Host–Guest Interactions and Guest-Release Behavior of 4-Phenoxyphenol Clathrate Capturing CO ₂

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 θ = 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.