Novel bis-carbacylamidophosphate and its complexes of rare earth elements

Abstract

Considering the unfading interest in lanthanide-based luminescent materials the novel bis-chelating ligand tetramethyl(1,3-phenylenedicarbonyl)-bis-amidophosphate (H₂L) was synthesized. Its coordination ability towards the rare earth elements and the effectivity of sensitization of their luminescence were investigated. X-ray analysis of H₂L points on its chain- like structure created by means of hydrogen bonds NH···OP. The two series of binuclear complexes of rare earth elements Ln₂L₃(H₂O)₂·2H₂O (Ln1) and Ln₂L₃bipy₂·2H₂O (Ln2), where Ln = Eu, Tb, Dy, Y and bipy = 2,2′-bipyridine, were obtained and characterized using elemental and thermal gravimetric analysis, IR, NMR, UV absorption spectroscopy at room temperature and luminescence spectroscopy at 298 and 77  K. The ligand absorbs in the UV region and effectively sensitizes the emission of Eu^III, Tb^III, and Dy^III ions. The complexes of dysprosium emit in visible and NIR regions despite the presence of water molecules in the complexes compositions as well as despite that the enegry gaps between the ligands’ lowest triplet state and the emissive levels of Dy^III are within the range for back energy transfer. The europium and terbium complexes possess bright respectively red and green luminescence with an emission lifetime at room temperature in the range of 1.13–2.60 ms.