Actinide complexes oxides

Another issue involving actinide complexes in the zero formal oxidation state is the possible formation of actinide-actinide bonds. For example, the molecule U2 has recently been described theoretically,6 in which the electronic structure is characterized by the existence of a large number of nearly... 

It has been shown that for many of the hard-hard complexation systems, there is a linear correlation between the experimental AH° and Ab° values. Figure 3.11 shows such a correlation for actinide complexes. These AH and AS data involve metal ions in the -i-3, +A, and +6 oxidation states and a variety of both inorganic and organic ligands. Such a correlation of AH° and Ab° has been termed the compensation effect. To illustrate this effect, reconsider the... 

Actinides, particularly the lighter ones, display multiple oxidation states and complex chemical behavior, which makes their chemistry quite fascinating. Some isotopes of these elements, such as 232Th, 233,235,238 and 239Pu, are important for the nuclear industry due to their utility as fissile/fertile materials. Therefore, the separation chemistry of different oxidation states of Th, U, and Pu need to be reviewed with respect to both basic as well as applied aspects. Some fundamental chemical properties of the lighter actinides, including oxidation states, hydrolysis, and complexation characteristics form the basis of their separation. 

This paper reports the first determination of the enthalpy of formation of a complex actinide(IV) oxide AHf (BaU03,s,... 

K) -1690 10 kJ mol 1. The preparation and properties of this and other actinide (IV) complex oxides are described and are compared with other perovskites BaM03. The relative stabilities of tetravalent and hexavalent uranium in various environments are compared in terms of the oxidation-reduction behavior of uranium in geological nuclear waste storage media in perovskite, uranium(IV) is very unstable in comparison with uranium(VI). ... 

In the dioxides each actinide is surrounded by 8 equidistant oxygens at the comers of a cube, but in complex oxides the actinide ion is usually surrounded by 6 oxygens at the apices... 

The two other most inportant actinide (IV) complex oxides are BaTh03 and BaPu03. The former has been prepared many times (15) however, there are disputes concerning its properties. 

Actinide complexes rarely follow the conventional rules, for example, 18-electron rule, typically found in inorganic and coordination chemistry of the transition metals. A prime example of the difference in actinide chemistry is the pervasiveness of the linear dioxo rmit, which is immatched in transition metal chemistry. For the actinides, the trans dioxo structure is maintained through different metal ions, oxidation states, and valence electron cormts, for example,... 

It is important to note that efforts to synthesize metal alkoxides and aryloxides (particularly lanthanide and actinide complexes) have sometimes produced unexpected products, incorporating halide or oxide ligands, for example. As a result, some early literature may contain incorrect formulations. ... 

Hydroxamate. Hydroxamate complexes of trivalent actinides can be prepared directly in aqueous solution and other polar solvents and extracted into organic solvents, but due to the high thermodynamic stability of the corresponding tetravalent actinide complexes they are rapidly oxidized. They can also be prepared in solution via electrochemical reduction of the tetravalent complexes. These complexes have been studied for their role in separating high and low valent actinides in nuclear fuel processing schemes. ... 

Phosphine oxide. Many reported actinide-phosphine oxide adducts are those of the actinide halide complexes (see Table 29). Most are obtained by direct reaction of the two constituents in nonaqueous media. UCl5(OPPh3) has been structurally characterized the coordination environment is best described as approximately octahedral. 

Morss, L. R. Complex Oxide Systems of the Actinides. In Actinides in Perspective, Edelstein, N., Pergamon, Oxford 1982, pp 381 07. 

The remainder of this section will focus on true SBMs, which have been the subject of vigorous research. Despite the electron deficiency of early transition metal, lanthanide, and actinide complexes, several groups reported that some of these d f" complexes do react with the H-H bond from dihydrogen and C-H bonds from alkanes, alkenes, arenes, and alkynes in a type of exchange reaction shown in equation 11.32. So many examples of SBM involving early, middle, and late transition metal complexes have appeared in the chemical literature over the past 20 years that chemists now consider this reaction to be another fundamental type of organometallic transformation along with oxidative addition, reductive elimination, and others that we have already discussed. 

Redox-related lanthanide and actinide complexes of cot have been described, usually without electrochemical studies. Potassium reduces [Ce(f/-cot)2] to mono- and dianions which are isolable as salts of the cation [K(monoglyme)2]+ (403). CV of [U( j-cot)2] shows that the dication is formed via two one-electron transfers the first oxidation leads to a geometric or solvation change so that the second occurs at a more negative potential. The dication subsequently reacts with [U( j-cot)2] to give [U2(>f-cot)4]2 + (404). 

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