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

Summary 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 NaClO4. The uranium concentration was 5 × 10−6M at ligand concentrations from 1 × 10−5to 1 ×−2M. The measured fluorescence lifetimes of the 1:1 and 1:2 uranyl(VI) malonate complexes are 1.24 ± 0.02 µs and 6.48 ± 0.02 µs, respectively. The fluorescence lifetime of the uranyl(VI) ion is 1.57 ± 0.06 µs 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 UO2C3H2O4°(aq)and UO2(C3H2O4)22−from results of spectra deconvolution using a least square fit algorithm (logβ1° = 4.48 ± 0.06, logβ2° = 7.42 ± 0.06 or logK2° = 2.94 ± 0.04). The results are compared with literature values obtained by potentiometric measurements.