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Scholarly Works (4 results)

  • Thesis
  • Peer Reviewed
UC Irvine Electronic Theses and Dissertations (2017)

This dissertation focuses on efforts to expand upon the discovery that the +2 oxidation state is available in molecular forms for all the rare earth metals, i.e. Sc, Y, and the lanthanides. In addition to the previously isolated +2 ion complexes of La, Ce, Nd, Sm, Eu, Dy, Tm, Yb, and Sc, the first complexes containing +2 ions of Y, Pr, Gd, Tb, Ho, Er, and Lu had been prepared under strongly reducing conditions with the (C5H4SiMe3)33− ligand set. This dissertation describes efforts to broaden the ligand sets available to isolate new +2 rare-earth metal ions and to study their reactivity and physical properties. Chapter 1 describes the use of (C5H5)33− and (C5H4Me)33− ligand sets to isolate more examples of Y2+ complexes, and compares their stability and properties with those of other ligand sets. For (C5H4Me)33−, reduction reactions with other rare-earth metals as well as some reactivity studies are also described. Chapter 2 describes the dinitrogen reactivity of the Y2+ species generated from the reductions of (C5H5)3Y and (C5H4Me)3Y. Chapter 3 describes the synthesis and reactivity of +2 ion complexes from the reduction of ( (C5Me4H)3Ln complexes. Chapter 4 describes the synthesis of the first crystallographically characterizable Sc2+ complex, {Sc[N(SiMe3)2]3}− including physical characterization by EPR and UV-vis spectroscopy. Chapter 5 describes the reactivity of the Sc2+ complex, [Sc[N(SiMe3)2]3}−, with dinitrogen to generate the first end-on bridging dinitrogen complex of a rare-earth metal, {[Sc[N(SiMe3)2]3]2(μ-η2:η2-N2)}2−. Chapter 6 describes additional reactivity studies of [Sc[N(SiMe3)2]3}− with carbon monoxide, carbon dioxide, and acetonitrile. Chapter 7 describes the mechanochemical synthesis of the sterically crowded complexes, (C5Me5)3Ln (Ln = Tb, Dy, Ho, Er).

    Cover page: Ligand Exploration in the Synthesis and Reactivity of +2 Ion Rare-Earth Metal Complexes
    • Article
    • Peer Reviewed
    UC Irvine Previously Published Works (2019)
    The proposal that paramagnetic transition metal complexes could be used as qubits for quantum information processing (QIP) requires that the molecules retain the spin information for a sufficient length of time to allow computation and error correction. Therefore, understanding how the electron spin-lattice relaxation time (T1) and phase memory time (Tm) relate to structure is important. Previous studies have focused on the ligand shell surrounding the paramagnetic centre, seeking to increase rigidity or remove elements with nuclear spins or both. Here we have studied a family of early 3d or 4f metals in the +2 oxidation states where the ground state is effectively a 2S state. This leads to a highly isotropic spin and hence makes the putative qubit insensitive to its environment. We have studied how this influences T1 and Tm and show unusually long relaxation times given that the ligand shell is rich in nuclear spins and non-rigid.
      Cover page: Engineering electronic structure to prolong relaxation times in molecular qubits by minimising orbital angular momentumCreative Commons 'BY' version 4.0 license
      • Article
      • Peer Reviewed
      LBL Publications (2021)
      The positive impact of having access to well-defined starting materials for applied actinide technologies - and for technologies based on other elements - cannot be overstated. Of numerous relevant 5f-element starting materials, those in complexing aqueous media find widespread use. Consider acetic acid/acetate buffered solutions as an example. These solutions provide entry into diverse technologies, from small-scale production of actinide metal to preparing radiolabeled chelates for medical applications. However, like so many aqueous solutions that contain actinides and complexing agents, 5f-element speciation in acetic acid/acetate cocktails is poorly defined. Herein, we address this problem and characterize Ac3+ and Cm3+ speciation as a function of increasing acetic acid/acetate concentrations (0.1 to 15 M, pH = 5.5). Results obtained via X-ray absorption and optical spectroscopy show the aquo ion dominated in dilute acetic acid/acetate solutions (0.1 M). Increasing acetic acid/acetate concentrations to 15 M increased complexation and revealed divergent reactivity between early and late actinides. A neutral Ac(H2O)6 (1)(O2CMe)3 (1) compound was the major species in solution for the large Ac3+. In contrast, smaller Cm3+ preferred forming an anion. There were approximately four bound O2CMe1- ligands and one to two inner sphere H2O ligands. The conclusion that increasing acetic acid/acetate concentrations increased acetate complexation was corroborated by characterizing (NH4)2M(O2CMe)5 (M = Eu3+, Am3+ and Cm3+) using single crystal X-ray diffraction and optical spectroscopy (absorption, emission, excitation, and excited state lifetime measurements).
        Cover page: Advancing understanding of actinide( iii ) (Ac, Am, Cm) aqueous complexation chemistry
        • Article
        • Peer Reviewed
        UC Irvine Previously Published Works (2017)
        The isolation of [K(2.2.2-cryptand)][Ln(C5H4SiMe3)3], formally containing LnII, for all lanthanides (excluding Pm) was surprising given that +2 oxidation states are typically regarded as inaccessible for most 4f-elements. Herein, X-ray absorption near-edge spectroscopy (XANES), ground-state density functional theory (DFT), and transition dipole moment calculations are used to investigate the possibility that Ln(C5H4SiMe3)31- (Ln = Pr, Nd, Sm, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb and Lu) compounds represented molecular LnII complexes. Results from the ground-state DFT calculations were supported by additional calculations that utilized complete-active-space multi-configuration approach with second-order perturbation theoretical correction (CASPT2). Through comparisons with standards, Ln(C5H4SiMe3)31- (Ln = Sm, Tm, Yb, Lu, Y) are determined to contain 4f6 5d0 (SmII), 4f13 5d0 (TmII), 4f14 5d0 (YbII), 4f14 5d1 (LuII), and 4d1 (YII) electronic configurations. Additionally, our results suggest that Ln(C5H4SiMe3)31- (Ln = Pr, Nd, Gd, Tb, Dy, Ho, and Er) also contain LnII ions, but with 4f n 5d1 configurations (not 4f n+1 5d0). In these 4f n 5d1 complexes, the C3h-symmetric ligand environment provides a highly shielded 5d-orbital of a' symmetry that made the 4f n 5d1 electronic configurations lower in energy than the more typical 4f n+1 5d0 configuration.
          Cover page: Evaluating the electronic structure of formal Ln II ions in Ln II (C 5 H 4 SiMe 3 ) 3 1− using XANES spectroscopy and DFT calculationsCreative Commons 'BY' version 4.0 license
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