Unusual Inertness of a Ta8+ Cluster in Dinitrogen Reactions

Abstract

Clusters serve as the optimal model to elucidate the structure–property relationship of materials, bridging condensed matter and individual atoms. The pursuit of exceptionally stable clusters has garnered significant interest. The distinctive electronic configuration and symmetrical geometry generally provide a consistent rationale for their stability. However, this principle does not quite correspond to the behavior of all transition metal clusters. Utilizing our customized apparatus, we successfully produced pure tantalum clusters Ta_n⁺ (n = 1–16) and examined their reactions with dinitrogen under sufficient gas-collision conditions. Significantly, with the introduction of N₂ gas reactants, the Ta₈⁺ cluster became the predominant species. Comprehensive theoretical analyses indicate that the inertness of Ta₈⁺ is due to not only its unique electronic configuration and superatomic feature but also its unfavorable N₂ adsorption dynamics and N≡N activation kinetics on the cluster. We demonstrate the contributions of frontier orbitals, the natural population of charges, and their interactions with lone-pair electrons of N₂, together with the rate coefficients derived from Rice–Ramsperger–Kassel–Marcus (RRKM) theory. This study provides comprehensive insights into the cluster stability and activity, which can be used as a reference for the development of gas separation materials that are resistant to N₂.