Structure Transition and Swapping Pattern of Clathrate Hydrates Driven by External Guest Molecules

We first report here that under strong surrounding gas of external CH₄ guest molecules the sII and sH methane hydrates are structurally transformed to the crystalline framework of sI, leading to a favorable change of the lattice dimension of the host−guest networks. The high power decoupling ¹³C NMR and Raman spectroscopies were used to identify structure transitions of the mixed CH₄ + C₂H₆ hydrates (sII) and hydrocarbons (methylcyclohexane, isopentane) + CH₄ hydrates (sH). The present findings might be expected to provide rational evidences regarding the preponderant occurrence of naturally occurring sI methane hydrates in marine sediments. More importantly, we note that the unique and cage-specific swapping pattern of multiguests is expected to provide a new insight for better understanding the inclusion phenomena of clathrate materials.