We also compared the presented INS results with those reported for Cu I Zn-MFU-4l previously (Figure , blue line). In contrast to the spectrum of Cu I Mn-MFU-4l showing four peaks in the low energy transfer region, there are only two somewhat broader peaks in the spectrum for Cu I Zn-MFU-4l, suggesting that the local clusters have a more uniform composition (likely Cu2Zn3 clusters). The splitting of the peaks (4.97 and 6.54 meV) is larger than that observed in Cu I Mn-MFU-4l, and the center at 5.76 meV is slightly lower, corresponding to a slightly longer calculated H-H bond of 0.85 Å. These observations suggest that the Cu-H2 interaction in Cu I Zn-MFU-4l is stronger and more anisotropic than in Cu I Mn-MFU-4l, consistent with H2 adsorption isotherms and analyses of in situ H2-dosed infrared spectra.