Issue Date: February 26, 2007
Charge flipping nets zeolite structure
An algorithm based on a technique known as charge flipping has been used to solve the complex crystal structure of a zeolite that has eluded determination since the material was first synthesized nine years ago (Science 2007, 315, 1113). In charge flipping, the signs of electron densities below a threshold value are switched from negative to positive. Lynne B. McCusker of the Swiss Federal Institute of Technology, Zurich, and coworkers show that the hydrocarbon-cracking catalyst IM-5 has 24 unique silicon atoms and 47 unique oxygen atoms in its framework structure. The zeolite has a distinctive pore structure with complex channel intersections that can accommodate bulky intermediates during catalysis. Initial electron-density maps for the algorithm were produced from X-ray powder diffraction intensities and high-resolution transmission electron microscopy images. This combination approach to solving crystal structures is widely applicable and could be used for other complex polycrystalline materials.
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