Carbon dioxide reduction catalyzed by a photoactive bimetallic zirconium/cerium metal–organic framework built with a (thieno)thiophene linker

The development of efficient and stable photocatalysts for CO₂ reduction remains a major challenge in solar fuel production. Herein, we report the synthesis and characterization of the novel bimetallic zirconium/cerium metal-organic framework [Zr_5.96Ce_0.04O₄(OH)₈(H₂O)₄(TTp)₄] [H₂TTp = (thieno)thiophene-2,5-dicarboxylic acid, Zr/Ce_TTp] used for CO₂ reduction under UV-visible light irradiation. Crystal structure characterization confirms the formation of a mixed-metal framework of fcu topology with uniform element distribution. The material is porous (BET SSA = 1054 m² g^-1) and shows a good thermodynamic affinity for CO₂ [Q _st = 23.0 kJ mol^-1]. Optical and electrochemical characterization studies reveal enhanced light-harvesting ability and superior charge separation properties compared to the monometallic analogues Zr_TTp and Ce_TTp. Under simulated solar irradiation, Zr/Ce_TTp displays significant photocatalytic activity for CO₂ reduction to CO (5.8 µmol g^-1 h^-1) with no need of auxiliary co-catalysts, while no activity is observed for the individual metal-based materials. The improved performance is attributed to the synergistic interaction between the redox-active Ce centers and the robust Zr nodes, as well as the light-absorbing capability of the H₂TTp linker. Periodic DFT calculations support the experimental findings, highlighting the role of open Ce^III sites in CO₂ activation and the improved spatial separation of the frontier orbitals in the bimetallic framework that reduces e-h⁺ recombination with respect to its homometallic analogues. These results highlight the potential of heterometallic MOFs featuring π-conjugated heterocyclic linkers as promising platforms for solar-driven CO₂ valorization.