Actinide complexes oxygen ligands

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 actinide nitrates whose structures are known are listed in Table 20.9, and a review of actinide complexes has been published by Casellato et al [413]. These are limited mainly to tetravalent Th and to uranyl complexes. In the Th(iv) and Pu(iv) compounds the NO3 ions are bidentate, which allows for large coordination numbers compared to the usual eight-fold coordination of these ions with monodentate ligands. In the uranyl complexes the two close actinyl oxygen atoms limit the available space for other bonded atoms, and the maximum number of equatorial oxygen atoms is six, even for bidentate NO3 ions. In Cs2lJ02(N03)4 all four NO3 ions are attached to the U atom even though space allows only two of them to be bidentate. 

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). 

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. 

Actinide halides and oxyhalides are known to form numerous complexes with oxygen and nitrogen donor ligands and the preparation and properties of such compounds have recently been reviewed (12, 13). Relatively few protactinium halide complexes are known, but this situation reflects the lack of research rather than a tendency not to form complexes. However, there is sufficient information available for certain ligands to permit a comparison with the behavior of other actinide halides, and to illustrate the similarities and differences observed with the tetrahalides of thorium to plutonium inclusive and, to a lesser extent, with the protactinium and uranium pentahalides. 

DMSO) complexes (18) are relatively unstable toward oxidative decomposition. The known complexes are listed in Table X, together with infrared data, and are compared with the complexes formed by other actinide halides in Table XI. The protactinium(IV) complexes have been prepared by reacting the anhydrous halide with the appropriate ligand in nonaqueous, oxygen-free solvents such as methylene dichloride, chloroform, or methyl cyanide. 

Even fewer complexes with nitrogen donor ligands have been reported and all are methyl cyanide adducts (Tables X and XI). Protactinium pentabromide forms a soluble 1 3 complex in contrast to the 1 1 complexes formed by niobium and tantalum pentahalides (46). Other actinide pentahalide-methyl cyanide complexes are still unknown. Protactinium tetrachloride, tetrabromide, and tetraiodide react with anhydrous, oxygen-free methyl cyanide to form slightly soluble 1 4 complexes (44, 48) which are isostructural with their actinide tetrahalide analogs. 

Hydroxamates, cupferron, and related ligands. As anionic oxygen donor ligands, hydroxamates have a strong affinity for the oxophilic tetravalent actinides, with solution complex formation constants generally greatest for Pu and decreasing as follows Pu > Np > > U. ... 

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