Computational Model and Characterization of Stacking Faults in ZIF-8 Polymorphs

Degradation of metal organic frameworks (MOFs) in aqueous, humid, and acid gas environments likely begins at defect sites. Until now, however, theoretical studies of MOFs have widely assumed an ideal defect-free structure. Here we present a computational model for low-energy extended defects in bulk zeolitic imidazolate frameworks (ZIFs) that are analogous to stacking faults in zeolites. We demonstrate the thermodynamic accessibility of stacking faults in ZIFs and examine the impact of these defects on pore diffusion and accessible surface area. We identify strong correlations between the defect density of a structure and its X-ray diffraction spectra. By examining a topologically isomorphic ZIF that has been reported experimentally we find characteristic defect-induced peak broadening and splitting in the reported powder patterns, giving strong evidence for the existence for stacking faults in this material.