Trivalent 4f Research Articles

A trivalent 4f complex with two bis-silylamide ligands displaying slow magnetic relaxation.

The best-performing single-molecule magnets (SMMs) have historically relied on pseudoaxial ligands delocalized across several coordinated atoms. This coordination environment has been found to elicit strong magnetic anisotropy, but lanthanide-based SMMs with low coordination numbers have remained synthetically elusive species. Here we report a cationic 4f complex bearing only two bis-silylamide ligands, Yb(III)[{N(SiMePh2)2}2][Al{OC(CF3)3}4], which exhibits slow relaxation of its magnetization. The combination of the bulky silylamide ligands and weakly coordinating [Al{OC(CF3)3}4]- anion provides a sterically hindered environment that suitably stabilizes the pseudotrigonal geometry necessary to elicit strong ground-state magnetic anisotropy. The resolution of the mJ states by luminescence spectroscopy is supported by ab initio calculations, which show a large ground-state splitting of approximately 1,850 cm-1. These results provide a facile route to access a bis-silylamido Yb(III) complex, and further underline the desirability of axially coordinated ligands with well-localized charges for high-performing SMMs.

On the Modeling of the S-Shaped Thermodynamic and Transport Behavior against the Atomic Number Z of Some Trivalent f-Element Ions in Aqueous Solutions at 298 K and Prediction for Completion of the Periodic Table of Chemical Elements

Ionic self-diffusion coefficients D of some trivalent lanthanide and actinide ions have been determined by the open-end capillary method (O.E.C.M.) in supporting lanthanide electrolyte 1 : 3 aqueous solutions at 25°C and optimal pH 2.50 in order to avoid hydrolysis, ion pairing and complexing of trivalent 4f ions. This study contributes to demonstrate similarities in transport and structure properties between 4f and 5f trivalent ions explained by a similar electronic configuration, ionic radius and same hydration number. These similarities are manifested in a strong causal correlation between certain properties by linear or S-shaped behaviors. In this context, we have suggested some expressions relating these properties and interesting to estimate or predict, by interpolation or extrapolation methods, some eventually not available experimental values, especially for the actinides for which the half-life is very short or the experimental conditions are very special and expensive. For this issue, we can contribute to the complement of periodic table of elements by some physicochemical properties, especially for the 5f-series, when we have some available data on the 4f‑series as well as the mathematical function of the causal correlation between these two nf-series.

Overlap integrals and excitation energies calculations in trivalent lanthanides 4f orbitals in pairs Ln-L (L = Ln, N, O, F, P, S, Cl, Se, Br, and I)

In this work, DFT-based calculations of overlap integrals (ρ) and excitations energies (Δε) associated with the diatomic-like pairs Ln3+-Ligand and Ln-Ln’ are presented. The ρ and Δε quantities are useful for the calculations of overlap polarizability, charge factors, intensity parameters (using the Simple Overlap and Bond Overlap models), 4f shielding factors, and energy transfer process (ligand-to-Ln and Ln-Ln). A comprehensive set of parametric curves of the type exp(a + bR + cR2) are presented to easily determine these properties at a given distance R. Some literature is presented to indicate the importance of ρ and Δε quantities in photophysical properties of lanthanide-based compounds.

PH-Metric studies of (2-pyrrole)-(5,6-diphenyl-[1,2,4]-triazin-3-yl)hydrazone with inner transition metals

The reaction of (2-pyrrole)-(5,6-diphenyl-[1,2,4]-triazin-3-yl)hydrazone with trivalent 4f lanthanide metal ions (LaIII, PrIII, NdIII, SmIII, EuIII, GdIII, TbIII, DyIII, HoIII, ErIII and YbIII) and 5f actinide metal ion UO2II has been studied potentiometrically in 75% (v/v) dioxane-water; at 283, 293, 303 and 313K. The ligand behaves as mono-protic species with the dissociation of hydrazo group proton and reacts with metal ion in molar ratio 1:2; M:L in solution. The formation constants were caulculated, which decrease as temprerature increases. The negative values of ΔH° and ΔG° indicate that the complexation are exothermic and proceeds spontaneously, respectivily. The electrostatic forces are weaker than non-electrostatic forces, where -DG°non is lower than -DG°el.

Distortion mode anomalies in bulk PrNiO3 : Illustrating the potential of symmetry-adapted distortion mode analysis for the study of phase transitions

The origin of the metal-to-insulator transition in RNiO3 perovskites with trivalent 4f ion has challenged the condensed matter research community for almost three decades. A drawback for progress in this direction has been the lack of studies combining physical properties and accurate structural data covering the full nickelate phase diagram. Here we focus on a small region close to the itinerant limit (R = Pr, 1.5K < T < 300K), where we investigate the gap opening and the simultaneous emergence of charge order in PrNiO3. We combine electric resistance, magnetization, and heat capacity measurements with high resolution neutron and synchrotron x-ray powder diffraction data that, in contrast to previous studies, we analyze in terms of symmetry-adapted distortion modes. Such analysis allows to identify the contribution of the different modes to the global distortion in a broad temperature range. Moreover, it shows that the structural changes at the MIT, traditionally described in terms of the evolution of the interatomic distances and angles, appear as abrupt increases of all nonzero mode amplitudes at TMIT = TN ~130K accompanied by the appearance of new modes below this temperature. A further interesting observation is the existence of a nearly perfect linear correlation between the amplitude of the breathing mode associated to the charge order and the staggered magnetization below the MIT. Our data also uncover a previously unnoticed anomaly at T* ~60K (~0.4 x TMIT), clearly visible in the electrical resistance, lattice parameters and some mode amplitudes. Since phase coexistence is only observed in a small temperature region around TMIT (~10K), these observations suggest the existence of a hidden symmetry in the insulating phase. We discuss some possible origins, among them the theoretically predicted existence of polar distortions induced by the non-centrosymmetric magnetic order.

Valence instability in the bulk and at the surface of the antiferromagnet SmRh2Si2

Using resonant angle-resolved photoemission spectroscopy and electron band-structure calculations, we explore the electronic structure and properties of Sm atoms at the surface and in the bulk of the antiferromagnet SmRh2Si2. We show that the Sm atoms reveal weak mixed-valent behavior both in the bulk and at the surface. Although trivalent 4f emission strongly dominates, a small divalent 4f signal near the Fermi energy can be clearly resolved for surface and bulk Sm atoms. This behavior is quite different to most other Sm-based materials which typically experience a surface valence transition to a divalent state of Sm atoms at the surface. This phenomenon is explained in analogy to the isostructural Ce compound, where strong 4f hybridization stabilizes mixed-valent ground state both in the bulk and at the surface, and which were described in the light of the single-impurity Anderson model. Implications for other RERh2Si2 (RE = rare-earth elements) compounds are discussed.

Structural study of complexes formed by acidic and neutral organophosphorus reagents

The coordination of the trivalent 4f ions, Ln = La3+, Dy3+, and Lu3+, with neutral and acidic organophosphorus reagents, both individually and combined, was studied by use of X-ray absorption spectroscopy. These studies provide metrical information about the interatomic interactions between these cations and the ligands tri-n-butyl phosphate (TBP) and di-n-butyl phosphoric acid (HDBP), whose behavior are of practical importance to chemical separation processes that are currently used on an industrial scale. Previous studies have suggested the existence of complexes involving a mixture of ligands, accounting for extraction synergy. Through systematic variation of the aqueous phase acidity and extractant concentration and combination, we have found that complexes with Ln and TBP : HDBP at any mixture and HDBP alone involve direct Ln-O interactions involving 6 oxygen atoms and distant Ln-P interactions involving on average 3-5 phosphorus atoms per Ln ion. It was also found that Ln complexes formed by TBP alone seem to favor eight oxygen coordination, though we were unable to obtain metrical results regarding the distant Ln-P interactions due to the low signal attributed to a lower concentration of Ln ions in the organic phases. Our study does not support the existence of mixed Ln-TBP-HDBP complexes but, rather, indicates that the lanthanides are extracted as either Ln-HDBP complexes or Ln-TBP complexes and that these complexes exist in different ratios depending on the conditions of the extraction system. This fundamental structural information offers insight into the solvent extraction processes that are taking place and are of particular importance to issues arising from the separation and disposal of radioactive materials from used nuclear fuel.

Thermally Stimulated Luminescence and First-Principle Study of Defect Configurations in the Perovskite-Type Hydrides LiMH3:Eu2+ (M = Sr, Ba) and the Corresponding Deuterides

Temperature-dependent photoluminescence (PL) as well as thermoluminescence (TL) were studied in the Eu2+-doped hydrides LiMH3 (M = Sr, Ba) and the corresponding deuterides. Here, thermally stimulated luminescence was observed for the first time in a Eu2+-doped hydrides and deuterides. The onset temperature of quenching (T95 %) and the quenching temperature (T50 %) were determined from photoluminescence intensities, and the energy barrier for thermal quenching was estimated. Then, a scheme with the localization of divalent and trivalent lanthanide 4f and 5d levels for the example LiSrH3 was proposed. In deuterides, the quenching temperatures are slightly higher than in hydrides, which can be related to the influence of the different phonon frequencies. In the TL measurements we observed very shallow and intense TL glow peaks in all samples. We also used density functional methods in order to show qualitative trends for the stability of possible defects. The model calculation suggest that energetically favo...

Uncovering f-element bonding differences and electronic structure in a series of 1 : 3 and 1 : 4 complexes with a diselenophosphinate ligand

Understanding the bonding trends within, and the differences between, the 4f and 5f element series with soft donor atom ligands will aid elucidation of the fundamental origins of actinide (An) versus lanthanide (Ln) selectivity that is integral to many advanced nuclear fuel cycle separation concepts. One of the principal obstacles to acquiring such knowledge is the dearth of well characterized transuranic molecules that prevents the necessary comparison of 4f versus 5f coordination chemistry, electronic structure, and bonding. Reported herein is new chemistry of selenium analogues of dithiophosphinate actinide extractants. LnIII and AnIII/IV complexes with the diselenophosphinate [Se2PPh2]− anion have been synthesized, structurally and spectroscopically characterized, and quantum chemical calculations performed on model compounds in which the phenyl rings have been replaced by methyl groups. The complexes [LnIII(Se2PPh2)3(THF)2] (Ln = La (1), Ce (2), Nd (3)), [LaIII(Se2PPh2)3(MeCN)2] (4), [PuIII(Se2PPh2)3(THF)2] (5), [Et4N][MIII(Se2PPh2)4] (M = Ce (6), Pu (7)), and [AnIV(Se2PPh2)4] (An = U (8), Np (9)), represent the first f-element diselenophosphinates. In conjunction with the calculated models, complexes 1–9 were utilized to examine two important factors: firstly, bonding trends/differences between trivalent 4f and 5f cations of near identical ionic radii; secondly, bonding trend differences across the 5f series within the AnIV oxidation state. Analysis of both experimental and computational data supports the conclusion of enhanced covalent bonding contributions in PuIII–Se versus CeIII–Se bonding, while differences between UIV–Se and NpIV–Se bonding is satisfactorily accounted for by changes in the strength of ionic interactions as a result of the increased positive charge density on NpIV compared to UIV ions. These findings improve understanding of soft donor ligand binding to the f-elements, and are of relevance to the design and manipulation of f-element extraction processes.

Self-diffusion coefficients of the trivalent f-element ion series in dilute and moderately dilute aqueous solutions: A comparative study between europium, gadolinium, terbium and berkelium

We have continued the studies on the trivalent ions of the 4f and 5f elements. In this paper, we compare the transport properties (self-diffusion coefficient) of the trivalent aquo ions over two ranges of concentrations (0 — 2×10−3M) and (2×10−3 — 1.5M). Self-diffusion coefficients, D, of the trivalent f-element aquo ion series have been determined in aqueous background electrolytes of Gd(NO3)3 and Nd(ClO4)3, at pH=2.5 (HNO3, HClO4) and at 25°C using the open-end capillary method (O.E.C.M.). This method measures the transportation time of ions across a fixed distance. In this paper, we complete a measurement of self-diffusion coefficient for terbium. We optimized the pH to avoid hydrolysis, ion-pairing and complexation of the trivalent 4f and 5f ions. The variation of D versus √C is not linear for dilute solutions (0 — 2×10−3M) and quasi-linear in moderate concentrations (C≤1.5 M). Similar behavior was observed for Tb, as compared with those for Bk, Eu and Gd. We complete the comparison variation of D/D° versus √C for all studied 4f and 5f elements from concentration 0 to 1.5M and we obtained the same variation with √C for all studied elements. All 4f and 5f elements studied follow the Nernst-Hartley expression.

Valence of “divalent” rare earth metals

It is generally recognized that light rare earths change their valence from 2 to 3 when forming a bulk metal while remaining divalent at the surface. However, performed DFT calculations ultimately indicate that the higher-binding-energy peaks in photoemission spectra (like the −5.3 eV peak for Sm), characteristic of the trivalent 4f n−1 5d 1 configuration, correspond not to the ground state, but to excited states induced by radiation. This means that the trivalent state is not inherent for the bulk of divalent rare earths, and therefore they do not become trivalent.

Pressure-Induced Superconducting State of Europium Metal at Low Temperatures

Divalent Eu (4f;{7}, J=7/2) possesses a strong local magnetic moment which suppresses superconductivity. Under sufficient pressure it is anticipated that Eu will become trivalent (4f;{6}, J=0) and a weak Van Vleck paramagnet, thus opening the door for a possible superconducting state, in analogy with Am metal (5f;{6}, J=0) which superconducts at 0.79 K. We present ac susceptibility and electrical resistivity measurements on Eu metal for temperatures 1.5-297 K to pressures as high as 142 GPa. At approximately 80 GPa Eu becomes superconducting at T_{c} approximately 1.8 K; T_{c} increases linearly with pressure to 2.75 K at 142 GPa. Eu metal thus becomes the 53rd known elemental superconductor in the periodic table.

An equation for self-diffusion coefficients of the trivalent lanthanide ion 152Eu (III) in concentrated asymmetrical 3:1 electrolyte aqueous solutions at pH 2.50 and at 298.15 K

Ionic self-diffusion coefficients D of the trivalent ion 152Eu (III) have been determined in aqueous Gd(NO 3) 3–HNO 3 concentrated solutions (pH = 2.50) at 25 °C by the open-end capillary method (O.E.C.M.). The method measures the transportation time of ion across a fixed distance. We optimized the pH in order to avoid the hydrolysis, pairing and complexing trivalent 4f ions. The diffusion data obtained in large range of concentration as well as the physicochemical properties, allow to derive the following information: ( i) the limiting value D° at zero ionic strength, as 6.115 10 − 6 cm 2 s − 1 for 152Eu (III), ( ii) the validity of the Onsager limiting law, ( iii) the ionic self-diffusion coefficient as a function of the ionic strength for asymmetrical 3:1 electrolytes in dilute solutions, ( iv) a competition between ion–ion interaction and ion–solvent interaction and ( v) a more extended law available for an intermediate range of concentration up to 0.114 mol L − 1 and for a concentrated range up to 1.5 mol L − 1 . This study contributes to demonstrate similarities transport and structure properties between 4f and 5f trivalent ions explained by a similar electronic configuration, ionic radius and same hydration number.

Self-diffusion coefficients and structure of the trivalent f-element ions, Eu, Gd, Am, Bk, Cf and Es in aqueous diluted and concentrated solutions

Self-diffusion coefficients D of the trivalent ions in aqueous solutions of Eu and Gd have been determined in electrolyte support Gd(NO 3) 3, and of Am, Bk, Cf and Es in electrolyte support Nd(ClO 4) 3, in concentrated solutions at (pH = 2.5) HNO 3, HClO 4 and at 25 °C using the open end capillary method (O.E.C.M.). This method measures the transportation time of ions across a fixed distance. In this paper we complete a measurement of self-diffusion coefficient at concentrated solution (1.5 M). We optimized the pH in order to avoid the hydrolysis, pairing and complexing trivalent 4f and 5f ions. The behavior of D and Dη are plotted versus √ C. The similarities observed of self-diffusion coefficients of trivalent f-elements ions can be explained by a similar electronic configuration and same hydration number. The variation of D versus the square root of the concentration of the solution was found to be quasi-linear in the studied concentration range ( C ≤ 1.5 M). Results of the diffusion for the two couples (Am–Eu) and (Bk–Gd) show us that 4f and 5f elements, having similar electronic configuration and/or sub shell half-filled configuration of trivalent ions, have the same behavior. We compared variation of D/ D° versus √ C for all studied 4f and 5f elements from concentration 0 to 1.5 M and we obtained the same variation with √ C for all studied elements. We have estimated activity coefficients for both 4f and 5f trivalent ion elements using Nernst–Hartley expression. We deduced that we can achieve self-diffusion experience using 4f support electrolyte as Nd(ClO 4) 3 in acid medium and needing only some 5f element tracer element. This method is adequate for the study of 5f element which is not available as a macro element such as heavy 5f elements fermium Fm 3+ and mendelevium Md 3+.

The interaction between trivalent 4f and 5f-block elements and thiocyanate ion

The formation constants of thiocyanate complexes of Eu(III) and Am(III) in trace concentrations were investigated in mixed solvent (CH3OH+H2O) solutions of different ionic strength. Furthermore, in paper electrophoresis, the moving velocities of the species of Eu(III) and Am(III) were investigated in 1.1M (H, Na)(SCN, ClO4) mixed solvent (CH3OH-H2O) solutions. The results showed that the difference between the velocities of Eu(III) and Am(III) is explained by the difference of the mean charges calculated by the formation constants of thiocyanate complexes of Eu(III) and Am(III) in the solution.

Electronic structure and photoemission properties of EuF 3 and EuCo 2X 2 (X = Si, Ge) compounds by ab initio methods

Electronic, magnetic and photoemission properties of the mixed-valence EuF 3and EuCo 2X 2 compounds have been studied theoretically. Calculations have shown that europium is trivalent (4f 6) in EuF 3 compound. In EuCo 2X 2, the Eu is of intermediate valence Eu 2.5+ (4f 6.5). EuF 3 compound is found nonmagnetic insulator. In EuCo 2X 2, only the europium is polarized magnetically. Photoemission (PE) measurements on EuF 3 proved the exchange splitting of core s-type levels of europium even though it is in nonmagnetic ( J = 0 ) state. The calculated exchange splitting of the Eu 4s and 5s states compares quantitatively well with the observed ones.

Structural study of trivalent lanthanide and actinide complexes formed upon solvent extraction

The coordination of the trivalent 4f ions, Ln = Nd3+, Eu3+ and Yb3+, as well as the trivalent 5f ion, Am3+, with diamide and dialkylphosphoric acid extractants, individually and in combination, was studied by use of X-ray absorption spectroscopy. These studies provide metrical information about the interatomic interactions between the f-ions (M3+) and the ligands, dihexylphosphoric acid (HDHP) and N,N'-dimethyl-N,N'-dioctylhexylethoxymalonamide (DMDOHEMA), that is of practical relevance to the control of metal-ligand binding in liquid-liquid extraction systems for the separation of trivalent actinide ions, An3+, from trivalent lanthanide ions, Ln3+. Through systematic variations of extraction conditions and extractant combinations, we have found that the HDHP complexes with M3+ involve MO6 coordination and distant M...P interactions, whereas the DMDOHEMA complexes with M3+ involve MO8 coordination. The combination of the EXAFS results with ancillary extraction data and IR results facilitates descriptions of the stoichiometries and structures of the molecular species formed in solution upon liquid-liquid extraction and leads to a new understanding of the binary extraction systems in terms of the strength and selectivity of An3+- vs. Ln3+-ligand interactions. This fundamental structure information affords insight into solvent extraction processes that are of contemporary and practical importance in heavy element chemistry and to environmentally related issues arising from the separation and disposal of radioactive materials, particularly actinides and selected fission products, in the field of nuclear waste reprocessing research.

Variation of 4f hybridization across the rare-earth series

4f photoemission spectra of TbRh reveal a broadening of the 8 S term of the 4f 7 final-state multiplet into a double peak while multiplet components at higher binding energies remain unaffected. As in case of Pr 5Rh 4 and Nd 5Rh 4, where similar but larger splittings have been observed, the phenomenon is analyzed in the light of a single-impurity Anderson model. As a result of this analysis, the hybridization parameter is found to decrease monotonously by a factor of 1.5 in going from the Pr–Rh to the TbRh compound as expected from calculated f→d hopping matrix elements. Two percent admixture of divalent 4f 9 configurations to the trivalent Tb 4f 8 ground state are concluded.

A comparison of analogous 4f- and 5f-element compounds: syntheses and crystal structures of triphenylphosphine oxide complexes of lanthanide(III) and uranium(III) triflates and iodides [MX 2(OPPh 3) 4][X] (X=OTf and M=Ce or U; X=I and M=Nd, Ce, La, U)

The X-ray crystal structures of the title complexes show that the differences between the U–O and Ln–O distances reflect the variation in the ionic radii of the trivalent uranium and lanthanide ions while the U–I bond lengths are smaller than those predicted from a purely ionic bonding model. The results indicate that the uranium ion interacts more strongly than the lanthanide ions with the softer iodide ligand, and that the counterions would have a major influence on the differentiation of trivalent 4f and 5f ions.

Covalency in f-element bonds

The actinide concept proposed by Seaborg in 1945 involves a close relationship between the trivalent 4f (Ln) and the 5f (An) elements. The trivalent ions of these two families have very similar properties due to strong ionic bonding and similar ionic radii. Their similarity led to the successful formation of element 95–103 over the next 30 years by accurate prediction of the chemistry of the undiscovered elements. In the early 1950s, a small degree of covalency was proposed in the bonding of the lanthanide elements. However, controversy continues today on the degree of covalency in the bonds of the 4f and 5f elements. The interpretation of data in terms of covalency in the M–L bonds is reviewed with emphasis on which orbitals are involved.