Expanding uranyl peroxide cluster chemistry via the introduction of superoxide radicals.

Herein we introduce uranyl peroxide clusters that incorporate superoxide radical anions (O2˙-) and provide structural and spectroscopic details for the first two examples of this new class of materials, Rb@U60Ox30-superoxo and K@U60Ox30-superoxo (compounds 1 and 2). Single crystal X-ray diffraction results revealed shortened O-O bond lengths at approximately 1.4 Å suggesting O2˙- replaces some of the peroxide moieties that are bound to UO22+ cations within each cluster. Spectroscopic characterization of 1 and 2 was done in the solid-state and solution using Raman, infrared, UV-Vis-NIR, electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), and resonance Raman spectroscopies, which probed the behavior of the uranyl, peroxide, and superoxide moieties. Both clusters break down into smaller uranyl fragments in solution, and this results in cascade reactions where superoxide radicals interact with solution components to form additional reactive oxygen species that were detected using solution state X-band EPR spectroscopy. To provide definitive spectroscopic confirmation of the presence of superoxide radical anions in the solid-state, resonance Raman spectroscopy was performed on single crystals of 1, which revealed peaks corresponding to the ν1 fundamental mode of O2˙- as well as superoxide bound to the uranyl cation.