A Tb-[Cu4I4] Heterometallic MOF for CO2 Fixation into Cyclic Carbonates

Converting CO2 into value-added carbonates is an important strategy for using an abundant C1 feedstock. However, developing noble-metal-free heterogeneous catalysts capable of simultaneously driving multiple CO2 fixation pathways under mild conditions remains a significant challenge. Here we report a heterometallic metal-organic framework, [Tb2(DMF)2(Cu4I4)(NIC)6] (Tb-Cu4I4), that combines hard Lewis acidic Tb-O nodes with soft Lewis acidic [Cu4I4] clusters. The crystalline framework is thermally stable to 350 °C and retains its structure after immersion in common organic solvents. Enabled by this dual-active-site architecture, the catalyst promotes the cycloaddition of epoxides with CO2 at 60 °C and the carboxylative cyclization of propargylic alcohols with CO2 at room temperature and under atmospheric pressure. Both reactions show good substrate tolerance and sustained activity over seven cycles. Time-dependent 1H NMR and FTIR monitoring confirm the formation of both carbonate products, while control experiments show that the intact Tb-Cu4I4 and the corresponding cocatalysts are required for efficient conversion. These results establish 3d-4f heterometallic MOFs as tunable platforms for integrating complementary CO2-fixation pathways.