Cations uranium

Umbelliferone, pH-dependent change of fluorescence color 44 Universal reagents 4,46,195,376,402,405, 412, 430, 434 Uracil derivatives 44,45 Uranium cations 144 Uranyl acetate reagent 44 Urea... 

For example, in 1963 the photochemistry of magnesium phthalocyanine with coordinated uranium cations was studied in pyridine and ethanol and indicated the occurrence of PET to the uranium complex . A rapid photoinduced electron transfer (2-20 ps) followed by an ultrafast charge recombination was shown for various zinc and magnesium porphyrins linked to a platinum terpyridine acetylide complex . The results indicated the electronic interactions between the porphyrin subunit and the platinum complex, and underscored the potential of the linking para-phenylene bisacetylene bridge to mediate a rapid electron transfer over a long donor-acceptor distance. 

Fig. 7.2 Fluorite UOj structure contains eightfold coordinated U atoms (grey spheres) and fourfold coordinated O atoms (black spheres)-, the cell unit length a=b = c = 5.47A. Uranium cations can have an oxidation state greater than U +, as a result of the removal of two electrons from the 5/ orbital, to become The UO system can be used as a model for oxidation/reduction reactions since it is an intermediate between the uranium metal (U ) phase and the most oxidized uranium phase (UO )...

The synthesis of the mixed-ring uranium(m) complex (COT)Cp U(THF) has been achieved by reaction of Cp UI2(THF)3 with K2(COT) in THF. Further treatment of (COT)Cp U(THF) with 4,4 -dimethyl-2,2 -bipyridine (Me2bipy) in toluene yielded the formally 10-coordinate complex (COT)Cp LJ(Me2bipy), which was structurally characterized by an X-ray analysis.152 The mixed-sandwich uranium(m) complex (COT)Cp U(HMPA) was isolated from the reaction of the uranium cation complex [(COT)U(HMPA)3][BPh4] with KCp (70% yield). The analogous tmp derivative (COT)LJ(tmp)(HMPA)2 was obtained upon reduction of the cationic uranium(iv) complex [(COT)U(tmp)(HMPA)2][BPh4] with sodium amalgam.153... 

This process produces a solution of thorium, rare earths, and uranium cations with sulfate and phosphate anions. 

A variety of phosphorylated chitin, whose structure is unknown, is reported to be a strong absorber of metallic cations. It will absorb large amounts of uranium cations from dilute aqueous solution and has potential use as an extractant [39]. 

Another propylene ammoxidation catalyst that was used commercially was U-Sb-0. This catalyst system was discovered and patented by SOHIO in the mid-1960s (26,27). Optimum yield of acrylonitrile from propylene required sufficient antimony in the formulation in order to ensure the presence of the USbaOio phase rather than the alternative uranium antimonate compound USbOs (28-30). The need for high antimony content was understood to stem from the necessity to isolate the uranium cations on the surface, which were presumed to be the sites for partial oxidation of propylene. Isolation by the relatively inactive antimony cation prevented complete oxidation of propylene to CO2. Later publications and patents showed that the activity of the U-Sb-0 catalyst is increased by more than an order of magnitude by the substitution of a tetravalent cation, tin, titanium, and zirconium (31). Titanium was found to be especially effective. The promoting effect results in the formation of a solid solution by isomorphous substitution of the tetravalent cation for Sb + within the catalytically active USbaOio- phase. This substitution produces o gen vacancies in the lattice and thus increases the facility for diffusion of lattice o gen in the solid structure. As is discussed below, the enhanced diffusion of o gen is directly linked to increased activity of selective (amm)oxidation catalysts based on mixed metal oxides. 

Srzic and coworkers (Kazazic et al., 2005, 2006 Srzic et al., 1997a,b) reported qualitative studies of reactions of U with polyaromatic hydrocarbons (PAHs). The results were complicated by competition between oxidation and adduct formation, but an intriguing observation was the addition of multiple PAH molecules to U, such as in [U(phenanthrene)3] dehydrogenation of PAHs was also observed. Duncan and coworkers also examined the formation of uranium cationic complexes with PAHs using covaporization of uranyl acetate and pyrene (Ayers et al., 2004) or corannulene (Ayers et al., 2005) in a laser plasma source with TOF-MS detection, observing the formation of UO (PAH) species with x=0-2 and y=l, 2. 

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