<p> Studies of the bonding and reactivity of transition metal complexes constitute a large fraction of current research in inorganic chemistry. The present thesis describes three contributions to this area. In each case, Nuclear Magnetic Resonance studies of paramagnetic complexes are involved. An introductory chapter briefly reviews some of the pertinent background. In the second chapter the NMR theory which forms the basis for interpreting the experimental results is developed. </p> <p> The major topic of the thesis is concerned with the effect of ligand substitution on the charge distribution of a transition metal complex. Interest in this topic is aroused by the many reports that the reactivity of transition metal complexes can be considerably affected by modification of the ligands. This is particularly notable in the area of homogeneous catalysis. It seemed possible that NMR studies of paramagnetic complexes might provide a probe for these effects. With this objective in view the NMR spectra of a series of trisβ diketonato V(III) complexes have been examined. It was found that substituent changes on one ligand brought about very large (several thousand Hz) changes in the isotropic shifts of protons or fluorine atoms located on another ligand. A rather complete study has been carried out on the series of complexes formed by systematically substituting CF₃ groups for CH₃ groups on tris-acetyl-acetonato V(III). Ninety-nine of the possible one hundred different ¹H and ¹⁹F resonances in this system have been observed and identified. This relatively large body of data enabled us to attempt an empirical analysis of the results in terms of changes in the charge distribution in the complex brought about by substitution. Arguments are presented to show that the isotropic shifts arise predominantly from contact interactions. It was found necessary to introduce two terms in the empirical equations describing the shifts. The first represents changes in the distribution of the unpaired electrons in the Vanadium(III) d orbitals brought about by modification of the crystal field potential produced by the ligands. The second represents variations in the ability of a ligand to accept electron density by metal to ligand charge transfer due to inductive effect of the substituent. Two term empirical equations of this type reproduce the observed shifts to within 2%. The significance of the parameters obtained from this analysis is discussed in some detail. These studies have been extended to include several other substituted β-diketone ligands. A similar analysis has proved feasible and a consistent pattern of substituent parameters is obtained. </p> <p> The second topic considered is closely related to the above study. The interest in this case was in the possible importance of dipolar shifts in determining the isotropic shifts of mixed chelates. A series of six coordinated Co(II) complexes wa.a chosen for this purpose. These compounds are known to possess considerable magnetic anisotropy and dipolar shifts are therefore to be expected. However analysis of the results reveals that the substituent shifts are very similar to those for the V(III) compounds. It appears that the mode of transmission of substituent effects proposed may be quite general for many transition metal complexes. </p> <p> The third topic involved in this thesis concerns the structure of the second coordination sphere of transition metal complexes. The participation of various solvents in the second coordination sphere of tris-pyrazolylborate Co(II) has been investigated. Equilibrium constants relative to carbon tetrachloride as a second sphere ligand have been obtained. The ability of a solvent to participate in the second sphere depends predominantly on its dipole moment and it is concluded that Van der Waals forces are responsible for outer sphere binding. </p> / Thesis / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/17483 |
| Date | 04 1900 |
| Creators | Chua, Kee-Lam |
| Contributors | Eaton, D. R., Chemistry |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
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