Despite the fact that much of the understanding of structure and function of modern materials in chemistry is derived from structures obtained by way of diffraction methods, these methods are limited to cases where samples have well-defined geometries and long-range structural order. Without such limitations, nuclear magnetic resonance (NMR) is a powerful tool to study samples with structural disorder, such as amorphous materials, materials with mixed phases, and surface-supported catalysts.
The goal of this thesis is to determine structural and electronic properties of paramagnetic inorganic materials by magic-angle spinning (MAS) NMR. MAS NMR is a crucial technique to study the structure around paramagnetic centers, but in such samples MAS NMR can suffer from limited sensitivity and resolution due to strong couplings between electrons and nuclei.
This thesis addresses these limitations by developing new NMR methods based on new equipment capable of fast (60-111 kHz) MAS rates. Low-power broadband RF pulse schemes are developed to tackle the problem of limited excitation bandwidth, and experimental broadband excitation/correlation schemes are adapted to the fast MAS regime. These methods combine to form a “toolkit” used, in conjunction with state-of-the-art computational methods, to acquire, assign, and subsequently determine the geometry and electronic structure around paramagnetic centers in mixed-phase Li-ion battery cathode materials, and homo- and heterogeneous catalytic systems.
We anticipate that these methods will become an essential tool to elucidate many unanswered questions about the structure and function of emergent paramagnetic materials in modern chemistry.