Samarium(III) chloride

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Overview

Samarium(III) chloride (SmCl₃), also known as samarium trichloride, is a compound of samarium and chlorine. It is a pale yellow solid which rapidly absorbs water on exposure to moist air to form a hexahydrate, SmCl₃.6H₂O. Simple rapid heating of the hydrate alone may cause small amounts of hydrolysis^[1]. The first five moles of water are lost at 110 °C^[2].

Chemical properties

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 insoluble samarium(III) compounds, for example samarium(III) hydroxide or samarium(III) fluoride:

SmCl₃(aq) + 3 NaOH(aq) → Sm(OH)₃(s) + 3 NaCl(aq)

SmCl_3(aq) + 3 KF(aq) → SmF₃(s) + 3 KCl(aq)

Preparation

Samarium(III) chloride can be prepared as a yellow aqueous solution by reaction of either samarium metal or samarium(III) carbonate and hydrochloric acid. The anhydrous halide may alternatively be prepared from samarium metal and hydrogen chloride^[6].

2 Sm(s) + 6 HCl(aq) → 2 SmCl₃(aq) + 3 H₂(g)

Sm₂(CO₃)₃(s) + 6 HCl(aq) → 2 SmCl₃(aq) + 3 CO₂(g) + 3 H₂O(l)

Anhydrous SmCl₃ can be made by dehydration of the hydrate either by slowly heating to 400 °C with 4-6 equivalents of ammonium chloride under high vacuum^[1],[4], or by heating with an excess of thionyl chloride for five hours^[1],[5]. The anhydrous halide may alternatively be prepared from samarium metal and hydrogen chloride^[6]. It is usually purified by high temperature sublimation under high vacuum.^[1]

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 lower the melting point, then it is melted and electrolysed to give the free metal^[3]. The anhydrous chloride may also be used to prepare organometallic compounds of samarium, such as bis(pentamethylcyclopentadienyl)alkylsamarium(III) complexes used as catalysts for hydrogenation and hydrosilylation of alkenes^[7]. Samarium(III) chloride can also be used as a starting point for the preparation of other samarium salts.

Precautions

Samarium compounds are of low to moderate toxicity, although their toxicity has not been investigated in detail.

References

1. F. T. Edelmann, P. Poremba, in: Synthetic Methods of Organometallic and Inorganic Chemistry, (W. A. Herrmann, ed.), Vol. 6, Georg Thieme Verlag, Stuttgart, 1997.
2. CRC Handbook of Chemistry and Physics (58th edition), CRC Press, West Palm Beach, Florida, 1977.
3. N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, Pergamon Press, 1984.
4. M. D. Taylor, P. C. Carter, J. Inorg. Nucl. Chem. 24, 387 (1962); J. Kutscher, A. Schneider, Inorg. Nucl. Chem. Lett. 7, 815 (1971).
5. J. H. Freeman, M. L. Smith, J. Inorg. Nucl. Chem. 7, 224 (1958).
6. L. F. Druding, J. D. Corbett, J. Am. Chem. Soc. 83, 2462 (1961); J. D. Corbett, Rev. Chim. Minerale 10, 239 (1973).
7. G. A. Molander, E. D. Dowdy, in Lanthanides: Chemistry and Use in Organic Synthesis, Springer-Verlag, Berlin, 1999, p119-154.