Ternary CaBe2B7- Cluster: A Turning Nanoclock.

Boron-based alloy clusters have unique structural and electronic properties, exotic chemical bonding, and intriguing dynamic fluxionality. Based on global structural searches and electronic structure calculations, we report on the rational design of a ternary CaBe₂B₇^- cluster. This boron-based alloy cluster turns out to adopt a quasi-triple-layered structure, which demonstrates dynamic structural fluxionality, analogous to a turning clock at the subnanoscale. The intramolecular rotation barrier is merely 0.08 kcal mol^-1 at the single-point CCSD(T) level. Chemical bonding analysis suggests that the ternary system features double 6π/6σ aromaticity, which underlies its thermodynamic stability and dynamic structural fluxionality. This work also highlights the potential to explore a heptagonal [B₇]^5- ring as inorganic ligand in chemistry.