Study of uranyl(VI) malonate complexation by time resolved laser-induced fluorescence spectroscopy (TRLFS)

The uranyl(VI) malonate complex formation was studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) at pH 4 and an ionic strength of 0.1 M NaCIO4. The uranium concentration was 5 x 10(-6) M at ligand concentrations from 1 x 10(-5) to 1 x 10(-2) M. The measured fluorescence lifetimes of the 1:1 and 1:2 uranyl(VI) malonate complexes are 1.24 +/- 0.02 mus and 6.48 +/- 0.02 mus, respectively. The fluorescence lifetime of the uranyl(VI) ion is 1.57 +/- 0.06 mus in 0.1 M perchloric media. The main fluorescence bands of the malonate complexes show a bathochromic shift compared to the uranyl(VI) ion and are centered at 494 nm, 515 nm and 540 nm for the 1:1 complexes and at 496 nm, 517 nm and 542 nm for the 1:2 complex. The spectra of the individual uranyl(VI) malonate complexes were calculated using a multi exponential fluorescence decay function for each intensity value at each wavelength, covering the entire wavelength range. Stability constants were determined for the complexes UO(2)C(3)H(2)O(4)degrees((aq)) and UO2(C3H2O4)(2)(2-) from results of spectra deconvolution using a least square fit algorithm (log beta(1)degrees = 4.48 +/- 0.06, log beta(2)degrees = 7.42 +/- 0.06 or log K(2)degrees = 2.94 +/- 0.04). The results are compared with literature values obtained by potentiometric measurements.