Single Crystal X-Ray Crystallography
X-Ray Diffraction is commonly used to determine the molecular structure of materials in the solid state. Such analysis is routinely performed on a variety of targets – including drug candidates, catalysts, organic LEDs and energy storage networks – using single crystals as small as 100μm.
IMSERC currently maintains two X-Ray diffractometers to support the broad spectrum of research at Northwestern. Both systems utilize 3kW sealed tube generators and state-of-the-art APEXII CCD detectors. Our “platform” diffractometer runs MoKα radiation for strongly diffracting samples which may have small unit cells or heavy X-Ray absorbers. The second diffractometer has a Kappa goniometer and runs CuKα radiation for weakly-diffracting samples with large unit cells. This instrument is also useful for determining absolute stereochemistry of light-atom materials (Z < Na). Each diffractometer is equipped with a nitrogen atmosphere low-temperature device providing temperature control at the sample from 80k to 400k during data collections.
Data collections are performed by IMSERC staff members and preliminary results are routinely returned within 24-48 hours from the start of the experiment. Publication-ready files are made available to users when the data allow. Facility users who are adept at structure solution and refinement may request the raw data files in order to perform the work-up themselves. Advanced users, who have been sufficiently trained, may request to be checked out on the IMSERC diffractometers and collect their own datasets during off-peak hours. Students interested in learning to solve and refine their own structures should attend the Chemistry 435 Class in X-Ray Crystallography offered during the winter quarter.
Collaborations with LS-CAT and ChemMatCARS afford IMSERC staff the opportunity to utilize the APS at Argonne National Lab for difficult samples. Materials submitted to the X-Ray facility that prove too challenging for our on-site instrumentation, will be taken to the APS for data collections on a routine basis (approximately once a month, or as time and sample load allows).
There are two high resolution, polarized light microscopes available for student use in the X-Ray facility. Our most recent addition (August 2009), a Nikon SMZ1500 stereozoom microscope is equipped with a digital camera and video monitor for visualization of crystalline samples. Users can perform visual inspection of their samples with these instruments to assess crystal quality. High resolution photographs can be taken and used for publications or other presentations.
A host of crystallographic software is available through the IMSERC terminal server and several programs are available for individual installation under site license agreements. IMSERC X-Ray staff are available for consultation about any aspects of the crystallographic experiment. Questions should be directed to Amy Sarjeant or Charlotte Stern, or see our X-Ray Crystallography FAQ.