Iron(III) iodide is an

inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

with the

chemical formula A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as pare ...

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 Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is t ...

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 Organic photochemistry encompasses organic reactions that are induced by the action of light. The absorption of ultraviolet light by organic molecules often leads to reactions. In the earliest days, sunlight was employed, while in more modern times ...

Iron pentacarbonyl Iron pentacarbonyl, also known as iron carbonyl, is the compound with formula . Under standard conditions Fe( CO)5 is a free-flowing, straw-colored liquid with a pungent odour. Older samples appear darker. This compound is a common precursor t ...

reacts with excess

iodine Iodine is a chemical element; it has symbol I and atomic number 53. The heaviest of the stable halogens, it exists at standard conditions as a semi-lustrous, non-metallic solid that melts to form a deep violet liquid at , and boils to a vi ...

in hexane under argon, releasing

carbon monoxide Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...

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 Actinism is the property of solar radiation that leads to the production of photochemical and photobiological effects. It is important in chemical photography and x-ray imaging, and causes sunburn and photodegradation of materials. Actinic chem ...

. 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 Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water- miscible organic liquid with low viscosity. It is ...

acetonitrile Acetonitrile, often abbreviated MeCN (methyl cyanide), is the chemical compound with the formula and structure . This colourless liquid is the simplest organic nitrile (hydrogen cyanide is a simpler nitrile, but the cyanide anion is not class ...

pyridine Pyridine is a basic (chemistry), basic heterocyclic compound, heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom . It is a highly flammable, weak ...

and

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

also promote this reaction: iron(III) iodide is extremely

hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption (chemistry), absorption or adsorption from the surrounding Natural environment, environment, which is usually at normal or room temperature. If water mol ...

. It is sparingly soluble in

dichloromethane Dichloromethane (DCM, methylene chloride, or methylene bichloride) is an organochlorine compound with the formula . This colorless, volatile liquid with a chloroform-like, sweet odor is widely used as a solvent. Although it is not miscible with ...

. It reacts with iodide to form the tetraiodoferrate(III) ion. :FeI₃ + I⁻ → FeI₄⁻ Iron(III) iodide undergoes ligand exchange or metathesis with certain

alkyl chloride Organochlorine chemistry is concerned with the properties of organochlorine compounds, or organochlorides, organic compounds that contain one or more carbon–chlorine bonds. The chloroalkane class (alkanes with one or more hydrogens substituted ...

s to reversibly form

iron(III) chloride Iron(III) chloride describes the inorganic compounds with the formula (H2O)x. Also called ferric chloride, these compounds are some of the most important and commonplace compounds of iron. They are available both in anhydrous and in hydrated f ...

and the corresponding

alkyl iodide Organoiodine chemistry is the study of the synthesis and properties of organoiodine compounds, or organoiodides, organic compounds that contain one or more carbon–iodine bonds. They occur widely in organic chemistry, but are relatively rare ...

s. :FeI₃ + 3 RCl ⇌ FeCl₃ + 3 RI

Adducts In chemistry, an adduct (; alternatively, a contraction of "addition product") is a product of a direct addition of two or more distinct molecules, resulting in a single reaction product containing all atoms of all components. The resultant is ...

of FeI₃ are well known. An orange complex can be prepared from FeI₂ and I₂ in the presence of

thiourea Thiourea () is an organosulfur compound with the formula and the structure . It is structurally similar to urea (), with the oxygen atom replaced by sulfur atom (as implied by the '' thio-'' prefix). The properties of urea and thiourea differ s ...

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

References

{{Iodides Iron(III) compounds Iodides

Preparation

Reactivity

See also

References