Cobalt(III) hexammine chloride

Cobalt(III) hexammine chloride

Chembox new
Name = Cobalt(III) hexammine chloride
ImageFile = CoA6Cl3.png ImageName =
IUPACName = Hexaamminecobalt(III) chloride
OtherNames = Cobalt hexammine chloride
Section1 = Chembox Identifiers
CASNo = 10534-89-1

Section2 = Chembox Properties
Formula = H18N6Cl3Co
MolarMass = 267.48 g/mol
Appearance = yellow or orange crystals
Density = ? g/cm3, ?
Solubility = 0.26M (20 °C)
tribromide: 0.04M (18 °C)
Solvent = other solvents
SolubleOther = soluble in NH3
MeltingPt = decomposes
pKa =
Wavelength Absorbtion = ?

Section3 = Chembox Structure
Coordination = octahedral
CrystalStruct =
Dipole = 0 D

Section7 = Chembox Hazards
ExternalMSDS =
MainHazards = poison
RPhrases = 36/37/38
SPhrases = none

Section8 = Chembox Related
OtherAnions = [Co(NH3)6] Br3
[Co(NH3)6] (OAc)3
OtherCations = [Cr(NH3)6] Cl3
[Ni(NH3)6] Cl2
Function = compounds
OtherFunctn = [Co(H2NCH2CH2NH2)3] Cl3
[Co(NH3)5(H2O)] Cl3
[Co(NH3)5Cl] Cl2

Cobalt(III) hexammine chloride is the chemical compound with the formula [Co(NH3)6] Cl3. This coordination compound is considered an archetypal "Werner complex", named after the pioneer of coordination chemistry, Alfred Werner. This salt consists of [Co(NH3)6] 3+ trications with three Cl anions. The term "ammine" refers to ammonia in its metal complexes. It is also known as "leuto," a classical name rarely used now outside of teaching laboratories, where it is used along with violeo, praseo, and other cobalt complexes for teaching basic coordination chemistry.

Properties and structure

[Co(NH3)6] 3+ is diamagnetic, with a low-spin octahedral Co(III) center. The cation obeys the 18-electron rule and is considered to be a classic example of an exchange inert metal complex. As a manifestation of its inertness, [Co(NH3)6] Cl3 can be recrystallized unchanged from concentrated hydrochloric acid: the NH3 is so tightly bound to the Co(III) centers that it does not dissociate to allow its protonation. In contrast, labile metal ammine complexes, such as [Ni(NH3)6] Cl2, react rapidly with acids reflecting the lability of the Ni(II)-NH3 bonds. Upon heating, hexamminecobalt(III) begins to lose some of its ammine ligands, eventually producing a stronger oxidant.

The chlorides in [Co(NH3)6] Cl3 can be exchanged with a variety of other anions such as nitrate, bromide, and iodide to afford the corresponding [Co(NH3)6] X3 derivative. Such salts are bright yellow and display varying degrees of water solubility.


Since CoCl3 is not available, [Co(NH3)6] Cl3 is prepared from cobalt(II) chloride. The latter is treated with ammonia and ammonium chloride followed by oxidation. Oxidants include hydrogen peroxide or oxygen in the presence of charcoal catalyst. [Bjerrum, J.; McReynolds, J. P. "Hexamminecobalt(III) Salts" Inorganic Syntheses, 1946, volume II, pages 216-221.] This salt appears to have been first reported by Fremy. [cite journal
author = M. E. Fremy
journal = Annales de chimie et de physique
year = 1852
volume = 35
pages = 257-312
url =
title = Recherches sur le cobalt

The acetate salt can be prepared by aerobic oxidation of cobalt(II) acetate, ammonium acetate, and ammonia in methanol. [Lindholm, R. D. "Hexamminecobalt(III) Salts" Inorganic Syntheses, 1978, volume XVIII, pages 67-69.] The acetate salt is highly water-soluble to the level of 1.9M (20 °C), vs. 0.26M for the trichloride.

[Co(NH3)6] 3+ is a component of some protein crystallization methods to help solve their structures by X-ray crystallography.


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