XXIII IUCr Congress and General Assembly

Continued from Volume 22, Number 3 

The third and final part is in Volume 23, Number 1

Biological macromolecules

Macromolecular and soft-matter aperiodic crystals

MS57 speakers. From left: Y. Matsushita, S. Föster, M. Engel, S. Yakamoto, K. Barkan, V. Raghuwanshi.

The quest for 'soft-matter quasicrystals' (QCs) is an integral part of quasicrystal research. Macromolecular and soft matter aperiodic crystals were the topic of microsym. MS57. S. Föster (Germany), who found 18-fold symmetry for the first time, presented X-ray scattering data of block-copolymer micelles combined with new molecular dynamic simulation results of a Witten-Pincus model potential having two length scales. He also described new micellar and microgel QC systems. Y. Matsushita (Japan) talked about complex polymer melts and showed exotic morphologies, one of which was an approximant of the decagonal phase. Progress concerning theoretical and computational work was given by K. Barkan (Oregon) who extended their mean-field theory and showed cluster liquid QCs. M. Engle (USA) successfully stimulated a single atom (tetrahedrally-bonded) icosahedral QC using a two-length scale potential, considered to be the Holy Grail in this field for 30 years. Y. Sakamoto (Japan) described mesoporous silica QCs as polyhedral packing with relation to the Frank-Casper phases, and showed a large-scale QC made of binary silica spheres.

Ultimate resolution and neutron crystallography

MS82 speakers and co-chairs. From left: Andrey Kovalevsky, Nobuo Niimura, Yu Hirano, Alberto Podjarny, Matthew Blakeley and Svetlana Antonyuk.

Microsym. MS82 focused on the information that can be derived from ultra-high resolution X-ray diffraction data (i.e. to 0.8Å or better) and neutron diffraction data extending to 2.5Å resolution or better. Z. Dauter (USA), Y. Hirano (Japan) and J. Kallio (Germany) illustrated the fine details revealed by ultra-high resolution X-ray studies, including the location of H atoms, bonding electrons, lone-pair electrons and multiple conformations. A. Podjarny (France), N. Niimura (Japan) and A. Kovalevsky (USA) described neutron crystallographic studies and showed that, despite the lower resolutions attained using neutrons, H atoms - including those that are relatively mobile - can be visualized, allowing the determination of protonation states and revealing details of hydrogen bonding and water structure that are important for a complete understanding of macromolecular function. The speakers emphasized the complementarity of X-rays and neutron studies. Y. Hirano (Japan) showed X-ray and neutron data for an 8.8kDa protein at ultra-high resolution, including detailed information for H atoms and some outer electrons.

Chemical crystallography

Supramolecular interactions in the solid state

Alkali cation exchange and transport through supramolecular polyhalide-induced stacks of crown ether molecules. (Courtesy of Katharina Fromm.)

The wide scope of microsym. MS43 covered the preparation and characterization of supramolecular systems. G. Resnati (Italy) reported the formation of supramolecular gels via cooperative halogen and hydrogen bonds. E. Boldyreva (Russia) presented variable temperature and pressure studies of continuous lattice strain, phase transition and crystallization. H. Uekusa (Japan) spoke about dynamic covalent bond formation and self-assembly in macrocyclic boronic esters. T. Mak (China) gave an overview of the in situ generation of silver-ethynide supramolecular synthons for high-nuclearity clusters. S. Chong (UK) described the study of purely organic molecular cage materials with significant porosity lacking strong directional interactions. K. Fromm (Switzerland) impressed the auditorium with 'supramolecular straws', compounds of DB18C6 macrocycle molecules, to form one-dimensional channels via halogen-halogen bonds using trihalides I₃⁻, BrI₂⁻ and BrIBr⁻ as anionic pillars. Potassium ions and water molecules are found inside three channel types, making ion transport possible. Using a single crystal as bridge between two compartments, one of which contains 1M NaOH and the other ultrapure water, the Fromm group was able to determine the kinetics at different temperatures by measuring the increase in ionic conductivity in the water compartment. The activation energy for Na⁺ and K⁺ transport through the channels corresponds to super-ionic conductors.

The role of crystallography in chemical reactivity and catalysis

MS59 speakers and chairs. From left: Masaki Kawano, Andrew Bond, Guillermo Mínguez Espallargas, Lee Brammer, Alessia Bacchi, Fernando Lahoz and Pance Naumov.

Microsym. MS59 was attended by over 150 participants who learned how crystals might be used as reaction flasks and how they react to external stimuli, and how they jump and dance. M. Kawano (South Korea) showed how to obtain metastable permanently porous metal-organic frameworks (MOFs) and use them to trap rare species such as S₃. Kawano described the challenge of using thermodynamic and kinetic control to obtain porous coordination networks. G. Mínguez Espallargas (Spain) explained that in stimuli-responsive dynamic MOFs it is possible to switch magnetic properties on and off by modifying the content of dynamic pores. They explored how physisorption of different gases such as CO₂ or N₂ modifies spin and temperature transitions. A. Bond (Denmark) followed the kinetics of hydration and dehydration of sodium naproxen as a function of relative humidity, showing that complete crystallographic knowledge is crucial for pharmaceutical applications; a series of elegant synchrotron powder diffraction experiments followed the dehydration processes in approximately real time. J. Popovic (Croatia) was able to obtain heterobimetallic polymeric precursors of nanocrystalline mixed metal-oxide phases. L. Brammer (UK) showed that silver-based coordination polymers may mimic the supramolecular arrangement of carboxylic acids and can be so flexible as to rearrange their structures to accommodate small guests in latent pores, which are formed on demand. Finally, P. Naumov (UK) explained how crystals might literally jump by reacting to a change in temperature: this thermosalient effect converts packing energy into mechanical energy and it is strictly related to changes in the structure upon heating. The discussions that followed the talks generally pointed out that crystallography is the central science to define properties and applications of solid materials in all fields of modern technology, from catalysis to magnetic materials and from pharmaceutical science to mechanical engineering.

Experimental and simulated structures in metal-organic frameworks (MOFs)

MS75 speakers and chairs. From left: Ben Gelfrand, Francois-Xavier Coudert, Mathew Cliffe, Felipé Gandara, Stephen Moggach, Igor Djerd, Shuhei Furukawa and Thomas Bennett.

Microsym. MS75 focused on MOF structure solution and understanding the physical properties of these hybrid materials. B. Gelfand (Canada) is designing humidity-dependent proton conductivity in phosphonate-containing MOFs. S. Furukawa (Japan) focused on the surfaces of soft porous frameworks that can be modified to produce desired properties. Complex 'multi-layer' MOFs, consisting of a framework shell surrounding a different chemical interior, are multi-functional. Such materials can resist single-crystal formation, and I. Djerdj (Croatia) used powder diffraction to determine the structures of vanadium-based compounds. M. Cliffe (UK) examined disorder using pair distribution function analysis to probe the presence and interaction of defects in the structure of Hf-UiO-66. F. X. Coudert (France) developed a methodology to evaluate the flexibility of MOF structures and S. Moggach (UK) described the high-pressure behavior of extremely flexible scandium MOFs.

Crystallographic education

Crystallography education and training in the 21st century: new pedagogies, new paradigms, Part II

MS92 speakers and chairs. From left: Louise Dawe, Joe Tanski, Peter Moeck, Graciela Diaz de Delgado, Amy Sarjeant and Saulius Grazulis. Not pictured are Elena Boldryeva and Wael Rabeh.

Microsym. MS92 concerned educational approaches from around the world. P. Moeck (USA) described his efforts to generate 3D-printed models of crystal structures from coordinate files and to work with the Crystallography Open Database. G. Diaz de Delgado (Venezuela) spoke about the rich crystallographic heritage of Latin America; workshops held there, books and teaching materials developed in Mexico, and the 1974 Direct Methods School in Brazil. E. Boldryeva (Russia) described outreach programs for school children, including French language students who were inspired to pursue careers in science after translating the French posters Voyage dans le Crystal into Russian. J. Tanski (USA), W. Rabeh (USA, UAE) and L. Dawe (Canada) described their methods to incorporate crystallography into undergraduate curricula, through laboratory experimentation or topical research and presentations.

Instrumentation, techniques and/or computation

Remote controls for crystallography at synchrotron and neutron sources

MS52 speakers and chairs. From left: (front row) Brian Toby and Ruslan Sanishvili; (back row) Dave Hall, Matt Suchomel, Marian Szebenyi, Craig Ogata, Daniele de Sanctis and Jean-Luc Ferrer.

While the benefits of remote operations are numerous, ranging from the simple conveniences of the home lab to significant travel-related financial, time and effort savings, they only work well if the functionality is not compromised for users, either by availability of tools normally offered at a beamline, or by cybersecurity and other restrictions. Effective communication between the on-site and remote components of the operation is also crucial. In microsym. MS52, the talks of C. Ogata (USA), D. Hall (UK), D. de Sanctis (France), M. Szebenyi (USA), J. Ferrer (USA) and M. Suchomel illustrated these points very well.

What became clear in this session was how far robotic systems for data collection have advanced. What seemed unthinkable just a few years ago, namely completely roboticized and automated handling of macromolecular crystals that are sensitive to mechanical impact, temperature, humidity and/or chemical environmental changes, now seems achievable.

The organizers could not locate any remote operation examples conducted at neutron sources. These instruments are often simpler than those found at synchrotrons and have very similar cybersecurity requirements. It is clear that such facilities will provide even greater benefit from remote operations, due to site-access restrictions and the longer data collection times. This is clearly a challenge for the future.

Grazing-incidence surface techniques

Dramatic advances in grazing-incidence surface analysis techniques have accompanied technical advances in X-ray neutron scattering. Recent advances including in situ studies were presented in this symposium. In microsym. MS56, grazing-incidence small-angle X-ray scattering studies of sample preparation by spray coating and post-production treatments such as solvent-vapor annealing demonstrated the potential of accessing temporal changes on surface nanostructures. Kinetic processes monitored with time resolution down to tens of milliseconds allowed for understanding complex non-equilibrium processes. Neutron scattering techniques are able to study difficult sample environments, such as hot and wet surroundings. Sample modifications induced by these environments were analyzed in detail. Using the transmitted signal in grazing-incidence geometry was discussed.

Simultaneous methods with SAS

MS71 speakers and chairs. From left: (front row) Manfred Burghammer, Kohji Tashiro, Sylvio Haas, Satoshi Koizumi, Aldo Craievich, Bo Iversen; (back row) F. Zhang, Wim Bras.

The subject of microsym. MS71 was the on-line combination of small-angle scattering with other experimental techniques. K. Tashiro (Japan) described combining Fourier transform infrared spectroscopy with SAXS from synchrotron and conventional sources. S. Haas (Germany) demonstrated co-analysis of data sets obtained with SAXS and other techniques. This new methodological development has the promise to reveal correlations in chemical and structural events, which would remain hidden when using a sequential analysis of the data. B. Iversen (Texas) used the combination of SAXS with pair distribution function analysis in studies on the growth of nanocrystals.

In operando and structure evolution - from atomic to micron

The speakers in microsym. MS79 addressed the study of materials used in construction, catalysis, gas purification, energy storage and nanotechnology under operating conditions. The structural changes during the simultaneous sorption of different gases by porous materials and the structural changes of new iron-based electrodes used in batteries are being characterized using wide-angle neutron diffraction. The switching process of thin films of thermoresponsive polymers is followed using time-resolved time-of-flight neutron reflectometry. The formation of metal layers on nanostructured polymer templates is investigated during the sputtering process. New instruments are being developed, such as the neutron diffractometers iMATERIA and SPICA at J-PARC, dedicated to the study of industrial materials and to in situ investigations of battery materials, respectively. Specialized sample environments, e.g. humidity chambers for neutron reflectometry and gas sorption systems, and sensitive methods, such as phase-sensitive and modulated enhanced X-ray powder diffraction, are becoming available.

Materials or minerals

Symmetry and isomorphism in material design and crystal growth

MS62 speakers and chairs. From left: J. Huot, R. Kozak, E. Vlieg, L. Suescun, T. Bekker, R. Černý, A Dąbkowski.

Crystal growth is a complex process, which classically can be described by thermodynamics and heat- and mass-transport terms. However, this approach cannot explain numerous observations - facets, crystal growth anisotropy, isomorphism (and isomorphic substitution), to name just a few. Knowing the crystallographic structure is necessary to fully understand the crystal growth process and to utilize isomorphic effects in synthetic procedures. The speakers in microsym. MS62 addressed these topics.

E. Vlieg (The Netherlands) told us about the breaking of symmetry in compound crystallization, an important problem in the synthesis of organic and inorganic materials. He also addressed effects of symmetry breaking on the crystal surface - an issue important to microscopic understanding of crystal growth and nucleation. R. Černý (Switzerland) introduced us to the peculiar properties of borohydride anions that are capable of forming metal borohydrides, which resemble metal oxides.

Recent development of wide band gap materials: semiconductors and oxides

MS94 speakers and chairs. From left: M. Lorenz, S. Pimputkar, S. Garcia-Granda, D. Klimm, E. Bøjesen, T. Oshima, S. Harada.

The papers by Teal et al. in Phys. Rev. (1950, 1951) marked the introduction of semiconductors into technology. Soon germanium was replaced by silicon, which is still the material of choice for most electronic devices. For some applications, such as optoelectronics in the visible or even ultraviolet spectral range, or for high-power electronics, 'wide band gap' semiconductors are needed, where the energy difference between the valence and conduction bands is considerably larger than for Si. In this session, the status of wide band gap research and application was reviewed. In microsym. MS94, talks by S. Harada (Japan) and S. Pimputkar (USA) were devoted to SiC or GaN, respectively. Both substances have already been introduced into commercial applications such as solid-state lighting, but nevertheless the improvement of bulk growth processes with respect to size, quality and cost efficiency is still an issue, and the application of crystallographic analysis methods has afforded remarkable technological progress. The other four talks were mainly devoted to semiconducting oxides, with focus on ZnO by L. Leipzig (Germany) and E. Bøjesen (Germany), CdS by G. Granda (Florida), and b-Ga₂O₃ by Oshima (Japan) in nanostructures and layers, as well as in the bulk. Impressive results were presented, ranging from in situ diffraction studies on phase formation during the growth of ZnO nanocrystals to oxide-based devices such as ZnO transistors or Ga₂O₃ based solar blind UV light detectors.

Physical and/or fundamental

Advances in X-ray FEL coherent scattering and diffraction

Single-shot X-ray coherent diffractive imaging experiment detects lattices of quantum vortices in rotating superfluid helium nanodroplets. (Courtesy of Oliver Gessner.)

Short-wavelength free-electron lasers (FELs) have been in operation since 2005. The first facility to provide this radiation was FLASH in Hamburg, operating in the XUV range. Ultra-short pulse duration, nearly complete transverse spatial coherence and very high pulse intensities provided the basis for new X-ray applications and scientific insight. Since 2010 the LCLS at SLAC, and since 2011 SACLA at SPring-8, also provide hard X-ray FEL radiation. Microsym. MS20 provided an overview of the recent advances of hard X-ray FEL coherent scattering and diffraction experiments, and their application to materials science, quantum systems and structural biology. The characterization of FEL coherence properties and the possibility to simulate complete FEL coherence experiments were discussed. All discussed applications used single particles to be studied, either mounted on a thin membrane or injected into the FEL beam. These single particles are, however, very different and include gold nanocrystals, Xe-doped He droplets, frozen hydrated cells mounted on Si₃N₄ (or C) membranes or free-flying bio-particles. Particularly stunning were the results obtained by coherent diffraction imaging at the LCLS from cryogenic ⁴He droplets. O. Gessner (LNBL) showed how it was possible, using this technique, to observe the existence of a vortex lattice with contrast enhancement by Xe doping and to measure the deformation of the droplets due to very high precession frequencies, and how these results contribute to determining the superfluidic state of the droplets.

Another very important talk presented the status of single biomolecule imaging using X-ray FEL radiation. S. Boutet (SLAC) showed the present status of experiments and explained the instrumentation developments in the areas of X-ray delivery, background suppression and sample injection still to be achieved, to bring this technique to fruition.

Methods: algorithms and software for powder diffraction

MS72 speakers and chairs. From left: Yifeng Yun, Reinhard Neder, Takashi Ida, Xim Bokhimi, Ryoko Oishi-Tomiyasu, Tsunehisa Kimura.

While powder diffraction methods are well established, there are still challenges for difficult samples. In microsym. MS72, R. Neder (Germany) examined the effects of preferred orientation on the pair distribution function (PDF). The Debye equation implies a spherical averaging and this assumption is invalidated by preferred orientation. The computational demands for such calculations are high. Computational methods were a theme of the session. X. Bokhimi (Mexico) described how CPU technology is powerful enough to fully ray-trace a diffractometer, and O. Oishi-Tomiyasu (Japan) demonstrated how mathematical methods have impacted powder indexing. Even 'grainy' samples can now lead to reasonable structural refinements, due to the statistical methods described by T. Ida (Japan).

Y. Yun (Sweden) described how electron diffraction could be used to solve structures in a multi-phase system. T. Kimura (Japan) showed how preferred orientation might be induced in a suspended sample by applying a magnetic field. By measuring 2D diffraction data from a magnetically oriented sample the crystal symmetry may be deduced.

Frustration, topology and chirality in metals and complex oxides

MS105 speakers and chairs.

The issues discussed in microsym. MS105 were related to frustration, topology and chirality of magnetic intermetallic or oxide compounds. The topics ranged from rather long-standing ones, such as frustrated and quantum magnets, to modern ones, including topological insulators and chiral skyrmion magnets.

Of particular note was a talk by J. Paddison (UK) who demonstrated that powder magnetic diffraction data could be used to retrieve the short-range spin correlations in crystalline frustrated magnets. He showed that even hidden multiple orders might be detected in gadolinium gallium garnet using this analysis method. This suggests a promising future of this approach for frustrated magnetism research.

Surfaces

MS111 speakers and chairs. From left: Yuki Fukaya, Joanne Stubbs, Christian Schlepuetz, Jim Ciston, Daniel Schwarz, Peter Moeck, Craig Bennett, Tetsuroh Shirasawa.

Microsym. MS111 highlighted probes ranging from charged particles (electrons and positrons) to scanning probe microscopies to X-rays. Attendees were introduced to total-reflection high-energy positron diffraction (TRHEPD), which 'sees' only the uppermost 1-3 layers of atoms on a surface, by Y. Fukaya (Japan), and saw examples of three-dimensional X-ray reciprocal space maps that allow for the discovery and exploration of unanticipated diffraction features, enabling the description of complex symmetries and structures in thin films, presented by C. Schlepuetz (USA). The use of polychromatic X-rays to collect rapid crystal truncation rod (CTR) data demonstrated this oft-used but usually slow technique could also be suitable for time-resolved studies by T. Shirosawa (Japan). We saw that scientific movies (made with low-energy electron microscopy or LEEM) not only illustrate and entertain, but can also be used to quantitatively describe surface nucleation rates and adsorbate structures by D. Schwarz (USA). A new approach to image processing based on plane group symmetry provoked a thoughtful reexamination of traditional STM image analysis and interpretation by P. Moek (USA), and a new description of charge-density waves in NbSe₃ by T. Bennett (UK) helps to resolve discrepancies in a variety of previously published data. Taken together, all of these methods provide exciting new opportunities for understanding crystallographic aspects of surfaces, interfaces and thin films.