Catalytic Investigation of CO2 Chemical Fixation and the Knoevenagel Condensation Reaction for a TmIII-Organic Framework

The delicate combination of wave-like [Tm-2(CO2)(6)(OH2)(2)](n), chains and [Tm-2(CO2)(4)(NO3)(OH2)] units with the aid of 2,6-bis(2,4-dicarboxylphenyl)-4-(4-carboxylphenyl)pyridine (H5BDCP) generates one highly robust dual-channel material of {[(CH3)(2)NH2](2)[Tm-3(BDCP)(2)(NO3)(OH2)(3)]center dot 4DMF center dot 2H(2)O}(n) (NUC-28) with excellent physicochemical properties including solvent-free dual channels, a bigger specific surface area, high porosity, water tolerance, and thermal stability. As far as we know, NUC-28 is one scarcely reported nitrate-functionalized microporous metal-organic framework (MOF) with N=O groups as Lewis base sites protruding on the inner surface of the channels. Thanks to the coexistence of Lewis acid-base sites including rich hexa-/hepta-coordinated Tm3+ ions, N=O and C=O groups from mu(1)-eta(1):eta(1) NO3- and CO2-, and N-pyridine atoms, NUC-28 displays high catalytic activity in the cycloaddition reaction of epoxides and CO2 into related cyclic carbonates under mild, solvent-free reaction conditions. In addition, Knoevenagel condensation reactions with aldehydes and malononitrile as substrates could be greatly accelerated in the presence of NUC-28. Hence, these catalytic results confirm that the introduction of Lewis base sites of NO3- anions on open metal sites in MOFs could effectively enhance its catalytic efficiency, which should be attributed to the recognized synergistic effect of Lewis base-acid active sites.