Electron crystallography of zeolites. 3. Calcined MCM-22 and MCM-49, a case of subtle differences

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Abstract
Single crystal electron diffraction intensity data, analyzed by direct methods for determining crystallographic phases, have been employed to seek differences between the crystal structures of calcined MCM-22 and MCM-49. A direct comparison of hk0 intensity data indicates such a difference and this is justified further when the respective structural models are refined. The MCM-22 data agree well with the ITQ-1 Si-framework model, but without adding the extraneous interstitial atoms imposed in an earlier powder X-ray diffraction determination. The T-sites in MCM-49 are placed similarly to the ones in MCM-22 but Fourier refinement indicates the presence of an oxygen site not seen for MCM-22. Also one of the oxygen positions found in MCM-22 is not observed in the MCM-49 potential maps.