Interplay of Linker Functionalization and Hydrogen Adsorption in the Metal-Organic Framework MIL-101

Functionalization of metal organic frameworks results in higher hydrogen uptakes owing to stronger hydrogen host interactions. However, it has not been studied whether a given functional group acts on existing adsorption sites (linker or metal) or introduces new ones. In this work, the effect of two types of functional groups on MIL-101 (Cr) is analyzed. Thermal-desorption spectroscopy reveals that the -Br ligand increases the secondary building unit's hydrogen affinity, while the -NH2 functional group introduces new hydrogen adsorption sites. In addition, a subsequent introduction of -Br and -NH2 ligands on the linker results in the highest hydrogen-store interaction energy on the cationic nodes. The latter is attributed to a push-and-pull effect of the linkers.