Selenium monochloride
{{chembox
|Verifiedfields = changed
|Watchedfields = changed
|verifiedrevid = 444677336
|Name = Diselenium dichloride
|ImageFile =Diselenium_dichloride.jpg
|ImageSize = 132
|IUPACName = Diselenium dichloride
|OtherNames = {{ubl|1,2-Dichlorodiselane|Dichlorodiselane|Dichlorodiselenide|Selenium chloride|Selenium monochloride}}
|Section1={{Chembox Identifiers
|CASNo_Ref = {{cascite|correct|??}}
|CASNo = 10025-68-0
|ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
|ChemSpiderID = 59591
|EINECS = 233-037-8
|PubChem = 66206
|UNII_Ref = {{fdacite|correct|FDA}}
|UNII = 2A5292FC4P
|SMILES = Cl[Se][Se]Cl
|InChI = 1/Cl2Se2/c1-3-4-2
|InChIKey = VIEXQFHKRAHTQS-UHFFFAOYAC
|StdInChI_Ref = {{stdinchicite|changed|chemspider}}
|StdInChI = 1S/Cl2Se2/c1-3-4-2
|StdInChIKey_Ref = {{stdinchicite|changed|chemspider}}
|StdInChIKey = VIEXQFHKRAHTQS-UHFFFAOYSA-N
}}
|Section2={{Chembox Properties
|Formula = {{chem2|Se2Cl2}}
|Se=2|Cl=2
|Appearance = Reddish-brown oily liquid
|Density = 2.7741 g/cm3
|Solubility = insoluble, hydrolyses
|SolubleOther = Soluble in chloroform, carbon disulfide, and acetonitrile
|Solvent=other solvents
|MeltingPtC = -85
|BoilingPtC = 127
|BoilingPt_notes = at 0.997 atm
|MagSus = −94.8·10−6 cm3/mol
}}
|Section3={{Chembox Hazards
|GHSPictograms = {{GHS05}}{{GHS06}}{{GHS08}}{{GHS09}}
|GHSSignalWord = Danger
|HPhrases = {{H-phrases|301|311|314|331|373|410}}
|PPhrases = {{P-phrases|260|261|264|270|271|273|280|301+310|301+330+331|302+352|303+361+353|304+340|305+351+338|310|311|312|314|321|322|330|361|363|391|403+233|405|501}}
}}
}}
Selenium monochloride or diselenium dichloride is an inorganic compound with the formula {{chem2|Se2Cl2|auto=1}}. 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 Selenium dichloride, Selenium tetrachloride, chlorine, and elemental selenium.{{Greenwood&Earnshaw2nd}} Diselenium dichloride is mainly used as a reagent for the synthesis of Se-containing compounds.
Structure and properties
Dielenium dichloride has the connectivity {{chem2|Cl\sSe\sSe\sCl}}. 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 {{chem2|Cl^{a}\sSe\sSe}} and {{chem2|Se\sSe\sCl^{b}|}} planes is 87°.{{cite journal |last1=Kniep |first1=Rüdiger |last2=Körte |first2=Lutz |last3=Mootz |first3=Dietrich |title=Kristallstrukturen von Verbindungen A2X2 (A = S, Se; X = Cl, Br) |journal=Zeitschrift für Naturforschung B |date=1 January 1983 |volume=38 |issue=1 |pages=1–6 |doi=10.1515/znb-1983-0102 |doi-access=free}}
Preparation
Early routes to diselenium dichloride involved chlorination of elemental selenium.{{cite journal |doi=10.1021/ja01680a025|title=The Preparation of Selenium Monochloride and Monobromide|journal=Journal of the American Chemical Society|volume=47|issue=3|pages=772–774|year=1925|last1=Lenher|first1=Victor|last2=Kao|first2=C. H.}} An improved method involves the reaction of a mixture of selenium, selenium dioxide, and hydrochloric acid:{{Cite book |last=Fehér |first=F. |chapter-url=https://archive.org/details/Handbook_of_Preparative_Inorganic_Chemistry_1_2_Brauer/page/n447 |title=Handbook of Preparative Inorganic Chemistry |publisher=Academic Press |year=1963 |editor-last=Brauer |editor-first=G. |edition=2nd |volume=1 |location=New York |pages=422-423 |chapter=Diselenium Dichloride}}
:{{chem2|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:
:{{chem2|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.
In acetonitrile solutions, it exists in equilibrium with {{chem2|SeCl2}} and {{chem2|SeCl4}}.{{cite journal |last1=Lamoureux |first1=Marc |last2=Milne |first2=John |year=1990 |title=Selenium chloride and bromide equilibria in aprotic solvents; a Se77 NMR study |journal=Polyhedron |volume=9 |issue=4 |pages=589–595 |doi=10.1016/S0277-5387(00)86238-5}} Selenium dichloride degrades to diselenium dichloride after a few minutes at room temperature:{{cite journal |journal=Inorganic Chemistry|year=1999|volume=38|issue=18|pages=4093–4097|doi=10.1021/ic981430h|title=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|last1=Maaninen|first1=Arto|last2=Chivers|first2=Tristram|last3=Parvez|first3=Masood|last4=Pietikäinen|first4=Jarkko|last5=Laitinen|first5=Risto S.}}
:{{chem2|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. Finally, the compound has been used to introduce bridging selenium ligands between the metal atoms of some iron and chromium carbonyl complexes.{{cite encyclopedia |author=Back, Thomas G. |author2=Moussa, Ziad|chapter=Diselenium Dichloride|title=Encyclopedia of Reagents for Organic Synthesis|year=2003 |doi=10.1002/047084289X.rn00201|isbn=0-471-93623-5}}
References
{{reflist}}
{{Selenium compounds}}
{{Chlorides}}