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21.
Burton-Pye BP Radivojevic I McGregor D Mbomekalle IM Lukens WW Francesconi LC 《Journal of the American Chemical Society》2011,133(46):18802-18815
Technetium-99 ((99)Tc) (β(-)(max): 293.7 keV; t(1/2): 2.1 × 10(5) years) is a byproduct of uranium-235 fission and comprises a large component of radioactive waste. Under aerobic conditions and in a neutral-basic environment, the pertechnetate anion ((99)TcO(4)(-)) is stable. (99)TcO(4)(-) is very soluble, migrates easily through the environment and does not sorb well onto mineral surfaces, soils, or sediments. This study moves forward a new strategy for the reduction of (99)TcO(4)(-) and the chemical incorporation of the reduced (99)Tc into a metal oxide material. This strategy employs a single material, a polyoxometalate (POM), α(2)-[P(2)W(17)O(61)](10-), that can be photoactivated in the presence of 2-propanol to transfer electrons to (99)TcO(4)(-) and incorporate the reduced (99)Tc covalently into the α(2)-framework to form the (99)Tc(V)O species, (99)Tc(V)O(α(2)-P(2)W(17)O(61))(7-). This occurs via the formation of an intermediate species that slowly converts to (99)Tc(V)O(α(2)-P(2)W(17)O(61))(7-). Extended X-ray absorption fine structure and X-ray absorption near-edge spectroscopy analysis suggests that the intermediate consists of a (99)Tc(IV) α(2)- species where the (99)Tc is likely bound to two of the four W-O oxygen atoms in the α(2)-[P(2)W(17)O(61)](10-) defect. This intermediate then oxidizes and converts to the (99)Tc(V)O(α(2)-P(2)W(17)O(61))(7-) product. The reduction and incorporation of (99)TcO(4)(-) was accomplished in a "one pot" reaction using both sunlight and UV irradiation and monitored as a function of time using multinuclear nuclear magnetic resonance and radio thin-layer chromatography. The process was further probed by the "step-wise" generation of reduced α(2)-P(2)W(17)O(61)(12-) through bulk electrolysis followed by the addition of (99)TcO(4)(-). The reduction and incorporation of ReO(4)(-), as a nonradioactive surrogate for (99)Tc, does not proceed through the intermediate species, and Re(V)O is incorporated quickly into the α(2)-[P(2)W(17)O(61)](10-) defect. These observations are consistent with the periodic trends of (99)Tc and Re. Specifically, (99)Tc is more easily reduced compared to Re. In addition to serving as models for metal oxides, POMs may also provide a suitable platform to study the molecular level dynamics and the mechanisms of the reduction and incorporation of (99)Tc into a material. 相似文献
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McGregor D Burton-Pye BP Howell RC Mbomekalle IM Lukens WW Bian F Mausolf E Poineau F Czerwinski KR Francesconi LC 《Inorganic chemistry》2011,50(5):1670-1681
The isotope (99)Tc (β(max), 293.7; half-life, 2.1 × 10(5) years) is an abundant product of uranium-235 fission in nuclear reactors and is present throughout the radioactive waste stored in underground tanks at the Hanford and Savannah River sites. Understanding and controlling the extensive redox chemistry of (99)Tc is important in identifying tunable strategies to separate (99)Tc from spent fuel and from waste tanks and, once separated, to identify and develop an appropriately stable waste form for (99)Tc. Polyoxometalates (POMs), nanometer-sized models for metal oxide solid-state materials, are used in this study to provide a molecular level understanding of the speciation and redox chemistry of incorporated (99)Tc. In this study, (99)Tc complexes of the (α(2)-P(2)W(17)O(61))(10-) and (α(1)-P(2)W(17)O(61))(10-) isomers were prepared. Ethylene glycol was used as a "transfer ligand" to minimize the formation of TcO(2)·xH(2)O. The solution structures, formulations, and purity of Tc(V)O(α(1)/α(2)-P(2)W(17)O(61))(7-) were determined by multinuclear NMR. X-ray absorption spectroscopy of the complexes is in agreement with the formulation and structures determined from (31)P and (183)W NMR. Preliminary electrochemistry results are consistent with the EXAFS results, showing a facile reduction of the Tc(V)O(α(1)-P(2)W(17)O(61))(7-) species compared to the Tc(V)O(α(2)-P(2)W(17)O(61))(7-) analog. The α(1) defect is unique in that a basic oxygen atom is positioned toward the α(1) site, and the Tc(V)O center appears to form a dative metal-metal bond with a framework W site. These attributes may lead to the assistance of protonation events that facilitate reduction. Electrochemistry comparison shows that the Re(V) analogs are about 200 mV more difficult to reduce in accordance with periodic trends. 相似文献
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Faulkner S Burton-Pye BP Khan T Martin LR Wray SD Skabara PJ 《Chemical communications (Cambridge, England)》2002,(16):1668-1669
Tetrathiafulvalene carboxylate associates with the charge neutral complex, Yb.DO3A, in methanolic solution to give rise to a novel ternary species; the tetrathiafulvalene unit transfers energy to the lanthanide, causing luminescence from the Yb metal, indicating for the first time that an electron donor chromophore can act as an efficient sensitiser in a self-assembled system containing a lanthanide acceptor. 相似文献
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In this contribution, we provide a comprehensive understanding of the speciation of the Eu(III) complex of the lacunary Wells-Dawson isomer, α1-[P(2)W(17)O(61)](10-) in organic media. The Wells-Dawson polyoxometalate, α1-[P(2)W(17)O(61)](10-) (abbreviated as α1) forms well-defined complexes with europium(III) (and other lanthanide(III)) ions in aqueous solution of predominantly 1 : 1 stoichiometries. The 8-coordinate Eu(III) ion is bound to 4 basic terminal oxygens (O(α1)) and four water molecules (O(H(2)O)) that complete the coordination sphere. Tetra-n-butylammonium (TBA) cations are employed to render the [(H(2)O)(4)Eu(α1-P(2)W(17)O(61))](7-) (Eu-α1) complex soluble in acetonitrile. Europium(III) provides the unique opportunity to employ luminescence spectroscopy and multinuclear NMR to probe the coordination environment. We interrogate the innermost coordination sphere of the Eu(III) ion in acetonitrile solution and in MeCN/H(2)O mixtures. We provide evidence toward the fractional displacement and coordination of acetonitrile within the TBA salts, that is consistent with recent EXAFS data. (31)P NMR and Stern-Volmer quenching studies suggest that dimerization to the 2 : 2 species is negligible in acetonitrile and MeCN-H(2)O mixtures. The decreasing transition energy in the excitation spectroscopy of the TBA-Eu-α1 analog upon dilution is consistent with a nephelauxetic effect, which is attributed to a slight increase in covalency upon replacement of water with acetonitrile. Determination of the number of bound waters (q) is also consistent with acetonitrile-water exchange. The reactivity of the 1 : 1 TBA-Eu-α1 with heterocyclic aromatic amines (1,10-phenanthroline, phen, and 2,2' bipyridine, bipy) in MeCN was probed by titrations monitoring the Eu(III) emission upon sensitization by the "antenna ligands". Binding constants for the products 1 : 1 TBA(x-y)H(y)[(Phen)(H(2)O)(2)Eu(α1-P(2)W(17)O(61))] and 1 : 2 TBA(x-y)H(y)[(Phen)(2)Eu(α1-P(2)W(17)O(61))] (denoted 1 : 1 TBA-Eu-α1:phen and 1 : 2 TBA-Eu-α1:phen, respectively), were determined: logK(1): 7.05 ± 0.04 and logK(2): 4.63 ± 0.10. These are reasonably strong formation constants for Ln phenanthroline complexes. In comparison the bipyridine complexes are much weaker. Excitation spectroscopy reveals that the coordination environment about the Eu(III) center is consistent with the ternary 1 : 1 TBA-Ln-α1:phen or 1 : 2 TBA-Ln-α1:phen complexes. Multinuclear NMR spectroscopy shows significant chemical shift changes at 1 : 1 and 1 : 2 stoichiometries and the chemical shift of bound water tracks with the titration to validate expulsion of the H(2)O upon coordination of phenanthroline. 相似文献
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In a search for evidence that a π cloud proximal halogen interaction is of importance to the mode of action of the thyroid hormones, the dipole moments of the 1'-naphthyl (I), (4.29 D), 4'-carboxymethylphenyl (II), (2.90 D), 2'-bromo4'-carboxymethylphenyl (III), (3.56 D), and methyl (IV), (3.24 D) ethers of 2,4dinitro-6-bromophenol were determined in benzene at 25 °C. The moments of (I), (II) and (III) are approximated best by those calculated for the twisted conformation in which the bromine closely approaches the face of the other ring. That of the naphthyl ether (I) can, however, be explained only by inclusion of an intramolecular electron donor-acceptor charge-transfer moment of 1.6 D directed from the π cloud of the naphthyl ring to the proximal nitro group of the other ring, or of 2.8 D to the proximal bromine of that ring. In the preferred conformation of the methyl ether (IV), the methoxy group is coplanar with the ring while the 2-nitro group is twisted 90° from coplanarity to accomodate it. A mesomeric moment of 2.3 D is estimated from this for the 2,4-dinitro-6-bromophenoxy moiety and is used in calculating the expected moments of the other ethers. 相似文献
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LI Xiang LI Zhong XI Hongxia LUO Lingai The Institute of Chemical Engineering South China University of Technology Guangzhou China LSGC-CNRS-ENSIC rue Grandville BP Nancy Cedex France 《Chinese Journal of Reactive Polymers》2004,(Z1)
1. INTRODUCTION With the development of municipalization in China, more and more cities are challenged by the problem of how to dispose of the dramatically increased municipal waste. Generally, most of municipal solid waste is landfilled or dumped openly in the suburbs. It causes not only land waste, but also serious environment pollution. In order to solve efficiently the environment pollution caused by municipal solid waste, incineration technique was introduced in some big cities such… 相似文献
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应用Ahlfors覆盖曲面的方法,在单位圆内构造了代数体函数的一个新的奇异半径(称为T半径),并应用无穷级的型函数推广了亚纯函数奇异方向的相关结论. 相似文献