Fluorinated 2D Terbium–Organic Framework for Efficient CO2-Epoxide Cycloaddition: Structure–Function Design and DFT Insights

Abstract

Engineering cooperative catalytic microenvironments within porous solids offers a promising route to overcoming the intrinsic inertness of CO2. Herein, a fluorinated two-dimensional terbium–organic framework, NUC-170a, was developed through a structure-directed ligand design strategy, furnishing a confined catalytic architecture that integrates coordinatively unsaturated Tb3+ centers, pendent carboxylic acid groups, pyridyl functionalities, and fluorinated pore surfaces. The Tb3+ and carboxylic acid sites provide cooperative substrate-activation centers, while the fluorinated pore environment contributes primarily to local polarity modulation and CO2 enrichment. Benefiting from its accessible nanoporous channels and multifunctional active landscape, NUC-170a efficiently catalyzed the solvent-free cycloaddition of CO2 with epoxides. Under the optimized conditions, epichlorohydrin afforded the corresponding cyclic carbonate in 98.1% yield with >99% selectivity, while a series of terminal epoxides gave the corresponding products in 82.5%–99.7% yields. Moreover, the catalyst could be reused for six consecutive cycles without an appreciable loss of activity. Notably, the catalyst remains highly effective under simulated flue-gas conditions, underscoring its potential for practical carbon-utilization applications. Density functional theory calculations reveal a cooperative activation mechanism in which carboxylic acid sites facilitate epoxide ring opening and CO2 insertion, while Lewis acidic Tb3+ centers preferentially stabilize the rate-determining ring-closing transition state. This work demonstrates how deliberate microenvironment engineering in low-dimensional metal–organic frameworks can unlock highly efficient CO2 conversion pathways and advance the development of next-generation porous catalysts for sustainable carbon fixation.