<i>trans</i>-9,10-Dihydro-9,10-ethanoanthracene-11,12-dicarboxylic Acid: Complete Host Selectivity for Guest Compound <i>para</i>-Dichlorobenzene during Crystal Growth from Mixed Isomeric Dichlorobenzenes
Benita Barton, Mino R. Caira, Ulrich Senekal, Eric C. Hosten
Abstract
Here, we report on the results obtained when trans-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylic acid (DED) crystals were grown from mixtures containing equimolar isomeric o-, m-, and p-dichlorobenzenes (o-DCB, m-DCB, and p-DCB). DED displayed a remarkable affinity for p-DCB in both binary and ternary recrystallization experiments involving this guest species, and near-quantitative amounts of p-DCB were measured in the resultant crystals (96.4–100.0%). The host selectivity was in the order p-DCB >>> m-DCB > o-DCB. This enhanced selectivity for p-DCB was also evident in binary mixtures in which molar quantities of the guests were varied: when employing 39/61% p-/o-DCB and p-/m-DCB, the recovered crystals contained as much as 83 and 98% p-DCB, respectively. At higher concentrations of p-DCB, DED then selected only this guest compound. Single-crystal X-ray diffraction experiments revealed that while host···guest interactions did not appear to be an important factor that guided the host selectivity behavior, the type of guest accommodation did indeed, and the preferred guest, p-DCB, was tightly held in highly constricted channels, while some of the other two isomers were retained in wide, open channels. Thermal analysis experiments confirmed this observation, and complexes in which some of the guests occupied wide, open channels possessed lower thermal stabilities compared with the p-DCB-containing complex, where the channels were significantly more constricted.