W0091
Crystal Structures of Micro-Crystals Using Sealed-Tube X-ray Sources: Pushing the Envelope. Peter C. Burns and Frances C. Hill, Department of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, IN 46556-0767, USA
The introduction of CCD-based X-ray area detectors permits the determination of the structures of micro-crystals using sealed-tube X-ray sources. How small must a crystal be before it is necessary to resort to synchrotron radiation? To address this question, the structures of several micro-crystals have been determined using a Bruker SMART CCD detector mounted on a PLATFORM goniometer with MoK X-radiation (40 kV, 20 mA). The CCD detector is sufficiently sensitive to permit the collection of useful data for well-diffracting crystals that are as small as a few hundred m3, although long count-times are required for each frame of data that is collected. As examples, structures were done for the mineral edoylerite, Hg3CrO4S2, and the synthetic phase Sr(UO2)3O3[CO2(OH)]2[CO(OH)2](H2O)5 using crystals having volumes less than 103 m3. Edoylerite is monoclinic, a = 7.5283(4), b = 14.8325(8), c = 7.4629(4) Å, = 118.746(1), space group P21/c. The structure was obtained for a crystal with an approximate volume of 400 m3 using a frame width of 0.1 and 120 s to accumulate each frame. The final R was 7.9% for 1193 unique observed reflections. The Sr uranyl carbonate has a monoclinic structure, a = 8.4029(8), b = 12.452(1), c = 10.757(1) Å, = 93.453(2), space group P21. The crystal studied had a volume of approximately 800 m3. Data was collected using a frame width of 0.2 and 120 s to accumulate each frame. The final R was 8.9% for 2096 observed reflections. Additional examples will be discussed, as well as the details of data-collection strategies for micro-crystals using CCD detectors and sealed-tube X-ray sources.