Lanthanide- and actinide-exchanged

Isotopic Enrichment of the Product of a Neutron Capture (n, y) Reaction in Lanthanide- and Actinide-Exchanged Zeolites... 

Apart from the lanthanide and actinide exchange reactions described in Sections 7 and 8, the photochemical investigations of the cyano-complexes of molybdenum(iv) mentioned in Section 4,i <-i and the n.m.r. investigations outlined above, no further kinetic studies of metal ions with high co-ordination numbers have appeared. 

The overall distribution of lanthanides in bone may be influenced by the reactions between trivalent cations and bone surfaces. Bone surfaces accumulate many poorly utilized or excreted cations present in the circulation. The mechanisms of accumulation in bone may include reactions with bone mineral such as adsorption, ion exchange, and ionic bond formation (Neuman and Neuman, 1958) as well as the formation of complexes with proteins or other organic bone constituents (Taylor, 1972). The uptake of lanthanides and actinides by bone mineral appears to be independent of the ionic radius. Taylor et al. (1971) have shown that the in vitro uptakes on powdered bone ash of 241Am(III) (ionic radius 0.98 A) and of 239Pu(IV) (ionic radius 0.90 A) were 0.97 0.016 and 0.98 0.007, respectively. In vitro experiments by Foreman (1962) suggested that Pu(IV) accumulated on powdered bone or bone ash by adsorption, a relatively nonspecific reaction. On the other hand, reactions with organic bone constituents appear to depend on ionic radius. The complexes of the smaller Pu(IV) ion and any of the organic bone constituents tested thus far were more stable (as determined by gel filtration) than the complexes with Am(III) or Cm(III) (Taylor, 1972). 

The applications of ion-exchange chromatography are exemplified by the selection shown in Table 4.18. Among the most notable are the separation of lanthanides and actinides using a citrate, lactate or EDTA eluting agent ... 

Wish, L., E. C. Freiling and R. Bunney Ion-Exchange as a Separation Method. VIII. Relative Elution Position of Lanthanide and Actinide Elements with Lactic Acid Eluant at 87° C. J. Amer. chem. Soc. 76, 3444 (1954). 

The measurement of stability constants of complexes of yttrium, lanthanide, and actinide ions with oxalate, citrate, edta, and 1,2-diaminocyclohexanetetra-acetate ligands has revealed that there is a slight increase in the stability of complexes of the /-electron elements, relative to the others. A series of citric acid (H cit) complexes of the lanthanides have been investigated by ion-exchange methods and the species [Ln(H2cit)]", [Ln(H2cit)2] , [Ln-(Hcit)], and [Ln(Hcit))2] were detected. Simple and mixed complexes of dl- and jeso-tartaric acid have been obtained with La " and Nd ions, and the stability constants of lactate, pyruvate, and x-alaninate complexes of Eu and Am " in water have been determined. 

The relaxation equations discussed here and in Section 3.4 and 3.5 take a different form in the case of lanthanides and actinides. For these systems, in fact, the J quantum number substitutes the S quantum number and gj substitutes ge. In the absence of chemical exchange phenomena (r 1 r ) the equations for the... 

There are various types of organic proton exchangers (34, 35, 38). Diesters of phosphoric acid, (RO)2P = 0(0H), phosphonic acids, R(RO)P = 0(0H), and phos-phinic acids, R2P = 0(0H), where R represents linear or branched alkyl or phenyl substituents, are the most common cation exchangers developed in liquid-liquid extraction for the extraction of trivalent 4/and 5/elements. They were initially developed for the American TALSPEAK and the Japanese DIDPA processes and have recently been introduced in the French DIAMEX-SANEX process. As for previously described NOPCs, these organophosphorus acids present oxygen-donor atoms (hard bases) in their structures and therefore will easily coordinate trivalent lanthanide and actinide cations, but they will not allow complete discrimination of the two families of elements. However, contrary to previously described neutral organophosphorus... 

The first application of pressurized ion exchange to lanthanide and actinide separations was initiated in 1967 to examine this technique for the final separation of trivalent actinides in the TRU facility. In initial work with rare earths, it was demonstrated that 200-mg quantities of Nd and Pr could be adequately separated in times under an hour (19). This pair is as difficult to separate as any actinide pair, and the time and scale of separation easily met the requirements projected for actinide production at TRU. Subsequently, separations of multimilligram quantities of all fifteen rare earths were demonstrated in times as short as about 1.5 h (20, 21). 

Fig. 14.11 Elution of Irivalenl lanthanide and actinide ions on a Dowex 50 calion-exchange resin with an ammonium a-hydroxyisobutyrate eluant. The band for is predicted. (From Katz. J. J. Morss, L. R. Seaborg. G. T. In The Chemistry of the Actinide Elements. Katz. J. J. Morss, L. R. Seaborg,...

A series of batch equilibrations was carried out to determine the relative affinities of selected lanthanides and actinides for niobate, zirconate, and titanate ion exchange materials as a function of pH. These affinities are expressed as distribution coefficients (l9 ), where ... 

The remainder of this section will focus on true SBMs, which have been the subject of vigorous research. Despite the electron deficiency of early transition metal, lanthanide, and actinide complexes, several groups reported that some of these d f" complexes do react with the H-H bond from dihydrogen and C-H bonds from alkanes, alkenes, arenes, and alkynes in a type of exchange reaction shown in equation 11.32. So many examples of SBM involving early, middle, and late transition metal complexes have appeared in the chemical literature over the past 20 years that chemists now consider this reaction to be another fundamental type of organometallic transformation along with oxidative addition, reductive elimination, and others that we have already discussed. 

The separation methods for Fm are the same as those used for separating other trivalent lanthanides and actinides. For separating the adjacent elements, Es and Md, a high-resolution chromatographic method is necessary. Either ion exchange, using strongly... 

NMR results are limited in so far as individual hydration numbers can only be foimd for ions for which the two peaks corresponding to coordinated water and the rest can be observed. This limits the study to ions for which there is slow exchange and means that alkali metal cations, and most of the alkaline earth metal cations are excluded. Nonetheless a considerable nmnber of cations have been studied with unambiguous results. The most common coordination number is six, but cations known to favour tetrahedral or square planar conhgiu ations show a coordination number of four. It is only with large cations such as the lanthanides and actinides that numbers greater than six are found. 

The last four actinides (Am, Cm, Bk, and Cf) have +3 as their most stable valency state in solution, just as the rare earth elemrats, and their chemistry is very similar to that of the lanthanides. This similarity in solution has been commonly used for id tification of a particular actinide Figure 16.7 shows elution curves for lanthanides and actinides from a cation exchange column. 

FIG. 16.7. Elution curves for 3+ lanthanide and actinide ions from Dowex-50 ion exchange resin with ammonium-a-hydroxy isobutyrate eluant. (From Katz and Seaborg.)... 

Ligand replacements for which kinetic data have been reported include [Ni(dgen)] + plus edta (parallel dissociative and associative paths), [Pb(edta)] plus R-( —)-pdta, polyether complexes of lead(n) plus nitrogen macrocycles, metal(ii)-oxine complexes plus edta, and a variety of analogous reactions involving lanthanide and actinide complexes (see Chapter 10). Kinetic data are also available for ligand exchange between trien and tetren complexes of cad-mium(ii) and the edta complex of copper(ii). ... 

Ion chromatography is increasingly used for the separation of lanthanides and actinides. Cation exchange of lanthanides has been performed in... 

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