NMR Spectroscopy in the Solid State

Abstract

Nuclear magnetic resonance spectroscopy of solid materials has seen substantial advances in the past two decades and has now become a powerful tool for the materials scientist. Its main strengths lie in the possibility of obtaining and dynamic information with molecular specificity in highly disordered and even fully amorphous materials. In this article, the fundamental interactions that affect the dynamics of nuclear spins are introduced. These include the chemical shift, dipolar spin–spin coupling, and quandrupolar coupling. In contrast to the liquid state, where molecules tumble rapidly compared to the timescale of NMR, all these interactions are aniostropic in the solid state, their magnitude depends on the orientation of the molecule with respect to the magnetic field. This anisotropy provides a wealth of structural and dynamic information, as discussed in the text. Solid‐state NMR provides numerous opporunities to influence spin evolution and therefore render spectra selectively sensitive to structural and/or dynamic information of a desired type. Several such schemes, including magic angle spinning (MAS), cross‐polarization, multiple‐pulse, and Lee–Goldburg decoupling, as well as multiple‐quantum techniques, are discussed. Finally, specific applications of NMR techniques to the study of organic and inorganic solids, including techniques such as rotor‐synchronized magic angle spinning and DECODER (for the study of orientational order), spin–lattice relaxation time measurements and two‐dimensional exchange spectroscopy (molecular dynamics on various timescales) and multiple‐quantum magic angle spinning (chemical information from transition‐metal nuclei) are introduced.