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Title: Photoelectron spectroscopy in inorganic chemistry : a study of transition metal complexes using ultraviolet and X-ray photoelectron spectroscopy
Author: Hamnett, A.
ISNI:       0000 0001 3529 0288
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 1973
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The ultra-violet and X-ray photoelectron spectra of the tris-hexafluoroacetylacetonato complexes of cone transition metals are reported and discussed. For many of these complexes there is either little or no literature experimental data available and, where necessary full details have been given in this thesis, both of the preparation and purification of the complexes. The gas-phase ultra-violet photoelectron spectra are discussed first, and it is shown how the spectra lead unambiguously to an energy level ordering similar to that assumed in ligand-field theory. However, in the high-spin complexes of Mn(III) and Fe(III) and in the low-spin Co(III) complex, the metal levels are observed to have ionisation energies which, for the most part, are higher than those of the least stable ligand molecular orbitals. This is in direct contradiction to the predictions of ligand-field theory and, in the case of the Co(III) complex, leads to an inversion of the trigonally split e and a1, metal d orbitals. The interpretation of the high-spin complex spectra is shown to be very difficult within the one-electron framework used for the other complexes and the ultra-violet spectra are shown to be the best guide to interpretation. The values for the ligand-field parameters so derived are similar to, though slightly larger than, those for the neutral species. The ESCA spectra of the complexes were measured and are reported in the second part of the thesis. The movements of the core levels so found are related by an expression derived by Siegbahn et al. to the charge shifts in the complexes as the metal is changed. These charge shifts are of three basic types: a polarisation of the andpi; framework of the ligand towards the metal as the metal-oxygen bond length contracts, a transfer of charge from the ligand andsigma;-system to the metal, increasing as the transition series is traversed and a charge shift from the anti-bonding metal d-orbitals back onto the andsigma;-system of the ligand as a natural consequence of its anti-bonding character. As a parallel study, the ESCA spectra of the metallocenes were also run and are reported at the end of the second part of the thesis. The charge shifts observed in these compounds show a remarkable parallel to those found in the hexafluoroacetylacetonato complexes, when the different metal charges and ligand characteristics are taken into account. These trends were shown to be in accord with other data on the metallocenes. In the last part of the thesis, the charge and orbital energy shifts deduced in the first two parts of the thesis for the hexafluoroacetylacetonato complexes are correlated with other physical measurements and a consistent picture of the bonding in these complexes shown to emerge. In particular, the shifts in ionisation energies found for many of the main bands in the ultra-violet photoelectron spectra receive a ready explanation once the ESCA data is considered. On this basis a case is made for the complementarity of the two techniques.
Supervisor: Orchard, A. F. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available