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Purification of the C₈ alkylaromatics o-xylene, m-xylene, p-xylene, and ethylbenzene remains among the most challenging industrial separations, due to the similar shapes, boiling points, and polarities of these molecules. Herein, we report the evaluation of the metal–organic frameworks Co₂(dobdc) (dobdc^4– = 2,5-dioxido-1,4-benzenedicarboxylate) and Co₂(m-dobdc) (m-dobdc^4– = 4,6-dioxido-1,3-benzenedicarboxylate) for the separation of xylene isomers using single-component adsorption isotherms and multicomponent breakthrough measurements. Remarkably, Co₂(dobdc) distinguishes among all four molecules, with binding affinities that follow the trend o-xylene > ethylbenzene > m-xylene > p-xylene. Multicomponent liquid-phase adsorption measurements further demonstrate that Co₂(dobdc) maintains this selectivity over a wide range of concentrations. Structural characterization by single-crystal X-ray …