Lanthanide Species Research Articles

Including and Declaring Structural Fluctuations in the Study of Lanthanide(III) Coordination Chemistry in Solution.

The physicochemical properties of lanthanide(III) ions are directly linked to the structure of the surrounding ligands. Rapid ligand exchange prohibits direct structure-property relationships from being formed for simple complexes in solution because the property measured will be an average over several structures. For kinetically inert lanthanide(III) complexes, the simpler speciation may alleviate the problem, yet the archetypical complexes formed by ligands derived from cyclen are known to have at least four different forms in solution-each with a variation in the crystal field that gives rise to significantly different properties. Slow interchange between forms has been engineered, so that a single complex geometry can be studied, but fast or intermediate interchange between forms is much more commonly observed. The rapid structural fluctuation can report on the changing chemical environment and can be disregarded if a specific property of a lanthanide(III) complex is exploited in an application. However, if we are to understand the chemistry of the lanthanide(III) ions in solution, we must include the structural fluctuation that takes place even in kinetically inert lanthanide(III) complexes in our studies. Here, we have scrutinized the processes that determine the speciation of lanthanide(III) complexes of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (DOTA)-like ligands, in particular the processes that enable exchange between forms that have different physicochemical properties, exemplified by the exchange between the diastereomeric capped square-antiprismatic (cSAP) and capped twisted-square-antiprismatic (cTSAP) forms of DOTA-like lanthanide(III) complexes. In the characterization of a kinetically inert f-element complex, understanding the structural fluctuation in the system is critical because a single observed property can arise from a weighted average, from all forms present, or from a single form with a dominating contribution. Further, the experimental condition will influence both the distribution of lanthanide(III) species in solution and the rates of the processes that change the coordination sphere of the lanthanide(III) ions. This is highlighted using data from a series of cyclen-derived ligands with different pendant arms and different denticity. The data were obtained in experiments that take place on different time scales to show that the rate of the process that results in a structural change must be considered against the time of the experiment. We conclude that the structural fluctuations must be taken into account and that they cannot be predicted from the ligand structure. Thus, an estimate of the exchange rates between forms, the relative concentrations of the specific forms, and the effect of the specific structure of each form of the complex must be included in the description of the solution properties of f-element chelates.

Tetracarbonatodiruthenium Fragments and Lanthanide(III) Ions as Building Blocks to Construct 2D Coordination Polymers.

Two-dimensional coordination polymers of [Pr(DMSO)2(OH2)3][Ru2(CO3)4(DMSO)(OH2)]·5H2O (Prα) and [Ln(OH2)5][Ru2(CO3)4(DMSO)]·xH2O (Ln = Sm (Smβ), Gd (Gdβ)) formulae have been obtained by reaction of the corresponding Ln(NO3)3·6H2O dissolved in dimethyl sulphoxide (DMSO) and K3[Ru2(CO3)4]·4H2O dissolved in water. Some DMSO molecules are coordinated to the metal atoms reducing the possibilities of connection between the [Ru2(CO3)4]3− and Ln3+ building blocks giving rise to the formation of two-dimensional networks. The size of the Ln3+ ion and the synthetic method seem to have an important influence in the type of two-dimensional structure obtained. Slow diffusion of the reagents gives rise to Prα that forms a 2D net that is built by Ln3+ ions as triconnected nodes and two types of Ru25+ units as bi- and tetraconnected nodes with (2-c)(3-c)2(4-c) stoichiometry (α structure). An analogous synthetic procedure gives Smβ and Gdβ that display a grid-like structure, (2-c)2(4-c)2, formed by biconnected Ln3+ ions and two types of tetraconnected Ru25+ fragments (β structure). The magnetic properties of these compounds are basically explained as the sum of the individual contributions of diruthenium and lanthanide species, although canted ferrimagnetism or weak ferromagnetism are observed at low temperature.

Raman studies of advanced gas-cooled reactor simulated spent nuclear fuels

Analysis of advanced gas-cooled reactor (AGR) simulated used nuclear fuels (SIMFuels) has been carried out using micro-Raman spectroscopy in order to understand the effect lanthanide species (e.g. Nd, Y, Ce), representative of fission products generated during fuel burnup, have on the structure of the UO2 matrix in spent AGR fuel. Results show a decrease in perfect fluorite character with increasing burnup as well as the development of a broad lattice distortion peak between 500 and 650 cm-1. Peak analysis of this broad band reveals in it comprised of three overlapping peaks at 534 cm-1, 574 cm-1 and 624 cm-1. The peak at 534 cm-1 has been examined and is suggested to be due to a local phonon mode associated with oxygen-vacancy-induced lattice distortion as a result of lanthanide 3+ ion incorporation into the UO2 bulk matrix.

Bond Covalency and Oxidation State of Actinide Ions Complexed with Therapeutic Chelating Agent 3,4,3-LI(1,2-HOPO).

The hydroxypyridinone ligand 3,4,3-LI(1,2-HOPO) is a promising agent for biological decorporation of radionuclides, and allows spectroscopic detection of many lanthanide (Ln) and actinide (An) species via sensitized luminescence. Despite the manifest uses of this ligand, the structural and thermodynamic properties of its complexes across the An series remain understudied. Theoretical investigations of the binding of An(III) and An(IV) ions, from actinium to einsteinium, by the 3,4,3-LI(1,2-HOPO) ligand, as well as experimental extended X-ray absorption fine structure (EXAFS) studies on the trivalent americium, curium, and californium complexes were employed to address the resulting structures, thermodynamic parameters, redox properties, and corresponding electronic configurations. An(IV) ions were found to form much stronger complexes than An(III) ions, consistent with experimental measurements. Complexation of both An(III) and An(IV) ions generally becomes more favorable for heavier actinides, reflecting increased energy degeneracy driven covalency and concomitant orbital mixing between the 5f orbitals of the An ions and the π orbitals of the ligand. Notably, the ability of this ligand to either accept or donate electron density as needed from its pyridine rings is found to be key to its extraordinary stability across the actinide series.

A Review of Recent Developments of Mesoporous Materials

This personal account concerns novel recent discoveries in the area of mesoporous materials. Most of the papers discussed have been published within the last two to three years. A major emphasis of most of these papers is the synthesis of unique mesoporous materials by a variety of synthetic methods. Many of these articles focus on the control of the pore sizes and shapes of mesoporous materials. Synthetic methods of various types have been used for such control of porosity including soft templating, hard templating, nano-casting, electrochemical methods, surface functionalization, and trapping of species in pores. The types of mesoporous materials range from carbon materials, metal oxides, metal sulfides, metal nitrides, carbonitriles, metal organic frameworks (MOFs), and composite materials. The vast majority of recent publications have centered around biological applications with a majority dealing with drug delivery systems. Several other bio-based articles on mesoporous systems concern biomass conversion and biofuels, magnetic resonance imaging (MRI) studies, ultrasound therapy, enzyme immobilization, antigen targeting, biodegradation of inorganic materials, applications for improved digestion, and antitumor activity. Numerous nonbiological applications of mesoporous materials have been pursued recently. Some specific examples are photocatalysis, photo-electrocatalysis, lithium ion batteries, heterogeneous catalysis, extraction of metals, extraction of lanthanide and actinide species, chiral separations and catalysis, capturing and the mode of binding of carbon dioxide (CO2 ), optical devices, and magneto-optical devices. Of this latter class of applications, heterogeneous catalysis is predominant. Some of the types of catalytic reactions being pursued include hydrogen generation, selective oxidations, aminolysis, Suzuki coupling and other coupling reactions, oxygen reduction reactions (ORR), oxygen evolution reactions (OER), and bifunctional catalysis. For perspective, there have been over 40,000 articles on mesoporous materials published in the last 4 years and about 1388 reviews. By no means is this personal account thorough or all inclusive. One objective has been to choose a variety of articles of different types to obtain a flavor of the breadth of diversity involved in the area of mesoporous materials.

Investigation of the structure and magnetism in lanthanide β-triketonate tetranuclear assemblies

The preparation of discrete tetranuclear lanthanide/alkali metal (Ae) assemblies bearing a tribenzoylmethane ligand (LH) is discussed. These assemblies have the general formula [Ln(Ae·HOEt)(L)4]2, where Ln3+ = Gd3+, Tb3+, Dy3+, Ho3+ and Ae+ = Na+, K+, Rb+. The coordination geometries of the lanthanide species were analyzed and compared, revealing a trend between an eight-coordinate square antiprism and triangular dodecahedron dependent on the nature of lanthanide, alkali metal, and lattice solvent. The potassium-containing analogs were also analyzed for their magnetic susceptibility.

Influence of synthesis conditions on physical properties of lanthanide-doped titania for photocatalytic decomposition of metazachlor

Heterogeneous photocatalysis is a very effective method for the decomposition of a whole range of water pollutants. In this work, the influence of synthesis conditions on the physical properties and photocatalytic activity of lanthanide-doped titanium dioxide photocatalysts was evaluated. Titanium dioxide was prepared via sol-gel synthesis followed by a solid state reaction under different conditions, including different temperatures (450, 550, and 650 °C) and reaction times (4, 8, and 12 h). The crystalline phase of the products was determined to be solely anatase using X-ray diffraction, and this result was confirmed by Raman spectroscopy. The structure, as well as particle size, of the samples was examined using scanning electron microscopy, and their specific surface area was calculated using Brunauer-Emmett-Teller analysis. The band gap energy of the samples was examined using ultraviolet-visible spectroscopy from diffuse reflectance measurements. Doping with lanthanide species, dysprosium and praseodymium, caused the absorption edge to shift towards higher wavelengths and enhanced photocatalytic activity in comparison with pure titania. The photocatalytic activity of the samples was studied in terms of the degradation of the commonly used herbicide metazachlor. The decomposition was carried under UV light and the decrease in metazachlor concentration was measured using high performance liquid chromatography. The best performance was obtained for samples treated at 550 °C for 8 h during the solid state reaction step.

Novel multi-component hybrids through double luminescent lanthanide unit functionalized zeolite L and titania

Zeolite L (ZL) is functionalized with inside-outside double modification paths (gas disperse (“ship in bottle”) and covalently grafting) with two kinds of luminescent lanthanide species (Tb3+ complex of acetylacetone (AA), lanthanide polyoxometalate (NaLnW10O36·32H2O, abbreviated as LnW10, Ln=Eu, Tb)) to prepare the hybrid materials. The prepared hybrids show the red and green luminescence, which provides a useful path to obtain multi-component lanthanide hybrids.

Multi-color luminescence of hybrids based with lanthanide functionalized zeolite A and titania

A so-called inside-outside double modification path is used to functionalize zeolite A (ZA) with two kinds of luminescent lanthanide species (Eu3+/Tb3+ complex of thenoyltrifluoroacetylacetone (TAA) and acetylacetone (AA), and lanthanide polyoxometalate (NaLnW10O36⋅32H2O (LnW10, Ln = Eu, Tb, Dy)) to prepare the multi-component hybrid materials. ZA is functionalized with Eu3+/Tb3+ through ion exchange reaction, and then TTA/AA ligands are introduced through gas dispersion (ship in bottle) method to the inside channel or pore structure of ZA. On the other hand, another species, LnW10, is fabricated onto the surface of ZA through ionic liquid (1-methyl-3-propionyloxy imidazolium bromide) coordinated to titania as linker. The prepared hybrids show the multi-color luminescence for different composition and excitation. The results provide a useful path to obtain multi-component lanthanide hybrids.

Rare-earth free p-type filled skutterudites: Mechanisms for low thermal conductivity and effects of Fe/Co ratio on the band structure and charge transport

A key driver of cost for a thermoelectric generator is the thermoelectric materials themselves, and the heavy reliance on rare earth (RE) elements as fillers, particularly for p-type formulations, represents a strategic risk. In the present study, we have investigated fully filled p-type skutterudites with nominal compositions CaFexCo4−xSb12 (2⩽x⩽3.5) using both experimental and theoretical methods. High purity samples were successfully synthesized using a combined melt-spinning (MS) and spark plasma sintering (SPS) technique. Structural analysis confirmed phase-pure samples with high filling fraction (>90%), homogeneous filler and transition metal distribution, and exceptionally low levels of oxygen contamination. Electrical and thermal transport property measurements revealed large power factors and unexpectedly low thermal conductivities. Electronic band structure calculations found a rapid increase in the density of states at the Fermi level with increasing Fe content. The large power factors observed in this system are attributable to this effect. Maximum zT of 0.9 was achieved in CaFe3CoSb12 at 773K. To understand the low lattice thermal conductivity in these compounds, lattice dynamics calculations were performed. The small size of Ca atoms and their concomitantly weak interactions with the surrounding Sb atoms result in a small force constant between fillers and the host, giving rise to a heretofore unreported low frequency optical phonon mode. This low frequency mode at 7meV is in addition to the previously described mode at 17meV identified by modeling the Ca as a simple harmonic oscillator. The lower energy phonon mode imparted by Ca filling results in a comparable lattice thermal conductivity reduction to early lanthanide species such as La.

A laboratory-based hard x-ray monochromator for high-resolution x-ray emission spectroscopy and x-ray absorption near edge structure measurements.

We report the development of a laboratory-based Rowland-circle monochromator that incorporates a low power x-ray (bremsstrahlung) tube source, a spherically bent crystal analyzer, and an energy-resolving solid-state detector. This relatively inexpensive, introductory level instrument achieves 1-eV energy resolution for photon energies of ∼5 keV to ∼10 keV while also demonstrating a net efficiency previously seen only in laboratory monochromators having much coarser energy resolution. Despite the use of only a compact, air-cooled 10 W x-ray tube, we find count rates for nonresonant x-ray emission spectroscopy comparable to those achieved at monochromatized spectroscopy beamlines at synchrotron light sources. For x-ray absorption near edge structure, the monochromatized flux is small (due to the use of a low-powered x-ray generator) but still useful for routine transmission-mode studies of concentrated samples. These results indicate that upgrading to a standard commercial high-power line-focused x-ray tube or rotating anode x-ray generator would result in monochromatized fluxes of order 10(6)-10(7) photons/s with no loss in energy resolution. This work establishes core technical capabilities for a rejuvenation of laboratory-based hard x-ray spectroscopies that could have special relevance for contemporary research on catalytic or electrical energy storage systems using transition-metal, lanthanide, or noble-metal active species.

Heterodimetallic [LnLn'] lanthanide complexes: toward a chemical design of two-qubit molecular spin quantum gates.

A major challenge for realizing quantum computation is finding suitable systems to embody quantum bits (qubits) and quantum gates (qugates) in a robust and scalable architecture. An emerging bottom-up approach uses the electronic spins of lanthanides. Universal qugates may then be engineered by arranging in a molecule two interacting and different lanthanide ions. Preparing heterometallic lanthanide species is, however, extremely challenging. We have discovered a method to obtain [LnLn′] complexes with the appropriate requirements. Compound [CeEr] is deemed to represent an ideal situation. Both ions have a doubly degenerate magnetic ground state and can be addressed individually. Their isotopes have mainly zero nuclear spin, which enhances the electronic spin coherence. The analogues [Ce2], [Er2], [CeY], and [LaEr] have also been prepared to assist in showing that [CeEr] meets the qugate requirements, as revealed through magnetic susceptibility, specific heat, and EPR. Molecules could now be used for quantum information processing.

Direct Observation of 4f Intrashell Excitation in Luminescent Eu Complexes by Time-Resolved X-ray Absorption Near Edge Spectroscopy

We report time-resolved X-ray absorption near edge structure (TR-XANES) measurements at the Eu L3 edge upon photoexcitation of several Eu(III)-based luminescent lanthanide complexes. We find an unambiguous signature of the 4f intrashell excitation that occurs upon energy transfer from the photoactive organic antennas to the lanthanide species. Phenomenologically, this observation provides the basis for direct investigation of a crucial step in the energy transfer pathways that lead to sensitized luminescence in lanthanide-based dyes. Interestingly, the details of the TR-XANES feature suggest that the degree of 4f-5d hybridization may itself vary depending on the excited state of the Eu(III) ion.

Thermally Reversible, Flexible, Transparent, and Luminescent Ionic Organosilica Gels

AbstractHerein, we report a facile method to prepare thermally reversible, flexible, transparent, and luminescent ionic organosilica gels with tunable emission colors. The reaction of an amino‐functionalized ionic liquid ([NH2‐Bim]Br) with 3‐(triethoxysilyl)propyl isocyanate results in an ionic‐liquid‐modified alkoxysilane, the hydrolysis and condensation of which lead to thermally reversible, flexible, and luminescent ionic gels in the presence of lanthanide species. The luminescence color can be fine‐tuned by changing the Ln3+ ions (Eu3+, Tb3+, or a mixture of Eu3+ and Tb3+) and by changing the excitation wavelength. The absolute quantum yields of the flexible luminescent gels with europium(III) and terbium(III) complexes are determined to be 15 and 21 %, respectively, by using an integrating sphere. The thermal reversibility of the organosilicas makes them attractive for the development of flexible optical devices and flexible luminescent devices such as organic light‐emitting diodes (OLEDs).

Lanthanide Speciation in Potential SANEX and GANEX Actinide/Lanthanide Separations Using Tetra-N-Donor Extractants

Lanthanide(III) complexes with N-donor extractants, which exhibit the potential for the separation of minor actinides from lanthanides in the management of spent nuclear fuel, have been directly synthesized and characterized in both solution and solid states. Crystal structures of the Pr(3+), Eu(3+), Tb(3+), and Yb(3+) complexes of 2,9-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-1,10-phenanthroline (CyMe4-BTPhen) and the Pr(3+), Eu(3+), and Tb(3+) complexes of 6,6'-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2'-bypyridine (CyMe4-BTBP) were obtained. The majority of these structures displayed coordination of two of the tetra-N-donor ligands to each Ln(3+) ion, even when in some cases the complexations were performed with equimolar amounts of lanthanide and N-donor ligand. The structures showed that generally the lighter lanthanides had their coordination spheres completed by a bidentate nitrate ion, giving a 2+ charged complex cation, whereas the structures of the heavier lanthanides displayed tricationic complex species with a single water molecule completing their coordination environments. Electronic absorption spectroscopic titrations showed formation of the 1:2 Ln(3+)/L(N4-donor) species (Ln = Pr(3+), Eu(3+), Tb(3+)) in methanol when the N-donor ligand was in excess. When the Ln(3+) ion was in excess, evidence for formation of a 1:1 Ln(3+)/L(N4-donor) complex species was observed. Luminescent lifetime studies of mixtures of Eu(3+) with excess CyMe4-BTBP and CyMe4-BTPhen in methanol indicated that the nitrate-coordinated species is dominant in solution. X-ray absorption spectra of Eu(3+) and Tb(3+) species, formed by extraction from an acidic aqueous phase into an organic solution consisting of excess N-donor extractant in pure cyclohexanone or 30% tri-n-butyl phosphate (TBP) in cyclohexanone, were obtained. The presence of TBP in the organic phase did not alter lanthanide speciation. Extended X-ray absorption fine structure data from these spectra were fitted using chemical models established by crystallography and solution spectroscopy and showed the dominant lanthanide species in the bulk organic phase was a 1:2 Ln(3+)/L(N-donor) species.

Recent developments in the manufacture of 173lutetium targets

To better model nuclear processes there is an interest in measuring neutron capture cross sections of lanthanide radioisotopes. A natural hafnium target was irradiated with 100 meV protons at the Los Alamos Isotope Production Facility at the Los Alamos Neutron Science Center (LANSCE) to produce neutron poor lutetium radioisotopes. After irradiation, the target was allowed to cool to allow shorter lived lutetium isotopes to decay. This left predominately 173Lu with small amounts of 174Lu. The hafnium target was then chemically processed to isolate the lanthanide fraction through ion exchange techniques. Recent efforts have focused on the separation of lanthanide species to produce an elementally pure lutetium product, the manufacture of small high density lutetium targets, and neutron capture cross section measurements.

Anion Effects in the Extraction of Lanthanide 2-Thenoyltrifluoroacetone Complexes into an Ionic Liquid

The extraction of trivalent lanthanides from an aqueous phase containing 1 M NaClO4 into the room temperature ionic liquid 1-butyl-3-methylimidazolium nonafluoro-1-butanesulfonate by the β-diketone extractant 2-thenoyltrifluoroacetone (Htta) was studied. Radiotracer distribution, absorption spectroscopy, time-resolved laser-induced fluorescence spectroscopy, and X-ray absorption fine structure measurements point to the extraction of multiple lanthanide species. At low extractant concentrations, fully hydrated aqua cations of the lanthanides are present in the ionic liquid phase. As the extractant concentration is increased 1:2 and 1:3 lanthanide:tta species are observed. In contrast, 1:4 Ln:tta complexes were observed in the extraction of lanthanides by Htta into 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

Tunable compositions and luminescent performances on members of the layered rare-earth hydroxides (Y1−xLnx)2(OH)5NO3·nH2O (Ln = Tb, Eu)

Members of the layered rare-earth hydroxides (LRHs) family with the generalized formula (Y(1-x)Ln(x))(2)(OH)(5)NO(3)·nH(2)O (Ln = Tb, Eu; 0% ≤x≤ 100%) (named as YTb-LRHs, YEu-LRHs) have been synthesized via a hydrothermal route. Crystal structures and elemental compositions have been investigated by X-ray diffraction (XRD), elemental analysis, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). These results show that Ln(3+) species are successfully incorporated into the LRH host lattice to form layered hydroxide solid solutions. The YTb-LRHs and YEu-LRHs samples exhibit well-defined photoluminescence. The color of the luminescence can be tuned by changing the concentration of Ln(3+). Furthermore, the ternary YTbEu-LRH system was also synthesized, an example of the host layers containing variable types of the lanthanide cations. This provides the possibility to tune the chemical composition and the luminescent properties of the lanthanide species with the flexibility of intercalation hosts for potential applications in luminescent materials and field emission displays.

Structure and luminescence of a nitrate-bridged heterotrinuclear Cu2-Pr complex with compartmental Schiff base ligand

A unique heterotrinuclear nitrate-bridged complex of hexanitrate praseodymium(III) and dicopper(II) compartmental species has been synthesized and characterized by X-ray single crystal structure analysis. The structure determination indicates that the dinuclear copper moiety undergoes a tilted deformation (with respect to the dicopper complex) upon connection to the lanthanide species via a rare nitrate bridge. The trinuclear species is highly fluorescent owing to the presence of praseodymium.

Ceria based mixed conductors with adjusted electronic conductivity in the bulk and/or along grain boundaries

Ceramic samples of Ce 1 − x Pr xO 2 − δ (CPO) and Ce 1 − x Gd xO 2 − δ (CGO) were obtained by different sintering schedules, including the use of cobalt as a sintering aid, added by mixing the precursor powders with cobalt nitrate solution; this allowed one to obtain different microstructural features and to change the transport properties, with emphasis on changes in grain boundary behaviour. Cobalt plays a double effect as sintering aid and also to induce important changes of grain boundary properties. Specific changes of grain boundary properties were ascribed by de-convolution of impedance spectra. Relatively high levels of mixed conductivity could be attained by adding a lanthanide species to yield ionic transport, whereas electronic conduction was promoted by the mixed valence character of PrO x, combined with the additional contribution of Co-rich grain boundaries. These effects can be used to tune preferential electronic conductivity at bulk or grain boundary level. Oxygen permeability and a modified e.m.f. method were used to obtain the overall ionic transport number under oxidising conditions and its dependence on processing conditions. Additions of PrO x induce bulk electronic conduction which assumes a greater role at lower temperatures. Further enhancement of electronic conductivity is attained by effects of Co-addition. Though Co-rich grain boundaries also yield significant levels of electronic conductivity in CGO, this contribution becomes minor at intermediate temperatures, due to differences between the activation energies for electronic and ionic conduction.