Cobalt(III) chloride is of very dubious existence and the bromide and iodide have never been prepared. These halides are expectedly redox unstable, the Co3+ ion being a strong oxidant. Dissolution of cobalt(III) oxide in hydrochloric acid leads to evolution of chlorine. Indeed cobalt(III) compounds are estimated volumetrically as a result of their liberation of iodine from potassium iodide in acid solution.
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Cobalt(III) chloride or cobaltic chloride, CoCl3, is an unstable and elusive compound. In this compound, the cobalt atoms have a formal charge of 13. The compound has been described to occur in the gas phase at high temperatures, in equilibrium with cobalt(II) chloride and chlorine gas. It has also been observed to be stable at very low temperatures, dispersed in a frozen argon matrix.
