Spectroscopic Observations of Host-Guest Hydrogen Bonding in Binary Cyclopropanemethanol plus Methane Hydrate

초록

Herein, we report a new structure II (sII) hydrate with cyclopropanemethanol (CPM) in the presence of methane (CH4) gas for the first time and investigate the host-guest hydrogen bonding in the binary CPM + CH4 hydrate via solid-state NMR, Raman spectroscopy, and synchrotron X-ray powder diffraction analysis. The crystal structure and guest distribution of the binary CPM + CH4 hydrate were characterized using solid-state C-13 NMR and powder diffraction analyses, which confirmed the formation of the binary sII CPM + CH4 hydrate. The CPM in the large cages of sII hydrate was predicted to be present in the dynamic Anti (Anti I or Anti II) form based on the measured- and calculated-NMR spectra. The inclusion of CH4 molecules in both the large and small cages of the sII hydrate was observed from the C-13 NMR and Raman spectra. No free OH signals of the CPM guest were observed in the Raman spectra of the binary CPM + CH4 hydrate, which indicated that the CPM guest participated in host-guest hydrogen bonding with the water framework. The powder diffraction pattern of the binary CPM + CH4 hydrate was refined using Rietveld analysis with the direct space method, and the results supported the hydrogen bonding of the hydroxyl group of the CPM guest to the host water molecules. The phase equilibrium temperature and pressure conditions of the binary CPM + CH4 hydrate were also measured, and the binary CPM + CH4 hydrate was found to be less stable than the binary tetrahydrofuran + CH4 hydrate.

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