Selected Tricyclic Fused Systems: Host Behavior in the Presence of Mixed Xylenes and Ethylbenzene

Abstract

Two tricyclic fused host systems, namely, N,N′-bis(5-phenyl-5-dibenzo[a,d]cycloheptenyl)ethylenediamine H1 and N,N′-bis(5-phenyl-10,11-dihydro-5-dibenzo[a,d]cycloheptenyl)ethylenediamine H2, were investigated for their selectivity behavior in xylene isomer (o-Xy, m-Xy, p-Xy) and ethylbenzene (EB) mixtures. H1 only formed a complex with p-Xy, and H2 only with o-Xy, in single solvent recrystallization experiments. When H1 and H2 were recrystallized from equimolar mixtures of every combination of the four organic solvents, contrasting host selectivities were observed: H1 favored p-Xy and H2 favored o-Xy. High selectivities for p-Xy (87.2–88.7%) were noted in equimolar binary experiments with H1, while H2 furnished crystals with 91.3% o-Xy from an o-Xy/p-Xy mixture. Remarkably, only the apohost was recovered when p-Xy or o-Xy (for H1 or H2) was absent from the mixtures. Constructed selectivity profiles affirmed observations from these equimolar experiments. Thermal analyses demonstrated that H1·p-Xy was significantly less stable than H2·o-Xy, and SCXRD analyses explained these observations: p-Xy, in its complex with H1, was accommodated in wide open channels and did not experience any noncovalent interactions with the host molecule; on the other hand, o-Xy in H2 was bound tightly in near-discrete cages and, furthermore, interacted with H2. Both host compounds demonstrated the ability to separate various of the mixtures reported in this work.