Robust {Cd2Zn}n–Organic Framework for Efficiently Catalyzing CO2 Cycloaddition and Knoevenagel Condensation

Generally, mixed-metal-based metal–organic frameworks (MOFs) own a broader application prospect such as gas adsorption, catalysis, and energy conversion because of their better physicochemical properties, which inspire us to develop new heterometallic materials by using designed multifunctional organic ligands. Herein, a highly robust CdZn–organic framework of {(Me2NH2)5[Cd2Zn(CPPDA)2(H2O)2]·5DMF·4H2O}n (NUC-86) was obtained by using the organic ligand of 4,4′-(4-(4-carboxyphenyl)pyridine-2,6-diyl)diisophthalic acid (H5CPPDA), which contains five carboxyl groups with three kinds of coordination modes of μ1-η1:η1 and μ1-η1:η0 to coordinate Cd2+ and Zn2+ ions. In NUC-86, Cd2+ ions are bridged by CPPDA5– to form a two-dimensional (2D) layer of [Cd2(CPPDA)]n with double-stranded left-handed chains of [Cd2(COO)3(H2O)]n as secondary building units (SBUs). Furthermore, 2D layers are propagated into a three-dimensional host framework of [Cd2Zn(CPPDA)(H2O)]n via [Zn(COO)4] units. As a result, there are rich Lewis acid–base sites such as Cd2+, Npyridine, and oxygen atoms on the inner surface of void volume, and activated NUC-86a has a moderate adsorption capacity for CO2 and displays a high heterogeneous catalytic performance on the cycloaddition of CO2 with epoxides and Knoevenagel condensation of aldehydes and malononitrile under mild conditions. Therefore, this work provides a new perspective for the more practical structural design of heterometallic MOFs, which can be potentially applied in wider fields such as heterogeneous catalysis, gas adsorption–separation–storage, proton conduction, fluorescence sensing, and so on.