Glycine complexation with uranyl ion: absorptiometric, luminescence, and X-ray structural studies of tetrakis(glycine)dioxouranium(VI) nitrate

Addition of glycine to uranyl nitrate in aqueous acidic solution induces shifts in both the highly structural absorption and emission bands in the visible region. An analysis by Job's method indicates the formation of a complex of stoicheiometry uranyl ion:glycine of 1:4. The structure determination of a single crystal of the complex [UO2(O2CCH2NH3)4][NO3]2 by X-ray diffraction methods confirms this formulation. The structure has been refined to an R factor of 0.026 using 2 281 'observed' measured intensities. The complex is triclinic, space group P1-bar, with hexagonal bipyramidal co-ordination about the uranium atom. All the glycine ligands are in the zwitterionic form, NH3+CH2CO2- and act as O-donors; two are bidentate [U-O = 2.562(5) - 2.489(6) A], and two unidentate [mean U-O = 2.437(4) A]. The uranyl U-O distance is 1.771(5) A (mean). (author)