8 CHIMIA 2014, 68, Nr. 1/2 Crystallography, past, present, Future

doi:10.2533/chimia.2014.8 Chimia 68 (2014) 8–13 © Schweizerische Chemische Gesellschaft ‘Seeing’ Atoms: The Crystallographic Revolution

Dieter Schwarzenbach*

Abstract: Laue’s experiment in 1912 of the diffraction of X-rays by crystals led to one of the most influential discoveries in the history of science: the first determinations of crystal structures, NaCl and diamond in particular, by W. L. Bragg in 1913. For the first time, the visualisation of the structure of matter at the atomic level became possible. X-ray diffraction provided a sort of microscope with atomic resolution, atoms became observable physical objects and their relative positions in space could be seen. All branches of science concerned with matter, solid-state physics, chemistry, materials science, mineralogy and biology, could now be firmly anchored on the spatial arrangement of atoms. During the ensuing 100 years, structure determination by diffraction methods has matured into an indispensable method of chemical analysis. We trace the history of the development of ‘small-structure’ crystallography (excepting macromolecular structures) in . Among the pioneers figure and Paul Scherrer with powder diffraction, and Paul Niggli and his School with space group symmetry and geometrical crystallography. Diffraction methods were applied early on by chemists at the Universities of Bern and . By the 1970s, X-ray crystallography was firmly established at most Swiss Universities, directed by full professors. Today, chemical analysis by structure determination is the task of service laboratories. However, the demand of diffraction methods to solve problems in all disciplines of science is still increasing and powerful radiation sources and detectors are being developed in Switzerland and worldwide. Keywords: Bragg · Laue · Service crystallography · Structure determination · X-ray diffraction

1. Introduction chemists, the indestructible elements of circumstantial.This conundrum was solved Mendeleev’s Periodic Table hinted at the by X-ray crystallography whose develop- Atomic theories postulating that mat- existence of atoms that were linked to form ment is one of the crucial scientific revo- ter is composed of discrete components molecules. The theory of atomic valence lutions because it provided a ‘microscope’ date back to antiquity.[1] However, before and schemes of bonding, particularly in with atomic resolution that made atoms the early 20th century atoms could not organic chemistry, was proposed in the and their arrangements in space visible. It be seen, they were invisible even for the 1850s by Kekulé, but atoms were invisible is perhaps important to explain here what highest-resolution instruments available. and ideas about their nature were vague. exactly is meant by ‘microscope’, ‘seeing’ During the 19th century, physical observa- (iii) The physicists’ theories of atoms were and ‘visible’. Crystallographic results in tions accumulated indicating the existence closest to our modern understanding. The the form of pictures consisting of spheres of atoms, or of a grainy submicroscopic physics of gases led to Avogadro’s propo- or ellipsoids connected by rods which rep- structure of matter: (i) Crystallographers, sition that equal volumes of different gases resent molecules or structural frameworks finding that the orientations of the faces at equal temperature and pressure contain are today ubiquitous. These pictures are not of polyhedral crystals could be represent- the same number of particles. Loschmidt quite the same as direct observations with a ed by proportions of small integer num- in 1865 determined the ‘size of air mol- high-resolution microscope; they only rep- bers (law of rational indices, Miller indi- ecules’, i.e. Avogadro’s number. In 1897, resent the average locations of atomic cen- ces), postulated the periodicity of crystal J. J. Thomson showed that cathode rays tres and some information on atomic ther- structures. But the lattice theory had little are composed of particles which he called mal vibrations and possibly other types of impact on physicists and chemists, the na- electrons, and then proposed the plum pud- disorder. The rods represent interpretations ture of the periodically repeated object or ding model of the atom. Atoms as counta- of short interatomic distances as chemical ‘atom’ being mysterious. Lattice theory ble items were first ‘seen’ by Rutherford bonds. Thus, bonds are inferred, not ob- turned out to be incapable of predicting when he identified α-rays to be composed served. Modern charge-density analysis physical properties of crystals. (ii) For of He ions. Rutherford’s atom model con- with accurate diffraction data may furnish sisting of a tiny nucleus surrounded by direct evidence on interatomic bonding, orbiting electrons was proposed in 1911. but this is certainly not an easy, efficient In 1913, Bohr published the first version experiment. Direct visualisation of atoms of his quantized planetary-like atom mod- had to wait for high-resolution electron mi- el. All these models developed by physi- croscopy and scanning probe microscopy. cists had little impact on the chemists at The discovery of X-ray diffraction by the time of their publications because they crystals is due to Friedrich, Knipping and gave no insight into chemical reactions, Laue in 1912,[3] the idea having occurred *Correspondence: Prof. D. Schwarzenbach even though Bohr hoped his model to be to Laue in a discussion with Ewald on the Ecole Polytechnique Fédérale de Lausanne of chemical relevance.[2] latter’s doctoral thesis. This is one of the IPSB - Cristallographie Thus, ideas about atoms remained quite most influential experiments whose reper- Le Cubotron (BSP) CH-1015 Lausanne disparate and depended on the scientific cussions cannot be overestimated. It was E-mail: [email protected] discipline, evidence on atoms was largely acclaimed immediately at the time of pub- Crystallography, past, present, Future CHIMIA 2014, 68, Nr. 1/2 9

lication as the first experimental proof of NaCl, diamond and ZnS are essentially 3. Crystallography to Become a the lattice periodicity of crystal structures, determined by symmetry, and they could Method of Chemical Analysis and it also established the wave nature be guessed directly from the diffraction of X-rays. Its history is well researched pictures without knowledge of diffraction The theoretical basis having been estab- and well documented.[4] But none of the physics. The theory of X-ray intensity and lished, the field grew with the development original authors were interested in crystal of what is today called data reduction to of laboratory equipment. The production structures and chemistry. The revolution derive structure amplitudes was formulat- of X-rays was simplified by the invention of X-ray crystallography is due to William ed in the immediately following years. In and perfection of easy-to-use sealed X-ray Lawrence Bragg who first realized, at age 1913 the sphere of reflection and the notion tubes that became commercially available 23, that Laue’s X-ray diffraction photo- of the structure factor by Ewald, in 1914 in the 1920s. Many types of single-crys- graphs contained information on the spatial the temperature factor by Debye (up to a tal X-ray cameras, such as the success- arrangement of the atoms in the crystal.[5] factor of 2, corrected for later by Waller), ful Weissenberg and precession cameras, the need for integrated intensities and the were invented in the 1920s and 1930s. In Lorentz factor, and two-beam dynamical the 1950s, 3- and 4-circle single-crystal 2. The First Crystal Structures diffraction by Darwin. In 1915, X-ray scat- diffractometers appeared, first for neutron tering by a gas and the atomic scattering crystallography in the USA, and for macro- In the publication[3] describing the first factor to be calculated using Bohr’s atomic molecular crystallography in England. X-ray diffraction experiments, Laue pro- model by Debye were described. Powder The powder method was developed with posed the Laue interference equations, diffraction was invented by Debye and highly efficient X-ray monochromators for and used them to interpret the diffraction Scherrer in 1917 and applied to the deter- film cameras and diffractometers. The con- photographs of cubic ZnS assuming a mination of the structure of graphite, and struction of new radiation sources such as primitive lattice and the presence of five independently at the same time by Hull for more efficient laboratory sources, synchro- different, well-defined wavelengths in the the determination of the structure of iron. trons and free-electron lasers, and of new X-ray beam. W. L. Bragg realized that this The model of the ideal mosaic crystal and two-dimensional area detectors continues interpretation was not entirely convincing, the theory of secondary extinction was for- to this day. and that these photographs could be inter- mulated by Darwin in 1922 in connection The heavy calculations necessary for preted more satisfactorily by supposing the with an experimental determination of the the solution of ever more complex crys- lattice to be face-centered and the incom- scattering factors of Na and Cl in NaCl by tal structures, mainly the summation of ing beam to contain X-rays with a contin- W. L. Bragg, James and Bosanquet. The Fourier series and the refinement of struc- uum of wavelengths that were reflected first space-group tables useful for structure tural parameters by least-squares meth- from the lattice planes. This specular re- determination were published by Niggli in ods, were major obstacles for now routine flection he described by the equation now 1919 (see below). work until a few decades ago. Modern known as Bragg’s law, 2dsinθ = nλ, where W. L. Bragg’s discovery of crystal struc- X-ray crystallography developed with the d is the interplanar spacing, θ the reflection ture determination gave him and his father invention of ever more efficient computers. angle, λ the wavelength and n an integer. an important advance in the development Crystallographers were important clients W. L. Bragg surmised that this equation is and application of the new crystallography. of computer centres operating big main- probably equivalent to the Laue equations. Crystallography as it is perceived today as frame machines. They also pushed the The fact that Bragg’s law was derived in- the technique of structure determination development of in-house computing, us- dependently and rigorously from the Laue became a science dominated by British ing the mini-computers driving automatic equations a few weeks later in Moscow scientists and laboratories, all the more so diffractometers also for structure solution by G. V. Wulff is rarely mentioned out- as Laue, Friedrich and Knipping were not and refinement. side Russia. The reflection law led father interested in this kind of research, and for In parallel with the increase of com- William Henry Bragg to construct the first Ewald it was not the main preoccupation. puting power, structure determination single-crystal diffractometer that was of Right after World War I, the Braggs divided evolved from educated guessing in the course also useful for X-ray spectrome- the field amongst themselves by establish- 1920s, Patterson and Fourier methods in try. The first crystal structure, the one of ing two separate schools of crystal structure the 1930s, phase relationships called direct NaCl, was proposed by W. L. Bragg,[6] research: the father at the Royal Institution methods starting in the 1950s, to ever more based on Laue-type photographs of many in London for organic structures, the son at automatic analyses of ever larger structures alkali halides, taken with polychromatic the University of Manchester for inorgan- in ever shorter times. The development of radiation, but in hindsight this structure is ic structures. During many years, British macromolecular crystallography is a suc- revealed much more evidently by slightly and Commonwealth institutions played a cess story quite analogous to, but 20 to 30 earlier single-crystal diffractometer scans leading role in the development of crystal years later than small-structure crystallog- of the (100) and (111) planes of NaCl.[7] structure determination. raphy. Readers are referred to ref. [9] for a The structures of NaCl (and of KCl, KBr, It should be mentioned that right af- more detailed account of the evolution of KI,...) were met with much disbelief and ter Laue’s discovery,[3] researchers started crystallography during the 100 years since opposition of chemists for several decades: to irradiate all kinds of substances with Laue’s experiment. it is a framework structure and no NaCl X-rays, not only crystals. X-ray diffraction molecules can be identified. It revolution- became an indispensible tool for charac- ised chemistry. Simultaneously, the Braggs terising materials, e.g. for determining the 4. Crystallography in Switzerland published the structure of diamond[8] that sizes, orientations and strains of grains in pleasingly showed tetrahedral carbon at- polycrystalline materials and worked met- A survey of the early regional devel- oms, and also provided the solution of the als, characterising epitaxial layers, or stud- opment of crystallography and crystal structure of cubic ZnS. W. L. Bragg then ying structures of partially crystalline and structure determination up to 1962 is solved the structures of pyrite (FeS ), flu- non-crystalline materials such as liquid available in ref. [10], for crystallography 2 orite (CaF ) and calcite (CaCO ) from dif- crystals and fibres, glasses and liquids. In in Switzerland see ref. [11]. Swiss scien- 2 3 fractometer data. this paper, we will follow the evolution of tists contributed fundamental work during Cubic structures such as those of crystal structure determination. the first years after Laue’s and the Braggs’ 10 CHIMIA 2014, 68, Nr. 1/2 Crystallography, past, present, Future

discoveries, without being particularly its salient features, including e.g. a pro- his visionary research on the very complex interested in structure determination as found discussion of site symmetries, and structures, phase transitions, twinnings such. Paul Scherrer is one of the co-dis- of reflection conditions for the determina- and intergrowths of feldspars using all coverers of powder diffraction, i.e. of the tion of space groups. Ref. [15] contains a methods at his disposition including X-ray Debye-Scherrer method. As professor of very rich presentation of lattice geometry and neutron diffraction, infrared spectros- Experimentalphysik at ETH Zürich from discussed in terms of positive-definite ter- copy, nuclear quadrupole resonance, elec- 1920, he directed work on ferroelectric nary quadratic forms, Niggli-reduced unit tron spin resonance, and electron micros- crystals, such as Rochelle salt. Debye was cells defined by the shortest non-coplanar copy. His Institut für Kristallographie und director of the Physics Institute at ETH translation vectors, lattice planes in terms Petrographie embraced a very wide range from 1920 to 1927, and was succeeded of reciprocal space, lattice complexes of competences from earth science to by Scherrer. Paul Niggli was appointed of space groups, and topological struc- mathematics, including classical mineralo- professor of Mineralogy and Petrography ture analysis using domains of influence gy and petrography, clay minerals, mineral at the ETH and the University of Zürich (Wirkungsbereiche) of symmetry elements collection, mineral chemical analysis, hy- in 1920 and became the central figure of defined as being the space inside which drothermal crystal growth, crystal optics, what has been called the Zurich School of the distances between points equivalent by spectroscopic methods, X-ray diffraction Crystallography.[12] a symmetry element are shorter than the with many single-crystal cameras, pow- distances to outside points of the complete der diffraction diffractometers and powder 4.1 The Zurich School orbit. Ref. [16] presents the symmetries film cameras, electron microscopy and ra- Paul Niggli (Fig. 1) was a towering of point configurations, building units in diometric rock dating. Alfred Niggli, a for- figure and highly influential scientist pro- crystal structures, interatomic bonding, mer student of Paul Niggli, was appointed

Fig. 1. Paul Niggli, 1888–1953. Photograph Fig. 2. Fritz H. Laves, 1906–1978.[12] Fig. 3. Werner Nowacki, 1909–1988.[12] taken around 1920 (collection of the author). ductive in crystallography, mineralogy and and classifications of important structures. professor in 1961. His main interest was petrography.[13] He understood very early Thus, Niggli’s crystallography represents in mathematical crystallography and group the importance of symmetry, both crystal abstract classifications of crystalline archi- theory. Crystallography in the accepted classes and space groups, for crystal-struc- tectures, rather than the determination of sense of structure determination was grad- tural science. He worked on general prin- crystal structures. ually developed only in the 1960s, the first ciples of crystalline architectures and on Paul Niggli’s successor at the ETH and 4-circle single crystal diffractometer was their classifications. Niggli collaborated the University of Zürich from 1954 to 1976 acquired in 1966. Walter M. Meier joined with mathematicians such as Georg Pólya was his former student Fritz H. Laves,[18] the Institute as third professor of crystal- and Heinrich Heesch of the University (Fig. 2), well-known for the concept of lography in 1966 and became well known of Zurich. His most seminal books intermetallic Laves phases of composi- in structure research of zeolites and struc- in crystallography are ‘Geometrische tion AB (structure types MgCu , MgZn , ture determination by powder diffraction. 2 2 2 Kristallographie des Diskontinuums’,[14] MgNi ). Like Paul Niggli, he was interested The institute of Laves was very influential 2 ‘Krystallographische und strukturtheore- in the general principles of crystal chemis- in the German-speaking world. 20 of its tische Grundbegriffe’[15] and ‘Grundlagen try based on symmetry and building units. collaborators became professors, mainly in der Stereochemie’.[16] All three of them He focused on the most difficult crystals Germany. Its last spin-off was the Institut are still worth reading. Ref. [14] is the first and complex crystalline assemblies rather de Cristallographie of the University version of today’s ‘International Tables for than on crystal structure determination for of Lausanne in 1973. The retirement of Crystallography’[17] and contains many of chemical analysis. He became famous for Meier in 1992 may be considered as the Crystallography, past, present, Future CHIMIA 2014, 68, Nr. 1/2 11

end of Paul Niggli’s Zurich School. A new Laboratory of Crystallography of the ETH and the University of Zurich headed by Walter Steurer was founded in 1993, and is attached today to Materials Science. It became a leading centre of quasi-crystal research, and of powder methods solving structures of record-breaking complex- ity due to Meier’s former collaborators, Christian Bärlocher and Lynne McCusker.

4.2 The Zurich School at the University of Bern Werner Nowacki (Fig. 3), a student of Paul Niggli, brought the mathemati- cal crystallography of the Zurich School to Bern.[19] His PhD thesis in 1935 dealt with homogeneous space partitions and domains of influence of symmetry ele- ments. In 1936, he moved to the University of Bern, and founded the Department of Crystallography in 1952. In addition to mathematical crystallography, he also de- veloped a very active, well-equipped and Fig. 4. Walter Feitknecht, 1899–1975.[21] Fig. 5. Kurt H. Meyer, 1883–1952.[23] successful laboratory of crystal structure determination. Many and diverse crys- tal structures have been elucidated there, synthetic ionophores, chemical reaction Chemistry of the University of Geneva by ranging from minerals to sterines, and or- paths, molecular motions, electron density Kurt H. Meyer[23] (Fig. 5). He attempted ganic compounds of high molecular sym- distributions, polymorphism, phase trans- structure determination of synthetic and metry. In a very productive collaboration formations in solids, solid-state chemical natural polymers using fibre diffraction. with mineralogists, he investigated the sul- reactions, analysis of weak intermolecular In 1934, his laboratory produced fibre fosalt minerals of the unique Lengenbach interactions in condensed phases and crys- diagrams of plastic sulfur and proposed deposit in the valley of Binn. In the field tal structure prediction (http://www.loc. a much-debated structural model. Later of structural systematics, he compiled ethz.ch/people/emerit/dunitz). work was on polypeptides and chitin. A the distribution of structures among the When X-ray crystallography became model of the structure of cellulose is note- space groups in collaboration with J. D. H. a generally accepted method of chemical worthy because the diffraction data were Donnay. After his retirement in 1979, crys- analysis in the 1970s, most of the Swiss supplemented by known interatomic dis- tallography was transferred to chemistry, Universities established crystallography tances and angles. directed by Hans-Beat Bürgi, a student of laboratories and service groups. Crystal Feitknecht’s student Hans-Rudolf J. D. Dunitz (see below) and interested in structure analysis not as a research topic Oswald brought research in structural all aspects of chemical crystallography and per se, but as a tool in chemical research inorganic chemistry to the University of structural chemistry. His successor is Piero was initiated in Switzerland by Volkmar Zurich where he was appointed director Macchi. The heritage of the Zurich School Kohlschütter,[20] and developed on a of the Institute of Inorganic Chemistry in was taken care of until very recently by large scale from 1936 onwards by Walter 1966. His research areas covered reactivity the mathematical research of Peter Engel, Feitknecht[21] (Fig. 4) at the Institute of solids, coordination compounds, cataly- a student of Nowacki. for Inorganic, Analytical and Physical sis, thermal analysis, electron microscopy, Chemistry of the University of Bern. These and structure determination from X-ray 4.3 Structure Determination in scientists are the pioneers of Swiss solid- powder and single-crystal diffraction. Out Chemistry state chemistry. Kohlschütter coined in of this grew the third diffraction facility The chemical laboratories of the ETH 1919 the term topochemistry for reactions in Zurich, headed from 1990 by the ser- Zürich, and in particular the Institut für or- in the solid state for which the orientations vice crystallographer Helmut Schmalle. A ganische Chemie, realized the importance of starting and product crystalline materi- fourth X-ray diffraction facility in Zurich of X-ray structure determination in chem- als are correlated. He also was a pioneer was developed by J. Bieri and R. Prewo istry at a time when the Zurich School was in the investigation of colloidal substanc- at the Institute of Organic Chemistry of not yet efficient in this type of research es. An early application of the Debye- the University in the 1980s. This service and did not serve chemistry. They founded Scherrer powder method is his demon- is headed since 1989 by Anthony Linden. their own crystallography group headed by stration that red and yellow PbO are poly- The chemical industries of Basel started Jack D. Dunitz in 1957. He brought the art morphic forms of the same compound.[22] service crystallography in the 1960s with of structure determination from Britain to Walter Feitknecht made extensive system- students educated by J. D. Dunitz. At the Zurich, and the introduction and evolution atic surveys of series of compounds, such , a service crystallogra- of chemical crystallography, mainly of or- as the basic salts of divalent metals, dou- phy group headed by Margareta Zehnder ganic compounds, in Switzerland is large- ble hydroxides and hydroxy salts (called started operating its first 4-circle diffrac- ly due to him and his students. Dunitz’ Feitknecht phases), using X-ray powder tometerin1983.ItisnowheadedbyMarkus scientific interests comprised all aspects diffraction and electron microscopy. Neuburger. The Chemical Crystallography of structural chemistry, and in particular Early pioneering work using X-ray group at the University of Neuchâtel was structure and reactivity of medium-ring diffraction was also performed at the developed by Helen Stoeckli-Evans. From compounds, ion-specificity of natural and Laboratory of Organic and Inorganic a modest start in 1971, it has become a ful- 12 CHIMIA 2014, 68, Nr. 1/2 Crystallography, past, present, Future

to Parthé’s research in the synthesis and by X-ray diffraction (excepting macro- structure of materials for hydrogen storage molecular structures) starting with the (K.Yvon, a student of Novotny), crystallo- pioneering, revolutionary discoveries of graphic computing, algorithms, and enan- the simplest structures such as NaCl and tiomorphism (H. D. Flack, a student of K. diamond 100 years ago by W. L. Bragg, Lonsdale, London), and service crystal- and then described the evolution of Swiss lography for chemistry (G. Bernardinelli, laboratories of crystallography. The crys- a student of Gerdil). Parthé was succeeded tallographic revolution consisted in the by R. Cˇerný, a solid-state physicist with realization that atoms can be ‘seen’, that research interests in inorganic and inter- molecules and non-molecular solids are metallic compounds, powder diffraction, three-dimensional geometrical objects crystal chemistry and real structure. observable with atomic resolution. The At the University of Lausanne, the driving force of the development was thus Institute of Crystallography was created chemical analysis. The pioneers worked in in 1973 and attached to Physics. Its pro- physics, or in German-speaking countries fessors were students of Fritz Laves and also in mineralogy laboratories, but they Alfred Niggli at ETH Zurich (see above). were often not recognized by fellow scien- Dieter Schwarzenbach worked on the de- tists to be true physicists or true earth sci- termination of charge densities, structure entists, a situation encountered already by refinement and one-dimensionally disor- W. L. Bragg.[25] For this reason, crystallog- dered structures. Gervais Chapuis special- raphers have developed a separate identity ised in phase transitions and incommen- and assemble in their own scientific socie- surate aperiodic crystals. Service crystal- ties, irrespective of, and in addition to, their Fig. 6. Erwin Parthé, 1928–2006.[24] lography was provided by Kurt Schenk. affiliations to chemistry, physics, materi- The Institute of Inorganic Chemistry of als science, earth science or biology. The the University later created its own well- International Union of Crystallography is ly equipped centre of crystallography with equipped and efficient structure determi- the only scientific association not attached teaching duties and many collaborations. nation service. to specific countries, and represents a very After the retirement of its director, it has diverse scientific community. now moved to the Centre Suisse d’Elec- 4.5 Neutron and Synchrotron The problem of structure determina- tronique et de Microtechnique. Headed by Radiations tion (the crystallographic phase problem) Antonia Neels, it applies diffraction meth- Neutron diffraction became feasible is now solved, at least for nicely ordered ods to solve a very wide range of problems after World War II when nuclear reactors crystals diffracting to atomic resolution. in chemistry and materials science. in the USA and Britain produced neu- Chemists can expect an efficient crystal- At the Department of Chemistry of the tron beams with sufficient intensities. In lographic service even for large structures University of Fribourg, Katharina Fromm’s Switzerland, Walter Hälg directed a very with hundreds of symmetrically independ- group works since 2006 on a wide range of active neutron scattering group at the re- ent atoms, provided that suitable crystals topics and crystal structures, such as crys- actor Saphir, and later at the reactor Diorit can be grown. Therefore, the central oc- tal engineering, supramolecular chemistry, of the Swiss Institute for Reactor Research cupation of traditional crystallographers biomaterials, nanomaterials, bioinorganic in Würenlingen from 1960. Saphir func- has become a technique. Consequently, chemistry. tioned until 1993. In 1996, the continuous institutes and university chairs of crys- neutron spallation source SINQ became tallography are disappearing and are re- 4.4 On the Shore of Lake Geneva operational at the placed by service laboratories attached to In the Suisse Romande, laboratories (PSI) in Villigen. chemistry departments. However, service specialised in crystallography and diffrac- The European Synchrotron Radiation crystallographers are still highly skilled tion were created rather late, in the early Facility (ESRF) at Grenoble was built in the scientists and usually lecturers at their uni- 1970s. At the University of Geneva, Erwin early 1990s. When the crystallographers of versities. Available crystals are often not Parthé[24] (Fig. 6) was appointed profes- the University of Lausanne realized that the ideally suitable: they may be disordered, sor of crystallography in 1970. He creat- plans did not foresee a beamline dedicated too small, unstable at ambient conditions. ed the Laboratoire Interdisciplinaire de to structure determination, they initiated a ‘Seeing’ atoms and their dynamics in all Cristallographie aux Rayons-X, a labora- Collaborating Research Group, that was kinds of situations is still, and will remain tory at the service of all interested research soon joined by Norwegian scientists, to a fundamental need in most scientific dis- groups and comprising all X-ray diffrac- construct the Swiss-Norwegian Beamline ciplines. Diffraction methods, new radia- tion equipment of the University, including (SNBL) with a split beam, one for EXAFS tion sources and new detectors continue to a 4-circle diffractometer, while the chem- and powder diffraction, the other equipped be vigorously developed: neutron sources, ical crystallographer, R. Gerdil, remained with a six-circle single-crystal diffractom- synchrotrons and free-electron lasers in attached to the Chemistry Department. eter. ESRF, together with SNBL, became research centres, and new X-ray sources Parthé earned his PhD under the supervi- operational in late 1994. At PSI, the syn- for local laboratories. They are applied to sion of Hans Novotny of the University of chrotron Swiss Light Source (SLS) started solve very diverse problems in chemistry, Vienna with a thesis on transition metal operations in 2001, and SNBL functions physics, materials science and biology, as carbides and silicides. During the 1960s at today in close collaboration with SLS. exemplified by the other articles in this is- the University of Pennsylvania, he worked sue. on intermetallic and related materials. He was a leading authority in inorganic and 5. Conclusions Received: November 5, 2013 intermetallic crystal chemistry. His labora- [1] C. Gruber, P.-A. Martin, ‘De l’atome antique à tory in Geneva was active in most aspects We have attempted to trace the history l’atome quantique’, Presses polytechniques et of crystallography, specialising in addition of the determination of crystal structures universitaires romandes, Lausanne, 2013. Crystallography, past, present, Future CHIMIA 2014, 68, Nr. 1/2 13

[2] H. Kragh, Physics Today 2013, 66, 36. [3] W. Friedrich, P. Knipping, M. Laue, Sitzungsber. Math. Phys. Kl. K. Bayer. Akad. Wiss. München 1912, 303. [4] M. Eckert, Acta Cryst.A 2012, 68, 30;A.Authier, ‘Early Days of X-Ray Crystallography’, Oxford University Press, Oxford, 2013. [5] S. W. Wilkins, Acta Cryst. A 2013, 69, 1. [6] W. L. Bragg, Proc. Roy. Soc. A 1913, 89, 248. [7] W. H. Bragg, W. L. Bragg, Proc. Roy. Soc. A 1913, 88, 428. [8] W. H. Bragg, W. L. Bragg, Proc. Roy. Soc. A 1913, 89, 277. [9] D. Schwarzenbach, Acta Cryst. A 2012, 68, 57. [10] ‘Fifty years of X-ray diffraction’, Ed. P. P. Ewald, International Union of Crystallography, Chester, 1962, http://www.iucr.org/publ/50years ofxraydiffraction/full-text [11] V. Gramlich, H. Grimmer, Chimia 2001, 55, 484. [12] J. J. Burckhardt, ‘Die Symmetry der Kristalle’, Birkhäuser, Basel, 1988. [13] P. P. Ewald, Acta Cryst. 1953, 6, 225. [14] P. Niggli, ‘Geometrische Kristallographie des Diskontinuums’, Borntraeger, Leipzig, 1919. [15] P. Niggli, ‘Krystallographische und struktur- theoretische Grundbegriffe’, in ‘Handbuch der Experimentalphysik’, Vol. 7, Ed. W. Wien, F. Harms, Akademische Verlagsgesellschaft, Leipzig, 1928. [16] P. Niggli, ‘Grundlagen der Stereochemie’, Birkhäuser, Basel, 1945. [17] ‘International Tables for Crystallography vol. A’, Ed. T. Hahn, International Union of Crystallography, Chester, 2006. http://it.iucr. org/A/ [18] E. Hellner, Z. Kristallogr. 1980, 151, 1. [19] P. Engel, Amer. Mineral. 1989, 74, 1394. [20] W. Feitknecht, Helv. Chim. Acta 1939, 22, 1059. [21] P. Schindler, Helv. Chim. Acta 1975, 58, i-iii. [22] V. Kohlschütter, P. Scherrer, Helv. Chim. Acta 1924, 7, 337. [23] H. Hopff, Starch 1953, 5, 53; R. E. Oesper, J. Chem. Educ. 1950, 27, 665. [24] S. C. Abrahams, W. Jeitschko, Acta Cryst. B 2007, 63, 1. [25] J. Jenkin, ‘William and Lawrence Bragg, Father and Son’, Oxford University Press, Oxford, 2008, p. 430.