Crystal Structure of MCM-65:  An Alternative Linkage of Ferrierite Layers

The crystal structure of calcined MCM-65 was determined by constrained model building suggested by a close comparison with as-synthesized MCM-47. Synthesized with a compact structure-directing agent (quinuclidine), as-synthesized MCM-65, unlike MCM-47, is found to retain its crystallinity after calcination. It crystallizes in space group Cmcm, where a = 7.373 Å, b = 18.006 Å, and c = 13.849 Å and represents a linkage of ferrierite layers oriented in a common direction to form a two-dimensional microporous structure of orthogonal eight-membered ring channels with respective dimensions 4.4 × 2.6 Å and 4.6 × 2.7 Å. Rietveld refinement of the model against synchrotron powder diffraction data (λ = 1.15201 Å) gives R wp = 0.12, R ( F 2 ) = 0.21. The crystal density is 1.95 g/cm 3, and the framework density for T sites is 19.4. Solid-state 29 Si NMR data for the as-synthesized MCM-65 are in agreement with the proposed structure and indicate that the silanol groups are linked after calcination. Although the structure-directing agent has a significant influence on calcination behavior it is found, e.g., by electron diffraction experiments, that MCM-47, MCM-65, ZSM-52, and ZSM-55 form a family of closely similar materials.