Competitive Guest Binding in a Metal-Organic Framework with Coordinatively Unsaturated Metals

Coordinatively unsaturated sites (CUS) within MOFs are crucial in determining the sorbent selectivity by acting as the strongest binding sites for guest molecules. This study elucidates the thermodynamics of solvent binding to CUS by using Raman spectroscopy while varying solvent ratios to measure their competitive binding. The experimentally obtained solvent relative binding free energies correlate with the theoretical enthalpies computed via density functional theory but are even better predicted by the electrostatic potential minimum of the solvents. The experimental determination of guest binding energies at the metal site provides an approach for predicting behavior in mixed solvent systems and highlights the molecular properties that are required for the activation of CUS-MOFs.