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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Cation Translocation around Single Polyoxometalate-Organic Hybrid Cluster Regulated by Electrostatic and Cation-π Interactions

We report herein an interesting dynamic translocation process of countercations around one polyoxometalate(POM)–organic hybrid anionic cluster at various concentrations and temperatures. It was found that both electrostatic interactions and cation–π interactions regulate the position of small countercations around single clusters. The dynamic geometry and the symmetry of the hybrid macroions are largely affected by the type of counterions, as shown by nuclear magnetic resonance (NMR) spectroscopy studies and all-atom molecular dynamics simulation. It is also shown that electrostatic interactions dominate over cation–π interactions in determining the locations of the counterions in the current system.

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

Connecting cation site location to alkane dehydrogenation activity in Ni/BEA catalysts

Ni-modified beta zeolite (Ni/BEA) catalysts activate carbon-hydrogen bonds in light alkanes, as demonstrated through isobutane reaction testing. Controlled synthesis of Ni/BEA allows for efficient introduction of ion-exchanged Ni sites at varying Ni loadings (0.43% - 1.8%). These catalysts exhibit site time yields (STY) for H2 production that increase with increasing Ni loading. A detailed analysis of secondary reactions and carbon deposition based on the relative molar flowrates of product C and H indicates that the observed increase in H2 STY with increasing Ni loading is likely attributed to both increasing alkane activation activity and increasing formation of hydrogen-deficient aromatic products retained within the catalyst pores. In situ diffuse-reflectance UV-visible-NIR absorbance and X-ray absorption spectroscopies indicate isolated, 4-coordinate Ni(2+) species for all loadings. Quantum mechanics/molecular mechanics modeling identifies two distinct Ni(2+) sites consistent with the structural characterization, but with differing relative stabilities due to their coordination environment. Computed reaction energetics for isobutane dehydrogenation demonstrate that the more stable Ni(2+) species at a six-membered 4Si-2Al ring, Ni-6MR, is less active for isobutane dehydrogenation than the less stable Ni(2+) at the five-membered 3Si-2Al ring, Ni-5MR. The differing local structure of the isolated cationic Ni sites in Ni/BEA offers a possible rationalization for the increased H2 STY observed at greater Ni loadings.

catalysts↗
DOE OSTI2016

Self-assembly of [UO{sub 2}X{sub 4}]{sup 2−} (X=Cl, Br) dianions with γ substituted pyridinium cations: Structural systematics and fluorescence properties

Room temperature self-assembly of [UO{sub 2}X{sub 4}]{sup 2−} (X=Cl, Br) with γ substituted pyridinium cations has resulted in the formation of twelve compounds that were studied via single crystal X-ray diffraction and fluorescence spectroscopy. Systematic variation of electron donating groups on the pyridinium species is shown to influence the presence and/or strength of various supramolecular synthons, including hydrogen bonding and pi interactions. Combinations of such non-covalent interactions (NCIs) have given rise to a range of supramolecular assemblies, and are shown to influence uranyl emission by way of second sphere coordination to equatorial ligands. - Graphical abstract: Supramolecular assembly of the [UO{sub 2}Cl{sub 4}]{sup 2−} dianion with pyridinium cations is a viable synthetic route to the growth of uranyl containing single crystals.

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

A Spectroscopic and Computational Evaluation of Uranyl Oxo Engagement with Transition Metal Cations

Here, we report the synthesis and characterization of five novel Cd 2+ /UO 2 2+ heterometallic complexes that feature Cd-oxo distances ranging from 78 to 171% of the sum of the van der Waals radii for these atoms. This work marks an extension of our previously reported Pb 2+ /UO 2 2+ and Ag + /UO 2 2+ complexes, yet with much more pronounced structural and spectroscopic effects resulting from Cd-oxo interactions. We observe a major shift in the U═O symmetric stretch and significant uranyl bond length asymmetry. The ρbcp values calculated using Quantum Theory of Atoms in Molecules (QTAIM) support the asymmetry displayed in the structural data and indicate a decrease in covalent character in U═O bonds with close Cd-oxo contacts, more so than in related compounds containing Pb 2+ and Ag + . Second-order perturbation theory (SOPT) analysis reveals that O sp x → Cd s is the most significant orbital overlap and U═O bonding and antibonding orbitals also contribute to the interaction (U═O σ/π → Cd d and Cd s → U═O σ/π*). The overall stabilization energies for these interactions were lower than those in previously reported Pb 2+ cations, yet larger than related Ag + compounds. Analysis of the equatorial coordination sphere of the Cd 2+ /UO 2 2+ compounds (along with Pb 2+ /UO 2 2+ complexes) reveals that 7-coordinate uranium favors closer, stronger M n+ -oxo contacts. These results indicate that U═O bond strength tuning is possible with judicious choice of metal cations for oxo interactions and equatorial ligand coordination.

cations↗
DOE OSTI2019

Destruction of the Uranyl Moiety in a U(V) “Cation–Cation” Interaction

A gas-phase uranyl peroxide dimer supported by three 12-crown-4 ether (12C4) ligands, [(UO 2 ) 2 (O 2 )(12C4) 3 )] 2+ (A), was prepared by electrospray ionization. Density functional theory (DFT) indicates a structure with two terminal 12C4 and the third 12C4 bridging the uranium centers. Collision induced dissociation (CID) of A resulted in elimination of the bridging 12C4 to yield a uranyl peroxide dimer with two terminal donor ligands, [(12C4)(UO 2 )(O 2 )(UO 2 )(12C4)] 2+ (B). Remarkably, CID of B resulted in elimination of the bridging peroxide concomitant with reduction of U(VI) to U(V) in C, [(12C4)(UO 2 )(UO 2 )(12C4)] 2+ . DFT studies indicate that in C there is direct interaction between the two UO2+ species, which can thus be considered as a so-called cation-cation interaction (CCI). This formal CCI, induced by tetradentate 12C4 ligands, corresponds to destruction of the linear uranyl moieties and creation of bridging U-O-U oxo-bonds. Finally, on the basis of the structural rearrangement to achieve the structurally extreme CCI interaction, it is predicted also to be accessible for PaO 2 + but is less feasible for transuranic actinyls.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Effect of Cation Rotation on Charge Dynamics in Hybrid Lead Halide Perovskites

Organic-inorganic hybrid halide perovskites are a promising class of materials for photovoltaic application with reported power efficiencies over similar to 22%. However, not much is known about the influence of the organic dipole rotation and phase transitions on charge carrier dynamics. Here, we report substantial changes in mobility and lifetime of charge carriers in CH 3 NH 3 PbI 3 after the low-temperature tetragonal (beta) to orthorhombic (gamma) phase transition. By using microwave conductivity measurements, we observed that the mobility and lifetime of ionized charge carriers increase as the temperature decreases and a sudden increment is seen after the beta-gamma phase transition. For CH 3 NH 3 PbI 3 , the mobility and the half-lifetime increase by a factor of 36 compared with the values before the beta-gamma phase transition. We attribute the considerable change in the dynamics at low temperature to the decrease of the inherent dynamic disorder of the organic cation (CH 3 NH 3+ ) inside the perovskite crystal structure.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Microhydrated aromatic cluster cations: Binding motifs of 4-aminobenzonitrile-(H{sub 2}O){sub n} cluster cations with n ≤ 4

Infrared photodissociation (IRPD) spectra of mass-selected 4-aminobenzonitrile-(water){sub n} cluster cations, ABN{sup +}-(H{sub 2}O){sub n} with n ≤ 4, recorded in the N–H and O–H stretch ranges are analyzed by quantum chemical calculations at the M06-2X/aug-cc-pVTZ level to determine the evolution of the initial microhydration process of this bifunctional aromatic cation in its ground electronic state. IRPD spectra of cold clusters tagged with Ar and N{sub 2} display higher resolution and allow for a clear-cut structural assignment. The clusters are generated in an electron impact source, which generates predominantly the most stable isomers. The IRPD spectra are assigned to single isomers for n = 1–3. The preferred cluster growth begins with sequential hydration of the two acidic NH protons of the amino group (n = 1–2), which is followed by attachment of secondary H{sub 2}O ligands hydrogen-bonded to the first-shell ligands (n = 3–4). These symmetric and branched structures are more stable than those with a cyclic H-bonded solvent network. Moreover, in the size range n ≤ 4 the formation of a solvent network stabilized by strong cooperative effects is favored over interior ion hydration which is destabilized by noncooperative effects. The potential of the ABN{sup +}-H{sub 2}O dimer is characterized in detail and supports the cluster growth derived from the IRPD spectra. Although the N–H bonds are destabilized by stepwise microhydration, which is accompanied by increasing charge transfer from ABN{sup +} to the solvent cluster, no proton transfer to the solvent is observed for n ≤ 4.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Solvation structure and transport properties of alkali cations in dimethyl sulfoxide under exogenous static electric fields

A combination of molecular dynamics simulations and pulsed field gradient nuclear magnetic resonance spectroscopy is used to investigate the role of exogenous electric fields on the solvation structure and dynamics of alkali ions in dimethyl sulfoxide (DMSO) and as a function of temperature. Good agreement was obtained, for select alkali ions in the absence of an electric field, between calculated and experimentally determined diffusion coefficients normalized to that of pure DMSO. Our results indicate that temperatures of up to 400 K and external electric fields of up to 1 V nm{sup −1} have minimal effects on the solvation structure of the smaller alkali cations (Li{sup +} and Na{sup +}) due to their relatively strong ion-solvent interactions, whereas the solvation structures of the larger alkali cations (K{sup +}, Rb{sup +}, and Cs{sup +}) are significantly affected. In addition, although the DMSO exchange dynamics in the first solvation shell differ markedly for the two groups, the drift velocities and mobilities are not significantly affected by the nature of the alkali ion. Overall, although exogenous electric fields induce a drift displacement, their presence does not significantly affect the random diffusive displacement of the alkali ions in DMSO. System temperature is found to have generally a stronger influence on dynamical properties, such as the DMSO exchange dynamics and the ion mobilities, than the presence of electric fields.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Bond energies of ThO{sup +} and ThC{sup +}: A guided ion beam and quantum chemical investigation of the reactions of thorium cation with O{sub 2} and CO

Kinetic energy dependent reactions of Th{sup +} with O{sub 2} and CO are studied using a guided ion beam tandem mass spectrometer. The formation of ThO{sup +} in the reaction of Th{sup +} with O{sub 2} is observed to be exothermic and barrierless with a reaction efficiency at low energies of k/k{sub LGS} = 1.21 ± 0.24 similar to the efficiency observed in ion cyclotron resonance experiments. Formation of ThO{sup +} and ThC{sup +} in the reaction of Th{sup +} with CO is endothermic in both cases. The kinetic energy dependent cross sections for formation of these product ions were evaluated to determine 0 K bond dissociation energies (BDEs) of D{sub 0}(Th{sup +}–O) = 8.57 ± 0.14 eV and D{sub 0}(Th{sup +}–C) = 4.82 ± 0.29 eV. The present value of D{sub 0} (Th{sup +}–O) is within experimental uncertainty of previously reported experimental values, whereas this is the first report of D{sub 0} (Th{sup +}–C). Both BDEs are observed to be larger than those of their transition metal congeners, TiL{sup +}, ZrL{sup +}, and HfL{sup +} (L = O and C), believed to be a result of lanthanide contraction. Additionally, the reactions were explored by quantum chemical calculations, including a full Feller-Peterson-Dixon composite approach with correlation contributions up to coupled-cluster singles and doubles with iterative triples and quadruples (CCSDTQ) for ThC, ThC{sup +}, ThO, and ThO{sup +}, as well as more approximate CCSD with perturbative (triples) [CCSD(T)] calculations where a semi-empirical model was used to estimate spin-orbit energy contributions. Finally, the ThO{sup +} BDE is compared to other actinide (An) oxide cation BDEs and a simple model utilizing An{sup +} promotion energies to the reactive state is used to estimate AnO{sup +} and AnC{sup +} BDEs. For AnO{sup +}, this model yields predictions that are typically within experimental uncertainty and performs better than density functional theory calculations presented previously.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

In Situ Probing and Synthetic Control of Cationic Ordering in Ni-Rich Layered Oxide Cathodes

Ni-rich layered oxides (LiNi1-xMxO2; M = Co, Mn, ...) are appealing alternatives to conventional LiCoO2 as cathodes in Li-ion batteries for automobile and other large-scale applications due to their high theoretical capacity and low cost. However, preparing stoichiometric LiNi1-xMxO2 with ordered layer structure and high reversible capacity, has proven difficult due to cation mixing in octahedral sites. Herein, in situ studies of synthesis reactions and the associated structural ordering in preparing LiNiO2 and the Co-substituted variant, LiNi0.8Co0.2O2, are made, to gain insights into synthetic control of the structure and electrochemical properties of Ni-rich layered oxides. Results from this study indicate a direct transformation of the intermediate from the rock salt structure into hexagonal phase, and during the process, Co substitution facilities the nucleation of a Co-rich layered phase at low temperatures and subsequent growth and stabilization of solid solution Li(Ni, Co)O-2 upon further heat treatment. Optimal conditions are identified from the in situ studies and utilized to obtain stoichiometric LiNi0.8Co0.2O2 that exhibits high capacity (up to 200 mA h g(-1) ) with excellent retention. The findings shed light on designing high performance Ni-rich layered oxide cathodes through synthetic control of the structural ordering in the materials.

Zhao, Jianqing↗
DOE OSTI2017

Cation Translocation around Single Polyoxometalate-Organic Hybrid Cluster Regulated by Electrostatic and Cation-π Interactions

We report herein an interesting dynamic translocation process of countercations around one polyoxometalate(POM)–organic hybrid anionic cluster at various concentrations and temperatures. It was found that both electrostatic interactions and cation–π interactions regulate the position of small countercations around single clusters. The dynamic geometry and the symmetry of the hybrid macroions are largely affected by the type of counterions, as shown by nuclear magnetic resonance (NMR) spectroscopy studies and all–atom molecular dynamics simulation. It is also shown that electrostatic interactions dominate over cation–π interactions in determining the locations of the counterions in the current system.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Cation-Directed Isomerization of the U 28 Uranyl-Peroxide Cluster: Cation-Directed Isomerization of the U 28 Uranyl-Peroxide Cluster

The conformational dynamics of nanometer-sized actinide ions are exceptionally sensitive to the choice of counter-cations. A new means of following these dynamics in solution is presented that follows 1H NMR signals. The direct bond between hydrogen and phosphorus atoms in the bridging phosphonic groups of the [(UO 2 ) 28 (O 2 ) 20 (PHO 3 ) 24 (H 2 O) 12 ] 32– (U28) cluster allows unparalleled recording of the orientations of these bridges in situ. The µ 3 -PHO 3 bridges are organized into two supersets of conformers (facing inward vs. outward from the cluster), but each of these supersets additionally have four subsets that can be identified based upon orientations of the lone pairs of electrons in the associated oxygen atoms. The ensemble of these subsets changes over days or weeks depending upon bulk solution chemistry, temperature, and pressure. They also reflect cations trapped within the molecule. The 1H NMR spectra at room temperature indicate that the molecular orientation of this enormous ion tunes itself in response to solution composition, which suggests a strategy for selecting host–guest combinations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Crosslinked anion exchange membranes with connected cations

The selective transport of ions has crucial importance in biological systems as well as modern-day energy devices, such as batteries and fuel cells, and water purification membranes. Control over ion movement can be exerted by ligation, ion channel dimensions, solvation, and electrostatic interactions. Polyelectrolyte hydrogels can provide aligned pathways for counter ion transport but lack mechanical integrity, while polyelectrolyte membranes typically suffer from the absence of an ion transport channel network. To develop polymer membranes for improved ion transport, we present the design of a novel material that combines the advantages of aligned pathways found in polyelectrolyte hydrogel and mechanical robustness in conventional membranes. The ionic species were organized via controlled copolymerization of a quaternizable monomer. Additionally, dimensional stability was then incorporated through a cast/crosslinking method to lock in the network of connected cationic groups. This strategy resulted in dramatically enhanced ion transport, as characterized by ionic conductivities (>80 mS/cm for Cl-, and approximate to 200 mS/cm for OH-).

Zhang, Wenxu↗
DOE OSTI2016

Glass–water interaction: Effect of high-valence cations on glass structure and chemical durability

Borosilicate glass is a durable solid, but it dissolves when in contact with aqueous fluids. The dissolution mechanism, which involves a variety of sequential reactions that occur at the solid-fluid interface, has important implications for the corrosion resistance of industrial and nuclear waste glasses. In this study, spectroscopic measurements, dissolution experiments, and Monte Carlo simulations were performed to investigate the effect of high–valence cations (HVC) on the mechanisms of glass dissolution under dilute and near-saturated conditions. Raman and NMR spectroscopy were used to determine the structural changes that occur in glass, specifically network formers (e.g., Al, Si, and B), with the addition of the HVC element hafnium in the Na2O–Al2O3–B2O3–HfO2–SiO2 system (e.g., Na/[Al+B] = 1.0 and HfO2/SiO2 from 0.0 to 0.42). Spectroscopic measurements revealed that increasing hafnium content decreases N4 (tetrahedral boron/total boron) and increases the amount of Si—O—Hf moieties in the glass. Results from flow–through experiments conducted under dilute and near–saturated conditions show a decrease of approximately 100× or more in the dissolution rate over the series from 0 to 20 mol% HfO2. Comparing the average steady-state rates obtained under dilute conditions to the rates obtained for near-saturated conditions reveals a divergence in the magnitude between the average steady state rates measured in these different conditions. The reason for this divergence was investigated more thoroughly using Monte Carlo simulations. Simulations indicate that the divergence in glass dissolution behavior under dilute and near-saturated conditions result from the stronger binding of Si sites that deposit on the surface from the influent when Hf is present in the glass. As a result, the residence time at the glass surface of these newly-formed Si sites is longer in the presence of Hf, which increases the density of anchor sites from which altered layers with higher Si densities can form. These results illustrate the importance of understanding solid–water/solid-fluid interactions by linking macroscopic reaction kinetics to nanometer scale interfacial processes.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2015

Cationic ordering and role of the B-site lanthanide(III) and molybdenum(V) cations on the structure and magnetism of double perovskites Sr{sub 2}LnMoO{sub 6}

Highlights: • Five new double perovskites of formula Sr{sub 2}LnMoO{sub 6} were synthesized. • All the samples crystallize in the monoclinic P2{sub 1}/n space group. • Strong reducing conditions were used in order to stabilized Mo(V) cations. • A complete ordering between the rare earth and molybdenum ions was observed. • Magnetism agrees with the crystal distortions observed from Rietveld analysis. - Abstract: We describe the preparation, crystal structure determination and magnetic properties of a new series of ordered double perovskite oxides Sr{sub 2}LnMoO{sub 6} (Ln = Eu, Gd, Dy, Ho, Er, Yb) with Mo{sup 5+} and Ln{sup 3+} electronic configurations. These compounds have been obtained by solid state reaction under reducing conditions in order to stabilize Mo{sup 5+} cations. Structural characterization by XRPD and NPD was performed when Ln = Ho, Er, Yb and just XRPD for absorbing Ln = Eu, Gd, Dy. At room temperature, an excellent Rietveld fit was obtained for all the samples in a monoclinic symmetry, space group P2{sub 1}/n, with long-range ordering of Ln and Mo atoms. Magnetic susceptibility measurements show that some of these materials present magnetic ordering below 25 K and the determined effective magnetic moments are consistent with those expected for the pair Ln{sup 3+}–Mo{sup 5+}. All the phases have negative values​​ of the Weiss temperature indicating dominance of antiferromagnetic interactions.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Anion exchange membranes composed of a poly(2,6-dimethyl-1,4-phenylene oxide) random copolymer functionalized with a bulky phosphonium cation

A random copolymer, tris(2,4,6-trimethoxyphenyl) phosphonium functionalized poly(2,6-dimethyl-1,4-phenylene oxide) (PPO-TPQP) was cast from three different solvents: dimethyl sulfoxide (DMSO), ethyl lactate, or a 41:59 vol% mixture of DMSO and ethyl lactate. Solvents were selected via analysis of the Hansen solubility parameters to vary the phase separation of the polymer in the films. An optimized mixture of DMSO and ethyl lactate chosen for film fabrication and this film was contrasted with films cast from the neat constituent solvents. Atomic force microscopy identified domains from nanometer to tens of nanometer sizes, while the light microscopy showed features on the order of micron. SAXS revealed a cation scattering peak with a d-spacing from 7 to 15 A. Trends in conductivity and water diffusion for the membranes vary depending on the solvent from which they are cast. The mixed solvent cast membrane shows a linear Arrhenius behavior indicating fully dissociated cationic/anionic groups, and has the highest bromide conductivity of 3 mS/cm at 95% RH, 90 degrees C. The ethyl lactate cast membrane shows a linear Arrhenius relation in conductivity, but a Vogel-Tamman-Fulcher behavior in its water self-diffusion. While water increases bromide dissociation, water and bromide transport in these films seems to be decoupled. This is particularly true for the film cast from ethyl lactate.

Liu, Ye↗
DOE OSTI2020

Trivalent f-Element Squarates, Squarate-Oxalates, and Cationic Materials, and the Determination of the Nine-Coordinate Ionic Radius of Cf(III)

The synthesis, structure, and solid-state UV–vis–NIR spectroscopy of four new f-element squarates, M 2 (C 4 O 4 ) 3 (H 2 O) 4 (M = Eu, Am, Cf) and Sm(C 4 O 4 )(C 4 O 3 OH)(H 2 O) 2 ·0.5H 2 O, four new cationic lanthanide squarate chlorides, [M 4 (C 4 O 4 ) 5 (H 2 O) 12 ]Cl 2 ·5H 2 O (M = Eu, Dy, Ho Er), and two new actinide squarate oxalates, M 2 (C 4 O 4 ) 2 (C 2 O 4 )(H 2 O) 4 (M = Am, Cf), are presented. All of the metal centers are trivalent. Single-crystal X-ray diffraction analysis reveals that M 2 (C 4 O 4 ) 3 (H 2 O) 4 and Sm(C 4 O 4 )(C 4 O 3 OH)(H 2 O) 2 ·0.5H 2 O have a two-dimensional sheet structure constructed from MO 7 (H 2 O) 2 monocapped square-antiprismatic (coordination number (CN) = 9) metal centers and SmO 6 (H 2 O) 2 square-antiprismatic (CN = 8) metal centers, respectively, whereas M 2 (C 4 O 4 ) 2 (C 2 O 4 )(H 2 O) 4 have a three-dimensional (3D) structure constructed from MO 7 (H 2 O) 2 monocapped square-antiprismatic (CN = 9) metal centers. Additionally, the cationic framework materials [M 4 (C 4 O 4 ) 5 (H 2 O) 12 ]Cl 2 ·5H 2 O have a 3D structure constructed from two crystallographically unique MO 5 (H 2 O) 3 square-antiprismatic (CN = 8) metal centers. In these structures, the squarate ligands bind to the metal centers with varying coordination modes and denticities. The results of this study provide another example of the nonparallel chemistry between the lanthanides and transplutonium elements. From the crystallographic data for the isotypic series M 2 (C 4 O 4 ) 3 (H 2 O) 4 (M = La–Nd, Sm, Eu) and the linear regression fit to a plot of the unit cell volume as a function of the cube of the ionic radius, the nine-coordinate ionic radius of Cf 3+ was determined to be 1.127 ± 0.003 Å. Lastly, computational analysis of the americium and californium complexes M 2 (C 4 O 4 ) 3 (H 2 O) 4 and M 2 (C 4 O 4 ) 2 (C 2 O 4 )(H 2 O) 4 reveals three important attributes: (i) the 5f orbitals are nonbonding in all cases, with the bonding differences occurring with the empty 6d orbitals; (ii) the Cf complexes exhibit more covalent character than their Am counterparts; and (iii) there is more covalent character in the squarate-oxalate complexes than in the squarate complexes.

Crystallography↗