Selenium monochloride
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Selenium monochloride or diselenium dichloride is an inorganic compound with the formula Se2Cl2. Although a common name for the compound is selenium monochloride, reflecting its empirical formula, IUPAC does not recommend that name, instead preferring the more descriptive diselenium dichloride.
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Structure and properties
Dielenium dichloride has the connectivity Cl−Se−Se−Cl. With a nonplanar structure, it has C2 molecular symmetry, similar to hydrogen peroxide and disulfur dichloride, which is referred to as gauche. The Se-Se bond length is 223 pm, and the Se-Cl bond lengths are 220 pm. The angle Se – Se – Cl is 104° and the dihedral angle between the Cla−Se−Se and Se−Se−Clb planes is 87°.cite-ref-2[2]
Preparation
Early routes to diselenium dichloride involved chlorination of elemental selenium.cite-ref-3[3] An improved method involves the reaction of a mixture of selenium, selenium dioxide, and hydrochloric acid:cite-ref-feher-4-0[4]
3 Se + SeO2 + 4 HCl → 2 Se2Cl2 + 2 H2O
A dense layer of diselenium dichloride settles from the reaction mixture, which can be purified by dissolving it in fuming sulfuric acid and reprecipitating it with hydrochloric acid. A second method for the synthesis involves the reaction of selenium with oleum and hydrochloric acid:cite-ref-feher-4-1[4]
The crude diselenium dichloride is removed via separatory funnel. Diselenium dichloride cannot be distilled without decomposition, even at reduced pressure.cite-ref-feher-4-2[4]
In acetonitrile solutions, it exists in equilibrium with SeCl2 and SeCl4.cite-ref-5[5] Selenium dichloride degrades to diselenium dichloride after a few minutes at room temperature:cite-ref-6[6]
3 SeCl2 → Se2Cl2 + SeCl4
Reactions
Diselenium dichloride is an electrophilic selenizing agent, and thus it reacts with simple alkenes to give bis(β-chloroalkyl)selenide and bis(chloroalkyl)selenium dichloride. It converts hydrazones of hindered ketones into the corresponding selenoketones, the structural analogs of ketones whereby the oxygen atom is replaced with a selenium atom.cite-ref-back-7-0[7] Finally, the compound has been used to introduce bridging selenium ligands between the metal atoms of some iron and chromium carbonyl complexes.cite-ref-back-7-1[7]
References
cite-note-11. ↑ citerefgreenwoodearnshaw1997Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. doi:10.1016/C2009-0-30414-6. ISBN 978-0-08-037941-8.
cite-note-feher-44. ↑ citereffeh-r1963Fehér, F. (1963). "Diselenium Dichloride". In Brauer, G. (ed.). Handbook of Preparative Inorganic Chemistry. Vol. 1 (2nd ed.). New York: Academic Press. pp. 422–423.
cite-note-66. ↑ citerefmaaninenchiversparvezpietik-inen1999Maaninen, Arto; Chivers, Tristram; Parvez, Masood; Pietikäinen, Jarkko; Laitinen, Risto S. (1999). "Syntheses of THF Solutions of SeX2(X = Cl, Br) and a New Route to Selenium Sulfides SenS8−n(n = 1−5): X-ray Crystal Structures of SeCl2(tht)2 and SeCl2·tmtu". Inorganic Chemistry. 38 (18): 4093–4097. doi:10.1021/ic981430h.