Guest-induced amorphous-to-crystalline transformation enables sorting of haloalkane isomers with near-perfect selectivity

Abstract

The separation of haloalkane isomers with distillation-free strategies is one of the most challenging research topics in fundamental research and also gave high guiding values to practical industrial applications. Here, this contribution provides a previously unidentified solid supramolecular adsorption material based on a leggero pillararene derivative BrP[5]L , which can separate 1-/2-bromoalkane isomers with near-ideal selectivity. Activated solids of BrP[5]L with interesting amorphous and nonporous features could adsorb 1-bromopropane and 1-bromobutane from the corresponding equal volume mixtures of 1-/2-positional isomers with purities of 98.1 and 99.0%, respectively. Single-crystal structures incorporating theoretical calculation reveal that the high selectivity originates from the higher thermostability of 1-bromoalkane–loaded structures compared to its corresponding isomer-loaded structures, which could be further attributed to the perfect size/shape match between BrP[5]L and 1-bromoalkanes. Moreover, control experiments using its counterpart macrocycle of traditional pillararene demonstrate that BrP[5]L has better adsorptive selectivity, benefiting from the intrinsic free-rotation phenylene subunit on its backbone.

A Water-Soluble Leggero Pillar[5]arene

“…Perbromoethylated macrocyclic derivatives BrP[5]L and BrP[5]A were synthesized according to the previous literature reports [ 21 , 43 ].…”

“…Inspired by pillararenes, many novel macrocyclic entities such as asar[n]arenes [ 28 ], hybrid[n]arenes [ 29 ], biphenyl-extended pillar[6]arene [ 30 , 31 , 32 , 33 ], tiara[5]arene [ 34 ], bowtiearene [ 35 ], leaning pillar[6]arene [ 36 , 37 ], geminiarenes [ 38 , 39 ], pagoda[4]arene [ 40 ] and biphenarenes [ 41 ] have been designed and synthesized in rapid succession, promoting the prosperity of modern synthetic macrocyclic chemistry and creating unlimited possibilities for supramolecular chemistry and materials. Very recently, we presented a new version of pillararene-derived macrocyclic arenes named leggero pillar[n]arenes [ 42 , 43 ], in which two substituents on a single one of the units of traditional pillararenes were selectively removed to expand their structural flexibility and cavity adaptability.…”

Pillararene-Inspired Macrocycles: From Extended Pillar[n]arenes to Geminiarenes

“…Supramolecular approaches have been employed to constructing complicated assembling architectures and intelligent functional systems, which display a distinct feature from any of its constituent species. By wisely using multiple weak intermolecular interactions, macrocycles with the combination character of host–guest recognition and complexation properties have been the major workhorses for supramolecular assembly. − Taking advantage of the diverse functional derivatives, differentiated cavity sizes, and binding capabilities of these PIMs, multitypes of functional supramolecular assemblies, such as supramolecular polymers, , supramolecular switches, − and crystalline/amorphous molecular adsorbent ,,,,, with prominent applications, have been successfully fabricated. Moreover, the synthesis of PIMs-based covalent organic polymers for adsorption and separation has also been achieved …”

“…Inspired by the above, the PIMs of leaning and leggero pillar[n]arenes with substituents absent from their aromatic backbones were subsequently designed and synthesized. 1,4,38 Per-alkylated leaning pillar [6]arenes (6a and 6b) with alkoxy functionalities absent from two of its six phenylene units in an opposite position were synthesized according to the same approach as that applied in 2. 1 By contrast, leggero pillar[n]arenes with a single one unsubstituted unit were obtained by cocyclization of two different types of precursors.…”

“…To address these issues, we have developed a versatile modular synthetic strategy and created a series of pillareneinspired macrocycles (PIMs), including extended pillar[n]arenes, 3,37,41 leaning pillar [6]arenes, 1,42−50 leggero pillar[n]arenes, 4,38 and geminiarene. 2,39 This Account mainly focuses on our research efforts on PIMs, launched from 2016 to the present.…”