Uranyl complexes structures

Among the known structures, the hexagonal bipyramidal (Has) geometry seems to be less common than others and it has only been definitely established for a few uranyl complexes (94—97). Probably an axial colHnear grouping, as in 0—U—0, is necessary for obtaining a geometry for the complexes. None of the octa-coordinated lanthanide complexes has a Hea geometry. 

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... 

Z = 16 hydrogen bonded co-crystal between the neutral uranyl complex [U02(H20)3] and [15] crown-5. The asymmetric unit contains a total of 32 independent molecules.76 Up-to-date information and a database of high Z structures is maintained online at http //www.dur.ac.uk/zprime. 

Contents J.A.Ibers, L.J.Pace, J.Martinsen, B.M.Hoffman Stacked Metal Complexes Structures and Properties. -M.J. Clarke, P.H.Fackler The Chemistry of Technetium Toward Improved Diagnostic Agents. - R.J.P. Williams The Chemistry of Lanthanide Ions in Solution and in Biological Systems. - C.K. Jorgensen, R.Reisfeld Uranyl Photophysics. 

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. 

Another expanded porphyrin previously known to form a complex with the uranyl cation was the pentaphyrin 232 [158, 187]. An improved synthesis of a new pentaphyrin derivative and its corresponding, structurally characterized, uranyl complex was recently reported [240]. This new uranyl pentaphyrin, has a very distorted solid state structure reminiscent of the closely related uranyl superphthalocyanine complex 160 [112] (Figures 22 and 23). 

The triacetate uranyl complex (24) is structurally similar to the trinitrate uranyl complex (6) (three bidentate ligands arranged equa-torially around the uranyl O—U—O axis). It was expected that the visible, near ultraviolet spectrum of the triacetate uranyl complex would be similar to the spectrum of U02(N03)3 as are the spectra of 1102(804)3, 1102(003)3 , and other uranyl complexes which apparently have the same structure (17). The absorption spectrum of uranyl acetate extracted into tri-n-octylamine in xylene from dilute acetic acid is different from the trinitrato uranyl spectrum. This indicates that the triacetate uranyl complex is probably not the species involved. By analogy to the uranyl nitrate system 14), formation of a tetraacetate uranyl complex might be expected. The purpose of this work is to determine the nature of the anionic hexavalent actinide acetate complexes and to identify the species involved in the amine extraction and anion exchange of the hexavalent actinides from acetate systems. 

Figure 5.5.5 Single Crystal X-Ray Diffraction Structure of Uranyl Complex 5.96 Confirming the Formal Attack by Methoxide at the Macrocyclic C(10) Position.

Subsequent to submitting this manuscript, a single crystal x-ray diffraction structure of the neutral uranyl complex of monoxasapphyrin 5.74 was obtained. The uranyl cation is pentaligated (with a long furan oxygen-uranium bond) and resides within the macrocyclic plane. " ... 

The U02 - XOs - H2O (X= C or N) systems have been chosen for analysis for two reasons. First, they are well studied experimentally, since carbonate and nitrate uranyl complexes are important from technological standpoints. Second, the isoelectronic anions XOs have the same planar structure (symmetry Dsh) and form bidentate coordination around uranyl ions (the type). However, their electron-donor characteristics are different El = 3.1 and 3.4 for the NOs and COs ions, respectively. From this viewpoint, it would be of interest to understand how the difference in the electron-donor properties influences complex formation in the U02 - XOs " - H2O systems. As in the case of aqua-complexes, we shall use the 18-electron rule to obtain answers to the following questions (a) what is the composition of stable complexes in aqueous solutions containing carbonate or nitrate uranyl complexes (b) what is the coordination number of U(VI) in these complexes. 

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