A new uranyl benzoate species characterized by different spectroscopic techniques

Abstract

AbstractFor the first time in the aqueous phase the existence of a U(VI)-benzoate complex with a 1:2 stoichiometry could be proven. Using UV-Vis spectroscopy and especially cryo time-resolved laser-induced fluorescence spectroscopy (TRLFS) it was possible to characterize this complex in detail.Room temperature TRLFS measurements revealed a static as well as a dynamic ligand-initiated quench process in the U(VI)-benzoic acid system. At these conditions no luminescence emission resulting from complex formation was found. Consequently cryo TRLFS was applied to increase the maximum detectable benzoate:U(VI) ratio. By this for the first time a luminescence spectrum of the 1:2 U(VI)-benzoate complex could be determined. This species is characterized by emission bands at 467, 485, 505, 526, and 550 nm which are blue-shifted compared to the ones of the UO22+ion. The luminescence lifetime of the 1:2 complex amounts to 9.21±0.01 μs at −18 ºC compared to 150.4±0.5 μs for UO22+.The stability constant of the newly found species logβ120has been calculated to be 4.48±0.24. The stability constant of the 1:1 complex was validated to amount to 2.64±0.19. UV-Vis spectroscopy combined with factor analysis yielded the molar absorption spectrum of the 1:2 U(VI)-benzoate species which is characterized by absorption bands at 406, 418, 432.5, 447, and 461 nm and a molar absorption coefficient of 22 L mol−1cm−1.