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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Magnetic and Magnetocaloric Properties of the A 2 LnSbO 6 Lanthanide Oxides on the Frustrated fcc Lattice

Frustrated lanthanide oxides are promising candidates for cryogen-free magnetic refrigeration due to their suppressed ordering temperatures and high magnetic moments. While much attention has been paid to the garnet and pyrochlore lattices, the magnetocaloric effect in frustrated face-centered cubic (fcc) lattices remains relatively unexplored. We previously showed that the frustrated fcc double perovskite Ba 2 GdSbO 6 is a top-performing magnetocaloric material (per mol Gd) because of its small nearest-neighbor interaction between spins. Here we investigate different tuning parameters to maximize the magnetocaloric effect in the family of fcc lanthanide oxides, A 2 LnSbO 6 (A = {Ba 2+ , Sr 2+ } and Ln = {Nd 3+ , Tb 3+ , Gd 3+ , Ho 3+ , Dy 3+ , Er 3+ }), including chemical pressure via the A site cation and the magnetic ground state via the lanthanide ion. Bulk magnetic measurements indicate a possible trend between magnetic short-range fluctuations and the field-temperature phase space of the magnetocaloric effect, determined by whether an ion is a Kramers or a non-Kramers ion. We report for the first time on the synthesis and magnetic characterization of the Ca 2 LnSbO 6 series with tunable site disorder that can be used to control the deviations from Curie–Weiss behavior. Taken together, these results suggest fcc lanthanide oxides as tunable systems for magnetocaloric design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Strong Relativistic Effects in Lanthanide-Based Single-Molecule Magnets

Lanthanide-based single-molecule magnets (SMMs) are promising building blocks for quantum memory and spintronic devices. Designing lanthanide-based SMMs with long spin relaxation time requires a detailed understanding of their electronic structure, including the crucial role of the spin-orbit coupling (SOC). While traditional calculations of SOC using the perturbation theory applied to a solution of the non-relativistic Schrödinger equation are valid for light atoms, this approach is questionable for systems containing heavy elements such as lanthanides. We investigate the accuracy of the perturbation estimates of SOC by variationally solving the Dirac equation for the [DyO] + molecule, a prototype of a lanthanide-based SMM. We show that the energy splittings between the M J states involved in spin relaxation depend on the interplay between strong SOC and dynamic electron correlations. Here, we demonstrate that this interplay affects the resonances between the spin and vibrational transitions, and, therefore, the spin relaxation time.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Liquid crystalline behavior and photoluminescence of lanthanide decanoate nanoparticles synthesized by microwave radiation

Luminescent lanthanide decanoate nanoparticles (LnC 10 NPs; Ln = Pr, Nd, Sm, Eu, Gd, Er) with spherical morphology (<100 nm) have been synthesized via a facile microwave (MWV) method using Ln(NO 3 ) 3 ·xH 2 O, ethanol/water, and decanoic acid. These hybrid nanomaterials adopt a lamellar structure consisting of inorganic Ln 3+ layers separated by a decanoate anion bilayer and exhibit liquid crystalline (LC) phases during melting. The particle size, crystalline structure, and LC behavior were characterized using transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and powder X-ray diffraction (ambient and heated). Thermal analysis indicated the formation of Smectic A LC phases by LnC 10 nanoparticles, with the smaller lanthanides (Ln = Sm, Gd, Er) displaying additional solid intermediate and Smectic C phases. The formation of LC phases by the smaller Ln 3+ suggests that these nanoscale materials have vastly different thermal properties than their bulk counterparts, which do not exhibit LC behavior. In this work, photoluminescence spectroscopy revealed the LnC 10 NPs to be highly optically active, producing strong visible emissions that corresponded to expected electronic transitions by the various Ln 3+ ions. Under long-wave UV irradiation (λ = 365 nm), bright visible luminescence was observed for colloidal suspensions of Nd, Sm, Eu, Gd, and ErC 10 NPs. To the best of the authors’ knowledge, this is the first reported synthesis of nanoscale metal alkanoates, the first report of liquid crystalline behavior by any decanoate of lanthanides smaller than Nd, and the first observation of strong visible luminescence by non-vitrified lanthanide alkanoates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Interplay of physically different properties leading to challenges in separating lanthanide cations – an ab initio molecular dynamics and experimental study

Lanthanide elements have well-documented similarities in their chemical behavior, which make the valuable trivalent lanthanide cations (Ln 3+ ) particularly difficult to separate from each other in water. Here, we apply ab initio molecular dynamics simulations to compare the free energies (Δ G ads ) associated with the adsorption of lanthanide cations to silica surfaces at a pH condition where SiO – groups are present. The predicted Δ G ads for lutetium (Lu 3+ ) and europium (Eu 3+ ) are similar within statistical uncertainties; this is in qualitative agreement with our batch adsorption measurements on silica. This finding is remarkable because the two cations exhibit hydration free energies (Δ G hyd ) that differ by >2 eV, different hydration numbers, and different hydrolysis behavior far from silica surfaces. We observe that the similarity in Lu 3+ and Eu 3+ Δ G ads is the result of a delicate cancellation between the difference in Eu 3+ and Lu 3+ hydration (Δ G hyd ), and their difference in binding energies to silica. We propose that disrupting this cancellation at the two end points, either for adsorbed or completely desorbed lanthanides ( e.g. , via nanoconfinment or mixed solvents), will lead to effective Ln 3+ separation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Bond dissociation energies of low-valent lanthanide hydroxides: lower limits from ion–molecule reactions and comparisons with fluorides

Despite that bond dissociation energies (BDEs) are among the most fundamental and relevant chemical properties they remain poorly characterized for most elementary lanthanide hydroxides and halides. Lanthanide ions Ln + = Eu + , Tm + and Yb + are here shown to react with H 2 O to yield hydroxides LnOH + . Additionally, under low-energy conditions such reactions must be exothermic, which implies a lower limit of 499 kJ mol -1 for the Ln + –OH BDEs. This limit is significantly higher than previously reported for YbOH + and is unexpectedly similar to the BDE for Yb + –F. To explain this apparent anomaly, it is considered feasible that the inefficient hydrolysis reactions observed here in a quadrupole ion trap mass spectrometer may actually be endothermic. More definitive and broad-based evaluations and comparisons require additional and more reliable BDEs and ionization energies for key lanthanide molecules, and/or energies for ligand-exchange reactions like LnF + OH ↔ LnOH + F. The hydroxide results motivated an assessment of currently available lanthanide monohalide BDEs. Among several intriguing relationships is the distinctively higher BDE for neutral LuF versus cationic LuF + , though quantifying this comparison awaits a more accurate value for the anomalously high ionization energy of LuF.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Coordination and thermophysical properties of select trivalent lanthanides in LiCl–KCl

The coordination chemistry of various fission and decay products, such as actinides and lanthanides, are crucial to the commercial deployment of molten salt reactors as they can affect the thermophysical properties. In this report we examined the structure, coordination environment, and physical properties such as the density and the vibrational density of states for three lanthanide species, namely Ce, Eu, and Sm in the LiCl–KCl eutectic system using a combination of quantum mechanics simulations and spectroscopic experiments. Quantum mechanics molecular dynamics (QM-MD) modelling was employed to determine the physical properties of each system resulting in accurate local coordination of each species. Then, the vibrational density of states (DOS) was determined using a two-phase thermodynamic modelling which was then compared to the experimentally obtained Raman spectra of the species in molten LiCl–KCl having the eutectic composition. We find that Ce 3+ , Eu 3+ and Sm 3+ all adopt octahedral local coordination environments in the eutectic salt composition in good agreement with experimental results. Ce3+ is found to fluctuate between an octahedral six-coordinated and a seven-coordinated structure due to the increased local proximity of Cl in the eutectic salt, resulting in a lower fluidicity/diffusivity than the other trivalent lanthanides studied. The thermophysical properties of the eutectic composition with trivalent lanthanides were not significantly different from the pure eutectic salt composition, but several changes were noted.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Metadynamics investigation of lanthanide solvation free energy landscapes and insights into separations energetics

Lanthanide ion solvation chemistry in nonaqueous phases is key to understanding and developing effective separation processes for these critical materials. Due to the complexity and inherent disorder of the solution phase, a comprehensive picture of the solvated metal ion is often difficult to generate solely from conventional spectroscopic approaches and electronic structure calculations, particularly in the extractant phase. In this work, we use classical molecular dynamics (MD) simulation with an advanced sampling technique, metadynamics, supplemented by experimental spectroscopy and speciation analysis, to measure lanthanide solvation free energy landscapes. We define coordination-based collective variables to probe the entire range of solvation configurations in the organic phase of lanthanum (La), europium (Eu), and lutetium (Lu) nitrate salts bound with a commonly used extractant, N,N′-dimethyl, N,N′-dioctylhexylethoxymalonamide (DMDOHEMA). The known lanthanide extraction trend of La ≈ Eu > Lu is readily explained by the measured free energy surfaces, which show consistent DMDOHEMA coordination from La to Eu, followed by loss of DMDOHEMA coordination from Eu to Lu. These simulations suggest how ligand crowding at the metal center can control selectivity, in this case resulting in the opposite extraction trend as observed with other conventional extractants, where the enthalpic contribution from increasing lanthanide charge density across the series dominates the extraction energetics. We also find that the presence of inner-sphere water, verified by time-resolved fluorescence, diversifies the accessible solvation structures. As a result, understanding solvation requires consideration of an entire thermodynamic ensemble, rather than the single dominant lowest-energy structure, as is often considered out of necessity in interpretation of spectroscopic data or in electronic structure-based ligand design approaches. In general, we demonstrate how metadynamics uniquely enables investigation of complex, multidimensional solvation energetic landscapes, and how it can explain selectivity trends where extraction is controlled by more complex mechanisms than simple charge density-based selectivity.

Wang, Xiaoyu↗
DOE OSTI2021

Selective Biosorption of Valuable Rare Earth Elements Among Co-Occurring Lanthanides

To meet the increasing demand for rare earth elements (REEs) essential for low carbon-intensity energy technologies, new methods are needed for selective REE extraction from unconventional resources. Only a few REEs have significant economic value, but isolation of target rare earths from co-occurring lanthanides is challenging due to their similar chemical behavior. We present a novel approach to enhance separation of specific REEs from lanthanide mixtures. Escherichia coli cells engineered with lanthanide binding tags (LBTs) were immobilized in nonadsorbing, permeable polyethylene glycol diacrylate beads and packed into continuous flow, fixed-bed columns. Breakthrough of 15 rare earths in the +3 oxidation state resulted in notable differences in adsorption selectivity, with greatest separation between europium (Eu) and lanthanum (La) due to competitive displacement. REE adsorption onto fixed-bed columns was predicted by coupling a surface complexation model to a calibrated one-dimensional dual porosity transport model that accounts for interbead advective and intrabead diffusive transport. A tradeoff between high-abundance, low-affinity native carboxyl sites and low-abundance, high-affinity engineered LBT sites dictates process recovery efficiency and selectivity. Key chemical and operational parameters are identified to maximize selective extraction of high-value lanthanides, achieving a threefold enhancement of Eu recovery relative to La in a mixed REE solution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

High-affinity amide-lanthanide adsorption to gram-positive soil bacteria

The gram-positive soil bacterium, Arthrobacter nicotianae, uses multiple organic acid functional groups to adsorb lanthanides onto its cell surface. At relevant soil pH conditions of 4.0–6.0, many of these functional groups are de-protonated and available for cation sorption and metal immobilization. However, among the plethora of naturally occurring site types, A. nicotianae is shown to possess high-affinity amide and phosphate sites that disproportionately affect lanthanide adsorption to the cell wall. We quantify neodymium (Nd)-selective site types, reporting an amide-Nd stability constant of log 10 K = 6.41 ± 0.23 that is comparable to sorption via phosphate-based moieties. These sites are two to three orders of magnitude more selective for Nd than the adsorption of divalent metals to ubiquitous carboxyl-based moieties. This implies the importance of lanthanide biosorption in the context of metal transport in subsurface systems despite trace concentrations of lanthanides found in the natural environment.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Electrochemical Oxidation and Speciation of Lanthanides in Potassium Carbonate Solution

Increasing lanthanide demand to support clean energy goals drives the need to develop more efficient approaches to separate adjacent lanthanides. Most approaches for lanthanide separations are not very selective and are based on small differences in lanthanide ionic radii. Concentrated potassium carbonate media has shown some potential to enable oxidation of praseodymium (Pr) and terbium (Tb) to their tetravalent states, which could ultimately enable a separation based on differences in oxidation states, but very little is known regarding the system's chemistry. This work completes a detailed examination of cerium (Ce) redox chemistry in concentrated carbonate media to support the development of Pr and Tb oxidation studies. The half-wave potential (E 1/2 ) of the Ce(III)/(IV) redox couple is evaluated under various solution conditions and computational modeling of carbonate coordination environments is discussed. Cyclic voltammetry shows higher carbonate concentrations and temperatures can lower the potential required to oxidize Ce(III) by 54 mV (3.5 to 5.5 M) and 39 mV (from 10 °C to 70 °C). Chronoabsorptometry shows Ce(III) and Ce(IV) carbonate complexes are chemically stable and reversible. Computational modelling suggests the most likely coordination environment for the Ce(IV) complex is Ce(CO 3 ) 4 (OH) 5– which is less entropically favorable than the lowest energy Ce(III) complex, Ce(CO 3 ) 4 5– .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Hydrothermal Growth of Magnetically Frustrated Crystals: Lanthanide Stannate Pyrochlores as a Prototype

One important test bed system for frustrated magnetism is the pyrochlore lattice with the formula A2B2O7 in the cubic space group Fd3(-)m. Both the A and B sites occupy crystallographic trigonal sites and both sites possess a tetrahedral relationship with the other similar metal ion sites. These symmetry relationships generate a 3 D frustrated structure. In frustrated magnetic systems, typically a trivalent lanthanide ion occupies the A site and a magnetically silent tetravalent ion (Ti, Zr, Sn, etc.) occupies the B site. A classical problem related to the crystal growth of these compounds is sample quality. As refractory oxides, the traditional synthesis and crystal growth techniques require high temperatures, which creates two problems that are quite common and endemic to the pyrochlores. One is oxide lattice defects and the other is A/B site disorder. Both issues often occur in the same crystals at the same time and can have a significant impact on the study of physical properties. A hydrothermal approach can be applied to this problem. The relatively low crystal growth temperatures (600-720˚C) greatly minimize nonstoichiometry, lattice defects and A/B site disorder. The reduction of these pervasive imperfections significantly increases the quality of the observed physical property data. This talk will focus on the lanthanide stannates Ln2Sn2O7 as a prototype test bed of these systems. The stannates are among the few building blocks that can stabilize the pyrochlore structure type for all the lanthanides and they serve as an excellent proving ground for a wide range of physical properties. The synthesis and crystal growth of the lanthanide stannates will be reviewed, along with a discussion of some of the physical properties that result from the frustrated magnetic states of these low defect crystals.

Hydrothermal, crystal growth↗
DOE OSTI2026

Hydrated Metal and Metal-Nitrate Complexes in Water: Full Lanthanide(III) Series plus Miscellaneous Metal Ions

This is a dataset of hydrated metal complexes and metal–nitrate hydrated complexes intended for public use, reproducibility, and downstream structural analysis. A key feature is coverage across the full lanthanide(III) series (La–Lu), enabling systematic comparisons of coordination motifs and bonding trends across the entire lanthanide sequence. In addition to the lanthanides, the dataset also includes other metal ions such as UO2(VI), Fe(II), and Fe(III). The dataset provides optimized geometries for hydrated and nitrate-containing hydrated complexes, together with representative ab initio molecular dynamics (AIMD) trajectories saved in standard XYZ formats. The accompanying NWChem input decks enable reproduction of the reported calculations and provide a starting point for extending the simulations to related coordination environments. Computationally, DFT calculations employ the B3LYP functional with DFT-D3BJ dispersion corrections and a COSMO continuum solvent model (dielectric constant 78.4) to represent solvation beyond the explicitly treated first hydration shell. AIMD simulations are performed with the NWChem qmd module at 298 K, integrating nuclear motion with the velocity-Verlet algorithm and controlling temperature using a Nosé–Hoover thermostat. Trajectories are approximately 4.8 ps in length and are used primarily to assess short-time stability of candidate coordination motifs, including (for lanthanides) differences between 8- versus 9-water coordination and comparisons between nitrate-bound and nitrate-free hydrated complexes.

Dinpajooh, Mohammadhasan [Pacific Northwest Nation↗
DOE OSTI2020

Countercurrent Actinide Lanthanide Separation Process (ALSEP) Demonstration Test with a Simulated PUREX Raffinate in Centrifugal Contactors on the Laboratory Scale

An Actinide Lanthanide Separation Process (ALSEP) for the separation of trivalent actinides (An(III)) from simulated raffinate solution was successfully demonstrated using a 32-stage 1 cm annular centrifugal contactor setup. The ALSEP solvent was composed of a mixture of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) and N,N,N',N'-tetra-(2-ethylhexyl)-diglycolamide (T2EHDGA) in n-dodecane. Flowsheet calculations and evaluation of the results were done using the Argonne’s Model for Universal Solvent Extraction (AMUSE) code using single-stage distribution data. The co-extraction of Zr(IV) and Pd(II) was prevented using CDTA (trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid) as a masking agent in the feed. For the scrubbing of co-extracted Mo; citrate-buffered acetohydroxamic acid was used. The separation of An(III) from the trivalent lanthanides (Ln(III)) was achieved using citrate-buffered diethylene-triamine-N,N,N',N",N"-pentaacetic acid (DTPA), and Ln(III) were efficiently back extracted using N,N,N',N'-tetraethyl-diglycolamide (TEDGA). A clean An(III) product was obtained with a recovery of 95% americium and curium. The Ln(III) were efficiently stripped; but the Ln(III) product contained 5% of the co-stripped An(III). The carryover of Am and Cm into the Ln(III) product is attributed to too few actinide stripping stages, which was constrained by the number of centrifugal contactors available. Improved separation would be achieved by increasing the number of An strip stages. The heavier lanthanides (Pr, Nd, Sm, Eu, and Gd) and yttrium were mainly routed to the Ln product, whereas the lighter lanthanides (La and Ce) were mostly routed to the raffinate.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2023

Effective Lanthanide Diffusivity through U-Zr Metallic Fuel

Fuel-cladding chemical interaction (FCCI) is one of the main concerns for the performance of U-Zr metallic fuels. Although FCCI results in complex phase transformations and morphological changes in both the fuel and cladding sides of the interface, the formation of a brittle layer in the cladding side of the interface (sometimes referred to as wastage) has one of the most significant impacts on the cladding mechanical integrity. This brittle layer is associated with the formation of intermetallic compounds between the cladding constituents Fe, Cr and the lanthanide fission product species. The formation of this cladding wastage layer has been the focus of recent efforts to develop a mechanistic modeling framework, including production of lanthanides in the fuel, transport through the fuel to the fuel-cladding interface, and phase transformation to form intermetallic phases. To calculate the rate of transport of lanthanides through the fuel, a multi-scale computational approach has been used. Atomistic calculations have been performed to determine the diffusivities of Nd, the most prevalent lanthanide species, through the solid fuel matrix and along pore surfaces. These diffusivities have been used as input parameters for a mesoscale model to determine an effective diffusion coefficient that accounts for the formation of porosity, its interconnection, and infiltration with bond sodium from the fuel-cladding gap. The effective diffusivity has been used in engineering-scale simulations using the BISON fuel performance code, and BISON simulations have been compared to representative validation cases from the EBR-II reactor.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Gas-phase stability of large lanthanide:diglycolamide clusters evaluated using collision-induced dissociation

Efficient utilization of long-term deep geologic storage repositories is critical for the large-scale deployment of nuclear energy. As the minor actinides (americium and curium) are the largest contributor to the decay heat of used nuclear fuel after a few hundred years, their removal from used fuel prior to disposal can significantly increase the amount of waste that can be stored in a given volume. The development of ligands that can effectively separate the minor actinides from other components of used nuclear fuel are crucial to efficient utilization of geological storage repositories. N,N,N’,N’-tetraoctyl diglycolamide (TODGA) is a promising extractant for the separation of lanthanides and the minor actinides from other components of used nuclear fuel. While the use of TODGA in f-element separations has been investigated in process-based formulations, gas-phase metal ion cluster experiments enable the study of covalent interactions in reprocessing systems absent from solvent effects. Exploring fundamental differences in lanthanide-ligand covalent interactions can impact the development and implementation of actinide-lanthanide separation systems in nuclear fuels reprocessing. In this study, lanthanide-TODGA clusters were synthesized in the gas-phase and identified using mass spectrometry fragmentation experiments. Large europium and samarium clusters were identified that contained up to 8 and 10 bound TODGA ligands, respectively; this was surprising due to the size and multidentate binding that is normal for TODGA. In addition, while smaller clusters showed evidence of sequential ligand fragmentation, larger clusters displayed the loss of neutral TODGA with applied collision voltage. Interestingly, the voltage required for this removal decreased as more TODGA ligands were bound to the metal, suggesting that the metal coordination sphere was becoming more saturated and TODGA ligands were more weakly bound as the clusters got larger.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Quantifying the Influence of Covalent Metal‐Ligand Bonding on Differing Reactivity of Trivalent Uranium and Lanthanide Complexes

Abstract Qualitative differences in the reactivity of trivalent lanthanide and actinide complexes have long been attributed to differences in covalent metal‐ligand bonding, but there are few examples where thermodynamic aspects of this relationship have been quantified, especially with U 3+ and in the absence of competing variables. Here we report a series of dimeric phosphinodiboranate complexes with trivalent f ‐metals that show how shorter‐than‐expected U−B distances indicative of increased covalency give rise to measurable differences in solution deoligomerization reactivity when compared to isostructural complexes with similarly sized lanthanides. These results, which are in excellent agreement with supporting DFT and QTAIM calculations, afford rare experimental evidence concerning the measured effect of variations in metal‐ligand covalency on the reactivity of trivalent uranium and lanthanide complexes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Selective Lanthanide-Organic Catalyzed Depolymerization of Nylon-6 to ϵ-Caprolactam

We report nylon-6 is selectively depolymerized to the parent monomer ϵ-caprolactam by the readily accessible and commercially available lanthanide trisamido catalysts Ln(N(TMS) 2 ) 3 (Ln = lanthanide). The depolymerization process is solvent-free, near quantitative, highly selective, and operates at the lowest Nylon-6 to ..epsilon..-caprolactam depolymerization temperature reported to date. The catalytic activity of the different lanthanide trisamides scales with the Ln 3+ ionic radius, and this process is effective with post-consumer Nylon-6 as well as with Nylon-6 + polyethylene, polypropylene or polyethylene terephthalate mixtures. Experimental kinetic data and theoretical (DFT) mechanistic analyses suggest initial deprotonation of a Nylon terminal amido N-H bond, which covalently binds the catalyst to the polymer, followed by a chain-end back-biting process in which ϵ-caprolactam units are sequentially extruded from the chain end.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Structural Trends and Vibrational Analysis of N,N,N′,N′−Tetramethylmalonamide Complexes Across the Lanthanide Series

Fundamental understanding of coordination chemistry across the lanthanide series is essential for explaining chemical behavior of rare-earth metals in complex liquid-liquid extraction processes, which in turn affects the distribution ratios and efficacy of separations as a whole. In this work, we explore the structural trends between the lanthanides and a neutral N,N,N',N'-tetramethylmalonamide (TMMA) ligand within four isolated families of solid-state compounds: Ln(trans-TMMA) 2 (NO 3 ) 3 Ln=La-Nd, Sm; Ln(cis-TMMA) 2 (NO 3 ) 3 Ln=Eu-Tb, Er; [Ln(TMMA) 3 (NO 3 ) 2 ][Ln(TMMA)(NO 3 ) 4 ] Ln=Dy-Tm; Ln(Κ 2 -TMMA)(iPrOH)(NO 3 ) 3 and Ln(Κ 1 -TMMA)(Κ 2 -TMMA)(NO 3 ) 3 Ln=Yb, Lu. Moving across the lanthanide series, we note the formation of both discrete charge-neutral complexes, as well as charged molecular anion-cation pairs, with variations in spatial ligand arrangement, coordination numbers, and ligand denticities. IR and Raman spectroscopy paired with DFT frequency calculations were used for an in-depth investigation of vibrational modes unique to each structural family. The collection of isolated model compounds was also discussed in the context of liquid-liquid separations based on reported distribution ratios from malonamide extraction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗