NMR (nuclear magnetic resonance) crystallography / ЯМР (ядерный магнитный резонанс) кристаллография

Since the earliest days of NMR, it has been recognized that the technique can provide information on matters concerning the disposition of atoms in the unit cells of crystals. Thus, the distance between protons in the water molecules of gypsum, CaSO4 · 2H2O, was determined by Pake and reported as 1.58 A in 1948. However, the term NMR crystallography has only recently come into common usage, and even now causes raised eyebrows within some parts of the diffraction community. On the other hand, the power of solid-state NMR to give crystallographic information has considerably increased since the CPMAS suite of techniques was introduced in 1976. In the first years of the 21st century, the ability of NMR to provide information to support and facilitate the analysis of single-crystal and powder diffraction patterns has become widely accepted. Indeed, NMR can now be used to refine diffraction results and, in favorable cases, to solve crystal structures with minimal (or even no) diffraction data. The increasing ability to relate chemical shifts (including the tensor components) to the crystallographic location of relevant atoms in the unit cell via computational methods has added significantly to the practice of NMR crystallography. Of course, NMR will never replace diffraction techniques in the determination of atomic positions in crystal structures, but diffraction experts will increasingly welcome NMR as an ally in their structural analyses. Indeed, it may be that in future crystal structures will be determined by simultaneously fitting diffraction patterns and NMR spectra

However, NMR can also supply information on crystal structures which is inaccessible or very difficult to obtain by diffraction methods. Prominent among such investigations is the determination of dynamics at the molecular level in crystalline materials. There are many NMR methods for studying such motion, including relaxation measurements as well as spectral features, and they cover a vast range of motional rates. NMR can frequently distinguish between static and dynamic disorders. Thus NMR crystallography can and should be considered as both complementary and supplementary to diffraction crystallography. At the time of writing there are few reviews and no books on NMR crystallography. It therefore seems to be timely to produce this handbook. The chapters herein, though taken from articles in the electronic version of the Encyclopedia of Magnetic Resonance, were commissioned specifically with this handbook in mind. The editors have attempted to produce a coherent set of chapters covering most aspects of NMR crystallography in a reasonably uniform way. Of course, since each chapter has its specific authors (expert in the topics in question) there will undoubtedly be some small degree of overlap between them and possibly a few lacunae. However, the handbook should be of value not only to students and practitioners of solid-state NMR but also to the wider crystallographic community. Some care has been taken to achieve consistency of symbols and notation, but there remain a few variations between chapters (for example, in the symbols used for dipolar coupling constants). Finally, it may be noted that single-crystal NMR work, though feasible, is relatively unusual, so most studies involve microcrystalline/polycrystalline samples. Little information is sacrificed by this usage. Heterogeneous systems containing crystalline components are also amenable to study. Moreover, structural information at the molecular level (including geometrical data) can be obtained by NMR from amorphous and glassy materials, again with little loss. Although that situation is hinted at in various parts of the handbook, it is not specifically covered, though matters such as defect and other nonstoichiometric structures are discussed <...>