Structure of the Polycrystalline Zeolite Catalyst IM-5 Solved by Enhanced Charge Flipping

Abstract

Despite substantial advances in crystal structure determination methodology for polycrystalline materials, some problems have remained intractable. A case in point is the zeolite catalyst IM-5, whose structure has eluded determination for almost 10 years. Here we present a charge-flipping structure-solution algorithm, extended to facilitate the combined use of powder diffraction and electron microscopy data. With this algorithm, we have elucidated the complex structure of IM-5, with 24 topologically distinct silicon atoms and an unusual two-dimensional medium-pore channel system. This powerful approach to structure solution can be applied without modification to any type of polycrystalline material (e.g., catalysts, ceramics, pharmaceuticals, complex metal alloys) and is therefore pertinent to a diverse range of scientific disciplines.

Intramolecular electron diffraction in vibrationally resolvedK-shell photoionization of methane

“…For example, they can efficiently diffract at crystals, exactly as normal waves do when they strike a diffraction grating. From the observed diffraction patterns, one can then deduce quantitative structural information such as lattice constants and symmetry [1][2][3][4]. When used with ultrahigh time resolution, they even allow one to map structural changes as those occurring in phase transitions [5,6].…”

The charge-flipping algorithm in crystallography

“…Unfortunately, the performance of the modified algorithm is not compared with the standard algorithm without the treatment of the overlapping reflections. The unmodified algorithm was shown to work well several times for powder diffraction data if the structures are not too complex and if the degree of overlap does not exceed the critical limit (Baerlocher, Gramm et al, 2007;Le Bail et al, 2009). It is thus difficult to judge how important the repartitioning scheme employed in this algorithm was for the solution of the examples presented.…”

“…In practice, the known phases are fixed for a certain number of iteration cycles, and then released to give the model more freedom to develop, and to correct possible errors in the supposedly known phases. Using this combination of charge flipping, histogram matching, structure envelope and known phases, some of the most complex zeolite structures could be elucidated (Baerlocher, Gramm et al, 2007;Baerlocher et al, 2008;Koyama et al, 2008;Sun et al, 2009).…”

Collecting 3D electron diffraction data by the rotation method

“…along [100], [010] and [001]. Recently, several zeolites with unit cell dimensions in the range 14-57 A have been solved by combining electron crystallography and powder X-ray diffraction (Gramm et al, 2006, Baerlocher et al 2007). These are the most complicated zeolites ever solved by crystallography (including X-ray crystallography).…”