Cerium IV Compounds

Pour a sodium hydroxide solution into a solution of cerium(IV) sulphate. What is observed Write the equation of the reaction. 

Add an equal volume of a sodium carbonate solution to a cerium nitrate one, next add dropwise a potassium permanganate solution. What is the composition of the precipitate Write the equation of the reaction. 

Add a potassium iodide solution to one of cerium(IV) sulphate acidified with sulphuric acid. How can you explain the change in the solution s colour Write the equation of the reaction. What properties do cerium(III) and cerium(IV) salts exhibit  

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It is a commonplace to say that there has been explosive growth in the use of lanthanides in organic chemistry. For many years, the use of cerium(iv) compounds as oxidants was widespread, but more recently a whole range of other compounds have made their appearance. Thus samarium(ii) compounds are now routinely used as one-electron reducing agents and the use of trifluoromethanesulfonate ( triflate ) salts of scandium and the lanthanides as water-soluble Lewis acid catalysts is widespread. Beta-diketonate complexes and alkoxides have also come into use there are even applications of mischmetal in organic synthesis. 

Cerium(III) tris(/3-diketonate) complexes are readily oxidized to the cerium(IV) compounds. They are volatile with vapor pressures high enough for MOCVD use. A number of diketonates are now better characterised, prompted by the possibility of using them as CVD materials and petrol additives, as well as a source of cerium oxide as an oxygen store for catalytic converters. [Ce Me3CCOCHCOCMe2(OMe) 4], Ce(acac)4 (Figure 32), Ce(dbm)4, [Ce(pmhd)4], and Ce(tmhd)4 all have square-antiprismatic coordination of cerium (in the [Ce(catecholate)4]" ion the coordination is dodecahedral). 

Unsymmetrical 1,4-diketones have been prepared in good yields by (NH4)2[Ce(N03)6] oxidative cross coupling between 1,2-disubstimted and 1-substituted trimethylsilyl eno-lates . The same cerium(IV) compound has been also applied to the preparation of 6-oxo-Q ,/ -unsaturated carbonyl compounds trimethylsilyl dienolates are easily oxidized... 

Cerium(IV) compounds with suitable reducing agents, readily initiate the redox polymerization of, for example, vinyl monomers [22]. This property is used to initiate graft polymerization of vinyl monomers onto cellulose, wool, starch, cotton, etc. in order to, e.g. improve mechanical strength, resist moisture penetration and reduce micro-organism attack. 

The better known methods for the removal of cerium from rare earth mixtures depend upon the ease of oxidation of cerium and the subsequent precipitation of cerium(IV) compounds by hydrolysis. Among these are the permanganate-phosphate/ the permanganate-cerium dioxide, the electrolytic, and the potassium bromate methods. The method of G. F. Smith, in which ammonium-cerium(IV) nitrate is crystallized from a nitric acid solution of the rare earths in the presence of an excess of ammonium nitrate, is particularly valuable as a commercial method for the production of large amounts of very pure cerium compounds. 

The readily occurring transition from colorless Ce + to bright yellow or orange Ce" + forms the basis for the use of cerium(IV) sulfate solutions in redox titrations ( cerimetric analysis). The ease of access to various tetravalent cerium compounds makes cerium(IV) most valuable in research as well as in various practical applications. Important fields of application for cerium(IV) compounds include organic syntheses, bioinorganic chemistry, materials science, and industrial catalysis (e.g., vehicle emissions control, oxygen storage). ... 

As mentioned previously, rare earth chemistry differs mainly from transition metal chemistry in that most rare earth ions are redox inactive under ordinary conditions. However, a few lanthanides can support the +2 or +4 oxidation state. Lanthanide chemistry in the +4 oxidation state is mostly limited to cerium(IV) compounds (Nair et al., 2003). On the other hand, low-valent chemistry is more nuanced than its high-valent counterpart (Nief, 2010). Table 1 lists the ionic radii for M " " (Shannon, 1976) and the spectroscopically estimated values for °(M " "/M +) (Nugent et al., 1973). 

The assignment of oxidation states in cerium compounds is not always an easy task. A well-known case is that of cerocene, bis(cyclooctatetraene)cerium, Ce() -C8H8)2. This complex was originally formulated as a cerium(IV) compound with two (j -CsHs) " anions (Greco et al., 1976). Later calculations indicated that the stoichiometry of cerocene is better described as [Ce + ()] -C8H8)2 ] (Neumann and Fulde, 1989). Ab initio calculations showed that cerocene is in fact a mixed valent compound, with a ground state consisting of 83%... 

Cerium(IV) compounds used for the preparation of standard solutions... 

The Ce + ion is one of the most active catalysts for peptide hydrolysis. Its activity is much higher than that of the trivalent lanthanide ions and other transition metal ions. In particular, Ce + is far superior to other tetravalent ions like Zr" or Hf +. Yashiro et al. (1994) reported that dipeptides and tripeptides were efficiently hydrolyzed under neutral conditions by the y-cyclodextrin complex of cerium(IV). Komiyama and coworkers (Takarada et al., 2000) studied the catalytic hydrolysis of oligopeptides by cerium(IV) salts. The hydrolysis is fast, especially when the oligopeptides contain no metal-coordinating side-chains. The hydrolysis rates of the dipeptides, tripeptides and tetrapeptides is similar. The hydrolysis reaction was performed at pH 7 and 50 °C and under these conditions, the half-life of the amide bond was only a few hours. The authors found that ammonium hexanitratocerate(IV) is more active than other cerium(IV) compounds like ammonium cerium(IV) sulfate, cerium(IV) sulfate and cerium(IV) hydroxide. The lower reactivity of ammonium cerium(IV) sulfate is ascribed to the competitive inhibition by sulfate ions, while the low reactivity of cerium(IV) sulfate and cerium(IV) hydroxide can be explained by their poor solubility in water. However, in the reaction mixtures at the given reaction conditions, most of the cerium(IV) consists in a gel of cerium(IV) hydroxides. No oxidative cleavage has been observed. 

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