Elucidation of the Bonding in Low-Valent Organoactinide Species

With support from the Chemical Synthesis Program of the Chemistry Division, Professor Suzanne Bart from the Department of Chemistry at Purdue University, is studying bonding in low valent organoactinide compounds. The very heaviest elements are the actinide elements and include uranium and thorium. Although these elements are very important in nuclear energy and in the handling of, e.g., nuclear waste, their chemistry is not understood nearly as well as that of lighter, more common metals. Even the types of chemical bonds that the actinide metals can form are not well established. This project will prepare new classes of uranium and thorium compounds where the metals have unusually low oxidation states and are attached to other atoms through multiple chemical bonds. This knowledge is important for differentiation of these elements from other metals to enable chemical separations, and for discovering future unique chemistries. An important goal of this research program is to integrate the uses and properties of the actinide elements into the curricula of high school, college, and graduate students. As the average age of chemists trained in handling actinide elements increases, it is essential to prepare the next generation of scientists in this area of national need. Toward this end, the project includes the training of graduate and undergraduate students in f-element chemistry and outreach components to educate high school students in the area. In addition, a series of programs aimed at aiding the mental health of graduate students will be conducted. This project will explore the degree of covalent bonding in actinide compounds. The approach is to perform synthesis, characterization, and reactivity of reduced uranium and thorium complexes for organometallic processes and small molecule activation. Specific aims include synthesizing U-pnictogen (Pn) single and multiple bonds with substituents that have varying steric and electronic properties, and to study the effect of soft donor ligands on actinide electronic structure and covalency. The formation of new thorium(III) derivatives from strong reducing agents will also be explored, as thorium is typically found in the +4 oxidation state. These understudied compounds are expected to have interesting electronic structures that will be important to study to understand potential applications. The work proposed includes synthetic methodology development, spectroscopic analysis, magnetization measurements and computational approaches to fully understand the electronic structure and reactivity of these important and underexplored low valent organoactinide compounds. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.