Nitrogen-Rich Mn-Based Metal-Organic Frameworks for Small Molecule Adsorption and Activation through Polarization

To address the far-reaching consequences of radioiodine contamination and CO₂ emissions, heteroatom engineering in materials has emerged as a promising strategy. In this study, three thermally and chemically stable Mn-based metal-organic frameworks (MOFs), 1-3, are synthesized using (i) a dicarboxylate ligand with an oxadiazole core, and (ii) nitrogen-rich ligands with varying spacers between the bis(tridentate) ends. The incorporation of a heterocyclic core and nitrogen atoms enhances polarity, while Lewis acidity of Mn²⁺ ion strengthens small molecule interactions. The strong iodine uptake, both in vapor (2.9-2.2 g g^-1) and aqueous phases (1.82-1.34 g g^-1), underscores their effectiveness in radioactive iodine remediation. Notably, these selectively capture iodide ions even in the presence of competing anions. The polar nature of 1-3 is also evidenced by CO₂ [isosteric heat of adsorption (Q_st): 30 kJ mol^-1] and H₂O (uptake range: 7.77-11.48 mmol g^-1) sorption studies. Exploiting their Lewis acidity and polar sites, 1-3 efficiently catalyze a solvent-free CO₂ fixation reaction with epoxide and aniline, yielding oxazolidinones with high conversions and turnover numbers. The configurational biased Monte Carlo (CBMC) simulations confirm interactions of 1-3 with ionic iodine and reactants of catalysis. These MOFs demonstrate excellent reusability, maintaining structural integrity without any metal leaching.