Programmed Pore-Shape Fixing in a Soft Porous Molecular Crystal-Navigating the Phase Interconversion Landscape.

Area of Science:

• Materials Chemistry
• Supramolecular Chemistry
• Crystallography

Background:

• Pore-shape fixing effects (PSFEs) in soft porous crystals remain underexplored.
• Dynamic van der Waals solids offer unique possibilities for structural manipulation.

Purpose of the Study:

• To investigate and report the PSFE in the prototypical dynamic van der Waals solid p-tert-butylcalix[4]arene (TBC4).
• To understand the molecular-level mechanisms governing guest-induced phase transformations in TBC4.

Main Methods:

• Variable-pressure (VP) single-crystal and powder X-ray diffraction.
• VP differential scanning calorimetry.
• Volumetric sorption analysis and attenuated total reflectance Fourier-transform infrared spectroscopy.

Main Results:

• Two distinct porous shape-fixed phases were programmed in TBC4 using CO2 pressure and temperature.
• Phase interconversion was found to be particle size-dependent: smaller crystals showed fixed metastable phases, while larger crystals exhibited reversible transitions.
• A comprehensive phase interconversion scheme for TBC4 was established.

Conclusions:

• This study provides the first example of PSFE in a porous molecular crystal.
• The findings highlight the potential for controlling porous crystal structures through external stimuli and particle size.
• The established phase interconversion scheme allows for predictable navigation of TBC4's structural landscape.