Progress in High-Resolution NMR in Solids

Abstract

This chapter describes the interactions, polarization transfer and irreversible processes, suppression of interactions, recovery of interactions, multi-quantum coherence, and zero-field in the solid-state NMR spectroscopy. The chapter focuses over the progress made in solid-state NMR over the last two decades, with emphasis placed on the latest advancements of theory and methodology in the past few years. In the solid-state NMR, the most important interactions are chemical shift, dipolar, and electric quadripolar interactions. Dipolar interactions can also be divided into direct and indirect parts according to their origins or into heteronuclear and homonuclear interactions according to the species of the coupling nuclei. Various types of techniques have been developed in the solid-state NMR to average out internal interactions. Multi-quantum spectroscopy is important in the solid-state NMR, because it has several valuable advantages: (1) it can be used to simplify a crowded spectrum, because the higher the order of the transitions the fewer in number they are; (2) it can directly reflect the structural and dynamic information, because the creation of a high-order quantum transition requires many spins to evolve cooperatively; (3) in some cases, multi-quantum decoupling is less demanding; and (4) the effect of a gradient field on an n-quantum transition is n times that of a single quantum transition.