The Department of Chemistry invites you to its departmental seminar today at 4:10 p.m. in Fulmer Hall, room 201.
Dr. May Nyman from the Department of Chemistry at Oregon State University will present, U(IV) and U(VI) clusters from water: Speciation, structure and dynamics.
Abstract: Aqueous polynuclear metal-oxo clusters are fascinating intermediates between monomers and infinite solids, and represent opportunity for controlled growth of functional materials; and in the case of actinides, cluster-based separations within the nuclear fuel cycle. Capsule-like clusters built of U(VI)O2 cations bridged by peroxide were initially discovered only ten years ago, and there has been around 40 different cluster topologies recognized to date. However, understanding growth mechanisms, stability, solution behavior, and developing applications for these clusters is far less studied, largely due to the difficulty in growing pure phase clusters. We are developing synthetic strategies to control cluster growth and understand solution behavior of clusters, utilizing pH and counterions. Small-angle X-ray scattering (SAXS), multinuclear NMR and Raman spectroscopy are our main tools to ‘peer’ into aqueous uranyl peroxide solutions. Finally, we have developed cluster-based phase transfer processes that exploit ion-association rather than ligation; also providing an opportunity to study uranyl peroxide cluster behavior in non-aqueous solvents.
Meanwhile, U(IV) cluster self-assembly in water is very difficult to control without the use of protecting organic ligands, due to the hard acid character of U(IV). We are exploiting U(0) metal as a starting material, where its dissolution/oxidation provides homogeneous (and therefore more controlled) pH increase to promote hydrolysis. Using this method, we have isolated a series of U(IV) polynuclear species and solids, including an unusual oxo-bridged dimer.
