Peter L. Rodríguez-Kessler, Alvaro Muñoz‐Castro
ABSTRACT Finding novel cluster templates is useful to envisage the formation of stable building blocks with particular functionality. Here, we evaluated the unusual bonding properties of boron clusters toward transition metals, describing the Ca 2 B 18 cluster as a highly stable double‐ring bicapped nonagonal antiprism structure, featuring a D 9d symmetry, confirmed as the global minimum. The resulting structure leads to a significant charge transfer from calcium to the boron framework, enhancing its stability. Energy decomposition analysis of the Ca 2 –B 18 interaction shows a sizable stabilization, attributed mainly to orbital interactions, supported by electrostatic effects and minor dispersion interactions. The charge distribution in Ca 2 B 18 gives rise to electron‐deficient σ‐hole regions at calcium sites, indicating Lewis acid behavior. Adaptive natural density partitioning shows a complex multicenter bonding network with planar aromatic character, supported by magnetic shielding. Overall, this work elucidates the plausible formation of Ca 2 B 18 as a three‐dimensional cluster, offering valuable insights for designing tunable clusters based on the B 18 toroid skeleton for achieving suitable molecular building blocks for extended materials.