The preparation, spectroscopic characterization and thermal stability of neutral complexes of uranyl ion, UO22+, with phosphonate ligands, such as diphenylphosphonic acid (DPhP), diphenyl phosphate (DPhPO) and phenylphosphonic acid (PhP)
are described. The complexes were prepared by a reaction of hydrated uranyl nitrate with appropriate ligands in methanolic
solution. The ligands studied and their uranyl complexes were characterized using thermogravimetric and elemental analyses,
ESI-MS, IR and UV–Vis absorption and luminescence spectroscopy as well as luminescence lifetime measurements. 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.