Understanding Adsorption-Induced Structural Transitions in Metal-Organic Frameworks: From the Unit Cell to the Crystal

TL;DR

This paper investigates the physical mechanisms behind adsorption-induced structural transitions in metal-organic frameworks, revealing how elastic and adsorption interactions drive layer-by-layer breathing transitions at the crystal level.

Contribution

It introduces a multiscale physical model and Hamiltonian to connect unit cell interactions with crystal-scale breathing transitions in MOFs.

Findings

Layer-by-layer shear drives breathing transitions.

The Hamiltonian captures host-host and host-guest interactions.

Transition behavior depends on energy barrier, elastic coupling, and system size.

Abstract

Breathing transitions represent recently discovered adsorption-induced structural transformations between large-pore and narrow-pore conformations in bistable metal-organic frameworks, such as MIL-53. We present a multiscale physical mechanism of the dynamics of breathing transitions. We show that due to interplay between host framework elasticity and guest molecule adsorption, these transformations on the crystal level occur via layer-by-layer shear. We construct a simple Hamiltonian that describes the physics of host-host and host-guest interactions on the level of unit cells and reduces to one effective dimension due to the long-range elastic cell-cell interactions. We then use this Hamiltonian in Monte Carlo simulations of adsorption-desorption cycles to study how the behavior of unit cells is linked to the transition mechanism at the crystal level through three key physical parameters: the transition energy barrier, the cell-cell elastic coupling, and the system size.