structural:scholar_edition, linguistic:translation
Chromium(III)

A large number of chromium(III) compounds are known, such as chromium(III) nitrate, chromium(III) acetate, and chromium(III) oxide. Chromium(III) can be obtained by dissolving elemental chromium in acids like hydrochloric acid or sulfuric acid, but it can also be formed through the reduction of chromium(VI) by cytochrome c7. The Cr ion has a similar radius (63 pm) to Al (radius 50 pm), and they can replace each other in some compounds, such as in chrome alum and alum.

Chromium(III) tends to form octahedral complexes. Commercially available chromium(III) chloride hydrate is the dark green complex Cl. Closely related compounds are the pale green Cl and violet Cl. 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.

Chromium(III) hydroxide (Cr(OH)) is amphoteric, dissolving in acidic solutions to form, and in basic solutions to form. It is dehydrated by heating to form the green chromium(III) oxide (Cr O), a stable oxide with a crystal structure identical to that of corundum.