Our findings reveal a linear relationship between the enthalpy and the increase in ionic radius (Figure ), with the strongest Cu-H2 interaction observed for Be 2+ (ΔH = -43.1 kJ/mol), which exhibits the smallest ionic radius of metal ions in the series. In addition, this search identifies a non-toxic alternative to Cu I Cd II -MFU-4l. Specifically, we found a new composition of SBU that incorporates a Ca II central ion and demonstrates an optimal binding enthalpy of -18.5 kJ/mol. We note that the set of selected atoms covers almost the entire possible range of radii that are possible for 2+ charged ions in the periodic table, from the smallest (Be II ) to the second largest (Ba II ), excluding the larger radioactive Ra II . This allows enthalpy tuning for Cu I M II -MFU-4l from -43.1 to -7.8 kJ/mol, offering significant flexibility that covers the optimal range of enthalpies required for the maximum usable capacity per site at ambient temperature. Such a broad range of tuning is notable, as typically, the ion replacement technique in other MOF systems yields more limited tunability. For example, when the identity of the open metal site is fixed, the change in H2 adsorption enthalpy is less than 7 kJ/mol in the largest case by substitution of the linker, its first coordination sphere, and pore size. Nevertheless, it is still not clear how the radius of the central atom correlates with the planarity of the Cu atom's coordination. Will this dependence also be linear? To analyze this, we must select a parameter that reports on the planarity of the coordination environment of the Cu atom. A potentially suitable parameter could be the distance between the Cu atom and the plane formed by the three nearest nitrogen atoms of the triazolate ligands. With this metric, if the distance is 0 pm, then the coordination environment is trigonal planar. The correlation between the Cu-N plane distance and enthalpy is shown in Figure . This relationship appears to be less linear and a relation between the degree of planarity and the binding enthalpy tends to curve, with less effect on enthalpy observed for the smaller Cu-N plane distance values. Although no saturation point was observed in the region from 50 pm to 110 pm, we anticipate that approaching 0 pm would likely result in saturation and plateau behavior. It is also important to note that the computed enthalpy of -7.8 kJ/mol for the Cu I Ba II cluster approaches the range for van der Waals interactions (-3 to -7 kJ/mol). Thus, we could expect that the enthalpy values will asymptotically approach that region. While the substitution of the central atom in the MFU-4-type frameworks offers a route to adjust binding enthalpies towards the optimal range, the synthetic feasibility of incorporating certain ions like Be II or Sr II remains uncertain, given the number of reported MOFs made with alkaline earth metals and azolate linkers. Consequently, our focus shifts towards the investigation of the impact of changes in the M I peripheral metal ion identity while employing experimentally viable central ions such as Zn II , Mn II , and Cd II . While the nature of the interaction between H2 and a M I ion can vary, we expect that the central ion effect (when the binding interaction of the peripheral metal ion with H2 becomes less favorable as the central ion size increases) would be more pronounced if the interactions between H2 and the M I atom will have some π-backdonation character, as observed with Cu I .