Plasma-Assisted Dinitrogen Activation on Small Cobalt Clusters: Co 4 N 9 + with Enhanced Stability.

We have performed a study on the accommodation of nitrogen doping toward superatomic states of transition metal clusters. By reacting cobalt clusters with N 2 in the presence of plasma radiation, a large number of odd-nitrogen clusters were observed, typically Co 3 N 2m-1 + (m=1-5) and Co 4 N 2m-1 + (m=1-6) series, showing N≡N bond cleavage in the mild plasma atmosphere. Interestingly, the Co 3 N 7 + , Co 4 N 9 + , and Co 5 N 9 + clusters exhibit prominent mass abundances. First-principles calculation results elucidate the stability of the diverse cobalt nitride clusters and find unique stability of Co 4 N 9 + with a swallow-kite structure of which four coordinated N 2 molecules causes a significantly enlarged HOMO-LUMO gap, while the single N atom doping gives rise to superatomic states of 1S 2 1P 3 ||1D 0 . We reveal an efficient dinitrogen activation strategy by reacting multiple N 2 molecules with cobalt clusters under a plasma atmosphere.