Many of the most valued chemical and physical processes in the energy sciences are governed by a delicate arrangement of multiple interactions in complex systems. The central goal of our research is to control behavior in complex inorganic systems by coupling the development of new conceptual models of bonding and electronic structure to the discovery of novel approaches in inorganic synthesis. Our approach leverages access to cutting-edge analytical tools and unique capabilities to synthesize compounds that are normally difficult to isolate and study. Of particular interest are the radioactive actinide elements, and the investigation of how 5f-orbital bonding impacts the electronic, magnetic, and reactivity characteristics of actinide molecules and materials. We target challenges with broad scope and complexity, and assemble large multidisciplinary teams of experimentalists and theorists to effectively manage resources and ensure steady progress towards research goals.
New Conceptual Frameworks for Bonding and f-electron Localization for Lanthanides and Actinides
Existing models of bonding are unable to fully capture the interplay between the multiple quantum mechanical many-body phenomena that control the behavior of topological insulators, heavy fermions, and other correlated electron systems featuring f-elements. Studies of self-contained systems – in particular, single molecule lanthanide and actinide organometallics – can help to unravel the design principles of quantum materials and lead to new applications for the f-elements as molecular qubits and in multi-qubit architectures. Our recent work has shown that metal–ligand covalency and multiconfigurational ground states can be probed experimentally with high resolution in f-element coordination compounds with X-ray absorption spectroscopy, XAS, using soft X-rays at the K-edges for the light atoms directly bound to metal centers (collectively referred to as ligand K-edge XAS). By examining periodic changes in electronic structure and orbital mixing in isostructural molecules and extended solids, we are able to quantify changes in electronic structure that would otherwise be obscured by the presence of uncontrolled variables.
John Arnold and Polly Arnold (UC Berkeley and LBNL); Corwin Booth, Wayne Lukens, David Shuh (LBNL); Taoxiang Sun (Tsinghua U.); David Clark, Stosh Kozimor (LANL); William Evans (UC Irvine)
Wibe de Jong (LBNL); Enrique Batista, Richard Martin, Ping Yang (LANL); Jochen Autschbach (Buffalo); Nikolas Kaltsoyannis (Manchester); Chantal Stieber (Cal Poly Pomona)
1. The duality of f-electron localization and covalency in lanthanide and actinide metallocenes (2020)
2. Quantitative evidence for lanthanide–oxygen orbital mixing in CeO2, PrO2, and TbO2. (2017)
3. A macrocyclic chelator that selectively binds Ln4+ over Ln3+ by a factor of 1029
4. Evidence for 5d-σ and 5d-π covalency in lanthanide sesquioxides from oxygen K-edge X-ray absorption spectroscopy
Controlling the Size and Composition of Multidimensional Actinide Nanomaterials
Nanometer-level modification to nuclear fuels can have macroscopic benefits by improving fission gas retention, reducing pressure from fuel cladding interactions, enhancing radiation tolerance, and improving heat transfer capabilities. Our research aims to harness this complex nanoscale chemistry by accessing a region of actinide synthetic space that is relatively unexplored and beyond current predictive capabilities. Using a novel templated directed synthesis approach, we can prepare sub 2-nm actinide nanoparticles on smaller reaction scales than required by conventional solution-phase syntheses, which are undesirable for transuranic systems given the high radioactivity and requirements for waste-minimization, recovery, and reuse. Selective characterization of the embedded nanoparticles within the complex three-dimensional inorganic-organic hybrid materials is achieved through a multi-pronged imaging and spectroscopic effort including TEM, PXRD, and SAXS (for size), and both soft and hard X-ray XAFS (for composition). In collaboration with Arnold and Mathur, we are also determining the mechanisms of decomposition for a new class of actinide molecules that are designed to function effectively as single-source precursors for the preparation of actinide solids and nanoparticles.
Dominic Russo, Mark Straub, Sheridon Kelly
John Arnold, Jeffrey Long (UC Berkeley and LBNL); Corwin Booth (LBNL); Sanjay Mathur (Cologne); Liane Moreau (WSU)
1. Synthesis of Ultra-Small Thorium and Uranium Dioxide Nanoparticles Embedded in a Covalent Organic Framework Tender X-ray probes of electronic structure in complex systems (2020)
2. Homoleptic U(III) and U(IV) amidate complexes
3. Chemical Vapor Deposition of Phase-Pure Uranium Dioxide Thin Films from Uranium(IV) Amidate Precursors
Probing Aluminum and Silicon Speciation and Chemical Structure in Heterogeneous and Radioactive Environments
Turning legacy radioactive wastes into durable waste forms is challenged by large amounts of Al and Si species that are heterogeneously distributed in tanks as soluble materials, suspended nanoparticles, and precipitated solids. In principle, STXM-XAS and EXAFS at the Al and Si K-edges are the perfect tools to determine electronic structure and speciation with spatial resolution for these highly radioactive and complex mixtures. The techniques are not well-developed, however, because many synchrotron beamlines are not optimized in the intermediate energy regime that includes the Al and Si K-edges, and measurements are often subject to reduced photon flux and poor energy resolution. Our research has demonstrated the potential of these techniques to provide molecular-level electronic structure insights that could not be obtained easily from NMR or X-ray diffraction. The work began with Al and Si K-edge studies of solid crystalline compounds and currently involves the study of reactive species generated in situ with liquid cells. Ultimately, this research will support innovation across the energy sciences in areas such as separations, heterogeneous catalysis, and polymer chemistry.
John Arnold and Don Tilley (UC Berkeley and LBNL); Louise Berben (UC Davis); Christopher Graves (Swarthmore)
David Prendergast (LBNL)
1. Dual roles of the f-electrons in mixing Al 3p character into the d-orbital conduction bands for lanthanide and actinide dialuminides (2018)
2. Chemical and morphological inhomogeneity of aluminum metal and oxides from soft X-ray spectromicroscopy
3. Theory and X-ray absorption spectroscopy for aluminum coordination complexes – Al K-edge studies of charge and bonding in (BDI)Al, (BDI)AlR2, and (BDI)AlX2 complexes