Unraveling Thermally Regulated Gating Mechanisms in TPT Pore-Partitioned MOF-74: A Computational Endeavor

This is the authors' abstract. We don't add key points for this paper.

In the pursuit of advanced gas adsorption materials, we investigate the thermally activated gating mechanism of functionalized TPT (2,4,6-tri(4-pyridyl)-1,3,5-triazine) ligands within the one-dimensional channels of Mg-MOF-74. These ligands induce the formation of ultramicroporous windows, whose sizes dynamically respond to substituent groups and temperature. Gas-phase DFT calculations reveal molecular rotator behavior in the TPT-X (X = H, F, CH3, Cl) ligands showing an inverse steric relationship between the functional group size and the barrier for rotation, indicating a propensity for larger functional groups to facilitate molecular rotation. Once incorporated into the channel of MOF-74, the larger functional groups result in energy landscapes marked by higher barriers, suggesting that portions of the landscape are only accessible at higher temperatures. These findings suggest temperature-driven pore size changes, hinting at thermally regulated gating. Molecular dynamics (MD) calculations corroborate these findings, showing an increase in the pore size of the −Cl and −CH3 functionalized systems with increasing temperature. Comparative analysis highlights TPT-X pore partitioned MOF-74's (mTPT-X) superiority over other ultramicroporous MOFs, making them promising for gas adsorption and separation applications. At lower (10% maximum) loading, the materials demonstrate ultramicroporosity with pore volumes akin to MOF-74, potentially leading to temperature-driven high capacity gas storage and gas separation. Conversely, higher loading (50% maximum) leads to a loss of pore volume and a subsequent loss of capacity, leading to lower feasibility for gas storage but potentially enhancing gas separation processes.