Topology-guided functional multiplicity of iron(iii)-based metal-organic frameworks

We report here the synthesis and characterization of a new series of mixed-linker iron(iii)-based metal-organic frameworks (MOFs) consisting of dicarboxylate linkers (1,4-benzenedicarboxylic acid ≡ BDC or its amino functionalized derivative) and tricarboxylate linkers (4,4′,4′′-[1,3,5-triazine-2,4,6-triyl]tribenzoic acid ≡ TATB or its nitro functionalized derivative). The resulting mesoporous MOFs with MIL-143 topology are stable under ambient water conditions for 14 d regardless of the functionalization of the organic linkers. Powder X-ray diffraction results reveal high crystallinity of the materials. This structure type is very tolerant to variation in the functional groups (e.g. nitro and/or amino) along the BDC and/or TATB linkers, but is less tolerant to changes in the size of the linkers themselves. It was attempted to replace linear BDC by biphenyl-4,4′-dicarboxylic acid (BPDC) and trigonal TATB by 2,4-bis(4′-carboxy-biphenyl-4-yl)-6-(4′-carboxy-2-methoxy-biphenyl-4-yl)-1,3,5-triazine (TAPB). Of the three additional structures made possible by combinations of these linkers (BDC/TAPB, BPDC/TATB, BPDC/TAPB), only one (BDC/TAPB) yields a crystalline product which, like the BDC/TATB crystal, exhibits MIL-143 topology. However, this material is not very stable and collapses upon guest removal. Our results suggest that the incorporation of diverse functional groups on linkers with different geometries in this new iron(iii)-based MOF series offers a simple method of precisely tuning the chemical environment within the pores. More importantly, our work expands the scope of mixed-linker MOFs to include a subset of multivariate MOFs characterized by different functionalities in each type of linker.