​Flexible Metal-Organic Frameworks (MOFs) show promise in a wide variety of applications such as gas separation, drug delivery and molecular sensing, because of their stimuli-responsive behaviours. Considerable research has been dedicated to improving our understanding of the structural changes of flexible MOFs in response to external stimuli. However, the general model used has been one of uniform pore deformation, and advances have been made in synthesising MOFs with pores that vary in size, shape, and environment.

In work published in Nature Communications, a team of researchers from the universities of Oxford and Cambridge, and Virginia Commonwealth University in the USA, used quasielastic neutron scattering on IRIS and inelastic neutron scattering on TOSCA to investigate the structural change seen in the flexible MOF ZIF-7 on CO₂ adsorption. They demonstrated that the change occurs because of CO₂ migration in its non-uniform porous structure, and not by its guest-hosting pores opening. This mechanism is distinct from the majority of guest-host interactions reported for other MOFs and extremely uncommon.

This work provides new insights into MOF flexibility and offers new methods for analysing adsorption mechanisms in flexible MOFs, which could help design new materials.

Related publication: “Structural dynamics of a metal–organic framework induced by CO₂ migration in its non-uniform porous structure" Nature Communications, 10, Article number: 999 (2019), DOI: 10.1038/s41467-019-08939-y

Authors: Pu Zhao (University of Cambridge; University of Oxford), Hong Fang (Virginia Commonwealth University), Sanghamitra Mukhopadhyay (ISIS), Aurelia Li (University of Cambridge), Svemir Rudić (ISIS), Ian J. McPherson (University of Oxford), Chiu C. Tang (Diamond Light Source), David Fairen-Jimenez (University of Cambridge), S. C. Edman Tsang (University of Oxford) & Simon A. T. Redfern (University of Cambridge).

 Instrument: IRIS and TOSCA