Iridium(III) chloride
{{Chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 443643874
| Name = Iridium(III) chloride
| ImageFile3 = IrCl3(aq)x.jpg
| ImageCaption3 = Trihydrate
| ImageName3 = Iridium(III) chloride trihydrate
| OtherNames = Iridium trichloride
| Section1 = {{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 10025-83-9
| CASNo_Comment =(anhydrous)
| CASNo1 = 14996-61-3
| CASNo1_Comment = (hydrate)
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 20278OEG45
| EINECS = 233-044-6
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 23837
| RTECS =
| PubChem = 82301
| StdInChI=1S/3ClH.Ir/h3*1H;/q;;;+3/p-3
| StdInChIKey = DANYXEHCMQHDNX-UHFFFAOYSA-K
| SMILES = [Cl-].[Cl-].[Cl-].[Ir+3]
}}
| Section2 = {{Chembox Properties
| Formula = IrCl3
| MolarMass = 298.58 g/mol (anhydrous)
316.60 g/mol (hydrate)
| Appearance = brown solid (α-anhydrous)
red solid (β-anhydrous)
dark green solid (trihydrate)
| Density = 5.30 g/cm3, solid{{cite book |editor1-last=Haynes |editor1-first=William |title=CRC Handbook of Chemistry and Physics |date=2014 |publisher=CRC Press |isbn=9781482208689 |page=4-68 |language=en}}
| Solubility = insoluble (anhydrous IrCl3), soluble (hydrated derivative)
| SolubleOther = Insoluble in HCl and alkanes
| MeltingPtC = 763
| MeltingPt_notes = (decomposes)
| MagSus = −14.4·10−6 cm3/mol }}
| Section3 = {{Chembox Structure
| CrystalStruct = Monoclinic, mS16
| SpaceGroup = C12/m1, No. 12
}}
| Section4 = {{Chembox Thermochemistry
| DeltaHf = −257 kJ/mol
}}
| Section7 = {{Chembox Hazards
| GHSPictograms = {{GHS07}}{{GHS09}}
| GHSSignalWord = Warning
| HPhrases = {{H-phrases|302|411}}
| PPhrases = {{P-phrases|}}
| FlashPt = non-flammable
}}
| Section8 = {{Chembox Related
| OtherAnions =
| OtherCations = Rhodium(III) chloride
| OtherCompounds = Platinum(II) chloride}}
}}
Iridium(III) chloride is the inorganic compound with the formula IrCl3. The anhydrous compound is relatively rare, but the related hydrate 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 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 as crystalline ammonium hexachloroiridate, (NH4)2[IrCl6], which can be reduced to iridium metal in a stream of hydrogen. The spongy Ir thus produced reacts with chlorine at 650 °C to give iridium(III) chloride.{{cite book |author1=Hermann Renner |title=Ullmann's Encyclopedia of Industrial Chemistry |chapter=Platinum Group Metals and Compounds |date=2018 |pages=1–73 |doi=10.1002/9783527306732.a21_075.pub2 |isbn=9783527303854 |s2cid=94472506 |language=en}}
Hydrated iridium trichloride is obtained by heating hydrated iridium(III) oxide with hydrochloric acid.
Structure
Like the related rhodium compound, IrCl3 adopts the structure seen for aluminium chloride.{{Greenwood&Earnshaw}} This is the monoclinic α polymorph.{{ cite journal | first1 = K. | last1 = Brodersen | first2 = F. | last2 = Moers | first3 = H. G. | last3 = Schnering | title = Zur Struktur des Iridium(III)- und des Ruthenium(III)-chlorids | journal = Naturwissenschaften | year = 1965 | volume = 52 | issue = 9 | pages = 205–206 | doi = 10.1007/BF00626459 | bibcode = 1965NW.....52..205B | s2cid = 43351743 }} A rhombohedral β polymorph also exists. Both polymorphs have effectively the same anion lattice but differ in the octahedral interstices the iridium ions occupy.{{ cite journal | first1 = A. | last1 = Meisel | first2 = G. | last2 = Leonhardt | title = Die Kristallstruktur von β-Iridium(III)-Chlorid | journal = Z. anorg. allg. Chem. | year = 1965 | volume = 339 | issue = 1–2 | pages = 57–66 | doi = 10.1002/zaac.19653390109 }} The α polymorph converts to the β polymorph when heated to around 650 °C.
{{multiple image
| align = center
| width = 200
| footer = Structures of the forms of iridium(III) chloride
| image1 = Alpha-iridium(III)-chloride-xtal-viewed-down-b-axis-3D-bs-17.png
| alt1 =
| caption1 = α-IrCl3
| image2 = Beta-iridium(III)-chloride-xtal-viewed-down-ab-diagonal-3D-bs-17-raw.png
| alt2 =
| caption2 = β-IrCl3}}
| class="wikitable plainrowheaders"
|+ Crystallographic data for the 2 polymorphs of iridium(III) chloride !Compound |
| Crystal Structure |
|---|
| Space Group
|C2/m |Fddd |
| Lattice constant a (Å)
|5.99 |6.95 |
| Lattice constant b (Å)
|10.37 |9.81 |
| Lattice constant c (Å)
|5.99 |20.82 |
| β
|109.4° | |
| Calculated density (g/cm3)
|5.33 |5.34 |
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, source of most of the world's acetic acid 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-[IrCl(CO)(PPh3)2].Vaska, L.; & DiLuzio, J. W. (1961) J. Am. Chem. Soc. 83:2784. Girolami, G.S.; Rauchfuss, T.B.; Angelici, R.J. (1999). Synthesis and Technique in Inorganic Chemistry (3rd Edn.). Sausalito: University Science Books. With the presence of the chloride anion, it forms hexachloroiridate(III), and produces hexachloroiridate(IV) in aqua regia. The trihydrate react with ammonia to form ammine complexes, such as pentaamminechloroiridium(III) chloride, formulated [IrCl(NH3)5]Cl2. It also reacts with concentrated ammonium hydroxide at 150 °C to form the fully ammoniated complex, [Ir(NH3)6]Cl3. The hydrate can also form complexes upon reaction with bipyridine, acetonitrile, and pyridine.C. E. Housecroft and A. G. Sharpe Inorganic Chemistry, p. 849.
Alkene 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. {{doi|10.1002/9780470132463.ch5}}. 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 hydrogen, it is directly reduced at 190 °C to iridium metal:{{cite journal |author1=A.E. Newkirk |author2=D.W. McKee |title=Thermal decomposition of rhodium, iridium, and ruthenium chlorides |journal=Journal of Catalysis |date=1968 |volume=11 |issue=4 |pages=370–377 |doi=10.1016/0021-9517(68)90061-4 |language=en}}{{cite journal |author1=W. B. Rowston |author2=J. M. Ottaway |title=Determination of noble metals by carbon furnace atomic-absorption spectrometry. Part 1. Atom formation processes |journal=Analyst |date=1979 |volume=104 |issue=1240 |pages=645–659 |doi=10.1039/AN9790400645 |bibcode=1979Ana...104..645R |language=en}}{{cite journal |author1=R. K. Kawar |author2=P. S. Chigare |author3=P. S. Patil |title=Substrate temperature dependent structural, optical and electrical properties of spray deposited iridium oxide thin films |journal=Applied Surface Science |date=2003 |volume=206 |issue=1–4 |pages=90–101 |doi=10.1016/S0169-4332(02)01191-1 |bibcode=2003ApSS..206...90K |language=en}}
:2 IrCl3 + 3 H2 → 2 Ir + 6 HCl
Safety
Iridium(III) chloride is not listed under Annex I of Directive 67/548/EEC, but is listed in the inventory of the Toxic Substances Control Act (TSCA). It is also known as a mild skin and eye-irritating agent.{{cite book|title=Encyclopaedia of Occupational Health and Safety|first=J.|last=Mager Stellman|chapter=Iridium|isbn=978-92-2-109816-4|date=1998|publisher=International Labour Organization|pages=[https://archive.org/details/encyclopaediaofo0003unse/page/63 63.19]|chapter-url=https://books.google.com/books?id=nDhpLa1rl44C&pg=PT125|oclc=35279504|url=https://archive.org/details/encyclopaediaofo0003unse/page/63}}
References
{{Iridium compounds}}
{{Chlorides}}
{{DEFAULTSORT:Iridium(Iii) Chloride}}