Eu Compounds Research Articles

Magnetic and electronic properties unveil polaron formation in Eu_5In_2Sb_6

The intermetallic compound Eu_5In_2Sb_6, an antiferromagnetic material with nonsymmorphic crystalline structure, is investigated by magnetic, electronic transport and specific heat measurements. Being a Zintl phase, insulating behavior is expected. Our thermodynamic and magnetotransport measurements along different crystallographic directions strongly indicate polaron formation well above the magnetic ordering temperatures. Pronounced anisotropies of the magnetic and transport properties even above the magnetic ordering temperature are observed despite the Eu^{2+} configuration which testify to complex and competing magnetic interactions between these ions and give rise to intricate phase diagrams discussed in detail. Our results provide a comprehensive framework for further detailed study of this multifaceted compound with possible nontrivial topology.

Liposome Biodistribution via Europium Complexes.

Vector biodistribution is a requirement prior pharmaceutical development. Radioactive tracers allow the most sensitive and quantitative assessment of biodistribution, and conventional fluorophores are widely used in academic laboratories. We propose here to use europium complexes as a label for nanoparticles or biotherapeutics taking liposomes as models. Time-resolved fluorimetry (TRF) has the tremendous advantage of taking into accounts the fluorescence decay time of the lanthanide chelates, resulting in an improved sensitivity in biological media. The work described aimed following liposome biodistribution by TRF. An octadecyl-DTPA.Eu compound has been prepared and incorporated into liposomes without altering its fluorescence signal. The method has been validated through a comparison with fluorophore-labeled liposomes. The way to proceed when using this method for liposomebiodistribution assessment is detailed. It could obviously be applied to other nanosystems, such as lipid nanoparticles.

Turn-off luminescence sensing, white light emission and magnetic studies of two-dimensional lanthanide MOFs.

The lanthanide metal organic framework compounds [Ln(BPTA)1.5(Bpy)]·0.5DMF (Ln = Y, Eu, Gd, Tb, Dy; 1a-5a) and [Ln(BPTA)1.5(Phen)]·0.5DMF (Ln = Y, Eu, Gd, Tb, Dy; 1b-5b) were prepared by employing 2,5-bis(prop-2-yn-1-yloxy)terephthalic acid (2,5-BPTA) as the primary ligand and 2,2'-bipyridine (1a-5a) and 1,10-phenanthroline (1b-5b) as the secondary ligands. Single-crystal structural studies on [Gd(BPTA)1.5(Bpy)]·0.5DMF (3a) and [Dy(BPTA)1.5(Phen)]·0.5DMF (5b) indicated that the compounds have a two-dimensional structure. The Y compound exhibits blue emission, and the other compounds exhibit emission in the expected regions (λex = 350 nm). White light emission was achieved by careful mixing of the red (Eu3+) and green (Tb3+) components in the blue emitting Y compound. Thus, Y0.96Tb0.02Eu0.02 (bpy) and Y0.939Tb0.06Eu0.001 (phen) were found to show white emission when excited using a wavelength of 350 nm. The introduction of N-N-containing ancillary ligands (i.e., bpy and phen) increased the overall quantum yield (QY) of white light emission to 31% and 43%, respectively. The high QY observed for the Tb and Eu compounds was found to be sensitive and selective for the fluorometric detection of azinphos-methyl pesticide and trinitrophenol (TNP) in an aqueous medium at the ppb level. The same behaviour was observed when utilising the compounds as onsite paper strip sensors. Their magnetic properties were also studied, revealing for the Tb and Dy derivatives slow relaxation of the magnetisation at low temperature. The present study highlights the usefulness of rigid π-conjugated molecules such as 2,2'-bipyridine and 1,10-phenanthroline in enhancing the many utilities of rare-earth-containing MOFs towards white light emission, the sensing of harmful and dangerous substances and magnetic properties.

Two Novel Pyrene Tetra-Sulfonate Europium Coordination Polymers: Structure Formation Mechanism Analysis and Sequential Modulation Strategy

For the purpose of broadening the understanding of the sulfonic acid coordination mechanism, a coordination system consisting of Eu(III) ion and 1,3,6,8-pyrene tetra-sulfonate (1,3,6,8-PTS) ligand was chosen as the typical research object. By step regulating the volume ratio of mixed solvents and the molar ratio of metal salts to ligands, two pyrene tetra-sulfonate europium coordination polymers, Eu6(μ6-O)(μ3-OH)8(NO3)6(1,3,6,8-H2PTS)(H2O)10 (1) and Eu(NO3)(1,3,6,8-PTS)0.5(H2O)3·0.5bipy (2), were obtained in sequence. Compound 1 shows a 1D chain-like structure interconnected with 1,3,6,8-PTS bridging ligands and rare [Eu6(μ6-O)(μ3-OH)8(NO3)6]2+ cluster nodes, while compound 2 shows a 2D layered structure. Further structural comparison with compound Eu(1,3,6,8-PTS)(H2O)7·4H2O·Hbipy (EuPTSbp-1) was discussed in detail and the structure formation mechanism was analyzed. On this basis, a sequential modulation strategy for pyrene tetra-sulfonate europium coordination polymers was proposed.

Spin-Orbital States and Strong Antiferromagnetism of Layered Eu2SrFe2O6 and Sr3Fe2O4Cl2.

The insulating iron compounds Eu2SrFe2O6 and Sr3Fe2O4Cl2 have high-temperature antiferromagnetic (AF) order despite their different layered structures. Here, we carry out density functional calculations and Monte Carlo simulations to study their electronic structures and magnetic properties aided with analyses of the crystal field, magnetic anisotropy, and superexchange. We find that both compounds are Mott insulators and in the high-spin (HS) Fe2+ state (S = 2) accompanied by the weakened crystal field. Although they have different local coordination and crystal fields, the Fe2+ ions have the same level sequence and ground-state configuration (3z2-r2)2(xz, yz)2(xy)1(x2-y2)1. Then, the multiorbital superexchange produces strong AF couplings, and the (3z2-r2)/(xz, yz) mixing via the spin-orbit coupling (SOC) yields a small in-plane orbital moment and anisotropy. Indeed, by tracing a set of different spin-orbital states, our density functional calculations confirm the strong AF couplings and the easy planar magnetization for both compounds. Moreover, using the derived magnetic parameters, our Monte Carlo simulations give the Néel temperature TN = 420 K (372 K) for the former (the latter), which well reproduce the experimental results. Therefore, the present study provides a unified picture for Eu2SrFe2O6 and Sr3Fe2O4Cl2 concerning their electronic and magnetic properties.

Crystal structure, fluorescence properties and biological activity of three µ2-O bridged Ln2 (Ln = Sm, Eu and Tb) compounds

In this paper, three new binuclear Ln‐based compounds with the formula [Ln2(dbm)2(L)2(C2H5OH)2](Ln = Sm (1), Eu (2) and Tb (3); dbm− = 1,3‐dioxo‐1,3‐ diphenylpropan‐2‐ide) have been synthesized via the solvothermal method by using a polyden‐tate Schiff base ligand (H2L = (E)‐N'‐(3‐ethoxy‐2‐hydroxybenzylidene)‐ 3‐hydroxypicolinohydrazide) reacting with Ln(dbm)3·2H2O. Single-crystal X-ray structures reveal that compounds 1–3 are mainly composed of two LnIII ions, two dbm−, two L2−, two C2H5OH, and the two central LnIII ions are connected by two µ2-O atoms forming a “parallelogram-shaped” Ln2O2 core. The investigations on the solid-state fluorescence properties show that the compounds 1–3 display the characteristic lanthanide luminescence at room temperature. Furthermore, biological activities research reveals that compounds 1–3 have greater antibacterial activity than the ligand H2L, and compounds 1–3 with DNA interaction are mainly intercalation, and supplemented by electrostatic binding or groove binding.

Tuning and reviving the luminescence of a new class of pyridyl β-diketonate Eu(III) metallomesogens: From molecules to entrapment in polymer particles

A new class of polynuclear Eu(III) compounds bearing pyridyl β-diketonate ligands have been synthesised, and their thermal and photophysical behaviour studied. Since they behave as highly emissive materials, polymer thin films were prepared by using the Eu(III) compounds as a dopant and poly(methyl methacrylate) as the matrix. Interestingly, the luminescence properties of the new materials can be tuned by protonation of the nitrogen atom at the pyridine moiety of the ligands, which allows controlling the energy transfer between the antenna ligands and the Eu(III) centre. This stimuli-responsive luminescence behaviour causes a drastic colour change from red to green that can be useful to detect highly acidic media. The antenna effect has been also explored at the nanoscale. Several colloidal dispersions of poly(methyl methacrylate) microparticles encapsulating the luminescent Eu(III) compounds have been obtained from oil-in-water droplets. The polymer matrix acts as a barrier and protects the coordination environment of the Eu(III) compounds, avoiding the quenching effect by water coordination. This method of entrapment can constitute a powerful tool to revive the luminescence of Eu(III) species in aqueous media.

Effect of the valence state on the band magnetocrystalline anisotropy in two-dimensional rare-earth/noble-metal compounds

In intermetallic compounds with zero orbital momentum $(L=0)$ the magnetic anisotropy and the electronic band structure are interconnected. Here, we investigate this connection in divalent Eu and trivalent Gd intermetallic compounds. We find by x-ray magnetic circular dichroism an out-of-plane easy magnetization axis in two-dimensional atom-thick ${\mathrm{EuAu}}_{2}$. Angle-resolved photoemission spectroscopy and density-functional theory prove that this is due to strong $f\text{\ensuremath{-}}d$ band hybridization and ${\mathrm{Eu}}^{2+}$ valence. In contrast, the easy in-plane magnetization of the structurally equivalent ${\mathrm{GdAu}}_{2}$ is ruled by spin-orbit-split $d$ bands, notably Weyl nodal lines, occupied in the ${\mathrm{Gd}}^{3+}$ state. Regardless of the $L$ value, we predict a similar itinerant electron contribution to the anisotropy of analogous compounds.

Crystal chemistry and ion‐irradiation resistance of Ln2ZrO5 compounds with Ln = Sm, Eu, Gd, and Tb

AbstractThe previously unattained fabrication of single phase Ln2ZrO5 (Ln = Sm, Eu, Gd, and Tb) compounds via relatively low sintering temperature (1400°C) is achieved in this study using a coprecipitation method. The crystal structures have been investigated by neutron, synchrotron X‐ray powder diffraction, and electron diffraction techniques. While the general long‐range structure may be well described by the defect‐fluorite type structure with Fmm symmetry, electron diffraction has highlighted a complex underlying modulated structure that varies between each compound. These compounds have been tested for ion‐irradiation response using in situ 1 MeV krypton ions and transmission electron microscopy characterization. None of the compounds undergo a crystalline to amorphous transition, even holding at 50 K. Both the underlying fluorite and modulated superstructures are little affected by the irradiation. However, some atomic rearrangements are observed in the postirradiated electron diffraction patterns for the Sm2ZrO5 specimen.

Crystal structure of the dodecanuclear coordination compounds [

By slow hydrolysis of solutions of [Eu(DMF)8]I3 or [Nd(DMF)8]I3 in dimethylformamide (DMF), single crystals of the coordination compounds [RE12(DMF)24 (HCOO)8(OH)16]I3·4DMF (RE = Eu, Nd) were obtained. Both compounds crystallise isotypically in a tetragonal structure with space group I422 (No. 97, Z = 2, a = 21.881(3), 21.6340(10) and c = 20.873(2), 21.0612(9) Å for Nd and Eu compounds, respectively). The crystal structure shows a [RE12O56] core unit with O atoms from formate and hydroxide anions μ3-bridging the metal centres. The dodecanuclear cationic units are arranged in a body-centred packing topology, surrounded by iodide anions in a β cage pattern. Rietveld refinement confirmed the structure model, and the presence of hydroxide anions was shown by FT-IR spectroscopy. Susceptibility measurements on the Nd compound showed paramagnetic behaviour and a temperature dependence of μeff typical for trivalent Nd cations.

Heavy Fermion Emerging from the Singular Fermi Liquid in Underscreened Kondo Model for Eu Compounds

An underscreened Kondo model for the impurity spin S = 7/2 in a weak crystal field is studied to elucidate the Kondo effect in the Eu compounds. By utilizing the numerical renormalization group met...

Y2O3:Eu and the Mössbauer isomer shift coefficient of Eu compounds from ab-initio simulations

We report on a full potential density functional theory characterization of Y2O3 upon Eu doping on the two inequivalent crystallographic sites 24d and 8b. We analyze local structural relaxation, electronic properties and the relative stability of the two sites. The simulations are used to extract the contact charge density at the Eu nucleus. Then we construct the experimental isomer shift (IS) versus contact charge density calibration curve, by considering an ample set of Eu compounds: EuF3, EuO, EuF2, EuS, EuSe, EuTe, EuPd3 and the Eu metal. The, expected, linear dependence has a slope of α = 0.054 mm s−1 Å− 3, which corresponds to nuclear expansion parameter ΔR/R = 6.0 × 10−5. α allows to obtain an unbiased and accurate estimation of the IS for any Eu compound. We test this approach on two mixed-valence compounds Eu3S4 and Eu2SiN3, and use it to predict the Y2O3:Eu IS with the result +1.04 mm s−1 at the 24d site and +1.00 mm s−1 at the 8b site.

Circularly polarized luminescence of Eu(III) complexes with chiral 1,1'-bi-2-naphtol-derived bisphosphate ligands.

The interest for lanthanide circularly polarized luminescence (CPL) has been quickly growing for 10 years. However, very few of these studies have involved correlation between the dissymmetry factor (glum ) and the chemical modifications in a series of chiral ligands. Four polymeric compounds of Eu(III) were prepared by using a series of binaphtyl derivatives for which the size of the π system as well as the number of stereogenic elements (i.e., the binaphtyl moiety) are modulated. The resulting {[Eu(hfac)3 ((S)/(R)-Lx )]}n (x = 1 and 3) and {[Eu(hfac)3 ((S,S,S)/(R,R,R)-Lx )]}n (x = 2 and 4) have been characterized by powder X-ray diffraction by comparison with the X-ray structures on single crystal of the Dy(III) analogs. In solution, the structure of the complexes is deeply modified and becomes monomeric. The nature of the ligand induces change in the shape of the CPL spectra in CH2 Cl2 solution. Furthermore, a large |glum | = 0.12 of the magnetic-dipole transition for the [Eu(hfac)3 ((S,S,S)/(R,R,R)-L2 )] complex involving the ligand with three stereogenic elements and an extended 𝜋 system has been measured. This report also shows CPL measurements in solid state for the series of {[Eu(hfac)3 ((S)/(R)-Lx )]}n (x = 1 and 3) and {[Eu(hfac)3 ((S,S,S)/(R,R,R)-Lx )]}n (x = 2 and 4) polymers.

Intrinsic anisotropy parameters of a series of lanthanoid complexes deliver new insights into the structure-magnetism relationship

Intrinsic anisotropy parameters of a series of lanthanoid complexes deliver new insights into the structure-magnetism relationship

LUMINESCENT DETERMINATION OF FAVIPIRAVIR USING THE EUROPIUM (III) COMPLEX

Of particular interest in recent years is the possibility of analytical application not only of the effects of sensitizing the luminescence of lanthanide ions, but also its quenching or increase for the indirect determination of a number of drugs. Favipiravir (FAV) - 6-fluoro-3-hydroxypyrazine-2-carboxamide - is an oral antiviral drug approved for the treatment of influenza in Japan. This drug is an analogue of purine nucleosides, which acts as a competitive inhibitor of RNA polymerase required for virus replication.
 Favipiravir is capable of forming a complex compound with Eu(III) ions, in which due to intramolecular transfer of excitation energy from the organic ligand to the Eu(III) ion there is a very slight sensitized luminescence of the latter due to dissipation of excitation energy from the triplet level (24390 cm-1), which cannot be used for analytical purposes.
 The influence of some surfactants and donor-active substances on the Ilum of the Eu(III) –FAV complex is considered. It was found that only batophenanthroline (BPh) significantly increases the luminescence intensity (Ilum) of the Eu(III)–FAV complex, approximately 10 times, due to more efficient intramolecular energy transfer from batophenanthroline (18100 cm-1) to the level of europium ions (17300 cm-1). A synergistic effect has been established, which is manifested in the combined action of two complexes (Eu(III)–BPh and Eu(III)–FAV) and exceeds the sum of the Ilum of each of them separately. The synergism is caused by formation of a multiligand complex. It was established that a mixed ligand complex Eu(III)–BPh–FAV (1:1:1) is formed.
 The possibility of using the complex compound Eu(III)-BPh as a new luminescent probe for the determination of favipivir has been shown. The luminescence intensity is maximum at pH 7.5 (urotropin buffer). The excitation band λexc = 315 nm was chosen for analytical purposes. It was found that the introduction of different amounts of favipiravir into aqueous solutions of the Eu(III)-BPh complex causes an increase in 4f-luminescence of europium (III) (transition 5D0 → 7F2, λemis = 615 nm) and the lifetime of its excited state.
 Calibration curve was linear over the concentration range of favipivir 0.5-10.0 μg/ml. The developed method is validated by the following parameters: specificity, linearity, accuracy, limit of quantitative determination. The proposed method is characterized by satisfactory metrological characteristics and ease of implementation and can be recommended for the determination of FAV in tablets.

Charge-Density-Wave Order and Multiple Magnetic Transitions in Divalent Europium Compound EuAl4

Multiple transition phenomena in divalent Eu compound EuAl$_4$ with the tetragonal structure were investigated via the single-crystal time-of-flight neutron Laue technique. At 30.0 K below a charge-density-wave (CDW) transition temperature of $T_{\rm CDW}$ = 140 K, superlattice peaks emerge near nuclear Bragg peaks described by an ordering vector $q_{\rm CDW}$=(0 0 ${\delta}_c$) with ${\delta}_c{\sim}$0.19. In contrast, magnetic peaks appear at $q_2 = ({\delta}_2 {\delta}_2 0)$ with ${\delta}_2$ = 0.085 in a magnetic-ordered phase at 13.5 K below $T_{\rm N1}$ = 15.4 K. By further cooling to below $T_{\rm N3}$ = 12.2 K, the magnetic ordering vector changes into $q_1 = ({\delta}_1 0 0)$ with ${\delta}_1$ = 0.17 at 11.5 K and slightly shifts to ${\delta}_1$ = 0.194 at 4.3 K. No distinct change in the magnetic Bragg peak was detected at $T_{\rm N2}$=13.2 K and $T_{\rm N4}$=10.0 K. The structural modulation below $T_{\rm CDW}$ with $q_{\rm CDW}$ is characterized by the absence of the superlattice peak in the (0 0 $l$) axis. As a similar CDW transition was observed in SrAl$_4$, the structural modulation with $q_{\rm CDW}$ could be mainly ascribed to the displacement of Al ions within the tetragonal $ab$-plane. Complex magnetic transitions are in stark contrast to a simple collinear magnetic structure in isovalent EuGa$_4$. This could stem from different electronic structures with the CDW transition between two compounds.

Microwave-assisted synthesis of anhydrous lanthanide-based coordination polymers built upon benzene-1,2,4,5-tetracarboxylic acid

A series of trivalent lanthanide and group 3 metal coordination polymers with pyromellitic acid [M(Hbtec)]n (M = Eu, Dy, Sm, Nd, Ce, Er, Y) has been synthesized and structurally characterized. Contrary to most of coordination polymers, the reported compounds do not present any crystallized solvent molecules, and consequently they are thermally stable until 400–500 °C. Moreover, they also exhibit good stability in water on a wide pH range. Compounds were synthesized by hydrothermal route with conventional heating but also with microwave-assisted heating, allowing to noticeably reduce the synthesis time to 1 h max. Efforts have been done to obtain nanoparticles with this strategy. Finally, the luminescence properties of the lanthanide counterparts emitting in the visible range (Dy, Sm, Eu) were thoroughly investigated, and the Eu compound exhibit good quantum yield.

A theoretical chemistry-based strategy for the rational design of new luminescent lanthanide complexes: an approach from a multireference SOC-NEVPT2 method.

Theoretical methods of the SOC-NEVPT2 type combined with a molecular fragmentation scheme have been proven to be a powerful tool that allows explaining the luminescence sensitization mechanism in Ln(III) coordination compounds through the antenna effect. In this work, we have used this strategy to predict luminescence in a family of compounds of the Eu(R-phen)(BTA)3 type where R-phen = 5-methyl-1,10-phenanthroline (Me-phen), 5-nitro-1,10-71 phenanthroline (Nitro-phen), 4,5-diazafluoren-9-one (One-phen), or 5,6-epoxy-5,6-dihydro-1,10-72 phenanthroline (Epoxy-phen); and BTA = fluorinated β-diketone. Possible sensitization pathways were elucidated from the energy difference between the ligand-centered triplet (3T) states and the emissive excited states of the Eu(III) fragments (Latva rules). Calculations show that the most probable mechanism occurs through the triplet state of the BTA which should be enriched by several parallel energy transfer pathways from R-phen substituents. The complexes were synthesized and structurally characterized by X-ray crystallography and various other physicochemical and spectroscopic methods to realize their optical properties and energy transfer pathways from dual antennae. Experimental results were in good agreement with the theoretical predictions, which reinforces the predictive power of the used theoretical methodology.

Multiple investigations of aqueous Eu(III)-oxalate complexes: the reduction in coordination number and validation of spectral linear correlation.

Detailed information on the An(iii)/Ln(iii) complexation properties in solution is essential for separation chemistry and the prediction of their potential for radionuclide migration from nuclear waste repositories into natural aquifers. In the present study, to better reveal and confirm the structural information of [Eu(Ox)x (H2O)h-2x]3-2x (h = 8, 9; x = 0-3) aqueous species, especially the variable coordination number (CN), and explore the validity of the spectral linear correlation between the luminescence lifetime and the residual hydration number in the first coordination sphere of Eu(iii) compounds in solution, a comparison between the spectral results and the theoretical calculations in a wide parametric space in terms of the pH value and oxalate concentration was carried out by combining time-resolved luminescence spectroscopy (TRLS) with speciation modelling and density functional theory (DFT) calculations. We have found direct and clear evidence for the 9-fold to 8-fold coordination number reduction of Eu(iii) atoms upon coordination with more than one oxalate in an aqueous medium, and as well systematically validated the applicability of the spectral linear correlation in an aqueous system (otherwise solid state) involving multiple species with the support of relatively reliable and clear speciation modelling.

Valence Fluctuation, Spin–Orbit Coupling, and Magnetic–Nonmagnetic Crossover in Eu Compounds

The crossover phenomena between magnetic and nonmagnetic states in the mixed-valent Eu compounds are investigated by focusing on the role of the spin–orbit coupling in the 4f electrons. An effectiv...