Rhodium(III) iodide is an inorganic compound with the formula RhI<sub>3</sub>. It is a black solid. Some rhodium(III) iodides are used as commercial catalysts.
RhI<sub>3</sub> adopts same crystal structure motif as AlCl<sub>3</sub> and YCl<sub>3</sub>. The structure consists of cubic close-packed iodide ions and rhodium ions filling a third of the octahedral interstices, forming a layers.
Rhodium(III) iodide can be synthesised by the reaction of aqueous potassium iodide with rhodium(III) bromide.
Rhodium(III) iodide is only known in the anhydrous form. Unlike the other rhodium(III) halides, it does not form hydrates. The related anion [RhI<sub>6</sub>]<sup>3âÂÂ</sup> was previously thought not to form but has since been prepared by diffusion of RhCl<sub>3</sub>÷3H<sub>2</sub>O through a layer of hydroiodic acid into piperazine.
Although RhI<sub>3</sub> and [RhI<sub>6</sub>]<sup>3âÂÂ</sup> remain laboratory curiosities, other rhodium(III) iodides have had a major impact technologically. They are catalysts used in the Monsanto process, which at one time was the dominant method for producing acetic acid, a commodity chemical. One intermediate in that cycle is [(CH<sub>3</sub>)Rh(CO)<sub>2</sub>I<sub>3</sub>]<sup>âÂÂ</sup>.