Copper(I) chloride

Copper(I) chloride (quite commonly called cuprous chloride), is the lower chloride of copper, with the formula CuCl. It occurs naturally as the mineral nantokite. This colorless solid is almost insoluble in water, and which tends to oxidize in air to green CuCl2. It is a Lewis acid which reacts with suitable ligands such as ammonia or chloride ion to form complexes, many of which are water-soluble. It is even able to form a stable complex with carbon monoxide.

In aqueous solution, CuCl would be unstable with respect to disproportionation into Cu and CuCl2, but is stable toward water due to its low solubility.