Iridium: reactions of elements
Reaction of iridium with air
Iridium is largely immune to atmospheric attack. On heating with oxygen, iridium metal gives iridium (IV) oxide, IrO2.
Ir(s) + O2(g) → IrO2(s) [black]
Usually second and third row d-block elements show similar chemistries, but in this case, rhodium (immediately above iridium in the periodic table) burns to give rhodium (III) oxide, Rh2O3. If Ir2O3 is formed in the above reaction, it must oxidize further to IrO2.
Reaction of iridium with water
Iridium does not react with water under normal conditions.
Reaction of iridium with the halogens
Metallic iridium reacts directly with fluorine gas to form the highly corrosive iridium(VI) fluoride, IrF6. This material, with care, can be heated to form iridium(V) fluoride, which has the yellow tetrameric structure [IrF5]4.
Ir(s) + 3F2(g) → IrF6(s) [yellow]
The trihalides iridium(III) fluoride, IrCl3, iridium(III) chloride, IrCl3, iridium(III) bromide, IrBr3, and iridium(III) iodide, IrI3, can be formed through the direct reaction of the metal with the halogen under anhydrous (dry) conditions. In the case of fluorine, some [IrF5]4 may also form.
2Ir(s) + 3F2(g) → 2IrF3(s) [black]
2Ir(s) + 3Cl2(g) → 2IrCl3(s) [red]
2Ir(s) + 3Br2(g) → 2IrBr3(s) [red-brown]
2Ir(s) + 3I2(g) → 2IrI3(s) [dark brown]
Reaction of iridium with acids
Iridium metal is notably inert to reaction with acids, including aqua regia (a mixture of hydrochloric acid, HCl, and nitric acid, HNO3, known for its ability to dissolve gold metal).