The Heavy Element Chemistry Program
The core mission of the LBNL Heavy Element Chemistry (HEC) program is basic research on the chemistry of actinides and transactinides to elucidate electronic and molecular structures and reactivity, with a particular focus on the roles of f-electrons and orbitals. Accompanying this core mission is the education and training of future scientific leaders in the field.
Research thrusts include the study of gas-phase actinide chemistry and the synthesis of new actinide materials, investigation of 5f-element bonding, and the elucidation of electronic, magnetic and reactivity characteristics of actinide molecules and materials. Specific topics pursued include actinide complexation, solution chemistry, thermodynamics, and the chemical control of troublesome radionuclides. The program also develops specialized instrumentation and techniques for use with radioactive materials, including mass spectrometry, fluorimetry and calorimetry, and makes extensive use of DOE synchrotron radiation light sources. Chemical and nuclear properties of the heaviest elements, those beyond Z=103, are actively investigated.
The LBNL HEC program consists of four integrated Project Areas: Actinide Coordination Chemistry, Chemistry and Physical Properties of Actinides in the Solid State, Solution and Gas-Phase Chemistry, and Chemistry of the Heaviest Elements.
Actinide Coordination Chemistry
Fundamental advances in actinide coordination chemistry are crucial across actinide science to understand and to control actinide behavior. Synthetic approaches to actinide complexes with desirable properties include the preparation of actinide complexes for characterization; advancing actinide materials synthesis using volatile precursors; preparing new actinide complexes with metal-metal bonds; development of complexants for spherically symmetric trivalent and tetravalent actinides; and studying actinide coordination/recognition by naturally occurring ligands and complexes.
A second emphasis examines how f-orbital interactions affect bonding and reactivity.
|General synthesis of a class of isostructural complexes with lanthanide and actinide bonds to Group 13 elements. [J. Arnold, S. Minasian, et al., J. Am.. Chem. Soc. 131, 13767 (2009)]|
Research includes inducing f-orbital covalency and evaluating the contribution of covalency to the overall bonding; studying how covalency affects ligand spin density and reactivity; gas-phase chemistry and spectroscopy, including comparisons with condensed-phase chemistry and the effects of covalency and 5f-orbital occupation on reactivity; and how ligand interactions with f-orbitals affect luminescence.
|The f-orbital covalency (top axis) and contribution to bond strength (bottom axis) in a series of f1 complexes. [W. Lukens, et al., J. Am. Chem. Soc. 135, 10742 (2013)].|
Chemistry and Physical Properties of Actinides in the Solid State
The unusual bonding of 5f orbitals in solid-state materials generates a wide variety of exotic electronic and magnetic behaviors that create challenges for developing a coherent understanding of bonding. Interactions and covalency of simple actinide oxides and other actinide materials with other light elements (C, N, S, etc.) are studied with state-of-the-art probes, including X-ray synchrotron radiation and luminescence techniques, to complement information derived from other physical measurements.
|Resonant X-ray emission spectroscopy (RXES) from alpha-plutonium as an example of a delocalized actinide intermetallic. [C. Booth et al., J. Electron. Spect. Relat. Phenom. 194, 57 (2014); Proc. Nat. Acad. Sci. 109, 10205 (2012)].|
Solution and Gas-Phase Chemistry
Actinide chemistry is explored in both solution and gas phases, which provides insight into key phenomena such as complexation, solvation, hydrolysis and oxidation/reduction from complementary perspectives. Solution studies address properties under realistic conditions, providing a basis to develop empirical models for the prediction and control of actinide behavior. Gas-phase results for simple systems present the opportunity to reveal intrinsic properties that can be accurately simulated by ab initio computations. The juncture of these two approaches provides a unique opportunity to understand and control actinide chemistry at a molecular level.
|Potential energy profiles for oxo-exchange of actinyl ions with water elucidate observed reactivity in gas and condensed phases [D. Rios et al., J. Am. Chem. Soc. 134, 15488 (2012)].|
Chemistry of the Heaviest Elements
The nuclear and chemical properties of the heaviest elements are explored at LBNL. Investigations of transactinide element (Z>103) chemistry are being conducted, and new techniques are being developed to facilitate these studies. Research is performed to improve the production of heavy element isotopes, with development of new types of targets for use at heavy ion accelerators. Microfluidic liquid-liquid extraction systems that have the potential to revolutionize the field are being pursued.
|Schematic of Sg(CO)6 in the gas phase interacting with the gradient thermochromatographic detector system that established its formation via alpha-particle decay upon adsorption. [J. Even. H. Nitsche et al., Science 345, 1491 (2014)].|