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.
Diselenium dichloride is a reddish-brown, oily liquid that hydrolyses slowly. It exists in chemical equilibrium with SeCl2, SeCl4, chlorine, and elemental selenium.[1] Diselenium dichloride is mainly used as a reagent for the synthesis of Se-containing compounds.
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:[4]
The crude diselenium dichloride is removed via separatory funnel. Diselenium dichloride cannot be distilled without decomposition, even at reduced pressure.[4]
In acetonitrile solutions, it exists in equilibrium with SeCl2 and SeCl4.[5]Selenium dichloride degrades to diselenium dichloride after a few minutes at room temperature:[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.[7] Finally, the compound has been used to introduce bridging selenium ligands between the metal atoms of some iron and chromium carbonyl complexes.[7]
^Lenher, Victor; Kao, C. H. (1925). "The Preparation of Selenium Monochloride and Monobromide". Journal of the American Chemical Society. 47 (3): 772–774. doi:10.1021/ja01680a025.
^ abcFehér, F. "Diselenium Dichloride". In Handbook of Preparative Inorganic Chemistry; Brauer, G., Ed.; Academic Press: New York, 1963; Vol. 1; p 422-433.
^Lamoureux, Marc; Milne, John (1990). "Selenium chloride and bromide equilibria in aprotic solvents; a Se77 NMR study". Polyhedron. 9 (4): 589–595. doi:10.1016/S0277-5387(00)86238-5.
^Maaninen, 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.
