Xylene Recognition in Flexible Porous Coordination Polymer by Guest-Dependent Structural Transition

Xylene isomers are crucial chemical
intermediates in great demand
worldwide; the almost identical physicochemical properties render
their current separation approach energy consuming. In this study,
we utilized the soft porous coordination polymer (PCP)’s isomer-specific
structural transformation, realizing o-xylene (oX)
recognition/separation from the binary and ternary isomer mixtures.
This PCP has a flexible structure that contains flexible aromatic
pendant groups, which both work as recognition sites and induce structural
flexibility of the global framework. The PCP exhibits guest-triggered
“breathing”-type structural changes, which are accompanied
by the rearrangement of the intraframework π–π
interaction. By rebuilding π–π stacking with isomer
species, the PCP discriminated oX from the other isomers by its specific
guest-loading configuration and separated oX from the isomer mixture
via selective adsorption. The xylene-selective property of the PCP
is dependent on the solvent; in diluted hexane solution, the PCP favors p-xylene (pX) uptake. The separation results combined with
crystallographic analyses revealed the effect of the isomer selectivity
of the PCP on xylene isomer separation via structural transition and
demonstrated its potential as a versatile selective adsorptive medium
for challenging separations.