Defect Engineering in a Nanoporous Thulium-Organic Framework in Catalyzing Knoevenagel Condensation and Chemical CO 2 Fixation.

Defect engineering is an extremely effective strategy for modifying metal-organic frameworks (MOFs), which can break through the application limitations of traditional MOFs and enhance their functionality. Herein, we report a highly robust nanoporous thulium(III)-organic framework, {[Tm 2 (BDCP)(H 2 O) 5 ](NO 3 )·3DMF·2H 2 O} n ( NUC-105 ), with [Tm(COO) 2 (H 2 O)] n chains and [Tm 2 (COO) 4 (H 2 O) 8 ] dinuclears as metal nodes and 2,6-bis(2,4-dicarboxylphenyl)-4-(4-carboxylphenyl)pyridine (BDCP) linkers. In NUC-105 , each of the four chains of [Tm(COO) 2 ] n and the two rows of [Tm 2 (COO) 4 (H 2 O) 8 ] units is unified by the organic skeleton, resulting in a rectangular nanochannel with dimensions of 15.35 Å × 11.29 Å, which leads to a void volume of 50%. It is worth mentioning that the [Tm 2 (COO) 4 (H 2 O) 8 ] cluster is very rare in terms of its higher level of associated water molecules, implying that the activated host framework can serve as a strong Lewis acid. NUC-105a exhibited great heterogeneous catalytic performance for CO 2 cycloaddition with epoxides under the reaction conditions (0.60 mol % NUC-105a , 5.0 mol % n -Bu 4 NBr, 65 °C, 5 h), ensuring exclusive selectivity and high conversion rates. In addition, NUC-105a 's strong catalytic impact on the Knoevenagel condensation of aldehydes and malononitrile can be attributed to the collaboration between the drastically unsaturated Lewis acidic Tm 3+ centers and Lewis basic pyridine groups.