Figure 4.

Hydrogen hydrate structures

3D structure of sI hydrate: the unit cell consists of 46 water molecules arranged into small cages with twelve pentagonal faces and large cages with two hexagonal and twelve pentagonal faces (A). 3D structure of sII hydrate with the unit cell composed of 136 water molecules arranged into small cages with twelve pentagonal faces and large cages with twelve pentagonal and four hexagonal faces (B). 3D structure of sH hydrate with the unit cell composed of 34 water molecules arranged into small cages with twelve pentagonal faces; medium cages with three hexagonal, six pentagonal, and three tetrahedral faces; and large cages with twelve pentagonal and eight hexagonal faces (C). (A), (B), and (C) are adapted with permission from (Momma et al., 2011). 2D view of hydrate structures and building blocks including small, medium, and large cages (D), adapted with permission from (Liang and Kusalik, 2015).