Lanthanides oxides

Selective Oxidation. Cerium, the most abundant lanthanide, can be separated easily after oxidation of Ce(III) to Ce(IV), simplifying the subsequent separation of the less abundant lanthanides. Oxidation occurs when bastnaesite is heated in air at 650°C or when the hydroxides are dried in air... 

Ranjit KT, Willner I, Bossmann SH, Braun AM (2001) Lanthanide oxide doped titanium dioxide photocatalysts Novel photocatalysts for the enhanced degradation of p-chlorophe-noxyacetic acid. Environ Sci Technol 35 1544—1549... 

A predominant feature of the atomic structure of the lanthanide group is the sequential addition of 14 electrons to the 4f subshell (Table 1). The /"electrons do not participate in bond formation and in ordinary aqueous solutions all of the lanthanides exhibit a principal (III) state. The common (III) state confers a similarity in chemical properties to all lanthanide elements. Some of the lanthanides can also exist in the (II) state (Nd, Sm, Eu, Tm, Yh) or in the (IV) state (Ce, Pr, Nd, Tb, Dy). Except for Ce(IV), Eu(II), and Yb(II), these unusual lanthanide oxidation states can only be prepared under drastic redox pressure and temperature conditions, and they are not stable in aqueous solutions. Cerium (IV) is a strong oxidizing agent... 

The lanthanide oxide cations [LnO]+ and the bare lanthanide ions Ln+ react differently with butadiene (162). Some bare Ln+ ions (La, Ce, Pr, Gd) activate butadiene but their oxide cations are inert toward butadiene. The lanthanides with weak M-O bonds, EuO and YbO, react by oxygen transfer to the butadiene. The oxide cations of Dy, Ho, Er, and Tm activate butadiene, whereas the bare metals of these lanthanides are unreactive with butadiene. The [HoO]+ ion has been studied in detail and is able to polymerize butadiene the mechanism of this reaction has been discussed. 

The rare earth metals. The rare earth metals are extremely reactive elements especially with respect to the normal atmospheric gases. The light trivalent lanthanides oxidize with air at room temperature they should be stored (and handled) in vacuum or under He or Ar. Divalent Eu oxidizes much more readily than any of... 

Ranjit, K.T., Cohen, H., Willner, I., Bossmann, S., Braun, A. 1999. Lanthanide oxide-doped titanium dioxide effective photocatalysts for the degradation of organic pollutants. J Mater Sci 34 5273-5280. 

The lanthanide oxides provide an interesting system for the study of pol5unor-phism. The structures of each of the three polymorphic forms are built up either from a single t57pe of coordination polyhedron MO7 in the hexagonal A-form, MOe in the cubic C-form or from a mixture of MOe and MO7 polyhedra as in the monocHnic B-form. 

Roih and Schneider 68) have recently studied the lanthanide oxide system in detail. They concluded that each oxide exists in one stable form only and that the C-form of NdaOs, Sm203, EU2O3 and Gd20s are metastable at lower temperatures. They also believe that all low temperature forms transform irreversibly to the most stable form at higher temperature. However, Warshaw and Roy 69) have shown... 

Figure 9.63 Properties of REEs (from above dissociation energies of lanthanide oxides ( ), sublimation enthalpies of REEs (U) and transition energies for the transition of the 5d electron from 4fn 5d6s2...

The unique properties of lanthanide-based materials, e.g., lanthanide-silicates and lanthanide-doped silicas, can be related to the special properties of the 4f" orbitals. Among lanthanide oxides, only Ce, Pr and Tb form dioxides, which crystallize in one simple structure with M4+ ions showing octahedral coordination [17]. For instance, cerium dioxide exhibits an 8 4 catiomanion coordination [18]. Its characteristic feature is the ability to undergo oxidation-reduction cycles in a reversible way [19], It was shown that the presence of Ce and La additives in mesoporous silicas, e.g., MCM-41 [10,11] and MSU-X [12], improves their thermal and hydrothermal stability. 

J. Paivasaari, M. Putkonen, L. Niinisto, A comparative study on lanthanide oxide thin films grown by atomic layer deposition, Thin Solid Films 472 (2005) 275-281. 

Newer immunodetection applications, and particularly the so-called microarrays, employ new fluorescent probes such as europium chelates (Scorilas et al., 2000), lanthanide oxide nanoparticles (Dosev et al., 2005 Nichkova et al., 2006), fluoro-phore loaded latex beads (Orth et al., 2003), dye-doped silica nanoparticles (Zhou and Zhou, 2004 Yao et al., 2006), and inorganic nanocrystals (Gerion et al., 2003 Geho et al., 2005). 

Highly pure lanthanide oxides (99.99% purity) that are commercially available can be used as starting materials for the preparation of lanthanide complexes after treatment at 1100°C... 

Hydrated chlorides, nitrates or perchlorates can be easily prepared by the dissolution of lanthanide oxides with concentrated HC1, HN03 or HCIO4, respectively. 

Hydrated lanthanide salts may also be obtained by the addition of an excess of lanthanide oxide to a concentrated acid solution, heating at 80°C until the pH is between 5 and 6. The residual oxide is removed by filtration, and the filtrate is subjected to rotary evaporation. This procedure may lead to the presence of oxo and hydroxy species in solution. At present hydrated lanthanide salts of 99.9% purity are available commercially. Salts of the highest purity are generally used in spectroscopic and magnetic studies. The purity of lanthanide salts can be determined by complexometric titration with ethylenediamine tetraacetic acid [1]. 

Synthesis of lanthanide triflates is achieved by adding an excess of lanthanide oxide to a concentrated solution of triflic acid in water at 80°C. The reaction is complete when the solution has a pH of 6.0. The solution is filtered, and evaporated in a rotary evaporator. The resulting solid is dried in a vacuum at 100°C for 12 hours. 

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