Harnessing Halogen Bonds in Porous Molecular Crystals for Efficient SF₆/N₂ Separation.

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Gas Separation

Background:

• Halogen bonding is a tunable noncovalent interaction with underexplored potential in designing porous materials.
• Developing materials with permanent porosity, stability, and processability is crucial for advanced applications.
• Selective gas capture remains a significant challenge in environmental and industrial processes.

Purpose of the Study:

• To design and synthesize a novel porous molecular crystal utilizing halogen bonding for selective gas adsorption.
• To investigate the structural transformation and gas interaction properties of the material.
• To achieve high selectivity for fluorinated gases like sulfur hexafluoride (SF₆) over nitrogen (N₂).

Main Methods:

• Synthesis and characterization of the porous molecular crystal FPMC-1-α and its desolvated form FPMC-1-β.
• Structural analysis revealing 1D channels with exposed bromine σ-holes in FPMC-1-β.
• Gas adsorption and selectivity measurements using SF₆ and N₂ at 298 K and 1 bar.
• Experimental and computational studies to elucidate the mechanism of selective gas binding.

Main Results:

• FPMC-1-β exhibits permanent porosity, high thermal stability, and solution processability.
• Desolvation of FPMC-1-α transforms it into the denser FPMC-1-β phase with accessible halogen bonding sites.
• FPMC-1-β achieved a record SF₆/N₂ selectivity of 178.6, surpassing all previously reported porous molecular crystals.
• Strong F⋯Br halogen bonding interactions between SF₆ and the material were identified as the key to high selectivity.

Conclusions:

• FPMC-1-β represents a significant advancement in porous materials design, leveraging halogen bonding for exceptional gas selectivity.
• The material demonstrates potential for highly efficient SF₆ capture and separation, addressing critical environmental concerns.
• The study highlights the potential of halogen bonding in creating functional porous materials for targeted molecular recognition and separation.