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

In metal-organic frameworks, the scaffold serves as a passive host matrix, relying primarily on the assembly of prefunctionalized ligands to define the pore environment. Constructing cooperative binding pockets via this approach is often impeded by synthetic complexity and the steric hindrance of bulky functional groups. Herein, we present the design of two robust, tertiary amine-embedded cyclen-based ligands: one tetratopic and the other T-shaped tritopic. The two ligands were used to synthesize three isostructural, highly porous Zr-metal-macrocyclic frameworks (MMCFs), denoted as MMCF-5, MMCF-7-AcOH, and MMCF-7-AA. We highlight that the tritopic ligand enabled the framework as a reactive matrix through a strategy termed in situ reticular editing (ISRE). Utilizing SO₂ as a probe to interrogate the pore environment, MMCF-7-AA exhibits an exceptional capacity of 12.5 mmol g^-1 at 1 bar and 1.43 mmol g^-1 at 2500 ppm. These metrics not only position it among the top-performing adsorbents at low partial pressures but, more importantly, corroborate the successful construction of the cooperative binding sites. We then elucidated this distinct SO₂ sorption behavior through X-ray crystallography, density functional theory (DFT) calculations, and in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. This work establishes ISRE as a versatile blueprint for pore editing, offering a feasible pathway to evolve sophisticated chemical environments by harnessing simple precursor scaffolds as reactive matrices.