Potassium tetrachloridocuprate(II) describes salts with chemical formula K<sub>2</sub>CuCl<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>. It is a greenish blue solid. This form also occurs naturally as the rare mineral mitscherlichite.
The dihydrate occurs rarely in nature near volcanic vents, e.g. in Mount Vesuvius, as the mineral mitscherlichite; which is named in honor of Eilhardt Mitscherlich (1794âÂÂ1863), the German crystallographer and chemist who first synthesized the compound. It was identified as pigment in some ancient artifacts. The dihydrate can be obtained by slow evaporation of a solution of potassium chloride () and copper(II) chloride () in 2:1 molar ratio.
The structure of hydrated potassium tetrachloridocuprate(II) has been confirmed by X-ray crystallography and neutron diffraction. Copper is square planar, being bound to two trans chloride ligands (d<sub>Cu-Cl</sub> = 228 pm and two water ligands (d<sub>Cu-O</sub> = 1.97 pm). The other chlorides are more distant (Cu-Cl = 289 pm). Structural studies on this salt are of historic interest. The compound is isostructural with and .
Anhydrous has a complicated history and may not exist. Instead it converts upon heating to a mixture of and potassium trichloridocuprate .
The ion has been intensively studied from the perspective of electronic structure. It is a planar complex, usually isolated as a salt with organic cations.