Unveiling Guest Structure and Hydrogen Bonding in Cyclohexanemethanol Clathrate Hydrates.

Clathrate hydrates are crystalline inclusion compounds traditionally described as host-guest systems stabilized predominantly by van der Waals interactions. Recent studies, however, have shown that polar guest molecules can engage in weak and transient hydrogen bonding with the hydrate water framework, challenging this classical picture. Here, we report cyclohexanemethanol as a new structure H hydrate former in a binary system with methane and elucidate its guest-host interaction behavior at the molecular level. ¹³C NMR spectroscopy, Raman spectroscopy, and powder X-ray diffraction confirm the formation of sH hydrate, with methane occupying the small and medium cages and cyclohexanemethanol preferentially encapsulated in the large cage in its low-energy conformation. Density functional theory calculations support the conformational stability of the guest molecule upon encapsulation. Molecular dynamics simulations reveal the presence of weak, temperature-dependent guest-host hydrogen bonding between the hydroxyl group of cyclohexanemethanol and the hydrate lattice, accompanied by transient local lattice distortions. These findings demonstrate that sH hydrates containing hydrogen-bond-capable organic guests exhibit interaction characteristics intermediate between true clathrate and semiclathrate hydrates, providing new molecular-level insight into hydrate stabilization mechanisms beyond purely van der Waals interactions.