Editing Iridium (section)

=== 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>