Indium(III) iodide or indium triiodide is a chemical compound of indium and iodine with the formula InI<sub>3</sub>.
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 P2<sub>1</sub>/c (space group no. 14), a = 9.837 à, b = 6.102 à, c = 12.195 à, ò = 107.69ð), which melts at 210 ðC to form a dark brown liquid and is highly soluble in water. Its crystals consist of dimeric molecules. The yellow ò form slowly converts to the red ñ form. In the presence of water vapor, the compound reacts with oxygen at 245 ðC to form indium(III) oxide iodide.
Distinct yellow and red forms are known. The red form undergoes a transition to the yellow at 57 ðC. 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 In<sub>2</sub>I<sub>6</sub> with 4 coordinate indium centres.