CeriumIII

Cerium(III), or cerous ion, refers to the trivalent oxidation state of cerium, Ce3+. In most aqueous and many solid compounds, cerium exists predominantly as Ce3+. The element also forms Ce4+ (ceric) under oxidizing conditions, and the two redox states together govern much of cerium chemistry. Ce3+ and Ce4+ can interconvert in solution, with Ce4+ acting as a strong oxidant in acidic media.

In solution, Ce3+ forms hydrated aqua complexes such as [Ce(H2O)9]3+. These ions readily bind to ligands including fluoride, hydroxide, phosphate and oxalate, forming various cerium(III) complexes. Ce3+ is prone to oxidation to Ce4+, especially in the presence of oxidants or oxygen, whereas Ce4+ salts (ceric) are typically yellow or orange. In some strongly reducing conditions, Ce3+ can undergo disproportionation to Ce4+ and Ce2+.

Cerium is a lanthanide found in minerals such as monazite and bastnäsite. Natural Ce distribution contains both Ce3+ and Ce4+ depending on the redox environment. Cerium(III) compounds, including cerium(III) chloride and cerium(III) salts, are common starting materials in inorganic synthesis and ore processing. Ce3+ can be oxidized to Ce4+ for applications requiring a strong oxidant, while Ce3+ itself serves as a relatively mild reducing agent in redox chemistry.

Applications and relevance include use of Ce4+ salts like ceric ammonium nitrate as oxidants in organic synthesis, and the widespread use of cerium oxide (CeO2, ceria) in catalysis and polishing. Ce3+/Ce4+ chemistry also underpins many analytical methods for cerium and phosphate detection. Safety considerations are typical for lanthanide compounds; Ce4+ salts are strong oxidizers, while Ce3+ salts are generally less hazardous but should be handled with standard precautions.