Probing Electronic Correlations in Actinide Materials Using Multipolar Transitions

We report nonresonant inelastic x-ray scattering from the semi-core 5d levels of several actinide compounds. Dipole-forbidden, high-multipole features form a rich bound-state spectrum dependent on valence electron configuration and spin-orbit and Coulomb interactions. Cross-material comparisons, together with the anomalously high Coulomb screening required for agreement between atomic multiplet theory and experiment, demonstrate sensitivity to the neighboring electronic environment, such as is needed to address long-standing questions of electronic localization and bonding in 5f compounds.Comment: LA-UR 09-0782

A Compact Dispersive Refocusing Rowland Circle X-ray Emission Spectrometer for Laboratory, Synchrotron, and XFEL Applications

X-ray emission spectroscopy is emerging as an important complement to x-ray absorption fine structure spectroscopy, providing a characterization of the occupied electronic density of states local to the species of interest. Here, we present details of the design and performance of a compact x-ray emission spectrometer that uses a dispersive refocusing Rowland (DRR) circle geometry to achieve excellent performance for the 2 - 2.5 keV energy range. The DRR approach allows high energy resolution even for unfocused x-ray sources. This property enables high count rates in laboratory studies, comparable to those of insertion-device beamlines at third-generation synchrotrons, despite use of only a low-powered, conventional x-ray tube. The spectrometer, whose overall scale is set by use of a 10-cm diameter Rowland circle and a new small-pixel CMOS x-ray camera, is easily portable to synchrotron or x-ray free electron beamlines. Photometrics from measurements at the Advanced Light Source show somewhat higher overall instrumental efficiency than prior systems based on less tightly curved analyzer optics. In addition, the compact size of this instrument lends itself to future multiplexing to gain large factors in net collection efficiency, or its implementation in controlled gas gloveboxes either in the lab or in an endstation.Comment: Submitted, Review of Scientific Instrument

Conversion of lanthanide glutarate chlorides with interstitial THF into lanthanide glutarates with unprecedented topologies

Using slow diffusion methods at room temperature (RT), we obtained four isomorphous lanthanide glutarate chlorides, accommodating interstitial THF and water molecules, [Ln2(Glut)2Cl2(H2O)8]•2H2O•THF (1 - 4), with Ln = La (1), Ce (2), Pr (3), Nd (4). They assemble as 3-dimensional (3D) lanthanide (Ln) coordination polymers with LnO10 coordination polyhedra. Their topology was elucidated to be a 4-coordinated sql net. 1 – 4 slowly dissolve in water liberating the entrapped THF molecules and reassemble as regular Ln-glutarate hydrates when the solution is deprived of THF and water by slow evaporation. The new products crystallize as [Ln2(Glut)3(H2O)3]•5H2O (5 - 7), with Ln = La (5), Ce (6), Pr (7), and [Nd2(Glut)3(H2O)2]•3.5H2O (8). 5 – 7 are isomorphous and crystallize as 3D-networks with two crystallographically independent LnO10 and LnO9 coordination spheres that assemble into Ln2O18 and Ln2O16 polyhedra via edge sharing. Their topology has not previously been observed and was found to be a 3,4,4,5,6-coordinated 3,4,4,5,6T61 net. The known compound 8 crystallizes also as a 3D-network and is isomorphous to other previously described lanthanide glutarate hydrates. 8 has a 3,4,5-coordinated 3,4,5T202 net topology, which has not been determined before

Synthesis and Characterization of A Tetrathiafulvalene-Salphen Actinide Complex

A new tetrathiafulvalene-salphen uranyl complex has been prepared. The system was designed to study the electronic coupling between actinides and a redox active ligand framework. Theoretical and experimental methods - including DFT calculations, single crystal X-ray analysis, cyclic voltammetry, NMR and IR spectroscopies - were used to characterize this new uranyl complex.Office of Basic Energy Sciences, U. S. Department of Energy (DOE) DE-FG02-01ER15186Ministry of Education, Science and TechnologyHeavy Element Chemistry Program by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, U.S. Department of EnergyGlenn T. Seaborg InstituteNational Nuclear Security Administration of U.S. Department of Energy DE-AC52-06NA25396Chemistr

Actinide covalency measured by pulsed electron paramagnetic resonance spectroscopy

Our knowledge of actinide chemical bonds lags far behind our understanding of the bonding regimes of any other series of elements. This is a major issue given the technological as well as fundamental importance of f-block elements. Some key chemical differences between actinides and lanthanides—and between different actinides—can be ascribed to minor differences in covalency, that is, the degree to which electrons are shared between the f-block element and coordinated ligands. Yet there are almost no direct measures of such covalency for actinides. Here we report the first pulsed electron paramagnetic resonance spectra of actinide compounds. We apply the hyperfine sublevel correlation technique to quantify the electron-spin density at ligand nuclei (via the weak hyperfine interactions) in molecular thorium(III) and uranium(III) species and therefore the extent of covalency. Such information will be important in developing our understanding of the chemical bonding, and therefore the reactivity, of actinides

Molecular and electronic structure of terminal and alkali metal-capped uranium(V) nitride complexes

Determining the electronic structure of actinide complexes is intrinsically challenging because inter-electronic repulsion, crystal field, and spin–orbit coupling effects can be of similar magnitude. Moreover, such efforts have been hampered by the lack of structurally analogous families of complexes to study. Here we report an improved method to U≡N triple bonds, and assemble a family of uranium(V) nitrides. Along with an isoelectronic oxo, we quantify the electronic structure of this 5f1 family by magnetometry, optical and electron paramagnetic resonance (EPR) spectroscopies and modelling. Thus, we define the relative importance of the spin–orbit and crystal field interactions, and explain the experimentally observed different ground states. We find optical absorption linewidths give a potential tool to identify spin–orbit coupled states, and show measurement of UV···UV super-exchange coupling in dimers by EPR. We show that observed slow magnetic relaxation occurs via two-phonon processes, with no obvious correlation to the crystal field