Many industrially relevant liquid-phase separations, such as the separation of xylenes isomers and the purification of mixtures of fluoroarenes, remain challenging due to the similar polarities and boiling points of the components. Although metal-organic frameworks have been widely studied for gas separations due to the tunability of host-guest interactions within the pores, their application for difficult liquid-phase separations remains underexplored. In particular, no general strategies have emerged for achieving these types of separations. Herein, we describe how controlling the interaction of guests with not one, but two adjacent metal centers in the M2(dobdc) (dobdc4- = 2,5-dioxidobenzene-1,4-dicarboxylate, M = Co, Mg) family of metal-organic frameworks is a potentially general strategy for partitioning mixtures of arenes. First, multicomponent liquid-phase adsorption measurements demonstrate that Co2(dobdc) is capable of partitioning the mixture of xylenes with the selectivity order o-xylene &gt; ethylbenzene &gt; m-xylene &gt; p-xylene, which single-crystal X-ray diffraction experiments confirm is due to the differing abilities of the xylene isomers to interact with two adjacent Co2+ centers. We were able to extended this strategy to an even more challenging separation, that of a mixture of o-, m-, and p-difluorobenzene, by using the Mg-based framework to maximize the strength of the M-F interactions. Single-crystal X-ray diffraction and DFT calculations confirm the selectivity order of p-difluorobenzene &gt; m-difluorobenzene &gt; o-difluorobenzene is also likely due to the bridging interactions between two adjacent Mg2+ centers. Therefore, controlling the interaction of adsorbates with multiple appropriately spaced metal centers in a metal-organic framework is likely a broadly applicable strategy for achieving liquid-phase separations.

Separations of arenes via interactions with two metal sites in metal-organic frameworks

2019 Spring National Meeting

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