THE IMPACT OF SYNCHROTRON SINGLE-CRYSTAL DIFFRACTION STUDIES ON SUPRAMOLECULAR CHEMISTRY

William Clegg, Simon J. Coles and Simon J. Teat

CLRC Daresbury Laboratory, Warrington WA4 4AD, U.K. and Department of Chemistry, University of Newcastle, Newcastle upon Tyne NE1 7RU, U.K.

Keywords: supramolecular chemistry, synchrotron radiation, single-crystal diffraction, crystal structure determination

The construction and commissioning of a new high-flux synchrotron radiation station for single-crystal diffraction in chemistry and materials science at CLRC Daresbury Laboratory has recently been completed [1]. The station is now a standard user facility available for beam-time applications in the normal way. It is designed for the investigation of very small and other weakly diffracting single-crystal samples which are not amenable to study with conventional laboratory equipment, as well as providing tunable wavelength X-rays for special purposes such as anomalous dispersion experiments and charge density studies. At a wavelength around 0.7A, the incident intensity is about 4-5 orders of magnitude greater than that from a laboratory sealed-tube or rotating anode generator. The station is equipped with an integrated goniometer and CCD area detector system, and with low-temperature and high-temperature facilities.

Supramolecular chemistry has featured prominently in the early results obtained from the facility. The tendency to produce very small crystals is high in this field of research, and even larger crystals are often poor X-ray scatterers because of the structural complexity, disorder, and the presence of significant amounts of solvent of crystallisation. Several different research groups have provided samples for investigation. These include:

catenanes;
rotaxanes;
calixarenes and their metal complexes;
porphyrins and other macrocycles, and their metal complexes;
model compounds for biological systems;
arrays based on hydrogen bonding and other intermolecular interactions;
inclusion complexes;
precursors of liquid crystals.

These results would not be obtainable by any other method. In most cases, diffraction effects from conventional equipment were very weak or even impossible to record.

A selection of results from these areas will be presented, together with a description of the equipment and methods used.

1. R.J.Cernik, W.Clegg, C.R.A.Catlow, G.Bushnell-Wye, J.V.Flaherty, G.N.Greaves, I.Burrows, D.J.Taylor, S.J.Teat and M.Hamichi, J.Synchrotron Rad. 1997, 4, 279-286