Preparation and characterization of uranyl complexes with phosphonate ligands

Abstract

The preparation, spectroscopic characterization and thermal stability of neutral complexes of uranyl ion, UO2 2? , with phosphonate ligands, such as diphenylphos- phonic acid (DPhP), diphenyl phosphate (DPhPO) and phenylphosphonic acid (PhP) are described. The com- plexes were prepared by a reaction of hydrated uranyl nitrate with appropriate ligands in methanolic solution. The ligands studied and their uranyl complexes were charac- terized using thermogravimetric and elemental analyses, ESI-MS, IR and UV-Vis absorption and luminescence spectroscopy as well as luminescence lifetime measure- ments. Compositions of the products obtained dependent on the ligands used: DPhP and DPhPO form UO2L2 type of complexes, whereas PhP forms UO2L complex. Based on TG and DTG curves a thermal stability of the complexes was determined. The complexes UO2PhP� 2H2O and UO2(DPhPO)2 undergo one-step decomposition, while UO2PhP � 2H2O is decomposed in a two-step process. The thermal stability of anhydrous uranyl complexes increases in the series: DPhPO \ PhP \ DPhP. Obtained IR spectra indicate bonding of P-OH groups with uranyl ion. The main fluorescence emission bands and the lifetimes of these complexes were determined. The complex of DPhP shows a green uranyl luminescence, while the uranyl emission of the UO2PhP and UO2(DPhPO)2 complexes is considerably weaker.