Pressure-Induced Encapsulation of Cs+ Cations within an 18-Crown-6 Cavity: Insights from X-ray Diffraction, Raman Spectroscopy, and DFT Calculations

This study utilizes single-crystal X-ray diffraction in a diamond anvil cell (DAC) to explore the structural response of [Cs(18-Crown-6)][SbCl6] under high pressure (HP). Notably, the pressure drives large Cs atoms closer to the center of the crown ether cavity, ultimately requiring pressures of 3 GPa for its complete encapsulation. Remarkably, the absence of short contacts in the crystal classifies the material as a "loose crystal" offering a unique model for understanding compression mechanisms. The crystal exhibits highly anisotropic compression behavior with an impressive volume reduction and non-linear pressure - unit-cell parameters relationships facilitated by the absence of short CH center dot center dot center dot Cl contacts up to 0.9 GPa. Beyond this pressure, steric repulsion due to shortening H center dot center dot center dot Cl and H center dot center dot center dot H interactions hinders further effective compression, so pressure dependence on unit cell parameters and volume becomes more linear. The behavior of [Cs(18-Crown-6)][SbCl6] at different conditions was studied using Raman spectroscopy and supplemented by DFT calculations.