Iron(III) iodide
Iron(III) and iodide tend to undergo a redox reaction 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. 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 Iron(III) iodide is metastable and 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 + 3RCl ⇌ FeCl3 + 3RI
Complexes of FeI3 (such as the orange urea complex) can be prepared indirectly from FeI2 and I2 in the presence of ligands, or even from Fe powder with iodine-containing ligands.
Reactivity
Iron(III) iodide is an inorganic compound with the chemical formula FeI3.