Eu Compounds Research Articles

Magnetic properties of RCoO3 cobaltites (R = La, Pr, Nd, Sm, Eu). Effects of hydrostatic and chemical pressure

We have investigated the temperature dependence of the magnetic susceptibility χ(T) of rare-earth cobaltites RCoO3 (R = La, Pr, Nd, Sm, Eu) in the temperature range 4.2–300 K and also the influence of hydrostatic pressure up to 2 kbar on their susceptibility at fixed temperatures T = 78 and 300 K. The specific dependence χ(T) observed in LaCoO3 and the anomalously large pressure effect (dln χ/dP ∼−100 Mbar−1 for T = 78 K) are analyzed in the framework of a two-level model with energy levels difference Δ. The ground state of the system is assumed to be nonmagnetic with the zero spin of Co3+ ions, and magnetism at a finite temperature is determined by the excited magnetic spin state. The results of the analysis, supplemented by theoretical calculations of the electronic structure of LaCoO3, indicate a significant increase in Δ with a decrease in the unit cell volume under the hydrostatic pressure. In the series of RCoO3 (R = Pr, Nd, Sm, Eu) compounds, the volume of crystal cell decreases monotonically due to a decrease in the radius of R3+ ions. This leads to an increase in the relative energy Δ of the excited state (the chemical pressure effect), which manifests itself in a decrease in the contribution of cobalt ions to the magnetic susceptibility at a fixed temperature, and also in a decrease in the hydrostatic pressure effect on the susceptibility of RCoO3 compounds, which we have observed at T = 300 K.

Thermodynamic investigations on K3Ln5(PO4)6 (Ln = Eu and Gd) compounds

Complex phosphates, such as K3Ln5(PO4)6 are considered as promising materials for immobilization of radioactive waste as well as for selective separation of radio nuclides from nuclear waste. In this paper, we report detail thermodynamic properties of phosphate compounds viz., K3Eu5(PO4)6 and K3Gd5(PO4)6 measured by calorimetric techniques. The standard molar heat capacity of these compounds has been measured in the temperature range 2–300 K by PPMS and 325 to 935 by high temperature Calvet calorimeter. The heat capacities and standard molar entropies of K3Eu5(PO4)6 and K3Gd5(PO4)6 at 298 K are: 688.0, 560.3 J K−1mol−1 and 792.7, 683.7 J K−1mol−1, respectively. The standard molar enthalpy of formation of K3Eu5(PO4)6, and K3Gd5(PO4)6 determined employing high temperature solution calorimeter are found to be −12234.8 ± 61.5 and −11790.9 ± 58.2 kJ mol−1, respectively. The temperature dependent standard molar free energy of formation and other thermodynamic functions for the compounds have been derived from above heat capacity and enthalpy of formation data.

A Eu and Tb co-doped MOF-5 compound for ratiometric high temperature sensing

In this work, a new Eu and Tb co-doped luminescent compound based on MOF-5, [Zn4O(BDC)3], (named as compound 1) was successfully synthesized. The structure and morphology characterizations demonstrate that the initial framework of MOF-5 is retained well after co-doping Eu and Tb. The systematic investigations of photoluminescence behaviors reveal that the heat-treated compound 1 (called as compound 1a) can be utilized as a multi-channel readout luminescent thermometer in emission intensity ratio, decay time ratio, and luminescence color. It simultaneously exhibits the excellent repetitiveness and reversibility under high temperature region from 303 to 473 K. The relative sensitivity of 1.8%/K at 473 K is much higher than the best one of 1.19%/K previously reported for the mixed-lanthanide MOF Tb0.8Eu0.2BPDA. Until now, such a ratiometric luminescent thermometer with a high sensitivity at the temperature as high as 473 K has been rarely explored.

Single Crystal Growth and Study of the Ferromagnetic Superconductor RbEuFe4As4

RbEuFe4As4 exhibits both superconducting order in the FeAs layers and ferromagnetic order in the Eu layers, providing a good platform to study the interaction and microscopic coexistence of these two traditionally incompatible orders. Growing high-quality RbEuFe4As4 single crystals is essential to investigate these phenomena at a deeper level. Here we report the successful growth of the RbEuFe4As4 single crystals with millimeter-size dimensions using a RbAs flux. The high-quality crystals were characterized via resistivity, magnetization, and heat capacity measurements. Single crystal X-ray diffraction data refinements reveal almost regular FeAs4 tetrahedra (As1–Fe–As1 = 108.60(7)°, As2–Fe–As2 = 109.01(8)°, and As1–Fe–As2 = 109.81(2)°) in RbEuFe4As4, providing structural support for the highest superconducting transition temperature (Tc = 36.8 K) among all known AAeFe4As4 (A = K, Rb, Cs; Ae = Ca, Sr, Eu) compounds. Our flux method using RbAs can also be employed to grow other desired transition metal comp...

Synthesis, characterization and cell imaging properties of rare earth compounds based on hydroxamate ligand

Six binuclear rare earth compounds were synthesized through the ligand of 4-Bromo-N-hydroxy-N-methyl-benzamide (sH2bha). Compounds 1–3 are isomorphous, and compound 1 is crystallized in the monoclinic system with the P21/c space group. Compounds 4 and 5 are isomorphous, and compound 4 is crystallized in the triclinic system with the P-1 space group. Compound 6 is crystallized in the triclinic system with the P-1 space group. The compounds were characterized by thermogravimetric analysis (TGA) and IR spectroscopy. The fluorescence spectrum in the visible area shows characteristic peaks of Eu, Tb, and Dy compounds. The efficiency of Eu compound on the viability of PC3 cells was assessed using CCK8 assays. From the CCK8 results, ionic concentration may have a great effect on PC3 cells' proliferation. Eu compound shows red fluorescence in the cytoplasm of PC3 cell. As for Eu compound, it might have potential application in cell imaging technology.

Frustrated antiferromagnetic honeycomb-tunnel-like latticeCuR2Ge2O8(R=Pr, Nd, Sm, and Eu)

New frustrated antiferromagnetic compounds CuRE2Ge2O8 (RE=Pr, Nd, Sm, Eu) have been investigated using high-resolution x-ray diffraction, magnetic and heat capacity measurements. These systems show different magnetic lattices depending on rare-earth element. The nonmagnetic Eu compound is a S=1/2 two-dimensional triangular antiferromagnetic lattice oriented in the ac plane with geometrical frustration. On the other hand, the Pr, Nd, and Sm compounds show a three-dimensional honeycomb-tunnel-like lattice made of RE^3+ running along the a axis with the characteristic behavior of frustrated antiferromagnets.

Sodium naphthalenide reduction of 1,3–diphenyl–6–(tert-butyl) fulvene: Stabilizing Eu2+ with a sterically demanding ansa–ligand framework

Stereoselective syntheses of three new rac di–(tert–butyl)ethano bridged metallocene compounds of Yb, Eu and Sm were carried out by a unique strategy involving hydrocarbon radical anion coupling of a trisubstituted pentafulvene followed by incorporation of the metal by K+ salt metathesis reactions. Reductive coupling of 1,3–diphenyl–6–(tert-butyl) fulvene with sodium naphthalenide gave the corresponding bis(cyclopentadiene) ansa–ligand precursor rac–[(CHBut)2(Ph2C5H3)2] HL. Subsequent reaction of HL with KN(SiMe3)2 afforded the corresponding di–potassium salt complex [(CHBut)2(Ph2C5H2)2]K2(THF)31. Reactions of 1 with LnI2 (Ln = Yb, Eu, Sm) afforded new lanthanide ansa–metallocenes, [(CHBut)2(Ph2C5H2)]2Yb(DME) 2, [(CHBut)2(Ph2C5H2)]2Eu(DME)23 and [(CHBut)2(Ph2C5H2)]2Sm(DME)24 in good yields. The ansa–europocene 3 is the first example of a Eu2+ ion complexed by an ethano–bridged cyclopentadienyl ligand. This work underscores the usefulness of hydrocarbon radical anion coupling in the construction of sterically demanding Ph2Cp based ansa–ligand frameworks for d- and f-block metallocenes.

Observation of bond enthalpy dependence of insulating character in rare earth substituted BiFeO3

The temperature dependence of impedance and dielectric properties of BiFeO3 (BFO) and Bi0.90R0.10FeO3 (where R = La, Nd, Eu, Gd and Ho) compounds were investigated. The detailed impedance studies indicated that substitution of rare earth elements significantly enhanced the insulating character of BFO. The enhancement of insulating character was attributed to the improved grain and grain boundary resistances in the substituted compounds. A systematic variation of grain and grain boundary resistances, relaxation times and activation energies in Bi0.90R0.10FeO3 compounds was observed and explained based on the concept of bond enthalpy. The dielectric anomaly in BFO around the temperature 493 K got suppressed with the substitution of rare earth elements and the amount of suppression was discussed on the strength of R–O bond enthalpies. The impedance, ac conductivity and dielectric data corroborated with the idea that the insulating character in Bi0.90R0.10FeO3 compounds was strongly dependent on the strength of bond enthalpies of R–O bonds.

Four New 3D Metal–Organic Frameworks Constructed by a V-shaped Tetracarboxylates Ligand: Selective CO2 Sorption and Luminescent Sensing

Employing a V-shaped rigid multicarboxylate ligand 1,3-di(2′,5′-dicarboxypheny)benzene acid (H4L), three microporous metal–organic frameworks (MOFs), H2[Co4(O)L2(H2O)2]·3DMA·8H2O (1), H3[Zn2.5L2]·NMP·5H2O (2), and H3[Cd2.5L2]·4DMF·3H2O (3) were synthesized and characterized. Compound 1 exhibits a cage-based (3,6)-connected rtl topological MOF with [Co4O(COO)8] clusters and highly selective adsorption of CO2 over CH4. Compounds 2 and 3 are isostructural and display a rare 4,8-connected flu net with linear trinuclear [Zn3(COO)6] clusters. Interestingly, when compound 3 was soaked in DMF solution containing Eu3+ ions, an Eu-loaded compound Eu@3 with bright red fluorescence was obtained, which reveals highly selective sensing for Cu2+, Fe3+, and Cr2O72– ions. This represents an unusual example to achieve the detection of Cu2+, Fe3+, and Cr2O72– ions simultaneously by fluorescence spectrometry based on a recyclable Eu-loaded MOF sensor.

Evolution of magnetism in LnCuGa3 (Ln = La–Nd, Sm–Gd) studied via μSR and specific heat

Muon spin rotation/relaxation (μSR) and specific heat measurements are presented for polycrystalline LnCuGa3, with Ln=La–Nd, and Sm–Gd. All materials undergo magnetic ordering transitions, apart from non-magnetic LaCuGa3, and PrCuGa3, which shows the onset of short range correlations below 3K but no long-range magnetic order down to T=25mK. While magnetic order in the Ce and Nd compounds is incommensurate with the lattice, the order is commensurate for the Sm and Eu compounds. The strong damping in GdCuGa3 prevents us from determining the nature of magnetism in that system. SmCuGa3 exhibits two precessional frequencies, which appear at different temperatures, suggesting inhomogeneous magnetic ordering or a second magnetic/structural phase transition.

Orthoborates LiCdRE5(BO3)6 (RE = Sm-Lu and Y) with Rare-Earth Ions on a Triangular Lattice: Synthesis, Crystal Structure, and Optical and Magnetic Properties.

Single crystals of LiCdY5(BO3)6 were successfully grown from a Li2O-B2O3 flux, and its lanthanide homotypic compounds, LiCdRE5(BO3)6 (RE = Sm-Lu), have been prepared by solid-state reaction. They crystallize in the noncentrosymmetric space group P6522 with cell parameters in the ranges of a = 7.0989(2)-6.9337(1) Å and c = 25.9375(1)-24.8960(6) Å. As a representative example, LiCdY5(BO3)6 features a triangular lattice in the ab plane composed of three distinct crystallographic Y sites. The triangular lattices spaced with the same distance of [Formula: see text]c are further stacked to build three-dimensional frameworks by reinforcement of the isolated planar BO3 groups and distorted LiO4 tetrahedra. Magnetic measurements show that Eu and Sm compounds exhibit typical Van Vleck-type paramagnetism and other rare-earth borates show weak antiferromagnetic behavior. In addition, UV-vis-near-IR diffuse-reflectance and photoluminescence spectra were performed to understand the transition energy levels of active rare-earth ions and their relationships to magnetism.

Microscopic Approach to the Magnetoelectric Coupling in RCrO3 (R = Y, La, Lu and Eu) Compounds

Microscopic Approach to the Magnetoelectric Coupling in RCrO3 (R = Y, La, Lu and Eu) Compounds

Unusual Mixed Valence of Eu in Two Materials-EuSr2Bi2S4F4 and Eu2SrBi2S4F4: Mössbauer and X-ray Photoemission Spectroscopy Investigations.

We have synthesized two new Eu-based compounds, EuSr2Bi2S4F4 and Eu2SrBi2S4F4, which are derivatives of Eu3Bi2S4F4, an intrinsic superconductor with Tc = 1.5 K. They belong to a tetragonal structure (SG: I4/mmm, Z = 2), similar to the parent compound Eu3Bi2S4F4. Our structural and 151Eu Mössbauer spectroscopy studies show that, in EuSr2Bi2S4F4, Eu-atoms exclusively occupy the crystallographic 2a-sites. In Eu2SrBi2S4F4, 2a-sites are fully occupied by Eu-atoms and the other half of Eu-atoms and Sr-atoms together fully occupy 4e-sites in a statistical distribution. In both compounds Eu atoms occupying the crystallographic 2a-sites are in a homogeneous mixed valent state ∼2.6-2.7. From our magnetization studies in an applied H ≤ 9 T, we infer that the valence of Eu-atoms in Eu2SrBi2S4F4 at the 2a-sites exhibits a shift toward 2+. Our XPS studies corroborate the occurrence of valence fluctuations of Eu and after Ar-ion sputtering show evidence of enhanced population of Eu2+-states. Resistivity measurements, down to 2 K, suggest a semimetallic nature for both compounds.

Unique Electronic States in Non-centrosymmetric Cubic Compounds

We succeeded in growing single crystals of \(\hbox {Yb}_{4}\hbox {Sb}_{3}\), Ullmannite(NiSbS)-type compounds, \(\hbox {Pd}_{3}\hbox {Bi}_{2}\hbox {Si}_{2}\), EuPtSi, and EuPtGe with the non-centrosymmetric cubic structures by the Bridgman method. Split Fermi surface properties are clarified for \(\hbox {Yb}_{4}\hbox {Sb}_{3}\) and \(\hbox {Pd}_{3}\hbox {Bi}_{2}\hbox {Si}_{2}\). As for EuPtSi and EuPtGe with the cubic chiral structure, we observed the first-order like antiferromagnetic ordering at the Neel temperatures \(T_N=4.0\,{\rm K}\) and 3.4 K, respectively, which are small in magnitude compared with ordering temperatures of 10–100 K in the usual divalent Eu compounds, reflecting the frustration of spins in the chiral structure.

Electron interactions, spin-orbit coupling, and intersite correlations in pyrochlore iridates

We perform combined density functional and dynamical mean-field calculations to study the pyrochlore iridates Lu$_2$Ir$_2$O$_7$, Y$_2$Ir$_2$O$_7$ and Eu$_2$Ir$_2$O$_7$. Both single-site and cluster dynamical mean-field calculations are performed and spin-orbit coupling is included. Paramagnetic metallic phases, antiferromagnetic metallic phases with tilted Weyl cones and antiferromagnetic insulating phases are found. The magnetic phases display all-in/all-out magnetic ordering, consistent with previous studies. Unusually for electronically three dimensional materials, the single-site dynamical mean-field approximation fails to reproduce qualitative material trends, predicting in particular that the paramagnetic phase properties of Y$_2$Ir$_2$O$_7$ and Eu$_2$Ir$_2$O$_7$ are almost identical, although in experiments the Y compound has a much higher resistance than the Eu compound. This qualitative failure is attributed to the importance of intersite magnetic correlations in the physics of these materials.

Synthesis and photoluminescence of Eu(III) complex compounds containing anions of perfluoro-3-methylbenzoic acid

Photoluminescent Eu(III) compounds with anions of the acid 3-CF3C6F4COOH (LH) of composition Eu(L)3·2H2O and Eu(phen)(L)3 were synthesized. The photoluminescence intensity of the complex Eu(phen)(L)3 is higher than that of a similar Eu(III) complex containing anions of the acid 4-CF3C6F4COOH as ligands.

Gadolinium(III)-sensitized fluorescence of europium in its mixed-metal compounds with trifluroacetate

The fluorescence properties of mixed-metal compounds of Eu(III) and Gd(III) with trifluoroacetic acid, Eu1−хGdx(С2F3O2)3·yD·zH2O, where D − 1,10-phenanthroline, 2,2-dipyridil, diphenylguanidine, x = 0, 0.25, 0.5, or 0.7, were studied. Luminescence spectroscopic evidence and the examination of excitation spectra indicate the occurrence of efficient energy transfer from the gadolinium to the europium ion. The greatest promotion of Eu3+ photoluminescence at 615 nm is observed when Eu:Gd = 1:1.

Lanthanide compounds as catalysts for the one-step synthesis of vinyl chloride from ethylene

The industrial manufacture of vinyl chloride relies on a two-step process involving CuCl2-catalyzed ethylene oxychlorination to ethylene dichloride followed by thermal cracking of the latter to vinyl chloride. This work evaluates a wide range of commercial and self-prepared lanthanide (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Er) compounds for the one-step production of vinyl chloride from ethylene in a fixed-bed reactor at 623–773K and 1bar using feed ratios of C2H4:HCl:O2:Ar:He=3–6:1–9.6:1–7:3:80–92 and space times of 6–252ghmol−1 (based on ethylene). Ex situ characterization by X-ray diffraction, electron microscopy, and X-ray photoelectron spectroscopy reveals that the oxide forms of all compounds, except CeO2, transform into their respective (oxy)chloride. Among all studied systems, CeO2 shows the highest activity but suffers from combustion forming COx, while europium oxychloride (EuOCl) leads to the best vinyl chloride selectivity of 96% at 20% C2H4 conversion for over 100h on stream. Temperature-programmed reduction with H2, temperature-programmed desorption of NH3, and oxidation tests (C2H4, CO, and HCl oxidation) unravel the unique balance of mild redox and enhanced acid properties of EuOCl compared to CeO2, which suppress over-oxidation and boost ethylene dichloride dehydrochlorination. Strategies to couple the excellent selectivity of EuOCl with the high activity of CeO2 are demonstrated through the synthesis of homogeneous europium-cerium mixed oxides, combining two functions on a single surface. In addition, the engineering of a dual-bed reactor, integrating a CeO2 bed first to produce ethylene dichloride in high yield which is subsequently transformed to vinyl chloride over EuOCl leads to vinyl chloride yields of up to 30% per pass. These very promising findings constitute a crucial step for process intensification of polyvinyl chloride production and exploring the potential of rare-earth compounds in industrially-relevant reactions.

Liposome Biodistribution via Europium Complexes.

The drug delivery field needs tools to follow vector biodistribution. Radioactive tracers and conventional fluorophores are widely used. We propose here to use europium complexes. Use of pulsed light source time-resolved fluorimetry takes into account the fluorescence decay time of the lanthanide chelates to gain sensitivity in biological media. The method was developed to follow liposome biodistribution. Octadecyl-DTPA.Eu compound has been prepared and incorporated into liposomes without alteration of its fluorescence signal. The method has been validated by comparison with fluorophore-labeled liposomes. The way to proceed to use this method for liposomes or other vectors is detailed.

(Pc)Eu(Pc)Eu[trans-T(COOCH3)2PP]/GO Hybrid Film-Based Nonenzymatic H2O2 Electrochemical Sensor with Excellent Performance.

A facile approach was developed for preparing the multilayer hybrid films of mixed (phthalocyaninato) (porphyrinato) europium(III) triple-decker compound (Pc)Eu(Pc)Eu[trans-T(COOCH3)2PP] (1) and graphene oxide (GO) using the solution-processing QLS method. The combination of the nature of relatively high conductivity and great surface area for GO with the electroactive and semiconductive triple-decker compound in ITO electrode renders the hybrid film excellent sensing property for H2O2, due to the optimized triple-decker molecular packing in the uniform-sized nanoparticles (ca. 70 nm) formed on the GO surface. The amperometric responses are linearly proportional to the concentration of H2O2 in the range of 0.05-1800 μM with a fast response time of 0.03 s μM-1, a low detection limit of 0.017 μM, and good sensitivity of 7.4 μA mM-1. The present work represents the best result of tetrapyrrole-based nonenzymatic electrochemical sensor for H2O2. Nevertheless, the triple-decker/GO/ITO also shows excellent stability, reproducibility, and selectivity, indicating the great potential of electroactive tetrapyrrole rare earth sandwich compounds in combination with GO in the field of nonenzymatic electrochemical sensors.