DETERMINATION OF STRUCTURAL PARAMETERS OF URANYL IONS COMPLEXED WITH ORGANIC-ACIDS USING EXAFS

Two compounds of known crystal structure, sodium triacetatodioxouraniu m(VI), Na[UO2(CH3COO)(3)], and dibenzoatodioxouranium(VI), UO2[C6H5(CO O)](2), were studied by uranium L-III-edge extended X-ray absorption f ine structure, EXAFS, spectroscopy to differentiate between bidentate and monodentate coordination of carboxylate ions on the basis of the u ranium-equatorial oxygen, Oeq, bond lengths. Bidentate coordination ca n be verified by detecting carboxyl carbon atoms and the neighboring d istal carbon atom of the organic rest. In contrast, EXAFS spectra for monodentate carboxylate complexes show no evidence of carbon atoms bey ond the Oeq coordination shell. The mode of coordination was determine d by EXAFS analysis for solid uranyl complexes with humic, methoxybenz oic, and salicylic acids. A correlation between the U L-III-edge X-ray absorption near-edge structure, XANES, and the U-Oeq bond distance ac cording to the relationship Delta E.R(Oeq)(2)=constant was observed. F or the samples studied, the constant was determined to be 197+/-8 eV A ngstrom(2). (C) 1998 Elsevier Science S.A.