(260e) Ethane Diffusion in a Mixed Linker ZIF-7-8 By Pulsed Field Gradient NMR in Combination with a Single Crystal IR Microscopy

Metal organic frameworks (MOFs) and zeolitic imidazolate frameworks (ZIFs), a class of MOFs, present an exciting opportunity to work with a robust library of materials whose metal ions and organic linkers can be tailored. As these materials become increasingly more complex, there is a growing need to understand their transport properties.

Here we report an experimental study where two complimentary techniques, pulsed field gradient (PFG) NMR and infrared microscopy (IRM), are applied to investigate ethane diffusion inside crystals of mixed linker ZIF-7-8. This material is formed by a combination of ZIF-8 and ZIF-7 imidazolate linkers within the same framework, and is expected to have a smaller aperture size in comparison with that in ZIF-8. Ethane diffusivities in ZIF-7-8 are compared with those in ZIF-8 and ZIF-7.

An application of ¹³C and ¹H PFG NMR in combination with IRM for studies of ethane diffusion revealed that, as expected, the ethane self- and transport diffusivities were significantly lower in ZIF-7-8 than in ZIF-8. The data obtained by both techniques indicate that ethane diffusivities are different in different ZIF-7-8 crystals, and the diffusivity ratio for different crystals can be as large as 8. Based on the IRM data, this observation was assigned to a difference in the fraction of the ZIF-7 and ZIF-8 linkers in different ZIF-7-8 crystals. A satisfactory agreement was observed between the corrected ethane diffusivities from IRM studies and the corresponding self-diffusivities measured by PFG NMR under similar conditions.