Search Results (17)

This work presents the results of studying dilute aqueous solutions of commercial Ln(NO₃)₃ · xH₂O salts with Ln = Ce-Lu using X-ray diffraction (XRD), IR spectroscopy, X-ray absorption spectroscopy (XAS: EXAFS/XANES), and pH measurements. As a reference point, XRD and XAS measurements for characterized Ln(NO₃)₃ · xH₂O microcrystalline powder samples were performed. The local structure of Ln-nitrate complexes in 20 mM Ln(NO₃)₃ · xH₂O aqueous solution was studied under total external reflection conditions and EXAFS geometry was applied to obtain high-quality EXAFS data for solutions with low concentrations of Ln³⁺ ions. Results obtained by EXAFS spectroscopy showed significant contraction of the first coordination sphere during the dissolution process for metal ions located in the middle of the lanthanide series. It was established that in Ln(NO₃)₃ · xH₂O solutions with Ln = Ce, Sm, Gd, Yb (c = 134, 100, 50 and 20 mM) there are coordinated and, to a greater extent, non-coordinated nitrate groups with bidentate and predominantly monodentate bonds with Ln ions, the number of which increases upon transition from cerium to ytterbium. For the first time, the antibacterial and antifungal activity of Ln(NO₃)₃ · xH₂O Ln = Ce, Sm, Gd, Tb, Yb solutions with different concentrations and pH was presented. Cross-relationships between the concentration of solutions and antimicrobial activity with the type of Ln = Ce, Sm, Gd, Tb, Yb were established, as well as the absence of biocidal properties of solutions with a concentration of 20 mM, except for Ln = Yb. The important role of experimental conditions in obtaining and interpreting the results was noted. Full article

A specialized empirical (Spec-zd Emp) system of ionic radii (SIR) for R = Y³⁺, La³⁺, Ln³⁺, and F¹⁻ (R rare earth elements (REE)) was derived from the dependence of lanthanide contraction (LC) on the atomic number (Z) of lanthanides (Ln). LC decreased the radius of the cation with increasing Z. The structures of t-RF₃ (LaF₃-NdF₃, “pseudo t-SmF₃”) of the LaF₃ type, 11 β-LnF₃ (Ln = Sm-Lu), and β-YF₃ of the β-YF₃ type were studied. The empirical basis of the shortest (F-F)_min and (R-F)_min distances was calculated from the structural data for the RF₃ complete series. The dependence of (F-F)_min on Z reached saturation at Z = 67 (Ho). The base F¹⁻ radius r₋ = 1.2539(16) Å was calculated as the arithmetic mean of five (F-F)_min in LnF₃ with Ln = Ho-Lu. For the LnF₃ series with Ln contributions up to 75 % wt., the dependence of (Ln-F)_min on Z reflected the non-uniformity of the 4f orbital filling. SIR was calculated as the difference in the empirical constants of RF₃ (ionic radii of (R,Ln)³⁺ (r₊) and F¹⁻ (r₋)), the change in which was continuous over the series and did not depend on the type of structure: r₊ = (_ZR-F)_min − ½(F-F)_min (Z = 57–71). The changes in LC in the LnF₃ series were described by a third-degree polynomial. LC reduced r₊ by 24% (percentage relative to less) from 1.1671(16) Å (La³⁺) to 0.9439(17) Å (Lu³⁺). In the Spec-zd Emp SIR, r₊ were constants that did not require corrections for a coordination number (CN). A comparison of r₊ in the Spec-zd Emp SIR with other SIRs was performed. Full article

A lanthanide contraction(LC) of 14 lanthanides (Ln) from ₅₈Ce to ₇₁Lu consists of the interaction of Ln nucleus with 4f-electrons. Rare earth elements (REEs—R) include Sc, Y, La, and 14 Ln. They are located in 4–6th periods of the subgroup of group III. The electronic structure divides R into short (d- Sc, Y, La) and long (14 f-elements Ce-Lu) homologous series. The most important chemical consequence of LC is the creation of a new conglomerate of 16 RF₃ by mixing fluorides of d- (Y, La) and f-elements. This determines the location of YF₃ among LnF₃. The location of YF₃ depends on the structural (formula volumes—V_form) and thermochemical (temperatures and heats of phase transformations, phase diagrams) properties. The location of YF₃ between HoF₃ and ErF₃ was determined by V_form at a standard pressure (P_st) and temperature (T_st). The location of YF₃ according to heats of phase transformations ΔH_fus and ΔH_trans is in a dimorphic structural subgroup (SSGr) D (Ln = Er-Lu), but without the exact “pseudo Z_Y”. According to the temperatures of phase transformations (T_trans) in LnF₃ (Ln = Dy-Lu), YF₃ is located in the SSGr D between ErF₃ and TmF₃. The ErF₃-YF₃ and YF₃-TmF₃ phase diagrams show it to be between ErF₃ and TmF₃. The crystals of five β-LnF₃ (Ln = Ho-Lu) and β-YF₃ were obtained in identical conditions and their crystal structures were studied. V_form (at P_st and T_st) with “pseudo” atomic number Z_Y = 67.42 was calculated from the unit cell parameters, which were defined with ±5 × 10⁻⁴ Å accuracy. It determines the location of YF₃ between HoF₃ and ErF₃. Full article

Based on density functional theory (DFT), theoretical models of three kinds of lanthanide rare earth metal ion-doped γ-Bi₂MoO₆ were constructed (Ln-BMO (Ln=Gd, Ho, Yb)). The geometric structure, electronic structure, and optical properties of the model were calculated, and the influence of doped Ln³⁺ ions on the structures and properties of the system was analyzed. The results revealed that the substitution of smaller ionic radius Ln³⁺ ions for Bi³⁺ ions caused a contraction of the lattice parameters. At the same time, the contribution of the [Ln]4d near valence band and conduction band reduced the bandwidth of γ-Bi₂MoO₆, forming the Ln-O ionic bond with different strengths to obtain higher charge conductivity and charge-separation ability. Secondly, Ln³⁺ ions have a strongly ionic charge, which leads to the appearance of optical absorption bands in the infrared region and part of the visible region. This reduces the reflection in the visible region, improves the utilization rate, delays the loss of electron energy, and promotes phase matching in the visible region. And the Gd³⁺-doped system has better photocatalytic activity than the other Ln³⁺-doped system. This research provides theoretical insights into doped lanthanide rare earth ions and also provides strategies for the modification of γ-Bi₂MoO₆ nanomaterials. Full article

The structural parameters of the rare-earth diacetate halide trihydrates, RE(OAc)₂Hal·3H₂O with RE = Ce − (Pm) − Lu and Hal = Cl, Br, have been determined by low temperature, high-resolution SCXRD in order to examine the effect of lanthanide contraction on the coordination geometry in this series of isomorphous compounds consisting of cationic, acetate-bridged, non-linear, one-dimensional coordination polymers of composition [RE(H₂O)₃(OAc)₂]⁺ and laterally hydrogen bonded halide ions, Hal⁻. Although the shrinkage of the unit cell volume follows lanthanide contraction very well over the complete range of investigated RE elements, many other parameters (i.e., lattice constants, angles and distances in the RE··· RE alignment, RE-O bond lengths, etc.) exhibit a more complex response on lanthanide contraction often expressed by sigmoid curves that can be ascribed to a continuous transition from CN9 (RE = Ce) to CN8 (RE = Lu) as one acetate group loses the chelate function, an effect accompanied by significant structural changes of the carboxylate group. Therefore, data are best analyzed by use of two subsets represented by the two different structure types of Ce and Lu, the structural features of which change with decreasing/increasing the size of RE³⁺, up to the borderline between both subsets. Full article

We present detailed first-principles density functional theory-based studies on RbRE₂Fe₄As₄O₂ (RE = Sm, Tb, Dy, Ho) hybrid 12442-type iron-based superconducting compounds with particular emphasis on competing magnetic interactions and their effect on possible magneto-structural coupling and electronic structure. The stripe antiferromagnetic (sAFM) pattern across the xy plane emerges as the most favorable spin configuration for all the four compounds, with close competition among the different magnetic orders along the z-axis. The structural parameters, including arsenic heights, Fe-As-Fe angle, and other relevant factors that influence superconducting T${}_c$ and properties, closely match the experimental values in stripe antiferromagnetic arrangement of Fe spins. Geometry optimization with inclusion of explicit magnetic ordering predicts a spin–lattice coupling for all the four compounds, where a weak magneto–structural transition, a tetragonal-to-orthorhombic structural transition, takes place in the relaxed stripe antiferromagnetic spin configuration. Absence of any experimental evidence of such structural transition is possibly an indication of nematic transition in RE-12442 compounds. As a result of structural distortion, the lattice contracts (expands) along the direction with parallel (anti-parallel) alignment of Fe spins. Introduction of stripe antiferromagnetic order in Fe sub-lattice reconstructs the low-energy band structure, which results in significantly reduced number of bands crossing the Fermi level. Moreover, the dispersion of bands and their orbital characteristics also are severely modified in the stripe antiferromagnetic phase similar to BaFe${}_2$As${}_2$. Calculations of exchange parameters were performed for all the four compounds. Exchange coupling along the anti-parallel alignment of Fe spins J${}_{1a}$ is larger than that for the parallel aligned spins J${}_{1b}$. A crossover between the super-exchange-driven in-plane next-nearest-neighbor exchange coupling J${}_2$ and in-plane exchange coupling J${}_{1a}$ due to lanthanide substitution was found. A large super-exchange-driven next-nearest-neighbor exchange interaction is justified using the construction of 32 maximally localized Wannier functions, where the nearest-neighbor Fe-As hopping amplitudes were found to be larger than the nearest- and the next-nearest-neighbor Fe-Fe hopping amplitudes. We compare the hopping parameters in the stripe antiferromagnetic pattern with non-magnetic configuration, and increased hopping amplitude was found along the anti-parallel spin alignment with more majority-spin electrons in Fe d${}_{xz}$ and d${}_{xy}$ but not in Fe d${}_{yz}$. On the other hand, the hopping amplitudes are increased in stripe antiferromagnetic phase along the parallel spin alignment with more majority-spin electrons in only Fe d${}_{yz}$. This difference in hopping amplitudes in the stripe antiferromagnetic order enables more isotropic hopping. Full article

The binding of calcium and magnesium ions to proteins is crucial for regulating heart contraction. However, other divalent cations, including xenobiotics, can accumulate in the myocardium and enter cardiomyocytes, where they can bind to proteins. In this article, we summarized the impact of these cations on myosin ATPase activity and EF-hand proteins, with special attention given to toxic cations. Optimal binding to EF-hand proteins occurs at an ionic radius close to that of Mg²⁺ and Ca²⁺. In skeletal Troponin C, Cd²⁺, Sr²⁺, Pb²⁺, Mn²⁺, Co²⁺, Ni²⁺, Ba²⁺, Mg²⁺, Zn²⁺, and trivalent lanthanides can substitute for Ca²⁺. As myosin ATPase is not a specific MgATPase, Ca²⁺, Fe²⁺, Mn²⁺, Ni²⁺, and Sr²⁺ could support myosin ATPase activity. On the other hand, Zn²⁺ and Cu² significantly inhibit ATPase activity. The affinity to various divalent cations depends on certain proteins or their isoforms and can alter with amino acid substitution and post-translational modification. Cardiac EF-hand proteins and the myosin ATP-binding pocket are potential molecular targets for toxic cations, which could significantly alter the mechanical characteristics of the heart muscle at the molecular level. Full article

We have undertaken a DFT study of the nitride cluster fullerenes (NCFs) Ln₃N@C₈₀ for the complete series of fourteen lanthanides plus lanthanum by using the PBE functional with the Grimme’s dispersion correction (PBE-D2). We tested the DN and DND basis sets, which are equivalent to 6-31G and 6-31G(d) Pople-type basis sets, respectively. Due to the known convergence problems when treating lanthanide-containing systems, only with the DN basis set was it possible to complete the calculations (geometry optimization and analysis of selected electronic parameters) for all the fifteen NCFs. We found that the bending of the Ln₃N cluster increases as the ionic radius increases, in general agreement with the available X-ray diffraction data. The Ln₃N cluster becomes more planar as the Ln–N bond length is contracted, and the C₈₀ cavity slightly deforms. The HOMO-LUMO energies and distribution, as well as the charge and spin of the encapsulated metal ions, are analyzed. Full article

The reaction of lanthanide (Ln) chloride hydrates ([Ln(H₂O)_n(Cl)₃]) with pyridine (py) yielded a set of dehydrated pyridinium (py-H) Ln-polychloride salts. These species were crystallographically characterized as [[py-H-py][py-H]₂[LnCl₆]] (Ln-6; Ln = La, Ce, Pr, Nd, Sm, Eu, Gd) or [[py-H]₂[LnCl₅(py)]] ((Ln-5; Ln = Tb, Dy, Ho, Er, Tm, Yb, Lu). The Ln-6 metal centers adopt an octahedral (OC-6) geometry, binding six Cl ligands. The −3 charge is off-set by two py-H moieties and a di-pyridinium (py-H-py) ion. For the Ln-5 species, an OC-6 anion is formed by the Ln cation binding a single py and five Cl ligands. The remaining −2 charge is offset by two py-H⁺ cations that H-bond to the anion. Significant H-bonding occurs between the various cation/anion moieties inducing the molecular stability. The change in structure from the Ln-6 to Ln-5 is believed to be due to the Ln-contraction producing a smaller unit cell, which prevents formation of the py-H-py⁺ cation, leading to the loss of the H-bonding-induced stability. Based on this, it was determined that the Ln-5 structures only exist when the lattice energy is small. While dehydrated polychloride salts can be produced by simply mixing in pyridine, the final structures adopted result from a delicate balance of cation size, Coulombic charge, and stabilizing H-bonding. Full article

Four new rare-earth metal–organic frameworks containing thieno[3,2b]thiophene-2,5-dicarboxylate (ttdc²⁻) with general formulae [M₂(DMF)₄(ttdc)₃] (M³⁺ = Y³⁺ for 1, La³⁺ for 2, Tb³⁺ for 3) and [M₂(H₂O)₂(ttdc)₃] (M³⁺ = Lu³⁺ for 4) were synthesized. Their crystal structures were determined by performing a single-crystal X-ray diffraction analysis. Coordination polymers 1–3 are based on the binuclear metal-carboxylate building units with the formulae {M₂(DMF)₄(OOCR)₆}. The six-connected blocks in 1–3 form a three-dimensional network with the primitive cubic (pcu) topology. Coordination framework 4 is based on chains comprised by stretched pseudo-binuclear metal-carboxylate building units. The chains are interconnected in four directions with ttdc²⁻ linkers forming the 3D framework. The luminescent properties were studied for the synthesized frameworks in the solid state. All the coordination frameworks show a broad blue emission band (λ_ex = 380 nm) typical for intra-ligand electron transitions. The sensing properties of 3 dispersions in solutions were investigated in detail and the luminescent response (quenching) was discovered in the presence of cinnamaldehyde and quinoline in diluted solutions at concentrations of as low as 4 × 10⁻¹ vol.% and 4 × 10⁻² vol.% (~3 × 10⁻³ M), respectively. Full article

The existing range of the centrosymmetric, triclinic RE(OAc)₃ · 2AcOH structure type has been extended for RE = Eu and Gd while the structure data of the Nd- and Sm-compounds have been revised and corrected, respectively, using low temperature (T = 100 K), well resolved (2θ_max = 56°), highly redundant SCXRD data in order to evaluate the structural evolution within this class of acetic acid solvates by statistical methods. Within the nine-fold mono-capped square-antiprismatic coordination spheres of the RE³⁺ ions, RE-O distances decrease as a result of lanthanide contraction; some with different rates depending on the coordination modes (2.11/2.21) of the acetate ions. The experimental data show that the internal structural parameters of the acetate ions also correlate with their coordination modes. Both acetic acid molecules act as hydrogen bond donors but only one as monodentate ligand. The geometries of the hydrogen bonds reveal that they are strongly influenced by the size of the rare earth atom. The non-linear, one-dimensional coordination polymer propagates with unequal RE···RE distances along the a-axis. Rods of the coordination polymer are arranged in layers congruently stacked above each other with the hydrogen bonded acetic acid molecules as filler in between. In most cases, data fitting is best described in terms of a quadratic rather than a linear regression analysis. Full article

A whole series of [Ln(H₂O)₄(Ala)₂]₂⁶⁺ dimeric cationic lanthanide complexes with both l- and d-alanine enantiomers was synthesized. The single-crystal X-ray diffraction at 100 and 292 K shows the formation of two types of dimers (I and II) in crystals. Between the dimer centers, the alanine molecules behave as bridging (μ₂-O,O’-) and chelating bridging (μ₂-O,O,O’-) ligands. The first type of bridge is present in dimers I, while both bridge forms can be observed in dimers II. The IR and vibrational circular dichroism (VCD) spectra of all l- and d-alanine complexes were registered in the 1750–1250 cm⁻¹ range as KBr pellets. Despite all the studied complexes are exhibiting similar crystal structures, the spectra reveal correlations or trends with the Ln–O1 distances which exemplify the lanthanide contraction effect in the IR spectra. This is especially true for the positions and intensities of some IR bands. Unexpectedly, the ν(C=O) VCD bands are quite intense and their composed shapes reveal the inequivalence of the C=O vibrators in the unit cell which vary with the lanthanide. Unlike in the IR spectra, the ν(C=O) VCD band positions are only weakly correlated with the change of Ln and the VCD intensities at most show some trends. Nevertheless, this is the first observation of the lanthanide contraction effect in the VCD spectra. Generally, for the heavier lanthanides (Ln: Dy–Lu), the VCD band maxima are very close to each other and the mirror reflection of the band of two enantiomers is usually better than that of the lighter Lns. DFT calculations show that the higher the multiplicity the higher the stability of the system. Actually, the molecular geometry in crystals (at 100 K) is well predicted based on the highest-spin structures. Also, the simulated IR and VCD spectra strongly depend on the Ln electron configuration but the best overall agreement was reached for the Lu complex, which is the only system with a fully filled f-shell. Full article

Lanthanides play an important role in modern technology because of their outstanding optical, electronic, and magnetic properties. Their current hydrometallurgical processing involves lixiviation, leading to concentrates of elements whose separation requires exhaustive procedures because of their similar chemical properties. In this sense, a new nanotechnological approach is here discussed, involving the use of iron oxide nanoparticles functionalized with complexing agents, such as diethylenetriaminepentaacetic acid (DTPA), for carrying out the magnetic extraction and separation of the lanthanide ions in aqueous solution. This strategy, also known as magnetic nanohydrometallurgy (MNHM), was first introduced in 2011 for dealing with transition metal recovery in the laboratory, and has been recently extended to the lanthanide series. This technology is based on lanthanide complexation and depends on the chemical equilibrium involved. It has been better described in terms of Langmuir isotherms, considering a uniform distribution of the metal ions over the nanoparticles surface, as evidenced by high angle annular dark field microscopy. The observed affinity parameters correlate with the lanthanide ion contraction series, and the process dynamics have been studied by monitoring the nanoparticles migration under an applied magnetic field (magnetophoresis). The elements can be reversibly captured and released from the magnetically confined nanoparticles, allowing their separation by a simple acid-base treatment. It can operate in a circular scheme, facilitated by the easy magnetic recovery of the extracting agents, without using organic solvents and ionic exchange columns. MNHM has been successfully tested for the separation of the lanthanide elements from monazite mineral, and seems a promising green nanotechnology, particularly suitable for urban mining. Full article

The structural, magnetic, electrical, and dilatation properties of the rare-earth NdCoO₃ and SmCoO₃ cobaltites were investigated. Their comparative analysis was carried out and the effect of multiplicity fluctuations on physical properties of the studied cobaltites was considered. Correlations between the spin state change of cobalt ions and the temperature dependence anomalies of the lattice parameters, magnetic susceptibility, volume thermal expansion coefficient, and electrical resistance have been revealed. A comparison of the results with well-studied GdCoO₃ allows one to single out both the general tendencies inherent in all rare-earth cobaltites taking into account the lanthanide contraction and peculiar properties of the samples containing Nd and Sm. Full article

The rare-earth carbonates represent a class of materials with great research interest owing to their intrinsic properties and because they can be used as template materials for the formation of other rare earth phases, particularly of rare-earth oxides. However, most of the literature is focused on the synthesis and characterization of hydroxycarbonates. Conversely, in the present study we have synthesized both rare-earth carbonates—with the chemical formula RE₂(CO₃)₃·2-3H₂O, in which RE represents a generic rare-earth element, and a tengerite-type structure with a peculiar morphology—and rare-earth hydroxycarbonates with the chemical formula RECO₃OH, by hydrothermal treatment at low temperature (120 °C), using metal nitrates and ammonium carbonates as raw materials, and without using any additive or template. We found that the nature of the rare-earth used plays a crucial role in relation to the formed phases, as predicted by the contraction law of lanthanides. In particular, the hydrothermal synthesis of rare-earth carbonates with a tengerite-type structure was obtained for the lanthanides from neodymium to erbium. A possible explanation of the different behaviors of lighter and heavier rare-earths is given. Full article