This hypothesis prompted us to design trigonal Cu I sites with an increased degree of planarity to modulate the strength of π-backbonding at the Cu I site. More specifically, while Cu I -MFU-4l has an octahedral Zn II ion at the center of the pentanuclear secondary building units, we hypothesized that replacing this central ion with larger metal ions could expand the tripodal ligand scaffold, thereby making the peripheral Cu I ion protrude less from the tripodal ligand scaffold to increase its planarity (Figure ). Here, we establish a series of Cu I M-MFU-4l frameworks (M = Zn, Mn, Cd; hereafter, the previously reported Cu I -MFU-4l will be denoted as Cu I Zn-MFU-4l) with different M II ions at the center of the pentanuclear cluster node (Figure ). Using in situ spectroscopy, computational studies, diffraction studies, and gas adsorption measurements, we demonstrate that H2 binding in this series can be systematically tuned, allowing the realization of new materials within the optimal range for ambient temperature hydrogen storage.