Methane Encapsulation in 4-Phenoxyphenol Framework under Ambient Conditions: Experimental Evidence and Computational Simulation

초록

4-Phenoxyphenol is an organic molecule that self-assembles into a hydrogen-bonded crystalline framework with well-defined channels aligned along the c-axis and is capable of accommodating various guest molecules. Here, we report for the first time the experimental evidence and computational simulation of a 4-phenoxyphenol clathrate that stably captures CH4 molecules under ambient conditions. The CH4-loaded 4-phenoxyphenol (CH4-4PP) clathrate was prepared via a gas-phase synthesis method between 4-phenoxyphenol powder and CH4 gas at 15 MPa and 298 K. Rietveld refinement combined with Fourier difference mapping reveals that CH4 molecules stably occupy the center of the hexagonal cages, which are periodically aligned along the c-axis of the 4-phenoxyphenol framework. The characteristic Raman bands at 2907 cm-1 and the solid-state 13C cross-polarization/magic angle spinning nuclear magnetic resonance peaks at -4.4 ppm confirm the presence of CH4 molecules encapsulated within the CH4-4PP clathrate frameworks. Molecular dynamics simulations, including mean squared displacement, radial distribution functions and mass density profile analyses, reveal that CH4 molecules remain spatially confined near the cage center of the 4-phenoxyphenol framework, exhibiting restricted mobility in the clathrate cages without intercage diffusion. Temperature-dependent Raman spectroscopy indicates that more than 50% of CH4 molecules are retained within the 4-phenoxyphenol clathrate cages until the melting point without any structural alterations of the crystalline framework.

키워드