Uranium macrocyclic complexes

The known uranium-macrocycle complexes of metal-templated origin are listed in table 22 all contain the trans-dioxouraniumCVI) ion, (uranyl), as the metal... 

It is by now well established that all lanthanide (III) ions, as well as the yttrium(III) and uranyl ions, are effective templates for the synthesis of macrocyclic complexes the scarcity of information on similar systems involving 5f-block elements other than uranium appears to be due to lack of investigation rather than to any intrinsic failure of these elements to function as templates in macrocyclic syntheses. 

Only An(III) and An(IV) ions have been inserted into macrocyclic crown-ethers, e.g., in [UCl3(18-crown-6)]2[U02Cl3(OH)H20]. Hydrogen bond interactions between etheric oxygen and coordinated water molecules were only observed in the corresponding U02+ complexes [282]. The infrared spectrum and isotope effect of uranium-crown-ether complexes were reported [435], as well as the crystal structures... 

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. 

The electrochemistry of the uranium(lV) and thorium(IV) complexes M(acac)2L (L = Pc, oep dianions) has been studied in benzonitrile solution. In the complexes of both elements, a series of reversible redox processes have been detected, most of which are centred on the macrocyclic rings (Table 21). 

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. " ... 

Examples of ( 7 -C4N) coordination in pyrrole-derived macrocyles may be found in the reaction products of uranium halides with the tetraanion of the macrocycle [(-CH2-)5]4-calix[4]tetrapyr-role. " " As described in Equation (30), the reaction of Ul3(THF)4 with the potassium salt of the tetrapyrrolide in THF generates a dinuclear complex, [ [(-CH2-)5]4-calix[4]tetrapyrrole -UK(THF)3]2(/4-0) 2THF the 0x0 group is proposed to come from deoxygenation of a THF molecule ... 

The parent oxacalix[3] arenas show little ability to bind alkali metals,however, a range of quaternary ammonium cations are attracted to the symmetric cavity. Deprotonation of the phenol moieties allows them to bind to transition metals (scandium, titanium, vanadium, rhodium, molybdenum, gold, etc.), lanthanides (lutetium. yttrium, and lanthanum), and actinides (uranium as uranyl). Oxacalix[3]arenes derivatized on the lower rim can complex gallium, mercury, and alkali metals, including sodium, in a manner reminiscent of natural transmembrane cation filters. One major use was to purify crude samples of fullerenes. The pseudo-Cs symmetry of the macrocyclic cavity is complementary to threefold symmetry elements of Cgo. which binds preferentially in... 

The resulting chelating macrocyclic ligand, hexaphyrin, rendered adequate space for coordination of the large late transition series cations of uranium, neptunium and plutonium. Subsequent addition of U02(0Ac)2 2H20 in the presence of a base gave the uranyl complex in 74% yield (Figure 15.3.2). 

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