Structural characteristics and guest dynamics of Xenon-loaded 4-phenoxy-phenol clathrate frameworks

초록

Hydrogen-bonded organic clathrates are a class of molecular materials for gas storage and separation, in which cage frameworks enable inclusion of small gas molecules. In this work, 4-phenoxyphenol clathrates were prepared using the gas-phase synthesis method between 4-phenoxyphenol hosts and Xe guests at 298 K and 5 MPa. The structural characteristics, guest inclusion and dynamics, and host-guest interactions of the as-synthesized Xe-loaded 4-phenoxyphenol (Xe-4PP) clathrates were characterized using synchrotron XRD combined with Rietveld refinement, X-ray fluorescence spectroscopy and solid-state Xe-129 NMR spectroscopy. These results comprehensively show that the hydrogen-bonded organic frameworks of Xe-4PP clathrates form one-dimensional hexagonal cages along the c-axis, and Xe atoms reside at the center of the cages of Xe-4PP clathrates with the cage occupancy of approximately 0.39. The solid-state Xe-129 NMR spectra show an axially symmetric powder pattern with the isotropic chemical shift of 205.7 ppm and the chemical shift anisotropy of 173 ppm, consistent with an axially symmetric shielding tensor and with an oblate-like shielding surface for confined Xe in which the c-axis is least shielded. In-situ temperature-dependent synchrotron XRD was performed to investigate the structural stability and thermal expansion of Xe-4PP clathrates. From 298 K to 353 K, there is no structural transition of Xe-4PP clathrates, exhibiting an anisotropic expansion by similar to 0.59% along the a-axis and similar to 0.18% along the c-axis, corresponding to a volumetric increase of similar to 0.97%. These results provide insights into host-guest interactions in organic molecular materials, elucidating the anisotropic structural response and dynamics of confined guest molecules.

키워드