Item – Theses Canada

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OCLC number
298133831
Link(s) to full text
LAC copy
LAC copy
Author
Brusso, Jaclyn Leigh,1978-
Title
The bandwidth challenge in thiazyl and selenazyl radical conductors.
Degree
Ph. D. -- University of Waterloo, 2006
Publisher
Ottawa : Library and Archives Canada = Bibliothèque et Archives Canada, [2007]
Description
3 microfiches
Notes
Includes bibliographical references.
Abstract
In the pursuit of single component molecular metals a number of novel resonance stabilized 'bis'-1,2,3-dithiazolyl radicals (R 2BPR1) have been prepared. New synthetic routes to 1,2,3-dithiazolo-1,2,3-dithiazolium salts, based on double Herz condensations, have been developed. Reduction of these salts with decamethylferrocene affords the corresponding radicals R2BPR1 as thermally stable crystalline solids. The radicals CIBPR1 (R1 = Me, Et, Pr) and HBPR1 (R 1 = Me, Et) have been characterized in solution by cyclic voltammetry and EPR spectroscopy. Measured electrochemical cell potentials and computed (B3LYP/6-31G**) gas phase disproportionation enthalpies are consistent with a low on-site Coulomb repulsion energy 'U' in the solid state. Their crystal structures, determined by X-ray crystallography, all consist of slipped [pi]-stacks of undimerized radicals, with many close S···S contacts. CIBPMe undergoes a phase transition at 93 K to a slightly modified slipped [pi]-stack arrangement. Variable temperature magnetic and conductivity measurements have been performed on all radicals and optical measurements were performed on HBPEt. The results have been interpreted in light of Extended Hûckel band calculations. The crystalline materials are paramagnetic above 100 K, with room temperature conductivities [sigma]RT of 10-7-10-6 S cm-1, suggesting a Mott Hubbard insulator ground state for these materials. A synthetic sequence to 1,2,3-thiaselenazolo-1,2,3-thiaselenazolyl radicals (R2BPTSR1), a mixed sulfur/selenium variant of R 2BPR1, has been developed based on a multi-step cyclization procedure. Reduction of the corresponding salts can be achieved either chemically or electrochemically. Crystals of the radicals HBPTSR1 (R 1 = Me, Et), grown by H-cell diffusion methods, are isostructural and consist of interpenetrating [pi]-stacked arrays of closed-shell Se-Se [sigma]-bonded dimers laced together with numerous short intermolecular Se···Se, Se···S and Se···N contacts. Variable temperature magnetic, conductivity and near-infrared optical, measurements have been performed and indicate that the bulk materials behave as small band gap semiconductors with room temperature conductivities [sigma]RT near 10-6 S cm-1 and thermal activation energies ' Ea' of 0.32 eV (R1 = Me) and 0.36 eV (R 2 = Et). LMTO band calculations on both compounds are consistent with this interpretation. The application of external pressure leads to dramatic increases in conductivity. Although the bulk conductivity remains activated for both compounds, the reduction in activation energy with applied pressure is indicative of a close approach to the metallic state. (Abstract shortened by UMI.)
ISBN
9780494174395
0494174390