This work presents three new classes of 6-oxoverdazyl radicals. Each of these classes of radicals bears a different substituent in the 3-position of the verdazyl ring. These classes include N-heteroaromatic monoverdazyls, oligopyridine diradicals, and ferrocenyl-based verdazyl radicals and diradicals. With the exception of the ferrocenyl-based radicals, these verdazyl radicals have been designed to serve as ligands and the direct metal-radical interactions have been explored. The ferrocenyl verdazyls have been designed to investigate the indirect interactions between iron(II) and the covalently linked verdazyl radical. All verdazyl radicals and precursors were fully characterized and the metal-radical magnetic interactions were investigated where structural characterization was available.
A series of bidentate verdazyl radical ligands were prepared and the metal-radical magnetic interactions have been investigated. The magnetic susceptibility data for the octahedral complexes indicates that cobalt(II) couples ferromagnetically (Jco_vd = +95 cm-l) and iron(II) antiferromagnetically (JFe_vd = -66 cm-1) to the verdazyl radical. The nature of these interactions appears to be dictated by orbital symmetry and is consistent with previously reported nickel and manganese verdazyl complexes. This work also demonstrates that imidizole-based verdazyl radicals are effective ligands in tetrahedral copper(I) complexes.
Oligopyridine-based diradicals have been designed as ligands, but decompose in solution preventing metal complexation. An attempt was made to construct grids as a higher order molecular structure. To this end, a diradical ligand with the topology necessary to form discrete grid architectures was synthesized, but has not yet demonstrated the ability to coordinate to metal ions. Other monoverdazyl radicals that are symmetrically substituted in the N1 and N5 positions were also investigated as potential grid forming ligands.
A series of ferrocenyl verdazyl and methylated ferrocenyl verdazyls were prepared to investigate the electronic and magnetic interactions between the ferrocene and verdazyl electrophores. As evidenced by UV-Vis and electrochemical solution
measurements, the two electrophores exhibit mutual electronic perturbations. In the case of the methylated ferrocene derivatives the degree and pattern of methylation appears to have a regiospecific influence on the verdazyl electrochemistry. In the solid state Mössbauer data is consistent with a Fe2+ ground state and there is no evidence of Fe3+ at or below room temperature. Weak antiferromagnetic behaviour (|J| < -13 cm-1) was observed within and between pairs of ferrocenyl monoverdazyls in the solid state.
In order to investigate the interactions between radicals separated by an organometallic spacer, a ferrocenyl verdazyl diradical was prepared. The ferrocene diradical demonstrated significant differences between the solid state and solution phase. While the ferrocene diradical and ferrocene monoverdazyl exhibited similar solution electronic properties, the magnetic properties were vastly different. In solution the spins associated with the diradical appeared to be weakly coupled, but in the solid state the diradical has been characterized as a strongly coupled antiferromagnetic π-dimer. This is the first example of a verdazyl π-dimer. The π-dimer appears to be diamagnetic with the lower limit of exchange estimated at Jinter ≈ 2000 cm 1.
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/1930 |
| Date | 02 December 2009 |
| Creators | Koivisto, Bryan Douglas |
| Contributors | Hicks, Robin Gary |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Rights | Available to the World Wide Web |
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