Cerium compounds
Chemical compounds
- 3 min read
- 3 chapters
Related on Lably
Through Lanthanide, Sulfur and Titration
Binary compounds
Halides
Cerium forms all four trihalides CeX3 (X = F, Cl, Br, I) usually by reaction of the oxides with the hydrogen halides. The anhydrous halides are pale-colored, paramagnetic, hygroscopic solids. Upon hydration, the trihalides convert to complexes containing aquo complexes [Ce(H2O)8−9]3+. Unlike most lanthanides, Ce forms a tetrafluoride, a white solid. It also forms a bronze-colored diiodide, which has metallic properties.
Aside from the binary halide phases, a number of anionic halide complexes are known. Fluoride gives the Ce(IV) derivatives CeF84− and CeF62−. Chloride gives the orange CeCl62−.
Oxides and chalcogenides
Cerium(IV) oxide ("ceria") has the fluorite structure, similarly to the dioxides of praseodymium and terbium. Ceria is a nonstoichiometric compound, meaning that the real formula is CeO2−x, where x is about 0.2. Thus, the material is not perfectly described as Ce(IV). Ceria reduces to cerium(III) oxide with hydrogen gas.
Many nonstoichiometric chalcogenides are also known, along with the trivalent Ce2Z3 (Z = S, Se, Te). The monochalcogenides CeZ conduct electricity and would better be formulated as Ce3+Z2−e−. While CeZ2 compounds are known, they are polychalcogenides with cerium(III): cerium(IV) derivatives of S, Se, and Te are unknown.
Other binary compounds
Cerium phosphide is a gray crystal, which can be obtained by reacting cerium dioxide and phosphine at 1300 °C in the presence of hydrogen, or by reacting sodium phosphide and cerium chloride at 700~800 °C.
Sign in to keep reading
2 more chapters are free with a Lably account.
Cerium(IV) complexes
The compound ceric ammonium nitrate ("CAN") (NH4)2[Ce(NO3)6] is the most common cerium compound encountered in the laboratory. The six nitrate ligands bind as bidentate ligands. The complex [Ce(NO3)6]2− is 12-coordinate, a high coordination number which emphasizes the large size of the Ce4+ ion. CAN is popular oxidant in organic synthesis, both as a stoichiometric reagent and as a catalyst. It is inexpensive, easily handled. It operates by one-electron redox. Cerium nitrates also form 4:3 and 1:1 complexes with 18-crown-6 (the ratio referring to that between cerium and the crown ether).
Classically CAN is a primary standard for quantitative analysis. Cerium(IV) salts, especially cerium(IV) sulfate, are often used as standard reagents for volumetric analysis in cerimetric titrations.
Cerium(III) and terbium(III) have ultraviolet absorption bands of relatively high intensity compared with the other lanthanides, as their configurations (one electron more than an empty or half-filled f-subshell respectively) make it easier for the extra f electron to undergo f→d transitions instead of the forbidden f→f transitions of the other lanthanides. Cerium(III) sulfate is one of the few salts whose solubility in water decreases with rising temperature.
Due to ligand-to-metal charge transfer, aqueous cerium(IV) ions are orange-yellow. Aqueous cerium(IV) is metastable in water and is a strong oxidizing agent that oxidizes hydrochloric acid to give chlorine gas.
In the Belousov–Zhabotinsky reaction, cerium oscillates between the +4 and +3 oxidation states to catalyze the reaction.
Organocerium compounds
Organocerium chemistry is similar to that of the other lanthanides, often involving complexes of cyclopentadienyl and cyclooctatetraenyl ligands. Cerocene (Ce(C8H8)2) adopts the uranocene molecular structure. The 4f electron in cerocene, Ce(C8H8)2, is poised ambiguously between being localized and delocalized and this compound is also considered intermediate-valent. Alkyl, alkynyl, and alkenyl organocerium derivatives are prepared from the transmetallation of the respective organolithium or Grignard reagents, and are more nucleophilic but less basic than their precursors.