Structural and photoluminescence properties of lanthanide (III) complexes with carbacylamidophosphate ligand and α,α′-bipyridine

Abstract

Two series of lanthanide coordination compounds, [Ln(NO3)(L)2(bipy)] and [Ln(L)3(bipy)], where Ln3+ = Eu, Gd, Tb, with the carbacylamidophosphate CAPh ligand N,N,N′,N′-tetraethyl-N″-(trichloroacetyl) phosphoric triamide HL = Cl3CC(O)N(H)P(O)(NEt2)2 and α,α’-bipyridine, were synthesized. The complexes were characterized using infrared, ultraviolet diffuse reflection, and luminescence spectroscopy, as well as elemental and X-ray analyses. The bidentate coordination of the deprotonated CAPh ligand was confirmed through the analysis of the complexes' IR spectra and by X-ray analysis of the bis-CAPh Eu(III) and Tb(III) complexes. The emission and excitation solid-state spectra of the Eu(III) and Tb(III) complexes, as well as the f → f luminescence decay times, were measured at room temperature. Phosphorescence spectra of the Gd(III) complexes were measured at 77 K. The lowest ligands’ triplet state energy depends on the number of coordinated CAPh ligands in the complexes. The Eu(III) and Tb(III) compounds exhibited a strong metal-centered emission with decay times ranging from 1.72 ms to 2.3 ms. Intrinsic quantum yields (QLnLn) equal 82 % for [Eu(NO3)(L)2(bipy)] and 70 % for [Eu(L)3(bipy)]. The Tb(III) complexes revealed a very efficient ligand-to-metal energy transfer at room temperature.