trans-9,10-Dihydro-9,10-ethanoanthracene-11,12-dicarboxylic Acid: Complete Host Selectivity for Guest Compound para-Dichlorobenzene during Crystal Growth from Mixed Isomeric Dichlorobenzenes

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.

trans-9,10-Dihydro-9,10-ethanoanthracene-11,12-dicarboxylic Acid: Remarkable Host Selectivities in the Presence of Mixtures of Anisole and Bromoanisole Isomers

“…The strengths of these interactions were all comparable and significant, the respective O•••O distances ranging between 2.625(2) and 2.674(2) Å with associated angles between 172 and 178°. Notably, the unit cell dimensions of 2(DED)•4-BA are very similar to those of an analogous complex of DED with pdichlorobenzene from a previous report, 22 and the space groups are identical. As a result, the host molecule arrangements in the crystals of 2(DED)•4-BA and the 2:1 complex containing pdichlorobenzene are thus isostructural.…”

“…As examples, Nassimbeni et al employed a binaphthyl-derived host compound in order to separate the lutidine isomers, while Barbour and co-workers achieved xylene isomer separations with a Werner complex . In our own laboratories, we have also focused on these separation challenges and considered a wide variety of isomers, including the methylpyridines, xylenes and ethylbenzene, dichlorobenzenes, and anilines (as examples), by making use of host compounds synthesized from xanthone, thioxanthone, anthracene, and tartaric acid. − …”

“…trans -9,10-Dihydro-9,10-ethanoanthracene-11,12-dicarboxylic acid ( DED , Scheme ) is a roof-shaped host compound that was first reported by Weber et al in 1996, together with the crystal structures of its complexes with ethanol, nitromethane, and benzene . This compound has also been reported to possess enhanced selectivities when recrystallized from various mixtures including ethylbenzene and the xylenes, dichlorobenzenes, and methylpyridines, selecting preferentially for p -xylene, p -dichlorobenzene, and o - or m -methylpyridine (experimental conditions-dependent), respectively. Since DED displayed such selectivity in mixtures, we embarked upon an investigation of its separation or purification potential for the bromoanisole isomers (together with unsubstituted anisole) through recrystallization experiments of DED from various mixtures of these potential guest solvents.…”

Host Compound DED: Guest Accommodation Type, Noncovalent Host···Guest Interactions, Crystal Densities, and Thermal Stabilities Ensure High Host Selectivities for 4-Methylanisole in Anisole and Methylanisole Mixtures

“…35 Interestingly, DED, when recrystallized from all possible combinations of equimolar mixtures of o-, m-, and p-dichlorobenzene (p-DCB), displayed a near-complete selectivity for the para isomer in every instance (in the present case, the para isomer was also the favored one). 25 In that work, it was shown that the complex containing this guest crystallized also in the triclinic crystal system and space group P1̅ , and a comparison of the unit cell dimensions revealed the host packing in 2(DED)•p-DCB to be isostructural with 2(DED)•4-MA.…”

“…These encouraging observations stimulated a closer scrutiny of the behaviors of related molecules DED , H1 , and H2 in analogous experimental conditions. While the selectivity of various roof-shaped host compounds has been explored in mixed picolines, dichlorobenzenes (DCBs), and ethylbenzene/xylenes with remarkable selectivity data being obtained in these instances, the host behavior of DED , H1 , and H2 has not been assessed when presented with anisole mixtures. As such, here, successfully formed complexes were analyzed by both single-crystal X-ray diffraction (SCXRD) and thermal analyses to understand any selectivity displayed by these host compounds, to observe noncovalent interactions responsible for guest retention and also to investigate the relative thermal stabilities of the so-formed complexes.…”