Type of Document Dissertation Author Stowe, Ashley Clinton Author's Email Address firstname.lastname@example.org URN etd-09172004-132435 Title Characterization of High Spin Molecular Magnets Degree Doctor of Philosophy Department Chemistry and Biochemistry, Department of Advisory Committee
Advisor Name Title Johan van Tol Committee Co-Chair Naresh Dalal Committee Co-Chair Albert Steigman Committee Member Oliver Stienbock Committee Member Piotr Fajer Committee Member Keywords
- high frequency EPR
- molecular magnets
Date of Defense 2004-09-15 Availability unrestricted AbstractThis dissertation describes the characterization of magnetic sandwich-type transition metal substituted polyoxotungstates and large Fe3+ containing clusters with large total spins. A series of isostructural copper trimer polyanions, [Cu3(H2O)3(á-XW9O33)2]n– (n = 12, X = AsIII, SeIII; n = 10, X = SeIV, TeIV), have been investigated to specifically understand the role of the diamagnetic hetero atom, which has a lone pair of electrons projecting into the magnetic plane, on the overall magnetic properties. We have discovered that the magnetic parameters can be tuned by controlling the hetero atom which is incorporated into the polyanion, though the magnitude of change is small. Further, we have sought to understand the spin-frustration of (Cu2+) in general and we have made comparison to the copper tetramer, [Cu4K2(H2O)8(a-AsW9O33)2]8-. The (Cu2+)4 polyanion is again spin-frustrated, however, addition of the fourth unpaired electron into the magnetic system changes the spin arrangements. Both antiferromagnetic and ferromagnetic exchange couplings are observed and the ground state spin is determined to be S = 1. We also explored replacement of the transition metal substituted into the core of the polyanion “sandwich”. Six Fe3+ ions are incorporated into [Fe6(OH)3(A-a-
GeW9O34(OH)3)2]11- forming a Keggin dimer each containing three Fe3+ centers. High freqeuncy EPR experiments indicate a diamagnetic ground state spin though a broad paramagnetic transition is observed at higher temperature originating from an excited state. The second foci of this dissertation concerns the nature of anisotropy within large Fe3+-containing clusters with high spin ground states. An assumption has been made that the electron Zeeman parameter, the g tensor, is isotropic and equal to 2.00 for such species. We have investigated a series of similar complexes with very large ground state spins and nominal D,E, and higher order anisotropy. Employment of a variable frequency EPR approach has revealed considerable Zeeman anisotropy in these complexes such that the assumption that g = 2.00 must be reexamined for other such Fe3+-containing species.
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