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.
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.
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 1.9M (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.