Size-Dependent Association of Cobalt Deuteride Cluster Anions Co₃D_n⁻ (n = 0–4) with Dinitrogen

Dinitrogen (N₂) activation by metal hydride species is of fundamental interest and practical importance while the role of hydrogen in N₂ activation is not well studied. Herein, the structures of Co₃D_n⁻ (n = 0–4) clusters and their reactions with N₂ have been studied by using a combined experimental and computational approach. The mass spectrometry experiments identified that the Co₃D_n⁻ (n = 2–4) clusters could adsorb N₂ while the Co₃D_n⁻ (n = 0 and 1) clusters were inert. The photoelectron imaging spectroscopy indicated that the electron detachment energies of Co₃D_2–4⁻ are smaller than those of Co₃D_0,1⁻, which characterized that it is easier to transfer electrons from Co₃D_2–4⁻ than from Co₃D_0,1⁻ to activate N₂. The density functional theory calculations generally supported the experimental observations. Further analysis revealed that the H atoms in the Co₃H_n⁻ (n = 2–4) clusters generally result in higher energies of the Co 3d orbitals in comparison with the Co₃H_n⁻ (n = 0 and 1) systems. By forming chemical bonds with H atoms, the Co atoms of Co₃H_2–4⁻ are less negatively charged with respect to the naked Co₃⁻ system, which leads to higher N₂ binding energies of Co₃H_2–4N₂⁻ than that of Co₃N₂⁻.

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