Tris(ethylenediamine)cobalt(III) chloride: Difference between revisions

| verifiedrevid = 418978983

|ImageFile=Coen3.png

|ImageSize=300px

|IUPACName=cobalt tris(ethylenediamine) chloride

|OtherNames= tris(ethylenediamine)cobalt(III) chloride

|Section1= {{Chembox Identifiers

| CASNo=207802-43-5

| PubChem=

| SMILES=

}}

|Section2= {{Chembox Properties

| Formula=C₆H₂₄N₆Cl₃Co

| MolarMass=345.59

| Appearance=yellow-orange solid

| Density=

| MeltingPt=275°C (decomp)

| BoilingPt=

| Solubility=water

|Section3= {{Chembox Hazards

| MainHazards=

| FlashPt=

| Autoignition=

'''Tris(ethylenediamine)cobalt(III) chloride''' is a [[coordination complex]] with the formula [Co(en)₃]Cl₃ (where "en" is the abbreviation for [[ethylenediamine]]). This complex was important in the history of coordination chemistry because of its stability and its [[stereochemistry]]. Many different salts have been described. The complex was first described by [[Alfred Werner]] who isolated this salt as yellow-gold needle-like crystals.<ref>{{cite journal

| doi = 10.1002/cber.19120450116}}</ref>

The compound is prepared from an aqueous solution of ethylenediamine and virtually any cobalt(II) salt, such as [[cobalt(II) chloride]]. The solution is purged with air to oxidize the cobalt(II)-ethylenediamine complexes to cobalt(III). The reaction proceeds in 95% yield, and the tri[[cation]] can be isolated with a variety of anions. A detailed product analysis of a large-scale synthesis revealed that one minor by-product was [Co(en)₂Cl(H₂NCH₂CH₂NH₃]Cl₃, which contains a rare monodentate ethylenediamine ligand (protonated).<ref>{{cite journal

| author = Jack M. Harrowfield, Mark I. Ogden, Brian W. Skelton, Allan H. White

| title = Alfred Werner revisited: Some subtleties of complex ion synthesis and isomerism

| journal = C. R. Chimie

| doi = 10.1016/j.crci.2004.10.013}}</ref>

The cation [Co(en)₃]³⁺ is [[octahedral molecular geometry|octahedral]] with Co-N distances in the range 1.947-1.981 [[angstrom|Å]]. The N-Co-N angles are 85° within the chelate rings and 90° between nitrogen atoms on adjacent rings.<ref name=Wit>{{cite journal

| title = The Crystal Structure of (+)-D-tris(ethylenediamine)cobalt(III) nitrate

| doi = 10.1107/S056774087200679X}}</ref>

The complex can be resolved into [[enantiomer]]s that are described as Δ and Λ. Usually the resolution entails use of [[tartrate]] salts.<ref>{{cite journal

| author = J. A. Broomhead, F. P. Dwyer, J. W. Hogarth

| editor1-last = Rochow

| editor1-first = Eugene G.

| title = Resolution of the Tris(Ethylenediamine)Cobalt(III) Ion

| journal = Inorganic Syntheses

| doi =10.1002/9780470132371}}</ref> The optical resolution is a standard component of inorganic synthesis courses.<ref>Girolami, G. S.; Rauchfuss, T. B. and Angelici, R. J., Synthesis and Technique in Inorganic Chemistry, University Science Books: Mill Valley, CA, 1999.ISBN 0935702482</ref> Because of its nonplanarity, the MN₂C₂ rings can adopt either of two [[Chemical structure|conformations]], which are described by the symbols λ and δ. The registry between these ring conformations and the absolute configuration of the metal centers is described by the nomenclature lel (when the en backbone lies parallel with the C₃ symmetry axis) or ob (when the en backbone is obverse to this same C₃ axis). Thus, the following [[diastereomer]]ic conformations can be identified: Δ-(lel)₃, Δ-(lel)₂(ob), Δ-(lel)(ob)₂, and Δ-(ob)₃. The mirror images of these species of course exist also.<ref>von Zelewsky, A. "Stereochemistry of Coordination Compounds" John Wiley: Chichester, 1995. ISBN 047195599.</ref>

[[Image:Coen3lel3.png|thumb|250px|center|Structure of the Δ-(lel)₃ (or Δ-(λλλ)) isomer of [Co(en)₃]³⁺. One of the three C₂ symmetry axes is shown in red.]]

Cationic coordination complexes of [[ammonia]] and [[alkyl]] amines typically crystallize with water in the [[water of crystallization|lattice]], and the stoichiometry can depend on the conditions of crystallization and, in the cases of chiral complexes, the optical purity of the cation. Racemic [Co(en)₃]Cl₃ is most often obtained as the di- or trihydrate. For the optically pure salt (+)-[Co(en)₃]Cl₃^.1.5H₂0, (+)-[Co(en)₃]Cl₃^.0.5NaCl^.3H₂O, and (+)-[Co(en)₃]Cl₃^.H₂O are also known.<ref name=Wit/>

<references/>

[[Category:Cobalt compounds]]

[[Category:Coordination compounds]]