Opportunities and challenges of applying advanced X-ray spectroscopy to actinide and lanthanide N-donor ligand systems

Pruessmann, Tim; Nagel, Peter; Simonelli, Laura; Batchelor, David; Gordon, R. A.; Schimmelpfennig, Bernd; Trumm, Michael; Vitova, T.

doi:10.1107/s1600577521012091

Cited by 6 publications

(5 citation statements)

References 107 publications

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“…Fig. 1a, b ) 17 , 18 . Figure 1a, b shows that the pre-edge probes the energy position of the 4f orbitals and gains intensity when Ln 4f are mixed with 5d orbitals in Yb 2 O 3 .…”

Section: Unusual Ln(ii)-based and Ln–(inter)metallic Cluster-based Ma...mentioning

confidence: 99%

Open questions on bonding involving lanthanide atoms

2022

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In-depth understanding of the bonding characteristics of the lanthanide ions in contemporary lanthanide-based materials is mandatory for tailoring their properties for novel applications. Here, the authors elaborate on open questions regarding the bonding situation in mainly molecular lanthanide (4f) compounds, where, as compared to their actinide (5f) analogs in which covalency of the bonds is a common feature, this is still under discussion for the 4f compounds.The bonding properties of the lanthanide 4f elements (Ln = La-Lu), and the electron-poor actinide 5f elements (An = Th-Cm) exhibit similarities in some regards, but generally, they show fundamental differences. Formally, the oxidation states span a range from +II to +IV for the lanthanides, whereas they vary from +II to +VIII for actinides. In nature, commonly found states are +III (Ln) or +IV/+VI (An). The general notion is that the lanthanides form predominantly ionic bonds, at least in their +III oxidation state, whereas the actinides are capable of undergoing covalent bonding, but to a lesser extent than the d-block transition metals. This again strongly depends on the oxidation state of the actinides, with the most prominent example being the covalent bonds formed in the actinyl ions [An(V)/(VI)O 2 ] 1+/2+ . However, this traditional view on the chemical behavior of the elements at the bottom of the periodic table is rapidly changing nowadays. Advances in spectroscopy give indications that lanthanide atoms can also be involved in covalent bonding interactions. This opens a question about the nature of such bonds, which will also affect further chemical and physical properties like reactivity, bond stability, and emission as well as magnetic behavior. Advances in Ln(II) and Ln-(inter)metallic coordination chemistry unveil new lanthanide-based materials with unexplored physical and chemical properties-a treasure chest for the development of novel applications with tailored properties. Covalency in lanthanide bondingThe classical definition for a covalent chemical bond is the accumulation of electron density between the involved atoms. The covalency of the bond can be described by the mixing coefficient, and it will increase if the orbital overlap is large or the energy difference between metal and ligand orbitals is minimized (cf. Fig. 1d) 1 . The interconnection between the orbital overlap and energy-degeneracy-driven covalency, and the subsequent impact on reactivity or bond stability for both lanthanide and actinide compounds, is not well understood and at the forefront of lanthanide and actinide research. Recently, the group of Gregory Nocton reviewed Yb, Eu, Tm, and Ce organometallic lanthanide compounds with intermediate oxidation states like for example LnCp 3 (Ln = Ce, Eu, or Yb; Cp = cyclopentadienide, (C 5 H 5 ) − ), [Cp* 2 Yb(bipy)], [Cp* 2 Yb(dad)], and [Cp* 2 Yb(phen)] (Cp* = pentamethylcyclopentadienide, (C 5 Me 5 ) − ; bipy = 2,2'-bipyridine, C 10 H 8 N 2 ; dad = 1,4-diazabutadiene; phen = phenanthroline, C 12 H 8 N 2 ) 2 . These materi...

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“…Fig. 1a, b ) 17 , 18 . Figure 1a, b shows that the pre-edge probes the energy position of the 4f orbitals and gains intensity when Ln 4f are mixed with 5d orbitals in Yb 2 O 3 .…”

Section: Unusual Ln(ii)-based and Ln–(inter)metallic Cluster-based Ma...mentioning

confidence: 99%

Open questions on bonding involving lanthanide atoms

2022

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“…Besides the scientific importance, actinide speciation studies are key to understanding extraction mechanisms and separation processes in fuel reprocessing (Dressler et al, 2022;Moeyaert et al, 2021;Pruessmann et al, 2022), the corrosion and the reduction-oxidation behavior of nuclear waste forms in storage facilities (Glasauer et al, 2022;Husar et al, 2022), the mechanisms by which actinides can contaminate the biosphere (Cot-Auriol et al, 2021;Estevenon et al, 2021;Pidchenko et al, 2020;Vitova et al, 2020), their mobility in contaminated sites and how best they can be removed from the environment (Dumas et al, 2022;Jegou et al, 2022;Le Pape et al, 2020). The clean up of the Rocky Flats Nuclear Weapons Plant, near Denver, is exemplary of the practical importance of these studies (Clark et al, 2006).…”

Section: Xas Experimentsmentioning

confidence: 99%

Synchrotron Radiation Techniques and their Application to Actinide Materials

Caciuffo¹,

Lander²,

Laan³

2022

Preprint

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Research on actinide materials, both basic and applied, has been greatly advanced by the general techniques available from high-intensity photon beams from x-ray synchrotron sources. The most important single reason is that such x-ray sources can work with minute (e.g., microgram) samples, and at this level the radioactive hazards of actinides are much reduced. We start by discussing the form and encapsulation procedures used for different techniques, then discuss the basic theory for interpreting the results. By reviewing a selection of x-ray diffraction (XRD), resonant elastic x-ray scattering (REXS), x-ray magnetic circular dichroism (XMCD), resonant and non-resonant inelastic scattering (RIXS, NIXS), dispersive inelastic x-ray scattering (IXS), and conventional and resonant photoemission experiments, we demonstrate the potential of synchrotron radiation techniques in studying lattice and electronic structure, hybridization effects, multipolar order, and lattice dynamics in actinide materials. CONTENTS I. Introduction 1 II. Samples and beamlines 3 References 49

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“…1−7 Despite their applications, their fundamental chemistry is not well understood, hindering the development of technologies that require f elements. 8,9 The electrons in f elements are subject to a combination of relativistic effects due to the high nuclear charges they experience and incomplete shielding of nuclear charge by electrons at lower energies. 10−12 This causes the 4f and 5f orbitals to be spatially retracted behind core orbitals.…”

Section: ■ Introductionmentioning

confidence: 99%

“…The f block of the periodic table, made up of the lanthanides (Ln) and actinides (An), is a unique set of elements that play an increasing role in modern society, where they can be found in a wide variety of sectors from energy and catalysis to disease treatment and organic synthesis. − Despite their applications, their fundamental chemistry is not well understood, hindering the development of technologies that require f elements. , The electrons in f elements are subject to a combination of relativistic effects due to the high nuclear charges they experience and incomplete shielding of nuclear charge by electrons at lower energies. − This causes the 4f and 5f orbitals to be spatially retracted behind core orbitals . The wider consequence of this orbital contraction is that metal–ligand bonding of Ln and An is traditionally thought to be directed by electrostatic interactions with little covalency .…”

Section: Introductionmentioning

confidence: 99%

Contemporary Assessment of Energy Degeneracy in Orbital Mixing with Tetravalent f-Block Compounds

Pereiro,

Galley,

Jackson

et al. 2024

Inorg. Chem.

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The f block is a comparatively understudied group of elements that find applications in many areas. Continued development of technologies involving the lanthanides (Ln) and actinides (An) requires a better fundamental understanding of their chemistry. Specifically, characterizing the electronic structure of the f elements presents a significant challenge due to the spatially core-like but energetically valence-like nature of the f orbitals. This duality led f-block scientists to hypothesize for decades that f-block chemistry is dominated by ionic metal–ligand interactions with little covalency because canonical covalent interactions require both spatial orbital overlap and orbital energy degeneracy. Recent studies on An compounds have suggested that An ions can engage in appreciable orbital mixing between An 5f and ligand orbitals, which was attributed to “energy-degeneracy-driven covalency”. This model of bonding has since been a topic of debate because different computational methods have yielded results that support and refute the energy-degeneracy-driven covalency model. In this Viewpoint, literatures concerning the metal- and ligand-edge X-ray absorption near-edge structure (XANES) of five tetravalent f-block systemsMO2 (M = Ln, An), LnF4, MCl6 2–, and [Ln(NP(pip)3)4]are compiled and discussed to explore metal–ligand bonding in f-block compounds through experimental metrics. Based on spectral assignments from a variety of theoretical models, covalency is seen to decrease from CeO2 and PrO2 to TbO2 through weaker ligand-to-metal charge-transfer (LMCT) interactions, while these LMCT interactions are not observed in the trivalent Ln sesquixodes until Yb. In comparison, while XANES characterization of AnO2 compounds is scarce, computational modeling of available X-ray absorption spectra suggests that covalency among AnO2 reaches a maximum between Am and Cm. Moreover, a decrease in covalency is observed upon changing ligands while maintaining an isostructural coordination environment from CeO2 to CeF4. These results could allude to the importance of orbital energy degeneracy in f-block bonding, but there are a variety of data gaps and conflicting results from different modeling techniques that need to be addressed before broad conclusions can be drawn.

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Opportunities and challenges of applying advanced X-ray spectroscopy to actinide and lanthanide N-donor ligand systems

Cited by 6 publications

References 107 publications

Open questions on bonding involving lanthanide atoms

Open questions on bonding involving lanthanide atoms

Synchrotron Radiation Techniques and their Application to Actinide Materials

Contemporary Assessment of Energy Degeneracy in Orbital Mixing with Tetravalent f-Block Compounds

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