The tetrahydrate crystallizes as  and two water molecules. The oxidation state of gold in  and  anion is +3. The salts of  (tetrachloroauric(III) acid) are tetrachloroaurates(III), containing  anions (tetrachloroaurate(III) anions), which have square planar molecular geometry. The Au–Cl distances are around 2.28 Å. Other d complexes adopt similar structures, e.g. tetrachloroplatinate(II) Potassium tetrachloroplatinate|.