Iridium(III) chloride is the

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

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

IrCl₃. The

anhydrous A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achie ...

compound is relatively rare, but the related

hydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...

is much more commonly encountered. The anhydrous salt has two polymorphs, α and β, which are brown and red colored respectively. More commonly encountered is the

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 ...

dark green trihydrate IrCl₃(H₂O)₃ which is a common starting point for iridium chemistry.

Preparation

Iridium is separated from the other

platinum group metals The platinum-group metals (PGMs) are six noble, precious metallic elements clustered together in the periodic table. These elements are all transition metals in the d-block (groups 8, 9, and 10, periods 5 and 6). The six platinum-group m ...

as crystalline ammonium hexachloroiridate, (NH₄)₂ rCl₆ which can be reduced to iridium metal in a stream of

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

. The spongy Ir thus produced reacts with

chlorine Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...

at 650 °C to give iridium(III) chloride. Hydrated iridium trichloride is obtained by heating hydrated iridium(III) oxide with

hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...

Structure

Like the related rhodium compound, IrCl₃ adopts the structure seen for

aluminium chloride Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula . It forms a hexahydrate with the formula , containing six water molecules of hydration. Both the anhydrous form and the hexahydrate are col ...

. This is the

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three Vector (geometric), vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in t ...

α polymorph. A

rhombohedral In geometry, a rhombohedron (also called a rhombic hexahedron or, inaccurately, a rhomboid) is a special case of a parallelepiped in which all six faces are congruent rhombus, rhombi. It can be used to define the rhombohedral lattice system, a Ho ...

β polymorph also exists. Both polymorphs have effectively the same anion lattice but differ in the octahedral interstices the iridium ions occupy. The α polymorph converts to the β polymorph when heated to around 650 °C. The structure of the trihydrate has not been elucidated yet.

Reactions and uses

Industrially, most iridium complexes are generated from ammonium hexachloroiridate or the related chloroiridic acid (H₂IrCl₆). The

Cativa process The Cativa process is a method for the production of acetic acid by the carbonylation of methanol. The technology, which is similar to the Monsanto process, was developed by BP Chemicals and is under license by BP Plc. The process is based on an ...

, source of most of the world's

acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main compone ...

relies on such catalysts. Hydrated iridium(III) chloride is used in the for the preparation of other iridium complexes such as Vaska's complex, ''trans''- rCl(CO)(PPh₃)₂ With the presence of the chloride anion, it forms hexachloroiridate(III), and produces hexachloroiridate(IV) in

aqua regia Aqua regia (; from Latin, "regal water" or "royal water") is a mixture of nitric acid and hydrochloric acid, optimally in a molar concentration, molar ratio of 1:3. Aqua regia is a fuming liquid. Freshly prepared aqua regia is colorless, but i ...

. The trihydrate react with

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

to form

ammine complex In coordination chemistry, metal ammine complexes are metal complexes containing at least one ammonia () ligand. "Ammine" is spelled this way for historical reasons; in contrast, alkyl or aryl bearing ligands are spelt with a single "m". Almost al ...

es, such as pentaamminechloroiridium(III) chloride, formulated rCl(NH₃)₅l₂. It also reacts with concentrated

ammonium hydroxide Ammonia solution, also known as ammonia water, ammonium hydroxide, ammoniacal liquor, ammonia liquor, aqua ammonia, aqueous ammonia, or (inaccurately) ammonia, is a solution of ammonia in water. It can be denoted by the symbols NH3(aq). Although ...

at 150 °C to form the fully ammoniated complex, r(NH₃)₆l₃. The hydrate can also form complexes upon reaction with

bipyridine Bipyridines are a family of organic compounds with the formula (C5H4N)2, consisting of two pyridyl (C5H4N) rings. Pyridine is an aromatic nitrogen-containing heterocycle. The bipyridines are all colourless solids, which are soluble in organic sol ...

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 ...

, and

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 ...

.C. E. Housecroft and A. G. Sharpe ''Inorganic Chemistry'', p. 849.

Alkene In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or at the terminal position. Terminal alkenes are also known as Alpha-olefin, α-olefins. The Internationa ...

complexes such as cyclooctadiene iridium chloride dimerWinkhaus, G.; & Singer, H. (1966). Iridium(I)-Olefinkomplexe. ''Chem. Ber.'' 99:3610–18.Herde, J. L.; Lambert, J. C.; & Senoff, C. V. (1974). Cyclooctene and 1,5-Cyclooctadiene Complexes of Iridium(I). ''Inorg. Synth.'' 1974, volume 15, pages 18–20. . and chlorobis(cyclooctene)iridium dimer can also be prepared by heating the hydrate with the appropriate alkene in water/alcohol mixtures.

Decomposition

The trihydrate decomposes to the anhydrous form at 200 °C, which then oxidizes in air at 763 °C to iridium(IV) oxide, which then decomposes to iridium metal at 1070 °C. However, under

, it is directly reduced at 190 °C to iridium metal: :2 IrCl₃ + 3 H₂ → 2 Ir + 6 HCl

Safety

Iridium(III) chloride is not listed under Annex I of

Directive 67/548/EEC The Dangerous Substances Directive (as amended) was one of the main European Union laws concerning chemical safety, until its full replacement by the new regulation CLP Regulation (2008), starting in 2016. It was made under Article 100 (Art. 94 i ...

, but is listed in the inventory of the

Toxic Substances Control Act The Toxic Substances Control Act (TSCA) is a United States law, passed by the Congress in 1976 and administered by the United States Environmental Protection Agency (EPA), that regulates chemicals not regulated by other U.S. federal statutes, ...

(TSCA). It is also known as a mild skin and eye-irritating agent.

References

{{DEFAULTSORT:Iridium(Iii) Chloride Chlorides Iridium compounds Platinum group halides