Fig. 1. Mechanistic illustrations for the efficient separation of xylene isomers.
(A and B) Schematic representation of contrast enhancement strategy used to amplify the difference of ΔEtot between typical (A) rigid and (B) flexible frameworks, where ΔEint is the interaction energy between guest and framework, ΔEdef is the framework deformation energy, and ΔEtot is the total adsorption energy. These schematics illustrate an idealized and qualitative description of the contrast enhancement mechanism, rather than quantitative calculated energy values. (C) Illustration of shape matching between xylene isomers and the transformed channel of Ni(BIC)2. Variations in shape matching between isomers and channels lead to corresponding differences in interaction energy, ultimately resulting in distinct adsorption behaviors. PX shows the best shape fitness and readily enters the pore, whereas poorly matched isomers show limited accessibility, hindered by the deformation energy barrier.