Single‐Atom Control of Aromaticity and Excited‐State Dynamics in Endohedral Zirconium–Antimony Zintl Clusters

Abstract

ABSTRACT Three‐dimensional (3D) aromaticity provides a powerful framework for understanding the stability and electronic structures of superatomic clusters, yet how such aromaticity evolves during atom‐by‐atom structural growth remains poorly understood. Herein, we report two endohedral zirconium‐antimony Zintl clusters, [Zr@Sb 12 ] 2− and [Zr@Sb 13 ] 3− , that offer a rare one‐atom comparison of nuclearity‐dependent aromaticity and photodynamics. Structural and bonding analyses reveal that [Zr@Sb 12 ] 2− behaves as an integrated Sb 12 framework rather than three discrete Sb 4 fragments coordinated to Zr. Adaptive natural density partitioning (AdNDP) and magnetic‐response analyses establish a closed‐shell S 2 P 6 superatomic configuration, giving rise to pronounced spherical all‐metal aromaticity. In contrast, incorporation of one additional Sb atom reorganizes the framework into a cage‐like [Zr@Sb 13 ] 3− cluster, disrupts superatomic shell closure, and produces an S 2 P 4 configuration with strongly attenuated spherical aromaticity. Femtosecond transient absorption (fs‐TA) spectroscopy further reveals that the aromatic [Zr@Sb 12 ] 2− cluster exhibits markedly longer‐lived excited‐state species than [Zr@Sb 13 ] 3− . These findings establish a direct structure–aromaticity–dynamics relationship, demonstrating that single‐atom control of cluster nuclearity can regulate not only ground‐state aromatic stabilization but also excited‐state robustness in all‐metal superatoms.