International Year of Crystallography Celebration: Europe and South Africa

2014 is the International Year of Crystallography which recognises that our understanding of the material nature of our world is grounded in our knowledge of crystallography. Modern crystallography has passed its 100th birthday with the centenary anniversary of the seminal work of W. H. and W. L. Bragg the father and son who determined the first X-ray structures of the inorganic materials sodium chloride, zinc blende and diamond. The significance of their work was rapidly recognised by the scientific community with the 1915 Nobel Prize in Physics. 23 Nobel prizes have been awarded for research dependent on crystallographic studies or on the continued development of crystallography itself, and crystallography remains a vital technique for a broad range of scientific endeavours. CrystEngComm is dedicated to reporting research in the design and understanding of solid-state and crystalline materials. Crystallography underpins most research in crystal engineering, from the determination of the structures of new crystal-engineered materials, to establishing phase purity for crystallisation experiments, to reaching an understanding of fundamental interactions through the investigation of the plethora of structural information collected routinely in hundreds of crystallography labs worldwide. This special issue is the last of four regional special issues of CrystEngComm to be published in 2014 that are dedicated to celebrating the International Year of Crystallography. We are delighted to present work from across Europe and South Africa.

The papers represent a diverse range of topics that comprise crystal engineering and the scope of papers in this issue is summarised below. They reflect both the range of crystal engineering studies being performed across the regions and the sophistication of modern crystallographic techniques. The latter being exemplified through studies performed at variable pressures, neutron diffraction studies of hydrogen bonding complexes, structural elucidation of dynamic processes such as photochemically induced linkage isomerism, and crystal structure determination for materials of high porosity.

Two of the mainstays of crystal engineering: hydrogen-bonded networks and coordination polymers and metal–organic framework materials are both well represented here. New materials with hydrogen bonded structures are presented including amino acid conjugates of carboxylic acids, and urea di-carboxylic acid complexes. Different papers report on new coordination polymers (CPs) from a diverse range of ligand types including glycine-derived salts, N-oxide functionalised cyclotriveratrylene host molecules, and tetrakis(4-tetrazolylphenyl)silane. Properties and behaviours of materials include photoluminescence properties of lanthanide-based CPs, magnetic behaviour of calixarene-supported Mn clusters and of square grid 2D coordination polymers, and dynamic breathing mechanisms in 2D coordination polymers which is induced by solvent sorption and de-sorption.

The study of interactions between molecules or ions in crystal lattices is of fundamental importance in crystal engineering and here we find papers that report theoretical studies on the nature of halogen–halogen interactions and variable pressure crystallographic studies that reveal insights on the relative importance of weak interactions throughout a crystal lattice. Such work may help inform future studies in crystal structure prediction. Studies of polymorphism also give fundamental insight into crystal structures and their predictions and several examples can be found in this issue. Co-crystals, especially of pharmaceutically-relevant compounds, is an area of increased activity and how crystal engineering can inform formulations chemistry is also represented. The papers collected in this special issue provide a valuable overview of the diversity of crystal engineering and demonstrates better than many words how crystallography is still changing and moving towards new goals.

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