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Iron(III) iodide
Names
	IUPAC name Iron(III) iodide
	Other names Ferric iodide
Identifiers
CAS Number	15600-49-4 ;
3D model (JSmol)	Interactive image;
ChemSpider	76688;
PubChem CID	85017;
CompTox Dashboard (EPA)	DTXSID50935338;
	InChI InChI=1S/Fe.3HI/h;3*1H/q+3;;;/p-3 Key: HEJPGFRXUXOTGM-UHFFFAOYSA-K;
	SMILES [Fe+3].[I-].[I-].[I-];
Properties
Chemical formula	FeI3
Molar mass	436.56 g/mol
Appearance	Black solid
Solubility in water	decomposes
Solubility	sparingly soluble in dichloromethane
Related compounds
Other anions	FeF3, FeCl3, FeBr3
Other cations	ScI3, TiI3, VI3, MoI3, WI3, RhI3, BiI3
Related compounds	FeI2
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Iron(III) iodide is an inorganic compound with the chemical formula FeI₃. It is a thermodynamically unstable compound that is difficult to prepare. Nevertheless, iron(III) iodide has been synthesised in small quantities in the absence of air and water.^[1]

Preparation

Iron(III) and iodide tend to undergo a redox reaction^[1] in which Fe³⁺ is reduced to Fe²⁺ and I⁻ is oxidised to I₂. This reaction can be avoided and iron(III) iodide can be synthesised by a photochemical reaction. Iron pentacarbonyl reacts with excess iodine in hexane under argon, releasing carbon monoxide and forming the complex diiodotetracarbonyliron(II), Fe(CO)₄I₂, as a light red solution.^[1]^[2]

Fe(CO)₅ + I₂ → Fe(CO)₄I₂ + CO

This complex then undergoes oxidative photodecarbonylation at −20 °C in the presence of further iodine and actinic light. A black film of FeI₃ is deposited as further carbon monoxide is evolved.^[1]^[2]

Fe(CO)₄I₂ + ½I₂ + hν → FeI₃ + 4CO

Reactivity

Iron(III) iodide is prone to light-induced decomposition to iron(II) iodide and iodine.^[2]^[3]^[4]

FeI₃ + hν → FeI₂ + ½I₂

Donor solvents such as tetrahydrofuran, acetonitrile, pyridine and water also promote this reaction: iron(III) iodide is extremely hygroscopic. It is sparingly soluble in dichloromethane. It reacts with iodide to form the tetraiodoferrate(III) ion.^[2]

FeI₃ + I⁻ → FeI₄⁻

Iron(III) iodide undergoes ligand exchange or metathesis with certain alkyl chlorides to reversibly form iron(III) chloride and the corresponding alkyl iodides.^[2]

FeI₃ + 3 RCl ⇌ FeCl₃ + 3 RI

Adducts of FeI₃ are well known. An orange complex can be prepared from FeI₂ and I₂ in the presence of thiourea.^[5]^[6] Iron powder reacts with iodine-containing proligands to also give adducts of ferric iodide.^[7]

References

^ ^a ^b ^c ^d Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. pp. 1083–1084. ISBN 978-0-08-037941-8.
^ ^a ^b ^c ^d ^e Yoon, K. B.; Kochi, J. K. (1990). "Ferric iodide as a nonexistent compound". Inorg. Chem. 29 (4): 869–874. doi:10.1021/ic00329a058.
^ Šima, Jozef; Brezová, Vlasta (2002). "Photochemistry of iodo iron(III) complexes". Coord. Chem. Rev. 229 (1–2): 27–35. doi:10.1016/S0010-8545(02)00018-8.
^ Housecroft, C. E.; Sharpe, A. G. (2008). Inorganic Chemistry (3rd ed.). Prentice Hall. p. 716. ISBN 978-0-13-175553-6.
^ Pohl, Siegfried; Bierbach, Ulrich; Saak, Wolfgang (1989). "FeI₃SC(NMe₂)₂, a Neutral Thiourea Complex of Iron(III) Iodide". Angew. Chem. Int. Ed. 28 (6): 776–777. doi:10.1002/anie.198907761.
^ Pohl, S.; Opitz, U.; Saak, W.; Haase, D. (1993). "Komplexe von FeI₂ und FeI₃ mit Tetramethylharnstoff". Z. Anorg. Allg. Chem. 619 (3): 608–612. doi:10.1002/zaac.19936190329.
^ Barnes, Nicholas A.; Godfrey, Stephen M.; Ho, Nicholas; McAuliffe, Charles A.; Pritchard, Robin G. (2013). "Facile synthesis of a rare example of an iron(III) iodide complex, [FeI₃(AsMe₃)₂], from the reaction of Me₃AsI₂ with unactivated iron powder". Polyhedron. 55: 67–72. doi:10.1016/j.poly.2013.02.066.