Samarium(III) chloride

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Samarium(III) chloride

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Template:Longitem	SmCl3
Molar mass	256.76 g/mol (anhydrous) 364.80 g/mol (hexahydrate)
Appearance	pale yellow solid (anhydrous) cream-coloured solid (hexahydrate)
Density	4.46 g/cm3 (anhydrous) 2.383 g/cm3 (hexahydrate)
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Template:Longitem	hexagonal, hP8
Template:Longitem	P63/m, No. 176
Template:Longitem	Tricapped trigonal prismatic (nine-coordinate)
Template:Longitem	Samarium(III) fluoride Samarium(III) bromide Samarium(III) oxide
Template:Longitem	Samarium(II) chloride Promethium(III) chloride Europium(III) chloride

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, SmCl₃^.6H₂O. The compound has few practical applications but is used in laboratories for research on new compounds of samarium.

Structure

Like several related chlorides of the lanthanides and actinides, SmCl₃ crystallises in the UCl₃ motif. The Sm³⁺ centres are nine-coordinate, occupying trigonal prismatic sites with additional chloride ligands occupying the three square faces.

Preparation and reactions

SmCl₃ is prepared by the "ammonium chloride" route, which involves the initial synthesis of (NH₄)₂[SmCl₅]. This material can be prepared from the common starting materials at reaction temperatures of 230 °C from samarium oxide:

10 NH₄Cl + Sm₂O₃ → 2 (NH₄)₂[SmCl₅] + 6 NH₃ + 3 H₂O

The pentachloride is then heated to 350-400 °C resulting in evolution of ammonium chloride and leaving a residue of the anhydrous trichloride:

(NH₄)₂[SmCl₅] → 2 NH₄Cl + SmCl₃

It can also be prepared from samarium metal and hydrochloric acid.

2 Sm + 6 HCl → 2 SmCl₃ + 3 H₂

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:

SmCl₃ + 3 KF → SmF₃ + 3 KCl

Uses

Samarium(III) chloride is used for the preparation of samarium metal, which has a variety of uses, notably in magnets. Anhydrous SmCl₃ 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.

In laboratory

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.