Chloropentamminecobalt chloride

Chloropentamminecobalt(III) chloride

Names
IUPAC name Pentaamminechlorocobalt(III) chloride
Other names Pentaamminechlorocobalt(III) chloride
Identifiers
CAS Number	13859-51-3
3D model (Jmol)	Interactive image
ECHA InfoCard	100.034.163
SMILES N.N.N.N.N.[Cl-].[Cl-].[Cl-].[Co+3]
Properties
Chemical formula	[Co(NH3)5Cl]Cl2
Molar mass	250.4 g/mol
Appearance	red-violet rhomb-shaped crystal
Density	1.783 g/mL
Boiling point	N/A
Solubility in water	0.4 g/100 mL
Vapor pressure	5990 mm Hg
Thermochemistry
Std enthalpy of formation (ΔfH^o298)	−1.0376E+06 Jmol^−1; Molar Gibbs energy of formation = −606480 J/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Chloropentamminecobalt chloride is a cobalt coordination compound. It is a red-violet, diamagnetic, water-soluble salt with the formula [Co(NH₃)₅Cl]Cl₂. The compound has been of academic and historical interest.

Synthesis and reactions

The complex is prepared with a two-step process starting with oxidizing a solution of cobalt chloride and ammonia.^[1]

2 CoCl₂,6H₂O + 8 NH₃ + 2 NH₄Cl + H₂O₂ → 2 [Co(NH₃)₅(OH₂)]Cl₃ + 12 H₂O

This intermediate is then heated to induce coordination of one of the outer sphere chloride ligands:

[Co(NH₃)₅(OH₂)]Cl₃ → [Co(NH₃)₅Cl]Cl₂ + H₂O

The complex is a dication with idealized C_4v symmetry.^[2]

In an aqueous solution, chloropentaamminecobalt(III) chloride reforms aquopentammine complex. With concentrated sulfuric acid, chloropentaamminecobalt(III) chloride forms the hydrogen sulfate complex.

History

Cobalt complexes have been of long interest because they are numerous, easily prepared, and colorful. It was partly on the basis of his study of cobalt coordination chemistry that Alfred Werner was awarded the Nobel Prize in Chemistry. Prior to Werner, the models of amine complexes postulated chains of pentavalent nitrogen centers. This Jørgensen–Bloomstrand model was ovethrown by Werner who introduced the idea that coordination complexes feature metal atoms of octahedral and tetrahedral shapes, with ammonia and other ligands attached individually to the metal. Werner's model accounted for the inner sphere ligands being less reactive.^[3] In [Co(NH₃)₅Cl]Cl₂, two chlorides are outer sphere and one is bound to the Co(III) center.

References

1. Gert G. Schlessinger (1967). "Chloropentaamminecobalt(III) Chloride". Inorganic Syntheses. 9: 160. doi:10.1002/9780470132401.ch43.
2. G. G. Messmer; E. L. Amma (1968). "Redetermination of the crystal structure of chloropentaamminecobalt(III) dichloride". Acta Crystallogr. B. 24: 417–422. doi:10.1107/S0567740868002475.
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