Chromium(III) tends to form octahedral complexes. Commercially available chromium(III) chloride hydrate is the dark green complex Closely related compounds are the pale green [CrCl(H2O)5Cl2 and violet If anhydrous violet chromium(III) chloride is dissolved in water, the violet solution turns green after some time as the chloride in the inner coordination sphere is replaced by water. This kind of reaction is also observed with solutions of chrome alum and other water-soluble chromium(III) salts. A tetrahedral coordination of Chromium(III) has been reported for the Cr-centered Keggin anion [α-CrW12O405–.