Ultrahigh stable heterometallic InCo-organic framework for efficiently catalyzing cycloaddition of CO2 with epoxides and Knoevenagel condensation

Due to versatile applications and fascinating topologies of heterometallic MOFs, developing new functional frameworks is of great significance and a great challenge. Inspired by this, we target to assemble rarely reported d-p heterometallic MOFs by using 4,4′-(4-(4-carboxyphenyl)pyridine-2,6-diyl)diisophthalic acid (H5CPPDA) as the organic linker, whose N and O donors have different affinities to d and p ions according to the soft-hard theory. Herein, a highly robust nanochannel-based InCo-organic framework of [InCo(CPPDA)(H2O)]·4DMF·6H2O}n (NUC-85) was successfully achieved under the acidic solvothermal condition. In the host framework of NUC-85, the ligand of CPPDA5− utilizes its five deprotonated carboxyl groups with three kinds of coordination modes (μ1-η1:η1, μ2-η1:η1 and μ3-η2:η1) as well as pyridine to combine In3+ and Co2+ ions into scarcely reported one-dimensional chains of [InCo(COO)5(H2O)]n, six of which are further arranged into hexagonal nano-channels (aperature ca. 14.5Å). After thermal activation, the inner surface of channels in NUC-85a is functionalized by open metal sites of octa-coordinated In3+ and penta-coordinated Co2+ ions. Performed experiments prove that NUC-85a is an excellent heterogeneous catalyst for the cycloaddition of CO2 with epoxides under the mild conditions. Moreover, the Knoevenagel condensation with benzaldehyde and malononitrile as substrates can be efficiently catalyzed by NUC-85a. In the above two kinds of organic reactions, NUC-85a displays the satisfied chemical stability, high selectivity and multiple repeatability. This research demonstrates that nanostructure-based heterometallic MOFs have a bright future as a catalyst for Lewis acid/base supported organic reactions because of their congenital advantages such as sufficient active sites, high stability and convenient recyclability.