Selenium monochloride

Diselenium dichloride
Names

IUPAC name Diselenium dichloride
Other names 1,2-Dichlorodiselane Dichlorodiselane Dichlorodiselenide Selenium chloride Selenium monochloride
Identifiers
CAS Number	10025-68-0^Y
3D model (JSmol)	Interactive image
ChemSpider	59591^Y
ECHA InfoCard	100.030.022
EC Number	233-037-8
PubChem CID	66206
UNII	2A5292FC4P^Y
CompTox Dashboard (EPA)	DTXSID1064902
InChI InChI=1S/Cl2Se2/c1-3-4-2^N Key: VIEXQFHKRAHTQS-UHFFFAOYSA-N^N InChI=1/Cl2Se2/c1-3-4-2 Key: VIEXQFHKRAHTQS-UHFFFAOYAC
SMILES Cl[Se][Se]Cl
Properties
Chemical formula	Se₂Cl₂
Molar mass	228.84 g·mol⁻¹
Appearance	Reddish-brown oily liquid
Density	2.7741 g/cm³
Melting point	−85 °C (−121 °F; 188 K)
Boiling point	127 °C (261 °F; 400 K) at 0.997 atm
Solubility in water	insoluble
Solubility in other solvents	Soluble in chloroform, carbon disulfide, and acetonitrile
Magnetic susceptibility (χ)	−94.8·10⁻⁶ cm³/mol
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H301, H311, H314, H331, H373, H410
Precautionary statements	P260, P261, P264, P270, P271, P273, P280, P301+P310, P301+P330+P331, P302+P352, P303+P361+P353, P304+P340, P305+P351+P338, P310, P311, P312, P314, P321, P322, P330, P361, P363, P391, P403+P233, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is ^YN ?) Infobox references

Chemical compound

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.

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 dihedral angle between the Cl^a−Se−Se and Se−Se−Cl^b planes is 87°.^[2]

Preparation

Early routes to diselenium dichloride involved chlorination of elemental selenium.^[3] An improved method involves the reaction of a mixture of selenium, selenium dioxide, and hydrochloric acid:^[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:^[4]

2 Se + 2 SO₃ + 3 HCl → Se₂Cl₂ + SO₂ + H₂O + SO₂(OH)Cl

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]

References

^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
^ Kniep, Rüdiger; Körte, Lutz; Mootz, Dietrich (1 January 1983). "Kristallstrukturen von Verbindungen A₂X₂ (A = S, Se; X = Cl, Br)". Zeitschrift für Naturforschung B. 38 (1): 1–6. doi:10.1515/znb-1983-0102.
^ 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.
^ ^a ^b ^c Fehér, F. (1963). "Diselenium Dichloride". In Brauer, G. (ed.). Handbook of Preparative Inorganic Chemistry. Vol. 1 (2nd ed.). New York: Academic Press. pp. 422–423.
^ 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 Se_nS_8−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.
^ ^a ^b Back, Thomas G.; Moussa, Ziad (2003). "Diselenium Dichloride". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rn00201. ISBN 0-471-93623-5.