Switching of Guest Selectivity for the Inclusion of Regioisomers of Monosubstituted Phenols with Crystals of p-tert-Butylcalix[4]arene

Abstract

To develop an inclusion method for hard-to-separate organic molecules with wide guest scopes, we examined the control of guest selectivity via external factors such as solvents, temperature, and additives for the competitive inclusion of monosubstituted phenol isomers with crystals of p-tert-butylcalix[4]arene 1. Guest selectivity was thus switched between two isomers in the inclusion of cresol, fluorophenol, and bromophenol and between three isomers in the inclusion of chlorophenol. The mechanism of guest selectivity in chlorophenol inclusion was mainly determined using X-ray crystal structural analysis and a comparison of the thermal stabilities and the formation rates of inclusion crystals with each isomer. Under kinetic control, the inclusion from decane at a low temperature selectively yielded type-A (host/guest = 1:1) inclusion crystals of p-isomer (1·p-chlorophenol) in which the host and guest molecules exhibited CH−π and OH–π interactions. In aqueous solutions at high temperatures, where water molecules inhibited the inclusion of m-isomer, thermally stable type-B (host/guest = 2:1) crystals of o-isomer (1 2·o-chlorophenol), in which a guest molecule was included in a capsule constructed by two host molecules, selectively formed. Furthermore, the inclusion from decane in the presence of methanol produced a co-inclusion crystal of type-C (host/guest/additive = 2:1:1) in which a 1:1 complex of m-isomer and methanol, connected via an intermolecular hydrogen bond, was selectively included by the distorted capsule of two host molecules to form 1 2·m-chlorophenol·CH3OH.

Selective Inclusion of Cyclohexanediol Stereoisomer by Crystals of Open-Chain Diol-Type Host Based on a Partial Structure of p-tert-Butylthiacalixarene

“…The guest selectivity can be switched in several cases. 47,48,53 Very recently, we also reported the application using salt crystals to the selective collection of lanthanide ions from water. 55 crystals with an accumulation of host−guest complexes after the collection of guest molecules.…”

Selective Inclusion of Cyclohexanone from a Mixture with Cyclohexanol Using 1,3-Diaminocalix[4]arene Crystals

“…It was also observed that guest selectivity can be switched in some cases. 46,47,52 In typical NMCs, channels in the crystals are also used in molecular recognition. 25−31 In contrast, when calix [4]arene crystals without a channel include organic molecules, they usually transform into crystals in which host−guest complexes accumulate.…”

“…38−41 We have developed an efficient separation method for organic molecules using the properties of calixarene crystals. 42−52 Selective inclusion of alcohols, 43,45 carboxylic acids, 43,47 amines, 46 alkanes, 50 and disubstituted benzene isomers 48,51,52 using crystals of p-tert-butylcalixarene (1) and p-tertbutylthiacalix [4]arene (2) and their derivatives has already been achieved (Chart 1). It was also observed that guest selectivity can be switched in some cases.…”

“…Calixarenes are representative hosts that provide non-channel NMCs, and their ability to capture inorganic gases and organic molecules has been actively investigated. − We have developed an efficient separation method for organic molecules using the properties of calixarene crystals. − Selective inclusion of alcohols, , carboxylic acids, , amines, alkanes, and disubstituted benzene isomers ,, using crystals of p - tert -butylcalixarene ( 1 ) and p - tert -butylthiacalix­[4]­arene ( 2 ) and their derivatives has already been achieved (Chart ). It was also observed that guest selectivity can be switched in some cases. ,, In typical NMCs, channels in the crystals are also used in molecular recognition. − In contrast, when calix[4]­arene crystals without a channel include organic molecules, they usually transform into crystals in which host–guest complexes accumulate. , Therefore, the difference in the guest structure is likely to be reflected in the difference in crystal stability (thermodynamic control), and the difference in the formation rate derived from the activation energy of the structural change can also be used to obtain guest selectivity (kinetic control). We considered that it would be possible to distinguish between cyclohexanone and cyclohexanol using these properties of calix[4]­arene crystals.…”

Selective collection of Yb(iii) over La(iii) and Eu(iii) from aqueous solution by bis(tetramethylammonium) salt crystals of p-tert-butylcalix[4]arene-1,3-diphosphonic acid

“…One of the central themes of our research work is the development of molecular crystals of calix[4]arene derivatives 3 for selective inclusion of hard to separate small organic molecules. 4,5 Inclusion crystals are formed through continuous interactions between host–guest complexes and differences in the guest structure are reflected in their stabilities (thermodynamic control) and/or the rate of formation (kinetic control). Backed by our experience in the field, we envisaged that by taking advantage of differences in the stability of inclusion crystals, in which metal complexes infinitely stack, precise recognition of rare metal ions may be possible by developing target specific supramolecular host materials.…”