The s-p Nonhybrid Nature Causes Adaptive Superatomic States of Bismuth Clusters

We report a joint experimental and theoretical study on the stability and reactivity of Bi_n ⁺ (n=5-33) clusters. The alternating odd-even effect on the reaction rates of Bi_n ⁺ clusters with NO is observed, and Bi₇ ⁺ finds the most inertness. First-principles calculation results reveal that the lowest energy structures of Bi_6-9 ⁺ exhibit quasi-spherical geometry pertaining to the jellium shell model; however, the Bi_n ⁺ (n≥10) clusters adopt assembly structures. The prominent stability of Bi₇ ⁺ is associated with its highly symmetric structure and superatomic states with a magic number of 34e closed shell. For the first time, we demonstrate that the unique s-p nonhybrid feature in bismuth rationalizes the stability of Bi_6-9 ⁺ clusters within the jellium model, by filling the 6s electrons into the superatomic orbitals (forming "s-band"). Interestingly, the stability of 18e "s-band" coincides with the compact structure for Bi_n ⁺ at n≤9 but assembly structures for n≥10, showing an accommodation of the s electrons to the geometric structure. The atomic p-orbitals also allow to form superatomic orbitals at higher energy levels, contributing to the preferable structures of tridentate binding units. We illustrate the s-p nonhybrid nature accommodates the structure and superatomic states of bismuth clusters.