Guest editorial – Carlo Mealli
This is my 35th year in the world of crystallography and structural chemistry. When I started, the discipline was just beginning to flourish. The first computers and diffractometers, together with new methods of crystal structure determination, were giving a tremendous boost to the development of modern chemistry (organic, inorganic, organometallics, solid state, biological, etc.). Indeed, during my working years, the Cambridge Structural Database has grown from a few thousand to about 300,000 entries. It is therefore no exaggeration to say that crystallography has provided the underpinning for much of structural chemistry. My personal scientific journey has also brought me into the realm of computational and theoretical chemistry. These tools are very important for the interpretation of molecular structure and chemical bonding. In this area, I had the unique and invaluable good fortune to collaborate with Roald Hoffmann, Nobel laureate in chemistry in 1981. From him, I learned how powerful the analysis of a phenomenon is by seeking its relationships with other phenomena of equal complexity. Such a 'horizontal' approach provides a counterpoint to the reductionist mode of understanding that makes a 'vertical' excursion through the hierarchy of the sciences (literature and social sciences would be explained by biological functions, biological ones by chemical ones, chemistry by physical laws and the latter by mathematics). Structural chemistry is perfectly suited to the horizontal way of thinking as the most subtle geometrical diversity can explain different chemical properties and behaviors (R. Hoffmann, The Same and not the Same Columbia University Press, 1995).
For a long time I have enjoyed discussions at crystallographic meetings with colleagues who use their insight to infer chemical properties from the 3D arrangement of molecules. Today, molecular structure is still the basis for any serious chemical study (consider, in this respect, the constantly increasing number of diffractometers sold world-wide). On the other hand, one may have the impression that the molecular crystallographer, once a main actor, is now a species doomed to extinction, rarely encountered at crystallographic conferences. Conversely, it is true that crystallographers, including those who provide structural results as a service and the chemists who solve their own structures, are the source of a tremendous amount of precious data that may be correlated. This is also the reason why I was one of the proponents of the Special Interest Group on 'Molecular Structure and Chemical Properties' within the European Crystallographic Assn.
When I accepted the honour and responsibility of organizing, the XXth IUCr congress together with other Florentine colleagues, not only did I want to demonstrate my still intact love for the discipline, but I also made a special promise. In addition to assembling a high level scientific program on all the multidisciplinary aspects of crystallography, I would like to revitalize the participation of the wider community of chemical crystallographers and structural chemists. In particular, I expect that Florence, the historical city of the Renaissance, will stimulate again discussions on structural problems in the most appropriate framework of the world congress. Finally, I want to reassure all crystallographers that even now, two years before the congress, the Florentine community is already deeply involved in the organizational details. Our primary goal is to provide a successful and unforgettable Congress.