Uranyl complexes Materials

Andersen prepared the first U amide traHj-[UO2 N(SiMe3)2 2(thf)2] (60) in 1979, from UO2CI2 and 2Na[N(SiMe3)2] in f. The structure of the ciystalline material was confirmed by X-ray data, albeit of poor quality recently a high-quality structure was obtained. The amido groups in 60 were readily displaced by treatment with ArOH and pyridine, yielding [UO2(OAr)2(py)3] (Ar = C6H3P 2-2,6). Reaction of 60 with the macrocyclic compound H4(10) (R = H or Me) resulted in the exclusive formation of the mono-uranyl complex [UO2 H2(10) (thf)] (61). " The latter upon addition of... 

The apparent contradiction between the empirical stoichiometry and the spectral characteristics of these new uranyl complexes was finally resolved by X-ray crystallography. Specifically, a single crystal X-ray structural analysis of the blue-black material formed from the reaction of the anhydrous uranyl chloride and o-dicyanobenzene [112] (Figures 22 and 23) revealed that the complex obtained was in fact an expanded five-subunit superphthalocyanine macrocycle in which a pentagonal bipyramidal coordination geometry pertains about the centrally-bound uranium atom. 

For simplicity, in this equation, we have assumed that activities are equal to concentrations and brackets refer to activities. C is a units conversion constant = Vy m relating void volume Vy (mL) in the porous media and the mass m (g) of the aquifer material in contact with the volume Vy, is the formation constant for an aqueous uranyl complex, and the superscripts i, j, k describe the stoichiometry of the complex. The form that the sorption binding constant takes is different for the different sorption models shown in Figure 4 (e.g., see Equation (5)). Leckie (1994) derives similar expressions for more complex systems in which anionic and cationic metal species form poly dentate surface complexes. Equation (7) can be derived from the following relationships for this system ... 

Under the electron microscope, the uranyl complexes of the oxy-polysac-charide formazans show a distinct shading effect which imparts a markedly dark appearance to these polysaccharide materials. It is hoped that this will lead to the elaboration of a new method for the study of the structures of polysaccharides. 

Figure 25. Laser-excited luminescence in fossil fish teeth from phosphorite beds in the Senonian Mishash formation, Israel. (A) Uranyl emission at 77 K indicating uranyl aqueous complexes. (B) after annealing at 1000 K the uranyl complexes are dehydrated . (C) Same as in A but spectrum collected at 300 K. From these data it was concluded that the uranyl resides in organic material and not in the apatite structure. Modified after Gaft et al. (1996b).

The need to understand metal extraction with ScFs, particularly uranium SFE, motivated the development of an on-line measurement technique for uranyl complexes in ScF CO2. In SFE processes, the extracted material is usually collected by depressurizing the ScF, followed by chemical or spectroscopic analysis. On-line monitoring of SFE can be preferable because it is fast, free of collection loss, and allows monitoring of process dynamics. However, depending on the specific analyte and the measurement matrix, the desired levels of sensitivity and selectivity can be difficult to achieve with on-line methods, particularly with detectors that can be coupled with pressurized ScF systems. 

The majority of U(V1) coordination chemistry has been explored with the trans-ddo s.o uranyl cation, UO " 2- The simplest complexes are ammonia adducts, of importance because of the ease of their synthesis and their versatihty as starting materials for other complexes. In addition to ammonia, many of the ligand types mentioned ia the iatroduction have been complexed with U(V1) and usually have coordination numbers of either 6 or 8. As a result of these coordination environments a majority of the complexes have an octahedral or hexagonal bipyramidal coordination environment. Examples iuclude U02X2L (X = hahde, OR, NO3, RCO2, L = NH3, primary, secondary, and tertiary amines, py n = 2-4), U02(N03)2L (L = en, diamiaobenzene n = 1, 2). The use of thiocyanates has lead to the isolation of typically 6 or 8 coordinate neutral and anionic species, ie, [U02(NCS)J j)/H20 (x = 2-5). 

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. 

For the other actinide elements the usual starting material will be the dioxide. Although these reactions appear to be simple, they are in fact quite complex. Uranium trioxide as prepared by thermal decomposition of uranyl nitrate hexahydrate, uranium peroxide, or ammonium diuranate may exist in any one of at least four crystal modifications and in an important amorphous form. The reduction of U03 appears to be related both to the crystal form and to the surface area, and depending on these and perhaps other still unspecified variables, the hydrofluorination reaction on the... 

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