17O NMR SPECTROSCOPIC STUDIES OF MOLECULAR DYNAMICS IN SOLIDS

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Authors
Dai, Yizhe
Keyword
Solid-state NMR , 17O NMR , Molecular dynamics , Binding energy , Hydrogen bonds
Abstract
Solid-state 17O NMR spectroscopy is a powerful tool for probing molecular dynamics in solid materials. Recent developments in 17O-isotope labeling methodologies and availability of high magnetic fields have made it possible to use 17O NMR as a direct probe of molecular dynamics. In many cases, 17O is the only feasible NMR probe for detecting molecular motions. In this thesis, we employ solid-state 17O NMR as a primary tool to detect molecular motions in various crystalline compounds, including an inorganic compound NaNO2 and two families of organic compounds containing hydrogen bonds (sulfonic acids and carboxylic acids). First, we acquired and analyzed variable-temperature 17O central-transition (CT) NMR spectra for all the compounds studied, from which kinetic information about the molecular motion was obtained. Second, we demonstrated that 17O transverse relaxation times for the satellite transition (ST) can be used as a new way of probing molecular motion in solids. Third, we performed extensive quantum chemical calculations not only to aid analysis of 17O NMR tensor parameters, but also to gain insights into hydrogen bonding interactions. In particular, we used the Density Functional based Tight Binding (DFTB) method to obtain information about hydrogen bonding interactions in the transition state during molecular rotations or jumps. To the best of our knowledge, this is the first demonstration of this approach in studying molecular dynamics in solids. Fourth, we obtained new solid-state 17O NMR data for two crystalline carboxylic acids where low-barrier hydrogen bonds (LBHBs) are present. Our results shed new lights into the energetics of LBHBs.
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