Síntesis y caracterización de nuevos materiales híbridos luminiscentes

Abstract

En condiciones hidrotermales, se sintetizaron dos nuevos succinatos de itrio, Y2(C4H4O4)3(H2O)4·6H2O (2) y Y2(C4H4O4)3(H2O)2 (3). Sus estructuras cristalinas, resueltas a partir de datos de difracción de rayos X de monocristal se discutiron a la luz de la del Y2(C4H4O4)3(H2O)2·H2O (1). El estudio del comportamiento térmico de los tres compuestos fue posible como consecuencia de su obtención como fases individuales de elevada pureza. El sistema presenta gran diversidad estructural, consecuencia de los diferentes modos de coordinación y la flexibilidad conformacional del ligando succinato que, condicionada por la composición del medio de reacción, dirige la síntesis hacia el producto deseado. La síntesis de nuevos polímeros de coordinación quirales de itrio(III), [NaY(Tart)(BDC)(H2O)2] (1) y [NaY(Tart)(biBDC)(H2O)2] (2) (H2Tart = ácido tartárico; H2BDC = ácido tereftálico; H2biBDC = ácido bifenil-4,4'-dicarboxílico), con la participación de ligandos quirales flexibles y aquirales rígidos, también se efectuó en condiciones hidrotermales. 1 y 2 son compuestos quirales de simetría ortorrómbica, que cristalizan en idéntico grupo espacial (C2221): a = 6.8854(2) Å, b = 30.3859(7) Å, c = 7.4741(2) Å para 1, y a = 6.8531(2) Å, b = 39.0426(8) Å, c = 7.4976(2) Å para 2. Sus estructuras han sido resueltas utilizando la difracción de rayos X de monocristal, asistida por datos de resonancia magnética nuclear en estado sólido (13C CPMASNMR), análisis térmico (TG-MS y DSC) y análisis elemental. Ambos materiales poseen hábito laminar, alcanzando la estabilidad tridimensional mediante enlaces de hidrógeno interlaminares. Los estudios de termodifracción de rayos X de polvo cristalino (HTpXRD) desvelaron el mecanismo del proceso de deshidratación/rehidratación, siendo modelizadas la estructura de las fases anhidras. La sustitución de itrio por lantánidos trivalentes permitió la síntesis de dos nuevas series de compuestos: [NaLn(Tart)(BDC)(H2O)2] y [NaLn(Tart)(biBDC)(H2O)2] (Ln = Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb). Estos materiales se caracterizaron mediante difracción de rayos X de monocristal y de polvo cristalino, análisis térmico (TG-MS y DSC), espectroscopia vibracional (FTIR), microscopia electrónica de barrido (SEMEDX), análisis elemental, y termodifracción de rayos X de polvo cristalino (HT-pXRD). Además de su actividad catalítica, es destacable el comportamiento fotoluminiscente de estos materiales, que presentan emisión sintonizable de luz UV-VIS-IR mediante una efectiva sensibilización de los cationes lantánidos trivalentes a través de los ligandos BDC2- y biBDC2-. irradiación por microondas, se utilizó como precursor en la síntesis hidrotermal de nuevos materiales híbridos organo-inorgánicos basados en metales lantánidos trivalentes (Ln = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu). Se obtuvieron materiales monofásicos de composición Ln[O3P(C6H4)PO3H] (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho), aunque sólo en el caso del compuesto de praseodimio (Za1) ha sido posible aislar monocristales de calidad suficiente para su determinación estructural mediante difracción de rayos X de cristal único. Za1 tiene simetría monoclínica (grupo espacial C2/c), con a = 5.6060(4) Å, b = 20.251(7) Å, c = 8.2740(6) Å, β = 108.52(1)º. Los demás compuestos anhidros de la serie son isoestructurales con Za1, y su estructura se refinó a partir de datos de difracción de rayos X de polvo cristalino. Sin embargo, los compuestos basados en Y, Er, Tm, Yb, y Lu cristalizan como fases hidratadas de estructura desconocida. Ambas series de compuestos se caracterizaron mediante análisis térmico (TG-MS, SDTA, y DSC), análisis elemental, espectroscopia infrarroja, termodifracción de rayos X de polvo cristalino (HT-pXRD), microscopia electrónica de transmisión (TEM) y de barrido (SEM-EDX). Estos materiales, que presentan tamaños de partícula variables (> 20 nm), exhiben una inusualmente alta estabilidad térmica. Todos ellos son paramagnéticos, con momentos magnéticos efectivos acordes con los esperados para cationes lantánidos en estado trivalente, mostrando fotoluminiscencia en la región visible del espectro electromagnético, con fuerte luminiscencia roja y verde, respectivamente, para los compuestos basados en europio y terbio

Two new members in the yttrium-succinates family have been reported. These yttrium-succinates coordination polymers, formulated as Y2(C4H4O4)3(H2O)4·6H2O (2) and Y2(C4H4O4)3(H2O)2 (3), have been synthesized under hydrothermal conditions. Their structures solved by single crystal X-ray diffraction, are compared with that of Y2(C4H4O4)3(H2O)2·H2O (1). The three compounds were obtained as single phases, and their thermal behaviour is described. The results suggest that the structural diversity obtained in this system is related to the coordination diversity and the conformational flexibility of the succinate ligand, which in turn depend on the synthesis conditions that play an important role in directing to one compound or another. New chiral metal organic frameworks, assembled from Y(III), Na(I) and chiral flexible-achiral rigid dicarboxylate ligands, formulated as [NaY(Tart)(BDC)(H2O)2] (1) and [NaY(Tart)(biBDC)(H2O)2] (2) (H2Tart = Tartaric acid; H2BDC = Terephthalic acid; H2biBDC = Biphenyl-4,4'-dicarboxylic acid), were obtained as single phases under hydrothermal conditions. Their structures were solved by single-crystal X-ray diffraction, and characterized by 13C CPMAS NMR, thermal analyses (TG-MS and DSC), elemental analysis, and X-ray powder diffraction. Both compounds crystallize in the orthorhombic chiral space group C2221 with a = 6.8854(2) Å, b = 30.3859(7) Å, c = 7.4741(2) Å for 1, and a = 6.8531(2) Å, b = 39.0426(8) Å, c = 7.4976(2) Å for 2. 1 and 2 are layered structures whose three-dimensional stability is ensured by strong hydrogen bond interactions. The X-ray powder thermodiffractometry study was performed, and reveals that the dehydration of both compounds is accompanied by phase transformation, while the spontaneous rehydration process is characterized by different kinetics. The crystal structures of anhydrous compounds have been modeled. (Ln = Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb), Na(I), and chiral flexible-achiral rigid dicarboxylate ligands, formulated as [NaLn(Tart)(BDC)(H2O)2] and [NaLn(Tart)(biBDC)(H2O)2] (H2Tart = Tartaric acid; H2BDC = Terephthalic acid; H2biBDC = Biphenyl-4,4'-dicarboxylic acid), were obtained as single phases under hydrothermal conditions. The compounds have been studied by single-crystal and powder X-ray diffraction, thermal analyses (TG-MS and DSC), vibrational spectroscopy (FTIR), scanning electron microscopy (SEM-EDX), elemental analysis, and X-ray powder thermodiffractometry. The activity catalytic has been also investigated. Photoluminescence studies of the investigated materials show room temperature tunable UV-VIS-IR light emission through an effective Ln3+ sensitization via BDC2- and biBDC2- ligands. Series of novel organic-inorganic hybrids materials based on trivalent lanthanide (Ln = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) and 1,4- phenylbis(phosphonate) has been obtained under hydrothermal conditions either by oven heat or microwave irradiation. Compounds based on La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Ho, formulated as Ln[O3P(C6H4)PO3H], has been obtained as single phases under hydrothermal conditions. In the praseodymium compound (Za1) single crystals have been obtained and the crystal structure determined. Za1 crystallizes in the monoclinic space group, C2/c, with a = 5.6060(4) Å, b = 20.251(7) Å, c = 8.2740(6) Å, β = 108.52(1)º. The compounds containing La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Ho, are anhydrous and isostructural to Za1 as confirmed by Rietveld refinement using X-ray powder diffraction data. However, the compounds based on Y, Er, Tm, Yb, and Lu are hydrated and their structures have not yet been solved. The series of compounds are characterized by thermal analyses (TG-MS, SDTA, and DSC), elemental analysis, IR spectra, X-ray powder diffraction, X-ray powder thermodiffractometry, transmission electron microscopy (TEM) and scanning electron microscopy (SEM-EDX). TEM study show a variable particles size with a minimum size of ca. 20 nm. These compounds exhibit unusual very high thermal stability. The size of particles and the thermal stability are depending on metal(III) cation features. All the investigated materials show paramagnetic behaviour. The magnetic susceptibility data follow a Curie-Weiss laws with paramagnetic effective moments in good agreement with those expected for Ln3+ free ions. The visible photoluminescence properties are also discussed. Eu- and Tb-based compounds exhibit strong red and green luminescence, respectively