Host compounds based on the rigid 9,10-dihydro-9,10-ethanoanthracene framework: selectivity behaviour in mixed isomeric dichlorobenzenes

Abstract

The behaviour of host compounds dimethyl trans-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylate (H1), trans-α,α,α′,α′-tetraphenyl-9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanol (H2) and trans-α,α,α′,α′-tetra(p-chlorophenyl)-9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanol (H3), based on the rigid 9,10-dihydro-9,10-ethanoanthracene framework, was investigated in the presence of singular dichlorobenzene (o-DCB, m-DCB and p-DCB) guest isomers as well as various mixtures of these in order to determine whether these guest compounds may be separated/purified by means of host–guest chemistry strategies. H1 failed to complex with these DCBs and so was disregarded for any further investigations, while H2 enclathrated each one; H3, on the other hand, only formed complexes with o-DCB and m-DCB. When presented with mixtures of the DCBs, H2 demonstrated a marginal affinity for o-DCB in most cases, and H3, complementarily, m-DCB. Remarkably, it was revealed that H3 has the ability to separate binary guest DCB mixtures with 17.2% m-DCB/82.8% p-DCB and 49.5% m-DCB/50.5% p-DCB (in favour of m-DCB, K = 24.0 and 14.0, respectively). This result is significant given that m-DCB/p-DCB mixtures, in particular, are extremely arduous to separate in the chemical industry by means of the more conventional distillation/crystallization methods. Of the five novel complexes produced in this work, three were subjected to SCXRD analyses (the remaining two complexes were powders): H2 retained the o-DCB and m-DCB guests in the complex through (host)C–H⋯π(guest), (host)C–H⋯C–Cl(guest) and (guest)C–H⋯C–C(host) contacts (in 3(H2)·m-DCB were also observed additional (host)C–H⋯Cl(guest) interactions). In H3·m-DCB, only one host⋯guest interaction could be identified, namely a (guest)C–Cl⋯π(host) contact measuring 3.864(2) Å (134.2(1)°): this complex therefore approaches that of a true clathrate. Finally, thermoanalytical experiments explained the marginal affinity of H2 for o-DCM (this complex possessed the greater thermal stability of the three inclusion compounds), while this technique was less informative with respect to understanding the preference of H3 for the meta isomer.