Cavity tetrakaidecahedron

Figure 2.5 Three cavities in gas clathrate hydrates (a) pentagonal dodecahedron (512), (b) tetrakaidecahedron (51262), (c) hexakaidecahedron (51264), (d) irregular dodecahedron (435663), and (e) icosahedron (51268).

Figure 1 Different cavities found in gas hydrates (a) pentagonal dodecahedron (b) tetrakaidecahedron (c) hexakaidecahedron.

The structure of a clathrate crystal, xenon hydrate. The xenon atoms occupy cavities (eight per unit cube) in a hydrogen-bonded three-dimensional network formed by the water molecules (46 per unit cube). The O—H- -0 distance is 276 pm, as in ice. Two xenon atoms, at 0, 0, 0 and i, are at the centers of nearly regular pentagonal dodecahedra. The other six, at 0, i, i 0, f, i i, 0, i i, 0, f i, i, 0 and i, 0, are at the centers of tetrakaidecahedra. Each tetrakaidecahedron (one is outlined, right center) has 24 comers (water molecules), two hexagonal faces, and 12 pentagonal faces. 

Fig. 10.2, they are pentagonal dodecahedron (5 " ), tetrakaidecahedron (5 6 ), hexakaidecahedron (5 6" ), irregular dodecahedron (4 5 6 ), and icosahedron (5 6 ). The formalism X" is used to describe the structure of each cavity, where X denotes the type of cage face (4—square, 5-pentagon, and 6-hexagon), and n represents the number of such kinds of face in that cavity. The three structures of gas hydrates comprise different cavities 5 and 5 6 cavities form si, 5 and 5 6 cavities form sll, and sH is formed by 5, 4 5 6, and 5 6 cavities. 

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