A Superatom Pt₂₁– Cluster with Unique Stability and Aromaticity

Platinum (Pt) clusters are vital in catalysis due to their stability and reactivity, yet their structure–property relationships remain inadequately comprehended. This study examines the stability of Ptn– (n = 6–35) clusters as a function of size and their reactions with varying doses of common gases. We find two predominant clusters, Pt10– and Pt21–, surviving sufficient N2 gas reactions. The Pt10– cluster derives its stability from a tetrahedral geometry, whereas Pt21– adopts a spheroidal and three-layer (7+7+7) structure with D6h symmetry, exhibiting superatomic orbital features and inorganic aromaticity. Adjacent clusters such as the cage-structured Pt22– and Pt23–, along with low-symmetry or distorted smaller Ptn– clusters (n = 11–20), further contrast the unique stability of the trilaminar superatom Pt21–. These findings elucidate critical structural and electronic factors that govern Pt cluster stability, enlightening atomic-level design of Pt catalysts with modest stability, devoid of N2 contamination and poisoning effects.