Robust heterometallic {In2CdO}-Organic framework for efficiently catalyzing CO2 cycloaddition and Knoevenagel condensation

Abstract

The catalytic performance of MOFs mainly comes from the coordination defects of their metal ions. However, developing promising MOF catalysts with a large number of small coordination molecules on metal ions remains a huge challenge. Herein, we report a highly robust heterometallic {In2CdO}-organic framework of {[In2Cd(CPPDP)(µ3 − OH)(H2O)5](NO3)2⋅2DMF⋅3H2O}n (NUC-103) with scarcely reported [In2Cd(OH)(O2CR)5(H2O)5] clusters (abbreviated as {In2CdO}) as secondary building units (SBUs), each of which contains five associated water molecules, implying that activated host framework can serve as strong Lewis acid. In NUC-103, three rows of {In2CdO} are shaped into hierarchical triangle-nanochannels of 17.42 × 17.98 Å2 and triangle-microchannels of 10.15 × 11.00 Å2 along c axis. On account of the following unique characteristics such as three kinds of active sites (Lewis acid sites of In3+ and Cd2+, Lewis base sites of free Npyridine atoms and electrophilic H-bond donors (HBD) of µ3 − OH moieties), large solvent-free channels, high thermal stability, and resistance to various solvents, NUC-103a is a promising catalytic platform. Catalytic experiments prove that NUC-103a is a significant heterogeneous catalyst for the cycloaddition of CO2 with epoxides with exclusive selectivity and high conversion. In addition, NUC-103a as a bifunctional catalyst displays the high catalytic performance on the Knoevenagel condensation reactions of aldehydes and malononitrile. Therefore, this work not only provides an indium(III) + cadmium(II)-based heterometallic cluster of {In2CdO}, but also provides a valuable insight into designing metal–organic catalytic materials with high defect coordination.