This situation is in sharp contrast to the H2 adsorption at Lewis acidic metal sites in MOFs, which is less tunable even by changing the identity of open metal sites. This study thus demonstrates a means of controlling the orbital-interaction-mediated H2 adsorption within MFU-4l-type frameworks featuring pentanuclear triazolate-bridged cluster nodes. We anticipate that this concept can be directly applied to other frameworks materials known to have the same cluster nodes. More broadly, because a myriad of such nodes are known to exist in extended framework structures, 83 a similar concept could potentially translate to other framework materials with secondary building units featuring an interstitial metal site. We therefore anticipate that the careful design of geometries and electronic structures of open metal sites may enable us to create MOFs that modulate the orbital-interaction-mediated H2 adsorption, giving rise to new materials that range from exhibiting an optimal binding strength for ambient temperature storage to facilitating dissociative H2 chemisorption and the realization of porous metal hydrides. While this study and previous studies have focused on how the hydrogen storage properties of a porous material can be estimated from its H2 adsorption isotherms, the assessment of such materials should also account for their performance under more realistic storage conditions. For instance, hydrogen fuel produced by water splitting likely contains O2 and H2O at ppm concentrations. Testing the charging cyclability of Cu I M-MFU-4l and traditional MOFs featuring Lewis acidic metal sites with fuel-grade hydrogen gas under practical fuel cell operation conditions will be of interest for the development of practically relevant hydrogen storage materials. Notably, Cu I Zn-MFU-4l has recently been examined for the separation of oxygen from air, demonstrating fully reversible O2 binding even the presence of water vapor. We expect that the low affinity of Cu I M-MFU-4l for potential impurities in hydrogen fuels will be advantageous for their use in storage applications, considering that classical Lewis acidic metal sites are typically hygroscopic, which could potentially deactivate metal sites in the presence of water. Relatedly, we note that V2Cl2.8(btdd), the only other MOF known to exhibit H2 binding in the optimal range, is irreversibly oxidized by air, permanently degrading the V II sites in the presence of O2. Clearly, it is worthwhile to pursue analogues of the Cu I M-MFU-4l materials that possess a higher density of Cu I sites per unit volume, thereby enhancing the volumetric H2 storage capacity. Efforts to synthesize such materials are ongoing.