Observation of Dinitrogen Adsorption by Rhodium Oxide Clusters

Nitrogen fixation is a challenging target in chemistry. N₂ adsorption on transition metal sites has been identified as a prerequisite for activating the stable N≡N triple bond in industrial and biological processes. The structural and bonding properties of the Rh₂O₂(N₂)_n^- (n = 1-2) complexes have been investigated via mass-selected photoelectron velocity-map imaging spectroscopy combined with quantum chemical calculations. The experimental and theoretical results indicate that the N₂ molecules in the Rh₂O₂(N₂)_n^- (n = 1-2) complexes possess the end-on bonding motifs. Adsorption and activation of dinitrogen are facilitated by charge transfer from Rh and O to N₂. The importance of π back-donation from the 4d orbital of the Rh atom to the antibonding π orbitals of N₂ for dinitrogen activation is discussed in detail; these results identify Rh₂O₂(N₂)_n^- (n = 1-2) as a key adsorbed species in the initial stage of dinitrogen activation by rhodium oxide clusters.