Synthesis, Characterization, and Spectroscopy of Uranyl Peroxides

This thesis explores the mechanisms by which uranyl peroxide complexes form, the detailed structural features of pyrophosphate functionalized nanoclusters, the spectroscopic signatures of uranyl peroxide monomers, the effect of pH on the identity of the products formed in the uranium-peroxide-pyrophosphate system, and stability of uranyl peroxide nanoclusters.

The composition of uranyl peroxide nanoclusters (i.e. U, O) imposed significant limitations on our ability to study their formation. Herein, reaction mixtures yielding pyrophosphate functionalized [(UO2)24(O2)24(P2O7)12, ({U24Pp12}) cluster were studied across a wide range of pH conditions using 31P NMR spectroscopy providing insights into the mechanism by which these clusters assemble. Single crystal time-of-flight (TOF) neutron diffraction provided unparalleled atomic resolution allowing unequivocal assignment of {U24Pp12} protonation state.

Raman signatures of a family of uranyl triperoxide monomers [UO2(O2)34-] are studied by combination of experimental (isotopic labeling) and computational (density functional theory) approaches resulting in assignment of previously unobserved asymmetric and mixed asymmetric/symmetric vibrations of peroxide ligands. Moreover, the identity of the signals appearing in the 600 - 800 cm-1 region is reassigned to the symmetric vibration of the uranyl.

The effect of pH on the identity of species formed in the uranium-peroxide-pyrophosphate system are studied by combination of single crystal X-ray diffraction, small angle X-ray scattering, 31P NMR, and 31P DOSY NMR spectroscopy. Results indicate that formation of uranyl peroxide nanoclusters follows a well-defined stepwise mechanism consisting of multiple assembly/disassembly steps showing retention of basic uranyl peroxide building blocks (e.g. [(UO2)4(O2)4], {U4}).

Finally, stability of [(UO2)20(O2)27(HPO4)6], {U20P6} nanocluster incorporating peroxide in an unusual µ:eta2:eta2 bridging mode is studied by combination of Raman, 31P DOSY NMR spectroscopy, small angle X-ray scattering, and single crystal X-ray diffraction. Results obtained in this study indicate that {U20P6}, upon dissolution in H2O, undergoes a rapid dissolution (t1/2 = 116.3 min) followed by reassembly into previously described {U24} nanocluster.