Lead-207 n.m.r. chemical shift data have been recorded for the following bivalent lead compounds (solvent in parentheses) : Pb(N03)2 (water), Pb(C104)2*3H20 (water), Pb(02CCH3)2*3H20 (water), Pb(02CC6F5)2 (tetrahydrofuran, thf), Pb[S,P(OR)J, (R = C2H5 or i-C4H9) (thf and dichloromethane). The nature of the solution species is discussed. The very high-field chemical shifts exhibited by the hydrated lead (11) dication and the monoacetato-and mononitrato-lead (ti) monocations are ascribed to efficient nuclear shielding resulting from the confinement of the lead(ii) lone pair to the metal 6s orbital.
The local atomic structure surrounding uranium in borosilicate glass has been investigated by fluorescence X-ray absorption spectroscopy. By employing angles of incidence either side of the critical angle for total external reflection, surface and near-surface structure can be distinguished. The results of leaching in water at 100 "C have been examined in detail. Wet and dried glass surfaces can be differentiated. Analysis of glancing-angle spectra demonstrates that uranium occupies a uranyl-like environment that hydrates as leaching progresses. Uranyl complexing occurs in a planar geometry. The initial corrosion process can be readily understood by using the modified random network model for glass structure, which predicts diffusion of cations and water taking place via percolation pathways through the network. Following extended corrosion treatment, evidence for the formation of hydrated uranyl silicates at the surface has been found.
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