Nanocage-based {SnEr2}-organic framework for high catalytic performance in cycloaddition of CO2 with epoxides and Knoevenagel condensation

Abstract

The integration of abundant active sites and robust chemical stability in metal–organic frameworks (MOFs) is pivotal for advancing their industrial-scale utilization. This study proposes a novel strategy to construct cluster-based heterometallic MOFs by incorporating rare-earth ions. Through a solvothermal synthesis approach, we successfully engineered {[SnEr₂(HBDCP)(H₂O)]_n·3DFM·5H₂O}_n (TYUT-13), a three-dimensional framework integrating Sn²⁺ (stannous(II) ions), Er³⁺ (erbium(III) ions) and designed flexible tetracarboxylic acid of 2,6-bis(2,4-dicarboxylphenyl)-4-(4-carboxylphenyl)pyridine (H₅BDCP). This architecture features a unique pore environment characterized by high porosity and dual-functional active sites (Lewis acidic Sn/Er centers and basic pyridinic N atoms), which synergistically enhance catalytic performance. Experimental results demonstrate that TYUT-13a exhibits exceptional activity in the solvent-free cycloaddition of CO₂ to epoxides under mild conditions (65 °C, 1 atm CO₂, 4 h), achieving >98% conversion efficiency. Furthermore, it displays broad applicability in Knoevenagel condensations between phenoxyacetaldehyde and malononitrile, with yields exceeding 97%. These findings highlight the effectiveness of rare-earth ion hybridization in balancing structural integrity and catalytic multifunctionality, offering a blueprint for designing next-generation MOF catalysts for sustainable chemical processes.