Samarium(III) chloride explained

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.^[1] 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:^[2]

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.^{[3] [4]}

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.^[5]

Notes and References

1. Book: F. T. Edelmann, P. Poremba . Synthetic Methods of Organometallic and Inorganic Chemistry . W. A. Herrmann . 6 . Georg Thieme Verlag . Stuttgart . 1997.
2. Book: Meyer, G.. The Ammonium Chloride Route to Anhydrous Rare Earth Chlorides-The Example of YCl₃. The Ammonium Chloride Route to Anhydrous Rare Earth Chlorides—The Example of Ycl ₃. Inorganic Syntheses. 25. 1989. 146–150. 10.1002/9780470132562.ch35. 978-0-470-13256-2.
3. 10.1021/ja01472a010 . L. F. Druding, J. D. Corbett . Lower Oxidation States of the Lanthanides. Neodymium(II) Chloride and Iodide . . 83 . 2462–2467 . 1961 . 11.
4. J. D. Corbett . Reduced Halides of the Rare Earth Elements . . 10 . 239 . 1973.
5. Book: G. A. Molander, E. D. Dowdy . Shu Kobayashi . Lanthanides: Chemistry and Use in Organic Synthesis. Springer-Verlag . Berlin . 1999 . 119–154 . 3-540-64526-8.