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Chemical compound From Wikipedia, the free encyclopedia
Hexaamminecobalt(III) chloride is the chemical compound with the formula [Co(NH3)6]Cl3. It is the chloride salt of the coordination complex [Co(NH3)6]3+, which is considered an archetypal "Werner complex", named after the pioneer of coordination chemistry, Alfred Werner. The cation itself is a metal ammine complex with six ammonia ligands attached to the cobalt(III) ion.
Names | |
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IUPAC name
Hexaamminecobalt(III) chloride | |
Other names
Cobalt hexammine chloride, hexaamminecobalt(III) chloride | |
Identifiers | |
3D model (JSmol) |
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ChemSpider | |
ECHA InfoCard | 100.030.991 |
EC Number |
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PubChem CID |
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UNII | |
CompTox Dashboard (EPA) |
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Properties | |
H18N6Cl3Co | |
Molar mass | 267.48 g/mol |
Appearance | yellow or orange crystals |
Density | 1.71 g/cm3, |
Melting point | decomposes |
0.26 M (20 °C) tribromide: 0.04 M (18 °C) | |
Solubility | soluble in NH3 |
Structure | |
octahedral | |
0 D | |
Hazards | |
Occupational safety and health (OHS/OSH): | |
Main hazards |
poison |
GHS labelling: | |
Warning | |
H315, H319, H335 | |
P261, P264, P271, P280, P302+P352, P304+P340, P305+P351+P338, P312, P321, P332+P313, P337+P313, P362, P403+P233, P405, P501 | |
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 otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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[Co(NH3)6]3+ is diamagnetic, with a low-spin 3d6 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.[1] 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 chloride ions in [Co(NH3)6]Cl3 can be exchanged with a variety of other anions such as nitrate, bromide, iodide, sulfamate to afford the corresponding [Co(NH3)6]X3 derivative. Such salts are orange or bright yellow and display varying degrees of water solubility. The chloride ion can be also exchanged with more complex anions such as the hexathiocyanatochromate(III), yielding a pink compound with formula [Co(NH3)6] [Cr(SCN)6], or the ferricyanide ion.[citation needed]
[Co(NH3)6]Cl3 is prepared by treating cobalt(II) chloride 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 1.9 M (20 °C), versus 0.26 M for the trichloride.
[Co(NH3)6]3+ is a component of some structural biology methods (especially for DNA or RNA, where positive ions stabilize tertiary structure of the phosphate backbone), to help solve their structures by X-ray crystallography[4] or by nuclear magnetic resonance.[5] In the biological system, the counterions would more probably be Mg2+, but the heavy atoms of cobalt (or sometimes iridium, as in PDB: 2GIS) provide anomalous scattering to solve the phase problem and produce an electron-density map of the structure.[6]
[Co(NH3)6]3+ is used to investigate DNA. The cation induces the transition of DNA structure from the classical B-form to the Z-form.[7]
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