Predictive Acid Gas Adsorption in Rare Earth DOBDC Metal-Organic Frameworks via Complementary Cluster and Periodic Structure Models

Eu-DOBDC metal-organic frameworks (MOFs) have demonstrated capabilities in the adsorption of acid gases, indicating that other rare earth (RE)-DOBDC MOFs are promising candidates for similar applications. To investigate the entire suite of RE-DOBDC MOFs, density functional theory (DFT) simulations of bulk periodic and cluster structure models were used to predict acid gas adsorption. Cluster models of M(L)(3), L = OOCH-, BDC-, and DOBDC-, were used to calculate binding enthalpies of NO2, SO2, and H2O directly to the metal sites, whereas bulk periodic DFT simulations of RE-DOBDC MOFs investigated the structural effects of the extended MOF framework on acid gas adsorption. From both sets of simulations, the metal center does not exhibit changes in the spin states, indicative of physisorption between the gas molecule and the metal center. However, a comparison of results identified that the presence of structural linkers in periodic DFT simulations increased binding energies between the guest molecule and the MOF over those found by cluster calculations. Additionally, the inclusion of the DOBDC linker in the periodic calculation results in delocalization of the charge between the acid gas and the DOBDC linker. Based on this comprehensive analysis, design of future RE-DOBDC MOFs can exploit differences in binding of the gas molecule with the linker or the metal center.