Lanthanides in aqueous solutions

Nitrogen donors usually form weak complexes with the lanthanides in aqueous solution. Sinha and Green 26) have measured the NMR spectra of complexes formed between 1,10-phenanthrohne and Ce(III), Pr(III), Nd(HI) and Eu(IH) in D2O. As the spectra were measured at room temperature, only time-average signals for the phenanthrohne protons were obtained. However, a plot of the shift of the protons as a function of the mole ratios of the hgand and metal ion (Fig. 2)... 

K.L. Nash and J.C. Sullivan, Kinetics of complexation and redox reactions of the lanthanides in aqueous solutions 347... 

The chemical properties of the actinides are much less similar to each other than those of the lanthanides, because the additional electrons added to the 5/ and 6d are bound less t tly than those of the 4/and 5d shells of the lanthanides. As shown in Table 9.4, the lanthanides in aqueous solutions exist principally in a single, tiivalent oxidation state, whereas four or more oxidation states are observed in the aqueous chemistry of uranium, neptunium, and plutonium. The actinide ions normally formed in solution by the oxidation states II through VI are M, M, M, MO2, MOj , respectively. 

KINETICS OF COMPLEXATION AND REDOX REACTIONS OF THE LANTHANIDES IN AQUEOUS SOLUTIONS ... 

The trivalent oxidation state is dominant for the lanthanides in aqueous solution. The two redox-active species most commonly known and widely studied are Ce(IV) and Eu(II). Oxidized and reduced forms of neighboring lanthanide elements (e.g. Pr(IV), Sm(II)) have been reported to exist, but these species are formed only in relatively exotic solutions hke concentrated carbonate media or as transients in the radiolysis of trivalent lanthanide aqueous solutions. As their stability is very limited, few significant studies of their redox chemistry exist. Our discussion of lanthanide redox reaction rates will deal almost exclusively with the reactions of Ce(IV) and Eu(II). Existing reviews of the hterature relating to the redox kinetics of the lanthanides cover the period up to 1979 (Benson 1976, McAuley 1981), so we will confine our discussion primarily to the results of the last 10 12 years. 

A certain amount of MCD work has been carried out for lanthanides in aqueous solution, from which a number of deductions can be made about the local site symmetry (Gbrller-Walrand and Godemont 1977a,b Gorller-Walrand et al. 1982). 

Nash, K.L., and J.C. Sullivan, 1991, Kinetics of complexation and redox reactions of the lanthanides in aqueous solutions, in Handbook on the Physics and Chemistry of Rare Earths, Vol. 15, eds K.A. Gschneidner Jr and L. Eyring (Elsevier, Amsterdam), pp. 347-391. 

As noted earlier, bands characteristic of the lanthanides are observed in non-aqueous solvents at lower energies than is possible in DCIO4. In a subsequent section, the quantitative treatment of band intensities is discussed. As a result of this work, the energies and intensities of all the transitions characteristic of the lanthanides in aqueous solution in the energy range 0-5500 cm can be computed. The corresponding bands are included in the spectra shown in figs. 24.4-24.12 and discussed in section 3.7. 

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