information:classification, structural:expansion
Coordination complexes

CuCl reacts with HCl or other chloride sources to form complex ions: the red − (found in potassium trichloridocuprate(II) K) (it is a dimer in reality, 2−, a couple of tetrahedrons that share an edge), and the green or yellow 2− (found in potassium tetrachloridocuprate(II) K).