Plasma-Assisted Dinitrogen Activation on Small Cobalt Clusters: Co4 N9 + with Enhanced Stability.

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We have performed a study on the accommodation of nitrogen doping toward superatomic states of transition metal clusters. By reacting cobalt clusters with N2 in the presence of plasma radiation, a large number of odd-nitrogen clusters were observed, typically Co3 N2m-1 + (m=1-5) and Co4 N2m-1 + (m=1-6) series, showing N≡N bond cleavage in the mild plasma atmosphere. Interestingly, the Co3 N7 + , Co4 N9 + , and Co5 N9 + clusters exhibit prominent mass abundances. First-principles calculation results elucidate the stability of the diverse cobalt nitride clusters and find unique stability of Co4 N9 + with a swallow-kite structure of which four coordinated N2 molecules causes a significantly enlarged HOMO-LUMO gap, while the single N atom doping gives rise to superatomic states of 1S2 1P3 ||1D0 . We reveal an efficient dinitrogen activation strategy by reacting multiple N2 molecules with cobalt clusters under a plasma atmosphere.