Steric and electronic effects in the host-guest hydrogen bonding in clathrate hydrates

Clathrate hydrates with polar guest molecules (dimethyl ether, ethylene oxide, trimethylene oxide, tetrahydrofuran, and tetrahydropyran) were studied by means of the density functional theory. A model of a large cage of structure-I clathrate was employed. Optimal configurations of encaged guests were investigated with a focus on the host-guest hydrogen bond formation. Weak hydrogen bonds were found to be formed by each guest, while for THP a strong hydrogen bond and formation of L-defect was also observed. This is in accord with previous computational and experimental studies. Steric factors were shown to play a key role for the strength of the hydrogen bond formed. Interestingly, the host-guest binding is influenced not only by the size of a guest molecule but also by its shape. This work demonstrates that both electronic and steric properties of a polar guest should be considered for a full description of clathrate systems.