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.