Ligand Effects on Kinetic and Thermodynamic Properties of Complexes of the Non-Traditional Rare-Earth (II) Ions
- Author(s): Moehring, Samuel Alexander
- Advisor(s): Evans, William J
- et al.
This dissertation details investigations into ligand effects on the non-traditional rare-earth(II) ions, i.e., those with 4fn5d1 electron configurations (as well as 3d1 Sc(II) and 4d1 Y(II)) instead of 4fn+1. Specifically, effects on kinetic stability and the reducing ability of complexes of these ions are explored as a function of ligand set and metal. Chapter 1 describes the synthesis and characterization of rare-earth(II) complexes of the aryloxide ligand 2,6-tBu2-4-Me-C6H2O and sets forth the hypothesis that kinetic stability of rare-earth(II) compounds depends on the steric saturation of the metal center. Chapter 2 expands on the steric argument made in Chapter 1 by synthesizing Y(III) and Y(II) complexes of the bulky aryloxide 2,6,-(1-adamantyl)2-4-tBu-C6H2O; the crystallographically-characterized Y(II) complex is kinetically stabilized compared to the thermally unstable Y(II) complex with 2,6-tBu2-4-Me-C6H2O in Chapter 1, which is detected only spectroscopically. Chapter 3 reports the synthesis of rare-earth(III) compounds of the asymmetric amide ligands N(SiMe3)R, where R = phenyl or cyclohexyl, which prove to be insufficiently sterically-saturating ligands for rare-earth(II) compound isolation. Chapter 4 compares the reducing power of Th(II) and U(II) complexes to Y(II) and La(II) complexes using EPR spectroscopy. Chapter 5 continues these comparisons with a wider range of rare-earth (II) compounds, varying the metal involved as well as the ligand set, and also describes ligand exchange reactivity leading to EPR evidence for heteroleptic rare-earth (II) compounds.