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

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

Robust Co(II)-Based Metal–Organic Framework for the Efficient Uptake and Selective Detection of SO₂

MUF-16 is a porous metal–organic framework comprising cobalt(II) ions and 5-aminoisophthalate ligands. Here, we measured its reversible SO2 adsorption–desorption isotherm around room temperature and up to 1 bar and observed a high capacity for SO2 (2.2 mmol g–1 at 298 K and 1 bar). The uptake of SO2 was characterized by Fourier transform infrared (FT-IR) spectroscopy, which indicated hydrogen bonding between the SO2 guest molecules and amino functional groups of the framework. The location and packing of the SO2 molecules were confirmed by computational studies, namely, density functional theory (DFT) calculations of the strongest adsorption site and grand canonical Monte Carlo (GCMC) simulations of the adsorption isotherm. Furthermore, MUF-16 showed a remarkable selective fluorescence response to SO2 compared to other gases (CO2, NO2, N2, O2, CH4, and water vapor). The possible fluorescence mechanism was determined by using time-resolved photoluminescence. Also, the limit of detection (LOD) was calculated to be 1.26 mM (∼80.72 ppm) in a tetrahydrofuran (THF) solution of SO2