Iridium(IV) oxide

Iridium, atomic number 77, is a metallic element in the period 6 transition group. It is quite rare and has relatively few compounds, natural or synthetic. Despite its scarcity, it can exist in oxidation states ranging from –3 to +9.

The most common oxide of iridium by far has the +4 oxidation state: iridium(IV) oxide, or IrO₂. Ir₂O₃ [Ir(III)] and IrO₄ [Ir(VIII)] are also known. As the image shows, crystalline IrO₂ adopts the rutile (TiO₂) structure with iridium coordinated to six oxygen atoms.

IrO₂ is prepared by heating elemental iridium or IrCl₃ in the presence of oxygen. Additional heating causes the oxide to decompose into its elements. Most current IrO₂ applications involve its deposition on substrates such as carbon nanotubes.

IrO₂ has beneficial properties such as inertness under biological conditions and usefulness in catalysis and electrical devices. Its applications include electrodes for industrial electrolysis and regenerative fuel cells and materials for minimally invasive devices such as stents for treating coronary heart disease.