Construction and DFT Elucidation of a 2D Europium-Organic Framework with Integrated Porosity and Acid–Base Microenvironments for Efficient CO2 Cycloaddition

Abstract

Developing structurally defined metal–organic catalysts that integrate CO2 enrichment, substrate activation, and catalytic durability remains essential for sustainable carbon utilization. Herein, a fluorinated two-dimensional europium-organic framework of {[Eu2(HFDPY)2(DMF)4]·2DMF·2H2O}n (NUC-171, H4FDPY = 2,6-bis(2,4-dicarboxyphenyl)-4-(o-fluorophenyl)pyridine) was constructed from the tetracarboxylate ligand H4FDPY through a self-assembly strategy. Upon activation, NUC-171a exhibits an accessible microporous architecture with cavity dimensions of 9.9 × 14.8 × 16.4 Å3, a BET surface area of 575.24 m2 g–1, coordinatively accessible Eu3+ centers, pendant carboxyl functionalities, and pyridyl groups, collectively generating a confined multifunctional catalytic environment for CO2 enrichment and epoxide activation. Benefiting from these integrated structural advantages, NUC-171a enables efficient solvent-free CO2 cycloaddition with a broad range of epoxide substrates, affording a maximum isolated yield of 97.9% for the styrene oxide cycloaddition product under 1.1 MPa CO2 pressure at 85 °C. Combined kinetic analysis, thermodynamic evaluation, and density functional theory calculations reveal that the catalytic transformation proceeds through a cooperative mechanism involving Eu-mediated epoxide coordination, bromide-induced ring opening, CO2 incorporation, and subsequent intramolecular cyclization. Furthermore, NUC-171a preserves its catalytic efficiency and structural integrity during recycling experiments and remains effective under simulated dry and humid flue gas atmospheres. This work highlights ligand-directed dimensional regulation coupled with multifunctional microenvironment construction as an effective strategy for developing durable MOF catalysts toward sustainable CO2 capture and conversion.