Chemical bonding and structural fluxionality of a boron-based B8Ca3 cluster

Boron exhibits intrinsic electronic defects, which contribute to the formation of boron-based binary clusters with distinct properties. This study presents a quantum chemical investigation of the B 8 Ca 3 cluster, which features an intuitive three-layered structure: a quasi-planar B 8 molecular wheel, a Ca Ca dimer positioned above the wheel, and a single Ca unit located beneath it. From the perspective of aromaticity, the B 8 Ca 3 cluster is a binary system with dual 6π/6σ aromaticity, and its electronic configuration complies with the (4n + 2) Hückel rule. Born-Oppenheimer Molecular Dynamics (BOMD) simulations were conducted to explore the dynamic behavior of the cluster, revealing that B 8 Ca 3 possesses dynamic fluxionality, with a negligible intramolecular torsional barrier between the B 8 molecular wheel and the Ca 2 ligand. Additionally, chemical bond analysis indicates charge transfer from the metal to the B 8 molecular wheel, leading to the formation of a formal [Ca Ca] 2+ [B 8 ] 4− [Ca] 2+ complex. In conclusion, the B 8 Ca 3 cluster provides a new example for investigating the dynamic structural fluxionality of molecular systems. B 8 Ca 3 cluster features an intuitive three-layered structure: a quasi-planar B 8 molecular wheel, a Ca Ca dimer positioned above the wheel, and a single Ca unit located beneath it. The system demonstrates dynamic fluxionality, akin to a compass at nanoscale. Chemically, B 8 Ca 3 breaks through the planar aromaticity limitation of the previous clusters by introducing a vertical 6c-2e σ delocalized bond between the lower Ca atom and the B 8 wheel, forming a three-dimensional aromaticity system. • B 8 Ca 3 features a three-layered structure: quasi-planar B 8 wheel, Ca Ca dimer above, and single Ca below, with verified thermodynamic stability. • The cluster acts as a “nanocompass”: Ca Ca dimer rotates tangentially on B 8 wheel with negligible torsional barrier. • Forms [Ca–Ca] 2+ [B 8 ] 4− [Ca] 2+ via metal-to-B 8 charge transfer, with B Ca interactions dominated by electrostatics. • The cluster features double 6π/6σ aromaticity conforming to the (4 n + 2) Hückel rule, which dictates its dynamic fluxionality.