Isostructural MFM-300(Sc) and MFM-300(In): Adsorption Behavior to Determine Their Differences

MFM-300(Sc) and MFM-300(In) are isostructural materials that experimentally exhibit similar benzene adsorption properties with a higher capture value for MFM-300(Sc). This difference is explained in this report with a theoretical study. Intermolecular interactions are analyzed with the electron density functional theory, using Quantum Theory of Atoms in Molecules (QTAIM) and Non-Covalent Interactions index (NCI). Theoretical results indicate the establishment of two interactions between the benzene molecule and two μ2-OH groups from MFM-300(In). Meanwhile, in MFM-300(Sc), there is only one interaction between a benzene molecule and the μ2-OH group. According to the NCI and QTAIM, this additional C–H···O contact is with a neighbor μ2-OH from MFM-300(In). Therefore, MFM-300(In) shows two occupied μ2-OH groups. These μ2-OH groups are also less directed to the center of the pore. In combination with a higher BET (Brunauer, Emmett, and Teller) surface area, this inactivates the adsorption sites, affording a higher benzene uptake for MFM-300(Sc). We present an interesting explanation of adsorption behavior beyond experimentally available parameters such as surface area or pore volume, focusing on different molecular interactions. In this investigation, experiments and theory together explain the similarities and differences of these isostructural materials.