Thermal and mechanical stability of zeolitic imidazolate frameworks polymorphs

TL;DR

This study uses molecular dynamics to assess the thermal and mechanical stability of 18 ZIF polymorphs, revealing stability limitations of some structures and diverse thermal expansion behaviors, informing future MOF design.

Contribution

It provides a systematic stability analysis of ZIFs under temperature and pressure, highlighting the importance of stability criteria in predicting new MOF structures.

Findings

Many hypothetical ZIFs are unstable at room temperature.

Some ZIFs exhibit large negative thermal expansion.

Stability varies significantly with framework topology.

Abstract

Theoretical studies on the experimental feasibility of hypothetical Zeolitic Imidazolate Frameworks (ZIF) have focused so far on relative energy of various polymorphs, by energy minimization at the quantum chemical level. We present here a systematic study of stability of 18 ZIFs as a function of temperature and pressure, by molecular dynamics simulations. This approach allows us to better understand the limited stability of some experimental structures upon solvent or guest removal. We also find that many of the hypothetical ZIFs proposed in the literature are not stable at room temperature. Mechanical and thermal stability criteria thus need to be considered for the prediction of new MOF structures. Finally, we predict a variety of thermal expansion behavior for ZIFs as a function of framework topology, with some materials showing large negative volume thermal expansion.