Selenium monochloride

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

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, hydrolyses
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

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]