Session: Lanthanide and Actinide Chemistry:

Uranium has become an increasingly crucial natural resource for alternative energy, and understanding its reactivity and bonding informs the chemical transformations it may undergo in fuel reprocessing, storage, or in the environment. Aqueous uranyl ion complexes such as uranyl nitrate are used for nuclear fuel reprocessing. Uranyl, [UO₂]²⁺, readily forms single-charged complexes with the halides and other anions, such as nitrate. In this study, mixed nitrate-halide uranyl complexes were created, and the influence of the halide present in the complex was examined. In this experiment, uranyl complexes containing nitrate and halide ion ligands as well as oxygen ligands were tested in a Thermo LTQ XL linear ion trap mass spectrometer. The ions were subjected to collision induced dissociation (CID) and ion-molecule reactions (IMRs), and the resultant mass spectra were collected for analysis. Once the various reaction pathways were determined, the complexes were studied using density functional theory (DFT), to find the lowest energy geometries of the complexes observed experimentally and determine the reaction energetics. The experiment showed the general trends in behavior for these uranyl complexes as the ligands dissociate from the complex; the results of the experiment showed that in dihalide complexes, the nitrate ions dissociate before the halide ions, and in the presence of two oxygen ligands, the oxygen also dissociates before any halide. Additionally, in complexes with one oxygen ligand, the oxygen dissociates first with the exception of bromide, which causes the loss of the halide ion. Additional experimental and energetic trends will also be discussed.

Michael Van Stipdonk

Duquesne University

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