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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.

Preparation

Iron(III) and iodide tend to undergo a redox reaction in which Fe is reduced to Fe 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.

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.

Fe(CO)₄I₂ + ½I₂ + hν → FeI₃ + 4CO

Reactivity

Iron(III) iodide is prone to light-induced decomposition to iron(II) iodide and iodine.

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.

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.

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. Iron powder reacts with iodine-containing proligands to also give adducts of ferric iodide.

See also

• Iron(II) iodide, FeI₂

References

1. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. pp. 1083–1084. ISBN 978-0-08-037941-8.
2. ^ Yoon, K. B.; Kochi, J. K. (1990). "Ferric iodide as a nonexistent compound". Inorg. Chem. 29 (4): 869–874. doi:10.1021/ic00329a058.
3. 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.
4. Housecroft, C. E.; Sharpe, A. G. (2008). Inorganic Chemistry (3rd ed.). Prentice Hall. p. 716. ISBN 978-0-13-175553-6.
5. 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.
6. 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.
7. 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, , from the reaction of Me₃AsI₂ with unactivated iron powder". Polyhedron. 55: 67–72. doi:10.1016/j.poly.2013.02.066.

• Iron(III) compounds
• Iodides