Ligand Effect on the Electronic Structure of Cobalt Sulfide Clusters: A Combined Experimental and Theoretical Study

Recent studies have shown that capping ligands offer a new dimension for fine-tuning the properties of clusters. Here we investigate this concept by measuring the anion photoelectron spectra of a series of hexanuclear cobalt sulfide clusters, Co₆S₈, passivated by different numbers of triethylphosphine ligands, PEt₃. We find that the addition of PEt₃ gradually shifts the electronic spectrum of the cluster to higher energy, leading to a decrease in its electron affinity. Density functional theory calculations reveal that adding ligands demagnetizes the Co₆S₈ core. The decrease in electron affinity results from a monotonic increase in the energy of the cluster lowest unoccupied molecular orbitals (LUMO). This effect is attributed to the electron donation from the ligands to the cluster core, which increases the charge density in the core region.