(Table ). The largest difference in interaction components among the Cu I M-MFU-4l cluster models is found in the charge transfer term (∆ECT) while the other terms are almost constant upon alteration of the identity of M. Specifically, the magnitude of ∆ECT follows the trend of Cu I Zn4 > Cu I Mn4 > Cu I Cd4 clusters. Further, the charge transfer from Cu I to H2 is the largest for the Cu I Zn4 cluster and the smallest for the Cu I Cd4 cluster. Overall, the DFT calculations support our hypothesis that having a larger metal ion at the center of a pentanuclear cluster leads to an open Cu I site with a more planar geometry that consequently shows weaker π-backbonding. Cu I Cd-MFU-4l. We therefore decided to focus on a powder neutron diffraction analysis of Cu I Mn-MFU-4l.