Actinide complexes carboxylates

Actinide complexes with carboxylic acids. U. Casellato, P. A. Vigato and M. Vidali, Coord. Chem. Rev., 1978, 26, 85-159 (276). 

The actinides have a high degree of specificity for neutral and anionic oxygen-containing organic molecules. The actinide complexes with O -donor ligands that are most widely studied include alkoxides, aryloxides amide, carboxylates, and oxalates. Complexes with alcohols, ethers, esters, ketones, aldehydes, ketoenolates, and carbamates have also been reported. 

The last major review in this area was that by Bombieri and de Paoli [14] who dealt with all types of actinide complex. Valuable additional material is also to be found in the Gmelin supplement volumes El and E2 [15]. We concentrate here on uranyl carboxylate complexes, for which many significant new structures have been published in recent years. 

The closest redox-stable analogue of Ce(IV) is thorium(IV), for which a large data base of thermodynamic parameters is available for the carboxylic add complexes (Martell and Smith 1977). Using the ionic radii of Shannon (1976) and recalling that the stability of lanthanide and actinide complexes is derived almost exclusively from electrostatics, we can estimate that a 16% increase in the log of the stability quotients for thorium (since AG oc Z /r oc log should provide a reasonable estimate for the corresponding complexes of cerium(IV) [rce(CN = 8) = 0.97 A, r iCN = 10) = 1.13 A, (l/rce)/(l/ xh) = 116, CN = coordination number]. 

A large number of urea and substituted urea complexes with actinide(IV) compounds are known in these the ligands are bonded to the metal via the carbonyl oxygen atom, and these complexes are therefore described in the section dealing with carboxylic add amide complexes (p. 1164). 

Table 37 Actinide(IV) Complexes with Carboxylic Acid Hydrazides, RCONHN=CHR1...

As in the SETFICS and TALSPEAK processes, the DIAMEX-SANEX/HDEHP process involves selectively back-extracting the trivalent actinides by a hydrophilic polyamino-carboxylate complexing agent, HEDTA, in a citric acid buffered solution (pH 3). However, the combination of HDEHP and DMDOHEMA at high acidity promotes the coextraction of some block transition metals, such as Pd(II), Fe(III), Zr(IV), and Mo(VI), which must be dealt with by specific stripping steps (as described on Figure 3.26) that increase the total volume of the output streams ... 

Structural aspects of the actinide carboxylate complexes have been reviewed235 from which the structures of many adducts that are likely to be involved in the extraction with carboxylic acid - neutral donor mixtures may be predicted. 

Catecholate. Am and Pu complexes of sulfonated and carboxylated catecholamide ligands (CAMS and CAMC), including potentially octadentate chelators have been studied for their potential utility in removing actinides from humans via chelation. The complex coordination is pH dependent, with a triscatecholate Pu complex forming above pH 12. The stoichiometry of the Am complex was not determined however, its optical absorbance characteristics were determined. ... 

---