Introduction

Beyond the horizon of the place we lived when we were young

In a world of magnets and miracles

Our thoughts strayed constantly and without boundary

..

Running before times took our dreams away

Leaving the myriad small creatures trying to tie us to the ground

To a life consumed by slow decay

(High Hopes - Pink Floyd)

Discovered by physicists and widely applied in chemistry, Nuclear Magnetic Resonance (NMR) is a phenomenon that nowadays finds a crucial importance in most fields of natural science (chemistry, biology, physics, pharmacy, agriculture, materials, earth, and environmental science) as well as in medicine and engineering. Common basic principles concerning the spin of atomic nuclei and its interaction with radio waves originated three main, equally important, experimental techniques, which through the years became more and more specialized: solution-state NMR spectroscopy, solid-state NMR spectroscopy (to which this book is devoted), and magnetic resonance imaging. The latter finds its main field of application in medicine, where it is nowadays of extraordinary importance. Solution-state and solid-state NMR spectroscopies obviously differ on the physical state of the sample under investigation. Although they are both strikingly important in the same fields, they have different applications and can be complementary. Solution-state NMR spectroscopy is generally unrivalled in the determination of unknown chemical structures, representing a vital tool for chemists, although its applications are not restricted to this field. The role of solid-state NMR spectroscopy is beyond determining chemical structures of insoluble samples: it also provides precious and detailed information on conformations, molecular packing, intermolecular interactions, polymorphism, structural order/disorder, molecular dynamics, and average phase domain dimensions, i.e. on "microscopic" properties that are crucial in defining the macroscopic behavior of a material. Moreover, it shows virtually no limits on the type of anisotropic phase to be investigated, which can either be crystalline or amorphous, solid or soft. For these reasons, solid-state NMR spectroscopy is one of the most powerful and versatile techniques for the characterization of materials.

As a physicochemist, my main interest in NMR in general, and solid-state NMR spectroscopy in particular, stems from its natural position between theory and experiments as these continuously superimpose and apply in NMR and throughout this book. However, as it was for Klaus, my approach to NMR spectroscopy is mostly experimental. In this book the theoretical description of the concepts is always directed to a better understanding of the techniques, their applications, and, finally, the interpretation of the experimental results.

Solid-state NMR spectroscopy is a field too large and varied to be exhaustively covered in a single book. Here we aimed at giving the essential tools to graduate and PhD students and to novice researchers in the field. Moreover, we wanted to present the possible applications of solid-state NMR spectroscopy to researchers of other fields, who could find them useful to exploit this technique for their studies.

The book is permeated by the concepts of anisotropy of the internal nuclear interactions and of peculiar linebroadening mechanisms and relaxation behavior occurring in solids and, more in general, in anisotropic phases, also including soft matter. On one hand, these concepts are treated in contrast to solution-state NMR, determining why and how in comparison solid-state NMR is theoretically and experimentally more complex, but, potentially, a richer source of information. On the other hand, the implications of such concepts on both low- and high-resolution solid-state NMR experiments and on their applications are dealt with in detail. Furthermore, we presented and described many useful pulse sequences (both 1D and 2D), and we tackled the crucial aspect of molecular dynamics, in attempts to describe their influence on nuclear properties and to provide a complete survey of the NMR techniques that allow their close investigation. Several subjects, which are certainly very important in the current research, could not be treated here, concerning theoretical aspects (e.g. Floquet theory), techniques (e.g. Dynamic Nuclear Polarization, DNP), and applications (e.g. structural biology studies), for which the reader should refer to more specialized books or scientific literature.

This book consists of eight chapters. Chapter 1 is both a summary of the main concepts at the basis of solution-state NMR and an introduction to the world of solid-state NMR. In Chapter 2, the main mathematical and quantum-mechanical tools necessary to understand the following subjects are briefly treated. Chapter 3 contains the formal description of the main external and internal nuclear spin interactions and their effects on nuclear energy spin levels. Chapters 4 and 5 are devoted to one-dimensional static and Magic Angle Spinning (MAS) approaches, respectively: in each chapter the main concepts are dealt with from both theoretical and experimental standpoints and a description of the most important experimental techniques is present, following a division among dilute spin ½, abundant spin ½, and quadrupolar nuclei. Chapter 6 treats two-dimensional solid-state NMR spectroscopy, providing a description of the main concepts and the main experiments, divided by type of exploited interaction: chemical shift, hetero- and homonuclear dipolar, indirect spin-spin, and quadrupolar. Chapter 7 is entirely dedicated to molecular dynamics: theoretical and experimental aspects of the many NMR quantities useful in this field are discussed, highlighting in particular the different motional timescales involved and the procedures to extract motional parameters. Finally, Chapter 8 deals with the application of solid-state NMR to several important classes of materials: pharmaceuticals, polymers, inorganics, organo metallic complexes and organic-inorganic hybrids and composites, and soft matter.

Many people have to be acknowledged for their contributions to this book. First of all, Beatrice Omiecienski, who was the only person who took part in all the phases of this work, representing, both ideally and in practice, the best possible bridge between Klaus and me. Without her extraordinary and tireless commitment throughout these years, and without her fierce determination in doing everything she could to complete Klaus's original project, this book would not exist. She constantly applied her skills and patience, supporting both Klaus and me in many aspects and, in particular, by editing, revising, and adapting all the many figures of this book.

I owe my special friend Alan Kenwright for the rest of my life for his dedication to greatly improve both the scientific content and English language of the whole book.

I am deeply grateful to Lucia Calucci, Silvia Borsacchi, Elisa Carignani, Francesca Martini, and Federica Balzano, who provided extensive and crucial contributions as well as precious suggestions to several parts of the book. Francesca Nardelli, Noemi Landi, and Elena Maurina are also acknowledged for their help in proof corrections.

I'm in debt with Giovanni Granucci, Giulia Mollica, and Giacomo Parigi, for their help and suggestions on selected subjects, for which my trust in them was much bigger than in myself.

I must acknowledge the authors of earlier and very important books on NMR and, in particular, solid-state NMR, which are listed in the following as further readings.

I also want to thank my many graduate students, who through the years have been giving me the stimulus and strength to learn more: I wish they could realize how important for me was and is every small piece of knowledge transferred to each of them.

In the end, I thank from the bottom of my heart my research group and my family, who suffered in several ways the consequences of my commitment to this book and supported me for several years.

Marco Geppi

Further Readings

General Text on NMR

1. Freeman, R. (1997). Spin Choreography. Oxford: Spektrum Academic Publishers.
2. Günther, H. (2013). NMR Spectroscopy. Weinheim: Wiley.
3. Keeler, J. (2010). Understanding NMR Spectroscopy. Chichester: Wiley.
4. Levitt, M.H. (2008). Spin Dynamics. Chichester: Wiley.
5. Slichter, C.P. (1990). Principles of Magnetic Resonance. Berlin: Springer-Verlag.

Texts on Solid-State NMR

1. Apperley, D.C., Harris, R.K., and Hodgkinson, P. (2012). Solid-State NMR: Basic Principles & Practice. New York: Momentum Press.
2. Duer, M.J. (2002). Solid-State NMR Spectroscopy: Principles and Applications. Oxford: Blackwell Science.
3. Haeberlen, U. (1976). High Resolution NMR in Solids. Selective Averaging. New York: Academic Press.
4. MacKenzie, K.J.D. and Smith, M.E. (2002). Multinuclear Solid-State NMR of Inorganic Materials. Oxford: Pergamon.
5. McBrierty, V.J. and Packer, K.J. (1993). Nuclear Magnetic Resonance in Solid Polymers. Cambridge: Cambridge...