cis-Dichlorobis(ethylenediamine)cobalt(III) chloride

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cis-dichlorobis(ethylenediamine)cobalt(III) chloride
Cis-Dichlorobis(ethylenediamine)cobalt(III) chloride.png
Identifiers
CAS number 14040-32-5 YesY
PubChem 407212
ChemSpider 360279 YesY
Jmol-3D images Image 1
Properties
Molecular formula C4H16Cl3CoN4
Molar mass 285.49 g mol−1
Appearance violet solid
Melting point dec.
Solubility in water good
Hazards
R-phrases R36/37/38
S-phrases S26 S36
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references
UV-vis spectra of various stages in the conversion of trans-[CoCl2(en)2]+ to the cis isomer.

cis-dichlorobis(ethylenediamine)cobalt(III) chloride is a coordination complex with the formula [CoCl2(en)2]Cl (en = ethylenediamine). It is a violet diamagnetic solid that is soluble in water. One chloride ion in this salt readily undergoes ion exchange but the two other chlorides are less reactive, being bound to the metal center.

Synthesis[edit]

Cis-dichlorobis(ethylenediamine)cobalt(III) chloride is obtained by heating a solution of trans-[CoCl2(en)2]Cl e.g. using a steam bath. The trans isomer is in turn synthesized by the reaction of cobalt chloride and ethylenediamine in hydrochloric acid in the presence of oxygen:

4 CoCl2 + 8 en + 4 HCl + O2 → 4 trans-[CoCl2(en)2]Cl + 2 H2O

The initial product contains HCl, which is removed by heating. Alternatively, (carbonato)bis(ethylenediamine)cobalt (III) chloride reacts with hydrochloric acid at 10 °C to give the same species.[1]

[Co(CO3)(en)2]Cl + 2 HCl → trans-[CoCl2(en)2]Cl + CO2 + H2O

Optical resolution[edit]

The racemate can be resolved into two enantiomers (Λ and Δ) by the formation of the d-α-bromocamphor-π-sulfonate salt. The diastereomeric salts are separated by recrystallization. After their purification, the individual diastereomers are converted back to the chloride salt by reaction with ice cold hydrochloric acid.[2]

Comparison of cis and trans isomers[edit]

This salt is less soluble than the dull-green isomeric trans-dichlorobis(ethylenediamine)cobalt(III) chloride (CAS#14040-33-6). This pair of isomers were significant in the development of the area of coordination chemistry.[3] The chiral cis isomer can be obtained by heating the trans isomer. Both isomers of dichlorobis(ethylenediamine)cobalt(III) chloride have often used in stereochemical studies and as intermediates (like Tris(ethylenediamine)cobalt(III) chloride) for the preparation of other cobalt salt complexes.

Crystals of trans-dichlorobis(ethylenediamine)cobalt(III) chloride.

The trans isomer cation has idealized D2h point group symmetry, whereas the cis isomer cation has C2 symmetry.

References[edit]

  1. ^ Springbørg, J.; Schaffer, C.E. “Dianionobis(Ethylenediamine)Cobalt (III) Complexes” Inorganic Synthesis, 1973; volume 14, pages 63-77. doi:10.1002/9780470132456.ch14
  2. ^ Bailar, J.C. “Cis- and Trans-Dichlorobis-(Ethylenediamine) Cobalt (III) Chloride and the Resolution of the Cis Form”. Inorganic Synthesis, 1946, volume 2, pages 222-225. doi:10.1002/9780470132333.ch71
  3. ^ Jörgensen, S.M. “Ueber Metalldiaminverbindungen“ J. prakt. Chem., 1889, volume 39, page 8. doi:10.1002/prac.18890390101