Ligand sensitized luminescence of uranyl by benzoic acid in acetonitrile medium: a new luminescent uranyl benzoate specie.
Benzoic acid (BA) is shown to sensitize and enhance the luminescence of uranyl ion in acetonitrile medium. Luminescence spectra and especially UV-Vis spectroscopy studies reveal the formation of tri benzoate complex of uranyl i.e. [UO2(C6H5COO)3](-) which is highly luminescent. In particular, three sharp bands at 431, 443, 461nm of absorption spectra provides evidence for tri benzoate specie of uranyl in acetonitrile medium. The luminescence lifetime of uranyl in this complex is 68μs which is much more compared to the lifetime of uncomplexed uranyl (20μs) in acetonitrile medium. In contrary to aqueous medium where uranyl benzoate forms 1:1 and 1:2 species, spectroscopic data reveal formation of 1:3 complex in acetonitrile medium. Addition of water to acetonitrile results in decrease of luminescence intensity of this specie and the luminescence features implode at 20% (v/v) of water content. For the first time, to the best of our knowledge, the existence of [UO2(C6H5COO)3](-) specie in acetonitrile is reported. Mechanism of luminescence enhancement is discussed.
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 structured 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 P, 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 UO distance is 1.771(5)A(mean).
On the Electron-transfer Reaction Rate between Different Molecular Species of Aromatic Hydrocarbons as Measured by ESR
The rate constants of electron-transfer reactions between the anthracene anion radical and pyrene, and those between the former radical and 1,2-benzanthracene, were measured by the ESR method in tetrahydrofuran containing 20 mM of tetra-n-butylammonium perchlorate. In the analysis of the experimental results, correction of the ESR line width was made for the change in the radical concentration caused by the addition of neutral molecules. The rate constants thus obtained were (2.0±0.4)×107M−1sec−1 and (8.1±1.0)×10−7M−1sec−1 respectively at 25°C. Under the same experimental conditions, the rate constants of the electron exchange of anthracene and pyrene with their respective anions were about one-tenth of the rate constants of free anions. This fact led us to the supposition that the anion radicals had been combined with tetra-n-butylammonium ions into stable ion-pairs in our experiment. A semi-empirical method was proposed for the theoretical calculation of the rate constant according to the theory of R. A...