Peristaltic Motion in Structurally Adaptive Molecular Crystals Enables Selective Propyne Capture.

Area of Science:

• Materials Science
• Chemical Engineering
• Crystallography

Background:

• Macrocyclic porous molecular crystals are promising adsorbents for hydrocarbon separations.
• Understanding guest-host interactions is crucial for designing efficient separation materials.

Purpose of the Study:

• To investigate cyclotetrabenzoin and its tetraacetate as adsorbents for C3 hydrocarbons.
• To elucidate the structure-property relationships governing propyne/propylene separation.

Main Methods:

• Adsorption experiments were conducted under ambient conditions.
• In situ synchrotron powder X-ray diffraction and molecular dynamics simulations were employed.
• Single-crystal X-ray diffraction was used to analyze crystal structures.

Main Results:

• Cyclotetrabenzoin tetraacetate demonstrated superior performance in separating propyne from propylene, achieving dynamic binary separation.
• The tetraacetate exhibited higher surface area (570 vs. 42 m² g⁻¹), enhanced uptake capacity (1.99 vs. 1.19 mmol g⁻¹), and faster kinetics.
• Molecular dynamics and X-ray diffraction revealed that structural adaptation, including pore enlargement and aromatic panel rotation, facilitates propyne capture in the tetraacetate.

Conclusions:

• Subtle structural adaptations in porous materials significantly impact gas sorption and separation performance.
• Cyclotetrabenzoin tetraacetate offers a new design strategy for gas separation using transiently porous and ultramicroporous molecules.