Sample records for 6hsub 5clcenter dotnhsub

  1. Structural investigation into the steric control of polyether complexation in the lanthanide series: Macrocyclic 18-crown-6 versus acyclic pentaethylene glycol

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    Rogers, R.D.; Rollins, A.N.; Etzenhouser, R.D.; Voss, E.J.; Bauer, C.B. )


    The complexation reactions of MCl[sub 3][center dot]nH[sub 2]O (M = Y, La-Pr, Sm-Lu) with pentaethylene glycol (EO5) and MCl[sub 3][center dot]nH[sub 2]O (M = La, Ce, Pr, Eu, Gd) with 18-crown-6 in 1:1 molar ratios in 3:1 CH[sub 3]CN:CH[sub 3]OH were investigated. X-ray structural analysis of 21 crystalline complexes were carried out. Comparison of all the crystalline complexes studied reveals that polyethylene glycols exhibit a helical wrapping pattern around the lanthanide ions, while the crown ethers attempt to fold around these cations. This feature of polyether complexation of the lanthanide(III) chlorides may be responsible for the ready isolation of EO5 complexes for all lanthanides and the lack of direct coordination of 18-crown-6 past M = Tb in normal 1:1 complexation reactions.

  2. Physicochemical investigation of UO/sub 2/SO/sub 3//centered dot/3H/sub 2/O

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    Blatov, V.A.; Serezhkina, L.B.; Serezhkin, V.N.


    The thermal stability of UO/sub 2/SO/sub 3//centered dot/3H/sub 2/O was investigated, and its crystallographic characteristics were determined. The IR spectra of UO/sub 2/SO/sub 3//centered dot/nH/sub 2/O ( n /equals/ 3 or 4, 5) are discussed. An assumption regarding the structure of uranyl sulfite hydrates and their affiliation with the AT/sup 3/M/sub 2//sup 1/ crystal-chemical group is expressed.

  3. Thermodynamics of technetium related to nuclear waste disposal: Solubilities of Tc(IV) oxides and the electrode potential of the Tc(VII)/Tc(IV)--oxide couple

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    Meyer, R E; Arnold, W D; Case, F I; O'Kelley, G D


    Solubilities of Tc(IV) oxides have been determined in a number of solutions in the pH range 1 to 10. Technetium oxide was prepared by precipitation upon purified sand with a 30% excess of hydrazine and by electrodeposition. The oxide-covered sand was transferred to a small column, and the solutions to be studied were continuously cycled through the column. The electrodeposited oxide was formed on a platinum mesh electrode, and after careful rinsing, the solution to be studied was added to the electrolytic cell. The concentrations of total technetium and Tc(IV) species in the solutions were periodically determined by separating the oxidized and reduced technetium species using a solvent extraction procedure and counting the beta activity of the /sup 99/Tc with a liquid scintillation counter. In basic solutions, the concentrations of Tc(IV) species in equilibrium with the oxide were in the range of 10/sup /minus/8/ to 10/sup /minus/9/ mol/L and tended to increase slightly with pH. In acid solutions the concentrations were much higher and were consistent with literature data on the hydrolytic species of Tc(IV). Solubilities appeared to reach a minimum in the intermediate pH range, and they were generally a factor of three or four lower for oxides electrodeposited in basic solutions compared to those for oxides electrodeposited from acid solution. The oxides were hydrated, and assuming a formula of TcO/sub 2//center dot/nH/sub 2/O, the value of n was found to be 1.63 +- 0.28. These data can be used to estimate Tc(IV) solubilities for cases where solubility limits transport of technetium in reducing environments of high-level waste repositories. 22 refs., 7 figs., 9 tabs.

  4. Electron transfer reactions in microporous solids

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    Mallouk, T.E.


    We have studied electron transfer quenching of the excited state of Ru(bpy){sub 3}{sup 2+} in aqueous suspensions of zeolites Y, L, and mordenite. The internal pore network of the zeolite is ion-exchanged with methylviologen cations, which quench the excited state of the surface-bound sensitizer. A detailed study of the quenching and charge recombination kinetics, using time-resolved luminescence quenching and transient diffuse reflectance spectroscopies, shows to remarkable effects: first, the excited state quenching is entirely dynamic is large-pore zeolites (L and Y), even when they are prepared as apparently dry'' powders (which still contain significant amounts of internally sited water). Second, a lower limit for the diffusion coefficient of the MV{sup 2+} ion in these zeolites, determined by this technique, is 10{sup {minus}7} cm{sup 2}sec, i.e., only about one order of magnitude slower than a typical ion in liquid water, and 2--3 orders of magnitude faster than charge transfer diffusion of cations in polyelectrolyte films or membranes such as Nafion. Surface sensitization of internally platinized layered oxide semiconductors such as K{sub 4-x}H{sub x}Nb{sub 6}O{sub 17}{center dot}nH{sub 2}O (x {approx} 2.5) yields photocatalysts for the production of H{sub 2} and I{sub 3{minus}} in aqueous iodide solutions. Layered alkali niobates and titanates form a class of zeolitic wide-bandap semiconductors, and are the first examples of photocatalysts that evolve hydrogen from an electrochemically reversible (i.e., non-sacrificial) electron donor with visible light excitation.