RESUMEN
A new class of lanthanide mixed-carboxylate ligands compounds with formula {[Ln2 (phthgly)4 (bdc)(H2 O)6 ]·(H2 O)4 }∞ , labelled as Ln3+ : Eu (1) and Gd (2) coordination polymers (CP) were synthesized under mild reaction conditions between lanthanide nitrate salts and a solution of N-phthaloylglycine (phthgly) and terephthalic (bdc) ligands. The (1) and (2) coordination polymers were formed by symmetric binuclear units, in which phthgly and bdc carboxylate ligands are coordinated to the lanthanide ions by different coordination modes. Surprisingly, all organic ligands participate in hydrogen bonding interactions, forming an extremally rigid crystalline structure. The red narrow emission bands from the 5 D0 â7 FJ transitions of the Eu3+ ion show a high colour purity. The intramolecular energy transfer process from LâEu3+ ion has been discussed. The experimental intensity parameters (Ω2,4 ) reflect lower angular distortion and polarizability of the chemical environment around the metal ion compared with other Eu3+ compounds reported in the literature. This novel class of coordination polymer offers a more attractive platform for developing luminescent functional materials for different applications.
Asunto(s)
Elementos de la Serie de los Lantanoides , Compuestos Organometálicos , Ácidos Ftálicos , Elementos de la Serie de los Lantanoides/química , Compuestos Organometálicos/química , Polímeros/química , Modelos Moleculares , Cristalografía por Rayos X , Ligandos , Ácidos CarboxílicosRESUMEN
Three principal factors may influence the final structure of coordination polymers (CPs): (i) the nature of the ligand, (ii) the type and coordination number of the metal center, and (iii) the reaction conditions. Further, flexible carboxylate aliphatic ligands have been widely employed as building blocks for designing and synthesizing CPs, resulting in a diverse array of materials with exciting architectures, porosities, dimensionalities, and topologies as well as an increasing number of properties and applications. These ligands show different structural features, such as torsion angles, carbon backbone number, and coordination modes, which affect the desired products and so enable the generation of polymorphs or crystalline phases. Additionally, due to their large coordination numbers, using 4f and 5f metals as coordination centers combined with aliphatic ligands increases the possibility of obtaining different crystal phases. Additionally, by varying the synthetic conditions, we may control the production of a specific solid phase by understanding the thermodynamic and kinetic factors that influence the self-assembly process. This revision highlights the relationship between the structural variety of CPs based on flexible carboxylate aliphatic ligands and f-elements (lanthanide and actinides) and their outstanding luminescent properties such as solid-state emissions, sensing, and photocatalysis. In this sense, we present a structural analysis of the CPs reported with the oxalate ligand, as the one rigid ligand of the family, and other flexible dicarboxylate linkers with -CH2- spacers. Additionally, the nature of the luminescence properties of the 4f or 5f-CPs is analyzed, and finally, we present a novel set of CPs using a glutarate-derived ligand and samarium, with the formula [2,2'-bipyH][Sm(HFG)2 (2,2'-bipy) (H2O)2]â¢(2,2'-bipy) (α-Sm) and [2,2'-bipyH][Sm(HFG)2 (2,2'-bipy) (H2O)2] (ß-Sm).
Asunto(s)
Elementos de la Serie de los Lantanoides , Luminiscencia , Ácidos Carboxílicos , Flúor , Elementos de la Serie de los Lantanoides/química , Ligandos , Modelos Moleculares , Polímeros/químicaRESUMEN
This paper reports on the preparation, characterization, and photoluminescence properties of novel hybrid materials, in which the EDTA-Ln-L complexes (where L: H2 O, acac, bzac, dbm, and tta ligands, and Ln: Eu, Gd, and Tb) were covalently linked to the precursor medium molecular weight chitosan surface (CS) matrices or on the chitosan surfaces previously crosslinked with epichlorohydrin (CSech). The emission spectra of these materials were characterized by intraconfigurational-4fN transitions centred on the Eu3+ and Tb3+ ions. Some broad bands from the polymeric matrix were also observed in the emission spectra, however the relative intensities of the intraconfigurational bands increased significantly for systems containing diketonate ligands when the antenna effect became more efficient. The values of the radiative rates (Arad ) were higher for crosslinked hybrid systems with epichlorohydrin, while nonradiative rates (Anrad ) presented the opposite behaviour. These data contributed to an increase in the values of emission quantum efficiency (η) for crosslinked materials. The effect of the modification process and antenna ligand on the values of intensities, intensity parameters Ω2 e Ω4 of the Eu3+ complexes were also investigated. The results showed that the crosslinked biopolymer surfaces have great potential for applications in molecular devices light converters.
Asunto(s)
Biopolímeros/química , Quitosano/química , Complejos de Coordinación/química , Ácido Edético/química , Cetonas/química , Elementos de la Serie de los Lantanoides/química , Ligandos , Luminiscencia , Mediciones LuminiscentesRESUMEN
Fourteen new complexes were obtained from Ln(III)(NO3)3ân-H2O and the chromophores 2-(1H-benzo[d]imidazol-2-yl)-phenol (Bzp1) or 2-(5-methyl-1H-benzo[d]imidazol-2-yl)-phenol (Bzp2). The complete characterization allowed us to assign unequivocally the structures of all the complexes. The techniques used for this purpose were Ultraviolet-Visible (UV-Vis) and Fourier-Transform Infrared (FT-IR) spectroscopies, High-Resolution Mass Spectrometry (HRMS), Magnetic Susceptibility (MS), Elemental Analysis (EA) and Molar Conductivity (MC). HRMS allowed us to find the molecular ion and its isotopic pattern. The FT-IR spectral data suggested that benzimidazolyl-phenol ligands coordinate with Ln(III) ions through iminic nitrogen and phenolic oxygen. Thermogravimetric Analysis (TGA) studies of NdBzp1 and GdBzp2 complexes indicate the presence of lattice water along with three nitrates and two benzimidazolyl-phenol ligands; the thermal decomposition was consistent with the minimal formula suggested by EA. The coordination type of the benzimidazolyl-phenol ligands, the geometry and the structural organization of these coordination complexes have been interpreted by Density Functional Theory (DFT) calculations, and they coincided with the physicochemical data suggesting a coordination number eight for the Ln(III) ions. The cytotoxicity of the chromophores and their coordination complexes was tested against a cancer cell line (HeLa), as compared with structure/support cells (NIH-3T3) and defense cells (J774A.1), revealing that three coordination complexes showed moderate cytotoxicity against the cell lines studied.
Asunto(s)
Bencimidazoles/química , Elementos de la Serie de los Lantanoides/química , Compuestos Organometálicos/síntesis química , Fenoles/química , Células 3T3 , Animales , Supervivencia Celular/efectos de los fármacos , Células Cultivadas , Eritrocitos/efectos de los fármacos , Fibroblastos/efectos de los fármacos , Células HeLa , Humanos , Ratones , Compuestos Organometálicos/farmacología , Compuestos Organometálicos/toxicidadRESUMEN
We show that filamentous fungi can emit green or red light after the accumulation of particulate lanthanide metal-organic frameworks over the cell wall. These new biohybrids present photoluminescence properties that are unaffected by the components of the cell wall. In addition, the fungal cells internalise lanthanide metal-organic framework particles, storing them into organelles, thereby making these materials promising for applications in living imaging studies.
Asunto(s)
Hongos/metabolismo , Microscopía Intravital/métodos , Elementos de la Serie de los Lantanoides/química , Luminiscencia , Estructuras Metalorgánicas/química , Color , Citoplasma/química , Citoplasma/metabolismo , Citoplasma/efectos de la radiación , Estudios de Factibilidad , Hongos/química , Hongos/citología , Hongos/efectos de la radiación , Elementos de la Serie de los Lantanoides/metabolismo , Elementos de la Serie de los Lantanoides/efectos de la radiación , Mediciones Luminiscentes/métodos , Estructuras Metalorgánicas/metabolismo , Estructuras Metalorgánicas/efectos de la radiación , Técnicas Microbiológicas/métodos , Orgánulos/química , Orgánulos/metabolismo , Orgánulos/efectos de la radiación , Rayos UltravioletaRESUMEN
Abstract This paper reports the synthesis and detailed characterization of six novel lanthanide complexes of La(III), Eu(III) and Nd(III) with N(4)-substituted thiosemicarbazones derived from the 2-carboxybenzaldehyde. The IR, 1H-NMR and 13C-NMR spectroscopic studies confirmed the coordination of the thiocarbonyl (C=S), azomethine (C=N) and carboxylate (COO-) groups to the metal centers, and the carboxylate was coordinated in a bidentate manner. The elemental and thermal analyses suggest that lanthanide complexes were formed in 1:2 molar ratios (metal:ligand). The molar conductivity values confirmed the non-electrolytic nature of the complexes. The interaction of these complexes with calf thymus DNA (CT-DNA) was investigated by UV absorption and viscosity measurements. It was found that the Eu(HI) and Nd(nI) complexes could roll along the DNA strands through groove interactions. Furthermore, lanthanide complexes could promote the oxidative cleavage of plasmid pBR322 in a high-oxidative stress environment. Finally, the Schiff base ligands (L) and their complexes were evaluated for their antibacterial activities against gram-positive and gram-negative bacteria using a microdilution procedure. The results indicate that the lanthanide complexes exhibit more potent antibacterial activity than the free ligands.
Resumen Este articulo reporta la síntesis y caracterización detallada de seis nuevos complejos lantánidos de La(III), Eu(III) y Nd(III) con tiosemicarbazonas N(4)-sustituidas derivadas del 2-carboxibenzaldehído. Los estudios espectroscópicos de IR, 1H-NMR y 13C-NMR confirmaron la coordinación de los grupos tiocarbonilo (C=S), azometina (C=N) y carboxilato (COO-) a los centros metálicos, y el carboxilato se coordinó de forma bidentada. Los análisis elemental y térmico sugieren que los complejos lantánidos se formaron en proporciones molares 1:2 (metal:ligando). Los valores de conductividad molar confirmaron la naturaleza no eléctrica de los complejos. Por medio de medidas de absorción UV y de viscosidad se investigó la interacción entre estos complejos con DNA de timo de ternera (CT-DNA). Se encontró que los complejos Eu(III) y Nd(III) podrían correr a lo largo de cadenas de DNA a través de interacciones en el surco. Además, los complejos lantánidos podrían promover el clivaje oxidativo del plásmido pBR322 en un ambiente de alto estrés oxidativo. Finalmente, se evaluaron las actividades antibacteriales de las bases de Schiff como ligandos (L) y sus complejos contra bacterias gram-positivas y gram-negativas usando un procedimiento de microdilución. Los resultados indican que los complejos lantánidos exhiben una actividad antibacterial más potente que los ligandos libres.
Resumo Este artigo reporta a síntese e caracterização detalhada de seis novos complexos lantanídeos de La(III), Eu(III) e Nd(III) com tiosemicarbazonas N(4)-substituídas derivadas do 2-carboxibenzaldeído. Os estudos espectroscópicos de IR, 1H-RMN e 13C-RMN confirmaram a coordenação dos grupos tiocarbonilos (C = S), azometina (C=N) e carboxilato (COO-) com os centros metálicos, e o carboxilato se coordenou de forma bidentada. As análises elementares e térmicas sugerem que os complexos lantanídeos se formaram em proporções molares 1:2 (metal:ligante). Os valores de condutividades molar confirmaram a natureza não-elétrica dos complexos. Se avaliou a interação entre estes complexos com DNA de vitela (CT-DNA) por meio de medidas de absorção UV e de viscosidade. Se observou que os complexos Eu(III) e Nd(III) poderiam deslocar-se ao longo da cadeia de DNA através de interações no sulco. Adicionalmente, os complexos lantanídeos poderiam promover a clivagem oxidativa do plasmídeo pBR322 em um ambiente de alto estresse oxidativo. Finalmente, se avaliaram as atividades antibacterianas das bases de Schiff como ligantes (L) e seus complexos contra bactérias gram-positivas e gram- negativas, usando o método de microdiluição. Os resultados indicam que os complexos lantanídeos exibem uma atividade antibacteriana mais potente que os ligantes livres.
Asunto(s)
Tiosemicarbazonas , ADN , Elementos de la Serie de los Lantanoides/química , AntibacterianosRESUMEN
Two families of accessory proteins, ß and γ, modulate BK channel gating and pharmacology. Notably, in the absence of internal Ca2+, the γ1 subunit promotes a large shift of the BK conductance-voltage curve to more negative potentials. However, very little is known about how α- and γ1 subunits interact. In particular, the association stoichiometry between both subunits is unknown. Here, we propose a method to answer this question using lanthanide resonance energy transfer. The method assumes that the kinetics of lanthanide resonance energy transfer-sensitized emission of the donor double-labeled α/γ1 complex is the linear combination of the kinetics of the sensitized emission in single-labeled complexes. We used a lanthanide binding tag engineered either into the α- or the γ1 subunits to bind Tb+3 as the donor. The acceptor (BODIPY) was attached to the BK pore-blocker iberiotoxin. We determined that γ1 associates with the α-subunit with a maximal 1:1 stoichiometry. This method could be applied to determine the stoichiometry of association between proteins within heteromultimeric complexes.
Asunto(s)
Transferencia Resonante de Energía de Fluorescencia , Elementos de la Serie de los Lantanoides/química , Canales de Potasio de Gran Conductancia Activados por el Calcio/química , Subunidades de Proteína/química , Compuestos de Boro/químicaRESUMEN
A new microporous lanthanide metal-organic framework, {[Yb(BTB)(H2O) (DEF)2}n (1, DEF=N,N-Diethylformamide), with 1D nano-sized channels has been constructed by bridging helical chain secondary building units with 1,3,5-benzenetrisbenzoic acid (H3BTB) ligand. Structural characterization suggests that this complex crystallizes in the hexagonal space group P6122 and possesses 1D triangular channels with coordinated water molecules pointing to the channel center. In addition, anti-myocarditis properties of compound 1 were evaluated in vivo. The results showed that compound 1 can improve hemodynamic parameters of, and it may be a good therapeutic option for heart failure in the future.
Asunto(s)
Antiinflamatorios/química , Cristalografía por Rayos X , Elementos de la Serie de los Lantanoides/química , Estructuras Metalorgánicas/química , Miocarditis/terapia , Animales , Antiinflamatorios/uso terapéutico , Masculino , Estructuras Metalorgánicas/uso terapéutico , Ratones , Modelos Moleculares , Difracción de Polvo , Termogravimetría , Difracción de Rayos XRESUMEN
The metal-organic framework [(La0.9 Sm0.1 )2 (DPA)3 (H2 O)3 ]∞ was synthetized and characterized by X-ray diffractometry, differential thermogravimetric analysis, and infrared spectroscopy. The material was tested for the development and validation of a matrix solid-phase dispersion procedure for extraction of atrazine, bifenthrin, bromuconazole, clofentezine, fenbuconazole, flumetralin, procymidone, and pirimicarb, from peppers, with analysis using gas chromatography with mass spectrometry in the selected ion monitoring mode. The method developed was linear over the range tested (50.0-1000.0 µg/kg for procymidone and 200.0-1000.0 µg/kg for all other pesticides), with correlation coefficients ranging from 0.9930 to 0.9992. Experiments were carried out at 250.0, 500.0, and 1000.0 µg/kg fortification levels, and resulted in recoveries in the range of 52.7-135.0%, with coefficient of variation values between 5.2 and 5.4%, respectively, for [(La0.9 Sm0.1 )2 (DPA)3 (H2 O)3 ]∞ sorbent. Detection and quantification limits ranged from 16.0 to 67.0 µg/kg and from 50.0 to 200.0 µg/kg, respectively, for the different pesticides studied. The results were compared with literature data. The developed and validated method was applied to real samples. The analysis detected the presence of residues of pesticides procymidone, fenbuconazole, flumetralin, clofentezine, atrazine, and bifenthrin.
Asunto(s)
Capsicum/química , Elementos de la Serie de los Lantanoides/química , Estructuras Metalorgánicas/química , Plaguicidas/aislamiento & purificación , Extracción en Fase Sólida , Compuestos de Anilina/química , Compuestos de Anilina/aislamiento & purificación , Atrazina/química , Atrazina/aislamiento & purificación , Compuestos Bicíclicos con Puentes/química , Compuestos Bicíclicos con Puentes/aislamiento & purificación , Carbamatos/química , Carbamatos/aislamiento & purificación , Clorobencenos/química , Clorobencenos/aislamiento & purificación , Furanos/química , Furanos/aislamiento & purificación , Cromatografía de Gases y Espectrometría de Masas , Estructuras Metalorgánicas/síntesis química , Nitrilos/química , Nitrilos/aislamiento & purificación , Plaguicidas/química , Piretrinas/química , Piretrinas/aislamiento & purificación , Pirimidinas/química , Pirimidinas/aislamiento & purificación , Triazoles/química , Triazoles/aislamiento & purificaciónRESUMEN
A new microporous lanthanide metal-organic framework, {[Yb(BTB)(H2O) (DEF)2}n (1, DEF=N,N-Diethylformamide), with 1D nano-sized channels has been constructed by bridging helical chain secondary building units with 1,3,5-benzenetrisbenzoic acid (H3BTB) ligand. Structural characterization suggests that this complex crystallizes in the hexagonal space group P6122 and possesses 1D triangular channels with coordinated water molecules pointing to the channel center. In addition, anti-myocarditis properties of compound 1 were evaluated in vivo. The results showed that compound 1 can improve hemodynamic parameters of, and it may be a good therapeutic option for heart failure in the future.
Asunto(s)
Animales , Masculino , Ratones , Antiinflamatorios/química , Cristalografía por Rayos X , Elementos de la Serie de los Lantanoides/química , Estructuras Metalorgánicas/química , Miocarditis/terapia , Antiinflamatorios/uso terapéutico , Estructuras Metalorgánicas/uso terapéutico , Modelos Moleculares , Difracción de Polvo , Termogravimetría , Difracción de Rayos XRESUMEN
The high interest in lanthanide chemistry, and particularly in their luminescence, has been encouraged by the need of understanding the lanthanide chemical coordination and how the design of new luminescent materials can be affected by this. This work is focused on the understanding of the electronic structure, bonding nature, and optical properties of a set of lanthanide hexaaza macrocyclic complexes, which can lead to potential optical applications. Here we found that the DFT ground state of the open-shell complexes are mainly characterized by the manifold of low lying f states, having small HOMO-LUMO energy gaps. The results obtained from the wave function theory calculations (SO-RASSI) put on evidence the multiconfigurational character of their ground state and it is observed that the large spin-orbit coupling and the weak crystal field produce a strong mix of the ground and the excited states. The electron localization function (ELF) and the energy decomposition analysis (EDA) support the idea of a dative interaction between the macrocyclic ligand and the lanthanide center for all the studied systems; noting that, this interaction has a covalent character, where the d-orbital participation is evidenced from NBO analysis, leaving the f shell completely noninteracting in the chemical bonding. From the optical part we observed in all cases the characteristic intraligand (IL) (π-π*) and ligand to metal charge-transfer (LMCT) bands that are present in the ultraviolet and visible regions, and for the open-shell complexes we found the inherent f-f electronic transitions on the visible and near-infrared region.
Asunto(s)
Electroquímica , Elementos de la Serie de los Lantanoides/química , Compuestos Macrocíclicos/química , Teoría Cuántica , Electrones , Modelos Moleculares , Estructura MolecularRESUMEN
Although the {CaMn4O5} oxygen evolving complex (OEC) of photosystem II is a major paradigm for water oxidation catalyst (WOC) development, the comprehensive translation of its key features into active molecular WOCs remains challenging. The [Co(II)3Ln(hmp)4(OAc)5H2O] ({Co(II)3Ln(OR)4}; Ln = Ho-Yb, hmp = 2-(hydroxymethyl)pyridine) cubane WOC series is introduced as a new springboard to address crucial design parameters, ranging from nuclearity and redox-inactive promoters to operational stability and ligand exchange properties. The {Co(II)3Ln(OR)4} cubanes promote bioinspired WOC design by newly combining Ln(3+) centers as redox-inactive Ca(2+) analogues with flexible aqua-/acetate ligands into active and stable WOCs (max. TON/TOF values of 211/9 s(-1)). Furthermore, they open up the important family of 3d-4f complexes for photocatalytic applications. The stability of the {Co(II)3Ln(OR)4} WOCs under photocatalytic conditions is demonstrated with a comprehensive analytical strategy including trace metal analyses and solution-based X-ray absorption spectroscopy (XAS) investigations. The productive influence of the Ln(3+) centers is linked to favorable ligand mobility, and the experimental trends are substantiated with Born-Oppenheimer molecular dynamics studies.
Asunto(s)
Cobalto/química , Elementos de la Serie de los Lantanoides/química , Compuestos Organometálicos/química , Agua/química , Catálisis , Ligandos , Modelos Moleculares , Estructura Molecular , Oxidación-ReducciónRESUMEN
The RM1 model for the lanthanides is parameterized for complexes of the trications of lanthanum, cerium, and praseodymium. The semiempirical quantum chemical model core stands for the [Xe]4fn electronic configuration, with n =0,1,2 for La(III), Ce(III), and Pr(III), respectively. In addition, the valence shell is described by three electrons in a set of 5d, 6s, and 6p orbitals. Results indicate that the present model is more accurate than the previous sparkle models, although these are still very good methods provided the ligands only possess oxygen or nitrogen atoms directly coordinated to the lanthanide ion. For all other different types of coordination, the present RM1 model for the lanthanides is much superior and must definitely be used. Overall, the accuracy of the model is of the order of 0.07Å for La(III) and Pr(III), and 0.08Å for Ce(III) for lanthanide-ligand atom distances which lie mostly around the 2.3Å to 2.6Å interval, implying an error around 3% only.
Asunto(s)
Cerio/química , Lantano/química , Modelos Químicos , Praseodimio/química , Algoritmos , Elementos de la Serie de los Lantanoides/químicaRESUMEN
Three new layered metal-organic frameworks (MOFs) based on 2-phenylsuccinic acid (H2psa) and lanthanide ions with the formula [Ln2(C10H8O4)3(H2O)] (Ln = Eu, Sm and Eu-Gd) have been synthesized under solvothermal conditions and fully characterized by single-crystal X-ray diffraction, thermal and vibrational analyses. The compounds are isostructural featuring 2D frameworks that consist of infinite zigzag chains composed of [LnO8] and [LnO8(H2O)] edge-sharing polyhedra linked by psa ligands leading to layers further connected by weak π-π interactions in an edge orientation. Moreover, a topological study was carried out to obtain the simplified net for better comparison with structurally related compounds. The crystals were exfoliated into nanolayers after miniaturization by addition of sodium acetate as a capping agent in the reaction medium. Scanning electron microscopy was applied to characterize the miniaturized samples whereas the exfoliated hybrid nanosheets were studied by atomic force microscopy. The photoluminescence (PL) properties of the bulk compounds as well as the miniaturized and exfoliated materials were investigated and compared with other related ones. An exhaustive study of the Eu(iii)-based MOFs was performed on the basis of the obtained PL parameters (excitation and emission spectra, kr, knr, intrinsic quantum yields and lifetimes) to explore the underlying structure-property relationships.
Asunto(s)
Elementos de la Serie de los Lantanoides/química , Luminiscencia , Succinatos/química , Cristalografía por Rayos XRESUMEN
Solid-state compounds of the general formulae [ML3] (M=Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y; L=ketoprofen) were synthesized and characterized using infrared, diffuse reflectance and luminescence spectroscopies. IR data suggested that the carboxylate group in ketoprofen is coordinated to the metals as a bidentate ligand. The triplet state energy level was determined using the Gd(3+) complex, which exhibited a ketoprofen blue luminescence when excited in the UV region. The compound containing Tb(3+) ion was sensitized by the ligand and emitted in the green region of the visible spectrum. On the other hand, for the analogous species containing the dysprosium ion, a competition for luminescence between the Dy(3+) and the ligand levels was observed. Finally, Tm(3+) complex exhibits only ligand luminescence. These optical behaviors are discussed based on rare earth energy diagrams. In addition, the compounds were evaluated for their anti-inflammatory activities. All the compounds showed a higher production of H2O2 and IL-10 than the ketoprofen, suggesting that the compounds exhibited an immunomodulatory effect and this opens up new perspectives for immunotherapeutic approaches.
Asunto(s)
Antiinflamatorios no Esteroideos/farmacología , Cetoprofeno/farmacología , Elementos de la Serie de los Lantanoides/química , Itrio/química , Células Cultivadas , Humanos , Técnicas In Vitro , Luminiscencia , Espectrofotometría InfrarrojaRESUMEN
Complexes of dysprosium, holmium, and erbium find many applications as single-molecule magnets, as contrast agents for magnetic resonance imaging, as anti-cancer agents, in optical telecommunications, etc. Therefore, the development of tools that can be proven helpful to complex design is presently an active area of research. In this article, we advance a major improvement to the semiempirical description of lanthanide complexes: the Recife Model 1, RM1, model for the lanthanides, parameterized for the trications of Dy, Ho, and Er. By representing such lanthanide in the RM1 calculation as a three-electron atom with a set of 5 d, 6 s, and 6 p semiempirical orbitals, the accuracy of the previous sparkle models, mainly concentrated on lanthanide-oxygen and lanthanide-nitrogen distances, is extended to other types of bonds in the trication complexes' coordination polyhedra, such as lanthanide-carbon, lanthanide-chlorine, etc. This is even more important as, for example, lanthanide-carbon atom distances in the coordination polyhedra of the complexes comprise about 30% of all distances for all complexes of Dy, Ho, and Er considered. Our results indicate that the average unsigned mean error for the lanthanide-carbon distances dropped from an average of 0.30 Å, for the sparkle models, to 0.04 Å for the RM1 model for the lanthanides; for a total of 509 such distances for the set of all Dy, Ho, and Er complexes considered. A similar behavior took place for the other distances as well, such as lanthanide-chlorine, lanthanide-bromine, lanthanide, phosphorus and lanthanide-sulfur. Thus, the RM1 model for the lanthanides, being advanced in this article, broadens the range of application of semiempirical models to lanthanide complexes by including comprehensively many other types of bonds not adequately described by the previous models.
Asunto(s)
Complejos de Coordinación/química , Elementos de la Serie de los Lantanoides/química , Modelos Moleculares , Conformación Molecular , Algoritmos , Disprosio/química , Erbio/química , Holmio/química , Teoría CuánticaRESUMEN
New anionic complexes of lanthanide picrates containing 1-ethyl-3-methylimidazolium (EMIm) as countercation have been prepared. The Ln(III) complexes were characterized by complexometric titration, elemental analyses, infrared spectroscopy and molar conductivity. The molecular structures of the (EMIm)2[Ln(Pic)4(H2O)2]Pic complexes, Ln(III)=Sm, Eu, Gd and Tb, and Pic=picrate, were determined by X-ray crystallography. In these structures the picrate anion appears in three forms: as uncoordinated counteranion, as monodentated and bidentate ligand. The coordination polyhedron around the Ln(III) atom can be described as tricapped trigonal prismatic molecular geometry. The theoretical molecular structures of the complexes were also calculated using the Sparkle/PM3 model for Ln(III) complexes, allowing analysis of intramolecular energy transfer processes of the Eu(III) compound. The spectroscopic properties of the 4f(6) intraconfigurational transitions of the Eu(III) complex were then studied experimentally and theoretically. The low value of emission quantum efficiency of (5)D0 emitting level (η) of Eu(III) ion (ca. 10%) is due to the vibrational modes of the water molecule that act as luminescence quenching. In addition, the luminescence decay curves, the experimental intensity parameters (Ωλ), lifetimes (τ), radiative (Arad) and non-radiative (Anrad) decay rates, theoretical quantum yield (q) were also determined and discussed.
Asunto(s)
Imidazoles/química , Elementos de la Serie de los Lantanoides/química , Luminiscencia , Picratos/química , Cristalización , Cristalografía por Rayos X , Transferencia de Energía , Líquidos Iónicos , Elementos de la Serie de los Lantanoides/metabolismo , Modelos Químicos , Modelos Teóricos , Picratos/metabolismoRESUMEN
A 1:1 complex between 3,3'-dihydroxyflavone (DHF) and La(III) (DHF-La(III)) is formed in methanolic solution with the relatively high apparent stability constant value of 2.3×10(6) and a calculated standard entropy change of 88.2 J mol(-1) K(-1), both at 25 °C. The photophysical properties of the complex and the free flavonoid are discussed in comparison to the well known related compound 3-hydroxyflavone. The ligand photogenerates O2((1)Δg) by energy transfer from its excited triplet state ((3)DHF(*)) to dissolved ground state oxygen, with a quantum yield of 0.13. (3)DHF(*) is quenched by La(III) with a rate constant close to the diffusion-controlled value. The respective abilities of the free flavonoid and DHF-La(III) as quenchers of the riboflavin-photogenerated reactive oxygen species singlet molecular oxygen (O2((1)Δg)) and superoxide radical anion (O2(-)) have been investigated. Both individual compounds were photoirradiated with visible light in the presence of the flavin as the only light-absorbing compound. A detailed kinetics and mechanistic study employing polarographic monitoring of oxygen uptake and time resolved detection of O2((1)Δg) phosphorescence indicates that DHF and the complex react with O2((1)Δg) and O2(-) by a non simple mechanism. The former deactivates O2((1)Δg) in a predominant physical fashion, a fact that constitutes a desirable property for antioxidants. It was found that metal chelation greatly enhances the ability of DHF as an overall O2((1)Δg) quencher.
Asunto(s)
Complejos de Coordinación/química , Flavonoides/química , Elementos de la Serie de los Lantanoides/química , Especies Reactivas de Oxígeno/química , Estructura Molecular , Riboflavina/químicaRESUMEN
This work reports on the photoluminescent properties of three new lanthanide complexes with acetoacetanilide (aaa), a ß-diketonate ligand. The complexes have the general molecular formulae [RE(aaa)3(H2O)], they are soluble in organic solvents such as ethanol and chloroform and insoluble in water. The energy of the triplet state was determined at about 4,700 cm(-1) higher than the (5)D4 emitting level of the Tb(III) ion, leading to an absolute quantum yield of 22% for the [Tb(aaa)3(H2O)] complex. The photoluminescent properties were studied and the luminescence parameters of the [Eu(aaa)3(H2O)] complex were experimentally determined. The photostabilities of the complexes under continuous UV irradiation were measured and the data indicate low stability of the [Tb(aaa)3(H2O)] complex when the system is excited at the band attributed to energy transfer from the ligand to terbium(III) ion. However, its photostability is significantly improved under inert atmosphere.
Asunto(s)
Acetanilidas/química , Complejos de Coordinación/química , Complejos de Coordinación/síntesis química , Elementos de la Serie de los Lantanoides/química , Luminiscencia , Factores de Tiempo , Rayos UltravioletaRESUMEN
The synthesis, crystal structure, and dielectric properties of four novel members of the family of double perovskites Pb(2)LnSbO(6) are described. The room-temperature crystal structures were refined from neutron powder diffraction (NPD) data in the monoclinic C2/c (No. 15) space group. They contain a completely ordered array of alternating LnO(6) and SbO(6) octahedra sharing corners, tilted in antiphase along the three pseudocubic axes, with a a(-)b(-)b(-) tilting scheme, which is very unusual in the crystallochemistry of perovskites. The lead atoms occupy highly asymmetric voids with 8-fold coordination due to the stereoactivity of the Pb(2+) electron lone-pair. Several trends are observed for the entire family of compounds upon heating. The Ln = Lu, Yb, and Er oxides display three successive phase transitions in a narrow temperature range, as shown by differential scanning calorimetry (DSC) data, while the Ln = Ho shows only two transitions. Different crystal structure evolutions have been found from temperature-dependent NPD and DSC, following the space-group sequence C2/c â P2(1)/n â R Ì 3 â Fm Ì 3m for Ln = Lu and Yb, the sequence C2/c â unknown â P2(1)/n â Fm Ì 3m for Ln = Er, and C2/c â P2(1)/n â Fm Ì 3m for Ln = Ho. The Ln/Sb long-range ordering is preserved across the consecutive phase transitions. Dielectric permittivity measurements indicate the presence of a paraelectric/antiferroelectric transition (associated with the last structural transition), as suggested by the negative Curie temperature from the Curie-Weiss fit of the reciprocal permittivity.