Its tetrahydrate can be formed by reacting iridium dioxide dihydrate with hydrobromic acid.

[1] It crystallizes in a highly disordered layered structure of aluminum(III) chloride or chromium(III) chloride type, where the monoclinic unit cell contains four formula units.

[4] The light olive green tetrahydrate is slightly soluble in water but insoluble in ethanol and ether.

When heated to 100 °C, it turns dark brown with release of water and decomposes to iridium and bromine at higher temperatures.

[1] It reacts with germanium dibromide in hydrobromic acid solution to form a compound containing Ir-Ge bond, and adding Cs+ to it can separate Cs3[Ir(GeBr3)nBr6−n] (n=1, 2, 3).