Trace of lanthanides

Cycloaddition with aldehydes 2-iminooxetanes.2 Lewis acids are not useful for this cycloaddition, but traces of lanthanide shift reagents, Yt(fod)3, Yt(hfc)3, or Eu(hfc)3 are very efficient catalysts for cycloaddition to a mixture of (cis)- and (fra/w)-2-iminooxetanes (2) in the case of both aliphatic and aromatic aldehydes. 

Flame atomic absorption spectrometry permits the determination of traces of lanthanides present in high-purity rare-earth oxides but is not that sensitive. Luo and Hu (1981) determined traces of holmium and erbium present in Y2O3 by employing a N2O-C2H2 flame. Electrothermal atomic absorption spectrometry was successfully used for the... 

Wavelength-dispersive X-ray fluorescence, with a tungsten target and LiF analyzing crystal, is widely used for the determination of traces of lanthanides in high-purity... 

In summary, the determination of lanthanides in high-purity rare-earth oxides depends on the ultimate use of rare-earth oxides in commercial devices. Derivative spectrophotometry and EDXRF (which are less costly) can be reliably used for monitoring lanthanides in 90% to 3 N purity rare-earth oxides. The determination of traces of lanthanides in high-purity rare-earth oxides (4N to 6N) invariably requires costlier ICP-MS or GD-MS techniques for liquid and solid samples. 

As mentioned in the introduction, early transition metal complexes are also able to catalyze hydroboration reactions. Reported examples include mainly metallocene complexes of lanthanide, titanium and niobium metals [8, 15, 29]. Unlike the Wilkinson catalysts, these early transition metal catalysts have been reported to give exclusively anti-Markonikov products. The unique feature in giving exclusively anti-Markonikov products has been attributed to the different reaction mechanism associated with these catalysts. The hydroboration reactions catalyzed by these early transition metal complexes are believed to proceed with a o-bond metathesis mechanism (Figure 2). In contrast to the associative and dissociative mechanisms discussed for the Wilkinson catalysts in which HBR2 is oxidatively added to the metal center, the reaction mechanism associated with the early transition metal complexes involves a a-bond metathesis step between the coordinated olefin ligand and the incoming borane (Figure 2). The preference for a o-bond metathesis instead of an oxidative addition can be traced to the difficulty of further oxidation at the metal center because early transition metals have fewer d electrons. 

Traces of water or acidic impurities can lead to the formation of insoluble, hydrated lanthanide adducts, or of paramagnetic lanthanum oxide80, adversely affecting spectral resolution. Careful purification of the solvents and substrate is advised, and filtration of the solution through glass-wool or cotton plugs may be useful. 

G. E. Boyd J. Schubert A.W. Adamson Demonstration of the applicability of ion exchange for adsorption of fission products in trace amounts (lanthanides). 1942... 

FIGURE 4.11 Distribution ratios of lanthanides (10 5 M), Am, and Cm (trace level) from 3 M HN03 solutions into NPHE with CPnl, CPn2, CPn3, and CPn4. 

Cj Bleaney s factor of lanthanide / (scaled to —100 Tr(z) trace of the magnetic susceptibility tensor... 

Chemical point of view and related experimental data 499 6.1. Trace amount determination of lanthanides and actinides 506... 

V. Bhagavathy, T. Prasada Rao and A.D. Damodaran, Trace determination of lanthanides in high-purity rare-earth oxides 367... 

The ratio of the size of the metal ion and the radius of the internal cavity of the macrocyclic polyether determines the stoichiometry of these complexes. The stoichiometry of these complexes also depends on the coordinating ability of the anion associated with the lanthanide. For example, 12-crown-4 ether forms a bis complex with lanthanide perchlorate in acetonitrile while a 1 1 complex is formed when lanthanide nitrate is used in the synthesis [66]. Unusual stoichiometries of M L are observed when L = 12 crown-4 ether and M is lanthanide trifluoroacetate [67]. In the case of 18-crown-6 ligand and neodymium nitrate a 4 3 stoichiometry has been observed for M L. The composition of the complex [68] has been found to be two units of [Nd(18-crown-6)(N03)]2+ and [Nd(NCh)<--)]3. A similar situation is encountered [69] when L = 2.2.2 cryptand and one has [Eu(N03)5-H20]2- anions and [Eu(2.2.2)N03]+ cations. It is important to note that traces of moisture can lead to polynuclear macrocyclic complexes containing hydroxy lanthanide ions. Thus it is imperative that the synthesis of macrocyclic complexes be performed under anhydrous conditions. 

---