chromiumIII

Chromium(III) refers to chromium in the +3 oxidation state, symbolized Cr3+. It is the most stable oxidation state for chromium in many aqueous and solid-state environments and is typically paramagnetic due to its d3 electronic configuration. In water, Cr3+ forms the hexaaqua complex [Cr(H2O)6]3+, which is violet in solution; this aqua complex can undergo hydrolysis with increasing pH to form hydroxo species and eventually insoluble chromium(III) hydroxide, Cr(OH)3. Cr3+ centers typically adopt octahedral coordination geometry and form a wide range of complexes with ligands such as water, hydroxide, halides, and multidentate chelators; ligand fields cause color changes across different Cr(III) complexes.

Chromium(III) compounds are widely used as pigments and in leather tanning. Chromium(III) oxide, Cr2O3, is a stable emerald-green pigment used in paints, ceramics, and glass. Cr3+ salts and complexes also serve as catalysts or Lewis acids in certain organic transformations, particularly in research settings.

Biology and safety: Cr(III) is considered a trace element in some nutrition contexts, with controversial evidence for essentiality; absorption from the diet is generally low. Cr(III) compounds are far less toxic than chromium(VI) species; environmental oxidation of Cr(III) to Cr(VI) is a concern because Cr(VI) is highly toxic and carcinogenic. In practical terms, Cr(III) is viewed as relatively low-risk when handled in typical industrial contexts.