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

The structure, bonding, and properties of a series of atypical pentanuclear nickel hydride clusters supported by electron-rich PrP of the type [(PrP)Ni]H ( = 4, 6, 8; , , ) and their anionic models where PrP are substituted by H (, , ) 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 small singlet-triplet gaps for and , similar to previously reported experimental values. Molecular orbital theory description clusters were investigated using the simplified model complexes [HNi]H ( = 4, 6, 8; , , ). The results show that there are three skeletal electron pairs (SEPs) in . The addition of two molecules of H to form and results in the partial or full occupation of two degenerate MOs ( set) that give two SEPs and one SEP, respectively. Indeed, the occupation of these low-lying weakly antibonding orbitals governs the multielectron chemistry available for these clusters and plays a role in their unique reactivity.