Gadolinium(III) iodide is an iodide of gadolinium, with the chemical formula of GdI<sub>3</sub>. It is a yellow, highly hygroscopic solid with a bismuth(III) iodide-type crystal structure. In air, it quickly absorbs moisture and forms hydrates. The corresponding oxide iodide is also readily formed at elevated temperature.
Gadolinium(III) iodide can be obtained by reacting gadolinium with iodine:
It can also be obtained by reacting gadolinium with mercury(II) iodide in a vacuum at 500 ðC:
Gadolinium(III) iodide can be obtained by the reaction between gadolinium(III) oxide and hydroiodic acid, crystallizing into the hydrate form. The hydrate form can be heated with ammonium iodide to form the anhydrous form.
Gadolinium(III) iodide reacts with gadolinium and zinc in an argon atmosphere heated to 850 ðC to obtain Gd<sub>7</sub>I<sub>12</sub>Zn. It reacts with gadolinium, carbon, and gadolinium nitride in a tantalum tube at 897 ðC to obtain nitrocarbide Gd<sub>4</sub>I<sub>6</sub>CN.