Recent findings on modified MFU-4l frameworks for hydrogen storage applications are encouraging and demonstrate the great synthetic flexibility of the MFU-4-type framework family. However, many details of the relationship between the binding enthalpy and the ionic radius of the central metal ion in MFU-4-type frameworks remain unclear. Specifically, does the correlation exhibit saturation, or does the enthalpy continue to increase up to the completely planar coordination of Cu I ion? Consequently, is it possible to more closely approach or even exceed optimal binding enthalpies for hydrogen storage applications and find a non-toxic analog of Cu I Cd II -MFU-4l? To address these questions, we computed the enthalpies of hydrogen binding to eight Cu I M II 4Cl3(bta)6 cluster models with different central M II atoms: Be II (r = 45 pm), Mg II (r = 72 pm), Zn II (r = 74 pm), Mn II (r = 83 pm), Cd II (r = 95 pm), Ca II (r = 100 pm), Sr II (r = 118 pm), and Ba II (r = 135 pm). Most of the considered structures were found to have the C3 symmetry for the SBU and feature a trigonal pyramidal Cu I site (Figure ), making them potentially synthesizable. However, in the cases of the Cu I Sr II and Cu I Ba II clusters, the three triazolates that chelate Cu I lean toward the metal center to break the pseudo-Td symmetry (Figure ). Moreover, significant structural distortions were observed in the H2•••Cu I Ba II cluster (Figures ), with triazolate ligands bending to lower the symmetry of the SBU. Therefore, we might expect that the corresponding solid-state material with a cubic crystal structure could be unstable. However, we anticipate that these cluster models should be able to elucidate the relationship between trigonal Cu I geometry versus H2 binding for fundamental understanding.