Unveiling the Structural Evolution of Europium‐Doped Boron Clusters: From Half Sandwich to a Novel 22‐Coordinate Molecular Drum

In recent years, lanthanide‐doped boron clusters have attracted considerable attention. However, the structural evolution and stability of medium‐sized boron clusters doped with Eu atoms remain largely unknown. In this study, a combination of particle swarm optimization and density functional theory is employed to systematically investigate the structural evolution and stability of Eu‐doped boron clusters, EuB n ( n = 1–24). The results show that the most stable configurations of the EuB n clusters transitioned from planar geometries to half‐sandwich molecular structures as the cluster size increased. Furthermore, for larger cluster sizes, such as n = 18, 20, and 22, the lowest‐energy configurations transitioned to tubular and drum‐type molecules featuring double B rings. Notably, the EuB 22 cluster has been identified as a twenty‐two‐coordinate complex, which is the highest coordination number achieved in lanthanide‐doped boron‐cluster chemistry. The research not only uncovers the structural evolution of Eu‐doped boron clusters but also delves into their electronic characteristics, offering valuable insights into the chemistry of rare‐earth‐element‐doped boron clusters.