Development and application of new NMR methods for paramagnetic inorganic materials

TL;DR: In this paper, a toolkit of suitably designed pulse sequences is assembled for broadband detection and interpretation of paramagnetic shifts in crystalline and non-crystalline solids, and the potential of this methodology is explored for elucidation of local geometry and electronic structure around paramagnetic metal sites in homogeneous and heterogeneous catalysts, and a set of mixed-phase Li-ion battery cathode materials.

Abstract: A precise understanding of the coordination geometry and electronic structure around metal cen- ters in catalysts and battery materials is crucial in order to control these complex systems, modify their behavior, and allow rational design of improved sites. However, such systems are not al- ways amenable for diffraction-based structural determination, and even if they are, obtaining atom-specific electronic structure can only be inferred indirectly from the atomic coordinates. As such, a direct probe of the electronic structure is highly desired. The aim of the present thesis is the investigation of structural and electronic properties of metal sites in catalysts and battery materials by magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. MAS NMR is a powerful technique for the investigation of local effects in solid materials, and offers a direct probe of highly resolved electronic structures in paramagnetic solids. However, it suffers from limited sensitivity and resolution for nuclei lying close to a paramagnetic center in general. We address these limitations by first tackling some of the bottlenecks in the acquisition and interpretation of MAS NMR by developing and applying new methodologies to paramagnetic solids using ultra-fast (60-111) kHz MAS rates. A "toolkit" of suitably designed pulse sequences is assembled for broadband detection and interpretation of paramagnetic shifts in crystalline and non-crystalline solids. The potential of this methodology is explored for the elucidation of local geometry and electronic structure around paramagnetic metal sites in homogeneous and heterogeneous catalysts, and a set of mixed-phase Li-ion battery cathode materials. We anticipate that the approaches described herein form an essential tool to elucidate many outstanding questions about the structure and function of metal sites in modern chemistry.