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|Title:||Electron Transfer in Oxo-Centered, Trinuclear, Mixed-Valence Iron-Acetate Complexes|
|Author(s):||Oh, Seung Mo|
|Department / Program:||Chemistry|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||It was found in this study that the three-dimensional packing arrangement in the solid state is the most crucial factor influencing the rate of intramolecular electron transfer in a series of oxo-centered, trinuclear, mixed-valence complexes of the composition Fe(,3)O(O(,2)CH(,3))(,6)(L)(,3) (S), where L is an axial ligand such as pyridine or substituted pyridines and S is a solvate molecule in the solid state lattice.
The intramolecular electron transfer rate is dramatically affected by changing the solvate molecule in the solid state for a mixed-valence iron acetate. From the single-crystal X-ray diffraction studies of several Fe(,3)O complexes it was found that complexes have different packing patterns depending on the identity and location of the solvate molecule in the lattice. It was also found that the electron transfer rate of the Fe(,3)O complexes changes in response to structural phase transitions.
Variable-temperature X-ray structures on Fe(,3)O(O(,2)CCH(,3))(,6)(4-Et-py)(,3) (4-ET-py) and Fe(,3)O(O(,2)CCH(,3))(,6)(3-Me-py)(,3) (3-Me-py) indicate that the Fe(,3)O triangular frameworks become more equilateral at higher temperatures. In both complexes, the onset of dynamic disorder of the ligand and/or solvate molecules precipitates a phase transition and the electron transfer rates are changed as a result. Heat capacity measurements on Fe(,3)O(O(,2)CCH(,3))(,6)(py)(,3) (py) and Fe(,3)O(O(,2)CCH(,3))(,6)(3-Me-py)(,3) (3-Me-py) give clear evidence of phase transitions. The phase transitions in Fe(,3)O(O(,2)CCH(,3))(,6)(py)(,3) (py) are identified with the intramolecular electron transfer between the three Fe sites, dynamic disorder of the solvate molecules and disorder phenomenon of the molecular distortions. The transition entropy calculated from these contributions accounts well for the observed value.
Solid-state Deuterium NMR studies have been carried out on two isostructural complexes Fe(,3)O(O(,2)CCH(,3))(,6)(4-Me-py)(,3) (C(,6)D(,6)) and Fe(,3)O(O(,2)CCH(,3))(,6)(C(,5)D(,5)N)(,3) (C(,5)D(,5)N). In the first case, a single-crystal study clearly established that the benzene solvate molecules are rotating about the crystallographic C(,3) axis and the benzene C(,6) axis at temperatures above 153 K. The pyridine solvate molecules in the latter complex start to rotate about the C(,3) axis at the phase transition temperature (185-190 K) as the temperature increases. This rapid rotational motion of the solvate molecules is believed to modify the ground-state potential-energy surface such that the electron transfer rate is increased. (Abstract shortened with permission of author.)
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1986.
|Date Available in IDEALS:||2014-12-15|