Small Guest-Free Structure II Hydrate Enclathrating Isoxazole

Clathrate hydrates hold promising potential as porous materials for energy storage and conversion, featuring safer and environmentally friendly alternatives to existing hydrate systems. Here, we report the impact of isoxazole, a five-membered molecule with two heteroatoms, on various clathrate hydrate systems, including methane (CH4), carbon dioxide (CO2), and ethane (C2H6) small guest molecules. We demonstrate that the isoxazole molecule forms structure II (sII) hydrates with CH4 and CO2 and acts as a thermodynamic inhibitor for structure I C2H6 hydrate. Interestingly, our results show that isoxazole forms an sII hydrate with C2H6 under low-pressure and low-temperature conditions. Moreover, it can form a small guest-free sII hydrate with a vacant 5(12 )cage at much lower temperatures than those required for forming tetrahydrofuran and cyclopentane hydrates. Our findings demonstrate that sII (isoxazole) hydrate exhibits no or very weak interaction between isoxazole and the water framework, unlike tetrahydrofuran hydrate implying guest-host interaction.