Theoretical and DFT Study of Atypical Pentanuclear [(iPr3P)Ni]5Hn (n = 4, 6, 8) Clusters: What are the Rules?

The structural, bonding and properties of a series of atypical pentanuclear nickel hydride clusters supported by electron rich iPr3P of the type [(iPr3P)Ni]5Hn (n = 4, 6, 8) (H4, H6, H8) and their anionic models where iPr3P are substituted by H− (H4, H6, H8) were investigated by density functional theory (DFT) calculations. All clusters were calculated to adopt a similar square pyramidal core geometry. Calculations indicate singlet ground states with low singlet-triplet gaps for H4 and H6, similar to previously reported experimental values. Molecular orbital theory description clusters were investigated using the simplified model complexes [HNi]5Hn5– (n = 4, 6, 8) (H4, H6, H8). The results show that there are three skeletal electron pairs (SEPs) in H4. The addition of two molecules of H2 to form H6 and H8 results in the partial or full occupation of two degenerate MOs (e* set) that give two SEPs and one SEP, respectively. Indeed, the occupation of these low-lying weakly antibonding orbitals govern the multielectron chemistry available for these clusters, and play a role in their unique reactivity.