Heptakaidecahedron

The lacunar pattern of this grain therefore includes six tetragonal and nine hexagonal faces. Relating this to polyhedrons, we find that no pentakaidecahedron with such a combination of faces can exist (see page 199). If, however, the two polar areas be regarded as filled-in hexagonal lacunae, making 17 lacunae in all, the pattern corresponds to a heptakaidecahedron with 6 tetragonal and 11 hexagonal faces, which appears to be the proper interpretation of this pattern.

The host lattice consists of 156 water molecules per unit cell, which form 16 identical heptakaidecahedra (17-hedra) and 12 identical octahedra (8-hedra) in a face sharing arrangement with cubic symmetry.

Other clathrates are the Br₂ hydrate with a pentakaidecahedral cage of water molecules or the tert-butylamine hydrate with a heptakaidecahedron cage of water molecules.