Theoretical and experimental studies of mixed-valence systems toward the development of molecular electronic devices.

摘要

Quantum-dot Cellular Automata (QCA) were originally proposed as islands of metal atoms composing each corner of a square on a surface. When two of the corners have an unpaired electron, they occupy opposite corners due to Coulombic repulsion. These correspond to energetically degenerate, but distinguishable quantum states that could serve as binary code. Possible molecular implementation of QCA with mixed-valence complexes, where a single metal atom replaces each corner, is the focus of this dissertation.; Three mixed-valence ruthenium dimers with different bridging ligands were studied using Hartree-Fock (HF) and hybrid density functional theory (DFT). The complexes represent the three Robin and Day classes. It was found that DFT geometries tend to agree better with experimental structures than HF. Analysis of orbital shapes and energies provided insights into the degree of localization. In general, it was found the more conjugated the bridging ligand is, the more delocalized the complex. Suitability of the molecules as QCA devices was studied computationally with respect to the effects of an input (biasing charge) on the system. The less conjugated the bridging ligand, the larger charge separation that can be induced. The polarization of the complex is also affected by the location of the input. When positioned below the complex, parallel to the Ru-Ru axis, a more gradual, linear charge variation is observed.; Experimentally, a mixed-valence, permanently biased Fe/Ru complex [Fe(CN) ₅(μ-pyrazine)Ru(NH₃)₅] was synthesized, characterized, and surface experiments were performed with it. The complex displays selective adsorption, binding only to hydrophilic, not hydrophobic surfaces. This provides a means to pattern QCA devices. Additional surface experiments were performed to determine the orientation of the complex on the surface, but conclusive results cannot be drawn.; A computational study was done on an oxygen-atom exchange reaction catalyzed by osmium and iridium complexes. Surprisingly there are very large differences in the rates of reaction, with the iridium complex reacting about 12 orders of magnitude faster than the osmium complex. The differences in rates of reaction can be well understood upon examination of the molecular orbitals of the complexes.