Enumeration of Subperiodic Zeolitic Tetrahedral Frameworks. III. Layers, Rods, Tubes, and Clusters

We describe a new database of 4-coordinated hypothetical “subperiodic” zeolitic frameworks, comprising 0-periodic (clusters), 1-periodic (rods and tubes), and 2-periodic (layers) structures. The structures are found by a combinatorial search over 4-coordinated directed graphs, given the space group and the number of unique tetrahedral vertices, as in our earlier database. However, the filters are now reversed to reject the 3-periodic zeolites. Being fully 4-coordinated, these subperiodic structures require no hydroxyl terminations at their free surfaces when realized as SiO₂ silicates. The layers closely resemble thin zeolites and are particularly interesting candidates for synthesis. The layer structures offer a rich library of structural possibilities for low-energy termination of the free surfaces of the known zeolites while maintaining full tetrahedral coordination. We present two examples of possible (001)-surface reconstructions for the LTL framework.