Erbium(III) chloride

Erbium(III) chloride is a violet solid with the formula ErCl3. It is used in the preparation of erbium metal.

Preparation
Anhydrous erbium(III) chloride can be produced by the ammonium chloride route. In the first step, erbium(III) oxide is heated with ammonium chloride to produce the ammonium salt of the pentachloride:
 * Er2O3 + 10 [NH4]Cl → 2 [NH4]2ErCl5 + 6 H2O + 6 NH3

In the second step, the ammonium chloride salt is converted to the trichloride by heating in a vacuum at 350-400 °C:
 * [NH4]2ErCl5 → ErCl3 + 2 HCl + 2 NH3

Structural data
Erbium(III) chloride forms crystals of the AlCl3 type, with monoclinic crystals and the point group C2/m.

Erbium(III) chloride hexahydrate also forms monoclinic crystals with the point group of P2/n (P2/c) - C42h. In this compound, erbium is octa-coordinated to form [Er(H2O)6Cl2]+ ions with the isolated Cl− completing the structure.

Optical properties
Erbium(III) chloride solutions show a negative nonlinear absorption effect.

Catalytic properties
The use of erbium(III) chloride as a catalyst has been demonstrated in the acylation of alcohols and phenols and in an amine functionalisation of furfural. It is a catalyst for Friedel–Crafts-type reactions, and can be used in place of cerium(III) chloride for Luche reductions.