Dysprosium(III) chloride (DyCl<sub>3</sub>), also known as dysprosium trichloride, is a compound of dysprosium and chlorine. It is a white to yellow solid which rapidly absorbs water on exposure to moist air to form a hexahydrate, DyCl<sub>3</sub>÷6H<sub>2</sub>O. Simple rapid heating of the hydrate causes partial hydrolysis to an oxychloride, DyOCl.
DyCl<sub>3</sub> is often prepared by the "ammonium chloride route", starting from either Dy<sub>2</sub>O<sub>3</sub> or the hydrated chloride DyCl<sub>3</sub>÷6H<sub>2</sub>O. These methods produce (NH<sub>4</sub>)<sub>2</sub>[DyCl<sub>5</sub>]:
The pentachloride decomposes thermally according to the following equation:
The thermolysis reaction proceeds via the intermediacy of (NH<sub>4</sub>)[Dy<sub>2</sub>Cl<sub>7</sub>].
Treating Dy<sub>2</sub>O<sub>3</sub> with aqueous HCl produces the hydrated chloride DyCl<sub>3</sub>÷6H<sub>2</sub>O, which cannot be rendered anhydrous by heating. Instead one obtains an oxychloride:
Dysprosium(III) chloride is a moderately strong Lewis acid, which ranks as "hard" according to the HSAB concept. Aqueous solutions of dysprosium chloride can be used to prepare other dysprosium(III) compounds, for example dysprosium(III) fluoride:
Dysprosium(III) chloride can be used as a starting point for the preparation of other dysprosium salts. Dysprosium metal is produced when a molten mixture of DyCl<sub>3</sub> in eutectic LiCl-KCl is electrolysed. The reduction occurs via Dy<sup>2+</sup>, at a tungsten cathode.
Dysprosium compounds are believed to be of low to moderate toxicity, although their toxicity has not been investigated in detail.