Complex zeolite structure solved by combining powder diffraction and electron microscopy

Abstract

Many industrially important materials, ranging from ceramics to catalysts to pharmaceuticals, are polycrystalline and cannot be grown as single crystals. This means that non-conventional methods of structure analysis must be applied to obtain the structural information that is fundamental to the understanding of the properties of these materials. Electron microscopy might appear to be a natural approach, but only relatively simple structures have been solved by this route. Powder diffraction is another obvious option, but the overlap of reflections with similar diffraction angles causes an ambiguity in the relative intensities of those reflections. Various ways of overcoming or circumventing this problem have been developed, and several of these involve incorporating chemical information into the structure determination process. For complex zeolite structures, the FOCUS algorithm has proved to be effective. Because it operates in both real and reciprocal space, phase information obtained from high-resolution transmission electron microscopy images can be incorporated directly into this algorithm in a simple way. Here we show that by doing so, the complexity limit can be extended much further. The power of this approach has been demonstrated with the solution of the structure of the zeolite TNU-9 (|H9.3|[Al9.3Si182.7O384]; ref. 10) with 24 topologically distinct (Si,Al) atoms and 52 such O atoms. For comparison, ITQ-22 (ref. 11), the most complex zeolite known to date, has 16 topologically distinct (Si,Ge) atoms.

Electron crystallography as a complement to X-ray powder diffraction techniques

“…Rietveld refinement of this model revealed that additional symmetry was present in the structure. That is, atomic positions related by a center of symmetry (not present in C2cm) were found to be insignificantly different from one another, so the structure Electron crystallography and powder diffraction [39]. The insets show the corresponding SAED pattern (left), the contrast-transfer-function corrected and symmetry-averaged image, from which the phases were calculated (middle), and the computer simulation from the structural data (right).…”

“…A further option is to use an approximate or partial model that has been deduced from HRTEM images as a seed for generating starting phase sets. Different combinations of these options eventually led to the determination of the three most complex zeolite structures known (TNU-9 [39], IM-5 [40] and SSZ-74 [41]). The relevant aspects of these structure solutions are given in the following sections to illustrate the procedure.…”

Stacking disorders in zeolites and open-frameworks – structure elucidation and analysis by electron crystallography and X-ray diffraction

“…Electron crystallography has several important advantages in structure analysis of these materials; single crystal electron diffraction can be collected from micro-and nano-sized crystals and high resolution transmission electron microscopy (HRTEM) images can be obtained, from which crystallographic structure factor phase information can be extracted [2]. During the past years, several of the most complicated zeolite structures were solved by electron crystallography alone [3,4] or together with PXRD [5][6][7][8][9].…”

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).…”