Theoretical Investigation on Bonding Properties and Low Oxidation States in SmB_n Clusters

Boron clusters doped with lanthanides reveal diverse topological structures and low oxidation states, expanding the types of boron-based nanomaterials and offering opportunities for the continuous expansion of the boundaries of the valence states of rare earth metals and boron chemistry. In this work, the crystal structure analysis by particle swarm optimization method combined with density-functional theory is applied for SmB_n clusters in the range n = 3-10 and elucidates the evolutionary patterns of geometrical structure. An analysis of chemical bonding patterns and natural atomic populations indicates that the Sm 4f electrons do not participate in bonding. In all the SmB_n clusters considered, the oxidation state of Sm atoms is +2, whereas the typical oxidation number of the lanthanide atoms is +3. The corresponding electronic configuration of the Sm atom in this oxidation state is 4f⁶ for SmB_3-10, and the 6s orbital are practically empty. The 2D planar SmB₃,₄ and 3D umbrella-shaped SmB₈ exhibit both σ and π aromaticity. The Sm atom forms localized σ bonds with the host cluster in SmB₃ and SmB₄, while in SmB₈, it forms delocalized π bonds with the host cluster, demonstrating the significant influence of the structural dimension on their interaction behavior.