Lanthanide Research Articles

Intermediate-valence state of the Sm and Eu in SmB6 and EuCu2Si2: neutron spectroscopy data and analysis

Magnetic neutron scattering data for Sm (SmB6, Sm(Y)S) and Eu (EuCu2Si2−xGex) intermediate-valence compounds have been analysed in terms of a generalized model of the intermediate-radius exciton. Special attention is paid to the correlation between the average ion’s valence and parameters of the low-energy excitation in the neutron spectra, such as the resonance mode, including its magnetic form factor. Along with specific features of the formation of the intermediate-valence state for Sm and Eu ions, common physical mechanisms have been revealed for systems based on these elements from the middle of the rare-earth series. A consistent description of the existing experimental data has been obtained by using the concept of a loosely bound hole for the Eu f-electron shell in the intermediate-valence state, in analogy with the previously established loosely bound electron model for the Sm ion.

Applications of functionalized nanomaterials in photodynamic therapy.

Specially designed functionalized nanomaterials such as superparamagnetic iron oxide, gold, quantum dots and up- and down-conversion lanthanide series nanoparticles have consistently and completely revolutionized the biomedical environment over the past few years due to their specially inferring properties, such as specific drug delivery, plasmonic effect, optical and imaging properties, therapeutic thermal energy productionand excellent irresistible cellular penetration. These properties have been used to improve many existing disease treatment modalities and have led to the development of better therapeutic approaches for the advancement of the treatment of critical human diseases, such as cancers and related malaise. In photodynamic therapy, for example, where the delivery of therapeutic agents should ideally avoid toxicity on nearby healthy cells, superparamagnetic iron oxide nanoparticles have been shown to be capable of making photodynamic therapy (PDT) prodrugs and their associative targeting moieties tumor-specific via their unique response to an external magnetic fields. In this review, the nanomaterials commonly employed for the enhancement of photodynamic therapy are discussed. The review further describes the various methods of synthesis and characterization of these nanomaterials and highlights challenges for improving the efficacy of PDT in the future.

Luminescence and energy transfer in β-NaGdF4:Eu3+,Er3+ nanocrystalline samples from a room temperature synthesis

β-NaGdF4:Eu3+,Er3+ nanoparticles were synthesized at room temperature. The synthesis is robust, easily scalable, and convenient. It is suitable for the whole lanthanide series.

The role of structure and the metal ion in the fluorescence sensing of nitro compounds for a series of lanthanide(iii) 9,10-anthracene dicarboxylate coordination polymers.

Twenty-eight lanthanide coordination polymers (CPs) containing 9,10-anthracene dicarboxylate (ADC) linkers have been synthesized and characterized. For the earlier class of lanthanides La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+ and Tb3+, the 3D pcu net was generated from dimethylformamide (DMF) while a 2D hcb net was formed using dimethylacetamide (DMA). Similarly for the later class of lanthanides, Dy3+, Ho3+, Er3+, Tm3+, Yb3+ and Lu3+, a 2D hcb net was formed when dimethylacetamide (DMA) was used. However, the formation of a crystalline product with DMF was possible only when DMSO was added together for these lanthanides, and they yielded 2D structures despite the usage of DMF. Only the single crystal structures of Er3+ and Ho3+ have been determined and the rest of the structures were confirmed by PXRD studies. These compounds have been used to sense various nitro compounds. In particular, they are the most sensitive to Brady's reagent, 2,4-dinitrohydrazobenzene. There was no difference in the quenching extent between the 3D and 2D early lanthanide CPs. For the later lanthanides which adopt 2D structures, the quenching efficiency is higher when DMA instead of DMSO is coordinated suggesting the solvent effect in emission quenching.

Lanthanide extraction selectivity of a tripodal carbamoylmethylphosphine oxide ligand system.

Four tripodal carbamoylmethylphosphine oxide (CMPO)-based ligands are reported here and assessed with regard to lanthanide (Ln) coordination chemistry and selective extraction of lanthanide ions from aqueous solution. Inspired by previous liquid-liquid extraction studies that suggested a preference for terbium(iii), the current work further probes the extraction behavior of a tris-(2-aminoethyl)amine (TREN) capped, ethoxy substituted CMPO ligand with respect to the entire series of lanthanides. Upon confirmation of Tb3+ extraction selectivity versus the whole series, experiments were conducted to assess the effect of increasing the alkyl chain length within the ligand TREN cap, as well as changing the CMPO substituents by replacing the ethoxy groups with more hydrophobic phenyl groups to promote solubility in the organic extraction solvent. Extraction efficiencies remained low for most lanthanides upon increasing the cap size, with %E values consistently around 5%, and a complete loss of Tb3+ preference was noted with a decrease in %E from 18% to 3.5%. For the agent employing the original, smaller TREN cap but with phenyl substituents on the CMPO units, an increase in extraction toward the middle of the row was again observed, albeit modest, with relatively high %E values for both Gd3+ and Tb3+versus the other lanthanides (13 and 11%, respectively). A more dramatic extraction selectivity for the phenyl substituted ligand was achieved upon modification of the ligand to metal ratio, with a 100 : 1 ratio resulting in a near linear decrease in %E from 41% for La3+ to 3.7% for Lu3+. Finally, modification of the TREN capping scaffold by adding an oxygen atom to the central nitrogen led to consistently low %E values, revealing the effect of TREN cap oxidation on Ln extraction for this tripodal CMPO ligand system.

Prediction of interstitial diffusion activation energies of nitrogen, oxygen, boron and carbon in bcc, fcc, and hcp metals using machine learning

Study of diffusion in solids is of fundamental importance in understanding the materials properties such as phase transformations, segregation, and corrosion in processing and operations. Reliable diffusion data is crucial in the successful design of materials and manufacturing processes. In this work, we use gradient boosting with decision tree regression, a robust machine learning method, to develop the model for predicting interstitial diffusion activation energies of the light element X (B, C, O, and N) in 54 metals with bcc, fcc and hcp lattices. With the introduction of elastic strain energy, a dominant concept of interstitial diffusion theory, we are able to train the machine learning model achieving high accuracy of R-squared 0.9 without being over-fitted by using 94 impurity – host binary systems reported in the literature. Furthermore, our study reveals that apart from elastic strain energy, the electronic interaction between the impurity and the host (represented by two fundamental parameters in the well-known Miedema model) also plays an important role. By accurately predicting the diffusion activation energies, we report their trends across 4th, 5th and 6th period and Lanthanides series of the host atoms. More importantly, our predicted data can be used to approximate the transport rates in materials for which little or no diffusion data are available, thus accelerating the design of a wide range of new application-specific materials.

Lanthanide-directed fabrication of three phenoxo-O bridged dinuclear compounds showing magnetic refrigeration and single-molecule magnet behavior

A series of lanthanide based dinuclear compounds, namely, [Ln(bfa)2L]2 (Ln = Gd (1), Tb (2), and Dy (3), bfa = benzoyltrifluoroacetone and HL = 2-[5-methyl-1,2-oxazol-imino]methyl]-8-hydroxyquinoline), were synthesized by employing a multidentate 8-hydroxyquinoline Schiff base derivative ligands (HL) and a bidentate β-diketonate coligand (bfa). The elemental analysis (EA), powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), single-crystal X-ray diffraction and magnetic properties of the three Ln2 compounds were completely characterized. Structures of 1–3 are similar to each other with a parallelogram Ln2O2 core. Magnetic properties study indicates that 1 exhibits antiferromagnetic exchange interaction between two nearby GdIII centers and shows magnetic refrigeration (−ΔSm = 17.78 J kg−1 K−1 for ΔH = 7 T at 2.0 K). Ac magnetic susceptibility measurements of 3 demonstrate that slow relaxation behavior is observed in 3, with effective energy barrier Ueff = 24.3 K and pre-exponential factor τ0 = 1.71 × 10−6 s.

Controlling the Structures of Lanthanide Complexes in Self‐Assemblies with Tripodal Ligands

The complexity of self‐assembled supramolecular systems is continuously evolving in the direction of large multicomponent polynuclear architectures. The self‐assembly of such systems requires the preparation of sophisticated organic receptors with “programmed” multidentate sites for binding metal ions. In this review we focus on the concept of tripodal receptors specifically designed for complexing lanthanide cations. A large palette of polytopic podands is described, and the structures of their anchoring and binding moieties are discussed together with their impact on the self‐assembly with LnIII. The crystal or calculated structures of mononuclear and polynuclear complexes are shown to illustrate typical structural features in relation to their properties. Moreover, thermodynamic speciation with several ligands is analysed along the lanthanide series in order to ascertain the effects of the ionic size. Understanding and controlling the different factors discussed here should help in rational designing of more complex architectures with LnIII.

Structures, fluorescence properties and magnetic properties of a series of dinuclear lanthanide(III) compounds: Dy2 compound showing single-molecule magnet behavior

A series of dinuclear lanthanide(III) compounds, namely, [Ln2(tmhd)2L2(CH3OH)2] (Ln(III) = Sm (1), Eu (2), Dy (3) and Er (4); H2L = 2-amino-benzoic acid (8-hydroxy-quinolin-2-ylmethylene)-hydrazide, Htmhd = 2,2,6,6-tetramethyl-3,5-heptanedione), have been synthesized, structurally and magnetically characterized. The X-ray structural analysis exhibit that 1–4 are phenoxo-O-bridged dinuclear compounds and central Ln(III) ions are eight-coordinated with one bidentate tmhd−, one CH3OH and two μ2-O bridging Schiff base ligands. Magnetic measurements indicated that slow magnetic relaxation behaviors were observed in 3, with energy barrier (ΔE/kB) of 13.14 K and τ0 = 4.58 × 10−6 s, however, no out-of-phase (χ″) alternating current (ac) signals noticed in 1, 2 and 4. Additionally, solid-state luminescence properties reveal that 1–3 display the characteristic LnIII luminescence at room temperature.

Enhancement of catalytic performance and resistance to carbonaceous deposit of lanthanum (La) doped HZSM-5 catalysts for decomposition of methyl mercaptan

A series of rare earth elements (La, Ce, Pr, Nd, Sm, Y and Er) modified HZSM-5 catalysts were prepared and evaluated their catalytic performance for CH3SH decomposition. XRD, N2 adsorption-desorption, FT-IR, CO2-TPD and NH3-TPD were conducted to analyze the relationships between catalytic behaviors and their structural characteristics. It indicated that addition of rare earth metal could significantly improve activity and stability of HZSM-5 catalyst for CH3SH decomposition, and the best one was La(13)/HZSM-5 sample. CH3SH can be completely converted over La(13)/HZSM-5 at 450 °C compared to parent HZSM-5 at 600 °C. The optimal La(13)/HZSM-5 catalyst exhibited excellent stability without significant deactivation even after 80h time-on-stream test, while parent HZSM-5 was rapidly deactivated within 20 h under same reaction conditions. The excellent performance of La(13)/HZSM-5 can be attributed to its tunable acid-base properties, which not only promote adsorption and activation of CH3SH molecule but also effectively inhibit the formation of coke deposit. In addition, spent La(13)/HZSM-5 catalyst can be easily regenerated and no significant deactivation was observed during regeneration process.

Prediction of trivalent actinide amino(poly)carboxylate complex stability constants using linear free energy relationships with the lanthanide series

ABSTRACTThere is a gap in the literature regarding the complexation of amino(poly)carboxylate (APC) ligands with trivalent actinides. The chemistry of the trivalent actinides is considered to be nearly identical to that of the trivalent lanthanides, but the trivalent actinides express a slight enhancement when binding APC ligands. Presented in this report is a method of predicting the stability constants of the Pu(III), Am(III), Cm(III), Bk(III) and Cf(III) using linear free energy relationships of the actinides and the lanthanide series for 91 APCs. This method produced actinide stability constants within uncertainties to those in available literature values for most ligands.

Investigation of electronic transport properties of lanthanides in liquid phase

ABSTRACTWe investigated electrical transport properties of lanthanide series in liquid phase using the self-consistent approximation employed by Khajil and Tomak [Phys Stat. Sol. B, 134 (1), 321–324 (1986)]. We used our model potential by implemented ionic and atomic radius which is incorporated with the Charged Hard Sphere, One Component Plasma and General Mean Spherical Approximation reference systems to study the electronic transport properties like electrical resistivity (ρ), thermal conductivity (σ) and thermoelectric power (Q). The screening effect on aforesaid properties has been studied by using different screening functions. The correlations of our results and others data within addition experimental values are profoundly promising to the scientists working in this field.

Highly luminescent Ln-MOFs based on 1,3-adamantanediacetic acid as bifunctional sensor

A series of lanthanide metal-organic-frameworks (Ln-MOFs) are synthesized under mild hydrothermal condition by introducing the ligand of 1,3-adamantanediacetic acid (H2ADA). They are three dimentional (3D) structures and have the formula of [Ln(ADA)1.5(phen)]n (Ln3+=Eu3+1a, Gd3+1b, Tb3+1c, La3+1d, Ce3+1e, Pr3+1f, Nd3+1g, Y3+1h; phen=1,10-phenanthroline). These Ln-MOFs are fully characterized by single-crystal X-ray diffraction, PXRD, TGA, EA and FT-IR. Luminescence properties, including luminescence spectra, luminescence decay lifetimes and luminescence quantum yields (QYs) are analyzed in detail. Eu3+ complex of 1a shows highly luminescence QYs of 58.61%, which due to that the triplet state of phen competes well with the excited emission state of Eu3+. Further investigation reveals that 1a is a bifunctional sensor, which can be used as a turn-off luminescence sensor for detecting Ni2+ and turn-on luminescence sensor for probing Val at the same time. Interestingly, the limit of detect (LOD) for sensing Ni2+ is an ultrahigh sensitive value of 1.0×10−9M (5.9×10−5mg/L), which is lower than the Chinese environmental quality standard (0.5mg/L of total Ni2+ content, GB25467-2010), and it is the most sensitive chemosensor for detecting Ni2+, to the best of our knowledge. Investigation also reveals there is a good linear relationship between luminescence intensity and the concentration of Ni2+ in 0.2–0.6μM. The sensing mechanism for detecting Ni2+ and Val are also discussed.

An experimental investigation into the reduced mobilities of lanthanide cations using high-resolution ion mobility mass spectrometry

Reduced mobilities for ground-state electronic configurations of the complete lanthanide series of cations, excluding promethium, have been measured. These values were obtained using an ion mobility mass spectrometer that utilizes a 2m drift tube to generate high-resolution ion mobility data. In all cases, lanthanide cations were generated using pulsed-laser vaporization of either a metal rod or foil target. The mobilities of Eu+, Gd+, Yb+, and Lu+ have been previously examined and these data are also included. All other lanthanide cation mobilities, measured in He, are reported here for the first time. A discussion of the observed trends in the mobilities of the lanthanide series is also provided.

Methane activation with nitrous oxide over bimetallic oxide Ca-lanthanide nanocatalysts

Bimetallic calcium-lanthanide oxides (Ln=La, Ce, Sm, Gd, Yb) were tested for the first time as catalysts in the oxidative coupling of methane (OCM) using nitrous oxide as oxidant. The reaction main products were C2 hydrocarbons. The best results were those obtained with bimetallic calcium-lanthanum and calcium-samarium oxides that achieve hydrocarbons yields comparable to the best reported in the literature using O2 as oxidant. The catalytic performance is clearly dependent of an interaction between calcium and f block element due to calcium ions incorporation on the lanthanide oxide matrix (except for CeO2) that renders oxygen less labile and increases hydrocarbons production. The other main factor that correlate with the variation of the activity and selectivity along the lanthanide series is the catalysts basic properties that increases hydrocarbon production. The catalysts present also an unusual and long stability in the gaseous stream.

CAT-ACT-A new highly versatile x-ray spectroscopy beamline for catalysis and radionuclide science at the KIT synchrotron light facility ANKA.

CAT-ACT-the hard X-ray beamline for CATalysis and ACTinide/radionuclide research at the KIT synchrotron radiation facility ANKA-is dedicated to X-ray spectroscopy, including "flux hungry" photon-in/photon-out and correlative techniques and combines state-of-the-art optics with a unique infrastructure for radionuclide and catalysis research. Measurements can be performed at photon energies varying between 3.4 keV and 55 keV, thus encompassing the actinide M- and L-edge or potassium K-edge up to the K-edges of the lanthanide series such as cerium. Well-established X-ray absorption fine structure spectroscopy in transmission and fluorescence detection modes is available in combination with high energy-resolution X-ray emission spectroscopy or X-ray diffraction techniques. The modular beamline design with two alternately operated in-line experimental stations enables sufficient flexibility to adapt sample environments and detection systems to many scientific challenges. The ACT experimental station focuses on various aspects of nuclear waste disposal within the mission of the Helmholtz association to contribute to the solution of one of the greatest scientific and social challenges of our time-the safe disposal of heat producing, highly radioactive waste forms from nuclear energy production. It augments present capabilities at the INE-Beamline by increasing the flux and extending the energy range into the hard X-ray regime. The CAT experimental station focuses on catalytic materials, e.g., for energy-related and exhaust gas catalysis. Characterization of catalytically active materials under realistic reaction conditions and the development of in situ and operando cells for sample environments close to industrial reactors are essential aspects at CAT.

Rare earth elements sorption to iron oxyhydroxide: Model development and application to groundwater

Iron oxyhydroxides are among the most important colloids that control rare earth elements (REE) concentrations and transport in natural hydrosystems. In this study, REE surface complexation to iron oxyhydroxides (Fe(OH)3(a)) was described by using the Donnan diffuse layer model and a two-site (i.e. ≡FesOH and ≡FewOH) model. The specific surface area and pH of zero charge were fixed as 100000 m2/mol and 8.0, respectively. The surface site density for weak and strong binding sites were fixed at 0.1 moL/mol Fe (≡FewOH) and 0.001 moL/mol Fe (≡FesOH) respectively. The two site types were used with pKa1int = 7.29 and pKa2int = 8.93. Using linear free energy relationship, the estimated equilibrium surface complexation constants (log K) increased from light REE (LREE) to heavy REE (HREE). Results of REE modeling calculation using the determined log K revealed a good fit of experimental data, showing an order of sorption on iron oxyhydroxides: HREE > MREE > LREE and preferential sorption of HREE at a lower pH. However, sorption edges only showed a slight change with ionic strength (0.1–0.7 moL/L) for the whole REE series. The generalized model was subsequently used to evaluate the impact of iron oxyhydroxides on REE speciation in groundwater. Application of the model to “model groundwater” showed that iron oxyhydroxide complexes of REE were significant in near neutral and weakly alkaline pH. This study contributes to putting forward a comprehensive database which would be useful for the application of surface complexation model to describe REE sorption by amorphous ferric hydroxides in nature.

New nanobidentate Schiff base ligand of 2-aminophenol with 2-acetyl ferrocene with some lanthanide metal ions: Synthesis, characterization and Hepatitis A, B, C and breast cancer docking studies

Three lanthanide complexes (La(III), Er(III) and Yb(III)) derived from ferrocene-based Schiff base ligand (HL) were synthesized from condensation of 2-aminophenol with 2-acetylferrocene. The ligand and metal complexes were characterized based on elemental analyses, IR, 1 H NMR, molar conductance, SEM and thermal analyses (TG, DTG). The molar conductance revealed that all the metal chelates were electrolytes having the general composition [M(L)(Cl)(H 2 O) 3 ]Cl·4H 2 O. HL and its complexes were screened for their antibacterial and antifungal activity by agar diffusion method. The results of these studies showed that the metal complexes are more effective antibacterial and antifungal agents as compared with the free ligand. The anticancer activity was screened against human breast cancer cell line (MCF-7). Results indicated that metal complexes showed an increased cytotoxicity in proliferation to cell lines as compared to free ligand. Molecular docking studies were performed to identify the binding orientation or conformation of a complex in the active site of the protein. HL and its complexes were docked with crystal structure of DDB1 of breast cancer, crystal structure of HCV, RNA-dependent RNA polymerase, receptors of HBV core protein, crystal structure of the Fab fragment of anti-HAV.

X-ray diffraction study of distorted perovskites R(Co3/4Ti1/4)O3 (R = La, Pr, Nd, Sm, Eu, Gd, Dy, Ho)

The crystal structure and powder patterns were prepared for the distorted perovskite series R(Co3/4Ti1/4)O3 (R = La, Pr, Nd, Sm, Eu, Gd, Dy, Ho). The R(Co3/4Ti1/4)O3 members are isostructural with each other and are crystallized in the orthorhombic crystal system with space group Pnma, Z = 4. From R = La to Ho, the lattice parameters a range from 5.4614(3) to 5.5368(2) Å, b range from 7.7442(4) to 7.4859(2) Å, and c range from 5.5046(3) to 5.2170(2) Å. The unit-cell volumes, V which range from 232.81(2) to 216.237(11) Å3 follow the trend of “lanthanide contraction”. The structure distortion of these compounds is evidenced in the tilt angles θ, ϕ, and ω, which represent rotations of an octahedron about the pseudo-cubic perovskite [110]p, [001]p and [111]p axes. All three tilt angles increase across the lanthanide series (for R = La to R = Ho: θ increases from 8.34° to 17.00°, ϕ from 6.24° to 8.53°, and ω from 10.41° to 18.96°), indicating a greater octahedral distortion as the ionic radius of R3+ [r(R3+)] decreases. The bond valence sum values for the (Co/Ti) site and the R site of R(Co3/4Ti1/4)O3 reveal no significant bond strain in these compounds. X-ray diffraction patterns of the R(Co3/4Ti1/4)O3 samples were submitted to the Powder Diffraction File.

Interplay between breathing mode distortion and magnetic order in rare-earth nickelates RNiO3 within DFT+U

We present a systematic density functional theory (DFT) plus Hubbard $U$ study of structural trends and the stability of different magnetically ordered states across the rare-earth nickelate series, $R$NiO$_3$, with $R$ from Lu to La. In particular, we investigate how the magnetic order, the change of the rare-earth ion, and the Hubbard interaction $U$ are affecting the bond-length disproportionation between the nickel sites. Our results show that structural parameters can be obtained that are in very good agreement with present experimental data, and that DFT+$U$ is in principle able to capture the most important structural trends across the nickelate series. However, the amplitude of the bond-length disproportionation depends very strongly on the specific value used for the Hubbard $U$ parameter and also on the type of magnetic order imposed in the calculation. Regarding the relative stability of different magnetic orderings, a realistic antiferromagnetic order, consistent with the experimental observations, is favored for small $U$ values, and becomes more and more favorable compared to the ferromagnetic state towards the end of the series (i.e., towards $R$=Pr). Nevertheless, it seems that the stability of the ferromagnetic state is generally overestimated within the DFT+$U$ calculations. Our work provides a profound starting point for more detailed experimental investigations, and also for future studies using more advanced computational techniques such as, e.g., DFT combined with dynamical mean-field theory.