp. 3257-3264, doi: 10.1063 /1.1677688 .
  9. B. Morosin, EJ Graeber: Crystal structures of manganese (II) and iron (II) chloride dihydrate. In: Journal of Chemical Physics , 42, 1965, 898-901, doi: 10.1063 / 1.1696078 .