title: Structural and Mechanistic Differences in Mixed-Linker Zeolitic Imidazolate Framework Synthesis by Solvent Assisted Linker Exchange and de Novo Routes.
abstract: Mixed-linker zeolitic imidazolate frameworks (ZIFs) are a subclass of metal-organic frameworks (MOFs) amenable to significant property tuning by altering the functional groups on the imidazolate linkers. Solvent assisted linker exchange (SALE) and de novo synthesis of mixed-linker ZIFs have been demonstrated, but the differences in structural properties-most importantly the linker distributions-and synthesis mechanisms of these two different types of hybrid ZIFs are unknown. In this work, a combination of1H NMR combined rotation and multiple pulse spectroscopy (CRAMPS), water adsorption, and nitrogen measurements reveal distinct differences in linker mixing between SALE and de novo ZIF-8-90 hybrids. Native-fluorescence confocal microscopy is shown to provide a direct means to visualize these differences. The effects of crystal size, temperature, and SALE duration were studied in detail, and a generalizable mechanism for SALE processes in ZIFs is proposed. The SALE process is found to follow a diffusion-limited behavior leading to core-shell morphologies. Under harsher SALE conditions, deviations from diffusion-limited behavior are found due to etching and partial dissolution of the initial ZIF-8 crystals. With the selection of appropriate reaction conditions, SALE processes appear to be capable of generating controlled core-shell ZIF structures of good morphological quality that complement the well-mixed structures obtained by de novo methods.
authors.affiliation: School of Chemical & Biomolecular Engineering, Georgia Institute of Technology , Atlanta, Georgia 30332-0100, United States.
authors.forename: Krishna C
authors.initials: KC
authors.lastname: Jayachandrababu
authors.affiliation: School of Chemical & Biomolecular Engineering, Georgia Institute of Technology , Atlanta, Georgia 30332-0100, United States.
authors.forename: David S
authors.identifier: 0000-0002-2771-9168
authors.initials: DS
authors.lastname: Sholl
authors.affiliation: School of Chemical & Biomolecular Engineering, Georgia Institute of Technology , Atlanta, Georgia 30332-0100, United States.
authors.forename: Sankar
authors.identifier: 0000-0001-5339-470X
authors.initials: S
authors.lastname: Nair