Open metal site (OMS)-inspired investigation of adsorption and catalytic functions in a porous metal–organic framework (MOF)

In this article, we report the adsorption and catalytic study of the three-dimensional (3D) metal-organic framework (MOF) {Mn2(1,4-bdc)2(DMF)2} (1) (1,4-bdcH2, 1,4-benzene dicarboxylic acid; DMF, N,N-dimethylformamide) together with the synthesis and structure of two new Mn(II)-MOFs {Mn3(Br-bdc)3(DMF)4} (2) and {Mn3(NO2-bdc)3(DMF)4} (3) (Br-bdcH2, 2-bromo-1,4-benzene dicarboxylic acid; NO2-bdcH2, 2-nitro-1,4-benzene dicarboxylic acid) under solvothermal conditions. Compounds 2 and 3 have two-dimensional (2D) extended structures and feature trimeric {Mn3(CO2)6} units that serve as secondary building units for the frameworks. The desolvated compound of 1, denoted as 1', having potential Mn(II) open metal sites (OMSs) lined in a one-dimensional (1D) Mn-chain interconnected by carboxylate groups, exhibits guest-selective adsorption of solvent vapours wherein the compound shows a stepwise profile with H2O vapour, while a gated isotherm was recorded with MeOH. After realizing the favourable interaction of 1' with polar solvent molecules, we have used Mn(II) OMSs in 1' for efficient cyanosilylation reactions of aromatic aldehydes. We have recorded 100% conversion for eight aromatic aldehydes, while several other aldehydes showed appreciable conversion. Notably, the recorded conversions in the case of many substrates are higher than those for many other reported MOF catalysts.