Unveiling the potential of superalkali cation Li3+ for capturing nitrogen

Abstract

The potential of the superalkali cation Li₃⁺ for capturing N₂ and its behavior in gaseous nitrogen have been theoretically studied at the MP2/6-311+G(d) level. The evolution of structures and stability of the Li₃⁺(N₂)_n (n = 1–7) complexes shows that the N₂ molecules tend to bind to different vertices of the Li₃⁺ core, and that Li₃⁺ might have the capacity to capture up to twelve nitrogen molecules in the first coordination shell. Based on natural population and molecular orbital analyses, Li₃⁺ keeps its superatom identity in the lowest-lying Li₃⁺(N₂)_n (n = 1–4) complexes. The change in the Gibbs free energies of possible fragmentation channels also indicates the thermodynamic stability of Li₃⁺ in the (N₂)_n clusters when n ≤ 4. Different from the case of Li₃⁺(H₂O)_n, where the electrostatic interaction is dominant, the electrostatic and polarization components are found to make nearly equal contributions to Li₃⁺(N₂)_n complex formation. In addition, it can be concluded that the superalkali cation Li₃⁺ surpasses heavy alkali metal cations in capturing N₂ molecules, since it has a larger binding energy with N₂ than Na⁺ and K⁺ ions.