Thorium(IV) iodide is an inorganic chemical compound composed of thorium and iodine with the chemical formula . It is one of three known thorium iodides, the others being and .
Thorium(IV) iodide can be made by reacting thorium(IV) carbide or elemental thorium with iodine at 500 ðC.
It can also be made from the reaction of Thorium(IV) hydride with hydrogen iodide.
Thorium(IV) iodide is an extremely air and moisture sensitive solid which exists in the form of crystal platelets that are orange when heated and yellow in the cold. It has a monoclinic crystal structure with the space group P2<sub>1</sub>/n (space group no. 14, position 2) and the lattice parameters a = 1321.6 pm, b = 806.8 pm, c = 776.6 pm, ò = 98.68ð. It can also form a decahydrate. It forms complexes with Lewis bases. It reacts with thorium to form thorium(III) iodide and thorium(II) iodide.
Thorium(IV) iodide is used as an intermediate for the production of high-purity thorium by thermal decomposition of the compound (see Van Arkel-de Boer process)