Novos complexos de lantanídeos contendo ânions carboxilatos e ligantes nitrogenados: busca por novos dispositivos moleculares conversores de luz

Abstract

The present work reports the synthesis and characterization of lanthanide (III) complexes containing 2,5-thiophenedicarboxylate (2,5-tdc2-) and hydrocinnamate (cin-) anions and nitrogen ligand 2,2’-bipyridine (bpy) in order to investigate its chemical and structural features and correlate with the photoluminescent properties. Two series of compounds obtained from the 2,5-thiophenedicarboxylate anion were formulated as: [Ln2(2,5-tdc)3(dmf)2(H2O)2]·2dmf·H2O (Ln = Dy (1), Tb (2), Eu (3), Gd (4), Er (5)), [Nd2(2,5-tdc)3(dmf)2(H2O)2]·dmf·H2O (7) and {[Ln2(2,5-tdc)3(dmso)2]·H2O}n ( Ln = Dy (8), Tb (9), Eu (10), Gd (11), Nd (12), Sm (13), Yb (14), Ho (15), Er (16), Tm (17), Pr (18)). Two series of compounds obtained from the cin- ligand were formulated as: [Ln(cin)3(H2O)3]·3Hcin (Ln = Dy (19), Tb (20), Eu (21), Er (22) e Gd (23)) e [Ln2(cin)6(bpy)2] ( Ln = Tb (24), Eu (25) e Gd (26)). All synthesized compounds were characterized by elemental analysis (CHN), thermal analysis (TG/DTA), vibrational spectroscopy in the infrared region (IR), reflectance diffuse spectroscopy (DR) and Xray diffraction (powder and single crystal). The study of their optical properties was obtained from the emission and excitation spectra and by the luminescent decay curve. Based on spectral data, the experimental intensity parameters (Ω2 and Ω4), radiative emission (Arad) and non-radiative (Anrad) coefficients and emission quantum efficiency (ɳ) of the 5D0 level the Eu(III) ion were determined. The crystal structures of complexes (7), (8) and (9) were determined using single crystal X-ray diffraction analysis, showing the formation of lanthanide (III) metal-organic porous frameworks (LnMOFs). The assignment of the triplet states (T1) of the 2,5-tdc2- ligand was taken from the emission spectra of the respective complexes of Gd(III), showing the possibility of intramolecular energy transfer in these compounds.All compounds containing the cin- ligand (19)-(26) had their structures determined by single crystal Xray diffraction analysis. Despite the possibility of the antenna effect of compounds (19), (20) and (21), the presence of three water molecules directly coordinated to lanthanide (III) ions, promotes the luminescence suppression. For [Eu2(cin)6(bpy)2] (25) complex, the intensity parameters (Ω2, Ω4 e Ω6), radiative decay (Arad), non-radiative (Anrad), energy transfer (WET), back energy transfer (WBT) rates and quantum efficiency were obtained. These data are in excellent agreement with experimental data with such complex having quantum efficiency (ɳ) of 67% suggesting that this system can be excellent for the development of luminescent devices.