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Spectroscopic and Computational Analysis of Rare Earth and Actinide Complexes in Unusual Coordination Environments and Oxidation States

  • Author(s): Fieser, Megan E.
  • Advisor(s): Evans, William J
  • et al.
Abstract

This dissertation describes the use of spectroscopic and computational methods to understand new classes of rare earth and actinide coordination complexes. In Chapters 1 and 2, the use of UV-vis spectroscopy and density functional theory (DFT) to understand a rare form of photochemical activation of rare earth mixed-ligand tris(cyclopentadienyl) complexes, (C5Me5)3-x(C5Me4H)xLn, and metallocene allyl complexes, (C5Me5)2Ln(C3H5) (Ln = Lu, Y) is described. The photochemistry involves a ligand-based reduction in a trivalent rare earth complex that generates a reducing system powerful enough to reduce dinitrogen. Chapter 3 describes the use of Raman spectroscopy to understand bond lengths in reduced dinitrogen rare earth complexes, [(C5Me5)2Ln](μ-η2:η2-N2), and analyze the degree of dinitrogen reduction based on the ancillary ligands. Chapter 4 describes the power of NMR spectroscopy to characterize complicated mixtures of heterobimetallic bridging hydride complexes, (C5Me5)2Ln(H)2Ln′(C5Me5)2, and tuckover hydride complexes, (C5Me5)2Ln(μ-H)(μ-η1:η5-CH2C5Me4)Ln′(C5Me5) (Ln, Ln′ = La, Y, Lu). DFT was used to investigate the metal site preferences in these complexes.

Chapters 5 through 10 describe different techniques to understand the first examples of molecular rare earth and actinide tris(cyclopentadienyl) complexes in the formal +2 oxidation state, [K(2.2.2-cryptant)][(C5R5)3Ln] (Ln = Y, lanthanides, Th, U). DFT is used to describe the configuration of these complexes as 4d1 for Y, [Ln3+]5d1 for 10 lanthanides and [An3+]6d1 for Th and U (Chapter 5 and 6). UV-vis spectroscopy was used to distinguish between different electron configurations of Ln2+ complexes (Chapter 7). Magnetic susceptibility measurements characterize two Ln2+ complexes to have record high single-ion magnetic moments (Chapter 8). Ligand and metal edge X-ray absorption spectroscopy were used to analyze the oxidation state of the metals (Chapter 9). Reactivity of cyclooctatetraene with Ln2+ complexes is described in Chapter 10. Chapter 11 presents the synthesis of new Ln3+ and Ln2+ complexes, using a tris(aryloxide)arene coordination environment. Chapter 12 describes the use of DFT to predict new coordination environments that could allow the stabilization of the +2 oxidation state for the rare earths and actinides.

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