Title

Spectroelectrochemistry of nitroxide biradicals and cation binding enhancement studies of anthraquinone crown compounds

Date of Award

1997

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemistry

First Committee Member

Luis Echegoyen, Committee Chair

Abstract

Chapter 1. Exchange interactions in six bis-nitronylnitroxides and in their corresponding metal complexes have been examined using ESR spectroscopy. In the bis-nitronylnitroxides, the radical centers are separated by various spacers. These spacers vary from pyridine, to dipyridyl substituted pyridazine, bipyridine and phenanthroline. The ESR spectra of these systems at room temperature are indicative of fast exchange interactions in these biradicals. The dependence of such interactions on temperature and geometrical constraints in these molecule have been evaluated.Electrochemical studies of these molecules reveal a two-electron quasi-Nernstian oxidation of the bis-nitronylnitroxides and the metal complexes to the corresponding nitrosonium dications. The bis-nitronylnitroxides are irreversibly reduced in a two-electron electrochemical step while the metal complexes exhibit quasi-Nernstian reductions of the nitroxide and spacer units. No metal centered oxidations or reductions were observed in the cyclic voltammograms of these complexes. Electrolytic reduction and oxidation of these molecule followed by ESR and UV-Vis examination of the products revealed liberation of the free ligands from the metal complexes and decomposition of the nitrosonium dications possible to products containing the iminonitroxides.Chapter 2. Cation binding enhancement of several anthraquinone crown derivatives has been studied. The crown units in these redox active molecules vary from none to 18-crown-6 derivatives. Molecules with no crown units exhibit some interesting cation binding properties. The cation binding enhancement studies of these acyclic compounds demonstrate the relationship between structural flexibility and binding capabilities of these anthraquinone crown compounds.Some of the anthraquinone crown compounds such as bis(azacrown ether) derivatives, exhibit interesting binding properties toward Li$\sp{+}$ and Na$\sp{+}.$ Upon reduction to the corresponding mono- and dianion, the anthraquinone crown derivatives exhibit enhanced cation binding properties. In a few cases, the voltammograms exhibited adsorption features after addition of cations. The majority of the ligands formed the 1:1 ligand-cation complex upon reduction in the presence of cations. However, some of these molecules with the crown rings of suitable sizes and placement formed the 1:2 ligand-cation complex.

Keywords

Chemistry, Physical

Link to Full Text

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