HOME

TheInfoList



OR:

Hexaamminecobalt(III) chloride is the chemical compound with the formula o(NH3)6l3. It is the chloride salt of the coordination complex o(NH3)6sup>3+, which is considered an archetypal "Werner complex", named after the pioneer of coordination chemistry,
Alfred Werner Alfred Werner (12 December 1866 – 15 November 1919) was a Swiss chemist who was a student at ETH Zurich and a professor at the University of Zurich. He won the Nobel Prize in Chemistry in 1913 for proposing the octahedral configuration of ...
. The cation itself is a metal ammine complex with six ammonia ligands attached to the cobalt(III) ion. Originally salts of o(NH3)6sup>3+ were described as the ''luteo'' (Latin: yellow) complex of cobalt. This name has been discarded as modern chemistry considers color less important than molecular structure. Other similar complexes also had color names, such as ''purpureo'' (Latin: purple) for a cobalt pentammine complex, and ''praseo'' (Greek: green) and ''violeo'' (Latin: violet) for two isomeric tetrammine complexes.


Properties and structure

o(NH3)6sup>3+ is diamagnetic, with a
low-spin Spin states when describing transition metal coordination complexes refers to the potential spin configurations of the central metal's d electrons. For several oxidation states, metals can adopt high-spin and low-spin configurations. The ambiguity o ...
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, o(NH3)6l3 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 i(NH3)6l2, 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 o(NH3)6l3 can be exchanged with a variety of other anions such as
nitrate Nitrate is a polyatomic ion A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zer ...
, bromide, iodide,
sulfamate Sulfamic acid, also known as amidosulfonic acid, amidosulfuric acid, aminosulfonic acid, sulphamic acid and sulfamidic acid, is a molecular compound with the formula H3NSO3. This colourless, water-soluble compound finds many applications. Sulfami ...
to afford the corresponding o(NH3)63 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 o(NH3)6Cr(SCN)6], or the Ferricyanide, ferricyanide ion.


Preparation

o(NH3)6l3 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. This salt appears to have been first reported by Fremy. The acetate salt can be prepared by aerobic oxidation of cobalt(II) acetate, ammonium acetate, and ammonia in methanol. The acetate salt is highly water-soluble to the level of 1.9 M (20 °C), versus 0.26 M for the trichloride.


Uses

o(NH3)6sup>3+ is a component of some structural biology methods (especially for DNA or
RNA Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...
, where positive ions stabilize tertiary structure of the phosphate backbone), to help solve their structures by X-ray crystallography or by nuclear magnetic resonance. In the biological system, the counterions would more probably be Mg2+, but the heavy atoms of cobalt (or sometimes iridium, as in ) provide anomalous scattering to solve the phase problem and produce an electron-density map of the structure. o(NH3)6sup>3+ is an unusual example of a water-soluble trivalent metal complex and is of utility for charge-shielding applications such as the stabilization of highly negatively charged complexes, such as interactions with and between nucleic acids.


Related compounds

*
Tris(ethylenediamine)cobalt(III) chloride Tris(ethylenediamine)cobalt(III) chloride is an inorganic compound with the formula
o(en)3 O, or o, is the fifteenth Letter (alphabet), letter and the fourth vowel letter in the Latin alphabet, used in the English alphabet, modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in ...
l3 (where "en" is the abbreviation for ethylenediamine). It is the chloride salt of the coordination complex
o(en)3 O, or o, is the fifteenth Letter (alphabet), letter and the fourth vowel letter in the Latin alphabet, used in the English alphabet, modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in ...
+. This trication was important in ...


References

{{reflist Cobalt complexes Cobalt(III) compounds Inorganic compounds Chlorides Metal halides Octahedral compounds Ammine complexes