No abstract

In this work,, a host compound that formed complexes with anisole (ANI), 2-bromoanisole (2-BA), and 4-bromoanisole (4-BA), was revealed to possess a remarkable affinity (93.1−98.6%) for 4-BA when recrystallized from any mixtures containing this guest species, be these binary (ANI/4-BA, 2-BA/4-BA, or 3-BA/4-BA), ternary (ANI/2-BA/4-BA, ANI/3-BA/4-BA, or 2-BA/3-BA/4-BA), or quaternary (ANI/2-BA/3-BA/4-BA) in nature. Furthermore, this striking host selectivity persisted even in binary solutions containing low concentrations of 4-BA (18−25%); near-complete selectivities in favor of 4-BA were observed here too. Single crystal X-ray diffraction analyses showed that the favored guest species, 4-BA, was the only one to experience short intermolecular contacts, through its phenyl ring, with the host molecule's carbonyl oxygen atom and the host hydrogen atom on the carbon bearing the second carboxylic acid group. Furthermore, ANI and 2-BA were accommodated in wide open channels, while the guest accommodation type for 4-BA was significantly more constricted. Thermal analyses confirmed that 2(DED)•3(ANI) and DED•2-BA, having the disfavored guests in open channels, were unstable at room temperature, while the preferred guest species, 4-BA, in its decidedly constricted channels, was only released at significantly higher temperatures (116.8 °C). Therefore, by employing host−guest chemistry strategies, DED has the ability to purify and separate any of these 4-BA-containing mixtures, a distinct advantage over fractional distillations which are cumbersome owing to physical property similarities of 2-, 3-, and 4-BA.

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 (H1) was assessed for its host behaviour in pyridine (PYR) and 2-, 3- and 4-methylpyridine (2MP, 3MP and 4MP). Each of these guest compounds was enclathrated, and host:guest...

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...