Amino Acid Residues Determine the Response of Flexible Metal-Organic Frameworks to Guests.

Yong Yan,Rebecca K Hylton,Rémi Pétuya,Ajay Verma,Neil G Berry,Dmytro Antypov,Elliot J Carrington,Alexandros P Katsoulidis,Matthew S Dyer,Matthew J Rosseinsky,George F S Whitehead,George R Darling,Chiu C Tang

doi:10.1021/jacs.0c03853

Yong Yan, Rebecca K Hylton + Show 11 more

Open Access

https://doi.org/10.1021/jacs.0c03853

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Abstract

Flexible metal–organic frameworks (MOFs) undergo structural transformations in response to physical and chemical stimuli. This is hard to control because of feedback between guest uptake and host structure change. We report a family of flexible MOFs based on derivatized amino acid linkers. Their porosity consists of a one-dimensional channel connected to three peripheral pockets. This network structure amplifies small local changes in linker conformation, which are strongly coupled to the guest packing in and the shape of the peripheral pockets, to afford large changes in the global pore geometry that can, for example, segment the pore into four isolated components. The synergy among pore volume, guest packing, and linker conformation that characterizes this family of structures can be determined by the amino acid side chain, because it is repositioned by linker torsion. The resulting control optimizes noncovalent interactions to differentiate the uptake and structure response of host–guest pairs with similar chemistries.

Highlights

Flexible metal−organic frameworks (MOFs) are a class of crystalline porous materials formed by coordination bonds between organic linkers and metal ions or clusters where the framework structure changes upon external stimuli
To expand the linker−metal coordination chemistry while retaining conformational and side chain diversity, we have developed a family of linkers (XPyr) where an amino acid (X) is coupled with a pyrazole (Pyr) compound through an amide
The ZnXPyr family of flexible MOFs derived from the amino acid residues X = Gly, Ala have an unusual trefoil-shaped porosity where a pinch point connects a central channel to three peripheral pockets

Summary

■ INTRODUCTION

Flexible metal−organic frameworks (MOFs) are a class of crystalline porous materials formed by coordination bonds between organic linkers and metal ions or clusters where the framework structure changes upon external stimuli. Computational Analysis of Guest-Free ZnGlyPyr and ZnAlaPyr. The observed pore segmentation of both materials upon CO2 sorption and the resulting new small-volume guestfree structure unique to ZnAlaPyr can be further understood with Density Functional Theory (DFT) calculations of the energy of the guest-free frameworks at different unit cell volumes (see section S18 in the Supporting Information). The E−V curves for the guest-free structures allow a rationalization of the differences between the ZnGlyPyr and ZnAlaPyr frameworks during removal of CO2 In both materials, CO2−host interactions overcome linker conformational energy penalties to afford cell volumes considerably smaller than those seen for liquid guests (Figure 3), forming a distinct set of structures where the peripheral pockets are isolated from the central channel to form a four-component pore topology as they encapsulate the CO2 guests (Figure 7). ZnAlaPyr accesses the small-volume guest-free form with four isolated pore components (Figure 7b) very close in volume to the CO2containing start point because the Ala side chains produce stabilizing attractive Me···Me vdW interactions that overcome the higher linker torsional energy required to place them in these positions

■ CONCLUSION

■ ACKNOWLEDGMENTS

■ REFERENCES