Trivalent Lanthanide and Actinide Ions

Figure 15.15 Variation of the ionic radii of trivalent lanthanide and actinide ions with increasing Z.

Sinkov, S.I. Choppin, G.R. Taylor, R.J. Spectrophotometry and luminescence spectroscopy of acetohydroxamate complexes of trivalent lanthanide and actinide ions, J. Solut. Chem., 36 (2007) 815-830. 

Beitz, J. 1994. Similarities and differences in trivalent lanthanide- and actinide-ion solution absorption spectra and luminescence studies. In Handbook on the Physics and Chemistry of Rare Earths (Vol. 18, Lanthanides/Actinides Chemistry), eds. K.A. Gschneider, J.L. Eyring, G.R. Choppin, G.H. Lander, pp. 159-193. Elsevier Science B.V., Amsterdam. 

J.V. Beitz, Similarities and differences in trivalent lanthanide- and actinide-ion solution absorption spectra... 

An electrostatic hydration model has been applied to the trivalent lanthanide and actinide ions in order to predict the standard free energy (AG°) and enthalpy (AHt) of hydration for these series. Assuming crystallographic and gas-phase radii for Bk(III) to be 0.096 and 0.1534 nm, respectively, and using 6.1 as the primary hydration number, AG298 was calculated to be -3357 kJ/mol, and A/Z298 was calculated to be -3503 kJ/mol (187). 

This paper reports the results of investigations of the complex formation between actinide or lanthanide ions and azide or orthophenanthroline. The aim of this work was first to confirm whether these relatively soft ligands give complexes of different stabilities with the trivalent lanthanide and actinide ions, as a consequence of the broader extension of 5f orbitals as compared with 4f. Secondly, we attempted to use the results in actinide chemical separation processes. 

These oxygen-donor type extractants have potential for co-extraction of trivalent lanthanide and actinide ions. For the mutual separation between trivalent actinides and lanthanides, so-called soft-donor (nitrogen-donor type and sulfur-donor type) extractants are promising and widely investigated for the application of nuclear waste treatment as follows. 

In addition to the nitrate system, AUen et al. (1997) reported a structural study of U02, Np02, Np ", and Pu " species in HCl solution by the EXAFS method. They also conducted (Allen et al. 2000) EXAFS experiments on the trivalent lanthanide and actinide ions in HCl solutions. In the dilute HCl solution, on average, the Am and Cm aqua ions are coordinated by 10.3 oxygens at 2.48 A and by 10.2 oxygens at 2.45 A, respectively, while 9.2 water molecules are coordinated to the Pu . The average distance between the Pu " ion and the oxygens of water molecules is 2.51 A. They observed Cl coordination to the Cm above the 10.5 M LiCl concentration. However, Pu does not form inner sphere chloride complexation. 

SIMILARITIES AND DIFFERENCES IN TRIVALENT LANTHANIDE- AND ACTINIDE-ION SOLUTION ABSORPTION SPECTRA AND LUMINESCENCE STUDIES... 

Observed spectra of aquated trivalent lanthanide and actinide ions 161 ... 

Comparison of experimental and theoretical studies of the solution absorption and luminescence spectra of lanthanide and actinide ions is the focus of this chapter. In aqueous solutions, the most stable oxidation state of lanthanide ions is 3+, but actinide-ion formal oxidation states ranging from 2+ to 7 -I- are known (Seaborg and Loveland 1990). Actinide elements heavier than plutonium exhibit more lanthanidelike behavior, however, in that 3-1- is their most stable formal oxidation state in aqueous solution. The visible and near-infrared absorption spectra of trivalent lanthanide and actinide ions in solution provide such rich detail that the spectra may fairly be said to fingerprint the ion for identification. The abundance of sharp spectral features long confronted theoretical and experimental spectroscopists with difficult problems. The efforts of numerous workers have provided interpretation of many aspects of the spectra of these f-transition elements significant challenges remain. 

Observed optical absorption spectra of trivalent lanthanide and actinide ions in aqueous solution at ambient temperature (nominally 295 K) are shown in figs. 1-21. The data are from the files of W.T. Carnall. The lanthanide-ion absorption data from Ce through Yb " are essentially those reported by Carnall (1979) and the actinide data somewhat extend the spectra given by Carnall (1986) for U through Es. The spectra were recorded in dilute mineral acid solution (generally HCIO ) and solvent... 

Although trivalent lanthanide- and actinide-ion f-f transitions usually are regarded as being insensitive to the nature of coordinated ligands, a few absorption bands of such ions do exhibit distinct sensitivity. These transitions satisfy the same selection rules as electric-quadruple radiation and have come to be termed hypersensitive transitions. Judd (1962) noted that large values of ( PJ P J Y, generally... 

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