Actinide cationic complexes

The actinide cations are hard acids, that is, their binding to ligands is described in terms of electrostatic interactions, and they prefer to interact with hard bases such as oxygen or fluorine rather than softer bases such as nitrogen or sulfur. The actinide cations do form complexes with the soft bases but only in nonaqueous solvents. 

This generalization may not apply to the analogous complexes of tetravalent actinide cations (Ostuni et al., 2003). 

As alluded to above, metal complexes of a number of lanthanide and actinide texaphyrin complexes have also been prepared. In the case of Dy(III) texaphyrin 9.74, as in the case of the bis-pyridine cadmium complex 9.61b, the metal center sits directly within the mean plane of the macrocycle (Figure 9.1.12). This result stands in direct contrast to the highly labile, typically sandwich-type 2 1 or 3 2 complexes observed for porphyrin complexes with these larger metal cations. ... 

Actinide cations have a strong tendency to react with various inorganic and organic ions or agents, forming complex ions. 

The extraction of trivalent actinides with /3-diketones in the presence of crown ethers has also been investigated. Trifluoroacetylacetone(HTFA), HTTA, benzoyltrifluoroacetone(HBFy, and 2-napthoyltrifluoroacetone (HNFA) have all been used with 18-crown-6 to remove Am and Cm from perchlorate media into 1,2-dichloroethane. It has been shown that the mechanism of extraction for all of the /3-diketones (HA) is the formation of a cationic complex via a synergistic ion-pair extraction (SIPE) as shown in Equation (66) ... 

The present review focuses first on actinide complexes of polymolybdates (section 2) and pol5durrgstates (section 3) that have beetr isolated and structurally characterized. There are currently no reported actinide polyvanadates, -niobates, or -tantalates. A final section (4) summarises solution studies of equilibria between actinide cations and polyoxometalate anions. 

The investigation of actinide cyclooctatetraenyl complexes continued to be an area of active research in recent years. Especially notable among the more recent developments is the synthesis and derivative chemistry of various cationic mono(cyclooctatetraenyl) uranium(iv) and (v) complexes.71,97 The chemistry of mono(cyclooctatetraenyl)uranium complexes has been reviewed by Ephritikhine et al.lso A highly interesting essay on the discovery and chemistry of uranocene has been published by Seyferth under the title Uranocene. The First Member of a New Class of Organometallic Derivatives of the/Elements. 151... 

Fig. 13.23). Kim (1993) and Silva and Nitsche (1996), among others, have noted that the stabilities of actinide (An) cation complexes with the same ligand most often decrease in the order... 

The actinide cations can form strong complexes with humic and fulvic acid ligands. This may reflect the presence of phenolic, amine, and alcoholic OH-groups, and also carbonate groups in... 

Which actinide cations form important organic complexes in natural waters and which do not. Why ... 

The thermodynamic data for complexation of trivalent lanthanide and actinide cations with halate and haloacetate anions are reported. These data are analyzed for estimates of the relative amounts of inner (contact) and outer (solvent separated) sphere complexation. The halate data reflected increasing inner sphere character as the halic acid pKa increased. Use of a Born-type equation with the haloacetic acid pKa values allowed estimation of the effective charge of the carboxylate group. These values were, in turn, used to calculate the inner sphere stability constants with the M(III) ions. This analysis indicates increasing the inner sphere complexation with increasing pKa but relatively constant outer sphere complexation. 

Trivalent lanthanide and actinide cations form labile, ionic complexes of both inner and outer sphere character. Consequently, they are useful probes to study inner-outer sphere complexation competition due to ligand properties. Two earlier papers have reported complexation of these cations by two series of related anions, the halates (9) and the chloroacetates (10). In this paper we offer a more extensive analysis of the inner-outer sphere competition in these complexes. 

---