Thulium(III) iodide
# Thulium(III) iodide

Thulium(III) iodide is an iodide of thulium, with the chemical formula of $TmI_3.$ Thulium(III) iodide is used as a component of metal halide lamps.

## Preparation

Mercury(II) iodide can be heated with thulium to obtain thulium(III) iodide:

    2 Tm + 3 $HgI_2$ → 2 $TmI_3$ + 3 Hg

The mercury produced in the reaction can be removed by distillation.

The thulium(III) iodide hydrate crystallized from solution can be heated with ammonium iodide to obtain the anhydrous form.

## Properties

Thulium(III) iodide is a yellow, highly hygroscopic solid with a bismuth(III) iodide-type crystal structure. It forms in the hexagonal crystal system. Its hydrate can be heated in air to obtain TmOI. Its anhydrous form can be heated with thulium to obtain $TmI_2:$

    2 $TmI_3$ + Tm → 3 $TmI_2$
