Electron Spin Resonance Studies of Reactions Involving Metal Ions and Free Radicals

Abstract

<p>This thesis is concerned with the application of Electron Spin Resonance to several problems of primarily inorganic interest. In each case the system examined contains both free radicals and metal ions or complexes and ESR has been used to probe the chemistry involved.</p> <p>An introductory chapter reviews the literature which is pertinent to the research. This is followed by discussion of those parts of ESR theory which are required to evaluate the results and by a description of the experimental aspects of the work.</p> <p>Chapter IV presents the results of a study of the synthesis and reactions of some "spin-labelled ligands". Such compounds are defined as molecules with two functional groups, one of which provides a Lewis base site suitable for complexing to a metal and other comprises a group bearing an unpaired electron. The ESR spectra obtained when these ligands are complexed to metal ions have been shown to provide information on the relative electron accepting power of the metal ions and, in some cases, on the rates of very rapid ligand exchange reactions.</p> <p>It was found that when some of these spin-labelled ligands interact with very strong Lewis acids, such as BF₃ and AlCl₃, new ESR spectra appeared. These spectra have been assigned to products arising from rearrangements of alkyl groups on the spin-labelled ligand. The chemistry of these processes is discussed in Chapter V.</p> <p>Chapter VI is concerned with the photochemistry of metal acetates. The electron accepting or donating abilities of metal ions in electronically excited states will be different from those of corresponding ions in their ground states. In some cases, electron transfer to or from associated ligands can lead to the formation of free radicals. Such processes have been investigated for wide variety of metal acetates. The radicals produced have been identified by means of the ESR spectra observed in frozen solutions.</p> <p>Finally, Chapter VII reports an investigation of certain satellite lines observed in association with methyl radical ESR spectra obtained by irradiating metal acetates. These satellites have been assigned to double quantum transitions arising from the simultaneous flip of the electron spin and the nuclear spin of a proton on a neighbouring solvent molecule. Measurement of the relative intensities of the satellites and the main lines provides information on the environment of methyl radicals in an ice matrix. Data on the variation with temperature of the average methyl radical-solvent molecule distance of separation is presented.</p>