Single-Crystal Diffraction

The Director of our Diffraction Facility, Principal Research Scientist Dr. Peter Mueller, is a crystallographer with almost two decades of experience and has gained a reputation as one of the world’s foremost experts on data-collection strategy, data reduction, structure solution and crystal structure refinement.

Dr. Mueller has successfully handled hundreds of complex and difficult structures and authored or co-authored approximately 150 articles in peer-reviewed scientific journals. He is frequently asked to give oral presentations on data collection strategy, structure refinement and atom type assignment and regularly teaches at crystallographic workshops and Summer Schools in Europe, the United States, Brazil, and China. In addition, Dr. Mueller is co-editor of Acta Crystallographica as well as editor and main author of a textbook on structure refinement (Crystal Structure Refinement, Oxford University Press 2006). Dr. Mueller has served and still serves on several committees for the American Crystallographic Association (ACA) and the International Union of Crystallography (IUCr) and advises Oxford University Press on crystallographic textbooks.

Diffraction data will be collected at one of the Facility’s single crystal diffractometers. For a typical diffraction experiment, the crystal will be mounted on a MiTeGen™ loop in Paratone oil at low temperatures. Temperature of choice is usually 100K, unless specified otherwise or unless a destructive low-temperature phase transition or other considerations require data collection at a higher temperature. In principle, temperatures between 90K and 500K are possible. Our Facility is equipped with modern and versatile Bruker diffractometers that allow collecting complete and highly redundant datasets in any given Laue class meeting or exceeding the International Union of Crystallography requirements for good data. These diffractometers are coupled to extraordinarily sensitive Bruker APEX and APEX2 CCD detectors that give rise to high-resolution data even on very small crystals (down to 10µm).

Data collection will be performed using Mo or Cu radiation, depending on the requirements of the project. Mo radiation gives rise to higher resolution data and is the preferred wavelength for most routine samples. Cu radiation is required to obtain anomalous signal from light-atom structures (at least one oxygen for every 10 carbon / nitrogen atoms is recommended) and is sometimes needed to obtain a good diffraction pattern from very small crystals.

Structure Determination consists of structure solution (typically performed with SHELXS or SHELXT) and structure refinement (performed with SHELXL). Provided the submitted sample is of sufficient quality, the final product is a publishable structural model consisting of all files required for submission of the structure to scientific journals (namely RES, LST, CIF as well as others).