Comparing the host behaviour of roof-shaped compounds trans-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylic acid and its dimethyl ester in the presence of mixtures of xylene and ethylbenzene guests

Here we compare the host behaviour of two roof-shaped compounds, trans-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylic acid H1 and its dimethyl ester, trans-dimethyl 9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylate H4, when presented with mixed xylene (o-Xy, m-Xy and p-Xy) and ethylbenzene (EB) guest solutions. Both host compounds formed complexes with all of these solvents, except H4/EB, where no inclusion occurred. When H1 was recrystallized from the various equimolar combinations of these guests, enhanced selectivities were observed for p-Xy. In fact, equimolar binary mixtures of o-Xy/p-Xy and m-Xy/p-Xy afforded complexes that showed near-complete host selectivity for p-Xy (96.6 and 93.6%, respectively). The selectivity displayed by H4 in analogous experimental conditions, however, was only ordinary at best. The complexes of H1 and H4 with p-Xy were explored in-depth by means of single crystal diffraction analyses. Owing to the scarcity in the number and type of host⋯guest interactions, both complexes may be defined as approaching that of true clathrates. Finally, data from thermoanalytical experiments concurred with the selectivity behaviour of both host compounds.