Lanthanide Cations Research Articles

Magnetocaloric Properties in Rare-Earth-Based Metal-Organic Frameworks: Influence of Magnetic Density and Hydrostatic Pressure.

Magnetic refrigeration based on the magnetocaloric effect (MCE) in metal-organic frameworks (MOF) is regarded as an attractive approach to create more sustainable cooling systems with higher efficiency than traditional ones. Here, we report a study of the MCE in a series of rare-earth-based MOFs. We have considered the selection of the rare-earth cation by investigating materials belonging to the α-rare-earth polymeric framework-4 (α-RPF-4) MOF family, synthesized with different rare-earth cations, and observed that paramagnetic moment and saturation magnetization play an important role in enhancing the magnetic entropy change ΔSM. The effect of structural parameters has also been considered by investigating three classes of metal-organic Gd materials built up from different types of inorganic secondary building units, including clusters (as in Gd-UiO-66), one-dimensional (as in α-RPF-4), and layered (as in Gd-LRH) conformations. Moreover, the analysis of the hydrostatic pressure influence reveals a significant increase in the -ΔSM and relative cooling power (RCP) with values between 4.3 and 16.3 and 121-509 J/kg. Specifically, the RCPmax found was ∼683 J/kg for Gd-UiO-66, which is higher than the one recently observed for Gd2SiO5 (649.5 J/kg). The present study demonstrates that the engineering of metal-organic framework systems based on high Gd densities may favor enhancing of magnetocaloric responses even at low pressures, thus promoting a new design strategy for efficient cooling devices.

Structure and Electronic Properties of Large Oligomeric Heterometallic 3d/CeIV Polyoxometalates.

Merging the rich chemistry of Ce(IV) polyoxometalates (POMs) with that of 3d polyanions remains a challenge due to the strong competition between these highly oxophilic lanthanide cations and 3d metallic ions for coordination to lacunary molecular metal oxides. We report herein the characterization of an unprecedented water stable hexameric CeIV/CoII POM (Ce12Co6) made of two {(SiW9)2Ce6} units connected to a {(SiW10)2Co6(PO4)2} core. In addition, the pentameric CeIV/NiII compound Ce6Ni8, where two {PW9Ni3W} and a {PW10Ni2} fragments are grafted on a {(PW9)2Ce6} moiety, has been obtained. Magnetic studies of Ce6Ni8 revealed ferromagnetic interactions between the NiII centers constituting the {Ni3PW10} fragments, in agreement with the geometry of such a trinuclear cluster. Related insoluble barium salts of Ce12Co6 and Ce6Ni8 were also prepared, allowing their solid-state electrochemical investigations and showing in particular that in Ce12Co6, both the cobalt, cerium, and silicotungstate moieties are electroactive. Finally, photophysical studies demonstrate the formation of long-lived reduced POMs photosensitized by [Ru(bpy)3]2+, suggesting that Ce12Co6 and Ce6Ni8 could be used as efficient reservoirs of reduction equivalents for photocatalytic reactions.

NdFeB magnet scrap valorization by leaching and recovery of rare earth metals by sorption on low-cost expanded clay

The search for new sources of rare earth metals (REM), such as neodymium and dysprosium, has ensued globally due to their strategic value for the sustainability of the energy sector. In this context, this work explored the potential of vermiculite as a sorbent for recovering rare earth cations from the leachate of end-of-life NdFeB magnets by kinetic, equilibrium, and desorption investigations. In which the REM uptake on vermiculite occurred by fast kinetics, and the significant sorbate-sorbate interactions at the equilibrium indicated that the REM sorption was a cooperative process; vermiculite sorbed the metals from the acid leachate in the following order: Fe(III) > Nd(III) > Zn(II) > Pr(III) > Co(II) > Dy(III) > Ni(II) > Al(III) > Mn(II); and the chelating agent ethylenediaminetetraacetic acid desorbed Nd(III) preferably over other metals, indicating the potential for further selective recovery processes. The characterization analyses indicated that the loaded vermiculite preserved the original structure, composition, functional groups, and thermal stability. Also, X-ray photoelectron spectroscopy corroborated the cation exchange mechanism between interlayer magnesium in the REM sorption. Thus, the experimental findings and a cost analysis compared to the literature demonstrated the cost-effectiveness and potential of vermiculite for the valorization of NdFeB magnet leachates.

Trivalent rare earth metal cofactors confer rapid NP-DNA polymerase activity.

A DNA polymerase with a single mutation and a divalent calcium cofactor catalyzes the synthesis of unnatural N3'→P5' phosphoramidate (NP) bonds to form NP-DNA. However, this template-directed phosphoryl transfer activity remains orders of magnitude slower than native phosphodiester synthesis. Here, we used time-resolved x-ray crystallography to show that NP-DNA synthesis proceeds with a single detectable calcium ion in the active site. Using insights from isotopic and elemental effects, we propose that one-metal-ion electrophilic substrate activation is inferior to the native two-metal-ion mechanism. We found that this deficiency in divalent activation could be ameliorated by trivalent rare earth and post-transition metal cations, substantially enhancing NP-DNA synthesis. Scandium(III), in particular, confers highly specific NP activity with kinetics enhanced by more than 100-fold over calcium(II), yielding NP-DNA strands up to 100 nucleotides in length.

HOMO- AND HETERONUCLEAR Yb(III) AND Lu(III) COMPLEXES WITH CALIX[4]ARENE MODIFIED WITH PORPHYRIN SUBSTITUENTS.

In this work we describe the approaches for the synthesis of lanthanide-containing homo- and heteronuclear complexes using 5,11,17,23-tetra-tert-butyl-25,27-dihydroxy-26,28-bis[(N-meso-­(p-aminophenyl)-meso-triphenylporphyrincarbonyl)methoxy]-calix[4]arene (1). Such spatially preorganizedcalix[4]arene macrocycle facilitates lanthanide cation coordination, impacting the structure and analytical signal of porphyrin substituents. The study employs two synthesis stra­tegies resulting in mononuclear and homobinuclear complexes, influenced by steric effects and changes in hydrogen bonding. The complexes exhibit changes in fluorescence spectra due to intramolecular dimerization and hydrogen bonding during complex formation. Mononuclear complexes (Ln-1) are synthesized under mild conditions, while homobinuclear complexes (Ln2-1) require high-boiling solvents and specific reaction conditions, detailed synthesis procedures are described. The structural changes during complex formation were analyzed with the use of NMR analysis. The absorption spectra of lanthanide complexes demonstrate shifts in maxima, reflecting coordination changes, with notable variations between mononuclear and homobinuclear complexes. Additionally, heteronuclear compounds with copper(II), zinc(II), and palladium(II) exhibit distinctive absorption patterns, emphasizing the role of d-metal ions. Luminescence stu­dies reveal the sensitization of 4f-luminescence by both calix[4]arene and porphyrin fragments. The use of deuterated solvents enhances 4f-luminescence intensity, highlighting solvent effects. Furthermore, 4f-luminescence characteristics were investigated in both solid and solution states for heterometallic compounds, emphasizing differences between copper-containing and zinc/palladium-containing complexes. The results offer valuable insights into the design, synthesis, and spectral properties of these complexes, showcasing their potential applications in various fields, and the findings contribute to the understanding of lanthanide-porphyrin systems and their coordination behavior.

Multiple magnetic transitions induced by Mn-doping in orthochromite HoCrO3

It has been established that both hybridization with magnetic rare earth cation and crystal field originating from structural anisotropy can affect the spin orientation of magnetic transition metal perovskite. In this work, we have systematically studied the crystal structure, magnetization, and magnetic structure of Mn-doped rare earth orthochromites HoCr1−xMnxO3 (x = 0–0.85) by means of X-ray diffraction, magnetometry, and neutron powder diffraction. With increasing Jahn–Teller active Mn3+-substitution for Cr3+, the crystallographic distortion is gradually enhanced and causes a systematic evolution of magnetism. With doping, the Cr(Mn) ordering temperature is gradually suppressed, and multiple magnetic configurations Γ2, Γ1, and Γ4 phases appear consecutively. The rich transition phenomena are ascribed to a competition between increased structural anisotropy and weakened Ho-Cr(Mn) hybridization with doping. In a low doping regime with x = 0.1–0.5, Γ2 phase is predominant in low temperature, and a magnetization reversal is observed, reflecting the opposite sign of Cr-Mn DMI coefficient with respect to the Cr-Cr and Mn-Mn interaction. In the high doping range with x = 0.6–0.8, the long-range order of Cr(Mn) sublattice is gradually suppressed while a short-range order becomes dominant. For x = 0.85, a magnetic structure resembling o-HoMnO3 is observed.

Donor Radii in Rare-Earth Complexes.

We present a set of donor radii for the rare-earth cations obtained from the analysis of structural data available in the Cambridge Structural Database (CSD). Theoretical calculations using density functional theory (DFT) and wave function approaches (NEVPT2) demonstrate that the Ln-donor distances can be broken down into contributions of the cation and the donor atom, with the minimum in electron density (ρ) that defines the position of (3,-1) critical points corresponding well with Shannon's crystal radii (CR). Subsequent linear fits of the experimental bond distances for all rare earth cations (except Pm3+) afforded donor radii (rD) that allow for the prediction of Ln-donor distances regardless of the nature of the rare-earth cation and its oxidation state. This set of donor radii can be used to rationalize structural data and identify particularly weak or strong interactions, which has important implications in the understanding of the stability and reactivity of complexes of these metal ions. A few cases of incorrect atom assignments in X-ray structures were also identified using the derived rD values.

Design of oxygen-storage/release materials with high-speed of oxygen-release in rare-earth trivalent cation M<sup>3+</sup>-doped ceria-zirconia system

Design of oxygen-storage/release materials with high-speed of oxygen-release in rare-earth trivalent cation M<sup>3+</sup>-doped ceria-zirconia system

Deferasirox Derivatives: Ligands for the Lanthanide Series.

Deferasirox is an FDA-approved iron chelator used in the treatment of iron toxicity. In this work, we report the use of several deferasirox derivatives as lanthanide chelators. Solid-state structural studies of three representative trivalent lanthanide cations, La(III), Eu(III), and Lu(III), revealed the formation of 2:2 complexes in the solid state. A 1:1 stoichiometry dominates in DMSO solution, with Ka values of 472 ± 14, 477 ± 11, and 496 ± 15 M-1 being obtained in the case of these three cations, respectively. Under the conditions of competitive precipitation in the presence of triethylamine, high selectivity (up to 80%) for lutetium(III) was observed in competition with La(III), Ce(III), and Eu(III). Theoretical calculations provided support for the observed selective crystallization.

Structural study of the rare earth compounds: Sm(OH)3, NdOHCO3, CeO2, and Ho2O3, prepared by Chemical Bath Deposition, and its correlation with crystal growth mechanism

We present the preliminary theoretical-experimental study of the structural properties for rare earths: hydroxide, hydroxycarbonate and Oxide; Sm(OH)3, NdOHCO3, CeO2, and Ho2O3 powders, respectively. In the experimental preparation, Chemical Bath Deposition (CBD) technique is applied at ~20 ±2 °C. In our experimental conditions, the parameters of crystal growth are: concentration of progenitor reagents, stirring, pH and temperature, remain constant. The chemical kinetics of crystal growth is systematically examined at key synthesis steps, considering the physicochemical and electrodynamic parameters: ionic radii, electron affinity, and hydration enthalpy of the rare earth (Sm3+, Nd3+, Ce3+, and Ho3+) cation. The main objective of this report is to investigate the theoretical-experimental correlation associated with the experimental conditions and the physicochemical parameters in the synthesis of hydroxide, hydrocarbonates and oxide. The crystallographic study of the powders is carried out using the X-ray Diffraction (XDR) technique. Analyzing the crystal phase, it is found that Sm(OH)3 and NdOHCO3 present hexagonal crystal phase, CeO2 and Ho2O3 are identified cubic crystal structure. The quantified grain size turns out to be: Sm(OH)3: ~1.40 - 2.03 nm, NdOHCO3: ~14.33 - 22.25 nm; CeO2: ~1.65 - 3.05 nm; and Ho2O3: ~3.72 - 6.08 nm. The Dislocation density (?) is: Sm(OH)3: ~2.47 - 5.10×1017 lines/m2; NdOHCO3: 2.01 - 4.68×1015 lines/m2; CeO2: 1.07 - 3.67×1017 lines/m2.

2D coordination polymers based on the interaction between cucurbit[5]uril and light lanthanide metal ions in the presence of copper salts, and use for the detection of nitrogenous bases

The coordination of cucurbit[5]uril (Q[5]) with lanthanide cations (Ln3+), in the presence of Cu2+ cations, led to the formation of 2D-network coordination polymers, which have been investigated using single crystal X-ray diffraction. Experimental results revealed that crystals were only readily affordable for the systems involving the lighter lanthanide cations (La3+, Ce3+, Pr3+, Sm3+, Eu3+ and Tb3+), with all six Ln3+- Q[5] complexes (1 ∼ 6) exhibiting similar coordination mode at the cucurbit[5]uril (Q[5]), and forming 2D-network coordination polymers with a 2D supramolecular assembly. One complex was found to detect Adenine (A) and Uracil (U) with high selectively.

Furancarboxylate Coordination Polymers of Gd3+ and Eu3+: Synthesis, Structural Variations, and Biological Properties

A series of polymer complexes of Gd(III) and Eu(III) with 3-furancarboxylic (HFur) and 5-nitro-2-furancarboxylic (HNfur) acids differed in the composition and coligands presented by solvent molecules(CH3OH/C2H5OH/H2O) is synthesized: [Gd(Fur)3(CH3OH)(C2H5OH)]n (I), [Gd(Nfur)3(CH3OH)2]n·CH3CN (II), [Eu(Fur)3(C2H5OH)]n (III), and [Eu(Nfur)3(H2O)2]n·3CH3CN (IV). According to the X-raydiffraction (XRD) data, all complexes are 1D coordination polymers in which the lanthanide cation has thecoordination number 8 (LnO8) to form the environment as a doubly augmented triangular prism (I, II) or asquare antiprism (III, IV). The supramolecular levels of the polymers are stabilized due to intra- and intermolecularhydrogen bonds between the coordinated solvent molecules and O atoms of the chelate-boundanions of the acid and via two types of noncovalent C–H…O and N–O…π interactions that significantly contributeto an additional stabilization of the crystal packings. The biological properties of complexes I, II, andIV are studied with respect to the model nonpathogenic strain Mycolicibacterium smegmatis.

Understanding Temperature Stability of Surface Cation Dopants on LSCF Electrodes

The widespread application of solid oxide fuel cells (SOFCs) is primarily inhibited by degradation issues impacting the stability and oxygen exchange kinetics of the oxygen electrode. State-of-the-art SOFC materials such as La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) boast fast oxygen ion and electron conduction as well as high oxygen reduction activity. Furthermore, materials such as LSCF provide a potential pathway to reduce the operating temperature of SOFCs from 800-100 ° C to 400-800 ° C. But degradation issues continue to impede LSCF, primarily through strontium segregation to the electrode surface and subsequent passivating poisoning reactions due to chromium- and sulfur-containing species.In this work, we investigate a solution infiltration technique to introduce cation dopants to the surface of LSCF porous electrodes on symmetrical cells to improve the stability and performance through suppression of Sr segregation. We have previously demonstrated that introducing more oxidizable transition metal cations on the LSC electrode surface improves both the stability and oxygen exchange kinetics. Others have demonstrated that lanthanides can electrochemically stabilize the LSCF surface as well (Yu Chen, et al. Energy Environ. Sci., 2017, 10, 964-971). However, the temperature dependence of these cation dopants on electrode surface composition and electrochemical stability is not well understood. Thus, we are interested in exploring more oxidizable transition metal and lanthanide cations as infiltrated dopants on the porous LSCF electrode as a function of temperature.Preliminary experiments demonstrate that both transition metal and lanthanide cation dopants diffuse into the LSCF lattice at SOFC operating temperatures (above 700 ° C) and Sr segregates to the surface with increasing temperature. We do also observe some fundamental differences between the transition metal and lanthanide cations, such as the temperature dependence of A:B site ratio. Our initial electrochemical measurements indicate that these cation dopants are found to improve the stability of LSCF electrodes when tested at SOFC operating temperatures (800 ° C in ambient air) despite having largely diffused into the lattice at these temperatures.These preliminary results indicate a potential electrode surface reconstruction as a function of cation type and temperature. We aim to elucidate 1) the temperature stability of these cations at the surface, 2) the impact of these cations on the electrode surface composition and cell electrochemical stability as a function of temperature, and 3) the mechanism for electrochemical influence of these sub-surface cations.We utilize electrochemical impedance spectroscopy and chronoamperometric stability studies to characterize the impact of infiltrated cations on electrode activity and stability. We investigate the stability of cation dopants and reasons for observed electrochemical changes through x-ray photoelectron spectroscopy and x-ray diffraction studies. This work aims to elucidate the impact of transition metal and lanthanide cation dopants on electrode stability and performance as well as the stability of the dopants at the surface at different operating conditions, with a focus on developing a mechanistic understanding of sub-surface dopant influence on electrochemical performance.

A-site cations tailoring the activity of LnMnO3 perovskites for CO and propane oxidation

To understand the role of A-site cations of perovskites on the reactivity, the LnMnO3 perovskites (Ln = La, Nd, Sm) with varied A-site cations were prepared by a facile glycine combustion method and evaluated for CO and propane oxidation. The activity for both reactions followed the trend: NdMnO3 > SmMnO3 > LaMnO3, demonstrating that lanthanide cations at A sites significantly affect the catalytic performance. Combined with Fourier transmission infrared spectra, temperature programmed reduction and desorption techniques, it was revealed that both the strength of Mn–O bonds and the adsorption of reactants played crucial roles on the activity for CO oxidation and C3H8 combustion on the LnMnO3. The adsorption of the reactants was responsible for the higher activity on the NdMnO3 than on the SmMnO3, while the strength of Mn–O bonds for the higher activity on the SmMnO3 than on the LaMnO3. The NdMnO3 possessed both weak Mn–O bonds and favorable adsorption of the reactants achieved the highest activity for CO oxidation and C3H8 combustion. The best NdMnO3 catalyst achieved CO and propane complete conversion at 160 and 360 °C, 90 and 60 °C lower than the LaMnO3, respectively.

Oxidation Kinetics of Nanocrystalline Hexagonal RMn1-xTixO3 (R = Ho, Dy).

Hexagonal manganites, RMnO3 (R = Sc, Y, Ho-Lu), are potential oxygen storage materials for air separation due to their reversible oxygen storage and release properties. Their outstanding ability to absorb and release oxygen at relatively low temperatures of 250-400 °C holds promise of saving energy compared to current industrial methods. Unfortunately, the low temperature of operation also implies slow kinetics of oxygen exchange in these materials, which would make them inefficient in applications such as chemical looping air separation. Here, we show that the oxidation kinetics of RMnO3 can be improved through Ti4+-doping as well as by increasing the rare earth cation size. The rate of oxygen absorption of nanocrystalline RMn1-xTixO3 (R = Ho, Dy; x = 0, 0.15) was investigated by thermogravimetric analysis, X-ray absorption near-edge structure, and high-temperature X-ray diffraction (HT-XRD) with in situ switching of atmosphere from N2 to O2. The kinetics of oxidation increases for larger R and even more with Ti4+ donor doping, as both induce expansion of the ab-plane, which reduces the electrostatic repulsion between oxygen in the lattice upon oxygen ion migration. Surface exchange rates and activation energies of oxidation were determined from changes in lattice parameters observed through HT-XRD upon in situ switching of atmosphere.

Influence of B-site rare-earth Yb cation on the crystal structure and microwave dielectric properties of Ca3Yb2Ge3O12 garnet ceramics

In this work, garnet structured Ca3Yb2Ge3O12 ceramics with a space group of Ia-3d were synthesized by a solid-state reaction method. Rietveld refinement analysis demonstrated that Yb3+with small ionic radius and large electronegativity entered the B-sites and shortened the bond length of B–O and Ge–O. The bond valence and P-V-L theory analysis results showed that Ca cations with a weakened rattling effect exerted a critical effect on the dielectric constant, and the Ge–O bond was the main factor that influenced dielectric loss. Ca3Yb2Ge3O12 with a high relative density (98.2%) and excellent microwave dielectric properties (εr= 10.2, Q × f = 98,400 GHz, τf = -48 ppm/°C) was obtained at 1360 °C for 4 h. Furthermore, the intrinsic dielectric constant and dielectric loss (εr =10.12, Q × f = 101,900 GHz) of Ca3Yb2Ge3O12 were obtained by infrared reflectivity spectroscopy.

Phase stability and cation partitioning in compositionally complex rare earth aluminates and aluminate‐zirconate mixtures

AbstractMulticomponent oxides have received significant recent attention due to their potential for improved property tunability. In simple structures, compositionally complex oxides can be stabilized by increased configurational entropy and are sometimes called “high entropy” ceramics. In phases with multiple cation sublattices or complex stoichiometries, it is more difficult to achieve high configurational entropy. However, there is limited knowledge about the factors influencing stability and solubility limits in many systems. This study investigated the limits on the stability of rare earth (RE) aluminates containing mixtures of RE cations including Gd, La, Nd, Yb, and Y in cases where (i) a fixed RE:Al ratio attempts to constrain the material into a single‐phase aluminate or (ii) a two‐phase aluminate, and in equilibrium with RE zirconates that readily dissolve multiple RE3+. The results show that it is difficult to form single‐phase, equimolar mixed‐RE aluminates encompassing a range of RE3+ sizes. Instead, the RE3+ selectively partition into specific phases based on RE‐size trends in the constituent binary systems. The results are discussed in terms of the phase stability and cation partition trends and potential applications.

Mechanism of inhibition of the oxygen-evolving complex of photosystem II by lanthanide cations

The process of the interaction of La3+and Tb3+ cations with the Ca-binding site of the oxygen-evolving complex of photosystem II samples depleted of calcium has been studied. The binding of cations to the Ca-binding site is irreversible and the bound cations cannot be washed out or replaced by Ca2+ cation. A feature of lanthanides to bind strongly to the Ca-binding site has been used to investigate if the bound Ln3+ cation has an effect on the high-affinity Mn-binding site of the oxygen-evolving complex. Therefore, in this work, hydroquinone was used for the extraction of manganese cations from the oxygen-evolving complex of the calcium-depleted photosystem II membranes with the Ca-binding site blocked by La3+ or Tb3+ and the activity of the high-affinity site was then examined using exogenous electron donors (Mn2+ + H2O2) and 1,5-di-phenylcarbazide. It was found that lanthanide cation bound to the Ca-binding site can significantly inhibit the oxidation rates of electron donors through the high-affinity Mn-binding site. The mechanism of the observed effect is discussed.

Mechanism of Inhibition of the Oxygen-Evolving Complex of Photosystem II by Lanthanide Cations

Mechanism of Inhibition of the Oxygen-Evolving Complex of Photosystem II by Lanthanide Cations

Phase stabilisation, thermal expansion and ionic conductivity of high content rare earth oxide (Lu2O3, Y2O3 and Gd2O3) stabilised cubic hafnia

For satellite propulsion, new material are developed to sustain harsh thermal and environmental conditions in the combustion chambers induced by the development of new “green” propellants less toxic than currently used hydrazine. In the present study, hafnia-based materials with different amounts and natures of stabilisers (Lu2O3, Y2O3 and Gd2O3) have been chosen for the ceramic part of the system. Microstructures, Thermal Expansion Coefficients (373–1673 K) and ionic conductivities (600–1273 K) of synthesised fully stabilised fluorite phases have been investigated. Lattice parameters have been determined and an abacus has been proposed as a function of the amount of RE2O3 and the ionic radius of the Rare Earth cation (RE3+). Moreover, it has been observed a TECs decrease from 14 to 40 mol% of RE2O3 and few changes in the ionic conductivity above 33 mol% of RE2O3. Finally, addition of Lu2O3 allows to reach the lowest TEC and ionic conductivity.