trans-Dichlorobis(ethylenediamine)cobalt(III) chloride

trans-Dichlorobis(ethylenediamine)cobalt(III) chloride is a salt with the formula [CoCl2(en)2]Cl (en = ethylenediamine). It is a green diamagnetic solid that is soluble in water. It is the monochloride salt of the cationic coordination complex [CoCl2(en)2]+. One chloride ion in this salt readily undergoes ion exchange but the two other chlorides are less reactive, being bound to the metal center. The more stable cis-dichlorobis(ethylenediamine)cobalt(III) chloride is also known.

trans-Dichlorobis(ethylenediamine)cobalt(III) chloride
Identifiers
3D model (JSmol)
Properties
C4H16Cl3CoN4
Molar mass 285.48 g·mol−1
Appearance green solid
Melting point decomposes
good
Hazards
GHS pictograms
GHS Signal word Warning
H315, H319, H335
P261, P305+351+338
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Synthesis

The compound is synthesized by the reaction of cobalt(II) 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
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 more soluble than the cis isomer. This pair of isomers was significant in the development of the area of coordination chemistry.[2]

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

References
  1. Springbørg, J.; Schaffer, C.E. "Dianionobis(Ethylenediamine)Cobalt(III) Complexes" Inorganic Syntheses, 1973; volume 14, pages 63-77. doi:10.1002/9780470132456.ch14
  2. Jörgensen, S.M. "Ueber Metalldiaminverbindungen" Journal für praktische Chemie (in German), 1889, volume 39, page 8. doi:10.1002/prac.18890390101
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