Editing Iridium (section)

== Chemistry ==
{{See also|Iridium compounds}}
{|class="wikitable" style="float:right;margin:1em"
|-
! colspan=2| Oxidation states{{efn|Most common oxidation states of iridium are in bold. The right column lists one representative compound for each oxidation state.}}
|-
| −3||{{chem|[Ir(CO)|3|]|3-}}
|-
| −1||{{chem2|[Ir(CO)3(PPh3)](1-)}}
|-
| 0||{{chem2|Ir4(CO)12}}
|-
| '''+1'''||{{chem2|[IrCl(CO)(PPh3)2]}}
|-
| '''+2'''||{{chem2|Ir(C5H5)2}}
|-
| '''+3'''||{{chem2|IrCl3}}
|-
| '''+4'''||{{chem2|IrO2}}
|-
| +5||{{chem2|Ir4F20}}
|-
| +6||{{chem|IrF|6}}
|-
| +7||{{chem2|[Ir(O2)O2]+}}
|-
| +8||{{chem2|IrO4}}
|-
| +9||{{chem2|[IrO4]+}}<ref name="IrIX" />
|}

=== Oxidation states ===
Iridium forms compounds in [[oxidation state]]s between −3 and +9, but the most common oxidation states are +1, +2, +3, and +4.<ref name="greenwood" /> Well-characterized compounds containing iridium in the +6 oxidation state include [[Iridium(VI) fluoride|{{chem2|IrF6}}]] and the oxides {{chem2|Sr2MgIrO6}} and {{chem2|Sr2CaIrO6}}.<ref name="greenwood">{{cite book |last=Greenwood |first=N. N. |author2=Earnshaw, A. |title=Chemistry of the Elements |edition=2nd |publisher=Oxford: Butterworth–Heinemann |date=1997 |isbn=978-0-7506-3365-9 |pages=1113–1143, 1294 |oclc=213025882}}</ref><ref>{{cite journal |last1=Jung |first1=D. |title=High Oxygen Pressure and the Preparation of New Iridium (VI) Oxides with Perovskite Structure: {{chem|Sr|2|MIrO|6}} (M = Ca, Mg) |journal=Journal of Solid State Chemistry |volume=115 |issue=2 |date=1995 |pages=447–455 |doi=10.1006/jssc.1995.1158 |bibcode=1995JSSCh.115..447J |last2=Demazeau |first2=Gérard}}</ref> [[iridium(VIII) oxide]] ({{chem2|IrO4}}) was generated under matrix isolation conditions at 6 K in [[argon]].<ref>{{cite journal|title=Formation and Characterization of the Iridium Tetroxide Molecule with Iridium in the Oxidation State +VIII|journal=Angewandte Chemie International Edition|volume=48 |date=2009|pages=7879–7883|author=Gong, Y.|author2=Zhou, M.|author3=Kaupp, M.|author4=Riedel, S. |doi=10.1002/anie.200902733|pmid=19593837|issue=42}}</ref> The highest oxidation state (+9), which is also the highest recorded for ''any'' element, is found in gaseous {{chem2|[IrO4]+}}.<ref name="IrIX" />

=== Binary compounds ===
Iridium does not form [[binary compound|binary]] [[hydride]]s. Only one [[binary phase|binary oxide]] is well-characterized: [[Iridium(IV) oxide|iridium dioxide]], {{chem|IrO|2}}.  It is a blue black solid that adopts the [[fluorite structure]].<ref name="greenwood" /> A [[sesquioxide]], {{chem|Ir|2|O|3}}, has been described as a blue-black powder, which is oxidized to {{chem|IrO|2}} by {{chem|HNO|3}}.<ref name="perry" /> The corresponding [[disulfide]]s, [[diselenide]]s, [[sesquisulfide]]s, and sesquiselenides are known, as well as {{chem|IrS|3}}.<ref name="greenwood" />

Binary trihalides, {{chem|IrX|3}}, are known for all of the halogens.<ref name="greenwood" /> For oxidation states +4 and above, only the [[Iridium(IV) fluoride|tetrafluoride]], [[Iridium(V) fluoride|pentafluoride]] and [[Iridium hexafluoride|hexafluoride]] are known.<ref name="greenwood" /> Iridium hexafluoride, {{chem|IrF|6}}, is a volatile yellow solid, composed of octahedral molecules. It decomposes in water and is reduced to {{chem|link=iridium tetrafluoride|IrF|4}}.<ref name="greenwood" /> Iridium pentafluoride is also a strong oxidant, but it is a [[tetramer]], {{chem|Ir|4|F|20}}, formed by four corner-sharing octahedra.<ref name="greenwood" />

=== Complexes ===
[[File:IrCl3(aq)x.jpg|thumb|left|Hydrated [[iridium trichloride]], a common salt of iridium.]]
Iridium has extensive [[coordination chemistry]].

Iridium in its complexes is always [[low-spin]]. Ir(III) and Ir(IV) generally form [[octahedral molecular geometry|octahedral complexes]].<ref name="greenwood" />  Polyhydride complexes are known for the +5 and +3 oxidation states.<ref>{{cite book| last = Holleman| first = A. F.| author2=Wiberg, E.| author3=Wiberg, N.| title=Inorganic Chemistry| edition=1st| publisher=Academic Press| date=2001| isbn=978-0-12-352651-9| oclc =47901436}}</ref> One example is {{chem2|IrH5(P<sup>i</sup>Pr3)2}} (<sup>i</sup>Pr = [[isopropyl]]).<ref>{{cite journal |doi=10.1021/acs.chemrev.6b00080|title=Polyhydrides of Platinum Group Metals: Nonclassical Interactions and σ-Bond Activation Reactions |year=2016 |last1=Esteruelas |first1=Miguel A. |last2=López |first2=Ana M. |last3=Oliván |first3=Montserrat |journal=Chemical Reviews |volume=116 |issue=15 |pages=8770–8847 |pmid=27268136 |doi-access=free |hdl=10261/136216 |hdl-access=free }}</ref> The ternary hydride {{chem|Mg|6|Ir|2|H|11}} is believed to contain both the {{chem|IrH|5|4-}} and the 18-electron {{chem|IrH|4|5-}} anion.<ref>{{cite journal| title = {{chem|Mg|6|Ir|2|H|11}}, a new metal hydride containing saddle-like {{chem|IrH|4|5-}} and square-pyramidal {{chem|IrH|5|4-}} hydrido complexes | last = Černý| first = R.| author2=Joubert, J.-M.| author3=Kohlmann, H.| author4=Yvon, K. | journal = Journal of Alloys and Compounds| volume = 340| issue = 1–2| date = 2002|pages = 180–188| doi=10.1016/S0925-8388(02)00050-6}}</ref>

Iridium also forms [[oxyanion]]s with oxidation states +4 and +5.  {{chem|K|2|IrO|3}} and {{chem|KIrO|3}} can be prepared from the reaction of [[potassium oxide]] or [[potassium superoxide]] with iridium at high temperatures.  Such solids are not soluble in conventional solvents.<ref>{{cite journal|title=The chemistry of ruthenium, osmium, rhodium, iridium, palladium and platinum in the higher oxidation states|journal=Coordination Chemistry Reviews|volume=46|date=1982 |pages=1–127|author=Gulliver, D. J.|author2=Levason, W.|doi=10.1016/0010-8545(82)85001-7}}</ref>

Just like many elements, iridium forms important chloride complexes. Hexachloroiridic (IV) acid, {{chem|H|2|IrCl|6}}, and its [[ammonium]] salt are common iridium compounds from both industrial and preparative perspectives.<ref name="ullmann-pt" /> They are intermediates in the purification of iridium and used as precursors for most other iridium compounds, as well as in the preparation of [[anode]] coatings. The {{chem|IrCl|6|2-}} ion has an intense dark brown color, and can be readily reduced to the lighter-colored {{chem|IrCl|6|3-}} and vice versa.<ref name="ullmann-pt" /> [[Iridium(III) chloride|Iridium trichloride]], {{chem|IrCl|3}}, which can be obtained in [[anhydrous]] form from direct oxidation of iridium powder by [[chlorine]] at 650&nbsp;°C,<ref name="ullmann-pt" /> or in hydrated form by dissolving {{chem|Ir|2|O|3}} in [[hydrochloric acid]], is often used as a starting material for the synthesis of other Ir(III) compounds.<ref name="greenwood" /> Another compound used as a starting material is potassium hexachloroiridate(III), {{chem2|K3IrCl6}}.<ref>{{cite book |doi=10.1002/9780470132432.ch42 |chapter=Pentaammineiridium(III) Complexes |date=1970 |last1=Schmidtke |first1=Hans-Herbert  |title=Inorganic Syntheses |volume=12 |pages=243–247 |isbn=978-0-470-13171-8 }}</ref>

=== Organoiridium chemistry ===
[[File: Ir2Cl2 cod 2improved.svg|thumb|left|[[Cyclooctadiene iridium chloride dimer]] is a common complex of Ir(I).]]

[[Organoiridium compound]]s contain iridium–[[carbon]] bonds. Early studies identified the very stable [[tetrairidium dodecacarbonyl]], {{chem|Ir|4|(CO)|12}}.<ref name="greenwood" /> In this compound, each of the iridium atoms is bonded to the other three, forming a [[Tetrahedron|tetrahedral]] cluster. The discovery of [[Vaska's complex]] ({{chem|IrCl(CO)[P(C|6|H|5|)|3|]|2}}) opened the [[door]] for [[oxidative addition]] reactions, a process fundamental to useful reactions. For example, [[Crabtree's catalyst]], a [[homogeneous catalyst]] for [[hydrogenation]] reactions.<ref>{{cite journal|first = R. H.| last = Crabtree| author-link =Robert H. Crabtree| title = Iridium compounds in catalysis| journal = Accounts of Chemical Research| date = 1979| volume = 12| pages = 331–337| doi = 10.1021/ar50141a005|issue = 9}}</ref><ref>{{cite book| title=The Organometallic Chemistry of the Transition Metals| url=http://chimicibicocca.altervista.org/data/chimica_lucidi.pdf| author=Crabtree, R. H.| date=2005| publisher=Wiley| isbn=978-0471662563| oclc=224478241| author-link=Robert H. Crabtree| url-status=dead| archive-url=https://web.archive.org/web/20121119073400/http://chimicibicocca.altervista.org/data/chimica_lucidi.pdf| archive-date=2012-11-19}}</ref>

[[File:C-HactnBergGrah.png|upright=2|left|thumb|Oxidative addition to hydrocarbons in [[organoiridium chemistry]]<ref name="RGB">{{cite journal|title=Carbon-hydrogen activation in completely saturated hydrocarbons: direct observation of M + R-H → M(R)(H)|author=Janowicz, A. H.|author2=Bergman, R. G.|journal=Journal of the American Chemical Society|date=1982|volume=104|issue=1|pages=352–354|doi=10.1021/ja00365a091}}</ref><ref name="WAGG">{{cite journal|title=Oxidative addition of the carbon-hydrogen bonds of neopentane and cyclohexane to a photochemically generated iridium(I) complex|author=Hoyano, J. K.|author2=Graham, W. A. G.|journal=Journal of the American Chemical Society|date=1982|volume=104|issue=13|pages=3723–3725|doi=10.1021/ja00377a032|bibcode=1982JAChS.104.3723H }}</ref>|alt=Skeletal formula presentation of a chemical transformation. The initial compounds have a C5H5 ring on their top and an iridium atom in the center, which is bonded to two hydrogen atoms and a P-PH3 group or to two C-O groups. Reaction with alkane under UV light alters those groups.]]
Iridium complexes played a pivotal role in the development of [[C-H bond activation|carbon–hydrogen bond activation]] (C–H activation), which promises to allow functionalization of [[hydrocarbon]]s, which are traditionally regarded as [[Reactivity (chemistry)|unreactive]].<ref>{{cite journal |doi=10.1039/c0cs00156b|title=Regioselectivity of the Borylation of Alkanes and Arenes |year=2011 |last1=Hartwig |first1=John F. |journal=Chemical Society Reviews |volume=40 |issue=4 |pages=1992–2002 |pmid=21336364 }}</ref>