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

Abstract

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, 5(12), 5(12)6(2), 5(12)6(3) and 5(12)6(4). We have found new stacking sequences as a minor phase coexisting with an Fd (3) over barm 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, 5(12) and 5(12)6(4), and these two layers are also the constituents of the Fd (3) over barm structure. The other layer consists of two different kinds of polyhedron, 5(12)6(2) and 5(12)6(3), corresponding to layer z, which were introduced in our recently published papers [e.g. Y. Sakamoto, et at, 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 is-phase. (C) 2010 Elsevier Masson SAS. All rights reserved.