MOFs in Motion

Abstract

Metal–organic frameworks (MOFs) are a class of hybrid materials with metal-based inorganic nodes connected by organic linkers via strong coordination bonds. These building blocks can be arranged in 3-D crystalline lattices to synthesize structures with varying pore sizes and a variety of structures (tuneability). These hybrid materials possess exceptional porosity and large surface areas, making them suitable for applications in gas separation and storage, catalysis, and biomedical fields. MOFs also exhibit remarkable flexibility, which is determined by the topology of the framework and the degrees of freedom between bond angles in the organic linkers or coordination bonds between the organic linkers and inorganic nodes. One among the major categories of flexibility in MOFs is the rotational dynamics of organic linkers. The structural dynamics can have a pronounced influence on gas adsorption, diffusion and optical properties. Chapter 4 and Chapter 5 study the rotational dynamics of terephthalate linkers in functionalized MIL-53 MOFs by varying the steric interactions between the linkers using computational methods like ab initio molecular dynamics and classical molecular dynamics. Using the remarkable porosity, structural flexibility, and tuneability features of MOFs as central handles, in this thesis, we aim to study the (a) Piezoelectric properties in MOFs for their application as energy harvesters and (b) Rotational dynamics of linkers in MOFs. It is well-known that MOFs possess a high degree of flexibility and permanent porosity. High porosity of MOFs leads to low dielectric constants. This, together with higher flexibility of MOFs, makes them promising candidates for piezoelectric energy harvesting. Although all non-centrosymmetric MOFs are piezoelectric, their piezoresponse has hardly been studied thoroughly. Chapter 2 and Chapter 3 of this thesis will investigate the structure-property relationships of piezoelectric properties in MOFs through computational methods, and provide design guidelines that can contribute to the development of high-performing piezoelectrics.