Flexing of a Metal–Organic Framework upon Hydrocarbon Adsorption: Atomic Level Insights from Neutron Scattering

Metal–organic frameworks (MOFs) offer considerable opportunities for gas uptake, storage, and separation due to their porosity, chemical tunability, and flexibility. Flexible MOFs undergo reversible structural transformations triggered by external stimuli such as adsorption of specific guest molecules. The MUF-16 family of materials has exceptional gas adsorption properties including selective uptake of carbon dioxide over other gases. We observed one member of this family, MUF-16(Mn), to be flexible upon the adsorption of hydrocarbon gases. We used a combination of in situ synchrotron X-ray and neutron diffraction to identify the framework–gas interactions that underlie the structural flexibility. Inelastic neutron scattering, along with calculations, also enables an understanding of the dynamics of the flexibility. In essence, C3 hydrocarbons effectively bridge across hydrogen-bonded carboxyl dimers in the framework, triggering pore expansion and inhibiting certain types of motion in the framework.