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Browsing Theses and Dissertations by Author "Anderson, Oren P., committee member"
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Item Open Access A study of magnetostructural parameters related to spin crossover and single molecule magnetism(Colorado State University. Libraries, 2013) Fiedler, Stephanie R., author; Shores, Matthew P., advisor; Kennan, Alan J., committee member; Anderson, Oren P., committee member; Crans, Debbie C., committee member; Patton, Carl E., committee memberHerein are described several methods to probe transition metal complexes that were designed by systematic structural modifications to allow for comparison of the resultant magnetic properties. In Chapter 1, a brief introduction is presented to introduce the broader goal of our research: controlling spin on the synthetic level. The introduction provides background regarding spin crossover and single molecule magnetism as well as some previous research to put our projects in context relative to endeavors by other researchers. In Chapter 2, heteroleptic complexes of the form [Fe(H2bip)2(pizR)]Br2 and [Fe(H2bip)2(pizR)](BPh4)2 are described, which have the opportunity to chelate an anion via hydrogen bonding to the H2bip ligand. The third ligand, pizR, is varied between two ligands that we predict will have similar ligand field strengths: pizH and pizMe. Because pizH has an additional hydrogen-bonding site, while pizMe does not, we selected these ligands in order to understand the effect of hydrogen bonding on the anion-binding/spin-state switching event independent from ligand field strength. From these studies, the pizH anion hydrogen bond is observed in crystallographic studies, but does not affect the anion-binding or spin-state switching properties in solution. In Chapter 3, we further investigate the geometry of the pizR ligand in Fe(II) complexes. What began as attempts to study hydrogen bonding in solution revealed unexpected structural distortions of the ligand that are correlated to the spin state of the complexes. The R-substituted nitrogen atom on the imidazoline moiety of the pizR ligand switches between a planar geometry, which is observed for high-spin species, and a pyramidalized geometry, which is observed for low-spin species. We reason that this occurs as a result of the weak-field, non-pizR ligands that influence the ligand field in the high-spin species. Chapters 4 and 5 delve deeper into understanding the relationship between structural parameters and magnetic properties in complexes with non-covalent interactions. In Chapter 4, a series of complexes with metallophilic Pt-Pt interactions show antiferromagnetic magnetic coupling of non-bonded transition metals through a Pt-Pt bond. By comparing complexes with Pt-Pt interactions to those without Pt-Pt interactions, we are able to determine that the Pt-Pt bond is a unique superexchange pathway for the transition metal coupling. Off-set complexes, exhibiting two Pt S interactions instead of one Pt-Pt interaction, do not show evidence of magnetic coupling between transition metals. Furthermore, by comparing magnetic properties of complexes where the apical ligand varies, we determine that the presence or absence of intermolecular interactions is largely independent from the strength of coupling through the Pt-Pt bond. In Chapter 5, an asymmetric trinuclear manganese complex with unique magnetic exchange properties and two high-spin square planar complexes of iron and cobalt, are investigated. The trinuclear manganese complex consists of a central octahedral Mn(II) ion that is coupled antiferromagnetically to another octahedral Mn(II) ion and ferromagnetically to a terminal tetrahedral Mn(II) ion. The different coupling is rationalized as a result of the change in geometry, which affects the orbital overlap that is predicted for each pair of ions. The high-spin square-planar Fe(II) and Co(II) complexes illustrate an unusual pairing of spin-state with square-planar geometry. Moreover, the Fe(II) complex exhibits signs of easy-axis molecular anisotropy and slow-relaxation of magnetization, albeit in the presence of a magnetic field. Lastly, in Chapter 6, we investigate a trinuclear Fe(III) complex bridged by a triethynylmesitylene ligand. The magnetic properties of the complex are compared to a previous Fe(III) complex bridged by a triethynylbenzene ligand. Steric interactions between the aromatic core of the ethynylmesitylene ligand and the auxiliary dimethylphosphinoethane ligands on Fe(III) are predicted to engender a ligand conformation to promote strong orbital overlap. Magnetic susceptibility data for the two complexes both exhibit ferromagnetic coupling between metal centers as expected. Further studies are necessary to confirm the observed behavior, but the new triethynylmesitylene complex appears to have slightly stronger coupling than the previous triethynylbenzene complex.Item Open Access Fluorine-containing fullerenes and endometallofullerenes: synthesis, structure, and spectroscopic characterization(Colorado State University. Libraries, 2010) Shustova, Natalia Borisovna, author; Strauss, Steven H., advisor; Anderson, Oren P., committee member; Szamel, Grzegorz, committee member; Elliott, Cecil Michael, committee member; Roess, Deborah A., committee memberMany new members of a relatively new class of exohedral fullerene derivatives with fluorine-containing electron-withdrawing groups have been prepared and studied by spectroscopic methods and X-ray crystallography. The fluorination and/or perfluoroalkylation reactions were performed with C60, C70, the higher hollow fullerenes C60+m (m = 14, 16, 18, 20, and 22), the endohedral metallofullerene Sc3N@C80-Ih(7), and the azafullerene dimer (C59N)2. Several efficient synthetic methods have been developed for perfluoroalkylation, which involved high-temperature reactions with AgCF3CO2 and with thermally or photochemically activated reactions with RFI reagents (RF = CF3, C2F5, n-C3F7, i-C3F7, n-C4F9, and n-C6F13). Structural studies of the C60(RF)n and C70(RF)n products demonstrated that variation of the size and structure of the RF radical led to the formation of derivatives with unprecedented addition patterns and hence unprecedented properties. Many of these derivatives were shown to have superior electron-accepting properties. Trifluoromethylation of a sample of insoluble hollow higher fullerenes resulted in the structural characterization of several new dodecakis(trifluoromethyl) fullerene compounds, and this led to the first experimental observation of fullerenes C74-D3h and C78-D3h(5). In the case of trifluoromethylation of (C59N)2, a strong effect of the heteroatom on the addition patterns of the products was discovered. The first X-ray crystal structure of a single regioisomer of C59N(CF3)5, as well as spectroscopic studies of C59N(CF3)7,9,11, revealed unexpected addition patterns which resemble that of Cs-C60X6 derivatives. The isolation and characterization of seventeen Sc3N@(C80-Ih)(CF3)n (even n = 2-16) compounds, including the X-ray structures of Sc3N@(C80-Ih(7))(CF3)10, Sc3N@(C80-Ih(7))(CF3)12, Sc3N@(C80-Ih(7))(CF3)14, and Sc3N@(C80-Ih(7))(CF3)16, have demonstrated for the first time a strong mutual effect of (i) the presence of the Sc3N cluster on the addition pattern and (ii) the addition pattern on the position of and structure of the Sc3N cluster.Item Open Access Synthesis and characterization of low-dimensional paramagnetic acetylide complexes(Colorado State University. Libraries, 2011) Hoffert, Wesley A., author; Shores, Matthew P., advisor; Anderson, Oren P., committee member; Prieto, Amy L., committee member; Bailey, Travis, committee member; Patton, Carl, committee memberTo view the abstract, please see the full text of the document.