Guest-dependent solid-state superstructure plasticity and its application to adsorptive benzene sieving.

Conformational plasticity offers a powerful route to adaptive molecular materials, yet its translation into guest-dependent superstructures with controllable function remains rare in the case of synthetic macrocycles. Here we show that two conformationally adaptive macrocycles, MeC3 and MeC4, provide a well-defined macrocyclic platform for investigating guest-dependent conformational plasticity in the solid-state. Specifically, supramolecular co-assembly of MeC3 with molecular guests that differ in geometry, polarity and electronic character affords a diverse set of guest-dependent macrocyclic polymorphs and higher-order solid-state host-guest superstructures. Combined spectroscopic, computational, and crystallographic analyses correlate guest identity with the stabilization of distinct macrocyclic conformations that then propagate into divergent packing modes and superstructures. As a presumed consequence of the adaptive solid-state behavior, MeC3 crystals selectively sieve benzene vapor from benzene/cyclohexane mixtures with >95% selectivity. The MeC3 sieve material can be readily regenerated through a reversible guest-loaded to guest-free crystal-to-crystal transformation. In contrast to MeC3, MeC4 proved effective as a solid-state receptor for fullerenes C60 and C70. This work highlights solid-state conformational plasticity as a promising design principle for the creation of functional solids with emergent recognition, assembly, and separation properties.