Prediction of the Glass Transition Temperatures of Zeolitic Imidazolate Glasses through Topological Constraint Theory

Abstract

A topological constraint model is developed to predict the compositional scaling of glass transition temperature ( T_g) in a metal-organic framework glass, a_gZIF-62 [Zn(Im_{2- x}bIm _x)]. A hierarchy of bond constraints is established using a combination of experimental results and molecular dynamic simulations with ReaxFF. The model can explain the topological origin of T_g as a function of the benzimidazolate concentration with an error of 3.5 K. The model is further extended to account for the effect of 5-methylbenzimidazolate, enabling calculation of a ternary diagram of T_g with a mixture of three organic ligands in an as-yet unsynthesized, hypothetical framework. We show that topological constraint theory is an effective tool for understanding the properties of metal-organic framework glasses.