MOF Structure Changing the Reactivity of its Components
Constanze N. Neumann, Max-Planck-Institut für Kohlenforschung, Mülheim an der Ruhr, Germany
Metal-organic frameworks are often extolled for their virtually infinite tunability, but for many MOFs, even small modifications to the structure of the linker can lead to the formation of a different phase or amorphous material. We set out to make use of the robustness of ZrIV-carboxylate MOFs to explore the post-synthetic installation of functional handles on the MOF linker. Beyond its practical utility in facilitating access to stable MOFs carrying functionalized linkers, we were particularly interested in the effect of the confined three-dimensional environment on the selectivity of linker functionalization. The ability to control the installation of functional groups within confined 3D environments would permit chemists to create catalysts featuring tailored microenvironments resembling those of enzymes. We argued that within a complex environment, such as that making up the pore space of a MOF, the existing structural complexity could template environment-selective installation of functional handles. When we subject a MOF that features three distinct pore environments to bromination, we find that carbon-bromine bonds can be selectively installed in linker molecules residing in only one of the three pores through a suitable choice of brominating reagent and solvent. In addition to this “pore selectivity”, we also find that for certain combinations of brominating reagent and solvent, the regioselectivity with which the linker in the MOF is brominated differs from that which is observed for a soluble analogue of the linker.