Precise Control of Molecular Self‐Diffusion in Isoreticular and Multivariate Metal‐Organic Frameworks

• Published in: Chemphyschem 2020-01, Vol.21 (1), p.32-35
• Main Authors: Osborn Popp, Thomas M., Plantz, Ariel Z., Yaghi, Omar M., Reimer, Jeffrey A.
• Format: Article
• Language: English
• Subjects: Apertures; Diffusion; Diffusion coefficient; Dimethylformamide - chemistry; Drug delivery systems; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; liquids; Metal-organic frameworks; Metal-Organic Frameworks - chemistry; Models, Molecular; Molecular diffusion; Molecular Structure; Multivariate analysis; nuclear magnetic resonance; Organic chemistry; Particle Size; Polarity; pulsed-field gradient; Single crystals; Solvents; Surface Properties
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.201901043

Understanding the factors that affect self‐diffusion in isoreticular and multivariate (MTV) MOFs is key to their application in drug delivery, separations, and heterogeneous catalysis. Here, we measure the apparent self‐diffusion of solvents saturated within the pores of large single crystals of MOF‐5, IRMOF‐3 (amino‐functionalized MOF‐5), and 17 MTV‐MOF‐5/IRMOF‐3 materials at various mole fractions. We find that the apparent self‐diffusion coefficient of N,N‐dimethylformamide (DMF) may be tuned linearly between the diffusion coefficients of MOF‐5 and IRMOF‐3 as a function of the linker mole fraction. We compare a series of solvents at saturation in MOF‐5 and IRMOF‐3 to elucidate the mechanism by which the linker amino groups tune molecular diffusion. The ratio of the self‐diffusion coefficients for solvents in MOF‐5 to those in IRMOF‐3 is similar across all solvents tested, regardless of solvent polarity. We conclude that average pore aperture, not solvent‐linker chemical interactions, is the primary factor responsible for the different diffusion dynamics upon introduction of an amino group to the linker. Diffusion of guests within the metal‐organic framework MOF‐5 is shown to linearly decrease as the isoreticular NH2‐functionalized linker is incorporated into the framework. This NH2 functionality is shown to slow the translational motion of guests by reducing the pore metrics of the framework, and not through hydrogen bonding.