t was a pleasure to be invited to act as editor for this themed issue in which we aim to assemble a series of invited and submitted papers which provide a look at some of the current research efforts defining the subject of “Chemical Crystallography”. Of course, the timing of this is to make a positive contribution to the celebration of this special year, 2014 - the UNESCO Year of Crystallography.
I opted to use this generic title since I have always considered that it suitably described the kind of research in which I have been involved throughout my academic career – using crystallography to study chemistry! This view stems from the time I began my PhD, in the Chemistry Department of King’s College London. I joined a small group, supervised by Mr Ralph Hulme, and on my “recommended” reading list was the core text book entitled “Chemical Crystallography”, written by C.W.Bunn [1]. The first edition was published in 1945, and although it contained chapters on other facets of crystallography, a number of others did focus on topics of relevance to chemistry, and it provided many good links between the two areas. It is amusing to note that a Google search using this title does not yield a specific dictionary entry for the subject of “Chemical Crystallography” in Wikipedia, although many University “Chemical Crystallography Groups” are identified, and it conveniently links to the website of the Chemical Crystallography Group of the British Crystallographic Association, and through this, to many other National sites. The search also links to a site from which one can download a free copy of Charles Bunn’s book!
My PhD, which involved the preparation and structure determination of solid forms, which we called “packing complexes”, prepared by crystallizing antimony trichloride from some organic molecules, such as dibenzyl and stilbene, and for which I actually built my own low-temperature device for use with a Weissenberg camera with a split cylindrical cassette, was followed by a period as a postdoctoral research fellow with Professor Donald Rogers, a trained physicist with a Chair in the Chemistry Department at Imperial College, and a remarkable scientist and teacher. My area of research here was the structure determination of natural products, all solved by making heavy atom derivatives, but I can recall having my first experience with structure-solving by direct methods, using triple products to attempt to solve a structure in two dimensions - by hand! Before the completion of my Fellowship, I was fortunate to be invited to take up a position as Lecturer in Inorganic Chemistry at Queen Mary College London, where my brief was to assemble suitable equipment in order to apply X-ray crystallography to structurally characterise new kinds of compounds which were then being synthesised in inorganic chemistry.
Thus, in these early days, my main interests in Chemical Crystallography, like many of my cohort, were drawn into “molecular” science – discovering the distribution of atoms and groups in new molecules and complexes. On the one hand was the type of work I was involved with at Imperial College – the determination of the structures of organic natural products [2]. Even using film methods, a structure determination by X-ray crystallography was much quicker than several years of work based on systematic degradation and re-assembly. On the other hand was the determination of the structures of the new types of compounds which were being synthesised. In the beginning, the main emphasis was directed at metal-containing compounds, especially in the buzz area of “organometallic” chemistry, in which these compounds, with metal-to-carbon bonds were yielding new types of structures with new types of bonding and new types of reactions [3]. A related class of compounds, generally referred to as metal-organics, comprised structures with organic ligands, but with direct bonds from the metal to non-carbon atoms of the organic ligands, also opened up new channels [4]. The bonding in these types of compound often required new thinking and this created pressure to generate bonding interpretations of structure. Fortunately, new ideas and software on the description of chemical bonding were now also rapidly developing in theoretical chemistry, and the champions of the two approaches which could be applied to bonding in molecular structures - valence bond theory [5] and molecular orbital theory [6] - competed to provide models, which could also be tested using other, mainly spectroscopic techniques. In the same period, we were also seeing the first activities in the development of computer programs using the empirical methods of molecular modelling [7]. As in crystallography, the development of these topics benefitted enormously through the increasing power of computers. Indeed, a diversity of procedures and associated software were rapidly developed and integrated in the general area we now know as “Computational Chemistry”. This provides us with a richness of valuable tools, not only to work in molecular and solid state science, but in most areas and techniques used in chemistry.