Samarium(III) chloride, also known as samarium trichloride, is an inorganic compound of samarium and chloride. It is a pale yellow salt that rapidly absorbs water to form a hexahydrate, SmCl<sub>3</sub><sup>.</sup>6H<sub>2</sub>O. The compound has few practical applications but is used in laboratories for research on new compounds of samarium.
Like several related chlorides of the lanthanides and actinides, SmCl<sub>3</sub> crystallises in the UCl<sub>3</sub> motif. The Sm<sup>3+</sup> centres are nine-coordinate, occupying trigonal prismatic sites with additional chloride ligands occupying the three square faces.
SmCl<sub>3</sub> is prepared by the "ammonium chloride" route, which involves the initial synthesis of (NH<sub>4</sub>)<sub>2</sub>[SmCl<sub>5</sub>]. This material can be prepared from the common starting materials at reaction temperatures of 230 ðC from samarium oxide:
The pentachloride is then heated to 350-400 ðC resulting in evolution of ammonium chloride and leaving a residue of the anhydrous trichloride:
It can also be prepared from samarium metal and hydrochloric acid.
Aqueous solutions of samarium(III) chloride can be prepared by dissolving metallic samarium or samarium carbonate in hydrochloric acid.
Samarium(III) chloride is a moderately strong Lewis acid, which ranks as "hard" according to the HSAB concept. Aqueous solutions of samarium chloride can be used to prepare samarium trifluoride:
Samarium(III) chloride is used for the preparation of samarium metal, which has a variety of uses, notably in magnets. Anhydrous SmCl<sub>3</sub> is mixed with sodium chloride or calcium chloride to give a low melting point eutectic mixture. Electrolysis of this molten salt solution gives the free metal.
Samarium(III) chloride can also be used as a starting point for the preparation of other samarium salts. The anhydrous chloride is used to prepare organometallic compounds of samarium, such as bis(pentamethylcyclopentadienyl)alkylsamarium(III) complexes.