Indium(III) iodide

Indium(III) iodide or indium triiodide is a chemical compound of indium and iodine with the formula InI₃.

Indium(III) iodide can be obtained by reacting indium with iodine vapor:

Indium(III) iodide can also be obtained by evaporation of a solution of indium in HI.

Indium(III) iodide is a pale yellow, very hygroscopic monoclinic solid (space group P2₁/c (space group no. 14), a = 9.837 Å, b = 6.102 Å, c = 12.195 Å, β = 107.69°), which melts at 210 °C to form a dark brown liquid and is highly soluble in water. Its crystals consist of dimeric molecules. The yellow β form slowly converts to the red α form. In the presence of water vapor, the compound reacts with oxygen at 245 °C to form indium(III) oxide iodide.

Distinct yellow and red forms are known. The red form undergoes a transition to the yellow at 57 °C. The structure of the red form has not been determined by X-ray crystallography; however, spectroscopic evidence indicates that indium may be six coordinate. The yellow form consists of In₂I₆ with 4 coordinate indium centres.