Investigation on the catalytic behavior of a novel thulium-organic framework with a planar tetranuclear {Tm 4 } cluster as the active center for chemical CO 2 fixation.

Herein, the exquisite combination of coplanar [Tm 4 (CO 2 ) 10 (μ 3 -OH) 2 (μ 2 -HCO 2 )(OH 2 ) 2 ] clusters ({Tm 4 }) and structure-oriented functional BDCP 5- leads to the highly robust nanoporous {Tm 4 }-organic framework {(Me 2 NH 2 )[Tm 4 (BDCP) 2 (μ 3 -OH) 2 (μ 2 -HCO 2 )(H 2 O) 2 ]·7DMF·5H 2 O} n (NUC-37, H 5 BDCP = 2,6-bis(2,4-dicarboxylphenyl)-4-(4-carboxylphenyl)pyridine). To the best of our knowledge, NUC-37 is the first anionic {Ln 4 }-based three-dimensional framework with embedded hierarchical microporous and nanoporous channels, among which each larger one is shaped by six rows of coplanar {Tm 4 } clusters and characterized by plentiful coexisting Lewis acid-base sites on the inner wall including open Tm III sites, N pyridine atoms, μ 3 -OH and μ 2 -HCO 2 . Catalytic experimental studies exhibit that NUC-37 possesses highly selective catalytic activity on the cycloaddition of epoxides with CO 2 as well as high recyclability under gentle conditions, which should be ascribed to its nanoscale channels, rich bifunctional active sites, and stable physicochemical properties. This work offers an effective means for synthesizing productive cluster-based Ln-MOF catalysts by employing structure-oriented ligands and controlling the solvothermal reaction conditions.