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+H₂+H₂O hydrate system, now suggest that H₂ 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 (4³5⁹6²7³) cage and in cavities formed from the disruption of smaller (4⁴5⁴) water cages. The ability of H₂ to occupy these interstitial sites and fluctuate position in the crystal lattice demonstrates the dynamic behavior of H₂ 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. [ABSTRACT FROM AUTHOR]