Síntese, caracterização espectroscópica, térmica, estrutural e estudo luminescente de redes de íons lantanídeos (Ln= Eu(III), Tb(III) E Dy(III))

Abstract

In this work were synthesized, through the diffusion method, (i) colorless co-crystals with molecular formula C24H18N4O4 (1) using the ligands H2-2,5-bipydc (2,2'-bipyridine-5,5'- dicarboxylic acid) and bpe (1,2-bis(4-pyridine)ethene) with hydrated sulfates of lanthanide ions [Ln2(SO4)3.xH2O, Ln= Tb(III), Eu(III) and Dy(III)], whose single crystal X-ray diffraction results revealed a crystalline structure containing both ligands, without the presence of lanthanide ions; (ii) yellow crystalline solids with proposed structures [Eu4(Hbttb3)]n (2) and [Dy4(bttb)3]n (3), obtained from the hydrothermal synthesis between the salts [Ln2(SO4)3.xH2O, Eu(III) and Dy(III)] and the organic linker H4-bttb ( H4-bttb = 1,2,4,5 tetrakis (4-carboxyphenyl) benzene); (iii) yellow single crystal [Tb(bttb)0.5(2,5pzdc)0.5]n (4) obtained via hydrothermal synthesis, which were manually separated from the mother solution between a yellow amorphous solid involving the reaction of terbium(III) sulfate and two organic ligands H4-bttb and 2,5-H2pzdc (2,5-H2pzdc=2,5-pyrazine dicarboxylic acid). In the single crystal X-ray diffraction results revealed the formation of a three-dimensional coordination polymer containing the Tb(III) ion coordinated to the fully deprotonated bttb4- and 2,5-pzdc2- ligands. The two-dimensional network of 4, it is also possible to observe the presence of cavities (voids), which makes this compound a potential adsorbent. In addition, vibrational spectroscopy results in the infrared region, revealed that for polymers (2-4), the absence of bands in the region of 1700 cm-1 , referring to COOH stretching, indicates that the ligands are completely deprotonated, suggesting that there was coordination to the metallic center. The differences between the symmetric and the unsymmetric stretching frequencies (Δ) of the carboxylate groups in (2) indicate the bridged and monodentate coordination mode, while in (4) bridge chelate and monodentate chelate coordination mode, confirmed by structural resolution. It is possible to note that the luminescent properties remain prominent in 4, even with temperature variation, and that there is not a large variation in the half-life of the emissions, making this a promising material for use as molecular optical thermometer.