Cobalt(III) hexammine chloride
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| Cobalt(III) hexammine chloride | |
|---|---|
| Image:CoA6Cl3.png | |
| IUPAC name | Hexammine cobalt(III) chloride |
| Other names | Cobalt hexammine chloride |
| Identifiers | |
| CAS number | |
| Properties | |
| Molecular formula | H18N6Cl3Co |
| Molar mass | 267.48 g/mol |
| Appearance | yellow or orange crystals |
| Density | ? g/cm3, ? |
| Melting point |
decomposes |
| Solubility in water | 0.26M (20 °C) tribromide: 0.04M (18 °C) |
| Solubility in other solvents | soluble in NH3 |
| Structure | |
| Coordination geometry | octahedral |
| Dipole moment | 0 D |
| Hazards | |
| Main hazards | poison |
| R-phrases | 36/37/38 |
| S-phrases | none |
| Related Compounds | |
| Other anions | [Co(NH3)6]Br3 [Co(NH3)6](OAc)3 |
| Other cations | [Cr(NH3)6]Cl3 [Ni(NH3)6]Cl2 |
| Related compounds | [Co(H2NCH2CH2NH2)3]Cl3 [Co(NH3)5(H2O)]Cl3 |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references | |
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.
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.
Preparation
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.[1] This salt appears to have been first reported by Fremy.[2]
The acetate salt can be prepared by aerobic oxidation of cobalt(II) acetate, ammonium acetate, and ammonia in methanol.[3] 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.
References
- ↑ Bjerrum, J.; McReynolds, J. P. "Hexamminecobalt(III) Salts" Inorganic Syntheses, 1946, volume II, pages 216-221.
- ↑ Fremy Annales de chimie et de physique, 1852, volume 35, page 257ff.
- ↑ Lindholm, R. D. "Hexamminecobalt(III) Salts" Inorganic Syntheses, 1978, volume XVIII, pages 67-69.
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
