Abstract
Designing nanoporous lanthanide-based metal-organic frameworks (MOFs) as robust heterogeneous catalysts has received a lot of interest in recent years. Herein, we successfully constructed a novel isomorphic nanoporous MOF {[Ho(2)(TDP) (H(2)O)(2)]·5H(2)O·4DMF} (n) (named as NUC-55, NUC = North University of China) by combining [Ho(2)(CO(2))(7)(H(2)O)(2)] (abbreviated as {Ho(2)}) clusters with 2,4,6-tri(2,4-dicarboxyphenyl)pyridine (H(6)TDP) as structure-oriented multifunctional ligands under acidic solvothermal conditions. NUC-55 is a holmium(iii)-based 3D MOF with a hierarchical porous architecture containing tetragonal microchannels (0.56 nm in diameter) and octagonal nanochannels (1.79 nm in diameter), In NUC-55, plenty of Lewis acidic and basic sites, including open Ho(3+) sites and N(pyridine) atoms, coexist. Moreover, it is worth mentioning that the void volume (∼65%) is significantly higher in NUC-55 than in most documented 3D lanthanide-based MOFs (Ln-MOFs). Catalytic experiments show that activated NUC-55 exhibits high catalytic activity in the CO(2)-styrene oxide cycloaddition reactions under mild conditions, with a high turnover number of 2475 and a high turnover frequency of 619 h(-1). In addition, activated NUC-55 can remarkably accelerate the deacetalization-Knoevenagel condensation reactions of benzaldehyde dimethyl acetal and malononitrile. Taken together, this work can not only establish an effective self-assembly strategy for fabricating highly porous Ln-MOFs, but also provide new insights into their catalytic mechanism.