Programming Heterofunctional Active Sites via In Situ Reticular Editing of Metal-Macrocyclic Frameworks

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Chemical Engineering

Background:

• Traditional metal-organic frameworks (MOFs) rely on pre-functionalized ligands, limiting cooperative binding site construction due to synthetic complexity and steric hindrance.
• Developing MOFs with tailored pore environments for specific applications like gas capture remains a significant challenge.

Purpose of the Study:

• To design and synthesize novel tertiary amine-embedded cyclen-based ligands for constructing metal-macrocyclic frameworks (MMCFs).
• To demonstrate the utility of a new strategy, in situ reticular editing (ISRE), for creating cooperative binding sites within the MOF matrix.
• To evaluate the SO2 sorption performance of the synthesized MMCFs and elucidate the underlying mechanisms.

Main Methods:

• Synthesis of tetratopic and T-shaped tritopic cyclen-based ligands.
• Construction of three isostructural, highly porous Zr-MMCFs (MMCF-5, MMCF-7-AcOH, MMCF-7-AA).
• SO2 sorption measurements, X-ray crystallography, density functional theory (DFT) calculations, and in situ DRIFT spectroscopy.

Main Results:

• The tritopic ligand facilitated the framework as a reactive matrix via ISRE.
• MMCF-7-AA demonstrated exceptional SO2 capture capacity (12.5 mmol g-1 at 1 bar) and performance at low partial pressures.
• Structural and computational analyses confirmed the formation of cooperative binding sites responsible for the enhanced SO2 sorption.

Conclusions:

• The ISRE strategy provides a versatile blueprint for pore editing in MOFs, enabling the creation of sophisticated chemical environments.
• The developed Zr-MMCFs exhibit superior SO2 capture capabilities, positioning them as advanced adsorbents for gas separation and purification.
• This work highlights the potential of using simple precursor scaffolds as reactive matrices for designing functional porous materials.