Actinide complexes chelating

Actinide complexes with chelating ligands containing sulfur and amidic nitrogen donor atoms. U. Casellato, M. Vidali and P. A. Vigato, Coord. Chem. Rev., 1979, 28, 231-277 (181). 

Coordination compounds of diphosphazane dioxides with uranyl or thorium ions were synthesized [475], The crystal structure of [U02(N03)2L1] [L, = Ph2P(0) N(Ph)P(0)Ph2] reveal the bidentate chelating mode of binding of the diphosphazane dioxide to these metals. The chemistry of other uranium organophosphorus and related compounds is described [476-479]. Some of the actinide complexes are presented in Table 5.16. 

Novel tetrahydroxamate chelators for Actinide complexation synthesis and binding studies. [A. S. Gopalan, V. J. Huber, O. Zincircioglu, P. H. Smith, J. Chem. Soc., Chem. Commun. 1992, 1266-1268] [ 13]. 

As to date, quantitative data on actinide complex species are very scarce and, when existing often limited to stability constants determinations. No direct calorimetric measurement of the enthalpy of complexing have sofar been published for those elements. The present communication deals with such measurements for the complexing of Pu and Am " with EDTA. We also report data on La complexing for comparison purpose. From the enthalpy change and knowing the stability constants of the chelates, the entropy variation on complexing can easily be calculated. 

A number of organic compounds, eg, acetylacetone [123-54-6] and cupferron [135-20-6] form compounds with aqueous actinide ions (IV state for reagents mentioned) that can be extracted from aqueous solution by organic solvents (12). The chelate complexes are especially noteworthy and, among these, the ones formed with diketones, such as 3-(2-thiophenoyl)-l,l,l-trifluoroacetone [326-91-0] (C4H2SCOCH2COCF2), are of importance in separation procedures for plutonium. 

We have considered typical examples of lanthanide and actinide solvent extraction by chelate formation, involving complexes with citric acid and with TTA, to prove that the labelling of a stable element by one of its radioactive isotopes can help to produce accurate data on the stability constants for complex formation. The method is applicable to elements with radioisotopes having a half-life allowing an ion concentration of 10 6m or less. Other methods of partition such as radiopolarography and radio-coulometry also result in accurate thermodynamical data when the same procedure of labelling is used (29). 

It is possible that soluble actinides may occur as a result of complexation of the actinides with iron chelators such as ferrioxamine. Stumm and Morgan (46) believe, on the basis of computer simulation studies, that soluble Fe(III) in seawater exists almost exclusively as a ferrioxamine chelate. A similar study with the actinides would be of considerable interest. 

The requirements for a successful agent for the removal of radioactive actinides from the body are even more stringent than for the use of lanthanides in diagnosis. For gadolinium it is necessary that the hydroxypyridinonate complex is very stable, to avoid significant release of toxic Gd (aq), is sufficiently soluble, and has an appropriate HLB. For actinide elimination it is also necessary for the chelator to be sufficiently soluble and to have suitable targeting properties. It is also desirable that the chelator does not have such a... 

The effects of tetracycline injection following injection of thorium-228 were not reported. Studies with a similar actinide element, plutonium, suggest that a thorium-tetracycline complex may be formed, which is excreted rapidly through the kidneys. Similarly, chelating agents such as EDTA... 

Chelating extractants such as beta-diketones, tropolones, hydroxyoximes, and 8-hydroxyquinolines (Figure 2.1), have been used extensively for the extraction of actinide ions from moderate to weakly acidic solutions (15-17). Beta-diketones such as acetylacetone (acac), HTTA, benzoyl trifluoroacetone (BTFA), and dibenzoyl-methane (HDBM) have been commonly used for the separation of actinide ions. The extraction mechanism involved formation of the enol form of the beta-diketone prior to complexation and extraction of the metal ion (Figure 2.2). 

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