Exploring the Effect of Different Secondary Building Units as Lewis Acid Sites in MOF Materials for the CO 2 Cycloaddition Reaction.

In order to explore the catalytic effect of different Lewis acid sites (LASs) in the CO 2 cycloaddition reaction, different secondary building units and N-rich organic ligand 4,4',4″- s -triazine-1,3,5-triyltri- p -aminobenzoate were assembled to construct six reported MOF materials: [Cu 3 (tatab) 2 (H 2 O) 3 ]·8DMF·9H 2 O ( 1 ), [Cu 3 (tatab) 2 (H 2 O) 3 ]·7.5H 2 O ( 2 ), [Zn 4 O(tatab) 2 ]·3H 2 O·17DMF ( 3 ), [In 3 O(tatab) 2 (H 2 O) 3 ](NO 3 )·15DMA ( 4 ), [Zr 6 O 4 (OH) 7 (tatab)(Htatab) 3 (H 2 O) 3 ]· x Guest ( 5 ), and [Zr 6 O 4 (OH) 4 (tatab) 4 (H 2 O) 3 ]· x Guest ( 6 ) (DMF = N , N -dimethylformamide, and DMA = N , N -dimethylacetamide). Large pore sizes of compound 2 enhance the concentration of substrates, and the multi-active sites inside its framework synergistically promote the process of the CO 2 cycloaddition reaction. Such advantages endow compound 2 with the best catalytic performance among the six compounds and surpass many of the reported MOF-based catalysts. Meanwhile, the comparison of the catalytic efficiency indicated that Cu-paddlewheel and Zn 4 O display better catalytic performances than In 3 O and Zr 6 cluster. The experiments investigate the catalytic effects of LAS types and prove that it is feasible to improve CO 2 fixation property by introducing multi-active sites into MOFs.