Size-dependent reactivity of rhodium deuteride cluster anions Rh3Dn− (n = 0–3) toward dinitrogen: The prominent role of σ donation

• Published in: The Journal of chemical physics 2022-02, Vol.156 (6), p.064303-064303
• Main Authors: Cheng, Xin, Li, Zi-Yu, Mou, Li-Hui, Wei, Gong-Ping, Liu, Qing-Yu, He, Sheng-Gui
• Format: Article
• Language: English
• Subjects: Adsorption; Anions; Biological activity; Chemists; Clusters; Energy levels; Nitrogen; Nitrogenation; Orbitals; Physics; Reactivity; Rhodium; Transition metals; Vapor phases
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/5.0077183

Nitrogen (N2) fixation is a challenging task for chemists. Adsorption of N2 on transition metal (TM) sites has been identified as a prerequisite for activating the very stable N≡N triple bond in both industrial and biological processes. The importance of π back-donation (filled orbitals of TM → π* orbitals of N2) between metal sites and N2 has been well elucidated while the role of another classic orbital interaction, namely σ donation (σ orbitals of N2 → empty orbitals of TM), remains ambiguous. Herein, the size-dependent reactivity of trinuclear rhodium deuteride cluster anions Rh3Dn− (n = 0–3) toward N2 adsorption in the gas phase was investigated experimentally and theoretically. A reverse relationship that higher electron-donating ability of clusters corresponds to lower N2 adsorption reactivity was experimentally observed, which is uncommon in N2 activation by gas-phase species. Theoretical analysis revealed that the σ donation rather than the π back-donation plays a predominant role in the adsorption complexes Rh3DnN2− and the enhanced reactivity upon D addition is ascribed to the lowered energy levels of active orbitals in Rh3Dn− as n increases. This study provides the first experimental evidence to declare the important role of σ donation and new clues for the design of reactive metal species in nitrogen fixation.