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

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.