trans-α,α,α′,α′-Tetraphenyl-9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanol and its tetra(p-chlorophenyl) derivative: roof-shaped host compounds for the purification of aromatic C8H10 isomeric guest mixtures

Roof-shaped host compounds trans-α,α,α′,α′-tetraphenyl-9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanol H3 and trans-α,α,α′,α′-tetra(p-chlorophenyl)-9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanol H6 were assessed for their host potential and selectivity behaviour when presented with single or mixed guest solvents comprising o-xylene, m-xylene, p-xylene and ethylbenzene (o-Xy, m-Xy, p-Xy and EB). H3 included each solvent with 3:1 host:guest ratios, while the ratios preferred by H6 were more varied (4:3, 1:1 and 3:2). More importantly, the selectivity behaviour of these two host compounds was observed to be entirely different: H3 possessed only a very modest preference for o-Xy (37.9–68.2%) when recrystallized from various equimolar binary, ternary and quaternary guest mixtures, while H6 was considerably more selective, preferring m-Xy (the least favoured guest of H3) with selectivities ranging from 57.7 to 91.4% in analogous conditions. The latter result was obtained in o-Xy/m-Xy mixtures and demonstrates that H6 may be employed as a purification tool for mixtures of these two xylenes via host–guest chemistry protocols. A single crystal diffraction experiment on 3(H3)·o-Xy (containing the preferred guest of H3) revealed that the guest was retained in the host crystal by means of a singular (host)m-Ar–H···π(guest) interaction that measured 2.73 A (148°) as well as numerous other host···guest interactions involving only the aromatic protons of the free host phenyl groups and the guest methyl protons or aromatic carbons and protons (2.20–2.54 A, 121–125°). Thermal analyses explained the preference of H3 for o-Xy, while these were less informative for the complexes of H6.