Observation of Interstitial Molecular Hydrogen in Clathrate Hydrates

The current knowledge and description of guest molecules within clathrate hydrates only accounts for occupancy within regular polyhedral water cages. Experimental measurements and simulations, examining the tert-butylamine broken vertical bar H-2 broken vertical bar H2O hydrate system, now suggest that H-2 can also be incorporated within hydrate crystal structures by occupying interstitial sites, that is, locations other than the interior of regular polyhedral water cages. Specifically, H2 is found within the shared heptagonal faces of the large (4(3)5(9)6(2)7(3)) cage and in cavities formed from the disruption of smaller (4(4)5(4)) water cages. The ability of H-2 to occupy these interstitial sites and fluctuate position in the crystal lattice demonstrates the dynamic behavior of H-2 in solids and reveals new insight into guest-guest and guest-host interactions in clathrate hydrates, with potential implications in increasing overall energy storage properties.