Chloropentaamminecobalt(III) chloride

Chloropentamminecobalt(III) chloride

Names
IUPAC name Pentaamminechlorocobalt(III) chloride
Other names Pentaamminechlorocobalt(III) chloride
Identifiers
CAS Number	13859-51-3
3D model (JSmol)	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 (ΔfHo298)	−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 the dichloride salt of the coordination complex [Co(NH₃)₅Cl]²⁺. It is a red-violet, diamagnetic, water-soluble salt. The compound has been of academic and historical interest.

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

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

The complex is a dication with idealized C_4vsymmetry.

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

Cobalt complexes have been of long-standing interest in inorganic chemistry 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. In [Co(NH₃)₅Cl]Cl₂, two chloride ions are outer sphere (counter ions) and one is bound to the Co(III) center: reaction with excess silver nitrate would immediately precipitate the two chloride counter ions, but the bound chloride ion would not be precipitated.