Pore opening and breathing transitions in metal-organic frameworks: Coupling adsorption and deformation

Soft porous crystals undergo large structural transformations under a variety of physical stimuli. Breathing-like transformations, occurring with a large volume change, have been associated with an existence of bi-stable or multi-stable crystal structures. Understanding of the mechanism of these transformations is essential for their potential applications in gas adsorption, separation and storage. However, the generic description is still missing. Here, we provide a detailed, multiscale qualitative and quantitative analysis of the adsorption-induced "breathing" transformations in two metal organic frameworks (MOFs): MIL-53(Al) which is a reference case of our approach, and recently synthesized JUK-8, which does not show any bistability without adsorbate. The proposed approach is based on atomistic simulations and does not require any empirical or adjustable parameters. It allows for a prediction of potential structural transformations in MOFs including the adsorption induced deformations derived from adsorption stress model. We also show that the quantitative agreement between calculated and experimental results critically depends on the quality of the dispersion energy correction. Our methodology represents a new, powerful tool for designing and screening of flexible materials, alternative and complimentary to experimental approaches.