A layer stacking with large repeating unit in multi-modal cage-type anionic-surfactant-templated silica mesoporous crystal

Cage-type anionic-surfactant-templated silica mesoporous crystals display rich structural diversity. Among them, cage-type mesoporous crystals with tetrahedrally close-packed (tcp) structures can be described by four types of polyhedron, 512, 51262, 51263 and 51264. We have found new stacking sequences as a minor phase coexisting with an Fd  3¯m structure, and have characterized their structures using transmission electron microscopy (TEM). The new stacking sequences can be explained by the stacking of three kinds of layer based on a description of the polyhedra. Two of the layers consist of two kinds of polyhedron, 512 and 51264, and these two layers are also the constituents of the Fd  3¯m structure. The other layer consists of two different kinds of polyhedron, 51262 and 51263, corresponding to layer z, which were introduced in our recently published papers [e.g. Y. Sakamoto, et al., Chem. Mater. 21 (2009) 223]. We have observed that one of the new stacking sequences, with a large repeating unit, contains these three layers and bears a close resemblance to one of the Frank–Kasper phases with rhombohedral symmetry, known as μ-phase.

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