cis-Dichlorobis(ethylenediamine)cobalt(III) chloride

cis-Dichlorobis(ethylenediamine)cobalt(III) chloride is a salt with the formula [CoCl2(en)2]Cl (en = ethylenediamine). The salt consists of a cationic coordination complex and a chloride anion. 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.

cis-Dichlorobis(ethylenediamine)cobalt(III) chloride
Identifiers
3D model (JSmol)
ChemSpider
Properties
C4H16Cl3CoN4
Molar mass 285.48 g·mol−1
Appearance violet solid
Melting point decomposes
good
Hazards
R-phrases (outdated) R36/37/38
S-phrases (outdated) S26 S36
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

Synthesis and optical resolution

Cis-dichlorobis(ethylenediamine)cobalt(III) chloride is obtained by heating a solution of trans-dichlorobis(ethylenediamine)cobalt(III) chloride, e.g. using a steam bath.

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.[1]

  • Λ-cis-[CoCl2(en)2]+
  • Δ-cis-[CoCl2(en)2]+
UV-vis spectra of various stages in the conversion of trans-[CoCl2(en)2]+ to the cis isomer.

Comparison of cis and trans isomers

This salt is less soluble than the dull-green isomeric trans-dichlorobis(ethylenediamine)cobalt(III) chloride. This pair of isomers were significant in the development of the area of coordination chemistry.[2] The chiral cis isomer can be obtained by heating the trans isomer. Both isomers of dichlorobis(ethylenediamine)cobalt(III) chloride have often been used in stereochemical studies and as intermediates (like tris(ethylenediamine)cobalt(III) chloride) for the preparation of other cobalt salt complexes.

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References
  1. Bailar, J.C. “Cis- and Trans-Dichlorobis-(Ethylenediamine)Cobalt(III) Chloride and the Resolution of the Cis Form”. Inorganic Syntheses, 1946, volume 2, pages 222-225. doi:10.1002/9780470132333.ch71
  2. Jörgensen, S.M. “Ueber Metalldiaminverbindungen“ J. prakt. Chem. (in German), 1889, volume 39, page 8. doi:10.1002/prac.18890390101
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