NMR studies of anisotropic nuclear spin interactions in solids: The importance of examining NMR interaction tensors.
Date
1996
Authors
Lumsden, Michael Darren.
Journal Title
Journal ISSN
Volume Title
Publisher
Dalhousie University
Abstract
Description
A combination of solid-state nuclear magnetic resonance (NMR) spectroscopy and ab initio molecular orbital calculations has been employed in this thesis to investigate the fundamental origins of anisotropic nuclear spin interactions. Valuable information has been obtained by examining the orientation-dependent or anisotropic nature of these spin interactions rather than the orientational average measured in solution NMR spectroscopy. Unequivocal experimental evidence is provided for the first time in this thesis for an anisotropic indirect spin-spin coupling tensor, J. Analysis of data obtained from phosphorus-31 single-crystal NMR investigations involving two mercury-phosphine complexes has revealed large anisotropies in the $\sp{199}$Hg-$\sp{31}$P J tensors, on the order of 4-5 kHz. These findings provide conclusive evidence that indirect spin-spin coupling mechanisms other than Fermi contact make important contributions to the transmission of nuclear spin information between $\sp{199}$Hg and $\sp{31}$P nuclei, contrary to previous assumptions in the literature. Valuable information concerning the orientation of the phosphorus chemical shift tensors in these complexes has also been obtained, representing only the second single-crystal study of the phosphorus chemical shift tensor for a metal-phosphine complex. The work in this thesis provides the first measurements of the orientation of the carbon chemical shift tensor for the thiocarbonyl group, C=S. Both experimental and theoretical evidence indicate that the orientations of the carbon chemical shift tensors for the C=S and C=O fragments are qualitatively analogous, contrary to the conclusions of an earlier investigation. A comparison of experimental and theoretical carbon chemical shift tensor data within a series of related carbonyl and thiocarbonyl-containing molecules reveals that the well-known carbon deshielding observed for the C=S fragment is not due to variations in $n\to\pi\sp*$ transition energies, dispelling earlier misconceptions in the literature.
Thesis (Ph.D.)--Dalhousie University (Canada), 1996.
Thesis (Ph.D.)--Dalhousie University (Canada), 1996.
Keywords
Chemistry, Physical.