The Case of Actinides

For actinides up to Am, the plot of atomic radii vs. Z is given in Fig. 3. In the same figure, the same plot is given for d-transition elements. The first obvious observation is that the situation does not ressemble at all the lanthanide one. The second observation is that, for the light actinides (up to Pu) the trend which is followed ressembles the (almost 

The measured metallic radii of the metals are drawn, in Fig. 4, on a network of dashed lines specifying the actinide contractions for f configurations progressively increasing by one electron at constant metallic valence (i.e. without change of the number of s, p, d electrons, which are thought to provide the only bonding). (The 

The full lines of Fig. 4 represent, on the contrary, the variation of atomic radii for (d-like type) metals, in which, for a certain f configuration, a valence electron is added. The f curve is a universal transition metal curve, on which the experimental radii of Ra (v = 2, 6d 7s ), Ac (v = 3, 6d 7s interpolated value), Th (v = 4, 6d 7s ), a-Pa (v = 5, 6d 7s ), a-U (v = 6, 6d 7s ), a-Np (v = 7, 6d 7s ) are seen to fit . The attributions of valencies in the brackets are consistent with the known chemistry of these elements (pentavalent Pa, hexavalent U, heptavalent Np in compounds and solutions). 

The electronic configurations given in brackets are consistent with the hypothesis of a metal series essentially of 6 d-character. 

In Table 2 (taken from ), the metalhc valences and the number of non-bonding f electrons are then predicted for all known phases of actinide metals. 

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This problem is handled differently by different authors, on the basis, usually, of reasonable assumptions suggested by the inspection of the plots of the (BI) s across the series. This is done also, in the case of actinides, for the 5f unsaturated shell. 

The inclusion of the crystal field destroys the rotational symmetry of the ion and lifts the degeneracy of J levels (except of course Kramer s degeneracy) the only good quantum numbers will be T s, the irreducible representations of the point-group symmetry operation. If the crystal field interaction is comparable to J-J splitting (and we see from Table 2 that this is the case of actinides) it will also cause an admixture of different J multiplets. 

Magnetic susceptibility measurements are basic to the study of the magnetic properties of a compound samples under powder form are sufficient to start with and, what is very important in the case of actinides, small amounts of material are satisfactory (typically 100 mg). When working with transuranium compounds, safety requirements are fulfilled by working with sealed containers ... 

Before introduction into the spectrometer, a mechanical and/or electrochemical polishing of the sample surface has to be performed. While a good empirical knowledge has been gained for most current materials the right procedure to follow in the case of actinide compounds is still not well established. 

The amount of unreacted target element that eluted was determined by measuring its radioactivity directly in the case of actinides, and by activation analysis in the case of lanthanides. The distribution of the radioactive neutron capture product was determined by counting both the eluate and the eluted zeolite. All irradiations were done in the Oak Ridge Research reactor in a pneumatic tube facility with a thermal neutron flux of about 4 X 1013 neutrons cm-2 sec-1 or, for a few long irradiations, in a tube adjacent to the reactor core at the fluxes stated in Table VI. 

In the case of actinide systems it was found possible to effect catalytic deuteration of the SiAfc3 groups using D2 and making use of a hydride leaving group.251... 

The speciation of rare earth elements and the interest in the topic arose due to the need for such information in the case of actinides. Both sets are f elements and the need... 

The double-double effect has been considered in review articles17-20) lectures21-24) and also in some monographs 10,25 27). In these publications, however, emphasis is placed on the double-double effect observed within the lanthanide series. The purpose of this paper is to review the literature data on the double-double effect observed in actinides. In contrast to lanthanides, in the case of actinides, the double-double effect cannot be observed in its full pattern because of the following reasons (i) the elements heavier than einsteinium are still hardly available, (ii) the stable oxidation state changes along the series, and (iii) there are only few data on stability constants or extraction coefficients for... 

The insertion of CO into a C-Ln bond has also been demonstrated. After some unsuccessful attempts (8), the formation of a dihapto complex in the first stage of reaction and of a dimeric enedione-diolate final structure has been described (9). Such non-classical activation of CO, also observed in the case of actinides (10) as well as of some d elements like Zr (11), affords an oxycarbene lone pair completing the valence shell of the metal, and results in a new carbon-carbon bond formations. The research on CO chemistry and on the understanding of its fundamental aspects is of increasing importance in today s shifting situation to coal-based processes. 

From fig. 1 it can be seen that in addition to the labile protein-bound fraction, metal-transferrin complexes in the case of actinides, there is also a low molecular mass fraction in which metal ions are bound to, and transported with, ligands such as the anions of amino and carboxylic acids. For the hard cations of the actinide elements, these complexing agents are predominantly carboxylic acids (from the citric acid cycle) (Duffield and Taylor 1986, Popplewell et al. 1975, Duffield et al. 1984, Metivier 1973) or inorganic anions such as carbonate, e.g., for uranium(VI) (Stevens et al. 1980). 

Fig. 3.25 presents some dispersion curves by Brooks et al for NpN, PuN and AmN. The most pronounced changes in this series are observed for the Aj band of 5/ origin. This band becomes more and more narrow when going along this series of compounds. Finally the bands of M5/ and of higher M5/, 6d and N2p states become separated. However, the hybridisation of 5/ and N2p states remains considerable. For example, the state Tjs of NpN consists of 47% df states and 53% N2p states, while Fj of AmN consists of 46% 5/ states and 50% N2p states. The calculated and experimental values of the lattice constant versus the atomic number of the actinides are presented in Fig. 3.26. As can be seen, the experimental dependence exhibits a minimum for UN and is very different from the dependence for rare earth nitrides. The latter is monotonic and exhibits an anomaly for CeN, where Ce has an anomalous valency. While the dependence observed for rare earth nitrides can easily be explained by lanthanide compression, in the case of actinide nitrides the interpretation of such a dependence is far from trivial. The explanation proposed by Brooks et al (1984) is based on a simplified equation of state using canonical band theory. The equation takes into account only /-/ and f-p...

Ma/bO oxides with composition in the range of 2>a/b>0.5 (in the case of actinide oxides up to 0.33) having effective molar volumes of oxides (M O) of the same metal decreasing linearly when the metal content decreases. 

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