A stable 3D Sr-MOF as an efficient heterogeneous catalyst for the cycloadditions of CO2 and knoevenagel condensation reactions

The catalytic activity of MOF is determined not only by its unique structure but also by the active sites from metal sites and functional ligands. A sTable 3D strontium complex, {[Sr2(BTCB)Cl(H2O)2]}n (Sr-BTCB), was synthesized under solvothermal condition. It is assembled with an amide-functionalized tricarboxylic acid and a Sr(II)-based infinite chain, where Sr2 repeating units are arranged sequentially. Two such 3D structures are interwoven to create a two-folded interpenetrated structure. The interpenetrated structure is strengthened by π-π interstacking between the central phenyl rings of ligands from different 3D structures. After solvent exchange and vacuum drying, the surface of nanochannels in desolvated Sr-BTCB is modified by unsaturated Sr2+ions. Complex Sr-BTCB has abundant Lewis acidic metal sites and Lewis basic sites of amide groups, as well as 1D rhombic channels. It exhibits excellent stability and heterogeneous catalysis on CO2 fixation reactions into cyclic carbonates and Knoevenagel condensation reactions of aldehydes and malononitrile.