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cobalt iii chromate is a brown or yellowish-brown powder that may be produced by the reaction of cobalt oxide with chromium trioxide. It is soluble in mineral acids and solutions of chromium trioxide; it is insoluble in water.
[Co(NH3)6]3+ is a diamagnetic metal ammine coordination complex, an archetypal “Werner complex” named for the pioneer of coordination chemistry, Alfred Werner. It is inert, having a low-spin 3d6 octahedral Co(III) center that obeys the 18-electron rule. It has high pH solubility.
The chloride ion in [Co(NH3)6]Cl3 can be exchanged with a wide range of other anions to give salts of varying degrees of water solubility, such as hexamminecobalt(III) nitrate and nitrate, bromide, iodide, sulfamate, and chromate. The chloride ion also can be exchanged with a variety of ammonium ions to give hexamminecobalt(III) ammonium nitrate, which has a pink color.
Stability Constants for hexamminecobalt(III) and chromium ii chromate (HCrO4) have been determined spectrophotometrically in acid solution. The thermodynamic equilibrium constants are 1.55 +- 0.02 M-1 for [M(NH3)5(HCrO4) 2+] and 3.56 +- 0.62 M-1 for [M(NH3)5(CrO4)]2+ at 25degC.
The hexamminecobalt(III) chloride complex has a relatively weak oxidizing activity and does not react quickly with acids. This is due to its inert nature, a feature that distinguishes it from labile metal ammine complexes such as [Ni(NH3)6]Cl2. The anionic form of the compound, hexamminecobalt(III) perchlorate, possesses a slightly stronger oxidizing activity and can be readily prepared from hexamminecobalt(III) by hydrochloric acid treatment.