Chemically Multifunctional Covalent 2D Crown Ether Framework

We report the gram-scale preparation and characterization of a new two-dimensional crystalline material, denoted C2O, composed primarily of carbon and oxygen in a 2:1 molar ratio. Its covalent framework contains regularly distributed crown ether cavities and shows excellent chemical resistance under acidic, basic, and various organic-solvent conditions. The rigid crown ether sites strongly coordinate K⁺ ions, thereby activating KI and increasing the nucleophilicity of I⁻. As a result, C2O markedly enhances the KI-catalyzed cycloaddition of CO₂ to epoxides. In the presence of C2O, the CO₂ conversion of epichlorohydrin increases from 5.7% to 99.9%, while that of allyl glycidyl ether rises from 2.9% to 74.2%.

In addition to its catalytic function, C2O contains both electrophilic and nucleophilic reactive sites along the framework edges, enabling post-synthetic modification and control of its physicochemical properties. Reaction with allyl glycidyl ether as an electrophile produces C2O-AGE, whereas modification with ethoxyethylamine as a nucleophile yields C2O-EEA. These functionalized materials exhibit further improved catalytic performance for CO₂ fixation with allyl glycidyl ether, achieving conversions of 97.2% and 99.9%, respectively, compared with 74.2% for pristine C2O. The combination of scalable synthesis, high chemical durability, catalytic activity, and structural tunability makes this covalent two-dimensional framework a promising platform for the development of multifunctional materials for diverse applications.