iron(II) iodide
{{Chembox
| ImageFile =
| ImageSize =
| IUPACName = Iron(II) iodide
| OtherNames = Ferrous iodide
|Section1={{Chembox Identifiers
| CASNo = 7783-86-0
| CASNo_Ref = {{cascite|correct|CAS}}
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = F5452U54PN
| PubChem = 82220
| RTECS =
| EINECS = 232-031-2
| SMILES = [Fe+2].[I-].[I-]
| ChemSpiderID = 74200
| InChI = 1/Fe.2HI/h;2*1H/q+2;;/p-2
| InChIKey = BQZGVMWPHXIKEQ-NUQVWONBAN
| StdInChI = 1S/Fe.2HI/h;2*1H/q+2;;/p-2
| StdInChIKey = BQZGVMWPHXIKEQ-UHFFFAOYSA-L
}}
|Section2={{Chembox Properties
| Formula = FeI2
| MolarMass = 309.65 g/mol
| Appearance = White to off-white or grey powder
| Density = 5.315 g/cm3
| MeltingPtC = 587
| BoilingPtC = 827
| Solubility = soluble
| SolubleOther =
| RefractIndex =
| MagSus = +13,600·10−6 cm3/mol
}}
|Section3={{Chembox Structure
| CrystalStruct =
}}
|Section4={{Chembox Hazards
| MainHazards =
| FlashPt =
| AutoignitionPt =
}}
| Section8 = {{Chembox Related
| OtherAnions = Iron(II) fluoride
Iron(II) chloride
Iron(II) bromide
| OtherCations = Manganese(II) iodide
Cobalt(II) iodide
| OtherFunction_label = Iron iodides
| OtherFunction = Iron(III) iodide
}}
}}
Iron(II) iodide is an inorganic compound with the chemical formula FeI2.{{Greenwood&Earnshaw2nd|pages=1083-1084}}[http://ull.chemistry.uakron.edu/erd/Chemicals/26000/24496.html University of Akron Chemical Database] {{webarchive|url=https://archive.today/20121212135447/http://ull.chemistry.uakron.edu/erd/Chemicals/26000/24496.html |date=2012-12-12 }} It is used as a catalyst in organic reactions.
Preparation
Iron(II) iodide can be synthesised by the reaction of iron with iodine at 500 °C:{{Cite book |title=Handbuch der präparativen anorganischen Chemie. 3 |date=1981 |publisher=Enke |isbn=978-3-432-87823-2 |edition=3., umgearb. Aufl |location=Stuttgart}}
:{{chem2|Fe + I2 -> FeI2}}
This is in contrast to the other iron(II) halides, which are best prepared by reaction of heated iron with the appropriate hydrohalic acid.
:{{chem2|Fe + 2 HX -> FeX2 + H2}}
Alternatively, the synthesis can be carried out by treating freshly reduced iron with concentrated hydriodic acid under a nitrogen atmosphere in methanol. The initially obtained hexamethanol solvate is then thermally decomposed to anhydrous iodide:
:{{chem2|Fe + 2 HI + 6 MeOH-> FeI2*6MeOH + H2}}
::{{chem2|FeI2*6 MeOH -> FeI2 + 6 MeOH}}
Extremely finely divided iron(II) iodide is obtained by thermal decomposition of tetracarbonyldiiodidoiron(II) (Fe(CO)4I2).
In contrast to the ferrous fluoride, chloride and bromide, which form known hydrates, the diiodide is speculated to form a stable tetrahydrate but it not been characterized directly.{{cite journal | last1=Wren | first1=J.C | last2=Glowa | first2=G.A | last3=Merritt | first3=J | title=Corrosion of stainless steel by gaseous I2 | journal=Journal of Nuclear Materials | volume=265 | issue=1–2 | year=1999 | pages=161–177 | issn=0022-3115 | doi=10.1016/s0022-3115(98)00504-2}}
Chemical properties
Iron(II) iodide is a hygroscopic red-violet to black solid that is soluble in water, ethanol and diethyl ether. Rapid oxidation occurs in solution and in moist air.{{Cite book |last=Lautenschläger |first=Karl-Heinz |title=Taschenbuch der Chemie |last2=Schröter |first2=Werner |last3=Wanninger |first3=Andrea |date=2007 |publisher=Deutsch |isbn=978-3-8171-1760-4 |edition=20., überarb. u. erw. Aufl., [Ausg. mit CD-ROM] |location=Frankfurt am Main}} It turns whitish when exposed to air. The solution in water is colorless.
Dissolving iron metal in hydroiodic acid is another route to aqueous solutions of iron(II) iodide. Crystalline hydrates precipitate from these solutions.{{Clarify | reason=What hydrates? What page of G&E? | date=March 2022}}
Physical properties
Iron(II) iodide adopts the same crystal structure as cadmium iodide (CdI2). It crystallizes in the trigonal crystal system of the cadmium hydroxide type with the space group P{{overline|3}}m1 (space group no. 164) and lattice constants a = 404 pm, c = 675 pm.{{Cite book |last=Ans |first=Jan d' |title=Elemente, anorganische Verbindungen und Materialien |last2=Ans |first2=Jan d' |date=1998 |publisher=Verlag nicht ermittelbar |isbn=978-3-540-60035-0 |edition=4., neubearb. u. rev. Aufl |series=Taschenbuch für Chemiker und Physiker / D'Ans |location=Ort nicht ermittelbar}}
Applications
Iron(II) iodide is used as an ingredient in homeopathic medicines. In the field of application it is known as Ferrum jodatum. However, the attributed effect, particularly against glandular diseases, has not been scientifically confirmed.
See also
- Iron(III) iodide, FeI3, unstable
References
{{reflist}}
{{Iron compounds}}
{{Iodides}}