Cerium compounds are compounds containing the element cerium (Ce), a lanthanide. Cerium exists in two main oxidation states, Ce(III) and Ce(IV). This pair of adjacent oxidation states dominates several aspects of the chemistry of this element. Cerium(IV) aqueous solutions may be prepared by reacting cerium(III) solutions with the strong oxidizing agents peroxodisulfateorbismuthate. The value of E⦵(Ce4+/Ce3+) varies widely depending on conditions due to the relative ease of complexation and hydrolysis with various anions, although +1.72 V is representative. Cerium is the only lanthanide which has important aqueous and coordination chemistry in the +4 oxidation state.[1]
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.[2]
Aside from the binary halide phases, a number of anionic halide complexes are known. Fluoride gives the Ce(IV) derivatives CeF4−8 and CeF2−6. Chloride gives the orange CeCl2−6.[1]
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.[3]
Many nonstoichiometricchalcogenides 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.[3]
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[4] and as a catalyst.[5] 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).
A white LED in operation: the diode produces monochromatic blue light but the Ce:YAG phosphor converts some of it into yellow light, with the combination perceived as white by the eye.
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.[9]Cerium(III) sulfate is one of the few salts whose solubility in water decreases with rising temperature.[10]
^Nair, Vijay; Deepthi, Ani (2007). "Cerium(IV) Ammonium NitrateA Versatile Single-Electron Oxidant". Chemical Reviews. 107 (5): 1862–1891. doi:10.1021/cr068408n. PMID17432919.
^Sridharan, Vellaisamy; Menéndez, J. Carlos (2010). "Cerium(IV) Ammonium Nitrate as a Catalyst in Organic Synthesis". Chemical Reviews. 110 (6): 3805–3849. doi:10.1021/cr100004p. PMID20359233.
^Lide, D. R., ed. (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton (FL): CRC Press. ISBN0-8493-0486-5.
^B. P. Belousov (1959).『Периодически действующая реакция и ее механизм』[Periodically acting reaction and its mechanism]. Сборник рефератов по радиационной медицине (in Russian). 147: 145.
^Mikhail N. Bochkarev (2004). "Molecular compounds of "new" divalent lanthanides". Coordination Chemistry Reviews. 248 (9–10): 835–851. doi:10.1016/j.ccr.2004.04.004.
^M. Cristina Cassani; Yurii K. Gun'ko; Peter B. Hitchcock; Alexander G. Hulkes; Alexei V. Khvostov; Michael F. Lappert; Andrey V. Protchenko (2002). "Aspects of non-classical organolanthanide chemistry". Journal of Organometallic Chemistry. 647 (1–2): 71–83. doi:10.1016/s0022-328x(01)01484-x.
