(687b) Thermodynamic Stability of Hypothetical ZIF-8 Polymorphs Using Molecular Simulations

Zeolitic imidazolate frameworks (ZIFs) are a class of metal-organic frameworks (MOFs) that are known to exhibit structural polymorphism. Despite the large number of reported ZIF polymorphs, the factors governing the stability of these materials remain poorly understood. In this work, we present a novel approach to investigate the thermodynamic stability of MOF polymorphs using molecular simulations. Our work employs a combination of thermodynamic integration (TI) and OFAST simulations to predict the free energy of solvation, ΔG_solv, and vibrational density of states (VDOS) calculations to determine the configurational energy of the framework. This approach is applied to a series of hypothetical ZIF-8 polymorphs under solvothermal conditions. Our simulations predict that the framework stability is governed by the configurational energy rather than the ΔG_solv of the framework. We find good agreement between OFAST and the more precise TI method for the prediction of the ΔG_solv of the framework. This methodology can be applied to study the effect of structural topology, solvent, and temperature on the stability of the framework for a wide range of nanoporous materials.