Iridium compounds

Only one binary oxide is well-characterized: Iridium dioxide, . It is a blue-black solid. The compound adopts the TiO2 rutile structure, featuring six coordinate iridium and three coordinate oxygen. It adopts the fluorite structure. The corresponding disulfides, diselenides, sesquisulfides, and sesquiselenides are known, as well as . This compound was formed by photochemical rearrangement of (η1-O2)IrO2 in solid argon at a temperature of . At higher temperatures, the oxide is unstable. The detection of the iridium tetroxide cation by infrared photodissociation spectroscopy with formal oxidation state +9 has been reported, the highest currently known of any element, though the +10 oxidation state has been theorized for platinum, but not confirmed. ==Halides==

Binary trihalides, are known for all of the halogens. For oxidation states +4 and above, only the tetrafluoride, pentafluoride and hexafluoride are known. Iridium hexafluoride, , is a volatile yellow solid, composed of octahedral molecules. It decomposes in water and is reduced to ,. Iridium pentafluoride is also a strong oxidant, but it is a tetramer, , formed by four corner-sharing octahedra. ==Complexes==

, a common salt of iridium. The coordination complexes of iridium are extensive. Iridium in its complexes is always low-spin. Ir(III) and Ir(IV) generally form octahedral complexes. One example is . The ternary hydride is believed to contain both the and the 18-electron anion. Iridium also oxyanions with oxidation states +4 and +5. and 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. As for many elements, the chlorides are key complexes. Hexachloroiridic(IV) acid, , and its ammonium salt are the most common iridium compounds from an industrial and preparative perspectives. Iridium trichloride, , which can be obtained in anhydrous form from direct oxidation of iridium powder by chlorine at 650 °C, or in hydrated form by dissolving in hydrochloric acid, is often used as a starting material for the synthesis of other Ir(III) compounds. Another compound used as a starting material is ammonium hexachloroiridate(III), . In the presence of air, iridium metal dissolves in molten alkali-metal cyanides to produce the (hexacyanoiridate) ion. ==Oxyanions==

Iridium forms oxyanions in the +4 oxidation state. It forms compounds such as lithium iridate (Li2IrO3), which forms black crystals with three slightly different layered atomic structures, α, β, and sometimes γ. Lithium iridate exhibits metal-like, temperature-independent electrical conductivity, and changes its magnetic ordering from paramagnetic to antiferromagnetic upon cooling to 15 K. Lithium iridate is a potential electrode material for the lithium-ion battery. == Organoiridium chemistry ==

is a common complex of Ir(I). Organoiridium compounds contain iridium–carbon bonds. Early studies identified the very stable tetrairidium dodecacarbonyl, . Iridium is usually supplied commercially in the Ir(III) and Ir(IV) oxidation states. Important starting reagents being hydrated iridium trichloride and ammonium hexachloroiridate. These salts are reduced upon treatment with CO, hydrogen, and alkenes. Illustrative is the carbonylation of the trichloride: :IrCl3(H2O)x + 3 CO → [Ir(CO)2Cl2]− + CO2 + 2 H+ + Cl− + (x-1) H2O |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. Many organoiridium(III) compounds are generated from pentamethylcyclopentadienyl iridium dichloride dimer. Many of derivatives feature kinetically inert cyclometalated ligands. Related half-sandwich complexes were central in the development of C-H activation. Iridium complexes played a pivotal role in the development of carbon–hydrogen bond activation (C–H activation), which promises to allow functionalization of hydrocarbons, which are traditionally regarded as unreactive. ==See also==