Plasma-Assisted Chain Reactions of Rh₃⁺ Clusters with Dinitrogen: N≡N Bond Dissociation

Dinitrogen activation is known as one of the most challenging subjects in chemistry. A number of well-defined metal complexes, nitrides, and clusters have been studied that show catalysis for dinitrogen activation. However, direct evidence of a complete cleavage of the N≡N triple bond at mild conditions is rather limited to date. Herein, we report a study on the dissociation of N₂ on small rhodium clusters assisted by surface plasma radiation. From mass spectrometry observation, a few rhodium nitride clusters with an odd number of nitrogen atoms are produced, such as the Rh₃N₂⁺ (m = 1-5) series, indicative of N≡N bond dissociation in the mild plasma atmosphere. Interestingly, Rh₃N₇⁺ is identified with outstanding mass abundance among the RhN₂⁺ products, and its ground-state structure is in the form of Rh₃N(N₂)₃⁺ by capping a nitrogen atom on the top of Rh₃⁺ plane and hanging three N₂ molecules beneath the three Rh atoms respectively, giving rise to a C₃ symmetry and excellent stability. We demonstrate the catalysis of such a three-atom rhodium cluster and reveal a dinitrogen activation strategy by thermodynamics- and dynamics- favorable chain reactions of multiple N₂ molecules with two rhodium clusters under plasma atmosphere.