Unraveling Metal Effects on CO2 Uptake in Pyrene-based Metal-Organic Frameworks through Integrated Lab and Computer Experiments

Pyrene-based metal-organic frameworks (MOFs) have tremendous potential for various applications, including carbon capture. With infinite structural possibilities, the MOF community is reliant on simulations to identify the most promising candidates for given applications. Among thousands of reported structures, many exhibit limited reproducibility - in either synthesis, performance, or both - owing to the sensitivity of synthetic conditions. Geometric distortions that may arise in the functional groups of pyrene-based ligands during synthesis and/or activation cannot easily be predicted. This sometimes leads to discrepancies between in-silico and experimental results. Here, we investigate a series of topologically similar pyrene MOFs for carbon capture, as in their orthorhombic crystal structure, the ligand stacks in a parallel fashion, creating a promising binding site for CO2. These structures share the same ligand 1,3,6,8-tetrakis(p-benzoic acid)pyrene (TBAPy), but have different metals (M-TBAPy, with M = Al, Ga, In, Sc). As predicted, the metal is shown to affect the pyrene stacking distance, and therefore the CO2 uptake. Interestingly however, our study reveals that the choice of metal also affects the rotational freedom of the ligand's benzoate groups, impacting the overall predicted ranking of the MOFs based on their CO2 uptake. Crystallographic analysis reveals the presence of additional phases where the metal node allows for geometric rearrangement. Considering these additional phases improves the prediction of adsorption isotherms, enhancing our understanding of pyrene-based MOFs for efficient carbon capture.