Host-Guest Interactions and Guest-Release Behavior of 4-Phenoxyphenol Clathrate Capturing CO2

초록

CO2-loaded 4-phenoxyphenol (CO2-4PP) clathrates were prepared by the gas-phase synthesis method between 4-phenoxyphenol hosts and CO2 guest molecules. The structural characteristics of the as-synthesized CO2-4PP clathrates were comprehensively observed using synchrotron X-ray diffraction (XRD) combined with Rietveld refinement and Raman spectroscopy, exhibiting that hydrogen-bonded organic frameworks of the CO2-4PP clathrates form one-dimensional hexagonal cages along the c-axis and CO2 molecules are confined at the center of the cages of CO2-4PP clathrates. The Raman bands at 1274 and 1379 cm-1 clearly show spectroscopic evidence of CO2 guest molecules confined in the cages of the CO2-4PP clathrates with a cage occupancy of theta = 0.7 as determined from the Rietveld refinement. We investigated the thermal stability and guest-release of the CO2-4PP clathrates by conducting a cross-examination of temperature-dependent synchrotron XRD and Raman spectroscopy. A gradual decrease in the Raman intensity of CO2 molecules was observed in the temperature range of 298-353 K, indicating an anisotropic thermal expansion and spontaneous guest release from the CO2-4PP clathrate framework without any structural alterations. These results establish CO2-4PP clathrates as a structurally coherent organic system capturing CO2 with excellent stability under ambient conditions and enabling controlled release of guests.

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