  We report a new hydrogen clathrate hydrate synthesized at 1.2 GPa and 298 K
documented by single-crystal X-ray diffraction, Raman spectroscopy, and
first-principles calculations. The oxygen sublattice of the new clathrate
hydrate matches that of ice II, while hydrogen molecules are in the ring
cavities, which results in the trigonal R3c or R-3c space group (proton ordered
or disordered, respectively) and the composition of (H2O)6H2. Raman
spectroscopy and theoretical calculations reveal a hydrogen disordered nature
of the new phase C1', distinct from the well-known ordered C1 clathrate, to
which this new structure transforms upon compression and/or cooling. This new
clathrate phase can be viewed as a realization of a disordered ice II,
unobserved before, in contrast to all other ordered ice structures.
