A Chiral Gas–Hydrate Structure Common to the Carbon Dioxide–Water and Hydrogen–Water Systems

We
present full in situ structural solutions of carbon dioxide
hydrate-II and hydrogen hydrate C0 at
elevated pressures using neutron and X-ray diffraction. We find both
hydrates adopt a common water network structure. The structure exhibits
several features not previously found in hydrates; most notably it
is chiral and has large open spiral channels along which the guest
molecules are free to move. It has a network that is unrelated to
any experimentally known ice, silica, or zeolite network but is instead
related to two Zintl compounds. Both hydrates are found to be stable
in electronic structure calculations, with hydration ratios in very
good agreement with experiment.