(520f) Computational Design of Electric Field Responsive Metal-Organic Frameworks for Directional Flow

Stimuli responsive MOFs, which undergo physical or chemical changes under an external stimulus, such as temperature, guest adsorption, pressure, magnetic field, and light absorption, gained much attention because of their vital importance in design of new dynamic and smart materials for different applications Recent studies have shown that it is possible to use an external electric field (E-field) to induce structural changes in MOFs and these structural changes can be used for separation of gas mixtures^1-3. In this study we propose and computationally demonstrate the concept of electric field controlled molecular gates mounted on the open-metal coordination sites in metal–organic framework (MOF) materials. The MOF-molecular gate complex functions by opening and closing under the effect of an electric field. Our design involves Mg-MOF-74, a MOF with hexagonal channels with open-metal coordination sites at each corner, and a multifunctional gate molecule with permanent dipole which anchors itself on the host MOF material and responds to changes in the direction of an electric field by rotating around its backbone which acts as an axle. By carrying out density functional theory (DFT) calculations and molecular dynamics (MD) simulations we show that the MOF-molecular gate complex can be switched between two stable configurations, open and closed, by turning on and off an external electric field. We further show that the molecular gate can be controlled to block or allow the diffusion of methane molecules through the channels of the MOF like a nanoscale butterfly valve. We then extend the same concept to demonstrate how an E-field can be used to control and stabilize the rotation of functionalized ligands in IRMOFs in order to restrict the diffusion of molecules within the pores and regulate their direction of flow.

1. Tam, B.; Yazaydin, O., Design of Electric Field Controlled Molecular Gates Mounted on Metal-Organic Frameworks. Journal of Materials Chemistry A 2017, 5, 8690-8696.
2. Ghoufi, A.; Benhamed, K.; Boukli-Hacene, L.; Maurin, G., Electrically Induced Breathing of the Mil-53(Cr) Metal–Organic Framework. ACS Central Science 2017, 3, 394-398.
3. Knebel, A.; Geppert, B.; Volgmann, K.; Kolokolov, D. I.; Stepanov, A. G.; Twiefel, J.; Heitjans, P.; Volkmer, D.; Caro, J., Defibrillation of Soft Porous Metal-Organic Frameworks with Electric Fields. Science 2017, 358, 347.