Ionic liquid induced structural transformation in a copper-based MOF synthesis: Experimental and DFT investigations

The development of advanced materials for carbon management has driven significant interest in hybrid systems based on metal-organic frameworks (MOFs) and ionic liquids (ILs), owing to their tunable structures and enhanced affinity for CO2. In this study, we demonstrate that the IL [BMIm][BF4], employed as an ionothermal medium, plays a dual role as both solvent and structure-directing agent, enabling the formation of a two-dimensional copper-terephthalate network (Cu-BDC-2), which differs from the material obtained via conventional solvothermal synthesis (Cu-BDC-1). Structural and spectroscopic analyses reveal that IL-derived species remain associated with the framework surface, directly influencing its physicochemical properties. CO2 adsorption measurements at 85 °C show that Cu-BDC-2 exhibits enhanced interactions with CO2, attributed to the effect of IL-derived species. In contrast, theoretical calculations indicate that, in Cu-BDC-1, van der Waals interactions between CO2 and the aromatic linkers dominate the adsorption process. Furthermore, the GFN1 - xTB method shows good agreement with DFT + U results, highlighting its potential as a computationally efficient approach for screening such systems. These findings demonstrate that ionothermal synthesis is an effective strategy for modulating both the structure and surface functionality of MOF-based materials, opening new perspectives for their applications.