An Allosteric Metal–Organic Framework That Exhibits Multiple Pore Configurations for the Optimization of Hydrocarbon Separation

Abstract

The function of allosterice nzymes can be activated or inhibitedt hrough binding of specifice ffector molecules.H erein, we describe how the skeletal deformation, pore configuration, and ultimately adsorptive behavior of ad ynamic metal-organic framework (MOF), (Me 2 NH 2 )[In(atp)] 2 (in which atp = 2-aminoterephthalate), are controlled by the allocation and orientation of its counter ions triggered by the inclusion/removal of different guest molecules. The powero fs uch allostericc ontrol in MOFs is highlighted throught he optimization of the hydrocarbon separation performance by achieving multiple pore configurations but without alteringt he chemical composition.Adsorptive separation of small hydrocarbons from cracking streamsa nd naturalg as has attracted great attention, empowered by the innovation of porousm aterials. [1, 2] As an abundant vehicle fuel and value-added chemical feedstock, [3] the purification of methane from co-existing alkanes is an energy-intensive process of cryogenic distillation, which differentiates the molecules by their boilingp oints (CH 4 , À161.5 8C; C 2 H 6 , À88.6 8C; C 3 H 8 , À42.1 8C). [4] In contrast, adsorptive separation at ambient temperature is an alternate and more sustainable process,w hich exploits differences in kinetic diameters (CH 4 , 3.758 ;C 2 H 6 ,4 .443 ;C 3 H 8 ,4 .3-5.148 )a nd polarizability (CH 4 ,2 5.93 10 25 cm 3 ;C 2 H 6 ,4 4.3-44.7 10 25 cm 3 ;C 3 H 8 ,6 2.9-63.7 10 25 cm 3 )t oachieveeffective separation. [5] Metal-organic frameworks (MOFs) are designablep orous materials that are createdb ys titching togetherg eometrically definedi norganic building units and tailoredo rganic linkers into predictable extendedn etworks. The resulting crystalline frameworks achieve structural regularity,a rchitectural robustness, and exceptional porosity. [6] In contrastt oc onventional porousm aterials, the most unique characteristic of MOFs is their dynamics, [7] which feature coherent structural transformations corresponding to external stimuli that allow for the creation of smarterm aterials with desired guest-, [8] thermo-, [9] electro-, [10] photo-, [11] and mechano-responses. [12] Indeed, several prominente xamples of MOFs have been shown to undergo structuralt ransformation during gas adsorption, which endows the material with exceptionalp roperties in selective gas adsorptiona nd gas storage. [13] However,s tructuralf lexibility usually imposes co-adsorption of multiple components from the fluent, thereby constituting am ajor challenge in designing dynamic MOFs for gas-adsorptive separation in practical applications. [14] In contrastt or igid frameworks that are typically associated with only one energy minimum, dynamic frameworks are capable of possessing two or more local energy minima in their energy landscapes (Scheme 1a) depending on the degrees of freedom for their structures and the energy barrier needingt o be overcomef or their transformations. [15] Recently,u nprecedented multiple energy minima (up to 9phases) were achieved upon inclusiono...

Post‐Synthetic Modification Unlocks a 2D‐to‐3D Switch in MOF Breathing Response: A Single‐Crystal‐Diffraction Mapping Study

“…We have previously reported the large‐amplitude 2D breathing behaviour and prominent host‐guest chemistry leading to CO 2 /CH 4 gas separation capabilities of the diamondoid MOF (Me 2 NH 2 )[In(BDC‐NH 2 ) 2 ] ( SHF‐61 ) [28, 29] . A recent report has extended the potential application to a wider range of hydrocarbons [30] . Here we report the post‐synthetic modification of SHF‐61 by reaction with acetic anhydride at 55 °C in CHCl 3 to yield the fully acetamide‐modified MOF (Me 2 NH 2 )[In(BDC‐NHC(O)Me) 2 ] ( SHF‐62 ).…”

“…Further exploration of different solvents and the effect of any water content would be needed to draw more detailed conclusions; these aspects are being actively explored alongside computational modelling. Recent studies of MOFs comprising deformable M-(O 2 CR) 4 nÀ nodes [28,30,33,34] illustrate that these represent an emerging class of responsive dynamic MOFs with tuneable behaviour. The amenability to study in situ by single-crystal diffraction provides a route to detailed characterisation and understanding of this behaviour as a platform to future applications.…”

“…[28,29] A recent report has extended the potential application to a wider range of hydrocarbons. [30] Here we report the postsynthetic modification of SHF-61 by reaction with acetic anhydride at 55 8C in CHCl 3 to yield the fully acetamidemodified MOF (Me 2 NH 2 )[In(BDC-NHC(O)Me) 2 ] (SHF-62). This occurs in a SC-SC transformation and has a dramatic effect on the flexibility of the framework.…”

Post‐Synthetic Modification Unlocks a 2D‐to‐3D Switch in MOF Breathing Response: A Single‐Crystal‐Diffraction Mapping Study

“…[ 28 , 29 ] A recent report has extended the potential application to a wider range of hydrocarbons. [30] Here we report the post‐synthetic modification of SHF‐61 by reaction with acetic anhydride at 55 °C in CHCl 3 to yield the fully acetamide‐modified MOF (Me 2 NH 2 )[In(BDC‐NHC(O)Me) 2 ] ( SHF‐62 ). This occurs in a SC‐SC transformation and has a dramatic effect on the flexibility of the framework.…”

“…Further exploration of different solvents and the effect of any water content would be needed to draw more detailed conclusions; these aspects are being actively explored alongside computational modelling. Recent studies of MOFs comprising deformable M(O 2 CR) 4 n − nodes[ 28 , 30 , 33 , 34 ] illustrate that these represent an emerging class of responsive dynamic MOFs with tuneable behaviour. The amenability to study in situ by single‐crystal diffraction provides a route to detailed characterisation and understanding of this behaviour as a platform to future applications.…”