Investigating rotational disorder by inexpensive multi-temperature X-ray diffraction experiments

• Applicant: Privatdozent Dr. Birger Dittrich
• Subject Area: Analytical Chemistry ; Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 259033420

A unique single-crystal diffractometer measurement setup had been established at the Free University Berlin. It combined a) a cryostat for multi-temperature measurements to approx. 30K, b) a vacuum cylinder permeable for X-rays and c) CCD-area detection. The setup was purchased and the diffractometer setup rebuild. Its functionality provides the foundation for this application. Rotational disorder is of fundamental interest in crystallography and there are strong indications that it is relevant for the stability of polymorphic crystal structures, an important topic in the pharmaceutical industry. Establishing an understanding of the conditions that lead to the occurrence of such disorder using suitable compounds is the main aim of this project. Multi-temperature experiments are vital to characterize continuous rotational disorder. Answering this scientific question requires carrying out diffraction experiments of several samples in a wide temperature range of 30 to 300 K on the same specimen; the X-ray source should be updated to reduce the duration of these measurements and to enable the study of smaller samples. Experimental data will be evaluated with special difference electron-density maps that allow accurate characterization of rotational disorder. In parallel, molecular dynamics simulations and QM/MM computations will be performed to complement the experiments. We ultimately aim to provide better modeling tools to deal with disorder in small-molecule crystallography. The new measurement setup will subsequently allow to study of a range of other solid-state research questions in the future. To enable the technical implementation as well as to carry out the proposed research we apply for a 2/3 TV-L E13 PhD position for three years.

• DFG Programme: Research Grants
• Major Instrumentation: Microsource Röntgenstrahlungsquelle ; Zentriervorrichtung
• Instrumentation Group: 4050 Meßelektronik und Zubehör für Röntgengeräte ; 4090 Röntgenröhren und sonstige Röntgengeräte