Unraveling\nThermally Regulated Gating Mechanisms in\nTPT Pore-Partitioned MOF-74: A Computational Endeavor

In the pursuit of advanced gas adsorption materials,\nwe investigate\nthe thermally activated gating mechanism of functionalized TPT (2,4,6-tri(4-pyridyl)-1,3,5-triazine)\nligands within the one-dimensional channels of Mg-MOF-74. These ligands\ninduce the formation of ultramicroporous windows, whose sizes dynamically\nrespond to substituent groups and temperature. Gas-phase DFT calculations\nreveal molecular rotator behavior in the TPT-X (X = H, F, CH<sub>3</sub>, Cl) ligands showing an inverse steric relationship between the\nfunctional group size and the barrier for rotation, indicating a propensity\nfor larger functional groups to facilitate molecular rotation. Once\nincorporated into the channel of MOF-74, the larger functional groups\nresult in energy landscapes marked by higher barriers, suggesting\nthat portions of the landscape are only accessible at higher temperatures.\nThese findings suggest temperature-driven pore size changes, hinting\nat thermally regulated gating. Molecular dynamics (MD) calculations\ncorroborate these findings, showing an increase in the pore size of\nthe −Cl and −CH<sub>3</sub> functionalized systems with\nincreasing temperature. Comparative analysis highlights TPT-X pore\npartitioned MOF-74’s (mTPT-X) superiority over other ultramicroporous\nMOFs, making them promising for gas adsorption and separation applications.\nAt lower (10% maximum) loading, the materials demonstrate ultramicroporosity\nwith pore volumes akin to MOF-74, potentially leading to temperature-driven\nhigh capacity gas storage and gas separation. Conversely, higher loading\n(50% maximum) leads to a loss of pore volume and a subsequent loss\nof capacity, leading to lower feasibility for gas storage but potentially\nenhancing gas separation processes.