The compound is prepared is a two-step process starting with oxidizing a solution of cobalt chloride and ammonia.[1]
2 CoCl2 + 8 NH3 + 2 NH4Cl + H2O2 → 2 [Co(NH3)5(OH2)]Cl3 + H2O
This intermediate is then heated to induce coordination of one of the outer sphere chloride ligands:
[Co(NH3)5(OH2)]Cl3 → Co(NH3)5Cl]Cl2 + H2O
The complex is a dication with idealized C4v symmetry.[2]
In aqueous solutoin chloropentamminecobalt(III) chloride reforms aquopentammine complex. With concentrated sulfuric acid, chloropentamminecobalt(III) chloride form hydrogen sulfate complex.