The words in () are my attempt at kewording the book. Comments invited or suggestions for improved keywords.
Title: Fundamentals of Crystallography
Author:
C. Giacovazzo, H.L. Monaco, G. Artioli, D. Viterbo, G. Ferraris,
G. Gilli, G. Zanotti and M. Catti
Note from Webeditor
Each chapter has it's author's initials in () for example (DV) D.Viterbo wrote Chapter 6
Publisher: Oxford University Press
Series: IUCr Monographs on Crystallography, Second Edition, 2002
Price: Price: £75.00 (hardback),
£39.50 (paperback)
ISBN 0-19-850957-X (hardback); 0-19-850958-8(paperback) + xxi +
825 pages and CD.
This is an impressive book, not only in its size but also as the possible inheritor of the reputation garnered by the first edition published in 1992. The authors acknowledge the extensive advances in crystallography over the past decade and set themselves the task of augmenting and updating the material in the first edition: for example, a new Chapter 4 draws together pre-existing and new material on non-ideal crystals. The book is organised into ten chapters, most penned by a single author. The majority of chapters have appendices containing supplementary material on specialist and mathematical topics, and the authors have included a CD with browser-based software to facilitate the teaching and learning of the crystallographic concepts described in Chapters 1-3.
The first Chapter (CG) is entitled "Symmetry in crystals" and covers the concepts required for the remainder of the book: these include symmetry elements, lattices, point groups, symmetry and Laue classes, crystal systems, Bravais lattices and of course space groups. The definitions, properties and consequences of all these are illustrated by well-chosen examples. This chapter has a substantial set of appendices to which the more advanced material is relegated, making the main text more accessible.
The second chapter (CG) entitled "Crystallographic Computing" covers a wide range of procedures implicitly or explicitly used in routine crystallographic calculations. These include metric aspects, reciprocal lattice calculations, relationships between parameters, basis transformations and orthogonalisation. Next, a number of simple but fundamental calculations are described: these involve torsion angles, least-squares mean planes and Niggli reduced cells. Electron density and structure factor calculations are dealt with, before beginning a major section on least squares refinement. The least squares problem is outlined in principle and the properties of both linear and non-linear refinement are explored. Their application to a wide range of crystallographic procedures is described, with particular emphasis on two areas, namely Rietveld refinement against powder data and structure refinement against observed structure factor moduli, the latter being most commonly associated with single crystal data. The treatment of key parameters such as atomic coordinates, atomic displacement parameters and overall scale, occupancy, absolute structure and extinction parameters is followed by a valuable section dealing with practical aspects of refinement such as the computing time required, different refinement approximations, possible problems, and the features to be expected in an effective least squares program. The sources and consequences of a range of systematic errors and the role of constraints and restraints are then discussed, before brief descriptions of maximum likelihood and gradient methods as alternative refinement methods. The next section is a substantial exposition of Rietveld refinement, beginning with descriptions of the main steps leading to the point where refinement can begin followed by the basis of the method ,including the establishment of the optimum peak shape function, and ending with an informative enumeration of some practical aspects. The next two sections cover related topics, the analysis of thermal motion and its effects on molecular geometry. A final section addresses the question of the accuracy of refined parameters.
Chapter 3 (CG) introduces the diffraction of X-rays by crystals, giving an account of the properties of X-rays and how they are scattered, and demonstrating Bragg's Law. A section on symmetry deals inter alia with Friedel's Law, systematic absences, space group identification and the phase problem. The aim here is to allow an understanding of diffraction effects by modelling the radiation, the crystal and their interaction. The description of Thomson scattering includes a derivation and explanation of the polarisation factor. There is a good explanation of atomic temperature factors, both isotropic and anisotropic, along with some of the assumptions and dependences involved. A major section is devoted to factors which affect diffraction intensities, including mosaic structure, various crystal defects, and primary and secondary extinction. Anomalous dispersion is considered, from its origins in resonance between bound electrons and an incident X-ray beam with similar frequency, through real and imaginary dispersion corrections and the effects on Friedel's Law. The appendices include a concise outline of neutron scattering which could equally well be associated with Chapter 5 (experimental methods), but some generalisations about the need for large crystals and deuterium substitution should be qualified. Other appendices cover charge density and electron diffraction studies.
Chapter 4 (CG) entitled 'Beyond Ideal Crystals' provides a useful introduction to eight topics ranging progressively further from the ideal crystalline state, starting with crystalline twins and finishing with gases. No attempt is made to give a comprehensive coverage of these topics, rather an overview of the area with key definitions is provided, and references are given to reviews and other more specialised texts in each of the areas covered. The areas included in this chapter are crystalline twins, diffuse scattering, modulated structures, quasicrystals, liquid crystals, the paracrystal concept, and amorphous and liquid states and gases, including a section on small angle scattering. The approach is more mathematical than some of the other chapters, but there are some good illustrations particularly for quasicrystals, and some useful tables, especially in the twinning section. Appendices include further practical information about twins including some examples taken from a paper by Herbst-Irmer and Sheldrick. The sections are illustrated by examples drawn from many areas of science - from minerals to biological materials - and overall it helps to illustrate the breadth of crystallography.
Chapter 5 (HLM & GA) gives an extensive and thoroughly updated review of 'Experimental methods in X-ray and neutron crystallography'. The chapter takes the reader from the production and definition of the radiation beam, through methods of detection and data collection strategies, to data reduction for both types of radiation and for both single crystals and polycrystalline materials - all in a very readable style. It includes information on laboratory and synchrotron X-ray sources, including a mention of the microsource, and of both reactor and pulsed neutron sources, with discussion of the optics and types of detector used. A wide range of camera and diffractometer geometries for both single crystal and powder diffraction is discussed and there is also a section on in situ measurements under non-ambient conditions. Data reduction covers commonly applied corrections such as Lorentz, polarisation (for both conventional and synchrotron X-ray sources), absorption and radiation damage corrections.
Entitled 'Solution and refinement of crystal structures', Chapter 6 (DV) is very skilfully written to make the material impressively accessible. The chapter opens with a description of statistical analysis of structure-factor amplitudes, and then moves on to give a description of the Patterson function and its uses in very clearly written text. This is followed by a discussion of the heavy atom method for structure solution with several worked examples in different space groups, and in one case with more than one heavy atom. Direct methods is then covered in a similarly lucid manner. The final sections of this chapter deal with completing and refining the structure and are largely concerned with the least-squares method. More mathematical detail of some of these topics is given in the appendices.
There then follow two complementary Chapters covering inorganic (GF) and molecular (GG) crystals, respectively. Chapter 7, whose full title is "Mineral and inorganic crystals" begins with an attempt to distinguish these from organic materials, but some of the wording is slightly unhelpful: stating that "almost the totality of minerals is based on elements other than H, C, N and O" could easily be read to mean the exclusion of these from mineral compositions, hardly what was intended! An extensive section then considers bonding aspects and how bond types (ionic, covalent, metallic, etc) affect properties such as hardness, conductivity, appearance, melting behaviour, cleavage and morphology. Ionic radii and their consequences for the structures of simple solids are explored, as are fundamental aspects such as the packing of spheres, coordination polyhedra and interstitial sites. The applications of the charge distribution method and the effective coordination number in order to rationalise structural features are explored. There follows one short section on polymorphism and the possible mechanisms of polymorphic transitions, and one on substitution and solid solutions. A survey of structural types includes closest-packed and close-packed structures (with and without the filling of interstitial sites), layer structures and structures containing complex anions, the most extensive, diverse and significant of the last being the silicates. The chapter ends with an account of modular structures, polytypism, order/disorder and modulated structures, and the phenomena which impinge on ideal crystals to produce real ones .
Chapter 8 'Molecules and molecular crystals' covers some of the key aspects of the analysis of the structures of small molecules, in particular of organic compounds. It is divided into an introduction and four main sections. The first of these sections is entitled 'the nature of molecular crystals' and discusses intermolecular forces including hydrogen bonding and how these lead into crystal structure predictions. The second section presents elements of classical stereochemistry providing useful definitions of some key aspects of conformation and configurations of structures, including a discussion of isomerism and analysis of ring conformation. The third main section, 'Molecular structure and chemical bond', presents various approaches to classifying or interpreting observed molecular geometries in terms of theories of chemical bonding, covering some of the most widely used methods. These include a short section on quantum-mechanical methods and some more qualitative approaches only applicable to particular types of structures such as VSEPR, ligand field theory and molecular mechanics. The final section is devoted to the interpretation of molecular structures, or what is often described as the study of structure-property relationships. Unsurprisingly, given the author's interests, this section also includes classifications of hydrogen bonds: one minor reservation concerning this section is that it possibly fails to indicate the level of controversy in classifying hydrogen bonds, and the examples chosen are less wide-ranging than they could have been.
Chapter 9 (GZ) provides a detailed description of protein (more precisely, macromolecular) crystallography, starting with an outline of some of the advances in the field since the first such structures were determined 40 years ago. Many of the advances, for example in computing hardware and software or the utilisation of area detectors, have parallels in chemical crystallography, but others such as isomorphous replacement are largely confined to macromolecules. One result of these advances is seen in the rapid increase in the annual number of additions to the Protein Data Bank. After an introduction to protein structure and function, the author embarks on the methodology, starting with the techniques of the key stage of protein crystallisation: extreme conditions much be avoided lest the protein degrade or the resulting structure be too different from that found in vivo, but variation of pH, salt concentration, organic solvent and precipitant, are possible. Although there are simpler methods, the most widely used today (such as hanging drop) are based on vapour diffusion. While cooling protein crystals can greatly extend their lifetime under irradiation, their high solvent content requires the use of a cryoprotectant regime to prevent icing: flash cooling then also confers many of the advantages seen for simpler compounds. The text describes the preparation and exploitation of isomorphous heavy-atom derivatives in solving novel protein structures via the location of the heavy atoms by single isomorphous replacement (SIR), multiple isomorphous replacement (MIR) and anomalous scattering, including multiple anomalous dispersion (MAD) experiments using tuneable sources. After optimisation of the heavy atom positions, the next step is to improve the electron density maps. Alternative methods of solving macromolecular structures include molecular replacement and, in special cases, direct methods. Model building proceeds by using molecular graphics which allow segments of protein chain to be fitted to the electron density. The complexity and limited resolution of typical structures require that refinement must employ extensive constraints and restraints but, even so, significant manual adjustments to the model may be needed. Useful geometric indicators include the Ramachandran plot, which flags amino acids with suspicious chain conformations. This chapter ends with a discussion of solvent regions, a cautionary sub-section on the relevance of crystal structure to in vivo structure, and finally a discussion of the challenging but promising field of dynamical biological crystallography.
Chapter 10 (MC) discusses the physical properties of crystals. This final chapter concerns crystal physics, which it considers as a bridging discipline between crystallography and solid state physics. The chapter is divided into two main areas: the first presents the effects of crystal anisotropy and symmetry on the physical properties of matter. An initial introduction is given into crystal anisotropy and tensors and this framework is used to present a number of physical properties broadly presented as electrical and mechanical properties with the example of piezoelectricity given which bridges these two areas. The presentation is somewhat dry for this section, but it is coherent, and the examples are carefully chosen to illustrate certain types of properties and use of tensors. Theoretical methods used to model these behaviours are also presented. The second part of the chapter is devoted to crystal defects and the necessity of considering them in explaining some very important phenomena of real crystalline solids, e.g. mechanical behaviour and all transport processes in crystals, e.g. diffusion and electrical conductivity. This section is more readable, and covers several types of defects: point defects, planar defects such as stacking faults, line defects or dislocations, and the effect of these deviations from an ideal crystalline state on the properties of the crystal. It also presents the use of X-ray topography in these studies.
One minor complaint is that some of the text would have benefited from some careful editing of the English, because in some cases it is not as clear or correct as it might have been. The authors have decided, possibly on grounds of space, to include only scant coverage of crystallographic databases such as the CSD and ICSD. In general, however, this is an extensive and thoroughly updated textbook gathering together a great of deal of information: it succeeds as an introduction to many areas of the field and provides a valuable indication of the breadth of our subject.
Title: "Super Materials."
Author: Wendy Madgwick
Publisher: Hodder Wayland (Science Starters series)
Price: £4.99 (paperback)
ISBN 0-7502 4142 X 32 pages
This booklet is intended to be used by adults to try to interest children in the differences between materials. It is aimed at children just starting primary school aged roughly between 5 and 7. Simple activities and experiments for the children are described in colourful pages with large print which some of the older children may be able to read for themselves. There are guidance notes for the adults, including pages of 'Materials you will need', 'Hints for helpers', a glossary of terms illustrated by simple colour drawings and an index. The materials are all common objects which could be found in most family homes and the activities ones which do not need batteries so the book could be useful to any parents faced with the plaintive cry 'What can I do now?' from a child cooped up in the house on a rainy day towards the end of school holidays. The booklet attempts to answer such questions as "Where do metals come from? or 'How are crystals formed?. They suggest growing crystals from washing soda.
Find out more by looking at the publishers website:
http://www.hodderheadline.co.uk
or by following up the suggestions in the 'Further Reading' section:
This booklet is very good value for money, and should provide hours of scientific activity.
Kate Crennell
22 December 2002
Title: Elements of Synchrotron Light for Biology,
Chemistry and Medical Research
Author:
Giorgio Margaritondo, École Polytechnique
Fédérale de Lausanne, Switzerland.
Publisher: Oxford University Press, 2002
Price: £49.95 (hardback), £24.95 (paperback)
ISBN 0-19-850931-X (hardback); 0-19-850931-6(paperback)
+ x + 260 pages.
Let me say right away that I have very mixed feelings about this book. It has much to commend it, and I was very favourably impressed as I started to read it. However, this was tempered by numerous shortcomings that emerged as I proceeded. It is, therefore, only a qualified recommendation that I finally make for it.
The book sets out "to present a simple, practical and broad picture of synchrotron light sources and of the corresponding experimental techniques." It is aimed particularly at readers who have little or no practical experience of synchrotron radiation (SR), particularly new graduate students. One of its main tasks, then, is to explain some of the jargon that has grown up with the development of SR over several decades.
The most positive aspects are the opening chapters, providing information about the basics of SR: its nature and properties, and the production and conditioning of radiation suitable for various experimental purposes. Explanations are given at two levels, a relatively qualitative one in the main text, and a more rigorously mathematical treatment in a series of clearly marked "Insets". The simpler explanation will satisfy many readers, while the deeper level is available for those who want more detail. I found these sections (skipping the Insets initially) easy to read and generally useful, and the informal style of writing helps. The different magnetic components of modern storage rings, responsible for generating SR with a range of characteristics, are well explained, together with some of the experimental arrangements and ways of operating SR facilities, and important properties such as coherence and polarisation. In this way, I reached the end of two of the book's five chapters (70 out of about 250 pages) with a generally very positive impression.
However, these sections are not without their problems, which include errors in some of the equations and incorrect units for physical quantities, and these are scattered throughout the book. Further flaws in later sections include the reversal of the definitions of cations and anions, errors such as the name potassium for the element with symbol P, and some symbols in equations that are confusingly different from those commonly used (such as f for structure factors and F for molecular scattering factors in the treatment of Fourier transforms in crystallography). The English is odd in places, which does not promote comprehension, and some of the descriptions of storage ring operations seem distinctly out of date and may be a legacy of material adapted from the author's previous and shorter text of 1985 (described in the Preface).
The longest chapter (more than half the book) is devoted to a description of applications of SR, divided into sections on imaging, spectroscopy, microscopy, EXAFS specifically, scattering and diffraction, and microfabrication techniques. The treatment here seems to me to be very variable, reflecting the author's own specialist interests. There is a clear bias towards biological and medical applications, which appear to be the best treatments, while applications in the physical sciences and engineering are less convincingly covered. The majority of examples in some of these areas are biological and medical, including a major emphasis on macromolecular rather than chemical crystallography, on medical imaging, and on biological spectroscopy. Since this is a review for Crystallography News, I should say that I found many of the explanations and arguments in the crystallography section far from convincing and clear, especially regarding the phase problem, Patterson functions (particularly confusing), structure factors, and convolution. These are topics that are not specifically SR-related, and they seem to betray a lack of expertise in this area for the author. This is certainly not a primary reference for the basics of the experimental techniques! You should go elsewhere for that.
The book reverts to its initial style and attractiveness in dealing with some advanced topics at the end, particularly in the treatment of free electron lasers.
In conclusion, the book (much less expensive, as a paperback, than some of OUP's other recent publications) is a useful introduction to synchrotron radiation for those who know little about it and its uses, but it needs to be read in conjunction with better descriptions of some of the scientific applications. It's a pity about some of the serious errors. It would be worth having a copy for research groups making (or considering making) limited use of synchrotron facilities as non-experts.
Three New IUCr Teaching Pamphlets
International Union of Crystallography, 2002, available free on their website, for you to browse on lines or print out at your site. Webmaster's NoteThe first 20 in the series can be obtained already printed on paper from the Polycrstal Book Service .
Elizabeth A. Wood
28 A4 pages.
No. 20 is a 'reprint' of a delightful booklet by Elizabeth A. Wood, first published in 1972. The author, aware that many school teachers may not themselves have had much introduction to crystals, provides a series of experiments/activities which can be carried out by children, with simple explanations and comments. As she says in the introduction, 'the essence of science is by observation and wonder, curiosity and the effort to satisfy that curiosity' and she provides an excellent guide for children to do just that, at school or at home.
There is an introductory section on aims, and then equipment and materials. The text of the main sections is suitable for children to use directly. They are about growing and examining crystals from solution (salt, borax, sugar, alum, copper sulphate, and magnesium sulphate), crystals from a melt (ice, phenyl salicylate, bismuth), crystals from vapour (ice, naphthalene), observations with polarised light, other crystals that can be observed (rocks and minerals in museums or in open country, crystals in building stone, in jewellery, etc.). The practical instructions are clear and simple and leave me with the strong expectation that they will work; the comments lead in to the ideas of characteristic crystal shape, crystal faces, cleavage, and the underlying structure. The equipment used is mostly very simple (measuring cup, teaspoon, microscope slide or upturned glass, polaroid film, etc.). The suggested procedures appear to be safe, and with cautions where appropriate, though a modern teacher would also check C.O.S.H.H. rules. The level looks appropriate for early years of secondary school, or upwards. All this should enable a young person to 'observe, wonder and ask questions ', the stated aims of the author; she also states that the booklet is 'for all schools, everywhere in the world', and in commendable support of this aim, the IUCr has provided translations in Arabic, Czech, Polish, Russian and Spanish in addition to the original English version.
The illustrations are the simple free-hand drawings of the 1972 original booklet, not as sophisticated as modern computer drawn figures, but completely clear and adequate. In republishing the booklet on the web the IUCr is quite right not to change this. It might, however, have been helpful to replace, or add to, the original three references given for further study; the latter were all published before 1965 and are not likely to be accessible. This is a very minor criticism, and the pamphlet can be very strongly recommended to all involved with encouraging young people to take an interest in crystals.
No. 21, Crystal Packing, is new. It is a simply and quite clearly presented introduction to the important factors in crystal packing, containing sections headed thermodynamics, the forces, crystal symmetry, symmetry elements, crystal structure descriptors, polymorphism (thermodynamics versus kinetics), chirality, experiments, and suggestions for the future. There is a simple description of intermolecular forces in ionic and molecular crystals, and formulae for the calculation of potential are presented. Hydrogen bonds are included, though there is little indication of the strength of these relative to ionic or covalent bonds or van der Waals interactions. The effectiveness of different symmetry elements for the packing of organic molecules in a crystal is then examined, and their combination in space groups. These are the factors which determine which packing arrangement is adopted in the crystal, and their consideration leads to an understanding of the observed distribution of space groups for these crystals.
Throughout, it is assumed that the reader is familiar with space group symmetry, and with the determination of crystal structures by X-ray diffraction, as well as with thermodynamic principles (free energy, enthalpy and entropy, G,H and S). In the general description of the series of teaching pamphlets the IUCr states that each is prefaced by a statement of aims, level, necessary background etc. Unfortunately no such statement is given here, nor does the material appear to live up to the IUCr's usual standards (as in their peer-reviewed journals) of presentation, quality of illustrations, accuracy and completeness of technical information. For example, in the section on crystal symmetry the author appears to say that the only symmetry elements which may contribute to the packing of organic molecules in crystals are the inversion centre, the 2-fold screw axis and the glide plane; while undoubtedly these are the commonest, others certainly do occur (3-, 4- and 6-fold screw axes, and pure rotation axes). Likewise, in Table 2 the heading should state that the space groups listed are the most commonly occurring ones, and that many others do occur, in smaller numbers. The blank entries in column 4 would be much more helpfully shown as (100%), and the heading of column 5 should be 'Point group symmetry of molecules in special positions'. Solvent molecules often play an important part in crystal packing, but there is no mention of them here. Finally, there is a brief statement that crystallisation from a racemic solution sometimes produces chiral crystals, in which only one isomer at a time appears, and that in these cases spontaneous resolution has been achieved. This appears to suggest that spontaneous resolution can occur, giving only crystals of one optical isomer; if it ever occurs, it is rare and unusual, and further evidence should be given. It would be helpful to state that the normal result of such a crystallisation is either racemic crystals, or equal amounts of chiral crystals of opposite chirality.
Despite these criticisms, a student with reasonable familiarity with crystallography could use this pamphlet to make a simple start on the topic of crystal packing, and perhaps go further with the set of references provided.
No. 22 is based on material provided for a summer school in Egypt in 1997. The first part is concerned with points and vectors, and with matrices and determinants. It gives careful definitions and examples, including instructions for inverting 2x2 and 3x3 matrices. This material provides the mathematical tools and concepts which are applied in the main section (representing six lectures and 3 problem sessions) to crystallographic topics - space group operations, crystallographic groups, a detailed explanation of the form of the space group tables in International Tables Volume A, followed by the use of matrices to express crystallographic symmetry operations. There are examples, and three problems involving coordinate transformations, with solutions (and reasoning) provided. The explanations are mostly full and clear, and there are a good Table of Contents and a good index.
Regrettably, this pamphlet does not state the kind of crystallographic applications for which the author hoped to prepare the summer school students, or the expected entry level. The careful, painstaking definitions and explanations might be helpful to some research students, but some of the treatment of symmetry is over-elaborate for students in chemical or biological crystallography; it may be important in solid state chemistry or in the consideration of phase transitions. For example the author distinguishes 'space groups' and 'space group types': according to the mappings which it describes, there are an infinite number of space groups, and 230 space group types (p40). However, since matrices and crystal symmetry are topics which many people working in crystallography find difficult to understand and use, and since this pamphlet is so readily available, it makes good sense that such people should look at it and see if they find the approach useful.
Cohesion, a Scientific History of Intermolecular Forces
J.S. Rowlinson,
Cambridge University Press, 2002
Price: £65 (hardback)
ISBN 0-521-81008-6 (hardback); x + 342 pages.
The problem of cohesion - why matter hangs together in its non-gaseous forms - is the fundamental problem of condensed matter physics, and has held the attention of scientists continuously since the dawn of the modern scientific enterprise. John Rowlinson, a distinguished liquid-state theorist, has written a fascinating and well-documented account of this history.
Having pointed out that some of the ablest scientific minds have worked on the puzzle of cohesion (Chapter 1), Rowlinson organised the main, and most detailed, parts of his study (Chapters 2 to 4) round three 'big names': Newton, Laplace and van der Waals. Newton's commitment to a corpuscular theory of matter and his theory of universal gravitation led rather naturally to speculations on the nature of inter-corpuscular forces. Since the direct study of these forces did not become possible until well into the twentieth century, scientists during earlier periods had to infer information about them from macroscopic phenomena, principally (in Rowlinson's account) capillarity (Laplace, Young and others), crystalline elasticity (Poisson, Navier, Cauchy, and others) and condensation (Andrews, van der Waals, and others). Studies of other phenomena, e.g. viscosity, also contributed. As we now know, a proper understanding of cohesion requires quantum mechanics to describe intermolecular forces, and statistical mechanics to relate them to bulk properties. These 20th-century developments are treated more briefly in Chapter 5.The chief strengths of this book are two. First, Rowlinson's grasp of the science enables him to guide the reader firmly through the sometimes-obscure reasoning of previous generations of scientists. (This does mean, however, that the book is technically demanding.) Secondly, the book is a bibliographic treasure trove, with more than 1000 references to original publications spread over all the main European languages as well as Latin. There are also short biographical notes on all but the most well known of the scientists involved.
I have two scientific reservations. First, Rowlinson does not appear to distinguish between cohesion and rigidity. On p. 1, he asks: 'Why do gases condense to form liquids, liquids freeze to solids or, as it has been put more vividly, why, when we lift one end of a stick, does the other end come up too?' Condensation is indeed a matter of cohesion and attractive intermolecular forces. But freezing is about the emergence of rigidity - crystals have finite zero-frequency shear moduli because they are symmetry-broken states. Moreover, as Rowlinson knows (pp. 285f), hard spheres crystallise at high density - attraction is not essential. A clearer distinction between these two issues is called for. Secondly, the final chapter is strangely silent on ionic and metallic systems. While, as Rowlinson himself has pointed out, a comprehensive treatment of 20th-century sources would require a book of its own, brief comments on these important classes of (charged) condensed systems would have given a more well-rounded finale.
To conclude, I should point out that reading this book, one gets a good sense of the fitful, untidy way in which science develops. Professional historians and philosophers, who have often lamented the tidily linear 'history' presented in science text books, should be impressed! On the other hand, I am not convinced by Rowlinson's claim that 'sociological, political, religious and economic' factors have had little effect on the development of the 'specialised' subject of cohesion. I have little doubt that future studies will show how the study of cohesion was as integrated with its social milieu as were any other areas of science. This fine volume by Rowlinson has laid a firm foundation for such studies.
Wilson C K Poon,
The University of Edinburgh
Single Crystal Neutron Diffraction from Molecular Materials
Chick C. Wilson, CLRC Rutherford Appleton Laboratory.
Series on Neutron Techniques and Applications, World Scientific Publishing,
Singapore, 2000.
Price: £44.00 (hardback)
ISBN 981-02-3776-6, xiii + 370 pages.
The book is the second in a monograph series on Neutron Techniques and Applications, edited by J. L. Finney and D. L. Worcester. The author, Chick Wilson, is Group Leader in Crystallography and beamline scientist at the ISIS spallation neutron facility at the CLRC Rutherford Laboratory in the UK.
As its title suggests, the monograph focuses on single crystal neutron diffraction, though on molecular crystals rather than materials per se. There is clearly scope for a book such as this, aimed at chemists and chemical crystallographers, which makes it clear what single crystal neutron diffraction has accomplished and may in future be able to accomplish. The book effectively comprises two parts, the first (chapters 1-3) in which an introduction to crystallography, neutron scattering and single crystal neutron diffraction is provided, and the second, longer section (chapters 4-7) in which studies conducted up to 1999 are reviewed. The book concludes with a brief look forward (chapter 8) at the potential for the technique in the future. This organisational style reminded me of Dunitz's classic book on "X-ray Analysis and the Structure of Organic Molecules" in which again there is a similar division between providing information on the fundamentals of the technique and demonstrating its chemical applications.
The book opens with a very brief introduction to crystallography in chapter 1. The majority of chapter 1, however, is devoted to outlining the areas that are covered in greater detail later in the book. Chapter 2 concentrates on neutron scattering, including very useful sections on different types of sources and detectors. The opening component on the properties of neutrons pertinent to scattering provides the necessary information but avoids the physics needed to understand the observed scattering lengths. Chapter 3 focuses on techniques, and takes the reader stepwise through aspects of a single crystal diffraction experiment that are specific to using neutrons rather than X-rays. These chapters are probably the strongest part of the book and reflect the author's many years of experience in single crystal neutron diffraction. However, while this section covers virtually all the important points, readers who are looking for more than an overview will probably need to seek an alternative source.
The next and largest section of the book is devoted to applications of single crystal neutron diffraction. The chapters on "The Accurate Location of Atoms," "Hydrogen Bonding," "Vibrations and Disorder" and "Materials Properties and Design." necessarily have some overlap, but most of the major areas of application to molecular crystals are covered. The main omissions are discussion of magnetic scattering and significant consideration of atoms other than hydrogen/deuterium.
Chapter 4 covers cases in which neutron diffraction can clarify structural ambiguities or inaccuracies in hydrogen atom position, e.g. tautomer identification, accurate bond length determination, structures of metal complexes with hydride and related ligands, and applications to structures of biological macromolecules, especially in characterising the water structure. This latter component is perhaps the best part of the chapter and provides valuable insight into an area that clearly has potential for important further development. Unfortunately, the major (25-page) component on hydride and related ligands is the weakest part of the book. The narrative works its way through studies of numerous compounds with 5-10 line descriptions, which read somewhat like a list. Too often, the chemical importance of the neutron diffraction study does not really come through, other than the common fact that neutron diffraction was necessary for accurate location of the hydride ligands. Given that there are comprehensive reviews on this specific topic in the literature, the most recent by Bau in 1997, a more valuable approach would have been to select a smaller number of case studies for more in-depth description. Such an approach could have been used to emphasise the importance of the neutron diffraction study and to bring out fully the chemical significance in each case. There are also a number of examples of incorrect chemical nomenclature and unclear wording, as well as misinterpretations or misunderstanding of the pertinent chemistry.
Chapter 5 provides a good overview of different types of hydrogen bonds (strong, weak, inter- and intramolecular, bifurcated, different donor and acceptor atoms, etc.) and different aspects of hydrogen bonding that have been studied by single crystal neutron diffraction. However, this is again an area in which there are many reviews available and more comprehensive coverage is likely to be found elsewhere. The narrative style improves upon Chapter 4, in that more extensive descriptions are provided for most examples presented. The chapter, however, does suffer from a number of inconsistencies and unclear statements, the worst offender being the overuse of the description "normal" or "as predicted", mostly without a frame of reference these terms. Section 5.2, entitled 'Normal' hydrogen bonds does define such interactions to be, in the author's view, hydrogen bonds of medium length and moderate strength. However, within the same section, for example, dialuric acid is described as having a "normal, strong hydrogenand to crystallographic models used to describe them. Special attention is given to hydrogen atom motions, where neutron diffraction has its greatest advantage over X-ray methods. The chapter then concludes with a few examples of disorder and phase transitions as studied by neutron diffraction.
Chapter 7, on "Materials, Properties and Design", is inevitably a difficult one to write given that the impact of neutron diffraction in this area does not primarily involve the study of molecular crystals. The chapter includes brief sections, with examples, on structure determinations of bioactive small molecules, hydrogen-bonded NLO molecular materials, organic conductors, and on X-H... hydrogen bonds studied in the context of crystal engineering.
The final chapter looks ahead to what improvements in instrumentation and sources might be attainable and what might be achieved with access to such facilities. Improvements in flux at the source and in utilization of those neutrons through multiple detector instruments are noted as exciting developments already in progress. The main area of study cited for major future development is in the study of biological macromolecules, while the core area of small molecule structural studies is expected to see increases in the rate of data collection and use of smaller crystals. Perhaps surprisingly omitted, is mention of magnetic scattering by neutrons, both here and throughout most of the book. Given the current high-profile work in molecular magnets based upon coordination networks, and the related area of single-molecule magnets, one might anticipate a valuable future role for polarised neutron single crystal diffraction studies.
In summary, this monograph should provide a valuable reference for chemists and chemical crystallographers seeking an overview of the technique of single crystal neutron diffraction and a perspective on its application to studies of molecular crystals. There is not an abundance of texts on neutron diffraction, and some of those most used were written many years ago. This monograph provides an up-to-date look at the practical aspects and applications of the technique and has an extensive list of references following each chapter. However, it is not without its problems, primarily in descriptions and interpretations of the chemical significance of results in parts of Chapters 4 and 5. It should nevertheless be a useful addition to Chemistry library holdings and, priced at ca. £40, to some personal collections.
Lee Brammer