Nanocage-based {In2Tm2}-organic framework for efficiently catalyzing the cycloaddition reaction of CO2 with epoxides and Knoevenagel condensation

Abstract

High density active sites and chemical stability for prepared MOFs are the prerequisites for their industrial applications, which prompted us to synthesize cluster-based metal–organic compounds. The combination of [In₂Tm₂(μ₂-OH)₂(CO₂)₁₀(H₂O)₂] clusters ({In₂Tm₂}) and the functional ligand 2,6-bis(2,4-dicarboxylphenyl)-4-(4-carboxylphenyl)pyridine (H₅BDCP) produced an extremely stable nanoporous skeleton of {(Me₂NH₂)₂[In₂Tm₂(BDCP)₂(μ₂-OH)₂(H₂O)₂]·2DMF·3H₂O}_n (NUC-56), whose inner surface is functionalized by Lewis acidic and basic groups of metal centers, μ₂-OH groups and N_pyridine atoms. To the best of our knowledge, NUC-56 is a rarely reported planar-cluster-based {In₂Ln₂}-organic framework, which possesses an excellent confined pore environment with high porosity, large specific surface area and abundant co-existing Lewis acid and base sites. Consequently, NUC-56a exhibited a good catalytic performance for the cycloaddition reaction of various epoxides with CO₂ and the Knoevenagel condensation reaction of different aldehydes and malononitrile under mild conditions. Therefore, this study can provide some guidance for the precise design of practical MOFs with excellent catalytic, stability and regeneration performances through the participation of rare earth ions.