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International Union of Crystallography

The IUCr is an International Scientific Union adhering to the International Science Council. Its objectives are to promote international cooperation in crystallography and to contribute to all aspects of crystallography, to promote international publication of crystallographic research, to facilitate standardization of methods, units, nomenclatures and symbols, and to form a focus for the relations of crystallography to other sciences.

IUCr Newsletter




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Michael M. Woolfson (1927–2019)

[Michael Woolfson]We are sad to report the death of Michael Woolfson (York University, UK) on 23 December 2019.

Professor Woolfson was awarded the 6th Ewald Prize at the 19th IUCr Congress in Geneva, Switzerland, in 2002, for his exceptional contributions in developing the conceptual and theoretical framework of direct methods along with the algorithm design and computer programs for automatic solutions that changed the face of structural science and for his contributions to crystallographic education and international collaboration, which have strengthened the intellectual development of crystallographers worldwide. The automated direct-methods program MULTAN, developed by him in conjunction with Gabriel Germain and Peter Main, was first distributed in 1971 and, for many years, was the method of choice for the solution of most small noncentrosymmetric structures worldwide.

Professor Woolfson's commitment to crystallographic education and international collaboration is evidenced by his many IUCr roles. He served as Co-editor of Acta Cryst. from 1977 to 1980, having previously held the position of Book-Review Editor for Acta Cryst. Sections A and B and the Journal of Applied Crystallography from 1968 to 1975. He was elected onto the IUCr Executive Committee in 1981 for a three-year term, during which he served as the first Convener of the IUCr Finance Committee. He was also a member of the IUCr Commission on Crystallographic Computing (1972–1975), and published extensively in IUCr journals.

A full obituary will be published in due course.

Posted 09 Jan 2020 

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Special issue on electron crystallography

[B cover Aug 19]Structure analysis of micro- and nanocrystalline materials has witnessed immense progress in the last decade thanks to the development of electron diffraction techniques. The automation of data collection, development of new data collection modes and improvements in the data treatment have allowed unprecedented progress in most aspects of crystallography dealing with very small crystals. Probably the most notable change of paradigm is observable in the structure determination of unknown phases by electron diffraction. Three-dimensional diffraction techniques now allow almost routine solution and of structures from single crystals as small as a few tens of nanometres, providing access to hitherto unsolvable crystal structures or to previously unattainable level of structural detail. Scanning diffraction techniques allow phase and orientation mapping with nanometre resolution and even three-dimensional reconstruction of phase and orientation distributions.

This special issue of Acta Cryst. B features a collection of original contributions covering a broad range of aspects of electron crystallography. An interested reader will find papers describing the foundations and methodological basis of structure solution by electron diffraction, theoretical and methodological advances in data processing, discussion of applications of electron diffraction outside the realm of perfectly periodic crystals as well as specific case studies showing the application of the methods to hot topics in current crystallography.

The collection of contributions in this special issue showcases the diversity of applications of current electron diffraction techniques, demonstrates the state of the development of the technique and also features work that further advances the electron diffraction methods. We believe that this special issue can serve as a starting point for anybody interested in electron crystallography and we are convinced that the contributions in this issue will become reference points for future research in this exciting field.

Joke Hadermann and Lukáš Palatinus
Guest Editors

Posted 15 Aug 2019

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New SasView release

The SasView Collaboration is pleased to announce two new releases of its popular data analysis package.

  • SasView-5.0.0-Beta2 is the latest preview of our next-generation, Python3-based, version of SasView. This Beta2 version builds on feedback received since Beta1 debuted at SAS-2018 in October and has almost all the functionality of versions 4.2.x
  • SasView-4.2.1 is a point release for version 4.2.0 addressing issues with the built-in model editor and the NXcanSAS file reader, in particular, but which also adds a few other improvements.

SasView is a Small Angle Scattering Analysis Software Package, originally developed as part of the NSF DANSE project under the name SansView, now managed by an international collaboration of facilities. Feedback and contributions are welcome and encouraged. Further details and downloads at the project web page https://www.sasview.org.

Posted 20 Feb 2019 

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Special issue on mineralogical crystallography

[B cover Dec 18]For many centuries crystallography and mineralogy were part of a single discipline, and it was impossible to separate one from the other. In fact even the early works of Theophrastus (On Stones) and Pliny's Natural History show that the beginnings of both sciences have the same roots. In fact, crystallography grew out of mineralogy because in Steno's time the only crystals available for study were those of minerals. In the 20th century, however, the two sciences went their separate ways, but even today crystallographic research is an important part of mineralogy and mineralogical research is still an important part of crystallography. The December 2018 issue of Acta Cryst. B includes a special issue devoted to mineralogical crystallography and collects some important contributions that demonstrate the diversity of crystallographic ideas and methods developed to solve valuable issues in mineralogy.

There are some 5 500 (and growing) different mineral species known today [1] compared with more than 1 200 000 biological species described so far! Some of these mineral species are rare and occur in only a few localities, whereas others crystallize in the range of millions of tons in the Earth's crust. The latter are called 'rock-forming minerals' and their study is of utmost importance for our understanding of the behaviour of rocks on and beneath the Earth's surface.

[1] Pasero, M. (2018). The new IMA list of minerals, accessed 4 December 2018.

Sergey V. Krivovichev, Janusz Lipkowski and Stuart J. Mills
Guest Editors

Posted 21 Dec 2018

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Special issue on Polyoxometalates

[me0669]The November 2018 issue of Acta Crystallographica Section C Structural Chemistry marks a special anniversary of an exciting class of inorganic compounds: polyoxometalates (POMs). In their Guest Editorial, José Ramón Galán-Mascarós and Ulrich Kortz note that the very first POM structure, the so-called Keggin ion ([PW12O40]3−), was structurally characterized by James F. Keggin 85 years ago in 1933 using powder X-ray diffraction. This was an important breakthrough for POM chemistry, as from then on structural aspects became more relevant and allowed the field to be developed more rationally. In the same year, Michael T. Pope was born, who went on to publish the book Heteropoly and Isopoly Oxometalates in 1983, widely agreed still to be the best introductory text to the field.

During the last half century or so, the development of POM chemistry has benefitted tremendously from single-crystal X-ray diffraction. Besides structural aspects, the study of the physicochemical properties of POMs has developed tremendously in recent decades. The multitude of attractive properties includes controllable size, composition, charge density, redox potential, acid strength, high thermal stability in the solid state, solubility in polar/nonpolar solvents and reversible electron/proton storage. Such versatility renders POMs of interest for academic and industrial applications, especially in catalysis but also in fields such as medicine, magnetism, photochemistry and materials science.

It is also worth mentioning how POM chemistry has contributed to the development of crystallography itself. The presence of POMs (in particular heteropolytungstates) in solution often allows large biomolecules to be crystallized, and facilitates X-ray structure solution and refinement due to their high symmetry, robust mol­ecular structure and heavy-atom content. The history of POMs has progressed from the seminal work of Keggin (working under the supervision of Lawrence Bragg and influenced by Linus Pauling) developing powder X-ray diffraction analysis in the early 20th century, to the role of POMs as cocrystallizing agents for large biologically relevant molecules, such as ribosomes, finally leading to the 2009 Nobel Prize in Chemistry (Ramakrishnan, Steitz and Yonath).

The contributions to this special issue on POMs provide an excellent overview of the current state of the subject, as well as providing updates to current research. Acta C is transforming from a structural (XRD) solid-state journal to a more general journal covering all aspects of structural chemistry, and the Guest Editors hope that this special issue on POMs will assist the journal in achieving its goals.

Posted 06 Nov 2018

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The importance of careful refinement

[fabry]

A large number of structural determinations of compounds containing 2-hydroxy-3,5-dinitrobenzoic acid and its various deprotonated forms, 2-hydroxy-3,5-dinitrobenzoate or 2-carboxy-4,6-dinitrophenolate, are biased. The reason for this follows from incorrectly applied constraints or restraints on the bridging hydrogen, which is involved in an intramolecular hydrogen bond between neighbouring carboxylic/carboxylate and oxo/hydroxy groups. This hydrogen bond belongs to the category of resonance-assisted hydrogen bonds. The position of the bridging hydrogen seems to be dependent on the pKa(base), though with some exceptions. A stronger basicity enhances the probability of the presence of a phenolate. The problem of the location and refinement of such a bridging hydrogen, as well as that of the hydrogen atoms involved in the hydroxy group, and primary and secondary amine groups, is discussed in a recent article by Fábry [Acta Cryst. (2018). E74, 1344-1357]. It appears that the best model, in many cases, is obtained by fixing the hydrogen-atom positions found in a difference electron-density map while refining its isotropic displacement parameter.

"It is almost futile to state that modern automated diffractometers have enabled single-crystal X-ray structure analysis to become widely applied even by non-experts," commented Dr Fábry. "At the same time, however, it is important to emphasize that a large number of structure determinations of even simple molecules suffer from defects that are caused by inappropriately applied constraints or restraints. These defects bias not only the structure determinations themselves but also - more importantly - the overall information contained in the crystallographic databases. The present study of a whole family of the title molecules demonstrates the importance of careful refinement as well as of inspection of difference electron-density maps. I hope that this experience will reach especially those scientists for whom crystallography is not their specialization but nevertheless use it in their studies."

Posted 14 Sep 2018