Structural and spectroscopy studies of complexes of the uranyl ion with 2,2′-bipyridine-N,N′-dioxide

2,2′-Bipyridine-N,N′-dioxide (bypO2 = L) complexes of the composition [UO2(bypO2)2(NO3)2]·2H2O (UO2–L2–NO3), [UO2(bypO2)2H2O](ClO4)2 (UO2–L2–ClO4) and [UO2bypO2(H2O)2SO4] (UO2–L–SO4) have been prepared by the reactions of the respective hydrated uranyl salts with the bypO2 ligand in water. The structures of the complexes were elucidated using elemental and thermal analyses, IR and luminescence spectroscopy as well as luminescence lifetime measurements. The IR spectra show that the bonding between uranium and bypO2, as well as uranium and water or a counter ion (NO3− and SO42−) is formed. The nitrate or sulfate groups coordinate to the central metal ions in a monodentate manner. From TG–DTA curves, the nature of the water molecules present in the complexes and the decomposition temperature of the dehydrated uranyl complexes were determined. The thermal stability of the anhydrous uranyl complexes increases in the series: (UO2–L2–NO3) < (UO2–L2–ClO4) < (UO2–L–SO4). All the compounds show green-yellow intense luminescence. The main fluorescence bands and the emission lifetimes in these complexes were determined. The luminescence spectra of all the prepared complexes differ from each other with respect to their peak maxima positions. The luminescence lifetimes also vary. The structure of the (UO2–L–SO4) complex was determined by X-ray single-crystal analysis.

2,2′-Bipyridine-N,N′-dioxide complexes with uranyl salts have been prepared and spectroscopically characterized. Structures of the uranyl complexes were elucidated using elemental and thermal analyses, IR, X-ray single-crystal analysis. The metal atom is seven-coordinate, and its first coordination sphere spans a distorted pentagonal bipyramide.Figure optionsDownload as PowerPoint slide